JP7745136B2 - Electric motor drive unit - Google Patents

Description

The present disclosure relates to an electric motor drive device.

Patent document 1 discloses a technology for reducing the capacity of the capacitor in an electric motor drive device in order to reduce the size and cost of the device.

Patent Document 2 discloses technology for maintaining a high power factor of an AC power supply and effectively supplying power from the AC power supply to an electric motor when the capacitor capacity is reduced. Specifically, Patent Document 2 discloses technology for controlling the current flowing to the electric motor in a substantially sinusoidal waveform with the same period as the half cycle of the AC voltage from the AC power supply and the same waveform as the AC power from the AC power supply.

Japanese Patent Application Laid-Open No. 2002-51589 Japanese Patent Application Laid-Open No. 2003-164179

This disclosure provides an electric motor drive device that satisfies the rated voltage and rated current of the components, or the demagnetization current of the motor, while expanding the load range of the motor's torque, speed, etc.

The electric motor drive device disclosed herein comprises an AC voltage detection means, a rectifier circuit, a capacitor, an inverter, an electric motor, a DC voltage detection means, a current detection means, and a control unit. The AC voltage detection means detects AC voltage from an AC power source. The rectifier circuit receives AC power from the AC power source and converts it into DC power. The capacitor has a capacitance set so that the output voltage of the rectifier circuit pulsates at twice the frequency of the AC power source and is connected in parallel to the output side of the rectifier circuit. The inverter receives a voltage applied to the capacitor and converts it into the desired AC voltage. The electric motor is provided on the output side of the inverter. The DC voltage detection means detects the voltage applied to the capacitor. The current detection means detects the current flowing through the electric motor, which is connected in series to the input side of the inverter. The control unit transmits information necessary to drive the electric motor with the desired load from the AC voltage detection means, DC voltage detection means, and current detection means to the inverter. The control unit has a first mode and a second mode. The first mode is a mode in which a current command in a DC coordinate system flowing through the motor is controlled to have a substantially sinusoidal waveform synchronized with a half cycle of AC power from the AC power supply, while controlling the current command so that the peak phase of the current command lags behind the peak phase of the AC voltage from the AC power supply. The second mode is a mode in which the maximum value of the current flowing through the motor during a half cycle of the AC voltage from the AC power supply is controlled to be smaller than in the first mode, while ensuring torque equivalent to that in the first mode. The control unit controls the current flowing through the motor in the first mode when the value detected by the DC voltage detection means is equal to or greater than a predetermined value, and controls the current flowing through the motor in the second mode when the value detected by the DC voltage detection means is less than the predetermined value.

The electric motor drive device disclosed herein satisfies the rated voltage and rated current of the components, or the demagnetization current of the electric motor, while also being able to expand the load range of the electric motor, such as torque and speed.

FIG. 1 shows a configuration of an electric motor drive device according to a first embodiment. FIG. 1 is a diagram showing the relationship between AC voltage and current in the first embodiment. FIG. 10 is a diagram showing the relationship between AC voltage and lead angle value in the first embodiment.

The following describes embodiments in detail with reference to the drawings. However, more detailed explanations than necessary may be omitted. For example, detailed explanations of matters that are already well known or redundant explanations of substantially identical configurations may be omitted.

The accompanying drawings and the following description are provided to enable those skilled in the art to fully understand the present disclosure, and are not intended to limit the subject matter described in the claims.

(Embodiment 1)
Hereinafter, an electric motor drive device 10 according to a first embodiment will be described as an example of an electric motor drive device according to the present disclosure with reference to FIGS. 1 to 3. FIG.

[1-1. Configuration]
FIG. 1 is a diagram showing the configuration of an electric motor drive device 10 according to a first embodiment. As shown in FIG. 1, the electric motor drive device 10 according to the first embodiment includes an AC voltage detection means 6, a rectifier circuit 2, a capacitor 3, an inverter 4, an electric motor 5, a DC voltage detection means 7, a current detection means 8, and a control unit 9. The AC voltage detection means 6 detects the AC voltage from an AC power source 1. The rectifier circuit 2 receives AC power from the AC power source 1 as input and converts it into DC power. The capacitor 3 has a capacitance set so that the output voltage of the rectifier circuit 2 pulsates at twice the frequency of the AC power source 1, and is connected in parallel to the output side of the rectifier circuit 2. The inverter 4 receives a voltage applied to the capacitor 3 as input and converts it into a desired AC voltage. The electric motor 5 is provided on the output side of the inverter 4. The DC voltage detection means 7 detects the voltage applied to the capacitor 3. The current detection means 8 detects the current flowing through the electric motor 5.

