CN113228497A

CN113228497A - Drive control device, motor drive device, and power steering device

Info

Publication number: CN113228497A
Application number: CN201980086659.4A
Authority: CN
Inventors: 锅师香织; 北村高志
Original assignee: Nidec Corp
Current assignee: Nidec Corp
Priority date: 2018-12-28
Filing date: 2019-12-10
Publication date: 2021-08-06
Anticipated expiration: 2039-12-10
Also published as: JP7444075B2; JPWO2020137511A1; WO2020137511A1; CN113228497B

Abstract

One embodiment of the drive control device is a drive control device that controls driving of a motor, and includes: a first inverter connected to one end of a winding of the motor; a second inverter connected to the other end opposite to the one end; a first control circuit that performs PWM control of the first inverter; and a second control circuit that PWM-controls the second inverter, wherein a frequency of a carrier signal of the PWM control has a frequency difference equal to or greater than a product of a maximum rotation speed of the motor and a number of pole pairs in the first control circuit and the second control circuit.

Description

Drive control device, motor drive device, and power steering device

Technical Field

The invention relates to a drive control device, a motor drive device, and a power steering device.

Background

Conventionally, a cordless motor having n-phase windings (coils) and having no wires connecting the coils to each other is known. As a method of driving such a cordless motor, a so-called full-bridge driving system is known in which an inverter is connected to both ends of a coil of each phase. In the driving of the full-bridge cordless motor, two inverters are normally driven, and one inverter is switched to a neutral point to perform three-phase control in an abnormal state. In addition, from the viewpoint of reducing the failure rate, a configuration is known in which two inverters are controlled by two control circuits. For example, in patent document 1, a first control unit controls driving of a first inverter, and a second control unit controls driving of a second inverter.

Documents of the prior art

Patent document

Patent document 1: japanese patent laid-open publication No. 2016-

Disclosure of Invention

Technical problem to be solved by the invention

From the viewpoint of reducing the failure rate, it is preferable that there is no independent driving of circuit portions which are common to the control circuits. However, in the case of the full-bridge drive system, if the frequencies of the PMW carrier signals of the control circuits are shifted in synchronization, the torque ripple of the motor is deteriorated, which causes problems such as noise and vibration. Therefore, an object of the present invention is to reduce the occurrence of torque ripple-induced problems while ensuring independence of control circuits.

Technical scheme for solving technical problem

One aspect of the drive control device according to the present invention is a drive control device that controls driving of a motor, including: a first inverter connected to one end of a winding of the motor; a second inverter connected to the other end opposite to the one end; a first control circuit that performs PWM control of the first inverter; and a second control circuit that PWM-controls the second inverter, wherein a frequency of a carrier signal of the PWM control has a frequency difference equal to or greater than a product of a maximum rotation speed of the motor and a number of pole pairs in the first control circuit and the second control circuit. In addition, one embodiment of the motor drive device of the present invention includes the drive control device and a motor controlled to be driven by the drive control device.

In addition, one embodiment of the power steering apparatus of the present invention includes: the drive control device described above; a motor driven by the drive control device; and a power steering mechanism driven by the motor.

Effects of the invention

According to the present invention, it is possible to reduce the occurrence of a problem due to torque ripple while ensuring the independence of the control circuits.

Drawings

Fig. 1 is a diagram schematically showing a typical block configuration of a motor drive unit of the present embodiment.

Fig. 2 is a diagram schematically showing a typical circuit configuration of the motor drive unit of the present embodiment.

Fig. 3 is a diagram showing the values of currents flowing through the coils of the respective phases of the motor.

Fig. 4 is a diagram schematically showing a state of voltage application in the switching operation under the PWM control.

Fig. 5 is a diagram schematically showing a state where application is stopped in the switching operation under the PWM control.

Fig. 6 is a diagram showing the PWM signal.

Fig. 7 is a graph showing the results of the first to fourth tests.

Fig. 8 is a graph showing the results of the fifth to eleventh tests.

Fig. 9 is a diagram showing a circuit configuration of a motor drive unit in a modification in which circuit wirings are different.

Fig. 10 is a diagram schematically showing the configuration of an electric power steering apparatus according to the present embodiment.

