WO2022176223A1

WO2022176223A1 - Motor control device

Info

Publication number: WO2022176223A1
Application number: PCT/JP2021/022215
Authority: WO
Inventors: 康正小平
Original assignee: 日本電産株式会社
Priority date: 2021-02-19
Filing date: 2021-06-10
Publication date: 2022-08-25

Abstract

This motor control device comprises: an inverter circuit that drives a motor; a converter circuit that steps down a voltage inputted from a direct current power source, to a predetermined direct current voltage, and outputs the stepped-down voltage; a means for determining, in the inverter circuit, a load state of the motor; and a power source switching unit that, in response to the load state, switches between a first power source supply mode for supplying power from the converter circuit to the inverter circuit, and a second power source supply mode for supplying power from the direct current power source to the inverter circuit, wherein the first power source supply mode corresponds to a state of a load lower than a predetermined load, and the second power source supply mode corresponds to a state of a load higher than a predetermined load.

Description

motor controller

The present invention relates to a motor control device that drives and controls a motor using an inverter circuit.

In electric vehicles, hybrid vehicles, etc., which use a motor as a drive source, the DC power from the battery is converted into AC power supplied to the motor, and the motor rotation speed, drive torque, etc. are controlled to accelerate and decelerate the vehicle. An inverter device (power conversion device) is installed.　

　The power supply for driving the motor to the inverter device includes a method of supplying power directly from an external battery, a method of supplying power generated by a converter to the inverter device, and the like. When using a converter, there is also known a method of varying the power supply voltage supplied from the converter to the inverter according to the load condition of the motor.　

For example, Patent Document 1 discloses a configuration for setting the input DC voltage of the inverter according to the load of the motor, that is, when the duty ratio of the inverter is equal to or higher than a predetermined value, the DC voltage booster circuit is controlled to input the DC voltage to the inverter. Disclosed is a motor driving device that changes the DC voltage applied to the inverter and stops boosting the input DC voltage of the inverter by the booster circuit if the duty factor is less than a predetermined value.　

In Patent Document 2, in an inverter device in which a current is input from a converter section that converts alternating current from an alternating current power supply into direct current and supplies drive current to a load such as a motor, the converter section is in a low load region. , discloses a configuration in which pulse width modulation (PWM) control for turning ON/OFF a switching element is not performed, and PWM control is performed in a high load region.

JP-A-10-174477 Japanese Patent No. 6596323

In Patent Document 1, the AC power supply voltage from the AC power supply is converted into a DC voltage having a voltage value approximately twice as high as that and is maintained, and the DC voltage is boosted by a booster circuit to increase the output DC voltage of the booster circuit. , is the input DC voltage of the inverter that drives the motor. In other words, since the boost converter is driven to supply current to the inverter when the load is high, components that support large capacity are required in the converter, and the size of the rectifying coil, smoothing capacitor, etc. increases in proportion to the capacity. Become. Also, there is a problem that the component size cannot be reduced even if the switching frequency of the converter is increased.　

Especially in the configuration of Patent Document 2, since the smoothing capacitor is shared with the switching capacitor, the size cannot be reduced, making it difficult to optimize the parts. As a result, the converter cannot meet the demand for large capacity, and miniaturization of the device cannot be achieved.　

Furthermore, when a boost converter is used, power conversion efficiency depends on the coil and capacitor. The coil becomes an obstacle on the current input side, and a voltage drop occurs at the smoothing capacitor on the output side. I have a problem with not going up.　

The present invention has been made in view of the problems described above, and an object thereof is to provide a motor control device capable of reducing noise generation in an inverter for driving a motor.

　The following configuration is provided as a means of achieving the above objectives and solving the above problems. That is, a first exemplary invention of the present application is a motor control device comprising an inverter circuit for driving a motor, a converter circuit for stepping down a voltage input from a DC power supply to a predetermined DC voltage and outputting the DC voltage, and means for determining a load condition of the motor in the inverter circuit; a first power supply mode for supplying power from the converter circuit to the inverter circuit according to the load condition; and supplying power from the DC power supply to the inverter circuit. a power supply switching unit for switching to any one of a second power supply mode, wherein the first power supply mode corresponds to a state in which the load state is lower than a predetermined load, and the second power supply mode corresponds to the load state. is characterized in that the load condition corresponds to a load condition higher than a predetermined load.

