JP2010051111A - Motor diving device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To solve the problem in which an on-time of a switching element of an inverter circuit 32 is shortened, and then the output of the inverter circuit 32 is reduced when a supply voltage to a driver IC 33 for generating a driving signal to drive the inverter circuit 32 is reduced, and to provide a motor driving device 1 capable of improving steering wheel feeling of an EPS while suppressing fluctuation in the output voltage of the inverter circuit 32. <P>SOLUTION: The motor driving device includes: the inverter circuit 32 in which DC power from a battery 23 is converted to AC power, and the converted AC power is output to the motor 21; the driver IC 33 which transmits a driving signal for driving the inverter circuit 32; and a microcomputer 34 which transmits a control signal for controlling the driver IC 33. In the motor driving device 1 provided between the battery 23 and the motor 21, a step-up or step-down circuit 31 is provided in which a voltage from the battery 23 is stepped up or down to a predetermined voltage by driving the switching element, and the stepped up or stepped down voltage is output to the driver IC 33 and the inverter circuit 32. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a motor drive device that controls an electric power steering device.

  In recent years, with the advancement of electronic control of vehicles, demand for electric power steering (EPS) in which steering power assist is performed by a motor is increasing. EPS improves motor efficiency compared to hydraulic power steering, which always rotates the hydraulic pump, because it can electronically control the motor current to achieve the optimum steering torque according to the driving conditions and can assist the driving force only when necessary. There is an advantage that you can. This electronic control is performed by an ECU for EPS which is a part of the motor driving device, and the electric power used for the motor driving device is taken directly from the in-vehicle battery.

Conventionally, an electric power steering device that boosts the voltage input to the inverter circuit that drives the motor when the battery is low has been proposed in order to further stabilize the EPS steering assist force and to reduce the EPS motor in size. (For example, refer to Patent Document 1).
JP 2001-260907 A

  However, no consideration has been given to a problem in the case where the supply voltage to the driver IC that generates the drive signal for the switching element of the inverter circuit decreases. That is, when the supply voltage to the driver IC decreases, the on-time of the switching element of the inverter circuit decreases and the output of the inverter circuit decreases.

  Further, the conventional configuration has a problem that when the battery voltage becomes excessive, the resolution of the PWM becomes rough and the control characteristics deteriorate.

  In view of the above problems, an object of the present invention is to provide a motor drive device that can improve the handle feeling of EPS while suppressing fluctuations in the output voltage of an inverter circuit.

  In the first aspect of the invention, an inverter circuit that converts DC power from a battery into AC power and outputs the AC power, a drive circuit that transmits a drive signal that drives the inverter circuit, and a control signal that controls the drive circuit are provided. And a control circuit for transmitting, comprising: a step-up / step-down circuit that drives the switching element to step up / down the voltage from the battery to a predetermined voltage and outputs the voltage stepped up / down to the drive circuit and the inverter circuit It is characterized by.

  According to the above configuration, the predetermined voltage stepped up / down by the same step-up / step-down circuit is input between the drive circuit and the inverter circuit. Thereby, the fluctuation | variation of the applied voltage applied to a switching element by the input voltage and drive circuit which are input into an inverter circuit can be suppressed. This eliminates the need for complicated control in consideration of voltage fluctuations, suppresses fluctuations in the ON period of the switching elements due to voltage fluctuations, and improves handle feeling in EPS.

  Since the winding resistance and winding inductance of the motor are designed in consideration of the minimum voltage for driving the motor, it is possible to reduce the size of the motor by boosting the battery voltage with a step-up / down circuit. .

  Furthermore, since the voltage is stepped down even when the battery voltage becomes excessive, it is possible to prevent the PWM resolution from becoming rough when the battery voltage increases.

  According to a second aspect of the present invention, the control circuit is supplied with electric power without going through the step-up / down circuit.

  According to the above configuration, since the step-up / down circuit is not interposed between the power line connecting the battery and the control circuit, the operation of the control circuit is reliably ensured even when an abnormality occurs in the step-up / down circuit. can do. As a result, the safety of the motor drive device can be improved.

  The invention described in claim 3 is characterized in that a switch for intermittently supplying power to the control circuit is provided in the power line for the control circuit that supplies power to the control circuit.

  According to the above configuration, since the power supplied to the control circuit is smaller than the power supplied to the buck-boost circuit, the switch provided in the power line for the control circuit may be a switch for small current. The operation of the motor drive circuit can be stopped using the switch.

  According to a fourth aspect of the present invention, the step-up / step-down circuit performs step-up / step-down operation based on the input voltage to the step-up / down step circuit and the output voltage from the step-up / step-down circuit so that the input voltage matches the predetermined target voltage. Switching between a pressure operation and a regenerative operation in which current flows from the inverter circuit toward the battery is characterized.