Detailed Description

Hereinafter, embodiments of the drive control device, the drive device, and the power steering device according to the present disclosure will be described in detail with reference to the drawings. However, in order to avoid unnecessarily long descriptions below, it is easy for those skilled in the art to understand that the detailed descriptions above may be omitted. For example, detailed descriptions of well-known matters and repetitive descriptions of substantially the same structures may be omitted.

In the present specification, an embodiment of the present disclosure will be described by taking as an example a drive control device that supplies power from a power supply to a three-phase motor having three-phase (U-phase, V-phase, W-phase) windings (sometimes referred to as "coils"). However, a drive control device that supplies electric power from a power supply to an n-phase motor having four-phase or five-phase (n is an integer of 4 or more) windings is also within the scope of the present invention.

(Structure of Motor drive Unit 1000)

Fig. 1 is a diagram schematically showing a block configuration of a motor drive unit 1000 of the present embodiment. The motor drive unit 1000 includes

inverters

101 and 102, a motor 200, and

control circuits

301 and 302.

In this specification, a motor drive unit 1000 having a motor 200 as a component will be described. The motor drive unit 1000 having the motor 200 corresponds to an example of the drive device of the present invention. However, the motor drive unit 1000 may be a device for driving the motor 200, the motor 200 of which component is omitted. The motor drive unit 1000 in which the motor 200 is omitted corresponds to an example of the drive control device of the present invention.

The motor drive unit 1000 converts electric power from the power source (403, 404 of fig. 2) into electric power to be supplied to the motor 200 through the two

inverters

101, 102. The

inverters

101 and 102 can convert dc power into three-phase ac power, which is a pseudo sine wave of U-phase, V-phase, and W-phase, for example. The two

inverters

101, 102 include

current sensors

401, 402, respectively.

The motor 200 is, for example, a three-phase ac motor. The motor 200 has coils of U-phase, V-phase, and W-phase. The winding manner of the coil is, for example, concentrated winding or distributed winding.

The first inverter 101 is connected to one end 210 of the coil of the motor 200, and applies a driving voltage to the one end 210, and the second inverter 102 is connected to the other end 220 of the coil of the motor 200, and applies a driving voltage to the other end 220. In this specification, "connection" of components (constituent elements) means electrical connection unless otherwise specified.

The

control circuits

301, 302 include

microcontrollers

341, 342, etc., which will be described in detail later. The

control circuits

301, 302 control the drive voltages of the

inverters

101, 102 based on input signals from the

current sensors

401, 402 and the

angle sensors

321, 322. As a control method of the

inverters

101 and 102 by the

control circuits

301 and 302, for example, a control method selected from vector control and Direct Torque Control (DTC) is used. A specific circuit configuration of the motor drive unit 1000 will be described with reference to fig. 2. Fig. 2 is a diagram schematically showing a circuit configuration of the motor drive unit 1000 of the present embodiment.

The motor drive unit 1000 is connected to the independent first power supply 403 and second power supply 404, respectively. The

power supplies

403 and 404 generate a predetermined power supply voltage (for example, 12V). As the

power sources

403 and 404, for example, a dc power source is used. However, the

power sources

403 and 404 may be AC-DC converters or DC-DC converters, or may be batteries (secondary batteries). In fig. 2, a first power supply 403 for the first inverter 101 and a second power supply 404 for the second inverter 102 are shown as an example, but the motor drive unit 1000 may be connected to a single power supply common to the first inverter 101 and the second inverter 102. The motor drive unit 1000 may include a power supply therein.

The motor drive unit 1000 includes a first system corresponding to the one end 210 side of the motor 200 and a second system corresponding to the other end 220 side of the motor 200. The first system includes a first inverter 101 and a first control circuit 301. The second system includes a second inverter 102 and a second control circuit 302. The inverter 101 and the control circuit 301 of the first system are supplied with power from the first power source 403. The inverter 102 and the control circuit 302 of the second system are powered by a second power source 404.

