JP2024047610A - Method for controlling inverter for driving motor - Google Patents

Abstract

[Problem] The present invention reproduces the three-phase currents required for driving in the overmodulation region in an inverter control device that performs overmodulation control. [Solution] In an inverter 1 for driving a motor 3 that performs overmodulation control, a one-phase motor current is detected by a one-shunt type current detection circuit 4 installed in the DC current section of the inverter 1. During three-phase overmodulation drive, the motor input current values for the other two phases in the overmodulation control region are estimated according to Kirchhoff's law, thereby realizing three-phase overmodulation drive. [Selected Figure] Figure 1

Description

The present invention relates to a technology for reproducing the three-phase current required for overmodulation control in an inverter control device that performs overmodulation control.

Conventionally, vector control has been known as a method of controlling an inverter that drives a motor. To achieve vector control, a position sensor that detects the rotor position and a current sensor that detects the input current to the motor are required.

The installation of current and position sensors increases the cost and size of the system, and may also reduce reliability. In particular, inverters for driving motors such as compressors are increasingly being designed without position and current sensors in order to reduce costs and space.

In place of the position sensor, it is possible to use information that estimates the rotor position from the voltage and current input to the motor (position sensorless control). As for the current sensor, the use of a one-shunt current detection method is known as an alternative (see Patent Document 1 below).

JP 2010-288359 A

The compressors are typically used in air conditioners, but in air conditioners, there is an operating mode in which the compressor is driven at high speed during rapid cooling, etc., and the load on the compressor increases according to the rotation speed, so the motor for the compressor is driven at high speed and high load.

Field-weakening control is used to drive motors at high speeds and high loads, but this can easily result in a decrease in efficiency at high speeds. In order to increase the maximum rotation speed, field-weakening control passes a current that weakens the magnetic flux of the permanent magnet, thereby lowering the back electromotive force. The copper loss caused by the current caused by this field-weakening reduces efficiency at high speeds.

Therefore, a method that employs overmodulation control is known to reduce the field weakening control region where motor efficiency decreases.

However, when using the one-shunt current detection method described above, three-phase current values are required to achieve position sensorless control during overmodulation, but during three-phase overmodulation, only one phase of current can be detected.

In this regard, the control device described in Patent Document 1 estimates the three-phase current by applying Kirchhoff's law using the averaged DC bus current, the instantaneous phase current for one phase, and the DC voltage during three-phase overmodulation drive.

In more detail, the control device has a current reproduction unit, a PWM generator, a dq inverse converter, a voltage command calculation unit, a speed command generation unit, and a position sensorless control unit, and the current reproduction unit reproduces the motor current (Id, Iq) on the rotation (dq) coordinate axis as a reproduced current (Idc, Iqc) using the DC bus current I0 detected by the DC bus current detector, the DC voltage (Ed) detected by the DC voltage detector, PWM signal information, applied voltage command values (Vd*, Vq*), and the inverter estimated rotation phase θdc.

The PWM generator generates a PWM signal from the AC applied voltage commands (Vu*, Vv*, Vw*), and the dq inverse converter converts the applied voltage command values (Vd*, Vq*) into AC applied voltage commands (Vu*, Vv*, Vw*). The voltage command calculation unit calculates the applied voltage command values (Vd*, Vq*) to the motor using the reproduced currents (Idc, Iqc) and the speed command value ω1*, and the speed command generation unit outputs the speed command value ω1* to the voltage command calculation unit 9.

The position sensorless control unit estimates the motor rotation phase θd using the reproduced current (Idc, Iqc) and the applied voltage command value (Vd*, Vq*). The current reproduction unit has an AD conversion unit, a filter processing unit, a current phase discrimination unit, and a current reproduction calculation unit. The AD conversion unit converts the DC bus current I0 and DC voltage Ed into I0-S and Ed-S, respectively.

The filter processing unit filters the AD converted DC bus current I0-S to output the average DC bus current I0-FL-S, and the current phase determination unit uses the PWM signal information to determine which phase current of the motor the AD converted DC bus current I0-S belongs to.

The current reproduction calculation unit uses the phase-identified DC bus current I0-S-W (if it is identified as W phase), the average DC bus current I0-FL-S, the AD-converted DC voltage Ed-S, the PWM signal information, the applied voltage command value (Vd*, Vq*), and the inverter estimated rotation phase θdc to obtain the motor current (Id, Iq) on the rotation (dq) coordinate axis as the reproduced current (Idc, Iqc).

