JP7631078B2 - Power conversion device and electric motor control method - Google Patents

Description

This disclosure relates to a power conversion device equipped with an inverter that drives an electric motor.

A power converter that converts the power of an AC power source into variable voltage and variable frequency power is known as a power converter that drives an electric motor. The main circuit of this power converter comprises a converter that converts AC to DC, a DC circuit connected to the converter, and an inverter that is connected to the converter via the DC circuit and converts DC to AC, with a smoothing capacitor in the DC circuit. This power converter controls the speed and torque of the electric motor by varying the magnitude and frequency of the AC voltage applied to the motor with the inverter.

A speed control system and a current control system are used as the control system for the electric motor. The speed control system detects the speed of the electric motor using a speed detector, and feeds back the value detected by the speed detector. The current control system detects the current flowing through the electric motor using a current detector, and feeds back the value detected by the current detector. There is also a method of making corrections to the command value to improve the accuracy of the control of the electric motor (Patent Documents 1 and 2).

There is a method in which the AC line voltage of a motor is detected by an AC line voltage detector, and this detection value is used to make corrections to the control. For example, in the control of an induction motor, the slip amount and speed electromotive force of the induction motor are controlled, but there is a risk of accuracy degradation due to deviations between the design values and actual values and changes in characteristics such as the motor's resistance and mutual inductance. Therefore, there is a correction control method in which the deviation between the design value and the actual value is extracted from the detection value of the motor's AC line voltage, and a correction amount is added to the slip amount and excitation current so as to make the deviation zero.

JP 2004-208397 A Japanese Patent Application Publication No. 09-149658

In the method of correcting control using the detected value of the AC line voltage described above, the AC line voltage detector detects the output voltage from the semiconductor elements in the power converter. The output voltage is a square wave caused by switching, and the detected value contains a large ripple component, which may degrade accuracy.

In addition, if a filter circuit with a large time constant is used to reduce this large ripple component and the output of the filter circuit is detected, a delay will occur in the detection of the output voltage, and this delay may result in a deterioration in accuracy.

In addition, in configurations that use an AC line voltage detector, an abnormality may occur in the AC line voltage detector, which may result in a deterioration in the accuracy of the correction control or, in the worst case, an unplanned shutdown.

One objective of this disclosure is to provide technology that enables highly accurate correction control without using an AC line voltage detector.

Another object of the present disclosure is to provide a technology that enables detection of an abnormality in an AC line voltage detector in a configuration that uses an AC line voltage detector.

A power conversion device according to one aspect of the present disclosure includes a converter that converts an AC input into a plurality of potentials, an inverter that converts the voltage of the plurality of potentials into an AC output to an electric motor, a smoothing capacitor that is connected between two of the plurality of potentials and suppresses potential fluctuations between the potentials, a DC voltage detector that detects the potential difference between the potentials to which the smoothing capacitor is connected as a DC voltage detection value, a current detector that detects the output current of the inverter and outputs it as an inverter output current, an inverter output current controller that generates an inverter output voltage command to the inverter so that the inverter output current matches the inverter output current command, a motor voltage calculator that calculates a motor voltage estimate that is an estimate of the AC line voltage of the motor from the inverter output voltage command and the DC voltage detection value, a correction control unit that calculates a correction value that corrects a signal for controlling the motor from the motor voltage estimate value, and an adder that adds the correction value to a control command signal to generate the inverter output current command.

A power conversion device according to another aspect of the present disclosure includes a converter that converts an AC input into a plurality of potentials, an inverter that converts the voltage of the plurality of potentials into an AC output to an electric motor, a smoothing capacitor that is connected between two of the plurality of potentials and suppresses potential fluctuations between the potentials, a DC voltage detector that detects the potential difference between the potentials to which the smoothing capacitor is connected as a DC voltage detection value, an AC line voltage detector that detects the output voltage of the inverter and outputs it as a motor voltage detection value, a correction control unit that calculates a correction value that corrects a signal for controlling the electric motor from the motor voltage detection value, and a control circuit that controls the correction value. It has an adder that adds to the command signal to generate an inverter output current command, a current detector that detects the output current of the inverter and outputs it as the inverter output current, an inverter output current controller that generates an inverter output voltage command to the inverter so that the inverter output current matches the inverter output current command, a motor voltage calculation unit that calculates a motor voltage estimate that is an estimate of the AC line voltage of the motor from the inverter output voltage command and the DC voltage detection value, and an AC line voltage detector abnormality determiner that determines an abnormality in the AC line voltage detector based on the motor voltage estimate value.

According to one aspect of the present disclosure, an estimate of the AC line voltage of the motor is calculated from the inverter output voltage command and the DC voltage detection value, and a correction value for correcting the signal for controlling the motor is calculated from the estimate, making it possible to perform highly accurate correction control without using an AC line voltage detector.

According to another aspect of the present disclosure, an estimate of the AC line voltage of the motor is calculated from the inverter output voltage command and the DC voltage detection value, and an abnormality in the AC line voltage detector is determined based on the estimate, making it possible to detect an abnormality in the AC line voltage detector in a configuration that uses an AC line voltage detector.

1 is an overall configuration diagram of a power conversion device according to a first embodiment; FIG. 4 is a diagram showing the magnetic flux saturation characteristics of a motor. FIG. 13 is a diagram showing the relationship between speed, excitation current, and speed electromotive force. FIG. 1 is a diagram showing a configuration of a conventional power conversion device for comparison with the power conversion device of the present embodiment. FIG. 2 is a diagram for explaining the configuration of a three-level motor voltage calculator 70. FIG. 13 is a diagram illustrating the relationship between a voltage command and an output rectangular wave voltage in a dipolar state. FIG. 2 is a diagram for explaining a three-level dipolar modulation voltage calculator 71. 5A and 5B are diagrams illustrating the relationship between a voltage command and an output rectangular wave voltage during unipolar modulation. FIG. 13 is a diagram for explaining a three-level unipolar modulation voltage calculator 72. FIG. 11 is an overall configuration diagram of a power conversion device according to a second embodiment. FIG. 2 is a diagram for explaining a two-level motor voltage calculator 80. 11 is a diagram for explaining the relationship between a voltage command and an output rectangular wave voltage in the case of two levels. FIG. FIG. 2 is a diagram for explaining a two-level modulation voltage calculator 81. FIG. 11 is an overall configuration diagram of a power conversion device according to a third embodiment. 4 is a flowchart of an abnormality diagnosis for an AC line voltage detector. FIG. 13 is an overall configuration diagram of a power conversion device according to a fourth embodiment. 13 is a diagram for explaining an abnormality-time calculation value switch 92. FIG.

Several embodiments will be described with reference to the drawings. Note that the embodiments described below do not limit the invention as claimed, and not all of the elements and combinations thereof described in the embodiments are necessarily essential to the solution of the invention.

In Example 1, a power conversion device using a three-level converter is illustrated.

Figure 1 is an overall configuration diagram of a power conversion device according to the first embodiment.

The power conversion device 100 is a device that converts AC power from an AC power source 1 to drive an electric motor 4. The power conversion device 100 includes a converter unit (also called a converter) 2 that converts AC power from the AC power source 1 into DC power, an inverter unit (also called an inverter) 3 that converts the DC power output by the converter unit 2 into the desired AC power and drives the electric motor 4, a converter control device 5 that controls the converter unit 2, and an inverter control device 6 that controls the inverter unit 3.