In addition, the control unit 9 transmits the information necessary to drive the electric motor 5 at the desired load from the AC voltage detection means 6, the DC voltage detection means 7, and the current detection means 8 to the inverter 4.

In addition, the electric motor drive device 10 may have a reactor connected in series between the AC power source 1 and the rectifier circuit 2 to reduce the peaks of the charging and discharging current to the capacitor 3. Furthermore, the AC voltage detection means 6 need only be capable of detecting the phase of the AC voltage, such as a zero-cross detection circuit, and does not necessarily require absolute value information.

The control unit 9 is also composed of a zero-cross detection unit 9a, an AC power supply phase/period measurement unit 9b, a speed control unit 9c, a dq-axis current command generation unit 9d, an advance angle control unit 9e, a current control unit 9f, a three-phase/two-phase conversion unit 9g, a two-phase/three-phase conversion unit 9h, a PWM (pulse width modulation) signal generation unit 9m, a magnetic pole position/speed estimation unit 9j, and a current command switching unit 9k. The control unit 9 includes a computer system having a processor and memory. The computer system functions as the control unit 9 when the processor executes a program stored in the memory. While the program executed by the processor is pre-recorded in the computer system's memory here, it may also be provided by recording it on a non-transitory recording medium such as a memory card, or via a telecommunications line such as the Internet.

The current command switching unit 9k is configured to be switchable between a first mode and a second mode based on the detection value of the DC voltage detection means 7. In each mode, the following current command is generated on the DC coordinate axes (hereinafter referred to as the dq axes) based on the PI (Proportional-Integral) calculation results of the speed control unit 9c and information from the AC power supply phase/period measurement unit 9b. That is, in the first mode, a roughly sinusoidal current command is generated, whose period is synchronized with the half-period of the AC power supply 1, whose area is equivalent to the PI calculation results over a half-period of the AC power supply 1, and whose peak phase on the DC coordinate axes lags behind the peak phase of the AC voltage over a half-period of the AC power supply 1. In the second mode, the PI calculation results are used as current commands on the dq axes.

Here, "approximately sine wave" includes "sine wave" and "waveform close to a sine wave." For convenience, an approximately sine wave having a cycle synchronized with the half cycle of AC power source 1 is referred to as an approximately sine wave having the same waveform as the AC power from AC power source 1.

[1-2. Operation]
The operation and function of the electric motor drive device 10 configured as above will now be described.

First, the AC power supply phase/period measurement unit 9b measures the phase and period of the AC power supply 1 based on information from the zero-cross detection unit 9a, which measures the timing when the AC voltage from the AC power supply 1 becomes zero.

The magnetic pole position/speed estimation unit 9j estimates the rotor magnetic pole position and rotational speed of the electric motor 5. These are estimated from the currents flowing through each phase (U phase, V phase, W phase) of the electric motor 5 and detected by the current detection means 8, the PWM signals applied to each phase of the electric motor 5 from the PWM signal generation unit 9m, and the DC voltage detection value detected by the DC voltage detection means 7.

The speed control unit 9c performs a PI calculation to determine the difference between the command speed at which the rotor of the electric motor 5 is desired to be driven and the speed of the rotor of the electric motor 5 estimated by the magnetic pole position/speed estimation unit 9j.

In addition, the current command switching unit 9k switches to the first mode when the detected value of the DC voltage detection means 7 is equal to or greater than a predetermined value, and switches to the second mode when it is less than the predetermined value. As a result, when the detected value of the DC voltage detection means 7 is equal to or greater than the predetermined value, d- and q-axis current commands are output in the first mode, and when the detected value of the DC voltage detection means 7 is less than the predetermined value, d- and q-axis current commands are output in the second mode.

