JP5392025B2 - Motor control device and electric power steering device using the same - Google Patents

Description

  The present invention calculates a duty command value for each phase for controlling the motor current by control calculation, forms a PWM waveform corresponding to the duty command value for each phase, and instructs the motor with a command current (voltage) by a PWM control inverter. And a motor control device for driving the motor by using the motor control device, and an electric power steering device for applying an assist torque by a motor to a steering mechanism of a vehicle. A single current detector is disposed on the side (ground side) for PWM control, and the PWM cycle is n (> 2) times per control cycle that requires a phase current value. One of the n cycles is set as the current detection cycle, and (n-1) times as the duty adjustment cycle to control the duty calculation, thereby reducing the size, weight, and cost. The present invention relates to a motor control device and an electric power steering device using the same.

  An electric power steering device for energizing a vehicle steering device with an auxiliary load by a rotational force of a motor energizes an auxiliary load to a steering shaft or a rack shaft by a transmission mechanism such as a gear or a belt via a speed reducer. It is supposed to be. Such a conventional electric power steering apparatus performs feedback control of motor current in order to accurately generate assist torque (steering assist force). In feedback control, the motor applied voltage is adjusted so that the difference between the current command value (steering assist command value) and the motor current detection value is small. The adjustment of the motor applied voltage is generally performed by PWM (pulse width). Modulation) It is done by adjusting the duty ratio of the control inverter.

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

  The control unit 30 is mainly composed of a CPU (including an MPU and MCU). FIG. 2 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. 2. The steering torque T detected by the torque sensor 10 is phase-compensated by the phase compensator 31 and input to the steering assist command value calculator 32, and the vehicle speed sensor The vehicle speed V detected at 12 is also input to the steering assist command value calculator 32. Based on the input steering torque T and vehicle speed V, the steering assist command value calculator 32 determines a steering assist command value I that is a control target value of the current supplied to the motor 20 with reference to the assist map. The steering assist command value I is input to the subtraction unit 30A and is also input to the feedforward differential compensation unit 34 for increasing the response speed, and the deviation (Ii) of the subtraction unit 30A is input to the proportional calculation unit 35. At the same time, it is input to the integral calculation unit 36 for improving the characteristics of the feedback system, and its proportional output is input to the addition unit 30B. The outputs of the differential compensator 34 and the integral calculator 36 are also added to the adder 30B, and the current control value E, which is the addition result of the adder 30B, is input to the motor drive circuit 37 as a motor drive signal. Electric power is supplied to the motor drive circuit 37 from the battery 14 via the ignition key 11 and the fuse 13, the motor current value i of the motor 20 is detected by the motor current detection circuit 38, and the motor current value i is input to the subtractor 30A. Feedback.

  A general configuration example of the motor drive circuit 37 will be described with reference to FIG. The motor drive circuit 37 includes a PWM control unit 37A and an inverter 37B. The PWM control unit 37A includes a duty calculation unit 371 for calculating the PWM control command values D1 to D6 for three phases according to a predetermined formula, and a gate of an FET as a switching drive element based on the PWM duty command values D1 to D6. And a gate drive unit 372 that turns ON / OFF by compensating for dead time, and the inverter 37B is constituted by a three-phase bridge of FET, and is turned on by PWM Duty command values D1 to D6. The motor 20 is driven by being turned off.

  In such a motor drive device, when driving a multi-phase brushless motor by 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. is there. In general, a motor drive device that detects a rotor position by a rotor position sensor such as a Hall element or a resolver and switches an inverter (FET) according to the detected rotor position has been put into practical use. . In addition, the relational expression between the current value flowing in each coil layer of the motor and the motor phase is known, and a motor drive device that measures the current value of each coil phase and detects the motor phase from the current value has been proposed. Yes.

  In order to calculate the current feedback system and the motor position as described above, it is necessary to measure the current value of each coil phase. On the other hand, one of the items of downsizing, weight saving, and cost reduction of the electric power steering device is required. For example, a single current detector is required. That is, it is required to measure each phase current with a single current detector.

  Regarding the detection of the phase current of each phase in response to such a request, for example, a PWM control inverter disclosed in JP-A-8-19263 (Patent Document 1) has been proposed. In the device described in Patent Document 1, a current sensor is connected immediately before and after switching of each phase switching element of the inverter main circuit, the DC bus current of the inverter main circuit is detected by the current sensor, and the change in the detected current is switched. According to the timing, each phase is distributed and used as a detection current for each phase. Thereby, phase current detection can be implemented by one current sensor.