The converter unit 2 is a so-called three-level converter, which converts AC power into DC power with a positive potential (first potential) level, a neutral point (zero) potential (second potential) level, and a negative potential (third potential) level. The inverter unit 3 is a so-called three-level inverter, which converts DC power with a positive potential (first potential) level, a neutral point (zero) potential (second potential) level, and a negative potential (third potential) level into AC power for the electric motor 4. Between the converter unit 2 and the inverter unit 3, the positive potential level is connected by P wiring 40, the neutral point potential level is connected by C wiring 41, and the negative potential level is connected by N wiring 42.

The converter unit 2 includes a converter power conversion section 21, a converter P-side smoothing capacitor 22 and a converter N-side smoothing capacitor 23 for suppressing fluctuations in DC voltage, a converter P-side DC voltage detector 25 for measuring the terminal voltage of the converter P-side smoothing capacitor 22, a converter N-side DC voltage detector 26 for measuring the terminal voltage of the converter N-side smoothing capacitor 23, and a converter neutral resistor 24 connected to the C wiring 41 for suppressing DC resonance.

The inverter unit 3 includes an inverter power conversion section 31, an inverter P-side smoothing capacitor 32 connected between the positive potential level and the neutral potential level to suppress potential fluctuations between these potentials, an inverter N-side smoothing capacitor 33 connected between the neutral potential level and the negative potential level to suppress potential fluctuations between these potentials, an inverter P-side DC voltage detector 35 for measuring the terminal voltage of the inverter P-side smoothing capacitor 32, an inverter N-side DC voltage detector 36 for measuring the terminal voltage of the inverter N-side smoothing capacitor 33, and an inverter neutral point resistor 34 connected to the C wiring 41 to suppress DC resonance.

The converter control device 5 controls the converter power conversion unit 21 so that the converted DC power has a desired value. The configuration of the converter control device 5 will be described later.

The inverter control device 6 controls the inverter power conversion unit 31 so that the output torque and speed of the electric motor 4 meet the desired characteristics. The configuration of the inverter control device 6 will be described later.

The power conversion device 100 further includes a current detector 7 that detects and outputs the output current of the converter unit 2, a speed detector 8 that is directly connected to the electric motor 4 and detects and outputs the speed of the electric motor 4, and a current detector 9 that detects and outputs the output current of the inverter unit 3.

The signal (output signal) of the detection value detected by the current detector 7 is input to the converter control device 5. In addition, the signal (output signal) of the detection value detected by the DC voltage detectors 25, 26 is also input to the converter control device 5. The converter control device 5 performs various calculation processes based on these input detection values and outputs a signal to control the converter power conversion unit 21.

The signal (output signal) of the detection value detected by the speed detector 8 and the signal (output signal) of the detection value detected by the current detector 9 are input to the inverter control device 6. The inverter control device 6 performs various calculations based on these input detection values and outputs a signal to control the inverter power conversion unit 31.

The converter control device 5 includes a DC voltage command generator 51, a DC voltage controller 52, a current controller 53, and a pulse generator 54.

The DC voltage command generator 51 outputs a DC voltage command value, which is a command value for the DC voltage to be output from the converter unit 2, to the DC voltage controller 52.

The DC voltage controller 52 calculates a converter output current command value based on the DC voltage command value input from the DC voltage command generator 51 and the DC voltage detection values input from the DC voltage detectors 25 and 26, and outputs the calculated value to the current controller 53. Specifically, the DC voltage controller 52 calculates the converter output current command value so that the sum of the DC voltage detection values input from the DC voltage detector 25 and the DC voltage detector 26 matches the DC voltage command value.

The neutral point voltage controller 55 calculates a voltage command that makes the neutral point voltage zero based on the difference between the detected DC voltages input from the DC voltage detectors 25 and 26, and outputs the voltage command to the current controller 53.

The current controller 53 calculates a converter voltage command value so that the converter output current detection value output from the current detector 7 matches the converter output current command value input from the DC voltage controller 52, and outputs the calculated value to the pulse generator 54. At this time, the current controller 53 calculates the converter voltage command value taking into account the voltage command input from the neutral point voltage controller 55.

The pulse generator 54 calculates a pulse signal for controlling the on/off of each switching element of the converter power conversion unit 21 so that the output voltage from the converter power conversion unit 21 matches the converter output voltage command value input from the current controller 53, and outputs the pulse signal to the converter power conversion unit 21.

The inverter control device 6 includes a speed command generator 61, a speed controller 62, a current controller 63, a pulse generator 64, and a neutral point voltage controller 65.

The speed command generator 61 outputs a speed command value, which is a command value for the speed at which the electric motor 4 operates, to the speed controller 62.

The speed controller 62 calculates a torque current command value for the motor so that the speed detection value input from the speed detector 8 matches the speed command value input from the speed command generator 61, and outputs the torque current command value for the motor to the current controller 63. Here, the combination of the torque current command value for the motor and the excitation current command value for the motor, which will be described later, is called the inverter output current command value.

The neutral point voltage controller 65 calculates a voltage command that makes the neutral point voltage zero based on the difference between the detected DC voltages input from the DC voltage detector 35 and the DC voltage detector 36, and outputs the voltage command to the current controller 63.

The current controller 63 calculates an inverter voltage command value so that the inverter output current detection value input from the current detector 9 coincides with the inverter output current command value, and outputs the calculated value to the pulse generator 64. At this time, the current controller 63 calculates the inverter voltage command value taking into account the voltage command input from the neutral point voltage controller 65.

The pulse generator 64 generates a pulse signal for controlling the on/off of each switching element of the inverter power conversion unit 31 so that the output voltage from the inverter power conversion unit 31 matches the inverter output voltage command value input from the current controller 63, and outputs the pulse signal to the inverter power conversion unit 31.

Next, we will explain the configuration for implementing correction control in the power conversion device 100 to improve the accuracy of control over the electric motor 4.

The inverter control device 6 of the power conversion device 100 further includes an excitation current command generator 66, a magnetic flux controller 67, a correction controller 68, an adder 69, and a three-level motor voltage calculator 70.

When the motor to be controlled is, for example, an induction motor, the control device controls the excitation current to set the magnetic flux of the induction motor to a predetermined value. Also, to effectively utilize the control range of the induction motor, a control that varies the magnetic flux according to the speed is used. To achieve this, the excitation current command generator 66 outputs a reference excitation current command value to the magnetic flux controller 67 to set the magnetic flux of the motor 4 to a predetermined value. The magnetic flux controller 67 receives the speed detection value output from the speed detector 8 as an input, calculates and outputs an excitation current command value that varies the reference excitation current command value according to the speed detection value.

Before explaining the correction control, we will explain the effect of magnetic flux saturation of the motor. As shown in equation (1), the magnetic flux Φ of the motor is the product of the excitation inductance M and the excitation current Im of the motor.

Φ=M×Im…(1)

Figure 2 shows the magnetic flux saturation characteristics of a motor.

In the magnetic flux controller 67, if the excitation current is controlled to decrease inversely proportional to the speed from a certain speed (called the "base speed") to the maximum speed (called the "top speed"), the speed electromotive force of the motor (= speed x magnetic flux) can be made constant from the base speed to the top speed. Figure 3 shows the relationship between speed, excitation current, and speed electromotive force.