Figure 2 shows the relationship between AC voltage and current. As shown in Figure 2, in the first mode, the dq axis current command is reduced near the peak phase of the AC voltage from AC power source 1, where the absolute value of the DC voltage is large, thereby reducing the instantaneous load.

This allows for suppression of fluctuations in the impedance terminal voltage and the input voltage of the rectifier circuit 2, even when the system inductance (mainly the impedance) of the AC power supply 1 is large. Furthermore, in the second mode, the current peak over a half cycle of the AC power supply can be suppressed more effectively than when the dq axis current commands are controlled with approximately sinusoidal waves.

In addition, in the regenerative state where power is supplied from the electric motor 5 to the AC power source 1, the rectifier circuit 2, or the capacitor 3, the torque of the electric motor 5 cannot be controlled according to the current command, so this may be omitted from the area calculation described above.

In addition, based on the detection value of the current detection means 8, if current is flowing from the electric motor 5 to the AC power supply 1, the rectifier circuit 2, or the capacitor 3, it is determined that the regenerative state is in effect.

In addition, based on information from the three-phase to two-phase conversion unit 9g, a regenerative state is determined when the q-axis detected current is negative.

Furthermore, in the regenerative state, power is supplied from the electric motor 5 to the AC power source 1 or the rectifier circuit 2, so that the rotation speed of the rotor of the electric motor 5 becomes lower than the command speed, or the DC voltage of the capacitor 3 becomes higher than the AC voltage from the AC power source 1.

For this reason, a determination may be made that the motor is in a regenerative state if the estimated speed of the motor 5 from the magnetic pole position/speed estimation unit 9j drops below a predetermined speed relative to the command speed. Alternatively, a determination may be made that the motor is in a regenerative state if the change in the detected DC voltage value in the DC voltage detection means 7 increases by a greater amount than a predetermined amount.

The advance angle control unit 9e maintains a table in which advance angle values corresponding to the speed, torque, etc. of the electric motor 5 are pre-registered.

Figure 3 shows the relationship between AC voltage and lead angle value.

To effectively supply power from AC power supply 1 to electric motor 5, it is desirable to set the lead angle so that the phase in which regeneration occurs is short near the phase where AC power supply 1 is zero, when power is likely to be regenerated from electric motor 5 to inverter 4 or AC power supply 1. Furthermore, it is desirable to set the lead angle so that the current required to output torque is minimized near the phase where AC voltage peaks.

Therefore, the lead angle value may be changed within half a power supply cycle as shown in Figure 3.

The dq-axis current command generation unit 9d generates d-axis and q-axis current commands based on information from the advance angle control unit 9e, current command switching unit 9k, speed control unit 9c and AC power supply phase/period measurement unit 9b.

The current control unit 9f performs a PI calculation on the difference between the d-axis and q-axis current command values generated by the dq-axis current command generation unit 9d and the d-axis and q-axis current detection values obtained by converting the currents flowing through each phase of the electric motor 5 detected by the current detection means 8 using a three-phase to two-phase conversion unit 9g, and generates d-axis and q-axis voltage commands.

The two-phase to three-phase conversion unit 9h generates voltage commands for each phase (U, V, W phase) of the motor 5 based on the d-axis and q-axis voltage command values from the current control unit 9f and the estimated magnetic pole position information from the magnetic pole position/speed estimation unit 9j.

The PWM signal generating unit 9m generates a PWM signal for each phase of the motor 5 from the voltage command for each phase of the motor 5 from the two-phase to three-phase conversion unit 9h and the detected value in the DC voltage detecting means 7.

Each switching element of the inverter 4 switches in accordance with the PWM signal from the PWM signal generating unit 9m, thereby driving the electric motor 5 at the desired speed and torque.

