JP4742797B2 - Motor drive control device and control device for electric power steering device using the same - Google Patents

Description

  In the present invention, a three-phase current command value is input to a PWM control unit, and a PWM duty value from the PWM control unit is given to a three-phase inverter composed of a plurality of drive elements (such as FETs) to drive the three-phase motor in PWM. More particularly, the present invention relates to a motor drive control device, and in particular, a motor drive control device optimal for a control device of an electric power steering device that applies a steering assist force by a motor to a steering system of an automobile or a vehicle, and control of the electric power steering device using the same. Relates to the device.

  An electric power steering device that assists an automobile or a vehicle steering device with an auxiliary load by the rotational force of a motor is a steering shaft or rack that transmits the driving force of the motor by a transmission mechanism such as a gear or a belt via a reduction gear. An auxiliary load is applied to the shaft. Such a conventional electric power steering apparatus performs feedback control of motor current in order to accurately generate assist torque (steering assist force). In the feedback control, the motor applied voltage is adjusted so that the difference between the current command value and the motor current detection value becomes small. Generally, the adjustment of the motor applied voltage is a duty of PWM (pulse width modulation) control. This is done by adjusting the tee ratio.

  Here, the general configuration of the electric power steering apparatus will be described with reference to FIG. 11. The column shaft 2 of the steering handle 1 is connected to the steering wheel via the reduction gear 3, the universal joints 4A and 4B, and the pinion rack mechanism 5. It is connected to the tie rod 6. The column shaft 2 is provided with a torque sensor 10 that detects the steering torque of the steering handle 1, and a motor 20 that assists the steering force of the steering handle 1 is connected to the column shaft 2 via the reduction gear 3. ing. The control unit 30 that controls the power steering device is supplied with electric power from the battery 14 and also receives an ignition key signal from the ignition key 11, and the control unit 30 detects the steering torque value T detected by the torque sensor 10. Based on the vehicle speed V detected by the vehicle speed sensor 12, the assist assist steering command value I is calculated using an assist map or the like, and the current supplied to the motor 20 based on the calculated steering assist command value I. To control.

  The control unit 30 is mainly composed of a CPU (or MPU or MCU). FIG. 12 shows general functions executed by a program in the CPU.

  The function and operation of the control unit 30 will be described with reference to FIG. 12. The steering torque T detected and input by the torque sensor 10 is phase-compensated by the phase compensator 31 in order to improve the stability of the steering system. The phase-compensated steering torque TA is input to the steering assist command value calculation unit 32. In addition, the vehicle speed V detected by the vehicle speed sensor 12 is also input to the steering assist command value calculation unit 32. The steering assist command value calculation unit 32 refers to an assist map (lookup table) 33 based on the input steering torque TA and vehicle speed V, and a steering assist command value that is a control target value of the current supplied to the motor 20. Iref is determined.

  The steering assist command value Iref is input to the subtraction unit 30A and is also input to the feedforward differential compensation unit 34 for increasing the response speed. The deviation (Iref-i) obtained by the subtraction unit 30A is a proportional calculation unit 35. And is input to the integral calculation unit 36 for improving the characteristics of the feedback system. The output of the proportional calculation unit 35 and the output of the integral calculation unit 36 are respectively input to the addition unit 30B, the output of the differential compensation unit 34 is also added to the addition unit 30B, and the current command value E which is the addition result in the addition unit 30B is obtained. The motor drive signal 37 is input as a motor drive signal. The motor current value i of the motor 20 is detected by the motor current detection circuit 38, and the motor current detection value i is input to the subtraction unit 30A and fed back.

  When the motor 20 is a three-phase brushless motor, the details of the motor drive circuit 37 are configured as shown in FIG. 13, for example, and include a PWM control unit 37A and an inverter 37B. The PWM control unit 37A drives a duty calculation unit 371 that calculates the PWM duty values D1 to D6 for three phases according to a predetermined formula for the current command value E, and drives the gate of the FET as a drive element with the PWM duty values D1 to D6. In addition, it is configured with a gate drive unit 372 that compensates for dead time and is turned on / off, and the inverter 37B is configured with a three-phase bridge of FET, and is turned on / off with PWM duty values D1 to D6. Thus, the motor 20 is driven.