The first inverter 101 includes a bridge circuit having three branches. Each branch of the first inverter 101 includes a high-side switching device connected between the power supply and the motor 200 and a low-side switching device connected between the motor 200 and the ground. Specifically, the U-phase arm includes a high-side switching device 113H and a low-side switching device 113L. The V-phase arm includes a high-side switching device 114H and a low-side switching device 114L. The W-phase arm includes a high-side switching device 115H and a low-side switching device 115L. As the switching element, for example, a field effect transistor (MOSFET or the like) or an insulated gate bipolar transistor (IGBT or the like) is used. In addition, when the switching element is an IGBT, a diode (free wheel) is connected in anti-parallel with the switching element.

The first inverter 101 is provided with

shunt resistors

113R, 114R, and 115R in each branch as, for example, a current sensor 401 (see fig. 1) for detecting a current flowing through each phase winding of the U-phase, the V-phase, and the W-phase. The current sensor 401 includes a current detection circuit (not shown) that detects a current flowing through each shunt resistor. For example, a shunt resistor may be connected between the low-

side switching elements

113L, 114L, and 115L and the ground. The shunt resistor has a resistance value of, for example, about 0.5m Ω to 1.0m Ω.

The number of shunt resistors may be other than three. For example, two

shunt resistors

113R and 114R, V for the U-phase and V-phase, two

shunt resistors

114R and 115R for the W-phase, or two

shunt resistors

113R and 115R for the U-phase and W-phase may be used. The number of shunt resistors to be used and the arrangement of the shunt resistors may be determined appropriately in consideration of product cost, design specifications, and the like.

The second inverter 102 includes a bridge circuit having three branches. Each branch of the second inverter 102 includes a high-side switching device connected between the power supply and the motor 200 and a low-side switching device connected between the motor 200 and the ground. Specifically, the U-phase arm includes a high-side switching device 116H and a low-side switching device 116L. The V-phase arm includes a high-side switching device 117H and a low-side switching device 117L. The W-phase arm includes a high-side switching device 118H and a low-side switching device 118L. The second inverter 102 includes, for example, shunt

resistors

116R, 117R, and 118R, as in the first inverter 101.

The motor drive unit 1000 includes

capacitors

105, 106. The

capacitors

105 and 106 are so-called smoothing capacitors, and absorb a circulating current generated by the motor 200 to stabilize a power supply voltage and suppress torque ripple. The

capacitors

105 and 106 are, for example, electrolytic capacitors, and the capacity and the number of capacitors to be used are appropriately determined in accordance with design specifications and the like.

Reference is again made to fig. 1. The

control circuits

301 and 302 include, for example,

power supply circuits

311 and 312,

angle sensors

321 and 322,

input circuits

331 and 332,

microcontrollers

341 and 342, drive

circuits

351 and 352, and

ROMs

361 and 362. The

control circuits

301, 302 are connected to the

inverters

101, 102. The first control circuit 301 controls the first inverter 101, and the second control circuit 302 controls the second inverter 102.

The

control circuits

301 and 302 can control the position (rotation angle), rotation speed, current, and the like of the target rotor to realize closed-loop control. The rotation speed is obtained by time-differentiating the rotation angle (rad), for example, and is indicated by the rotation speed (rpm) at which the rotor rotates in a unit time (e.g., 1 minute). The

control circuits

301 and 302 can also control the target motor torque. The

control circuits

301 and 302 may be provided with torque sensors for torque control, but torque control is possible even if the torque sensors are omitted. Further, a sensorless algorithm may be provided instead of the

angle sensors

321 and 322. The

power supply circuits

311 and 312 generate DC voltages (e.g., 3V and 5V) necessary for the respective blocks in the

control circuits

301 and 302.

The

angle sensors

321, 322 are, for example, resolvers or hall ICs. The

angle sensors

321, 322 may also be realized by a combination of a Magnetoresistive (MR) sensor having an MR element and a sensor magnet. The

angle sensors

321, 322 detect the rotation angle of the rotor of the motor 200, and output rotation signals showing the detected rotation angle to the

microcontrollers

341, 342. Depending on the motor control method (e.g., sensorless control), the

angle sensors

321 and 322 may be omitted.

The

input circuits

331 and 332 receive motor current values (hereinafter referred to as "actual current values") detected by the

current sensors

401 and 402. The

input circuits

331 and 332 convert the level of the actual current value into the input level of the

microcontrollers

341 and 342 as needed, and output the actual current value to the

microcontrollers

341 and 342. The

input circuits

331 and 332 are analog-digital conversion circuits.