An exemplary second invention of the present application is an electric oil pump, characterized in that the motor control device according to the exemplary first invention is used as a pump driving section.

An exemplary third invention of the present application is a shift-by-wire system, characterized in that the motor control device according to the exemplary first invention is used as a shaft rotation driving portion of a rotary actuator.

According to the present invention, when the load of the motor is low, a low-voltage power source is supplied from the step-down converter to the inverter, and when the load is high, the converter is deactivated and high-voltage power is supplied. It can reduce the generation and avoid the decrease in efficiency (loss) at high load.

FIG. 1 is a block diagram showing the overall configuration of a motor control device according to an embodiment of the invention. FIG. 2 is a flowchart showing a control procedure for power supply to the inverter circuit in the motor control device in chronological order. FIG. 3 is a diagram showing the voltage waveform of the power supply to the inverter circuit in this embodiment in comparison with the conventional example. FIG. 4 is a diagram showing an example in which the switching voltage between the low load state and the high load state has hysteresis. FIG. 5 is a block diagram showing a first configuration example for supplying a plurality of systems of DC power sources with different voltage values to an inverter circuit. FIG. 6 is a block diagram showing a second configuration example for supplying a plurality of systems of DC power sources with different voltage values to the inverter circuit.

Hereinafter, embodiments according to the present invention will be described in detail with reference to the accompanying drawings. FIG. 1 is a block diagram showing the overall configuration of a motor control device according to an embodiment of the invention.

The motor control device 1 shown in FIG. 1 includes a motor control unit 10 composed of a microprocessor, for example, which controls the entire device, an inverter circuit 20 which supplies a predetermined drive current to the motor 15 and functions as a motor drive unit, and a DC power supply. A converter circuit 30 is provided for stepping down the input DC voltage to a predetermined DC voltage.

The inverter circuit 20 includes an FET bridge circuit composed of a plurality of semiconductor switching elements (FET1 to FET6), an inverter control section 21, and the like. The inverter control section 21 has a pre-driver section (not shown) that receives a control signal from the motor control section 10 and generates a motor drive signal (PWM signal).

The motor 15 is, for example, a three-phase brushless DC motor, and the FET1 to FET6 forming the inverter circuit 20 correspond to the respective phases of the motor 15 (U phase, V phase, W phase). That is, FETs 1 and 2 correspond to the U phase,

FETs

3 and 4 correspond to the V phase, and FETs 5 and 6 correspond to the W phase.

FETs

1, 3, and 5 are upper arm (high side (HiSide)) switching elements of the U, V, and W phases, respectively, and FETs 2, 4, and 6 are lower switching elements of the U, V, and W phases, respectively. It is an arm (low side (LoSide)) switching element. A switching element (FET) is also called a power element, and uses a switching element such as a MOSFET (Metal-Oxide Semiconductor Field-Effect Transistor) or an IGBT (Insulated Gate Bipolar Transistor).

The drain terminals of

FETs

1, 3, and 5 that constitute a bridge circuit are connected to the power supply side, and the source terminals are connected to the drain terminals of FETs 2, 4, and 6. Source terminals of FETs 2, 4 and 6 are connected to the ground (GND) side. In FIG. 1, illustration of a switching FET for supplying a drive current to the motor 15 is omitted.

The pre-driver section of the inverter circuit 20 drives the FET1 to FET6 that constitute the FET bridge circuit, thereby supplying each motor coil of the motor 15 with a drive current.

Further, the inverter circuit 20 includes

current sensors

23 and 25 in the current supply lines of the U-phase and W-phase of the motor 15 to detect the current flowing through the motor 15 . Current values detected by the

current sensors

23 and 25 are input to the motor control section 10 . The

current sensors

23 and 25 are, for example, phase current sensors using Hall elements.

The current flowing into the motor 15 can be detected by providing current sensors in at least two phases of the U-phase, V-phase, and W-phase (U-phase and W-phase in the above example). A current sensor may be provided on the power line to detect the current.