The present invention discloses an inverter control method that employs a single-shunt current detection method similar to the technology described in Patent Document 1, but that can reproduce three-phase currents (motor input currents) in a simpler manner during three-phase overmodulation in overmodulation control.

The inverter control method described in claim 1 is characterized in that in a control device for a motor drive inverter that performs overmodulation control, the motor current for one phase is detected by a one-shunt type current detection circuit installed in the DC current section of the inverter, and during three-phase overmodulation drive, the motor input current value for the other two phases is estimated according to Kirchhoff's law.

According to the inverter control method described in claim 1, it is possible to estimate the motor input current values for three phases in the simplest possible manner. In addition, since the system configuration is simple, it has the advantages of being highly versatile, reducing system costs, and improving robustness and responsiveness.

1 is a circuit diagram showing a motor drive device according to the present invention; FIG. 2 is an equivalent circuit diagram of the motor. 5 is an image diagram showing a change in an operating region depending on whether or not each control method is adopted by the motor drive device. FIG. 5 is a diagram showing a switching operation of an upper arm constituting an inverter main circuit in a normal modulation region (linear region) by the motor drive device. FIG. 5A is a simplified circuit diagram illustrating the currents flowing through the upper and lower arms in the (1) region shown in FIG. 4 , and FIG. 5B is a simplified circuit diagram illustrating the currents flowing through the upper and lower arms in the (2) region shown in FIG. 4 . 1A is a diagram showing the switching operation of an upper arm constituting an inverter main circuit during one-phase (U-phase) overmodulation by the motor drive device, and FIG. 1B is a diagram showing the switching operation of an upper arm constituting an inverter main circuit during one-phase (W-phase) overmodulation. 6(a) is a simplified circuit diagram illustrating the currents flowing through the upper and lower arms in the (1) region shown in FIG. 6(a), and (b) is a simplified circuit diagram illustrating the currents flowing through the upper and lower arms in the (2) region shown in FIG. 6(b). 6A is a simplified circuit diagram illustrating the currents flowing through the upper and lower arms in the (1) region shown in FIG. 6B, and FIG. 6B is a simplified circuit diagram illustrating the currents flowing through the upper and lower arms in the (2) region shown in FIG. 6B. 5 is a switching operation diagram of an upper arm constituting an inverter main circuit during two-phase overmodulation by the motor drive device. FIG. 10A is a simplified circuit diagram illustrating the currents flowing through the upper and lower arms in the (1) region shown in FIG. 9 , and FIG. 10B is a simplified circuit diagram illustrating the currents flowing through the upper and lower arms in the (2) region. 5 is a switching operation diagram of an upper arm constituting an inverter main circuit during three-phase overmodulation by the motor drive device. FIG. FIG. 12 is a simplified circuit diagram illustrating currents flowing through upper and lower arms during three-phase overmodulation shown in FIG. 11 .

Below, examples of the present invention are described. Note that the embodiments described below are intended to facilitate understanding of the present invention and are not intended to limit the present invention. In other words, the present invention may be modified or improved without departing from the spirit of the invention, and of course, the present invention includes equivalents.

Figure 1 shows a motor drive device A according to the present invention. The motor drive device A is generally composed of an inverter 1 and an inverter control device 2. The inverter 1 is composed of an inverter main circuit 1a consisting of upper and lower arms made up of IGBTs and diodes, and a gate driver (not shown) that generates gate signals for the upper and lower arms of the inverter main circuit 1a based on a PWM signal from the inverter control device 2.

The inverter 1 turns the upper and lower arms on and off based on the PWM signal from the inverter control device 2, converts the DC voltage VDC supplied from the DC power source into a three-phase AC voltage, and supplies it to the compressor motor 3.

In FIG. 1, 4 denotes a one-shunt type current detection circuit (hereinafter referred to as one-shunt resistor) that detects the current iDC flowing in the DC part of the inverter 1 using a DC shunt resistor and outputs it to the inverter control device 2. The inverter control device 2 drives the compressor motor 3 using a vector control method based on the current iDC detected by the one-shunt resistor 4. Note that the motor 3 is assumed to be a permanent magnet synchronous motor or an induction motor.