  In the motor driving device as described above, when driving a multi-phase brushless motor with an inverter, it is necessary to grasp the position of the rotor, that is, the motor phase, and sequentially switch the energization state to each phase according to the motor phase. There is. Therefore, conventionally, a Hall element is incorporated in a brushless motor to detect the rotor position. And the motor drive device which performs switching of an inverter according to the detected rotor position is put into practical use. That is, the relational expression between the current value flowing in each coil layer of the motor and the motor phase is known, and a motor driving device that measures the current value of each coil phase and detects the motor phase from the current value has been proposed. Yes.

  However, in a device that drives a motor using a Hall element, there are problems with the durability of the Hall element, which is a semiconductor element, and deterioration of characteristics in a high temperature environment. The circuit configuration around the Hall element is affected by noise, static electricity, etc. There is a problem that is easy to receive.

  As a motor control device that solves such a problem, there is one disclosed in Japanese Patent Laid-Open No. 2003-284374 (Patent Document 1). That is, in the apparatus of Patent Document 1, current detection means (three-phase downstream shunt method) for measuring the current flowing through the switching element is connected to the switching element that drives each coil phase, and the measured element current value is based on the measured element current value. Thus, the coil phase current value of each coil phase is calculated, and the brushless motor is controlled based on the motor phase calculated based on the coil phase current value.

In the three-phase downstream shunt system, as shown in FIG. 14, shunt resistors RS1 to RS3 are connected in series to the downstream side FETs 4 to 6, and the three-phase current is determined from the voltage drop caused by the shunt resistors RS1 to RS3 and their resistance values (known). This is a method of measuring I _U , I _V , and I _W.
JP 2003-284374 A

  However, the circuit configuration disclosed in Patent Document 1 has a problem that when the PWM duty value is close to 100%, the time during which the phase current flows through the shunt resistor is shortened, and an accurate current detection value cannot be obtained.

  To solve this problem, check the PWM duty value when the current detection value is A / D converted, and if it exceeds the threshold, the phase current detection value is not used, and the calculation is based on the current detection values of the other two phases. This is dealt with by switching calculation to obtain the current value. However, even in such a countermeasure, if two of the three phases command the current detection limit duty value or more at the same time, the logic of the switching operation is not established, and current control is performed in a state where accurate current detection cannot be obtained. There was a problem that.

  The present invention has been made for the above-mentioned circumstances, and an object of the present invention is a simple, small and low-cost configuration with a PWM duty value of around 100% while performing current detection by a three-phase downstream shunt method. The present invention is to provide a motor drive control device that can accurately detect and reliably control the phase current even if it becomes, and a control device for an electric power steering device using the motor drive control device.

The present invention relates to a motor drive control apparatus that inputs a three-phase current command value to a PWM control unit, applies a duty value from the PWM control unit to a three-phase inverter composed of a plurality of drive elements, and PWM drives a three-phase motor. The above-described object of the present invention is to provide a detection limit phase detection unit that detects that two phases of the three-phase current command value are simultaneously greater than or equal to a predetermined threshold, and the detection limit phase detection unit is configured such that two phases simultaneously exceed a predetermined threshold. An intermediate value output unit for outputting an intermediate value of the three-phase current command value when detected; and a subtracting unit for subtracting a difference between the intermediate value and a predetermined threshold from the three-phase current command value, respectively; A three-phase downstream shunt connected to the three-phase inverter is achieved by inputting the three-phase current command value subtracted in step 3 to the PWM controller. Or by detecting the sum of the three-phase current command values, the maximum value of the three-phase current command values, and the minimum value of the three-phase current command values, This is achieved more effectively by subtracting the maximum and minimum values to determine the intermediate value.