However, as shown in Figure 2, when magnetic flux saturation occurs, the excitation inductance M increases as the magnetic flux decreases. In other words, M_Top>M_Base. Therefore, in control that reduces the excitation current in inverse proportion to the speed, there is a risk that the magnetic flux and speed electromotive voltage will become larger than expected. And if the effect of this increase in speed electromotive voltage exceeds the output voltage of the power conversion device, there is a risk that it will become uncontrollable.

Therefore, correction control is performed to suppress the increase in speed electromotive voltage caused by the magnetic flux saturation of the motor.

Figure 4 is a diagram showing the configuration of a conventional power conversion device for comparison with the power conversion device of this embodiment. In Figure 4, the same components as those of the power conversion device of the first embodiment shown in Figure 1 are given the same reference numerals. The power conversion device 101 in Figure 4 includes an AC line voltage detector 10 and a filter circuit 11, and the AC line voltage detection value output by the AC line voltage detector 10 is input to a correction controller 68 via the filter circuit 11. The correction controller 68 calculates and outputs a correction value for lowering the excitation current when the AC line voltage detection value is higher than expected.

The adder 69 adds the correction value from the correction controller 68 to the excitation current command value output from the magnetic flux controller 67. Specifically, in the case of magnetic flux saturation as shown in FIG. 2, when the magnetic flux controller 67 outputs an excitation current command value inversely proportional to the speed, the speed electromotive voltage increases. Therefore, the correction controller 68 outputs a negative correction value that further reduces the excitation current so that the actual speed electromotive voltage becomes a predetermined value. By adding the negative correction value to the excitation current command value by the adder 69, the excitation current Im becomes an excitation current (Im_Top) that is smaller than the inversely proportional value as shown in the middle part of FIG. 3, and as a result, the speed electromotive voltage becomes constant.

By performing correction control in this way, it is possible to suppress an increase in the speed electromotive voltage of the motor. However, in the conventional method using an AC line voltage detector 10 as shown in FIG. 4, the detection accuracy is poor because the detected voltage value is a square wave. If a filter circuit with a large time constant is inserted to reduce the ripple of the square wave, there is an issue that the accuracy of the correction control decreases due to delay. In addition, there is a risk of malfunction due to an abnormality in the AC line voltage detector 10.

The power conversion device 100 according to this embodiment has the following measures in place to address these issues:

The three-level motor voltage calculator 70 according to the first embodiment will now be described in detail.

In FIG. 1, the three-level motor voltage calculator 70 receives the inverter voltage command values (AC phase voltage command values Vuref, Vvref, Vwref) output from the current controller 63, the positive side DC voltage detection value EpFB output from the DC voltage detector 35, and the negative side DC voltage detection value EnFB output from the DC voltage detector 36. The three-level motor voltage calculator 70 uses these input signals to calculate the AC line voltage estimates (Vuvh, Vvwh) of the motor 4. The AC line voltage estimates of the motor 4 are input to the correction controller 68.

Next, the three-level motor voltage calculator 70 according to the first embodiment will be described in more detail.

Figure 5 is a diagram for explaining the configuration of the three-level motor voltage calculator 70.

The three-level motor voltage calculator 70 includes a three-level dipolar modulation voltage calculator 71, a three-level unipolar modulation voltage calculator 72, a correction calculation selection unit 73, and an AC line voltage calculator 74.

The three-level motor voltage calculator 70 calculates the motor voltage from the AC phase voltage command values (Vuref, Vvref, Vwref) and the DC voltage detection values (EpFB, EnFB). However, there are three-level inverters that use dipolar modulation for low voltage and unipolar modulation for high voltage, and the calculation method of the motor voltage differs for each modulation method. Therefore, the correction calculation selection unit 73 selects whether to output a dipolar or unipolar motor AC phase voltage estimate value based on a signal indicating dipolar or unipolar. The signal indicating dipolar or unipolar is, for example, a voltage command value. If the voltage command value is larger than a certain set value, it is determined to be unipolar, and if it is smaller, it is determined to be dipolar.

Then, the AC line voltage calculator 74 calculates and outputs the motor AC line voltage estimates (Vuvh, Vvwh) from the motor AC phase voltage estimates (Vuh, Vvh, Vwh) selected by the correction calculation selection unit 73.

Next, we will explain the calculation method for the estimated motor AC phase voltage value for dipolar modulation and unipolar modulation.

<Calculation method for dipolar modulation>

First, we will explain how to calculate the estimated motor AC phase voltage during three-level dipolar modulation.

Figure 6 shows the relationship between the voltage command and the output square wave voltage when dipolar.

The power conversion device converts the magnitude of the voltage command into a pulse width and controls the on/off of each switching element in the power conversion section to output a voltage that matches the command as an average voltage. In the case of dipolar modulation, a pulse signal is generated so that the difference between the area of the positive side voltage and the area of the negative side voltage matches the command. For example, when outputting zero voltage, the positive and negative sides are made to have the same pulse width, making the average voltage zero.

Here, if the positive DC voltage Ep and the negative DC voltage En are the same, that is, if the positive and negative sides are balanced, the voltage will be zero. However, if the positive DC voltage Ep and the negative DC voltage En are different, that is, if the positive and negative sides are unbalanced, the voltage will not be zero. Therefore, when estimating the AC phase voltage of an actual motor, it is necessary to take into account the fluctuation due to the DC voltage. However, during dipolar modulation, the output voltage is determined by the difference between the Ep side and the En side, so the AC phase voltage of the motor cannot be estimated by reflecting the ratio of Ep or En in the voltage command. Therefore, in this embodiment, an estimation is performed by adding a correction amount to the original voltage command as follows. That is, the correction amount ΔVh is calculated using equation (2).

ΔVh=Vdb×α×ΔEp−Vdb×(1−α)×ΔEn…(2)

Here, Vdb is the reference voltage command when dipolar, and α indicates the pulse width on the Ep side, and is calculated using formula (3).

α = (AC voltage command % + 50%) / 100% … (3)

For example, if a voltage command of 50% or less is expressed using dipolar modulation, Vdb is set to 50% voltage, the pulse width on the Ep side is set to α calculated using formula (3), and the pulse width on the En side is set to 1-α, so that when the voltage command is 25%, it becomes 50% voltage x (75/100) - 50% voltage x (1-75/100) = 25% voltage. The correction amount is calculated by taking into account the fluctuations of Ep and En. ΔEp is the fluctuation of Ep and is calculated using formula (4). ΔEn is the fluctuation of En and is calculated using formula (5).

ΔEp=EpFB/Eb-1...(4)

ΔEn=EnFB/Eb-1...(5)

Here, EpFB is the P-side DC voltage detection value detected and output by DC voltage detector 35. EnFB is the N-side DC voltage detection value detected and output by DC voltage detector 36. Eb indicates the reference value of the DC voltage. If there is no variation from the reference value, ΔEp and ΔEn are zero.