  According to the above configuration, since the energization path through which the regenerative current flows is formed based on the input / output voltage of the step-up / step-down circuit, it is possible to prevent an excessive voltage from being applied to the step-up / down circuit while charging the battery.

(Motor drive device 1)
FIG. 1 is a schematic diagram showing the configuration of the motor drive device 1. The motor drive device 1 is provided between the battery 23 and the motor 21, generates three-phase alternating current from direct current power of the battery 23, and controls the motor 21.

  The ECU 22 provided in the motor drive device 1 includes a step-up / step-down circuit 31, an inverter circuit 32, a driver IC 33 that is a drive circuit, and a microcomputer 34 that is a control circuit. The inverter circuit 32 has a pair of switching elements S1 to S6 connected in series for each of the U phase, the V phase, and the W phase, and the winding of each phase of the motor 21 is at the midpoint of the switching element of each phase. It is connected. The inverter circuit 32 is driven by a drive signal transmitted from the driver IC 33. Further, the driver IC 33 is controlled by a control signal transmitted from the microcomputer 34.

  The step-up / down circuit 31 drives a built-in switching element to step up / down the voltage from the battery 23 to a predetermined voltage, and outputs the stepped up / down voltage to the driver IC 33 and the inverter circuit 32. The microcomputer 34 calculates a current command value to be supplied to the motor 21 based on the steering angle, steering torque, and the like, and controls the driver IC 33 based on the current command value. The driver IC 33 applies a voltage to the switching elements S1 to S6 in accordance with a control signal from the microcomputer 34 to drive the switching elements S1 to S6 on and off. The inverter circuit 32 drives the switching elements S <b> 1 to S <b> 6 on and off, thereby converting DC power from the battery 23 via the step-up / step-down circuit 31 into three-phase AC power and outputting it to the motor 21.

  The microcomputer 34 is supplied with power without going through the step-up / down circuit 31. Furthermore, a switch 24 for intermittently supplying power to the microcomputer 34 is provided in a microcomputer power line 35 (control circuit power line) for supplying power to the microcomputer 34.

  Since the microcomputer 34 is supplied with electric power from the battery 23 without going through the step-up / down circuit 31, even if an abnormality occurs in the step-up / down circuit 31, the microcomputer 34 can be safely controlled without affecting the microcomputer 34. it can.

Further, by turning off the switch 24 between the microcomputer 34 and the battery 23, the power supply to the microcomputer 34 is cut off and the driver IC 33 is stopped. As a result, the inverter circuit 32 and the motor 21 can be stopped. . In general, since the current supplied to the inverter circuit 32 is a large current of 50A to 100A, the switch 24 disposed on the inverter circuit 32 to stop the inverter circuit 32 is large and expensive for a large current. . On the other hand, since the current supplied to the microcomputer 34 is about 1 A, there is an advantage that the switch 24 for stopping the microcomputer 34 is excellent in durability and inexpensive.
(Buck-boost circuit 31)
FIG. 2 shows a configuration example of the step-up / down circuit 31 included in the motor driving device 1. The step-up / down circuit 31 has a first switching element Q1 having one end connected to the input terminal IN, a second switching element Q2 connected between the other end of the first switching element Q1 and the ground, and one end Are connected to the other end of the first switching element Q1, the third switching element Q3 connected between the other end of the inductor L and the ground, the output terminal OUT, and the other end of the inductor L. And a fourth switching element Q4 connected between the two. In addition, a smoothing capacitor C is provided between the output terminal OUT and the ground.

The step-up / step-down circuit 31 has a PWM circuit 41 that generates a drive signal for driving the first to fourth switching elements Q1 to Q4.
(Operation of the buck-boost circuit)
A case where the step-up / step-down circuit 31 is operated as a booster circuit will be described. In this case, the voltage of the battery 23 is boosted by turning on and off the third switching element Q3 and the fourth switching element Q4. The drive signals for the third switching element Q3 and the fourth switching element Q4 are in a reverse synchronization relationship.

  When the third switching element Q3 is off and the fourth switching element Q4 is on, current flows in the order of the input terminal IN → the switching element Q1 → the inductor L → the switching element Q4 → the output terminal OUT.

  When the third switching element Q3 is on and the fourth switching element Q4 is off, the energy accumulated in the inductor L is released, and the current flows through the inductor L → the switching element Q3 → the ground.

  As a result, when the duty ratio of the switching element Q3 is D3, the voltage Vout of the output terminal OUT can be expressed as follows using the voltage Vin of the input terminal IN.

Vout = Vin / D3
Here, since D1 is 1 or less, boosting is performed.