The

microcontrollers

341, 342 receive the rotation signals of the rotors detected by the

angle sensors

321, 322, and receive the actual current values output from the

input circuits

331, 332. The

microcontrollers

341 and 342 set a target current value based on the actual current value and the rotor rotation signal, generate PWM signals, and output the generated PWM signals to the

drive circuits

351 and 352. For example, the

microcontrollers

341 and 342 generate PWM signals for controlling the switching operation (on or off) of the switching elements in the

inverters

101 and 102.

Each

microcontroller

341, 342 has an

internal clock

371, 372. The generation of the PWM signal in each

microcontroller

341, 342 is performed in accordance with a clock signal from the

internal clock

371, 372. That is, each of the

microcontrollers

341 and 342 frequency-converts a clock signal obtained from the oscillator of the

internal clock

371 or 372 to generate a carrier signal for PWM control.

The fundamental frequency of the PWM signal generated by each microcontroller 341, 342 (i.e., the frequency of the carrier signal in PWM control) has a frequency difference of, for example, 1kHz between the

microcontrollers

341, 342. As a result, as described later in detail, even if torque ripple due to the frequency difference occurs, it occurs in a sufficiently high frequency range. Therefore, noise, vibration, and the like associated with the torque ripple deviate from a frequency range that can be perceived by a human, and noise and vibration that are unpleasant to the human are suppressed.

The

driver circuits

351, 352 are typically gate drivers. The

drive circuits

351 and 352 generate control signals (for example, gate control signals) for controlling the switching operation of the switching elements in the first inverter 101 and the second inverter 102 based on the PWM signals, and supply the generated control signals to the switching elements. The

microcontrollers

341, 342 can have the function of a

driver circuit

351, 352. In this case, the

drive circuits

351, 352 are omitted.

The

ROMs

361, 362 are, for example, writable memory (e.g., PROM), rewritable memory (e.g., flash memory), or read-only memory. The

ROMs

361, 362 store control programs including instruction sets for causing the

microcontrollers

341, 342 to control the

inverters

101, 102, and the like. For example, the control program is temporarily expanded in a RAM (not shown) at the time of startup.

(operation of the Motor drive Unit 1000)

Hereinafter, a specific example of the operation of the motor drive unit 1000 will be described, and mainly, specific examples of the operation of the

inverters

101 and 102 will be described.

The

control circuits

301, 302 drive the motor 200 by performing three-phase energization control using both the first inverter 101 and the second inverter 102. Specifically,

control circuits

301 and 302 perform three-phase energization control by performing switching control of switching elements of first inverter 101 and switching elements of second inverter 102. Fig. 3 is a diagram showing the values of currents flowing through the respective coils of the respective phases of the motor 200.

Fig. 3 illustrates current waveforms (sine waves) obtained by plotting current values flowing through the respective coils of the U-phase, V-phase, and W-phase of the motor 200 when the first inverter 101 and the second inverter 102 are controlled in accordance with three-phase energization control. The horizontal axis of fig. 3 shows the motor electrical angle (deg) and the vertical axis shows the current value (a). I is_pkThe maximum current value (peak current value) of each phase is shown. In addition to the sine wave illustrated in fig. 3, the

inverters

101 and 102 may drive the motor 200 using, for example, a rectangular wave.

The current waveform illustrated in fig. 3 is generated by applying a voltage having a waveform corresponding to such a current waveform to the motor 200. Such a voltage is generated by switching the switching elements of the first inverter 101 and the switching elements of the second inverter 102 at a high speed of, for example, 20kHz by PWM control. Fig. 4 and 5 are diagrams schematically showing the switching operation under PWM control, fig. 4 showing a state where voltage is applied, and fig. 5 showing a state where application is stopped.

In fig. 4 and 5, for example, U-phase branches among the branches that the

inverters

101, 102 have are shown. As described above, the U-phase branch includes the high-side switching device 113H and the low-side switching device 113L on the first inverter 101 side, and the high-side switching device 116H and the low-side switching device 116L on the second inverter 102 side.

The high-side switching device 113H and the low-side switching device 113L on the first inverter 101 side are not in an on state at the same time, and when one is in an on state, the other is in an off state. Similarly, the high-side switching device 116H and the low-side switching device 116L on the second inverter 102 side are not turned on at the same time.