  Furthermore, the object of the present invention is to provide a sum calculation unit for detecting the sum of the three-phase current command values, a maximum value output unit for outputting the maximum value of the three-phase current command values, and the three-phase current command values. A minimum value output unit that outputs a minimum value; an intermediate value calculation unit that calculates an intermediate value based on the sum, maximum value, and minimum value; a comparison unit that obtains a difference between the intermediate value and a predetermined threshold; A subtractor for subtracting the difference from each current command value; and a duty adjustment unit for selecting and processing the three-phase current command value or the current command value subtracted by the subtractor based on the difference, A three-phase downstream shunt-type current detection means that is achieved by inputting an output three-phase current command value from a duty adjustment unit to the PWM control unit, and that connects the phase current of the three-phase motor to the three-phase inverter. By detecting with Alternatively, the intermediate value calculation unit subtracts the maximum value and the minimum value from the sum to calculate the intermediate value, or when the duty adjustment unit is less than 0, the three-phase By outputting a current command value and outputting the three-phase current command value subtracted by the subtracting unit when the difference is positive, or the duty adjusting unit subtracting the three-phase current command value by the subtracting unit This is achieved more effectively by shifting the current command value to 0 and outputting the current command value when one phase of the values is smaller than 0.

  Furthermore, in the present invention, by using the motor drive control devices described above for motor control of the electric power steering device, it is possible to provide an electric power steering device that is inexpensive and has high steering performance.

  According to the motor drive control device of the present invention, the current detection by the three-phase downstream shunt method is performed, and the motor phase current is accurately obtained even when the PWM duty value is close to 100% with a simple, small and low-cost configuration. Since it can be detected, the three-phase brushless motor can be reliably controlled over a wide range.

  In the present invention, all three-phase duty command values are shifted to the ground side (0% side), and only the absolute value is reduced while maintaining the relative values of the three-phase duty command values. The application range of the current detection method by the three-phase downstream shunt method in which accurate current detection cannot be performed can be expanded. And since at least two-phase current detection can always be made possible, the safety of motor control increases.

  The present invention includes a drive control device that drives a brushless motor having a plurality of coil phases (three phases) by ON / OFF switching using an inverter having a plurality of drive elements (FETs). The drive element that drives each coil phase of the motor is connected to current detection means using a three-phase downstream shunt method for measuring the current value flowing through each drive element. Then, based on the measured phase current values, the phase current values flowing through the coil phases are calculated, and the brushless motor is PWM-controlled.

  Since the motor current is controlled by the potential difference between each motor terminal, adding or subtracting a predetermined duty value from the PWM duty value that determines each motor terminal voltage does not change the potential difference between the terminals and does not affect motor control. There is. The present invention applies this feature and adopts means for subtracting the current corresponding to the predetermined duty value from the current command value corresponding to the duty command value of each phase in order to solve the problem of the current detection method of the downstream shunt method. is doing.

  Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 shows an example of the basic configuration of the present invention, in which a steering torque T from a torque sensor (not shown) and a vehicle speed V from a vehicle speed sensor (not shown) are input to a current command value calculation unit 100. The current command value Irf calculated by the command value calculation unit 100 is input to the subtraction unit 101. Each phase current I (I _U , I _V , I _W ) detected by the current detection means 120 using the three-phase downstream shunt method is fed back to the subtraction unit 101, and a three-phase current command value Irf (IUrf, The deviation between IVrf, IWrf) and each phase current I is input to the PI control unit 102, and the three-phase current command values Ir (IUr, IVr, IWr) PI-controlled by the PI control unit 102 are described with reference to FIG. The PWM control unit 103 is input. The PWM duty values D1 to D6 calculated by the PWM control unit 103 are input to the inverter 104 as described in FIG. 13, and the inverter 104 drives the three-phase brushless motor 110 according to the PWM duty values D1 to D6. The inverter 104 is provided with the current detection means 120 of the three-phase downstream shunt method described in FIG. 14, and each of the phase currents I detected by the current detection means 120 is fed back to the subtraction unit 101.