The detection of the current flowing into the motor 15 is not limited to the example using the phase current sensor described above. may be detected.

Converter circuit 30 converts (steps down) input voltage (voltage of DC power supply BT) Vcc to predetermined voltages VL and VM by controlling switching elements (FET) Q1 and Q2 by converter control unit 31. DC power converter. The converter circuit 30 has a switching element (high-side switch) Q1 arranged between the supply side of the power supply voltage Vcc indicated by symbol A in FIG. 1 and the output terminal indicated by symbol B. is connected in series with a switching element (low-side switch) Q2 arranged between the ground side indicated by .

The converter control section 31 sends control signals to Q1 and Q2 based on the signal from the motor control section 10, and controls ON/OFF with a predetermined switching frequency.

Specifically, converter control unit 31 outputs a pulse signal that switches Q1 and Q2 at a switching frequency (f _CONV ) required for outputting a predetermined voltage from converter circuit 30 . As a result, a pulse voltage waveform (pulse width modulated voltage waveform) having a predetermined duty ratio according to _fCONV is output from the connection point B of Q1 and Q2.

The output from the connection point B is a filter circuit composed of an inductor (coil) L1, one end of which is connected to the connection point B, and an output capacitor C2, which is connected between the other end of L1 and the ground side G. (low-pass filter) and smoothed. Thereby, the power supply voltage Vout to be supplied to the inverter circuit 20 is generated.

The converter circuit 30 feeds back the voltage Vout of the output terminal C to the terminal FB of the converter control section 31 to monitor whether the output voltage value is within a predetermined range.

The switching frequency (f _CONV ) in the converter control unit 31 of the converter circuit 30 is, for example, a frequency outside the audible band (20 kHz or higher), or 10 times the frequency (f _INV ) of the motor drive signal (PWM signal) in the inverter circuit 20. or higher frequency. By increasing the switching frequency of the converter circuit 30 in this manner, the sizes of the rectifying coils and capacitors used can be reduced, and the cost and size of the motor control device can be reduced.

Next, the operation and the like of the motor control device according to this embodiment will be specifically described.

In the motor control device 1 according to this embodiment, power is supplied to the inverter circuit 20 in two different power supply modes. That is, in the first power supply mode, the power generated by the converter circuit 30 is supplied to the inverter circuit 20, and in the second power supply mode, the DC power supply (external battery) BT is supplied via the power supply switching unit 3 to be described later. The inverter circuit 20 is supplied with power for driving the motor.

A power supply from the battery BT (the voltage of which is expressed as Vcc or VH as described later) is smoothed by an input capacitor C1, which is a power supply smoothing capacitor, and supplied to the inverter circuit 20.

FIG. 2 is a flowchart showing the control procedure for power supply to the inverter circuit in the motor control device 1 in chronological order. The motor control unit 10 of the motor control device 1 performs power supply control (switching between the first power supply mode and the second power supply mode) according to the load state of the motor 15 according to the processing program stored in the memory 13. to run.

The memory 13 temporarily stores, together with the power supply control processing program, command values and the like required for duty generation of the pulse width modulation signal (PWM signal) for the pre-driver section to drive the motor 15. be done.

FIG. 3 shows an example of the power supply voltage waveform supplied to the inverter circuit. FIG. 3(a) shows a conventional power supply voltage waveform. Here, when the load of the inverter circuit (motor current, etc.) shifts from a low load to a high load, the crest value of the power supply voltage waveform is kept constant. Control is performed to increase the ON duty ratio step by step.

Therefore, in the conventional method, the duty ratio is increased (the ON time τ is increased) when the output voltage is to be increased, and the duty ratio is decreased (the ON time τ is decreased) when the output voltage is to be decreased. Therefore, in the example shown in FIG. 3A, "ON duty ratio of power supply voltage waveform at low load (τ1/T1)" is less than "ON duty ratio of power supply voltage waveform at high load (τ2/T2)". It has to do with being small.

On the other hand, the motor control device 1 according to the present embodiment, as shown in FIG. The ON duty ratio (τ/T) of is constant in both low load and high load states, and the voltage peak value is increased step by step according to the change from low load to high load. conduct.