  However, in the PWM control inverter disclosed in Patent Document 1, there are cases where the voltage command value becomes 0 for all three phases, or the voltage command values for two phases become substantially equal. As a result, for example, when the three-phase switching elements are simultaneously switched, the former is obtained, and when the two-phase switching elements are simultaneously switched, the latter is obtained. Therefore, in the PWM control inverter described in Patent Document 1 that detects the DC bus current with a single current sensor, for example, when the v-phase voltage and the w-phase voltage rise and fall simultaneously, the current information of each phase is transferred to the DC bus. The time that appears is short and current detection is difficult, and the v-phase current and the w-phase current cannot be separated. This is the case not only when the switching is completely simultaneous, but also when the interval from one phase switching to the other phase switching is short, it is difficult to detect or detect the DC bus current between switching There is a problem in that the accuracy is lowered and the current of each phase cannot be obtained properly.

  A PWM control inverter disclosed in Japanese Patent No. 3664040 (Patent Document 2) is one that solves such a problem and detects a phase current using a single current detector to drive a motor. The configuration is a method of changing the duty command value to be different in the first half and the second half of 1PWM when the difference in the magnitude of the duty is less than the duty amount corresponding to the current detection time. In the first half, the middle duty (second largest duty) of the three-phase duty is used as a reference, and the maximum duty and the minimum duty are changed so that the current detection time can be secured. In the second half, the average value is the original duty command value. This is the duty command value that adjusts the duty changed in the first half.

  However, in the PWM control inverter described in Patent Document 2, since the duty is changed within one PWM period, there is a problem that the software load becomes very high when the one PWM period is short. In addition, since the duty to secure the current detection time is calculated based on the intermediate duty, the duty can be changed to ensure the current detection time when the maximum duty is 100%. There is a possibility of disappearing.

  Further, in the apparatus disclosed in Japanese Patent No. 3931079 (Patent Document 3), the duty is corrected so that the time required for one phase to be ON and two phases to be ON can be ensured for the time required for current detection. The amount of increase / decrease due to correction is adjusted by the carrier so that the average value is the same as the original duty command value. As described above, since the duty change is performed for each carrier, the apparatus disclosed in Patent Document 3 causes a problem in the apparatus described in Patent Document 2, that is, the software load becomes very high when one PWM cycle is short. This problem can be alleviated.

  However, in the apparatus disclosed in Patent Document 3, the method of calculating the duty to be corrected is not clearly described, and the duty correction for detection is adjusted only within the next carrier period, so that the amount of duty that can be corrected The restriction of the Duty range at the time of adjustment greatly affects. In particular, in a system with a short PWM cycle, the ratio of time required for current detection with respect to one PWM cycle is large, so that the degree of influence increases, and there is a problem that the duty range in which current detection is possible is narrowed. For example, if the time required for current detection is set to 12% duty, the maximum duty is 100%, and the minimum duty is 0%, the influence on the motor applied voltage is suppressed only in the range of 6% ≦ intermediate duty ≦ 94%. There is a problem that the phase current can be detected and the phase current cannot be detected in other regions.

  In general, in a configuration in which current detection is performed with a single current detector, it is necessary to limit the duty within the duty range within which current detection is possible, and the motor characteristics may not be fully displayed accordingly, so current detection is possible as much as possible. It is desirable to expand the possible duty range. Moreover, it is desired to reduce the software load as much as possible due to the diversification of functions required for software in recent years.

JP-A-8-19263 Japanese Patent No. 3664040 Japanese Patent No. 3931079

  The present invention has been made under the circumstances described above, and the object of the present invention is to detect and feed back a motor phase current using a single current detector and drive the motor with a PWM control inverter. Even when the PWM period is short, it is possible to perform duty correction to ensure the current detection time even when the maximum duty becomes 100% without increasing the software load, and the duty range in which current detection is possible An object of the present invention is to provide a motor control device and an electric power steering device using the motor control device that are compact, light weight, and cost-reduced without reducing the size.