[1-3. Effects, etc.]
As described above, in this embodiment, the electric motor drive device 10 includes an AC voltage detection means 6, a rectifier circuit 2, a capacitor 3, an inverter 4, an electric motor 5, a DC voltage detection means 7, a current detection means 8, and a control unit 9. The AC voltage detection means 6 detects the AC voltage from the AC power source 1. The rectifier circuit 2 receives AC power from the AC power source 1 and converts it into DC power. The capacitor 3 has a capacitance set so that the output voltage of the rectifier circuit 2 pulsates at twice the frequency of the AC power source 1, and is connected in parallel to the output side of the rectifier circuit 2. The inverter 4 receives a voltage applied to the capacitor 3 and converts it into a desired AC voltage. The electric motor 5 is provided on the output side of the inverter 4. The DC voltage detection means 7 detects the voltage applied to the capacitor 3. The current detection means 8 detects the current flowing through the electric motor 5, which is connected in series to the input side of the inverter 4. The control unit 9 transmits information required to drive the electric motor 5 at a desired load from the AC voltage detection means 6, the DC voltage detection means 7, and the current detection means 8 to the inverter 4. The control unit 9 has a first mode and a second mode. The first mode is a mode in which a current command in a DC coordinate system flowing through the electric motor 5 is controlled to have a substantially sinusoidal waveform synchronized with a half cycle of the AC power from the AC power supply 1, while controlling the current command so that the peak phase of the current command lags behind the peak phase of the AC voltage from the AC power supply 1. The second mode is a mode in which, while ensuring torque equivalent to that in the first mode, the maximum value of the current flowing through the electric motor 5 during a half cycle of the AC voltage from the AC power supply 1 is controlled to be smaller than that in the first mode.

The control unit 9 controls the current flowing to the electric motor 5 in a first mode when the value detected by the DC voltage detection means 7 is greater than or equal to a predetermined value, and controls the current flowing to the electric motor 5 in a second mode when the value detected by the DC voltage detection means 7 is less than the predetermined value.

As a result, the electric motor drive device 10 with a reduced capacity capacitor 3 satisfies the rated voltage and rated current of the components that make up the electric motor drive device 10, or the demagnetization current of the electric motor 5, and can expand the load range of the electric motor 5, such as torque and speed, more than before.

This disclosure provides an electric motor drive device that satisfies the rated voltage and rated current of the components, or the demagnetization current of the motor, while also expanding the load range of the motor's torque, speed, etc. Therefore, it can be used to drive electric motors in, for example, air conditioners, refrigerators, vacuum cleaners, washing machines, etc.

REFERENCE SIGNS LIST 1 AC power supply 2 Rectifier circuit 3 Capacitor 4 Inverter 5 Electric motor 6 AC voltage detection means 7 DC voltage detection means 8 Current detection means 9 Control unit 9a Zero cross detection unit 9b AC power supply phase/period measurement unit 9c Speed control unit 9d DQ axis current command generation unit 9e Lead angle control unit 9f Current control unit 9g Three-phase to two-phase conversion unit 9h Two-phase to three-phase conversion unit 9j Magnetic pole position/speed estimation unit 9k Current command switching unit 9m PWM signal generation unit 10 Electric motor drive device

Claims (1)

AC voltage detection means for detecting an AC voltage from an AC power supply;
a rectifier circuit that receives AC power from the AC power source and converts it into DC power;
a capacitor connected in parallel to the output side of the rectifier circuit, the capacitor having a capacitance set so that the output voltage of the rectifier circuit pulsates at twice the frequency of the AC power supply;
an inverter that converts the voltage applied to the capacitor into a desired AC voltage;
an electric motor provided on the output side of the inverter;
DC voltage detection means for detecting the voltage applied to the capacitor;
a current detection means for detecting a current flowing through the electric motor connected in series to the input side of the inverter;
a control unit that transmits information required to drive the electric motor with a desired load from the AC voltage detection means, the DC voltage detection means, and the current detection means to the inverter,
The control unit
a first mode in which a current command in a DC coordinate system flowing through the electric motor is controlled to have a substantially sinusoidal waveform synchronized with a half cycle of the AC power from the AC power supply, and the peak phase of the current command is controlled to lag behind the peak phase of the AC voltage from the AC power supply;
a second mode in which a maximum value of a current flowing to the electric motor during a half cycle of an AC voltage from the AC power supply is controlled to be smaller than that in the first mode while ensuring a torque equivalent to that in the first mode,
An electric motor drive device that controls the current flowing to the electric motor in the first mode when the value detected by the DC voltage detection means is equal to or greater than a predetermined value, and controls the current flowing to the electric motor in the second mode when the value detected by the DC voltage detection means is less than the predetermined value.