Therefore, as shown by the dashed line in FIG. 3(b), the converter circuit 30 has an average voltage when the peak value of the voltage is lowered and the ON duty ratio is increased at the time of low load. The output voltage Vout is generated so as to have the same voltage value as the average voltage at low load in the conventional method shown in FIG.

It should be noted that it is also assumed that the average voltage of the power supply voltage fluctuates according to load fluctuations in the inverter circuit. In that case, as described above, the peak value of the voltage supplied to the inverter circuit is increased stepwise according to the transition from low load to high load, and the ON duty ratio of the voltage waveform is changed to obtain a predetermined average voltage. The configuration may be changed as appropriate.

First, in step S11 of FIG. 2, the motor control unit 10 of the motor control device 1 shown in FIG. Then, the position (rotational angle) of the motor 15 obtained from magnetic field detection by the position detection unit 12 made up of, for example, a Hall element is acquired.

The motor control unit 10 determines the load state (operating state) of the motor 15 in subsequent step S13. Specifically, it is determined whether or not the current value obtained in step S11 and the motor rotation speed calculated from the rotation angle are in a "low load state" below a predetermined value.

If the motor 15 is in the "low load state", then in step S15, the mode is shifted to the first power supply mode. Therefore, the motor control unit 10 sends a control signal to the converter control unit 31 to turn off the power switching unit 3 (non-energized state). As a result, in step S<b>17 , the path for supplying output voltage Vcc of DC power supply BT to inverter circuit 20 is cut off, and output voltage Vout from converter circuit 30 is supplied to inverter circuit 20 .

Here, the converter circuit 30 controls the voltage Vout supplied to the inverter circuit 20 to be the minimum voltage VL required to drive the motor 15, as shown in FIG. 3(b).

In step S19, the motor control unit 10 determines that the ON duty of the motor drive signal (PWM signal) in the inverter circuit 20 is set to 80% for a predetermined period of time, for example, 10 cycles, based on the current value flowing into the motor 15 and the motor rotation speed. is exceeded (referred to as load state 1).

If the load state 1 is not satisfied in the inverter circuit 20, the converter circuit 30 continues the process of step S17 where Vout=VL. On the other hand, when the load state 1 is established, in step S21, a process of increasing the converter output voltage Vout by one step is executed.

Specifically, it is determined that the motor 15 is in a state requiring a larger drive current, and the converter output voltage Vout is reduced as shown in FIG. Raise from VL to VM.

In step S23, the motor control unit 10 determines whether or not the motor 15 in the inverter circuit 20 is in a load state (high load state) exceeding the maximum supply voltage VM of the converter circuit 30.

If the inverter circuit 20 has not reached the high load state, the motor control unit 10 determines whether or not the inverter circuit 20 is in the load state 2 in step S25. Here, as load state 2, it is determined whether or not the ON duty of the motor drive signal (PWM signal) of the inverter circuit 20 is below 20% for a predetermined period of time, for example, 10 cycles.

When the inverter circuit 20 is in load state 2, it is determined that the drive current required by the motor 15 has decreased, and in step S27, the converter output voltage Vout is decreased by one step. Here, one step is set to 10% of Vout, for example, and the converter output voltage Vout is lowered from VM to VL (see FIG. 3(b)).

On the other hand, in step S13, the motor control unit 10 determines that the load state of the motor 15 based on the current value obtained in step S11 and the motor rotation speed calculated from the rotation angle exceeds a predetermined value ("high load state"). , the process proceeds to step S31.

Alternatively, if it is determined in step S23 that the inverter circuit 20 is in a high load state, the motor control unit 10 also proceeds to step S31.

In step S31, the motor control unit 10 sends a control signal to the converter control unit 31 to turn on the power supply switching unit 3 (energized state), and shifts to the second power supply mode. As a result, in step S<b>33 , the path through which the output voltage from converter circuit 30 is supplied to inverter circuit 20 is cut off, and output voltage Vcc of DC power supply BT is supplied to inverter circuit 20 .

In this case, if Vcc=VH, then in step S33 the power supply voltage changes from VM to VH as shown in FIG. 3(b).