The present invention calculates a duty command value for each phase for controlling the motor current by control calculation, forms a PWM waveform according to the duty command value for each phase, and controls the motor by an inverter based on the PWM waveform. The present invention relates to a motor control device for driving, and the object of the present invention is to connect a single current detector to the power input side or the power output side of the inverter and to control the phase current value once. On the other hand, the PWM cycle has a configuration of n (> 2) times, and one of the PWM cycles n is set as a current detection cycle, and (n−1) times is set as a duty adjustment cycle. In the function for determining the maximum duty, intermediate duty, and minimum duty of the value, and in the current detection period, the difference between the maximum duty and the minimum duty is smaller than twice the current detection required duty amount τ, and the intermediate duty is Greater than the current detection required duty amount τ , (100% −τ) under a first condition that is smaller than (100% −τ), the intermediate duty is used as a reference, and the value obtained by adding the current detection required duty amount τ to the reference intermediate duty and the maximum duty The larger one is the maximum duty for detection, the value obtained by subtracting the current detection required duty amount τ from the intermediate duty to be the reference, and the smaller one of the minimum duty is the minimum duty for detection, and the reference is the above By calculating the intermediate duty as it is as the detection intermediate duty, each phase duty for detection of the current detection cycle is calculated. Under the second condition other than the first condition, the maximum duty is used as a reference. The maximum duty as a reference is directly used as the maximum duty for detection. However, when the maximum duty is smaller than twice the current detection required duty amount τ, 2τ is set as the maximum duty for detection, and the maximum duty for detection As a standard, the standard When the difference between the outgoing maximum duty (or the maximum duty) and the intermediate duty is smaller than the current detection required duty amount τ (referred to as the first time), the current detection required duty amount τ from the detection maximum duty. Is the detection intermediate duty, and when the intermediate duty is smaller than the current detection required duty amount τ (referred to as the second time), the current detection required duty amount τ is set as the detection intermediate duty, In cases other than the first time and the second time, the intermediate duty is directly used as the detection intermediate duty, and the difference between the detection intermediate duty and the minimum duty is smaller than the current detection required duty amount τ (third) The value obtained by subtracting the current detection required duty amount τ from the detection intermediate duty is used as the detection minimum duty. In cases other than the third time, the minimum duty is used as it is as the detection minimum duty. it allows to calculate the detection phase Duty, the Duty adjustment Period, the sum of the value obtained by dividing the difference (n-1) between the phase Duty command value and the current the detection phase Duty calculated in the detection period, the phase Duty command value the value obtained by, is achieved by and a function of the adjustment phase Dut y.

  According to the motor control device of the present invention, since only one duty change is required during n PWM cycles, the software (CPU) load can be reduced. Moreover, since the period for adjusting the duty is set to be as long as (n−1) period, the adjustment duty amount to be added can be reduced to 1 / (n−1) for one duty adjustment period. Since it is possible to widen the duty range in which phase current can be detected while suppressing the influence on the motor applied voltage, there is an advantage that the duty output can be relaxed and the motor output characteristics can be fully utilized.

  Further, according to the motor control device of the present invention, when the difference amount of each phase duty is smaller than the duty amount necessary for securing the current detection time in the current detection cycle, the intermediate duty is used as a reference, and the maximum duty is obtained. In addition, the current detection time is secured by correcting the minimum duty, and other than that, the intermediate duty and the minimum duty are corrected based on the maximum duty, so even when the maximum duty is 100%, current detection is possible. Duty correction can be performed to secure the necessary time, and the duty range in which phase current can be detected can be widened. This has the advantage that the duty output can be relaxed and the motor output characteristics can be fully utilized.

  Since a motor control device having the above features can be realized by providing a single current detector, if such a motor control device is mounted on an electric power steering device, the electric power steering device can be made compact, light weight, and cost reduced. Can be planned. Further, by using the motor control device of the present invention, it becomes possible to detect the phase current in a practical duty range, so that the control of the electric power steering device can be carried out reliably and stably.

It is a figure showing an example of composition of a general electric power steering device. It is a block diagram which shows the structural example of the control unit of the conventional electric power steering apparatus. It is a connection diagram which shows an example of the motor drive circuit of a three-phase motor. It is a connection diagram which shows the structural example of the inverter using a single electric current detector. It is a figure for demonstrating the operation example (A phase ON) of an inverter. It is a figure for demonstrating the operation example ((A phase + B phase) ON) of an inverter. It is a figure for demonstrating the Duty correction method in an electric current detection period and a Duty adjustment period. It is a block diagram which shows the structural example of the apparatus which performs Duty correction | amendment in an electric current detection period and a Duty adjustment period. It is a flowchart which shows the operation example of the duty correction method in an electric current detection period and a duty adjustment period. It is a wave form diagram which shows an example of the PWM waveform (sawtooth carrier) in case 2 phase Duty is balanced. FIG. 6 is a waveform diagram showing an example of a PWM waveform (sawtooth carrier) in which the three-phase duty is balanced and the differences between the respective phases are all within the current detection required duty amount τ. It is a wave form diagram which shows an example of a PWM waveform (sawtooth carrier) in case the three-phase duty is balanced and only the difference between the maximum duty and the intermediate duty can be detected. It is a figure which shows the range of each phase Duty command value which can be adjusted with a duty adjustment period. It is a figure which shows the range of each phase Duty command value which can be adjusted with the Duty adjustment period by the difference in a carrier waveform. It is a wave form diagram which shows an example of the PWM waveform (triangular wave carrier) in case 2 phase Duty is balanced.

