JP3283155B2 - Power converter - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a power converter.
In particular, the present invention relates to a power conversion device including a converter that generates a DC power supply of an inverter that drives a motor and regenerates power.

[0002]

2. Description of the Related Art A DC power source generated by a power conversion device having a converter capable of reversible conversion using a transistor is used as a DC power source for an inverter that operates a motor used as a drive source of a machine tool at a variable speed. Is done. In this type of power converter, the operating energy of the motor can be regenerated to the AC power source when the motor is decelerated. However, in recent years,
When a regenerative current having a large amount of distortion is regenerated to an AC power supply, there is a problem that adverse effects such as malfunction of other machines are caused. So, in order to solve such a problem,
Conventionally, a power converter shown in FIG. 5 has been used, and it has been practically used to regenerate a sine wave current with less distortion. In the power converter shown in FIG. 5, DC voltage Vdc generated by converter 1 is converted into AC by an inverter circuit. The variable speed operation of the AC motor is performed by the converted AC. The three-phase alternating current input / output to / from the converter 1 is insulated via the current detector 14 and detected. The alternating current input / output based on this detection value is feedback-controlled so as to be a sine wave.

Here, the operation of the control circuit within the dotted line shown in FIG. 5 will be described. A target voltage of the DC voltage Vdc charged in the smoothing capacitor 2 is set in the reference voltage source 21, and the target voltage and the DC voltage Vdc are subtracted by the subtractor 19.
Is subtracted from the detected value to obtain a voltage deviation signal. This voltage deviation signal is amplified by the amplifier 18, and the amplified voltage deviation signal is input to the vector rotator 15.
From the vector rotator 15, a sine wave current command having the same phase as the three-phase AC power supply voltage is generated. That is, the isolator 3
The line voltage waveform of the three-phase AC voltage detected through the converter is converted into a phase voltage waveform by the converter 22. Thereafter, the phase voltage waveform is multiplied by the output of the amplifier 18 to output a sine wave current command. . This current command is subtracted by the subtractor 17 from the value detected via the current detector 14, and the subtracted value is input to the PWM control circuit 20 after being amplified by the amplifier 23. In the PWM control circuit 20, the command signal is pulse-width modulated by the carrier signal, and an ON / OFF control signal for the transistor is created. This P
The operation of the WM control circuit 20 is generally used for the control circuit of the inverter circuit, and a detailed description is omitted. By the operation of these circuits, the current flowing through the converter 1 is feedback-controlled according to the sine wave current command output from the vector rotator 15, and the current flowing through each phase is shaped into a sine wave. In addition, the choke coil 7 inserted between the AC power supply and the converter 1 smoothes the ripple of the AC current input and output by the switching of the converter 1 so that a shaping closer to a sine wave is performed.

[0004]

In the above-described conventional power converter, the alternating current of each phase input to and output from the converter 1 is detected, and the feedback control is performed based on this detection. For this reason, a plurality of current detection means are required, and as a result, the power converter becomes expensive. Also,
In order to perform sine wave regeneration, the transistors of the converter 1 need to be constantly switched at a high speed, and the transistors generate heat due to switching loss. The present invention has been made to solve the above problems, the present invention,
It is an object of the present invention to provide an inexpensive power converter that can minimize a loss and realize a regenerative current with less distortion by feedback control of one current detector.