Figure 2 shows the equivalent circuit of the compressor motor 3 shown in Figure 1. iU, iV, and iw shown in Figure 2 indicate currents mainly composed of fundamental waves that flow due to the filter characteristics of the RL circuits when the inverter 1 outputs a pulse voltage to the RL circuits of each phase inside the motor 3 based on the gate signal generated by the inverter control device 2 shown in Figure 1. Also, R in Figure 2 indicates phase resistance, L indicates phase inductance, and eu, ev, and ew indicate phase induced voltages.

The motor drive device A shown in FIG. 1 does not have a position sensor or a current detection sensor required for vector control, and estimates the rotor position of the motor 3 from the voltage and current input to the compressor motor 3. In addition, the use of the one-shunt resistor 4 described above instead of the current detection sensor reduces product costs.

The inverter control device 2 of the motor drive device A employs overmodulation control, as shown in FIG. 3. By employing overmodulation control, the operable range (rotation speed of the motor 3) with high torque can be expanded. In addition, it is possible to improve the ratio (voltage utilization rate) of the output voltage of the inverter 2 to the power supply voltage (PN voltage) VDC shown in FIG. 1.

Figure 4 is a switching operation diagram of the upper arm constituting the inverter main circuit 1a in the region of normal modulation control (normal modulation region or linear region) by the motor drive device A shown in Figure 1. In normal modulation control, the phase voltage command values vu*, vv*, and vw* of each phase are set within the amplitude of the triangular wave (carrier wave).

In this case, the upper arm that constitutes the inverter main circuit 1a is ON when the phase voltage command values vu*, vv*, and vw* of each phase exceed the carrier wave, and is OFF otherwise.

Figure 5 (a) shows a simplified circuit diagram depicting the currents flowing through the upper and lower arms in region (1) shown in Figure 4. As shown in Figure 5 (a), in region (1), the upper arms of U-phase and V-phase are ON, and the upper arm of W-phase is OFF. Accordingly, the lower arms of U-phase and V-phase are OFF, and the lower arm of W-phase is ON.

As a result, it is believed that the current between the inverter main circuit 1a and the motor 3 flows in the direction of the arrow shown in Figure 5 (a). As a result, it becomes possible to detect the current (-iw) flowing through the W phase of the motor 3 using the shunt resistor 4.

Figure 5 (b) is a simplified circuit diagram depicting the currents flowing through the upper and lower arms in region (2) shown in Figure 4. In this region, only the upper arm of U-phase is ON, and the upper arms of V-phase and W-phase are OFF. Accordingly, the lower arm of U-phase is OFF, and the lower arms of V-phase and W-phase are ON.

Then, the current flowing between the inverter main circuit 1a and the motor 3 is considered to flow in the direction of the arrow shown in Figure 5 (b), and the current (iu) flowing through the U phase of the motor 3 can be detected by the shunt resistor 4.

In this way, in the linear region, two phases of current (iu, -iw in the case of Figures 4 and 5) can be detected in one cycle of the carrier wave, and the remaining phase of current can be calculated from the detected two phases of current, making it possible to obtain three phases of current. By obtaining three phases of current, position sensorless vector control using normal overmodulation control can be realized.

Figure 6 is a switching operation diagram of the upper arm constituting the inverter main circuit 1a in the region of one-phase overmodulation control (referred to as the one-phase overmodulation region) by the motor drive device A shown in Figure 1. In one-phase overmodulation control, only one of the phase voltage command values is set to exceed the peak of the amplitude of the triangular wave (carrier wave). In Figure 6 (a), the phase voltage command value vu* of the maximum phase, U-phase, is set to exceed the peak of the amplitude of the carrier wave, and in Figure 6 (b), the phase voltage command value vw* of the minimum phase, W-phase, is set to exceed the peak of the amplitude of the carrier wave.

In this case, as in the case of FIG. 4, the upper arm constituting the inverter main circuit 1a is ON when the phase voltage command values vu*, vv*, and vw* of each phase exceed the carrier wave, as shown in FIG. 6(a) and (b), and is OFF otherwise.