  The present invention requires the phase current value of the PWM control inverter of the motor control device while satisfying the demand for the unification of the current detector which is one of the items of downsizing, weight reduction and cost reduction of the electric power steering device. The configuration is such that there are n PWM cycles (n> 2) for one control cycle, and one of the n PWM cycles is the current detection cycle, and the remaining (n-1) cycles are the duty adjustment cycle. As a duty calculation (correction). In the motor control device of the present invention, since only one duty correction is required during n PWM cycles, the software (CPU) load can be reduced. Furthermore, since the period for adjusting the duty is set to be as long as (n-1) period, the amount of adjustment duty to be added can be reduced to 1 / (n-1) for one duty adjustment period. The duty range in which the phase current can be detected can be widened while suppressing the influence on the applied voltage. For example, if the time required for current detection is set to 12% duty, the maximum duty is 100%, the minimum duty is 0%, and n = 5, the influence on the motor applied voltage is suppressed in the range of 2.4% ≤ intermediate duty ≤ 97.6%. In addition, the phase current can be detected.

  Also, in the current detection cycle, if the difference amount of each phase duty is all smaller than the duty amount necessary to secure the current detection time, the current duty is corrected by correcting the maximum duty and the minimum duty based on the intermediate duty. Other than that, it has a function of correcting the intermediate duty and the minimum duty with the maximum duty as a reference. As a result, even when the maximum duty becomes 100%, the duty can be changed to ensure the time required for current detection.

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

  First, a configuration example of an inverter to which a single current detector is connected will be described with reference to FIG. In this configuration example, the A- to C-phase three-phase motor 50 is PWM-controlled by six FETs having a bridge configuration, and power is supplied from a power source (battery) 51 to the high-side FET, A single current detector 60 is connected to the ground side. In this case, the current flowing through the current detector 60, that is, the motor detection current varies depending on the ON / OFF state of each FET. FIG. 5 shows an example in which the A-phase high-side FET is ON (the A-phase low-side FET is OFF) and the B-phase and C-phase high-side FETs are both OFF (the B-phase and C-phase low-side FETs are ON). The current path is shown. FIG. 6 shows a state in which both the A-phase and B-phase high-side FETs are ON (A-phase and B-phase low-side FETs are OFF) and the C-phase high-side FET is OFF (C-phase low-side FETs are ON). The current path is shown. As can be seen from FIGS. 5 and 6, the total value of the phases in which the high-side FET is ON appears as a current in the current detector 60. This is the same when the current detector 60 is connected to the power input side of the inverter.

As described above, when the current is detected by the current detector 60 in the one-phase ON state and in the two-phase ON state and the characteristic that the three-phase current sum is 0 is used, the current of each of the three phases Can be detected. It will detect the current I _A of the A phase in the case of FIG. 5, the sum of the current I _B of the current I _A and the B-phase A-phase is detected by the current detector 60 in the case of FIG. 6 However, since there is a relationship of I _A + I _B + I _C = 0, the C-phase current I _C is detected as I _C = − (I _A + I _B ). That is, even when current is detected by a single current detector 60, the current of each phase can be detected by utilizing the characteristic that the current sum of the three phases is zero.

  However, in order to accurately detect the current while removing noise components such as rigging noise flowing in the current detector 60 immediately after each FET is turned on, a certain detection time is required. Therefore, it is necessary to continue the one-phase ON state and the two-phase ON state for the time required for current detection. However, when each phase Duty is balanced, that is, when each phase Duty is approximate, the time Can not be secured. Also, the normal PWM period is generally set to a period shorter than the control calculation period in order to suppress the sampling theorem and motor noise. Since the phase current detection value is actually used for the control calculation, it is only necessary to detect the phase current value in the period immediately before the start of the control calculation in the PWM period.

  Therefore, in the present invention, the PWM cycle is configured to be n (n> 2) times per control cycle that requires the phase current value, and one of the n PWM cycles is set as the current detection cycle. (N-1) Let the period be the duty adjustment period. Then, in the current detection cycle, each phase duty correction value is added to or subtracted from each phase duty command value so that the time required for the current detection can be ensured for the time when the one phase is ON and the two phases are ON. In the duty adjustment cycle, the duty correction value obtained by dividing the duty correction value corrected for current detection in the current detection cycle by (n-1) is subtracted and corrected to each phase duty command value. By doing in this way, in the current detection cycle, the time necessary for detecting each phase current is secured, current detection is performed, the detected current value is used for the control calculation, and the PWM cycle in which the current detection value is not necessary By compensating for the corrected duty for current detection, the duty to be given can be matched with the average duty of the n PWM cycles so that the phase current can be detected without affecting the motor applied voltage as much as possible. I have to.