For example, if we assume that there is a 1.1-fold fluctuation on the Ep side and a 0.9-fold fluctuation on the En side, the output voltage when the voltage command is 0% will be 50% voltage x (50/100) x 1.1 - 50% voltage x (1 - 50/100) x 0.9 = 5% voltage. Furthermore, from equation (2), the correction amount ΔVh = 50% voltage x (50/100) x 0.1 - 50% voltage x (1 - 50/100) x (-0.1) = 5%. By adding the correction amount ΔVh = 5% to the voltage command of 0%, an estimate of the motor AC phase voltage can be obtained.

Figure 7 is a diagram to explain the three-level dipolar modulation voltage calculator 71.

The three-level dipolar modulation voltage calculator 71 receives the AC phase voltage command values (Vuref, Vvref, Vwref) and the DC voltage detection values (EpFB, EnFB) as inputs, and calculates α for each phase according to equation (3) in the Ep side pulse width calculator 711, outputting αu, αv, and αw. The DC voltage fluctuation calculator 712 calculates and outputs ΔEp and ΔEn from EpFB and EnFB according to equations (4) and (5). ΔEp, ΔEn, αu, αv, and αw are input to the correction amount calculator 713.

The correction amount calculator 713 calculates and outputs the correction amounts ΔVhu, ΔVhv, and ΔVhw for each phase according to equation (2). The correction amounts ΔVhu, ΔVhv, and ΔVhw are input to the dipolar motor phase voltage calculator 714 together with the AC phase voltage command value. The dipolar motor phase voltage calculator 714 adds the correction amount to the AC phase voltage command for each phase to calculate and output the motor AC phase voltage estimate values Vuh_d, Vvh_d, and Vwh_d during dipolar modulation.

<Calculation method for unipolar modulation>

Next, we will explain how to calculate the estimated motor AC phase voltage value when using three-level unipolar modulation.

Figure 8 shows the relationship between the voltage command and the output square wave voltage during unipolar modulation.

In the case of unipolar modulation, unlike dipolar modulation, a pulse signal is generated so that the area that changes depending on the pulse width on the positive and negative sides matches the command. For example, when outputting a 50% voltage, the positive side has a 50% pulse width, and the average voltage is 50%.

At this time, if the positive DC voltage Ep fluctuates with respect to the reference, the output will not be 50% voltage. Therefore, when estimating and calculating the AC phase voltage of an actual motor, it is necessary to take into account the fluctuation due to the DC voltage. In the case of unipolar modulation, it is sufficient to reflect the fluctuation ratio of Ep in the voltage command. Similarly, the negative side can be calculated by reflecting the fluctuation ratio of En in the voltage command. Therefore, in this embodiment, the estimated value of the AC phase voltage is calculated by multiplying the original voltage command by the fluctuation ratio, as shown in equations (6) and (7).

Vhp = AC voltage command % × Epk (when AC voltage command is positive) … (6)

Vhn = AC voltage command % × Enk (when AC voltage command is negative) … (7)

Here, Epk is the fluctuation ratio of the P-side DC voltage detection value, and is calculated using formula (8). Enk is the fluctuation ratio of the N-side DC voltage detection value, and is calculated using formula (9).

Epk=EpFB/Eb…(8)

Enk=EnFB/Eb…(9)

Here, EpFB is the P-side DC voltage detection value detected and output by DC voltage detector 35. EnFB is the N-side DC voltage detection value detected and output by DC voltage detector 36. Eb indicates the reference value of the DC voltage. When the DC voltage does not fluctuate from the reference value, Epk and Enk are 1.

Figure 9 is a diagram to explain the three-level unipolar modulation voltage calculator 72.

The three-level unipolar modulation voltage calculator 72 receives the AC phase voltage command values (Vuref, Vvref, Vwref) and the DC voltage detection values (EpFB, EnFB) as inputs, and calculates and outputs the fluctuation ratios Epk and Enk in the DC voltage fluctuation ratio calculator 721 according to equations (8) and (9). Epk, Enk, Vuref, Vvref, and Vwref are input to the phase voltage calculator 722. The phase voltage calculator 722 calculates and outputs Vhp and Vhn, respectively, according to equations (6) and (7). Vhp and Vhn of each phase are input to the unipolar motor phase voltage calculator 723 together with the AC phase voltage command value. The unipolar motor phase voltage calculator 723 outputs Vhp if the polarity of the AC voltage command value is positive, and outputs Vhn if it is negative. In this way, the motor AC phase voltage estimates Vuh_u, Vvh_u, and Vwh_u for unipolar modulation are generated.

As described above, in the first embodiment, in the three-level power converter, the DC voltage fluctuation is taken into account in the AC phase voltage command, and the calculation method is switched between dipolar modulation and unipolar modulation to calculate the motor AC line voltage estimates (Vuvh, Vvwh) from the motor AC phase voltage estimates (Vuh, Vvh, Vwh), and correction control is performed based on this. This allows for highly accurate correction control that is not affected by ripple components due to square waves or filter delays, compared to when a conventional motor AC line voltage detector is used. In addition, because an AC line voltage detector is not used, risks such as malfunction of correction control or unplanned stoppage due to an abnormality in the AC line voltage detector are eliminated.

In Example 2, a power conversion device using a two-level converter is illustrated.

Figure 10 is an overall configuration diagram of a power conversion device according to Example 2. In the power conversion device 102 of this embodiment shown in Figure 10, the same components as those of the power conversion device 100 of Example 1 shown in Figure 1 are given the same reference numerals. The power conversion device 102 of Example 2 differs from the power conversion device 100 shown in Figure 1 in that it does not have parts related to the neutral point, which is a characteristic of a three-level converter, such as converter neutral point resistors 24, 34 and neutral point voltage controllers 55, 65, and the like, and that the DC voltage detector 37 detects Vdc between the P side and the N side.

Here, we will mainly explain the differences between Example 2 and Example 1.

In the power conversion device 102 of the second embodiment, the inverter control device 6 includes a speed command generator 61, a speed controller 62, a current controller 63, a pulse generator 64, an excitation current command generator 66, a magnetic flux controller 67, a correction controller 68, an adder 69, and a two-level motor voltage calculator 80. The speed command generator 61, the speed controller 62, the current controller 63, the pulse generator 64, the excitation current command generator 66, the magnetic flux controller 67, the correction controller 68, and the adder 69 are basically the same as those of the first embodiment.

Here, we will explain the two-level motor voltage calculator 80 in detail.

As shown in FIG. 10, the inverter voltage command values (AC phase voltage command values Vuref, Vvref, Vwref) output from the current controller 63 and the positive side DC voltage detection value VdcFB output from the DC voltage detector 37 are input to the two-level motor voltage calculator 80. Using these input signals, the two-level motor voltage calculator 80 calculates and outputs the AC line voltage estimates (Vuvh, Vvwh) of the motor. The AC line voltage estimates of the motor are input to the correction controller 68.

Next, the two-level motor voltage calculator 80 according to the second embodiment will be described in more detail.

Figure 11 is a diagram for explaining the two-level motor voltage calculator 80. The three-level inverter and the two-level inverter use different methods for calculating the motor voltage. The two-level motor voltage calculator 80 includes a two-level modulation voltage calculator 81 and an AC line voltage calculator 82. The two-level motor voltage calculator 80 calculates and outputs the motor AC phase voltage estimates (Vuh, Vvh, Vwh) and motor AC line voltage estimates (Vuvh, Vvwh) from the AC phase voltage command values (Vuref, Vvref, Vwref) and the DC voltage detection value (VdcFB).