[0005]

In order to solve the above problems, according to the first aspect of the present invention, the diodes are arranged in reverse.
A converter is composed of a plurality of transistors connected in columns.
And convert it by ON / OFF control of the PWM control circuit.
Regenerates the power on the DC voltage output side of the motor to the three-phase AC power supply side
A three-phase AC from the converter.
Means for detecting a three-phase AC voltage connected to a power supply;
Ratio to determine the magnitude of each phase voltage of the three-phase AC voltage put out
A comparator , a converter that outputs a voltage command for each phase based on the detected three-phase AC voltage, and a DC voltage of the converter .
And one current detector for detecting the output side DC currents, the
The voltage command output by the converter is detected by the current detector.
And means for correcting the direct current was, the PWM
The control circuit is configured to determine whether the comparator determines the magnitude relationship.
That is, the transistor connected to the phase having the maximum absolute value is always kept on, and the current detector detects
DC current flowing through the transistor held in the ON state
Based on the corrected voltage command, the remaining two phases
It is characterized in that ON / OFF control of a connected transistor is performed . The invention according to claim 2 is the power conversion device according to
The device further comprises a DC voltage output side of the converter.
Voltage detecting means for detecting a voltage, and compensating the voltage command.
The means for correcting the phase of the phase determined by the comparator
The voltage command of the phase whose absolute value is the maximum and the current detection
Flows to the transistor that is kept in the ON state detected by the detector.
DC current, and the DC voltage detected by the voltage detecting means.
Further, the voltage command of each phase is corrected. Ma
The invention according to claim 3 is a method for correcting the voltage command.
The stage is an absolute phase among the phases for which the comparator has determined the magnitude relation.
The voltage command of the phase whose value is the maximum, and the target of the DC voltage
From the reference voltage and the difference between the detected DC voltage,
Generating a current command for the phase having the maximum absolute value,
Current command and the ON state detected by the current detector
The difference between the DC current flowing through the
It is characterized in that the command is corrected. Further, according to claim 4
The invention according to claim 1, wherein the DC current detected by the current detector is P
The triangle wave of the triangle wave carrier signal used in WM control is
Provide a means to sample / hold at the point
The means for correcting the voltage command includes the sample / e
More Rudo by direct current, to correct the phase of the voltage command
It is characterized by that.

[0006]

In the power converter according to the present invention, the magnitude relationship between the three-phase AC voltages connected to the converter is detected, and one transistor of the converter is turned on for a certain period, so that the number of switching operations can be reduced and switching loss can be reduced. Can be suppressed. In the power converter according to the present invention, the DC current output from the converter is further sampled / held at the timing when the triangular wave of the carrier signal reaches the peak, and a current equal to the current flowing through the transistor held in the ON state is detected. An AC current command is generated from the DC current command corresponding to the DC voltage and the AC voltage detection value of the phase held in the ON state. That is, the current command corresponding to the current to be passed to the transistor held in the ON state is compared with the sampled / held current value, and the ON state of the transistor connected to two phases other than the phase connected to the transistor turned ON is compared. Control can be performed while correcting the / OFF signal. Therefore, feedback control can be realized with one current detector.

[0007]

Embodiments of the present invention will be described below with reference to the drawings. In the present embodiment, the elements denoted by the same reference numerals as those shown in FIG. 5 described above have the same functions, and the description thereof will be omitted. FIG. 1 is a block circuit diagram of an example of a power conversion device according to the present invention.
First, when converting power from AC to DC (during power running), the diodes d1 to d
The AC voltage is converted without control by the operation of 6, and the smoothing capacitor 2 is charged to generate the DC voltage Vdc. The current (iR, iS, iT) flowing through each phase of the AC power supply at this time
Is a waveform shown in FIG. When the AC motor is decelerated, the DC voltage Vdc rises due to the power regenerated from the inverter circuit side. At this time, the diodes d1 to d6 are in the reverse blocking state, and the power is not regenerated to the AC power supply side.

Therefore, the transistors Tr1 to Tr6 are controlled to perform regeneration to the AC power supply. Hereinafter, the operation of the control circuit within the dotted line shown in FIG. 1 will be described. The control circuit in the dotted line is realized using a microprocessor or the like,
The operation of this control circuit can be easily realized by software. First, the line voltage of the three-phase power supply voltage is detected via the isolator 3. The magnitude relationship between the voltages is determined by the comparator 8, and as shown in FIG.
Divided into two sections. From this section data, selection of a transistor corresponding to the section and selection of switches 9 and 10 are performed, and ON / OFF control is performed by the PWM control circuit 5. The converter 6 converts the line voltage to the phase voltage, and outputs a voltage command for each phase. The voltage regenerated and output from the AC side of converter 1 by only this voltage command is equal to the power supply voltage.