  Next, a case where the step-up / step-down circuit 31 is operated as a step-down circuit will be described. In this case, the voltage of the battery 23 is stepped down by turning on and off the first switching element Q1 and the second switching element Q2. The drive signals of the first switching element Q1 and the second switching element Q2 are in a reverse synchronization relationship.

  When the first switching element Q1 is on and the second switching element Q2 is off, current flows in the order of input terminal IN → switching element Q1 → inductor L → switching element Q4 → output terminal OUT.

  When the first switching element Q1 is off and the second switching element Q2 is on, the energy stored in the inductor L is released, and the inductor L → the switching element Q4 → the output terminal OUT → the ground → the switching element Q2 → A current flows in the closed circuit of the inductor L.

  As a result, when the duty ratio of the switching element Q1 is D1, the voltage Vout of the output terminal OUT can be expressed as follows using the voltage Vin of the input terminal IN.

Vout = Vin * D1
Here, since D1 is 1 or less, step-down is performed.

Next, the operation of the step-up / down circuit 31 when a counter electromotive force is generated in the motor 21 will be described. The motor 21 may be in a state of generating counter electromotive force depending on the steering state. Therefore, when the power generation state is caused by the back electromotive force, that is, when the output voltage Vout becomes larger than the input voltage Vin, the switching element Q1 and the switching element Q4 are turned on to charge the battery 23 as regenerative energy. Let When switching element Q1 and switching element Q4 are turned on, a current flows in the direction of switching element Q4 → inductor L → switching element Q1, and as a result, battery 23 is charged by the counter electromotive force generated in motor 21.
(Control flowchart)
The step-up / step-down circuit 31 is based on the input voltage to the step-up / down step circuit 31 and the output voltage from the step-up / step-down circuit 31, and a step-up / step-down operation for performing step-up / step-down operation so that the input voltage matches a predetermined target voltage The regenerative operation of flowing current from 32 toward the battery 23 is switched. This point will be described with reference to a control flowchart of the step-up / step-down circuit 31 shown in FIG. In step 010 in which the voltage is stepped down by the step-up / down circuit 31, initial settings such as initialization of the microcomputer 34, detection of the input voltage Vin, and detection of the output voltage Vout are performed, and the process proceeds to step 020. In step 020, it is determined whether or not the output voltage Vin2 from the PWM circuit 41 is smaller than a boost threshold Vth21 that is a reference line for determining whether or not the voltage is an undervoltage. If it is determined that Vin2 is smaller than the boost threshold Vth21, it is determined that the output voltage has not reached the reference voltage, and in step 030, the switching elements Q3 and Q4 are driven to perform the boosting operation. On the other hand, if it is determined that Vin2 is equal to or higher than the boost threshold Vth21, it is determined that boosting is unnecessary, and the process proceeds to step 040, which is the next determination condition. In step 040, it is determined whether or not the output voltage Vin2 from the PWM circuit 41 is greater than a step-down determination threshold Vth22 that is a reference line for determining whether or not the voltage is an excessive voltage. When Vin2 is equal to or lower than the step-down determination threshold Vth22, the process proceeds to step 080, assuming that the output voltage from the PWM circuit 41 is an appropriate value, does not perform the step-up / step-down operation, and stops the switching operation of the switching elements Q1 to Q4 To do. On the other hand, if Vin2 is larger than the step-down determination threshold value Vth22, the process proceeds to step 050, which is the next determination condition. In step 050, it is determined whether or not the input voltage Vin1 to the PWM circuit 41 is smaller than the regeneration determination threshold value Vth12. When it is determined that Vin1 is smaller than the regeneration determination threshold value Vth12, the process proceeds to step 060 where the switching elements Q1 and Q4 are turned on and the battery 23 is charged using the back electromotive force generated in the motor 21. On the other hand, if it is determined that Vin1 is greater than or equal to the regeneration determination threshold value Vth12, the process proceeds to step 070 to drive the switching elements Q1 and Q2 to step down the input voltage.

  The magnitude relationship between the threshold values used for comparison with the input voltage and the output voltage is “step-down determination threshold Vth22> step-up determination threshold Vth21> regeneration determination threshold Vth12”.

  Switching to the regenerative operation is determined using a threshold value, but may be determined using a relative value that is a difference between the output voltage and the input voltage.

  Next, the influence of the drop in the supply voltage to the driver IC 33 on the inverter circuit 32 and the effect of the step-up / step-down circuit according to the present invention will be described below.