  1, in the first embodiment of the present invention, the minimum value Min (IUr, IVr, IWr) of the current command values IUr, IVr, IWr is selected as shown in FIG. A minimum value selection unit 130 to output and subtraction units 131 to 133 that subtract the minimum value Min (IUr, IVr, IWr) selected by the minimum value selection unit 130 from the current command values IUr, IVr, IWr, respectively.

Then, the outputs IUra, IVra, and IWra of the subtraction units 131 to 133 are input to the PWM control unit 103, and the motor 110 is PWM-driven in the same manner as described above.

  Thus, by subtracting the minimum values Min (IUr, IVr, IWr) from the current command values IUr, IVr, IWr, respectively, to obtain PWM duty values D1-D6, the PWM duty characteristics as shown in FIGS. Improved. That is, FIG. 3 shows a conventional characteristic in which the minimum value is not subtracted, and the maximum duty that the two phases overlap among the three-phase duty values is about 96%, but the minimum value is subtracted as in the present invention. As a result, as shown in FIG. 4, the aforementioned maximum duty was reduced to about 92%.

  Next, an example of the second embodiment of the present invention will be described with reference to FIG.

  In the second embodiment, the limit detection signal SL is detected by detecting that two of the three-phase current command values IUr, IVr, and IWr are simultaneously equal to or greater than the detection limit value of the current detection by the three-phase downstream shunt method. Detection limit phase detection unit 140 that outputs the output value, intermediate value output unit 141 that outputs the intermediate value Mid of the current command values IUr, IVr, and IWr when the limit detection signal SL is output, and the intermediate value Mid A comparison unit 143 that obtains a difference DT from a threshold 142 having a predetermined duty, and subtraction units 144 to 146 that subtract the difference DT from current command values IUr, IVr, and IWr are provided.

  In such a configuration, an example of the operation will be described with reference to the flowchart of FIG.

  First, the detection limit phase detection unit 140 and the intermediate value output unit 141 take in the three-phase current command values IUr, IVr, and IWr (step S1), and the detection limit phase detection unit 140 includes the three-phase current command values IUr, IVr, and IWr. It is monitored whether or not the two phases simultaneously exceed the detection limit value (step S2), and the limit detection signal SL is output when the two phases simultaneously exceed the detection limit value. When the limit detection signal SL is input to the intermediate value output unit 141, the intermediate value output unit 141 selects the intermediate value, that is, between the maximum value and the minimum value, from among the three-phase current command values IUr, IVr, IWr that are taken in. The intermediate current command value is selected as the intermediate value Mid and input to the comparison unit 143 (step S3). The comparison unit 143 calculates a difference DT between the threshold 142 and the intermediate value Mid (step S4), and inputs the difference DT to the subtraction units 144 to 146, thereby calculating the difference DT from the three-phase current command values IUr, IVr, and IWr. Subtracted current command values IUrb, IVrb, and IWrb can be obtained (step S5).

  Next, an example of the third embodiment of the present invention will be described with reference to FIG.

  In the third embodiment, a sum calculation unit 150 that calculates a sum ST (= IUr + IVr + IWr) of three-phase current command values IUr, IVr, IWr, and a maximum value Max (IUr, IWr, IWr, IWr) A maximum value output unit 151 for obtaining (IVr, IWr), and a minimum value output unit 152 for obtaining a minimum value Min (IUr, IVr, IWr) among the current command values IUr, IVr, IWr. Then, an intermediate value calculation unit 153 that calculates an intermediate value Mid from the sum ST, the maximum value Max, and the minimum value Min, a comparison unit 155 that calculates a difference ΔD between the intermediate value Mid and the threshold Th, and current command values IUr, IVr, Subtractors 157 to 159 that subtract the difference ΔD from IWr, respectively, and a duty adjuster 156 that adjusts the duty of the current command values IUrc, IVrc, and IWrc subtracted from the subtractors 157 to 159 according to the difference ΔD are provided.