As the reference voltage 21, a target value of the DC voltage Vdc is set, and a value allowable for the withstand voltage of the element used in the converter 1 or the withstand voltage of the inverter is set. The subtractor 19 calculates a deviation between the target value and the detected value of the actual DC voltage Vdc. The calculated value is input to the PWM control circuit 5, and when positive, a control signal to the transistor is output to start regeneration, and when either zero or negative, an OFF signal is output to the transistor to regenerate. Is stopped. The operation value is amplified by the error amplifier 18. The amplified value is multiplied by the voltage command selected by the switch 9 to create an AC current command. The sample / hold circuit 24 holds the current value detected by the current detector 4 at a detection timing described later. The current command is subtracted from the current value held by the subtractor 13, and the subtracted difference is amplified by the amplifier 11. The amplified value is multiplied by the voltage command of each phase and corrected. Note that the output of the amplifier 11 is (1 + A) where e is the deviation value from the subtractor 13 and A is the amplification factor.
× e), and even if the output from the subtractor 13 is zero, 1
Is output. In the corrected phase voltage command value, the switch 10 separates the command signal of the phase that holds the data for each section in the ON state, and becomes the command having the waveform shown in FIG.

Next, the operation of the example PWM control circuit 5 for section 1 will be described with reference to FIG. FIG. 4 shows an ON / OFF signal of the transistor Tr. This signal is created by pulse width modulation of a command of each phase by a carrier signal. The PWM control circuit 5 outputs a base signal that keeps the S-phase transistor Tr3 in the off state and the transistor Tr4 in the on state based on the section data shown in FIG. The S-phase AC voltage command is disconnected by the switch 10 shown in FIG. 1 and is not used. Transistor Tr connected to R-phase and T-phase
The AC voltage command for switching 1, Tr2, Tr5, and Tr6 includes a line voltage detected from the isolator 3 to a voltage value calculated by the converter 6, and an AC current command output from the multiplier 16. A value obtained by multiplying the deviation between the current detection value output from the sample / hold circuit 24 and the value amplified by the amplifier 11 is used. In other words, by multiplying, a correction proportional to the magnitude of the voltage value is performed. A large correction is applied to a portion where the voltage value is large, and a large amount of current flows. Will flow. Next, based on the R-phase AC voltage command and the T-phase AC voltage command obtained by performing the correction, the ON / O of the transistor Tr shown in FIG.
An FF signal pulse is created. The detected value of the current detector 4 fed back to the subtractor 13 is a value detected by the sample / hold circuit 24 using a negative peak value of the carrier signal as a trigger.

The detection timing of the sample / hold circuit 24 is the transistor Tr held in the ON state in the section 1.
The timing must be such that the current flowing through 4 can be measured accurately. That is, when there is no influence of the current flowing through the diode d, the transistors Tr1 and Tr5 are turned on.
The timing to do it is good. Therefore, if the carrier signal has a negative peak value, the transistor Tr must be used.
1 and Tr 5 are simultaneously turned on. If the transistor Tr connected to the positive side of the DC voltage output is held in the ON state, the detection is performed with the positive peak value of the carrier signal as a trigger. When the transistor Tr connected to the negative side of the carrier signal is kept in the ON state, the detection is performed using the negative peak value of the carrier signal as a trigger. Therefore, in the sample / hold circuit 24, the detection timing is determined by the carrier signal from the PWM control circuit 5 and the signal from the comparator 8.

The other sections can be performed in the same manner as section 1. When the converter 1 is controlled by the ON / OFF signal of the transistor Tr thus created, regeneration of a current having the same phase as the power supply voltage shown in FIG. 3 can be realized.