Next, we will explain how to calculate the estimated motor AC phase voltage in Example 2.

Figure 12 is a diagram to explain the relationship between the voltage command and the output square wave voltage in the two-level case.

In the case of two levels, unlike the case of three levels, pulse signals are generated so that the area of one pulse on both the positive and negative sides matches the command. For example, when 100% voltage is output as a voltage command, a pulse signal with a 100% pulse width on the P side is generated. When 0% voltage is output, a pulse signal with a 50% pulse width on the P side and a 50% pulse width on the N side is generated. When -100% voltage is output, a pulse signal with a 100% pulse width on the N side is generated.

Here, if the DC voltage Vdc between the P side and N side fluctuates with respect to the reference, the voltage command and the actual output voltage will not match. Therefore, to estimate and calculate the actual AC phase voltage of the motor, it is necessary to take into account the fluctuation due to the DC voltage. In the two-level system, the estimated AC phase voltage of the motor can be calculated by reflecting the fluctuation ratio of the DC voltage Vdc in the AC voltage command. Therefore, in this embodiment, the AC phase voltage is estimated and calculated by multiplying the original voltage command by the fluctuation ratio, as in equation (10).

Vh = AC voltage command % × Vdck … (10)

Here, Vdck is the fluctuation ratio of the DC voltage detection value and is calculated using formula (11).

Vdck=VdcFB/Vdcb...(11)

Here, VdcFB is the DC voltage detection value between the P side and N side detected and output by the DC voltage detector 37. Vdcb indicates the reference value of the DC voltage. If the DC voltage does not fluctuate from the reference value, Vdck will be 1.

Figure 13 is a diagram for explaining the two-level modulation voltage calculator 81.

The two-level modulation voltage calculator 81 receives the AC phase voltage command values (Vuref, Vvref, Vwref) and the DC voltage detection value (VdcFB). The DC voltage fluctuation ratio calculator 811 calculates and outputs Vdck from VdcFB according to equation (11). Vdck, Vuref, Vvref, and Vwref are input to the phase voltage calculator 812. The phase voltage calculator 812 calculates and outputs the motor AC phase voltage estimation values Vuh, Vvh, and Vwh according to equation (10).

As described above, in the second embodiment, the two-level converter takes into account DC voltage fluctuations in the AC phase voltage command, calculates the motor AC line voltage estimate (Vuvh, Vvwh) from the motor AC phase voltage estimate (Vuh, Vvh, Vwh), and uses this to perform correction control. This allows correction control to be performed with high accuracy without being affected by ripple components due to square waves or filter delays, compared to when a conventional motor AC line voltage detector is used. In addition, because an AC line voltage detector is not used, risks such as correction control malfunctions and unplanned stoppages due to abnormalities in the AC line voltage detector can be eliminated.

In the correction control in this embodiment, the fluctuation of the speed electromotive voltage caused by the change in excitation inductance due to magnetic flux saturation is controlled to a predetermined value by correcting the excitation current based on the motor voltage estimated value in this embodiment. In addition, the slip control error caused by the change in the secondary resistance of the motor can also be appropriately controlled by correcting the slip amount based on the motor voltage estimated value in this embodiment.

In Example 3, a power conversion device is illustrated that has an AC line voltage detector and has a self-check function for diagnosing an abnormality in the AC line voltage detector in a configuration in which the detected value is used for correction control.

Figure 14 is an overall configuration diagram of a power conversion device according to Example 3.

In the power conversion device 103 of this embodiment shown in FIG. 14, the same components as those of the power conversion device 100 according to the first embodiment shown in FIG. 1 are denoted by the same reference numerals. The power conversion device 103 of the third embodiment differs from the power conversion device 100 shown in FIG. 1 in that it includes an AC line voltage detector 10 and a filter circuit 11, and that an AC line voltage detector abnormality determiner 90 and a display 91 are added.

Here, we will mainly explain the differences between Example 3 and Example 1.

As described above, in equipment equipped with an AC line voltage detector, an unplanned stop may occur due to a malfunction of the correction control caused by an abnormality in the AC line voltage detector. Therefore, the power conversion device 103 of the third embodiment is configured to diagnose an abnormality in the AC line voltage detector using an estimated motor voltage value.

Next, the AC line voltage detector abnormality judger 90 according to the third embodiment will be described in detail.

As shown in FIG. 14, the inverter control device 6 includes a speed command generator 61, a speed controller 62, a current controller 63, a pulse generator 64, a neutral point voltage controller 65, an excitation current command generator 66, a magnetic flux controller 67, a correction controller 68, an adder 69, a three-level motor voltage calculator 70, an AC line voltage detector abnormality judger 90, and a display 91. The speed command generator 61, the speed controller 62, the current controller 63, the pulse generator 64, the neutral point voltage controller 65, the excitation current command generator 66, the magnetic flux controller 67, the correction controller 68, the adder 69, and the three-level motor voltage calculator 70 are basically the same as those in the first embodiment.

Here, we will explain in detail the AC line voltage detector abnormality judgement device 90.

As shown in FIG. 14, the AC line voltage detector anomaly judger 90 receives the AC line voltage detection values (VuvFB, VvwFB) from the AC line voltage detector 10 via the filter circuit 11, and receives the AC line voltage estimates (Vuvh, Vvwh) of the motor from the three-level motor voltage calculator 70. The AC line voltage detector anomaly judger 90 performs an anomaly diagnosis of the AC line voltage detector based on these input signals.

Figure 15 is a flowchart for diagnosing an abnormality in an AC line voltage detector.

Normally, unless the power converter is stopped, the output of the AC line voltage detector is not zero. If there is some abnormality, such as a break or loosening of the AC line voltage detection loop, only the output of the AC line voltage detector will be zero.

In the abnormality diagnosis 201 shown in FIG. 15, if the output of any of the AC line voltage detectors is zero in step 202, then in step 203 it is determined that there is an abnormality in the AC line voltage detection loop at the relevant location, i.e., an abnormality in the wiring connected to the AC line voltage detector, and a message is displayed indicating that there is an abnormality in the AC line voltage detection loop. Note that at this time, if the output of the AC line voltage detector is sufficiently close to zero, it may be determined that the output of the AC line voltage detector is essentially zero. Therefore, if the output of the AC line voltage detector is equal to or lower than a predetermined threshold value, it is determined that there is an abnormality in the AC line voltage detection loop at the relevant location.

If the output of any of the AC line voltage detectors is not zero in step 202, then in step 204, the estimated UV AC line voltage Vuvh is used as a reference, and the detected UV AC line voltage VuvFB is compared with that reference. If there is a deviation of a predetermined threshold or more between the detected UV AC line voltage VuvFB and the reference, it is determined that there is an abnormality in the AC line voltage detector, and in step 205, a message is displayed indicating that there is an abnormality in the Vuv AC line voltage detector.

If in step 204 there is no deviation of a predetermined threshold or more between the UV-to-AC line voltage detection value VuvFB and the UV-to-AC line voltage estimate value Vuvh, then in step 206 the VW-to-VW AC line voltage detection value VvwFB is compared with the VW-to-VW AC line voltage estimate value Vvwh as a reference. If there is a deviation of a predetermined threshold or more between the VW-to-VW AC line voltage detection value VvwFB and the reference, it is determined that there is an abnormality in the AC line voltage detector, and in step 207 a message is displayed indicating that there is an abnormality in the Vvw AC line voltage detector.