  The duty adjustment unit 156 is directly input with the three-phase current command values IUr, IVr, IWr, and the current command values IUrc, IVrc, IWrc obtained by subtracting the difference ΔD by the subtraction units 157-159. Yes. The duty adjustment unit 156 receives the difference ΔD from the comparison unit 155. When the difference ΔD is 0 or less, the current command values IUr, IVr, IWr are selected and output as the current command values IUrd, IVrd, IWrd. If the difference ΔD is positive, that is, greater than 0, the current command values IUrc, IVrc, IWrc are selected and processed, and output as current command values IUrd, IVrd, IWrd.

  In such a configuration, an example of the operation will be described with reference to the flowchart of FIG.

First, the sum calculation unit 150, the maximum value output unit 151, and the minimum value output unit 152 take in the three-phase current command values IUr, IVr, and IWr (step S10), and the sum calculation unit 150 sets the three-phase current command values IUr, IVr, and IWr. Sum ST (= IUr + IVr + IWr) is calculated (step S11), and the maximum value output unit 151 outputs the maximum value Max (IUr, IVr, IWr) among the current command values IUr, IVr, IWr (step S12). The minimum value output unit 152 outputs the minimum value Min (IUr, IVr, IWr) among the current command values IUr, IVr, IWr (step S13). The order of steps S11 to S13 is arbitrary.
Next, the intermediate value calculation unit 153 determines the intermediate value Mid according to the following equation (1) (step S14).

Mid = ST-Max-Min
= IUr + IVr + IWr-Max (IUr, IVr, IWr)
-Min (IUr, IVr, IWr) (1)

The intermediate value Mid calculated by the above equation (1) is input to the comparison unit 155, and a difference ΔD from the duty threshold Th indicating the detection limit value of current detection by the three-phase downstream shunt method is obtained according to the following equation (2). (Step S15).

ΔD = Mid−Th (2)

The difference ΔD is input to the duty adjustment unit 156, and the duty adjustment unit 156 determines whether or not the difference ΔD is positive (step S20). When the difference ΔD is negative with 0 or less, the duty adjustment unit 156 selects the current command values IUr, IVr, IWr and outputs them as the current command values IUrd, IVrd, IWrd. The unit determines the duty according to a predetermined arithmetic expression (step S24). If the difference ΔD is positive, that is, greater than 0, the current command values IUrc, IVrc, IWrc obtained by subtracting the difference ΔD by the subtracting units 157 to 159 are selected (step S21), and the current command values IUrc, It is determined whether there is any negative value smaller than 0 in IVrc and IWrc (step S22).

  If current command values IUrc, IVrc, IWrc are all positive, duty is determined according to current command values IUrc, IVrc, IWrc, and if current command values IUrc, IVrc, IWrc are negative, they are forced. The duty is shifted to 0 (step S23), and the duty is determined according to the current command value including 0 at this time.

  FIG. 9 shows a state where the two phases (U, V) exceed the threshold when the duty threshold is set to 87%, and FIG. 10 shifts the current command value exceeding the threshold to the threshold. Since the duty value becomes negative depending on the threshold, the result of the third embodiment forcibly shifting to 0% is shown. That is, according to this embodiment, the two phases do not exceed the threshold at the same time. This is because the excess is absorbed because the lowest duty is negative.

  In each of the above embodiments, the motor control in the electric power steering apparatus has been described. However, the present invention is also applicable to the control of a three-phase brushless motor as a general power source.

It is a block diagram which shows the structural example of this invention. It is a block block diagram which shows the example of 1st Embodiment of this invention partially. It is a wave form diagram which shows the example of the control characteristic by the conventional PWM duty value. It is a wave form diagram which shows the example of the control characteristic by 1st Embodiment of this invention. It is a block block diagram which shows the example of 2nd Embodiment of this invention partially. It is a flowchart which shows the operation example of 2nd Embodiment. It is a block block diagram which shows the example of 3rd Embodiment of this invention partially. It is a flowchart which shows the operation example of 3rd Embodiment. It is a wave form diagram which shows the example of the control characteristic by the conventional PWM duty value. It is a wave form diagram which shows the example of the control characteristic by 3rd Embodiment of this invention. It is a figure which shows the general structural example of an electric power steering apparatus. It is a block diagram which shows the structural example of a control unit. It is a connection diagram which shows an example of the motor drive circuit by PWM control. It is a connection diagram which shows an example of the electric current detection means by a three-phase downstream shunt system.