  FIG. 4 shows a configuration diagram of the driver IC 33 and its peripheral devices. The driver IC 33 is connected to the output of the microcomputer 34 via input terminals IND1 and IND2, connected to the battery 23 via the power supply voltage terminal VDD1, and connected to the switching element Si of the inverter circuit 32 via the output terminals OUTD1 and OUTD2. Connected to the switching element Sj. Here, a control signal used for driving the switching element Si of the upper arm is transmitted to the input terminal IND1 and the output signal OUTD1, and a control used for driving the switching element Sj of the lower arm is transmitted to the input terminal IND2 and the output terminal OUTD2. A signal is transmitted. The driver IC 33 receives a control signal from the microcomputer 34 and generates a drive signal. And a drive signal is transmitted to switching element Si and Sj, and switching element Si and Sj are driven.

  FIG. 5 shows a correspondence relationship between the control signal from the microcomputer 34 and the drive signal output from the driver IC 33. The top waveform shown in FIG. 5 is the control signal input to the IND1 terminal, the second waveform from the top is the drive signal output from OUTD1, and the third waveform from the top is input to the IND2 terminal. The control signal and the bottom waveform indicate the drive signal output from OUTD2.

  The voltage at the output terminal OUTD1 of the driver IC 33 rises triggered by the rise of the control signal input to the IND1 terminal. On the other hand, the output voltage OUTD2 of the driver IC 33 falls with the falling edge of the control signal input to the IND2 terminal as a trigger. Here, the voltage value VDD <b> 1 after rising is a voltage from the battery 23. For this reason, when the voltage of the battery 23 decreases, the voltage after the rising of the output terminal VDD1 also decreases. Here, VDD (1) shown in FIG. 6 indicates a voltage value when the battery 23 voltage is normal, and VDD (2) indicates a voltage value when the voltage of the battery 23 decreases.

  When the voltage of the drive signal output from OUTD1 and OUTD2 becomes equal to or higher than the threshold voltage THvdd, the switching elements Si and Sj are turned on. Therefore, when the voltage VDD of the battery 23 decreases, the rise time until the turn-on voltage changes from OV to THvdd becomes longer, and the fall time until the turn-off voltage changes from VDD to THvdd becomes shorter. Become. As a result, the on-time (2) of the lower-arm switching element Sj when the battery 23 voltage drops is shorter than the on-time (1) of the lower-arm switching element Sj when the battery 23 voltage is normal. The on-time (2) of the upper-arm switching element Si is also shorter than the on-time (1) of the upper-arm switching element Si when the battery 23 voltage is normal.

  Thus, when the supply voltage to the driver IC 33 varies, the on-time of the switching elements Si and Sj also varies, and the output voltage from the inverter circuit 32 also varies. For this reason, when the input voltage to the driver IC 33 fluctuates, the inverter circuit 32 must perform control in consideration of fluctuations in the supply voltage, which complicates the control and degrades the handle feeling. End up. In this regard, in the present invention, since the step-up / step-down circuit 31 is provided between the driver IC 33 and the battery 23, it is possible to prevent deterioration in controllability due to fluctuations in the input voltage to the driver IC 33.

It is the schematic which shows the structure of the motor drive device which concerns on the Example of this invention. It is the schematic which shows the structure of the buck-boost circuit based on the Example of this invention. It is a control flowchart of the step-up / step-down circuit according to the embodiment of the present invention. It is the schematic of a driver IC and its peripheral devices. It is a contrast diagram which shows the waveform of the control signal input into driver IC, and the drive signal output from driver IC.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Motor drive device 21 Motor 22 ECU
23 Battery 24 Switch 31 Buck-Boost Circuit 32 Inverter Circuit 33 Driver IC (Drive Circuit)
34 Microcomputer (control circuit)
35 Power line for microcomputer (Power line for control circuit)
Q1 to Q4 Switching element L Inductor

Claims (4)

An inverter circuit that converts DC power from the battery into AC power and outputs the AC power; a drive circuit that transmits a drive signal that drives the inverter circuit; and a control circuit that transmits a control signal that controls the drive circuit; In a motor drive device comprising:
A motor drive device comprising a step-up / step-down circuit that drives a switching element to step up / down a voltage from the battery to a predetermined voltage and outputs a voltage stepped up / down to the drive circuit and the inverter circuit.   The motor driving apparatus according to claim 1, wherein the control circuit is supplied with electric power without passing through the step-up / down circuit.   3. The motor drive device according to claim 2, wherein a switch for interrupting power supply to the control circuit is provided in a control circuit power supply line for supplying power to the control circuit. The step-up / down circuit is
Based on the input voltage to the step-up / step-down circuit and the output voltage from the step-up / down circuit, the step-up / step-down operation for increasing / decreasing the input voltage to match a predetermined target voltage and the current from the inverter circuit to the battery The motor driving device according to claim 1, wherein the motor driving device is switched between a regenerative operation for flowing a current.

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