If an abnormality is indicated in any of steps 203, 205, or 207, a message prompting inspection and replacement of the abnormal part is displayed in step 208 of FIG. 15, and the series of operations ends.

As described above, in a power conversion device having an AC line voltage detector, by comparing the estimated AC line voltage value with a reference, it is possible to detect an abnormality in the AC line voltage detector and perform efficient maintenance by displaying a message recommending inspection and replacement of the defective AC line voltage detector.

In Example 4, a power conversion device is illustrated that has an AC line voltage detector and a function for continuing operation when an abnormality occurs in the AC line voltage detector in a configuration in which the detection value is used for correction control. Continuing operation using an alternative signal instead of the detection value when an abnormality occurs in the AC line voltage detector is referred to as "standby operation."

Figure 16 is an overall configuration diagram of a power conversion device according to Example 4.

In the power conversion device 104 of Example 4 shown in FIG. 16, the same components as those of the power conversion device 103 of Example 3 shown in FIG. 14 are denoted by the same reference numerals. The power conversion device 104 of Example 4 differs from the power conversion device 103 of Example 3 in that it additionally includes an abnormality calculation value switch 92.

Here, we will mainly explain the differences between Example 4 and Example 3.

The abnormality calculation value switch 92 receives the AC line voltage detection value (VuvFB, VvwFB) from the AC line voltage detector 10 via the filter circuit 11, together with abnormality determination information indicating whether or not there is an abnormality in the AC line voltage estimate value (Vuvh, Vvwh) of the motor output from the AC line voltage detector abnormality determiner 90. If the abnormality determination information does not indicate that there is an abnormality in the AC line voltage detection value of the motor, the abnormality calculation value switch 92 outputs the detection value of the AC line voltage detector 10 to the correction controller 68. However, if the abnormality determination information indicates that there is an abnormality in the AC line voltage detection value of the motor, the abnormality calculation value switch 92 outputs an alternative signal to the correction controller 68, rather than the detection value of the abnormal AC line voltage detector 10.

Next, the abnormality calculation value switch 92 in Example 4 will be described in detail.

Figure 17 is a diagram to explain the abnormality calculation value switch 92.

In FIG. 17, the abnormality calculation value switch 92 receives the AC line voltage detection values VuvFB and VvwFB, and further receives the AC line voltage estimate values (Vuvh, Vvwh) and signals indicating whether the detection value of the AC line voltage detector 10 is abnormal (VuvFB abnormality judgment signal, VvwFB abnormality judgment signal) from the AC line voltage detector abnormality judger 90. The VuvFB abnormality judgment signal is a signal indicating whether the AC line voltage detection value VuvFB is abnormal. The VvwFB abnormality judgment signal is a signal indicating whether the AC line voltage detection value VvwFB is abnormal.

If VuvFB is abnormal, the abnormality calculation value switch 92 outputs the motor AC line voltage estimate value Vuvh to the correction controller 68 as Vuvout instead of VuvFB. Also, if VvwFB is abnormal, the abnormality calculation value switch 92 outputs the motor AC line voltage estimate value Vvwh to the correction controller 68 as Vvwout instead of VvwFB. The correction controller 68 calculates the correction amount based on Vuvout and Vvwout.

As described above, in this embodiment, as in the third embodiment, in a power conversion device having an AC line voltage detector, an abnormality in the AC line voltage detector is determined by comparing the estimated AC line voltage value as a reference, and a display is displayed recommending inspection and replacement of the defective AC line voltage detector, thereby enabling efficient maintenance.

Furthermore, in this embodiment, if it is determined that an abnormality exists in the AC line voltage detector, a display is displayed recommending inspection and replacement of the abnormal AC line voltage detector, and at the same time, the abnormal AC line voltage detection value is replaced with the corresponding AC line voltage estimate value, allowing operation to continue and reducing the risk of unplanned shutdown of a system equipped with a power conversion device. For example, this allows the system to continue operation by running it until the next regular inspection, and during the regular inspection, the identified abnormal AC line voltage detector can be quickly replaced, etc.

Note that, although examples 3 and 4 have been described using a three-level converter, the present invention is not limited to this. It is also applicable to the case where a two-level converter is used.

The embodiment described above includes the items listed below. However, the items included in the embodiment described above are not limited to those listed below.

(Item 1)
A converter that converts an AC input into a plurality of potentials;
an inverter for converting the voltages of the plurality of potentials into an AC output for an electric motor;
a smoothing capacitor connected between two of the plurality of potentials to suppress potential fluctuation between the potentials;
a DC voltage detector that detects a potential difference between potentials to which the smoothing capacitor is connected as a DC voltage detection value;
a current detector that detects an output current of the inverter and outputs the detected current as an inverter output current;
an inverter output current controller that generates an inverter output voltage command for the inverter so that the inverter output current coincides with an inverter output current command;
a motor voltage calculator that calculates a motor voltage estimation value, which is an estimation value of an AC line voltage of the motor, from the inverter output voltage command and the DC voltage detection value;
a correction control unit that calculates a correction value for correcting a signal for controlling the electric motor from the electric motor voltage estimation value;
an adder that adds the correction value to a control command signal to generate the inverter output current command;
A power conversion device having the following:
According to this, an estimate of the AC line voltage of the motor is calculated from the inverter output voltage command and the DC voltage detection value, and a correction value for correcting the signal for controlling the motor is calculated from the estimate, making it possible to perform highly accurate correction control without using an AC line voltage detector.

(Item 2)
The power conversion device is capable of switching between a plurality of modulation methods,
The motor voltage calculator calculates the motor voltage estimation value using a calculation method corresponding to a modulation method of the power conversion device.
2. The power conversion device according to item 1.
This makes it possible to realize a power conversion device that can switch between a plurality of modulation methods depending on the application, etc.

(Item 3)
the power converter is a three-level power converter;
The plurality of modulation methods includes a dipolar modulation method,
The motor voltage calculator includes:
a pulse width calculator that calculates positive and negative pulse widths from the inverter output voltage command; a DC voltage fluctuation calculator that calculates a fluctuation amount of the DC voltage detection value with respect to a predetermined reference voltage; and a correction amount calculator that calculates a correction amount using the pulse width and the fluctuation amount.
Equipped with
When the dipolar modulation method is used, the correction amount is calculated using the pulse width calculator, the DC voltage fluctuation amount calculator, and the correction amount calculator, and the inverter output voltage command is corrected by the correction amount to calculate the motor voltage estimation value.
3. The power conversion device according to item 2.
This allows for highly accurate control of the motor when a three-level dipolar modulation scheme is used.

(Item 4)
the power converter is a three-level power converter;
The plurality of modulation methods includes a unipolar modulation method,
The motor voltage calculator includes:
a DC voltage fluctuation ratio calculator that calculates a fluctuation ratio of the DC voltage detection value to a predetermined reference voltage, and a phase voltage calculator that calculates an AC phase voltage estimation value when the AC voltage command is positive and when the AC voltage command is negative, from the AC voltage command, which is the inverter output voltage command, and the fluctuation ratio,
When the unipolar modulation method is used, the DC voltage fluctuation ratio calculator and the phase voltage calculator calculate the AC phase voltage estimation value, and output the AC phase voltage estimation value according to the polarity of the AC voltage command, thereby generating the motor voltage estimation value.
3. The power conversion device according to item 2.
This allows for highly accurate control of the motor when a three-level unipolar modulation scheme is used.