Explanation of symbols

1 steering handle 2 column shaft 10 torque sensor 12 vehicle speed sensor 12 battery 20, 110 motor 30 control unit 100 current command value calculation unit 102 PI control unit 103 PWM control unit 104 inverter 120 current detection means 140 detection limit detection unit 141 intermediate value output Unit 142 thresholds 143 and 155 comparison unit 150 sum calculation unit 151 maximum value output unit 152 minimum value output unit 153 intermediate value calculation unit 156 duty adjustment unit

Claims (10)

  In the motor drive control apparatus that inputs a three-phase current command value to a PWM control unit, applies a duty value from the PWM control unit to a three-phase inverter composed of a plurality of drive elements, and PWM drives a three-phase motor. A detection limit phase detection unit that detects that two phases of the current command value simultaneously exceed a predetermined threshold; and when the detection limit phase detection unit detects that the two phases simultaneously exceed the predetermined threshold, the three-phase current command value An intermediate value output unit for outputting an intermediate value; and subtracting means for subtracting a difference between the intermediate value and a predetermined threshold from the three-phase current command value, respectively, and the three-phase current command value subtracted by the subtracting means A motor drive control device, wherein the motor drive control device inputs to the PWM control unit.   2. The motor drive control device according to claim 1, wherein a phase current of the three-phase motor is detected by a three-phase downstream shunt type current detection unit connected to the three-phase inverter.   The sum of the three-phase current command values, the maximum value of the three-phase current command values, and the minimum value of the three-phase current command values are obtained, and the intermediate value is obtained by subtracting the maximum value and the minimum value from the sum. The motor drive control device according to claim 1, wherein:   4. A control device for an electric power steering device, wherein the motor drive control device according to claim 1 is used for motor control of the electric power steering device.   In the motor drive control apparatus that inputs a three-phase current command value to a PWM control unit, applies a duty value from the PWM control unit to a three-phase inverter composed of a plurality of drive elements, and PWM drives a three-phase motor. A sum calculation unit for detecting a sum of current command values; a maximum value output unit for outputting a maximum value of the three-phase current command value; a minimum value output unit for outputting a minimum value of the three-phase current command value; An intermediate value calculation unit that calculates an intermediate value based on the sum, maximum value, and minimum value, a comparison unit that calculates a difference between the intermediate value and a predetermined threshold, and a subtraction unit that subtracts the difference from the three-phase current command value, respectively. And a duty adjustment unit for selecting and processing the three-phase current command value or the current command value subtracted by the subtraction unit based on the difference, and an output three-phase current command value from the duty adjustment unit The PW Motor drive control device, characterized in that the input to the control unit.   6. The motor drive control device according to claim 5, wherein the phase current of the three-phase motor is detected by a three-phase downstream shunt type current detection means connected to the three-phase inverter.   The motor drive control device according to claim 5, wherein the intermediate value calculation unit calculates the intermediate value by subtracting the maximum value and the minimum value from the sum.   The duty adjustment unit outputs the three-phase current command value when the difference is smaller than 0, and outputs the three-phase current command value subtracted by the subtraction unit when the difference is positive. The motor drive control device according to any one of claims 5 to 7.   9. The duty adjustment unit shifts the current command value to 0 and outputs the current command value when one phase is smaller than 0 among the three-phase current command values subtracted by the subtraction unit. The motor drive control device described.   10. A control device for an electric power steering device, wherein the motor drive control device according to claim 5 is used for motor control of the electric power steering device.

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