Therefore, the DC voltage step-down operation in the converter circuit 30 stops, the converter circuit 30 is bypassed, and the voltage Vcc of the DC power supply BT is supplied to the inverter circuit 20 in the second power supply mode.

Turning on the power supply switching unit 3 during high load means that power is supplied from the power supply line to the inverter circuit 20 only through the low resistance switch during high load. As a result, the power loss is generated only by the loss in the switch, so that the voltage Vcc of the battery BT can be supplied to the inverter circuit 20 almost losslessly, thereby suppressing a decrease in motor drive efficiency under high load.

The power switching unit 3 also functions as a reverse connection protection unit connected between the battery BT, which is a DC power supply, and the inverter circuit 20 in the second power supply mode. Therefore, the elements already installed in the motor control device can be used for both reverse connection prevention and power switching, so that the circuit configuration can be simplified and the cost can be reduced.

In the following step S35, the motor control unit 10 determines whether or not the load state of the inverter circuit 20 is in the "low load state" (here, the load state is changed from the "high load state" to the "low load state") as in the above step S13. ). If the "high load state" continues, the motor control unit 10 continues the process of step S33. mode to the first power supply mode.

As a result, in step S39, the voltage supplied to the inverter circuit 20 is changed from VH to VM. That is, the converter circuit 30 starts the DC voltage step-down operation, and the output voltage Vout (=VM) from the converter circuit 30 is supplied to the inverter circuit 20 .

As described above, the converter circuit 30 changes the output voltage Vout according to the load state of the inverter circuit 20 as shown in FIG. VM (VL<VM). At this time, the ON duty ratio of Vout is increased (the pulse width is widened) to maintain the average voltage of Vout, and the power supply voltage corresponding to the load state is supplied to the inverter circuit 20 .

By varying the output voltage of the converter circuit 30 according to the operating conditions of the motor 15 at low load when the converter circuit 30 operates in this way, the generation of EMI noise, vibration noise, etc. from the inverter circuit 20 can be further reduced. .

Note that when the load state of the motor 15 in the inverter circuit 20 shifts from the "low load state" to the "high load state" and when it shifts from the "high load state" to the "low load state", the converter circuit If the output voltage VM of 30 is set to a fixed value, it is assumed that "low load state" and "high load state", that is, VM and VH, are repeated around that voltage.

Therefore, as shown in FIG. 4, two voltages, VM1 and VM2, are defined as VM, and when the "low load state" changes to the "high load state", the power supply voltage for the inverter circuit 20 is switched from VM1 to VH. , and the power supply voltage is switched from VH to VM2 when shifting from the "high load state" to the "low load state".

Here, by setting VM1>VM2 and giving a hysteresis to the switching voltage in the "low load state" and the "high load state", the output voltage supplied from the converter circuit 30 to the inverter circuit 20 in the vicinity of the switching voltage is inadvertently generated. can be prevented from switching to

In the motor control device shown in FIG. 1, a semiconductor switch (FET) is used as the power switching unit 3, but it is not limited to this, and for example, a mechanical switch such as a relay may be used.

As described above, the motor control device according to the present embodiment has a configuration in which low-voltage power is supplied from the step-down converter circuit to the inverter circuit when the load on the inverter circuit is low, thereby reducing the switching control voltage of the inverter circuit. EMI noise, vibration noise (noise), etc. can be reduced. Also, it is possible to suppress the occurrence of overshoot and ringing in the switching control voltage.

In addition, since power conversion is performed using the converter circuit only when the load is low, the converter circuit can be configured with parts and circuit formats that are small in rating, size, etc., and that match the load capacity of the motor when it is operating at low load. . In addition, the motor can be driven with high efficiency for a wide range of load conditions in the inverter circuit.

For example, in an electric oil pump, by using the motor control device according to the above embodiment as a pump drive section, noise generated from the pump drive section during operation of the electric oil pump can be reduced.

Furthermore, for example, in a shift-by-wire system (SBW), by using the motor control device according to the above-described embodiment as a shaft rotation drive section of a rotary actuator, noise generated from the rotation drive section during operation of the shift-by-wire system can be reduced. can be reduced.