  In addition, by dividing the adjustment duty amount for matching the average duty of the PWM cycles of n times with the duty to be given into (n−1) times, the correction amount of the duty in one PWM cycle in the duty adjustment cycle can be obtained. Can be reduced. For this reason, the influence on the motor current due to the duty correction amount can be minimized, and it is advantageous for the duty restriction in the adjustment (0% ≤ (Duty command value + Duty adjustment value) ≤ 100%). The possible Duty area can be widened.

  Next, a method for changing (correcting) the duty in the current detection cycle and the duty adjustment cycle will be described with reference to FIG.

In the duty command value of each phase, the maximum duty, intermediate duty, and minimum duty are determined in descending order of the duty value, and it is determined whether the current detection is possible. Each phase of Duty
(Each phase for detection Duty) is calculated.

In condition (1), the difference amount (MAX_Duty-MIN_Duty) between the maximum duty (MAX_Duty) and the minimum duty (MIN_Duty) is more than twice the current detection required duty amount τ required to secure the time required for current detection. And the intermediate duty (MID_Duty) is larger than the current detection required duty amount τ and smaller than (100% -τ), the maximum duty (MAX_Duty) and the maximum duty (MAX_Duty) and The minimum Duty (MIN_Duty) is the correction target. That is, in the case of the condition (1), the maximum duty (MAX_Duty) is larger of the value obtained by adding the current detection required duty amount τ to the intermediate duty (MID_Duty) (MID_Duty + τ) or the maximum duty (MAX_Duty). Is selected as the maximum detection duty, and the minimum duty (MIN_Duty) is the smaller of the value obtained by subtracting the current detection required duty amount τ from the intermediate duty (MID_Duty) (MID_Duty-τ) or the minimum duty (MID_Duty) Is selected as the minimum duty for detection of the current detection cycle.
In the condition (2), when the condition is other than the above condition (1), the intermediate duty (MID_Duty) and the minimum duty (MIN_Duty) are set as correction targets based on the maximum duty (MAX_Duty). However, when the maximum duty (MAX_Duty) becomes smaller than twice the current detection required duty amount τ, a value obtained by correcting the maximum duty (MAX_Duty) to “2τ” is set as the maximum detection duty, which is used as a reference. That is, in the condition (2), when the difference between the maximum detection duty (or maximum duty (MAX_Duty)) and the intermediate duty (MID_Duty) (maximum detection duty (MAX_Duty) -MID_Duty) is smaller than the current detection required duty amount τ. The intermediate duty (MID_Duty) is corrected to (maximum detection duty-τ), and when the intermediate duty (MID_Duty) is smaller than the current detection required duty amount τ, the intermediate duty (MID_Duty) is corrected to the current detection required duty amount τ. To detect the intermediate duty. When the difference between the detection intermediate duty and the minimum duty (MID_Duty) (detection intermediate duty-MID_Duty) is smaller than the current detection required duty amount τ, the minimum duty (MIN_Duty) is corrected to (detection intermediate duty−τ). This is the minimum duty for detection.

  On the other hand, the calculation of each phase duty command value in the duty adjustment cycle is performed as follows. That is, a value obtained by dividing (n−1) the difference between the calculated detection phase Duty and the base phase Duty command value is calculated and added to the original phase Duty command value. Let it be the phase Duty.

  As exception processing, when each duty is outside the current detectable region, duty correction is not performed, and a flag indicating that current detection is impossible is set and output.

  Next, a configuration example of an apparatus for realizing the above processing is shown in FIG. 8, and an example of the software operation will be described in detail with reference to a flowchart of FIG.

  A CPU 70 that performs overall control, arithmetic processing, and the like is provided. The CPU 70 inputs a current control value E and calculates a duty command value for each phase, and determines a maximum duty, a maximum phase, and the like. Duty determination unit 72, condition determination unit 73 that determines whether the condition (1) or condition (2) is satisfied, each change duty calculation unit 74 that calculates each change duty, and maximum detection duty Are connected to a detection maximum duty calculation unit 75 for calculating a detection minimum duty, a detection minimum duty calculation unit 76 for calculating a detection minimum duty, and an adjustment phase duty calculation unit 77 for calculating each adjustment phase duty. . The CPU 70 further includes a τ setting unit 80 for setting a current detection required duty amount τ necessary for securing a time required for current detection as a parameter, a detection intermediate duty calculation unit 81 for calculating a detection intermediate duty, The comparison unit 82 that compares various data, the current detection cycle / duty adjustment cycle determination unit 83 that determines the current detection cycle and the duty adjustment cycle, and outputs the corrected or calculated duty to the gate drive unit 85. A duty output unit 84 to be applied and a current input unit 61 for inputting a current detected by the current detector 60 are connected.