(Item 5)
the power converter is a two-level power converter;
The motor voltage calculator includes:
a DC voltage fluctuation ratio calculator for calculating a fluctuation ratio of the DC voltage detection value to a predetermined reference voltage,
Calculating the fluctuation ratio by the DC voltage fluctuation ratio calculator, and calculating the motor voltage estimated value from the AC voltage command, which is the inverter output voltage command, and the fluctuation ratio.
2. The power conversion device according to item 1.
This enables highly accurate control of the motor in a two-level modulation system.

(Item 6)
A converter that converts an AC input into a plurality of potentials;
an inverter for converting the voltages of the plurality of potentials into an AC output for an electric motor;
a smoothing capacitor connected between two of the plurality of potentials to suppress potential fluctuation between the potentials;
a DC voltage detector that detects a potential difference between potentials to which the smoothing capacitor is connected as a DC voltage detection value;
an AC line voltage detector that detects an output voltage of the inverter and outputs the detected voltage as a motor voltage detection value;
a correction control unit that calculates a correction value for correcting a signal for controlling the electric motor from the detected electric motor voltage value;
an adder that adds the correction value to a control command signal to generate an inverter output current command;
a current detector that detects an output current of the inverter and outputs the detected current as an inverter output current;
an inverter output current controller that generates an inverter output voltage command for the inverter so that the inverter output current coincides with the inverter output current command;
a motor voltage calculation unit that calculates a motor voltage estimation value that is an estimation value of an AC line voltage of the motor from the inverter output voltage command and the DC voltage detection value;
an AC line voltage detector abnormality determiner that determines an abnormality in the AC line voltage detector based on the motor voltage estimate value;
A power conversion device having the following:
According to this, an estimate of the AC line voltage of the motor is calculated from the inverter output voltage command and the DC voltage detection value, and an abnormality in the AC line voltage detector is determined based on the estimate, making it possible to detect an abnormality in the AC line voltage detector in a configuration that uses an AC line voltage detector.

(Item 7)
the AC line voltage detector abnormality determiner determines that there is an abnormality in wiring connected to an AC line voltage detector whose output is equal to or lower than a predetermined threshold value;
7. The power conversion device according to item 6.
According to this, in a configuration using an AC line voltage detector, it is further possible to detect an abnormality in the wiring connected to the AC line voltage detector.

(Item 8)
and an abnormality-time calculation value switch that, when the AC line voltage detector abnormality determiner determines that the AC line voltage detector is abnormal, inputs the motor voltage estimated value calculated by the motor voltage calculation unit to the correction control unit instead of the motor voltage detection value from the AC line voltage detector determined to be abnormal.
7. The power conversion device according to item 6.
According to this, an abnormality in the AC line voltage detector is determined and the motor voltage detection value from the abnormal AC line voltage detector is switched to the motor voltage estimate value calculated by the motor voltage calculation unit. Therefore, in a configuration using an AC line voltage detector, it is possible to continue control of the motor normally even if the AC line voltage detector becomes abnormal.

(Item 9)
when determining that an abnormality has occurred in the AC line voltage detector, the AC line voltage detector abnormality determiner causes a display device to display information about the abnormality.
9. The power conversion device according to any one of items 6 to 8.
According to this, when an abnormality is determined in the AC line voltage detector, information regarding the abnormality is displayed, making it possible to easily know the abnormality of the AC line voltage detector in a configuration that uses an AC line voltage detector.

(Item 10)
A converter that converts an AC input into a plurality of potentials;
an inverter for converting the voltages of the plurality of potentials into an AC output for an electric motor;
a smoothing capacitor connected between two of the plurality of potentials to suppress potential fluctuation between the potentials;
a DC voltage detector that detects a potential difference between potentials to which the smoothing capacitor is connected as a DC voltage detection value;
A method for controlling an electric motor using a power conversion device comprising:
Detecting an output current of the inverter as an inverter output current;
generating an inverter output voltage command for the inverter such that the inverter output current coincides with an inverter output current command;
calculating a motor voltage estimate value, which is an estimate value of an AC line voltage of the motor, from the inverter output voltage command and the DC voltage detection value;
calculating a correction value for correcting a signal for controlling the motor from the motor voltage estimation value;
adding the correction value to a control command signal to generate the inverter output current command;
Electric motor control method.

(Item 11)
A converter that converts an AC input into a plurality of potentials;
an inverter for converting the voltages of the plurality of potentials into an AC output for an electric motor;
a smoothing capacitor connected between two of the plurality of potentials to suppress potential fluctuation between the potentials;
a DC voltage detector that detects a potential difference between potentials to which the smoothing capacitor is connected as a DC voltage detection value;
an AC line voltage detector that detects an output voltage of the inverter and outputs the detected voltage as a motor voltage detection value;
An abnormality detection method for detecting an abnormality in a power conversion device comprising:
calculating a correction value for correcting a signal for controlling the electric motor from the detected electric motor voltage value;
adding the correction value to a control command signal to generate an inverter output current command;
Detecting an output current of the inverter as an inverter output current;
generating an inverter output voltage command for the inverter such that the inverter output current coincides with the inverter output current command;
calculating an estimated motor voltage value, which is an estimated value of an AC line voltage of the motor, from the inverter output voltage command and the detected DC voltage value;
determining whether or not the AC line voltage detector is abnormal based on the estimated motor voltage value;
Anomaly detection methods.

1...AC power supply, 2...converter unit, 3...inverter unit, 4...electric motor, 5...converter control device, 6...inverter control device, 7...current detector, 8...speed detector, 9...current detector, 10...AC line voltage detector, 11...filter circuit, 21...converter power conversion section, 22...converter P-side smoothing capacitor, 23...converter N-side smoothing capacitor, 24...converter neutral point resistor, 25...converter P-side DC voltage detector, 26...converter N-side DC voltage detector, 31... inverter power conversion section, 32... inverter P-side smoothing capacitor, 33... inverter N-side smoothing capacitor, 34... inverter neutral point resistor, 35... inverter P-side DC voltage detector, 36... inverter N-side DC voltage detector, 37... DC voltage detector, 40... P wiring, 41... C wiring, 42... N wiring, 51... DC voltage command generator, 52... DC voltage controller, 53... current controller, 54... pulse generator, 55... neutral point voltage controller, 61... speed command generator, 62... speed controller, 6 3...current controller, 64...pulse generator, 65...neutral point voltage controller, 66...excitation current command generator, 67...magnetic flux controller, 68...correction controller, 69...adder, 70...three-level motor voltage calculator, 71...three-level dipolar modulation voltage calculator, 72...three-level unipolar modulation voltage calculator, 73...correction calculation selection unit, 74...AC line voltage calculator, 80...two-level motor voltage calculator, 81...two-level modulation voltage calculator, 82...AC line voltage calculator, 90...AC line voltage detector abnormality judgment device, 91... display device, 92... abnormality-time calculation value switch, 100... power conversion device, 101... power conversion device, 102... power conversion device, 103... power conversion device, 104... power conversion device, 711... Ep side pulse width calculator, 712... DC voltage fluctuation amount calculator, 713... correction amount calculator, 714... dipolar motor phase voltage calculator, 721... DC voltage fluctuation ratio calculator, 722... phase voltage calculator, 723... unipolar motor phase voltage calculator, 811... DC voltage fluctuation ratio calculator, 812... phase voltage calculator