When a voltage is applied to the windings of the motor 200, the high-

side switching elements

113H and 116H are turned on in one of the two inverters 101 and 102 (the second inverter 102 in the case of fig. 4), and the low-

side switching elements

113L and 116L are turned on in the other inverter (the first inverter 101 in the case of fig. 4). As a result, a current flows from the one side to the other side as indicated by arrows in the drawing.

When the application is stopped, all the switching elements are turned off. Immediately after the off state, a circulating current from the motor 200 flows through the capacitors (105 and 106 in fig. 2), but no current flows thereafter. In addition, the circulating current does not contribute to the torque of the motor 200.

In the two

inverters

101 and 102, the state in which the voltage shown in fig. 4 is applied and the state in which the application is stopped shown in fig. 5 are repeated at high speed. The repetition of the voltage application and the application stop in the

inverters

101, 102 is performed in accordance with the PWM signals generated by the

microcontrollers

341, 342 of the

control circuits

301, 302. Fig. 6 is a diagram showing the PWM signal.

The PWM signal is a 2-value pulse signal, and a first value showing voltage application and a second value showing application stop are alternately generated. The pulses of the PWM signal are repeated with a period T0, the period T0 being divided into a first value of duration T1 and a second value of duration T2.

Since the PWM signal is a high-frequency signal such as 20kHz as described above, the period T0 is a short period such as 50 μ sec. Therefore, the effective voltage (effective voltage) applied to the motor 200 becomes a voltage averaged in the period T0, and the ratio (duty ratio) of the period T0 to the duration T1 of the first value is equal to the ratio of the power supply voltage to the effective voltage. The effective voltage is, for example, a voltage that changes with time in accordance with a current value that changes as in the current waveform shown in fig. 3. This temporal variation of the effective voltage is achieved by controlling the duty cycle of the PWM signal by the

microcontroller

341, 342.

The two

microcontrollers

341, 342 each generate a carrier signal of period T0 from which a PWM signal is generated, but as described above, the

microcontrollers

341, 342 differ from one another in the frequency of the carrier signal. Thus, the period T0 does not coincide between the

microcontrollers

341, 342, and the PWM signals are offset synchronously with respect to each other in frequency. Such a synchronization deviation generates torque ripple in the motor 200. Here, a simulation test of torque ripple generated by the frequency difference between the PWM signals will be described. Table 1 shows test conditions from the first test to the fourth test.

[ Table 1]

Test number	Frequency difference	PWM frequency of first inverter	PWM frequency of second inverter
				1	50Hz	20.0kHz	19.95kHz
2	5Hz	20.0kHZ	19.995kHz
				3	0.5Hz	20.0kHz	19.9995kHz
4	0.05Hz	20.0kHz	19.99995kHz

In the first to fourth tests, the frequency of the PWM signal (the frequency of the first system) generated by the microcontroller 341 of the first control circuit 301 to drive the first inverter 101 was fixed to 20 kHz. Then, the frequency of the PWM signal (frequency of the second system) generated by the microcontroller 342 of the second control circuit 302 to drive the second inverter 102 is changed. In the first test, the frequency of the second system was set to 19.95kHz, and the frequency difference between the first system and the second system was 50 Hz. In the second test, the frequency of the second system was set to 19.995kHz, and the frequency difference between the first and second systems was 5 Hz. In a third test, the frequency of the second system was set to 19.9995kHz, and the frequency difference between the first and second systems was 0.5 Hz. In the fourth test, the frequency of the second system was set to 19.99995kHz, and the frequency difference between the first system and the second system was 0.05 Hz. Fig. 7 is a graph showing the results of the first to fourth tests. Fig. 7 shows a three-dimensional graph, in which the height axis shows the torque intensity, the left depth axis shows the frequency, and the right depth axis shows the test number. The large peak near 500Hz in the graph is a peak of the frequency component corresponding to the rotation speed of the motor, and is not torque ripple.

In the graph showing the results of the first test, there are many peaks in the frequency region of several hundreds of Hz, and the peak at the 100Hz position corresponding to 2 times the frequency difference is particularly large. It is found that under the conditions of the first test, a large torque ripple corresponding to the large peak is generated.