As shown in FIG. 6(a), when the phase voltage command value vu* of the U phase is set to exceed the peak of the amplitude of the carrier wave, in the (1) region shown in FIG. 6(a), the upper arms of the U and V phases are ON, and the upper arm of the W phase is OFF, as shown in FIG. 7(a). Accordingly, the lower arms of the U and V phases are OFF, and the lower arm of the W phase is ON.

Then, the current flowing between the inverter main circuit 1a and the motor 3 is considered to flow in the direction of the arrow shown in Figure 7 (a), and the current (-iw) flowing through the W phase of the motor 3 can be detected by the shunt resistor 4.

In the (2) region shown in FIG. 6(a), only the upper arm of the U phase is turned ON, and the upper arms of the V phase and W phase are turned OFF, as shown in FIG. 7(b). Accordingly, the lower arm of the U phase is turned OFF, and the lower arms of the V phase and W phase are turned ON.

Then, the current flowing between the inverter main circuit 1a and the motor 3 is considered to flow in the direction of the arrow shown in Figure 7 (b), and the current (iu) flowing through the U phase of the motor 3 can be detected by the shunt resistor 4.

As shown in FIG. 6(b), when the phase voltage command value vw* of the W phase is set to exceed the peak of the amplitude of the carrier wave, in the (1) region shown in FIG. 6(b), the upper arms of the U and V phases are turned ON, and the upper arm of the W phase is turned OFF, as shown in FIG. 8(a). Accordingly, the lower arms of the U and V phases are turned OFF, and the lower arm of the W phase is turned ON.

Then, the current flowing between the inverter main circuit 1a and the motor 3 is considered to flow in the direction of the arrow shown in Figure 8 (a), and the current (-iw) flowing through the W phase of the motor 3 can be detected by the shunt resistor 4.

In the (2) region shown in FIG. 6(b), only the upper arm of the U phase is ON, and the upper arms of the V phase and W phase are OFF, as shown in FIG. 8(b). Accordingly, the lower arm of the U phase is OFF, and the lower arms of the V phase and W phase are ON.

As a result, the current flowing between the inverter main circuit 1a and the motor 3 is considered to flow in the direction of the arrow shown in Figure 8 (b), and the current (iu) flowing through the U phase of the motor 3 can be detected by the shunt resistor 4.

In this way, in the single-phase overmodulation region, two-phase currents (iu, -iw in the case of Figures 6 to 8) can be detected in one cycle of the carrier wave, and the remaining one-phase current can be calculated from the detected two-phase currents, making it possible to obtain three-phase currents. Therefore, position sensorless vector control can be achieved even in single-phase overmodulation control.

Figure 9 is a switching operation diagram of the upper arm constituting the inverter main circuit 1a in the region of two-phase overmodulation control (referred to as the two-phase overmodulation region) by the motor drive device A shown in Figure 1. In two-phase overmodulation control, two of the phase voltage command values are set to exceed the peak of the amplitude of the triangular wave (carrier wave). In Figure 9, the phase voltage command value vu* of the maximum phase, U-phase, and the phase voltage command value vw* of the minimum phase, W-phase, are set to exceed the peak of the amplitude of the carrier wave.

In the case of FIG. 9, the upper arm that constitutes the inverter main circuit 1a is ON when the phase voltage command values vu*, vv*, and vw* of each phase exceed the carrier wave, and is OFF otherwise.

In other words, as shown in Figure 9, the phase voltage command value vu* of the U phase always exceeds the maximum value of the carrier wave, and the phase voltage command value vw* of the W phase always falls below the minimum value of the carrier wave, so the upper arm of the U phase is always ON and the upper arm of the W phase is always OFF.

In the (1) region shown in FIG. 9, the upper arms of the U and V phases are ON, and the upper arm of the W phase is OFF, as shown in FIG. 10(a). Accordingly, the lower arms of the U and V phases are OFF, and the lower arm of the W phase is ON.

As a result, the current flowing between the inverter main circuit 1a and the motor 3 is considered to flow in the direction of the arrow shown in Figure 10 (a), and the current (-iw) flowing through the W phase of the motor 3 can be detected by the shunt resistor 4.

In addition, in region (2) shown in FIG. 9, only the upper arm of U-phase is ON, and the upper arms of V-phase and W-phase are OFF, as shown in FIG. 10(b). Accordingly, the lower arm of U-phase is OFF, and the lower arms of V-phase and W-phase are ON.