  When the operation starts in such a configuration, the duty calculation unit 71 calculates and inputs each phase duty command value based on the current control value E, and the duty determination unit 72 determines the maximum duty, intermediate duty, and minimum duty. At the same time, the maximum phase and the minimum phase are determined (step S10). Then, the condition determining unit 73 determines whether or not the relationship between the duty duty command values of each phase satisfies the condition (1), that is, the difference amount (MAX_Duty−MIN_Duty) between the maximum duty (MAX_Duty) and the minimum duty (MIN_Duty) is set to τ. Condition in which the current detection required duty amount τ set in the unit 80 is smaller than twice and the intermediate duty (MID_Duty) is larger than the current detection required duty amount τ and smaller than (100% −τ). (1) is determined (step S11).

  When the condition determination unit 73 determines that the condition (1) is satisfied in step S11, each change duty calculation unit 74 determines the maximum duty lower limit value, the minimum duty upper limit value, (intermediate duty + τ), (intermediate duty). -Τ) is calculated (step S12), and in the maximum duty phase determined by the duty determination unit 72, the maximum detection duty calculation unit 75 limits the maximum duty with the maximum duty lower limit value and detects the maximum duty. (Step S13), and in the intermediate duty phase, the detection intermediate duty is set without correction (step S14). In the minimum duty phase, the detection minimum duty calculation unit 76 limits the minimum duty to the maximum duty lower limit value. The minimum duty for detection is set (step S15).

Thereafter, each adjustment phase duty calculation unit 77 calculates each adjustment phase duty according to the following equation 1 using the detection maximum duty, detection intermediate duty, and detection minimum duty obtained above (step S16). .
(Equation 1)
Each phase for adjustment Duty = each phase Duty + (each phase Duty−each phase Duty for detection) / (n−1)

Then, in the current detection cycle determined by the current detection cycle / Duty adjustment cycle determination unit 83, each detection duty is set in the Duty output unit 84 (step S17), and the current detection cycle / Duty adjustment cycle determination unit 83 In the determined duty adjustment cycle, the adjustment phase duty is set in the duty output unit 84 and the process ends (step S18).

On the other hand, if it is determined in step S11 that the condition determination unit 73 does not satisfy the condition (1), whether or not the maximum duty is smaller than “2τ” by the comparison unit 82 in the maximum duty phase. When the maximum duty is smaller than “2τ”, the maximum detection duty is set to “2τ” (step S21), and when the maximum duty is “2τ” or more, the maximum duty is detected without correction. The maximum duty is set (step S22). The comparison unit 82 further determines whether or not the difference between the maximum detection duty and the intermediate duty (maximum detection duty−intermediate duty) is smaller than the current detection required duty amount τ (step S23). When the maximum duty−intermediate duty) is smaller than the current detection required duty amount τ, the detection intermediate duty calculation unit 81 calculates the detection intermediate duty according to the following formula 2 (step S24).
(Equation 2)
Intermediate Duty for detection = Maximum Duty for detection -τ

If the difference (maximum detection duty−intermediate duty) is equal to or greater than the current detection required duty amount τ, the detection intermediate duty calculation unit 81 outputs the detection maximum duty as it is without correction (the detection intermediate duty). Step S25).
Further, in the intermediate duty phase when it is determined in step S11 that the condition (1) is not satisfied, the comparator 82 determines whether or not the intermediate duty is smaller than the current detection required duty amount τ (step S26). ), When the intermediate duty is equal to or greater than the current detection required duty amount τ, the process proceeds to step S23. When the intermediate duty is smaller than the current detection required duty amount τ, the detection intermediate duty calculation unit 81 sets the detection intermediate duty to “τ” (step S27), and the comparison unit 82 obtains the obtained detection intermediate duty. It is determined whether or not the difference between the minimum duty and the detection duty (intermediate duty for detection minus minimum duty) is smaller than the current detection required duty amount τ (step S30), and the difference (intermediate duty for detection minus minimum duty) requires current detection. When it is smaller than the duty amount τ, the minimum detection duty calculation unit 81 calculates the minimum detection duty according to the following equation 3 (step S31), and the process proceeds to step S16.
(Equation 3)
Minimum duty for detection = Intermediate duty for detection -τ

If the difference (detection intermediate duty−minimum duty) is equal to or greater than the current detection required duty amount τ, the process proceeds to step S16 without correction (step S32).

  As described above, in order to make each phase current detectable, the one-phase ON state and the two-phase ON state are secured only for the current detection required duty amount τ necessary for securing the current detection required time. There must be. That is, the difference between the maximum duty and the minimum duty among each phase duty must be at least “2τ” or more. In condition (1), when the difference between the maximum duty and the minimum duty is smaller than “2τ”, the intermediate duty is used as a reference, the difference between the maximum duty and the intermediate duty, and the difference between the intermediate duty and the minimum duty is the current. Duty is calculated in such a way as to secure a detection-necessary duty amount τ or more, and it is determined whether the maximum duty and the minimum duty need to be corrected, and is used as each phase duty for detection. For this reason, only the minimum necessary phase can be corrected, and even if the correction amount is maximum, the current detection required duty amount τ and the correction amount can be minimized, and the degree of influence thereof can be minimized. Can do.