In the second to fourth tests, a large peak was not generated in a frequency region of several hundred Hz. Therefore, it is found that if the frequency difference is about 5Hz or less, torque ripple hardly occurs. However, in the case of a clock element of a quartz resonator, for example, a frequency difference of 10Hz or more is likely to occur due to individual differences of the quartz resonators, and it is difficult to suppress the frequency to 5Hz or less between the

independent microcontrollers

341, 342. Therefore, an analog test of enlarging the frequency difference is performed in reverse. Table 2 shows test conditions from the fifth test to the eleventh test.

TABLE 2

Test number	Frequency difference	PWM frequency of first inverter	PWM frequency of second inverter
				5	0Hz	20.0kHz	20.0kHz
6	+1000Hz	21.0kHz	20.0kHz
				7	-1000Hz	20.0kHz	19.0kHz
8	+500Hz	20.5kHz	20.0kHz
				9	-500Hz	20.0kHz	19.5kHz
10	+100Hz	20.1kHz	20.0kHz
				11	-100Hz	20.0kHz	19.9kHz

In the fifth test, the frequency of the first system and the frequency of the second system were both set to the fundamental frequency of 20.0kHz, and the frequency difference between the first system and the second system was 0 Hz. That is, the frequencies of the PWM signals are completely synchronized in the first system and the second system.

In the sixth test, the frequency of the first system was set to 21.0kHz at +1000Hz and the frequency of the second system was set to 20.0kHz with respect to the fundamental frequency.

In the seventh test, the frequency of the first system was set to the fundamental frequency of 20.0kHz, and the frequency of the second system was set to 19.0kHz at-1000 Hz relative to the fundamental frequency.

In the eighth test, the frequency of the first system was set to 20.5kHz at +500Hz with respect to the fundamental frequency, and the frequency of the second system was set to 20.0kHz at the fundamental frequency.

In the ninth test, the frequency of the first system was set to the fundamental frequency of 20.0kHz, and the frequency of the second system was set to 19.5kHz at-500 Hz relative to the fundamental frequency.

In the 10 th test, the frequency of the first system was set to 20.1kHz at +100Hz with respect to the fundamental frequency, and the frequency of the second system was set to 20.0kHz at the fundamental frequency.

In the eleventh test, the frequency of the first system was set to the fundamental frequency of 20.0kHz, and the frequency of the second system was set to 19.9kHz at-100 Hz relative to the fundamental frequency. Fig. 8 is a graph showing the results of the fifth to eleventh tests. Also shown in fig. 8 is a three-dimensional graph with the height axis showing torque intensity, the left depth axis showing frequency, and the right depth axis showing test number. In fig. 8, the large peak near 500Hz in the graph is a peak of the frequency component corresponding to the rotation speed of the motor, and is not torque ripple. In the graph showing the result of the fifth test, no particular peak is generated in the frequency region of several hundred Hz. Therefore, it is found that torque ripple does not occur if the frequencies are synchronized.

In the graphs showing the results of the tenth test and the eleventh test, there are many peaks in the frequency region of several hundreds of Hz, and the peak at the 200Hz position corresponding to 2 times the frequency difference is particularly large. It is found that under the conditions of the tenth test and the eleventh test, a large torque ripple corresponding to the large peak is generated.

In the sixth to ninth tests, a large peak was not generated in a frequency region of several hundred Hz. In the eighth to ninth tests, 2 times the frequency difference was 1kHz, and a peak having a certain degree of magnitude was generated at a position of 1kHz in the graph. Then, torque ripple corresponding to the peak value is generated. However, since the vibration at 1kHz is a vibration beyond the human sense region, it is possible to suppress a noise or the like associated with the torque ripple. In the sixth test to the seventh test, 2 times the frequency difference was 2kHz, and noise and the like further deviated from the human sensory region.

For example, when used in a power steering apparatus or the like, the rotation speed of the motor 200 varies depending on the situation. As a result of the change in the rotation speed of the motor, if the rotation speed of the motor 200 overlaps with the frequency of the torque ripple, there is a possibility that the drive control of the motor will be disturbed.