As a result, the current flowing between the inverter main circuit 1a and the motor 3 is considered to flow in the direction of the arrow shown in Figure 10 (b), and the current (iu) flowing through the U phase of the motor 3 can be detected by the shunt resistor 4.

In this way, in the two-phase overmodulation region, two phases of current (iu, -iw in the case of Figures 9 and 10) can be detected in one cycle of the carrier wave, and the remaining one phase of current can be calculated from the detected two phases of current, making it possible to obtain three phases of current. Therefore, position sensorless vector control can be achieved even in two-phase overmodulation control.

Figure 11 is a switching operation diagram of the upper arm constituting the inverter main circuit 1a in the region of three-phase overmodulation control (referred to as the three-phase overmodulation region) by the motor drive device A shown in Figure 1. In three-phase overmodulation control, all of the phase voltage command values vu*, vv*, and vw* are set to exceed the peak of the amplitude of the triangular wave (carrier wave).

In the case of FIG. 11, the upper arm that constitutes the inverter main circuit 1a is ON when the phase voltage command values vu*, vv*, and vw* of each phase exceed the carrier wave, and is OFF otherwise.

In other words, as shown in FIG. 11, the phase voltage command value vu* of the U phase always exceeds the maximum value of the carrier wave, so the upper arm of the U phase is always ON, and the phase voltage command values vv*, vw* of the V and W phases always fall below the minimum value of the carrier wave, so the upper arms of the V and W phases are always OFF.

In other words, in the entire region shown in FIG. 11, the upper arm of the U phase is ON as shown in FIG. 12, and the upper arms of the V phase and W phase are OFF. Accordingly, the lower arm of the U phase is OFF, and the lower arms of the V phase and W phase are ON.

As a result, the current flowing between the inverter main circuit 1a and the motor 3 is considered to flow in the direction of the arrow shown in Figure 12, and the current (iu) flowing through the U phase of the motor 3 can be detected by the shunt resistor 4.

During three-phase overmodulation control, it is necessary to calculate the current values of the remaining two phases from the current value of this one phase. This calculation method is the gist of the present invention, and involves solving for the current difference value Δi of the closed circuit between the V- and W-phases on the equivalent circuit of the motor 3 shown in Figure 2. First, according to Kirchhoff's second law, the voltage between the V- and W-phases has the relationship shown in the following [Equation 1].

The induced voltage e between the V-W phases is related as shown in the following equation (2).

The current difference value Δi between the VW phases in the previous period has the relationship shown in the following [Equation 3].

Therefore, the current difference value Δi between the V-W phases can be estimated using the following [Equation 3].

Using Kirchhoff's first law in the following equation (5), it is possible to calculate the W-phase current iW using the following equation (6).

In this way, in the three-phase overmodulation region, the current for one phase (iu in the case of Figures 11 and 12) can be detected in one cycle of the carrier wave, and the current for the remaining two phases can be calculated from the current for the detected one phase, making it possible to obtain the current for three phases. Therefore, position sensorless vector control can be achieved even in three-phase overmodulation control.

As described above, the inverter control method of the present invention employs overmodulation control to improve the ratio (voltage utilization rate) of the inverter output voltage to the power supply voltage (PN voltage), and to improve the high-speed operating range of the motor.

In addition, the motor input current for three phases can be reproduced regardless of whether one-phase or three-phase overmodulation is occurring, enabling position sensorless vector control to be achieved.

In addition, no filters are used in the DC voltage and current detection sections, and filter wiring is not required, making it possible to reproduce DC current values with a simple configuration, thereby reducing costs and increasing versatility. Furthermore, because no filters are used, no current delay occurs, and high responsiveness can be achieved.

In addition, each input information of the inverter control device is not affected by external disturbances, which improves robustness.

The present invention can be used in any control device that applies overmodulation control.

REFERENCE SIGNS LIST 1 inverter 1a inverter main circuit 2 inverter control device 3 motor 4 1 shunt resistor A motor drive device

Claims (1)

A control method for a motor drive inverter that performs overmodulation control, in which the motor current for one phase is detected by a one-shunt type current detection circuit installed in the DC current section of the inverter, and during three-phase overmodulation drive, the motor input current values for the other two phases in the overmodulation control region are estimated according to Kirchhoff's law to achieve three-phase overmodulation drive.