In addition, these electric oil pumps and shift-by-wire systems as in-vehicle products are originally equipped with a reverse connection protection unit between the battery BT and the inverter circuit as described above. A function similar to that of the motor control device according to the embodiment can be realized.

The present invention is not limited to the above-described embodiments, and various modifications are possible.

<Modification 1>
A plurality of converter circuits may be provided in the motor control device so that the voltage can be stepped down to a plurality of DC voltages according to the output voltage of the DC power supply (battery). In this case, the plurality of converter circuits may be provided for each phase of the three-phase motor. As a result, when the load is low, a low voltage can be supplied for each phase to the inverter circuit that drives the three-phase motor.

<Modification 2>
From the viewpoint of making the power supply voltage to the inverter circuit variable according to the operating state of the motor, a plurality of systems of DC power supplies with different voltage values supplied to the inverter circuit are provided, for example, by the configuration shown in FIGS. , DC power supplies VH, VM, VL of a system corresponding to the load state may be selected from a plurality of systems and supplied to the

inverter circuits

20a, 20b. By appropriately selecting the power supply voltages of a plurality of systems according to the operating state of the motor and making the power supply voltage to the inverter circuit variable, noise generation can be more effectively reduced.

<Modification 3>
In the above-described embodiment, the inverter control unit 21, the converter control unit 31, and the motor control unit 10 that performs switching control of the power supply switching unit 3 are separately provided, and control is decentralized and controlled according to each function. However, it is not limited to this. For example, the functions of these

controllers

10, 21, and 31 may be configured to be executed by a single controller. This enables centralization and simplification of control.

1 motor control device 3 power supply switching unit 10 motor control unit 12 position detection unit 13 memory 15 motor 20 inverter circuit 21

inverter control units

23, 25 current sensor 30 converter circuit 31 converter control unit BT battery

Claims

an inverter circuit that drives the motor;
a converter circuit for stepping down a voltage input from a DC power supply to a predetermined DC voltage and outputting the DC voltage;
means for determining a load state of the motor in the inverter circuit;
Power supply switching between a first power supply mode in which power is supplied from the converter circuit to the inverter circuit and a second power supply mode in which power is supplied from the DC power supply to the inverter circuit according to the load state. Department and
with
The first power supply mode corresponds to a state in which the load state is lower than a predetermined load, and the second power supply mode corresponds to a state in which the load state is higher than the predetermined load. and a motor controller.
2. The apparatus according to claim 1, wherein said converter circuit performs output control by pulse width modulation of a first switching frequency, and said inverter circuit performs output control by pulse width modulation of a second switching frequency different from said first switching frequency. A motor controller as described.
3. The motor control device according to claim 2, wherein in the output control, the converter circuit lowers the output voltage as the load condition becomes lower and raises the output voltage as the load condition becomes higher.
3. The motor control device according to claim 2, wherein said first switching frequency is outside the audible band and is ten times or more as high as said second switching frequency.
The motor control device according to claim 1, wherein the power switching unit is a switch.
The motor control device according to claim 1, wherein the power switching unit also functions as a reverse connection protection unit connected between the DC power supply and the inverter circuit in the second power supply mode.
2. The motor control device according to claim 1, wherein a plurality of systems of DC power sources having different voltage values supplied to said inverter circuit are provided, and the DC power source of said plurality of systems corresponding to said load state is supplied to said inverter circuit. .
The motor control device according to claim 1, wherein a control section for the inverter circuit, a control section for the converter circuit, and a switching control section for the power supply switching section are provided separately.
The motor control device according to claim 1, wherein control of the inverter circuit, control of the converter circuit, and switching control of the power switching unit are performed by a single control unit.
The motor control device according to claim 1, wherein a plurality of said converter circuits are provided.
The motor control device according to claim 10, wherein the motor is a three-phase motor, and the plurality of converter circuits are provided corresponding to each of the three phases.
An electric oil pump having the motor control device according to any one of claims 1 to 11 as a pump driving part.
A shift-by-wire system in which the motor control device according to any one of claims 1 to 11 is used as a shaft rotation driving part of a rotary actuator.