In the first system and the second system, when the frequency of the carrier signal of the PWM control has a frequency difference of 2n times (n is a natural number) the frequency difference of the product of the maximum rotation speed of the motor 200 and the number of pole pairs or more, the frequency of the torque ripple generated at 2n times the frequency difference deviates from the rotation speed of the motor 200 and also deviates from the human feeling region. As a result, it is possible to suppress noise, vibration, control disturbance, and other problems associated with the torque ripple.

The frequency difference of the carrier signal in PWM control is preferably a value obtained by dividing the mechanical angle by 3n times (n is a natural number) of the product. Even when the frequencies of the carrier signals in the first system and the second system are completely synchronized, the torque ripple is generated in the motor 200 6n times. If the frequency difference of the carrier signal is 3n times the above-mentioned product of the mechanical angles, it is possible to avoid the torque ripple caused by the frequency difference from overlapping the torque ripple of 6n times. As a specific structure for obtaining the frequency difference between the carrier signals from each other, two structures can be considered.

The first configuration is a configuration in which two

internal clocks

371 and 372 shown in fig. 1 use clock elements whose clock signals have frequencies different from each other by, for example, about 5%. By using such a clock element, the same program can be used as a program for drive control in the two microcontrollers 341, 342 (in particular, a program for generation of a carrier signal and PWM control).

The second configuration is a configuration in which the frequency conversion coefficients differ from each other by, for example, about 5% in the two

microcontrollers

341, 342. The conversion coefficient is used when the two

microcontrollers

341 and 342 convert the frequency of the clock signal from the

internal clocks

371 and 372 to generate a carrier signal for PWM control. The microcontroller 341 of the first control circuit 301 performs frequency conversion at a first conversion ratio and the microcontroller 342 of the second control circuit 302 performs frequency conversion at a second conversion ratio different from the first conversion ratio.

In this configuration, clock elements of the same frequency can be used as the

internal clocks

371 and 372, and the carrier signals having a desired frequency difference can be easily obtained by converting coefficients. The clock elements of the same frequency are, for example, clock elements incorporating crystals of the same specification, and the increase in the number of parts is avoided. In addition, the

internal clocks

371, 372 may also differ from each other individually. That is, in the crystal of the same specification, as described above, the individual difference of about 50Hz is generated, but if the conversion coefficients differ by about 5%, a frequency difference far exceeding such individual difference is generated, and thus the existence of the individual difference does not become a problem.

As another configuration, the following configuration may be considered: a circuit for checking the synchronization state of the frequencies of the carrier signals is provided, and the frequency of the carrier signal is changed according to the checked synchronization state, thereby obtaining a desired frequency difference. In this structure, there are the following advantages: for example, even when the same variable is set erroneously as the conversion coefficient, a desired frequency difference can be obtained. Next, a modified example of the present embodiment will be described. Fig. 9 is a diagram showing a circuit configuration of the motor drive unit 1000 in a modification in which circuit wirings are different. In the modification shown in fig. 9, the grounded ends of the first inverter 101 and the second inverter 102 are separated from each other. Even with such a separate structure, torque ripple occurs when the frequency of the carrier signal varies. Therefore, in the modification shown in fig. 9, in the first system and the second system, by setting the above-described difference in the frequency of the carrier signal of the PWM control, the frequency of the torque ripple is deviated from the rotation speed of the motor 200 and also deviated from the human sensory region. As a result, it is possible to suppress noise, vibration, control disturbance, and other problems associated with the torque ripple.

(embodiment of Power steering apparatus)

Vehicles such as automobiles generally include a power steering device. The power steering apparatus generates an assist torque for assisting a steering torque of a steering system generated by a driver operating a steering handle. The assist torque is generated by the assist torque mechanism, and the burden of the operation of the driver can be reduced. For example, the assist torque mechanism is constituted by a steering torque sensor, an ECU, a motor, a speed reduction mechanism, and the like. The steering torque sensor detects a steering torque in the steering system. The ECU generates a drive signal based on a detection signal of the steering torque sensor. The motor generates an assist torque corresponding to the steering torque based on the drive signal, and transmits the assist torque to the steering system via the speed reduction mechanism.

The motor drive unit 1000 of the above embodiment is applied to a power steering apparatus. Fig. 10 is a diagram schematically showing the configuration of an electric power steering apparatus 2000 according to the present embodiment. The electric power steering apparatus 2000 includes a steering system 520 and an assist torque mechanism 540.