  When the condition is other than the condition (1), the value obtained by adding or subtracting the current detection required duty amount τ from the intermediate duty exceeds 0% or 100%, so that the detection duty cannot be calculated. Condition (2) makes it possible to calculate the detection phase Duty even under this condition. Since the maximum duty needs to be turned on for at least the current detection time of two times, first, the maximum duty for detection is calculated so as to secure the maximum duty of “2τ” or more. Next, in order to keep the one-phase ON state for at least the current detection time for one time, calculate the detection intermediate duty so that the difference from the maximum detection duty is equal to or greater than the current detection required duty amount τ. To do. Also, since the intermediate duty needs to be turned on for at least the current detection time of one time, if the intermediate duty is less than the current detection required duty amount τ, the current detection required duty amount τ is set as the detection intermediate duty To do. Since the maximum detection duty is 2τ at least, the detection intermediate duty is never lower than τ. Also, in order for the two-phase ON state to be ON for at least one current detection time, the minimum detection duty is calculated so that the difference from the detection intermediate duty is equal to or greater than the current detection required duty amount τ. . Note that the detection minimum duty τ is secured at least for the detection intermediate duty, so the calculated minimum detection duty does not become 0% or less.

Next, specific numerical examples when the present invention is applied and PWM waveform examples at that time will be described with reference to Examples 1 to 3 below using a carrier as a sawtooth wave. Examples of PWM waveforms of Examples 1 to 3 are shown in FIGS. 10 to 12, respectively. In this example, for simplicity, the A phase is the maximum Duty phase, the B phase is the intermediate Duty phase, the C phase is the minimum Duty phase, and n = 5 times and τ = 12%.
(A) Example 1: When two-phase duty is balanced (see FIG. 10)
Phase A Duty: 85% ---- No correction (85% for detection and adjustment)
B phase Duty: 84% --- Duty for detection: 73% (Correction: 11%)
---- Duty for adjustment: 86.75% (Correction: 11 / (5-1) = 2.75%)
Phase C Duty: 19% --- No correction (19% for detection and adjustment)
(B) Example 2: The three-phase duty is balanced, and the differences between the respective phases are all within τ (see FIG. 11).
Phase A Duty: 51% --- Detection Duty: 62% (Correction: 11%)
−−− Duty for adjustment: 51.5% (Correction: 11 / (5-1) = 2.75%)
Phase B Duty: 50% --- No correction (50% for both detection and adjustment)
Phase C Duty: 49% --- Duty for detection: 38% (Correction: 11%)
---- Adjustment Duty: 51.75% (Correction: 11 / (5-1) = 2.75%)
(C) Example 3: Three-phase duty is balanced, and only the difference between the maximum duty and the intermediate duty is current detection
(See Figure 12)
Phase A Duty: 54% Duty for detection: 64% (Correction: 10%)
−−− Duty for adjustment: 51.5% (Correction: 10 / (5-1) = 2.5%)
Phase B Duty: 52% --- No correction (52% for detection and adjustment)
Phase C Duty: 39% --- No correction (39% for both detection and adjustment)

By the way, even in the present invention, there are cases where the duty changed to detect the phase current cannot be adjusted to the duty adjustment cycle. Specifically, the adjustment duty is less than 0% and more than 100% in the duty adjustment cycle.
(D) Example 4: When each phase Duty command value is outside the duty adjustable range A phase Duty: 100% --- No correction 100% for both detection and adjustment)
B phase Duty: 98% --- Duty for detection: 88% (Correction: 10%)
−−− Duty for adjustment: 100.5% (Correction: 10 / (5-1) = 2.5%)
Phase C Duty: 2% --- No correction (2% for detection and adjustment)

In this case, since the intended adjustment duty cannot be generated by the inverter, it is impossible to make the desired duty equal to the n-time average duty, and there is a concern about occurrence of torque ripple and deterioration of the operating sound performance. . However, when torque ripple or deterioration of operating sound performance is not a big influence on the system to which this content is applied, for example, as a method of adjusting the duty as much as possible by limiting the adjustment duty to 0% to 100% Also good.

  In addition, the range of each phase Duty command value which can output the adjustment Duty required in the Duty adjustment cycle is as shown in FIG.

  Next, another embodiment of the present invention will be described.