Claims (11)

A converter that converts an AC input into a plurality of potentials;
an inverter for converting the voltages of the plurality of potentials into an AC output for an electric motor;
a smoothing capacitor connected between two of the plurality of potentials to suppress potential fluctuation between the potentials;
a DC voltage detector that detects a potential difference between potentials to which the smoothing capacitor is connected as a DC voltage detection value;
a current detector that detects an output current of the inverter and outputs the detected current as an inverter output current;
an inverter output current controller that generates an inverter output voltage command for the inverter so that the inverter output current coincides with an inverter output current command;
a motor voltage calculator that calculates a motor voltage estimation value, which is an estimation value of an AC line voltage of the motor, from the inverter output voltage command and the DC voltage detection value;
a correction control unit that calculates a correction value for correcting a control command signal for controlling the electric motor from the electric motor voltage estimation value;
an adder that adds the correction value to the control command signal to generate the inverter output current command;
A power conversion device having the following: The power conversion device is capable of switching between a plurality of modulation methods,
The motor voltage calculator calculates the motor voltage estimation value using a calculation method corresponding to a modulation method of the power conversion device.
The power conversion device according to claim 1 . the power converter is a three-level power converter;
The plurality of modulation methods includes a dipolar modulation method,
The motor voltage calculator includes:
a pulse width calculator that calculates positive and negative pulse widths from the inverter output voltage command; a DC voltage fluctuation calculator that calculates a fluctuation amount of the DC voltage detection value with respect to a predetermined reference voltage; and a correction amount calculator that calculates a correction amount using the pulse width and the fluctuation amount.
Equipped with
When the dipolar modulation method is used, the correction amount is calculated using the pulse width calculator, the DC voltage fluctuation amount calculator, and the correction amount calculator, and the inverter output voltage command is corrected by the correction amount to calculate the motor voltage estimation value.
The power conversion device according to claim 2 . the power converter is a three-level power converter;
The plurality of modulation methods includes a unipolar modulation method,
The motor voltage calculator includes:
a DC voltage fluctuation ratio calculator that calculates a fluctuation ratio of the DC voltage detection value to a predetermined reference voltage, and a phase voltage calculator that calculates an AC phase voltage estimation value when the AC voltage command is positive and when the AC voltage command is negative, from the AC voltage command, which is the inverter output voltage command, and the fluctuation ratio,
When the unipolar modulation method is used, the DC voltage fluctuation ratio calculator and the phase voltage calculator calculate the AC phase voltage estimation value, and output the AC phase voltage estimation value according to the polarity of the AC voltage command, thereby generating the motor voltage estimation value.
The power conversion device according to claim 2 . the power converter is a two-level power converter;
The motor voltage calculator includes:
a DC voltage fluctuation ratio calculator for calculating a fluctuation ratio of the DC voltage detection value to a predetermined reference voltage,
Calculating the fluctuation ratio by the DC voltage fluctuation ratio calculator, and calculating the motor voltage estimated value from the AC voltage command, which is the inverter output voltage command, and the fluctuation ratio.
The power conversion device according to claim 1 . A converter that converts an AC input into a plurality of potentials;
an inverter for converting the voltages of the plurality of potentials into an AC output for an electric motor;
a smoothing capacitor connected between two of the plurality of potentials to suppress potential fluctuation between the potentials;
a DC voltage detector that detects a potential difference between potentials to which the smoothing capacitor is connected as a DC voltage detection value;
an AC line voltage detector that detects an output voltage of the inverter and outputs the detected voltage as a motor voltage detection value;
a correction control unit that calculates a correction value for correcting a control command signal for controlling the electric motor from the detected electric motor voltage value;
an adder that adds the correction value to the control command signal to generate an inverter output current command;
a current detector that detects an output current of the inverter and outputs the detected current as an inverter output current;
an inverter output current controller that generates an inverter output voltage command for the inverter so that the inverter output current coincides with the inverter output current command;
a motor voltage calculation unit that calculates a motor voltage estimation value that is an estimation value of an AC line voltage of the motor from the inverter output voltage command and the DC voltage detection value;
an AC line voltage detector abnormality determiner that determines an abnormality in the AC line voltage detector based on the motor voltage estimate value;
A power conversion device having the following: the AC line voltage detector abnormality determiner determines that there is an abnormality in wiring connected to an AC line voltage detector whose output is equal to or lower than a predetermined threshold value;
The power converter according to claim 6. and an abnormality-time calculation value switch that, when the AC line voltage detector abnormality determiner determines that the AC line voltage detector is abnormal, inputs the motor voltage estimated value calculated by the motor voltage calculation unit to the correction control unit instead of the motor voltage detection value from the AC line voltage detector determined to be abnormal.
The power converter according to claim 6. when determining that an abnormality has occurred in the AC line voltage detector, the AC line voltage detector abnormality determiner causes a display device to display information about the abnormality.
The power conversion device according to any one of claims 6 to 8. A converter that converts an AC input into a plurality of potentials;
an inverter for converting the voltages of the plurality of potentials into an AC output for an electric motor;
a smoothing capacitor connected between two of the plurality of potentials to suppress potential fluctuation between the potentials;
a DC voltage detector that detects a potential difference between potentials to which the smoothing capacitor is connected as a DC voltage detection value;
A method for controlling an electric motor using a power conversion device comprising:
Detecting an output current of the inverter as an inverter output current;
generating an inverter output voltage command for the inverter such that the inverter output current coincides with an inverter output current command;
calculating a motor voltage estimate value, which is an estimate value of an AC line voltage of the motor, from the inverter output voltage command and the DC voltage detection value;
calculating a correction value for correcting a control command signal for controlling the motor from the motor voltage estimation value;
adding the correction value to the control command signal to generate the inverter output current command;
Electric motor control method. A converter that converts an AC input into a plurality of potentials;
an inverter for converting the voltages of the plurality of potentials into an AC output for an electric motor;
a smoothing capacitor connected between two of the plurality of potentials to suppress potential fluctuation between the potentials;
a DC voltage detector that detects a potential difference between potentials to which the smoothing capacitor is connected as a DC voltage detection value;
an AC line voltage detector that detects an output voltage of the inverter and outputs the detected voltage as a motor voltage detection value;
An abnormality detection method for detecting an abnormality in a power conversion device comprising:
calculating a correction value for correcting a control command signal for controlling the electric motor from the detected electric motor voltage value;
adding the correction value to the control command signal to generate an inverter output current command;
Detecting an output current of the inverter as an inverter output current;
generating an inverter output voltage command for the inverter such that the inverter output current coincides with the inverter output current command;
calculating an estimated motor voltage value, which is an estimated value of an AC line voltage of the motor, from the inverter output voltage command and the detected DC voltage value;
determining whether or not the AC line voltage detector is abnormal based on the estimated motor voltage value;
Anomaly detection methods.

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