[0013]

As described above, according to the present invention,
Feedback control is performed by one current detector, and a sine-wave regenerative current can be generated, and an inexpensive power converter can be realized. In addition, the current is charged by the diode during power running, and the transistor through which the largest current flows is held in the ON state during regeneration, so that a power conversion device with minimal loss can be realized.

[Brief description of the drawings]

FIG. 1 is a system configuration diagram of a motor control power conversion device capable of performing power regeneration according to an embodiment of the present invention.

FIG. 2 is a diagram showing a relationship between a power supply voltage and a command of the power converter shown in FIG.

3 is a diagram showing a relationship between a power supply voltage and a current of the power converter shown in FIG.

FIG. 4 is a diagram showing a relationship between a command signal of the power converter shown in FIG. 1 and a control signal to each transistor.

FIG. 5 is a system configuration diagram of a power conversion device according to the related art.

[Explanation of symbols]

1 converter, 2 smoothing capacitor, 3 isolator, 4,14 current detector, 5,20 PWM control circuit, 6,22 converter, 7 choke coil, 8 comparator, 9,10 switch, 11,18,23 amplifier,
12, 16 multiplier, 13, 17, 19 subtractor, 15
Vector rotator, 21 reference voltages, 24 sample / hold circuits.

──────────────────────────────────────────────────続 き Continued on the front page (58) Field surveyed (Int.Cl. ⁷ , DB name) H02M 7/219 H02M 7/155 H02M 7/48 H02M 7/797 H02P 3/18

Claims (4)

(57) [Claims] 1. A diode is connected in anti-parallel.
A converter is composed of a plurality of transistors and PWM
The DC power of the converter is controlled by the ON / OFF control of the control circuit.
In a power converter for regenerating electric power on the voltage output side to a three-phase AC power supply, a three-phase AC power supply connected to the three-phase AC power supply from the converter is provided.
Means for detecting a pressure, on the basis of the comparator and the three-phase AC voltage the detector to determine <br/> the magnitude of each phase voltage of the three-phase AC voltage the detector, and outputs the phase voltage command A converter, and detecting a DC current on a DC voltage output side of the converter.
One current detector and a voltage command output by the converter are detected by the current detector.
The PWM control circuit determines the magnitude relationship with the comparator.
The transistor connected to the phase having the largest absolute value among the connected phases is always kept on, and the current detector
Flows to the transistor that is kept in the ON state detected
Based on the voltage command corrected by the DC current, the remaining
ON / OFF control of transistors connected to two phases
Power converter, characterized in that that. 2. The power conversion device further comprises the converter
Voltage detector that detects the DC voltage on the DC voltage output side of the
Comprising a stage, means for correcting the voltage command, the magnitude relationship in said comparator
Voltage command of the phase whose absolute value is the largest among the phases for which
The ON state detected by the current detector.
The DC current flowing through the transistor and the voltage detection means detect the DC current.
Correcting the voltage command of each phase with the output DC voltage
The power converter according to claim 1, wherein: 3. The means for correcting the voltage command, wherein the absolute value of the phase of which the magnitude relationship is determined by the comparator is the smallest.
The voltage command of the larger phase and the target base of the DC voltage
From the reference voltage and the difference between the detected DC voltage,
A current command of a phase having a maximum pair value is generated, and the current command and the ON state detected by the current detector are maintained.
The difference from the DC current flowing through the transistor
Ri, serial to claim 2, characterized in that for correcting the voltage command
On-board power converter. 4. A DC current detected by said current detector.
Is the triangle of the triangular carrier signal used in the PWM control.
Hand that samples / holds at the timing when the wave reaches the top
Comprising a stage, means for correcting the voltage command, the sample / hole
Voltage command for each phase with the applied DC current.
The electronic device according to any one of claims 1 to 3, wherein
Force converter.