  In the above embodiment, the carrier waveform is a sawtooth wave, but even if the carrier waveform is a triangular wave, the phase current can be detected by the same method. In this case, the current detection required duty amount τ necessary for securing the detection time required for current detection may be set to double that of the sawtooth wave. However, the amount of duty change in the current detection cycle and the duty adjustment cycle increases by the amount that the current detection required duty amount τ is doubled, and the range of each phase duty command value that can be adjusted to the duty adjustment cycle is narrowed. Become. FIG. 14 shows this, and the maximum duty command value is in the range of 100 to 4.8% in the case of the sawtooth wave, but narrows to 100 to 9.6% in the case of the triangular wave. The command value is in the range of 97.6 to 2.4% in the case of a sawtooth wave, but narrows to 95.2 to 4.8% in the case of a triangular wave, and the minimum duty command value is 95.2 to 0 in the case of a sawtooth wave. In the case of a triangular wave, the range is 90.4 to 0%.

A specific numerical example when changing to a triangular wave carrier is shown as Example 5 below. The current detection required duty amount τ is 24%, which is twice that of the triangular wave carrier.
(E) Example 5: When two-phase duty is balanced (see FIG. 15)
Phase A Duty: 85% --- No correction (85% for detection and adjustment)
B phase Duty: 84% --- Duty for detection: 61% (Correction: 23%)
−−− Duty for adjustment: 89.75% (Correction: 23 / (5-1) = 5.75%)
Phase C Duty: 19% --- No correction (19% for detection and adjustment)

1 Handle 2 Column shaft 3 Reduction gear 10 Torque sensor 12 Vehicle speed sensor 20 Motor 30 Control unit 37 Motor drive circuit 50 Three-phase motor 51 Power supply (battery)
60 Current detector 61 Current input unit 70 CPU
71 Duty calculation unit 72 Duty determination unit 73 Condition determination unit 74 Duty calculation unit for change 75 Maximum duty calculation unit for detection 76 Minimum duty calculation unit for detection 77 Duty calculation unit for adjustment 80 τ setting unit 81 Intermediate duty for detection Calculation unit 82 Comparison unit 83 Current detection cycle / Duty adjustment cycle determination unit 84 Duty output unit 85 Gate drive unit

Claims (2)

Motor control for calculating each phase duty command value for controlling the motor current by control calculation, forming a PWM waveform corresponding to each phase duty command value, and driving the motor by an inverter based on the PWM waveform In the device
A single current detector is connected to the power input side or power output side of the inverter, and the PWM cycle is n (> 2) times per control cycle that requires a phase current value. One out of n PWM cycles is set as a current detection cycle, and (n−1) times is set as a duty adjustment cycle.
A function for determining the maximum duty, intermediate duty, and minimum duty of each phase duty command value;
In the current detection period,
A difference between the maximum duty and the minimum duty is smaller than twice the current detection required duty amount τ, and the intermediate duty is larger than the current detection required duty amount τ and smaller than (100% −τ). Under the condition of the above, the intermediate duty is used as a reference, the value obtained by adding the current detection required duty amount τ to the intermediate duty as a reference, and the maximum duty whichever is larger is set as the maximum detection duty, and the reference The value obtained by subtracting the current detection required duty amount τ from the intermediate duty and the minimum duty whichever is smaller is used as the detection minimum duty, and the reference intermediate duty is used as the detection intermediate duty as it is. Calculate each phase Duty for detection of the current detection cycle,
Under a second condition other than the first condition, the maximum duty is used as a reference, and the reference maximum duty is directly used as the detection maximum duty, where the maximum duty is the current detection required duty amount. When less than 2 times τ, 2τ is set as the maximum detection duty, and the maximum detection duty is used as a reference.
When the difference between the maximum detection duty (or the maximum duty) as a reference and the intermediate duty is smaller than the current detection required duty amount τ (referred to as the first time), the current detection is performed from the detection maximum duty. The value obtained by subtracting the required duty amount τ is set as the detection intermediate duty, and when the intermediate duty is smaller than the current detection required duty amount τ (referred to as the second time), the current detection required duty amount τ is determined as the detection intermediate duty. In the case other than the first time and the second time, the intermediate duty is directly used as the detection intermediate duty.
When the difference between the detection intermediate duty and the minimum duty is smaller than the current detection required duty amount τ (referred to as the third time), a value obtained by subtracting the current detection required duty amount τ from the detection intermediate duty In each case other than the third time, the minimum duty for detection is calculated as the minimum duty for detection by setting the minimum duty as it is for the minimum duty for detection.
In the duty adjustment cycle, a value obtained by dividing the difference between each phase duty command value and each detection phase duty calculated in the current detection cycle by (n−1) is used as each phase duty command. motor control apparatus characterized by a value obtained by adding to the value, and and a function of the adjustment phase Dut y. An electric power steering device comprising the motor control device according to claim 1 .

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