The steering system 520 includes, for example, a steering handle 521, a steering shaft 522 (also referred to as a "steering column"),

universal shaft joints

523A and 523B, and a rotary shaft 524 (also referred to as a "pinion shaft" or an "input shaft").

The steering system 520 includes, for example, a rack and pinion mechanism 525, a rack shaft 526, left and right ball joints 552A and 552B,

tie rods

527A and 527B,

knuckles

528A and 528B, and left and right steered wheels (e.g., left and right front wheels) 529A and 529B.

The steering handle 521 is connected to the rotary shaft 524 via the steering shaft 522 and the

universal shaft joints

523A and 523B. A rack shaft 526 is connected to the rotating shaft 524 via a rack and pinion mechanism 525. The rack and pinion mechanism 525 has a pinion 531 provided on the rotating shaft 524 and a rack 532 provided on the rack shaft 526. A right steering wheel 529A is connected to a right end of the rack shaft 526 via a ball joint 552A, a tie rod 527A, and a knuckle 528A in this order. Similarly to the right side, a left steered wheel 529B is connected to the left end of the rack shaft 526 via a ball joint 552B, a tie rod 527B, and a knuckle 528B in this order. Here, the right and left sides correspond to the right and left sides, respectively, as viewed by a driver sitting on the seat.

According to the steering system 520, a steering torque is generated by the driver operating the steering handle 521 and is transmitted to the left and right steering wheels 529A and 529B via the rack and pinion mechanism 525. This allows the driver to operate the left and right steerable wheels 529A and 529B.

The assist torque mechanism 540 includes, for example, a steering torque sensor 541, an ECU542, a motor 543, a reduction mechanism 544, and an electric power supply device 545. The assist torque mechanism 540 applies assist torque to the steering system 520 from the steering handle 521 to the left and right steered wheels 529A and 529B. In addition, the assist torque is sometimes referred to as "additional torque".

As the ECU542, for example, the

control circuits

301 and 302 shown in fig. 1 and the like are used. As the power supply device 545, for example,

inverters

101 and 102 shown in fig. 1 and the like are used. As the motor 543, for example, the motor 200 shown in fig. 1 and the like is used. The ECU542, the motor 543, and the power supply device 545 may constitute what is generally called an "electromechanical integrated motor". A mechanism including elements other than the ECU542, the motor 543, and the power supply device 545 among the elements shown in fig. 10 corresponds to an example of the power steering mechanism driven by the motor 543.

The steering torque sensor 541 detects a steering torque of the steering system 520 applied by the steering handle 521. The ECU542 generates a drive signal for driving the motor 543 based on a detection signal (hereinafter referred to as "torque signal") from the steering torque sensor 541. The motor 543 generates an assist torque corresponding to the steering torque based on the drive signal. The assist torque is transmitted to the rotary shaft 524 of the steering system 520 via the speed reduction mechanism 544. The reduction mechanism 544 is, for example, a worm gear mechanism. The assist torque is also transmitted from the rotating shaft 524 to the rack and pinion mechanism 525.

The power steering apparatus 2000 is classified into a pinion assist type, a rack assist type, a column assist type, and the like according to a portion where assist torque is applied to the steering system 520. Fig. 10 shows a pinion assist type power steering apparatus 2000. However, the power steering device 2000 is also applicable to a rack assist type, a column assist type, and the like.

Not only a torque signal, for example, a vehicle speed signal, may be input to the ECU 542. The microcontroller of the ECU542 can PWM-control the motor 543 based on the torque signal, the vehicle speed signal, and the like.

The ECU542 sets a target current value based on at least the torque signal. Preferably, ECU542 sets the target current value in consideration of a vehicle speed signal detected by a vehicle speed sensor, and further, in consideration of a rotor rotation signal detected by an angle sensor. The ECU542 can control a drive signal, i.e., a drive current, of the motor 543 so that an actual current value detected by a current sensor (see fig. 1) matches a target current value.

According to the power steering apparatus 2000, the left and right steering wheels 529A and 529B can be operated by the rack shaft 526 using a composite torque obtained by adding the assist torque of the motor 543 to the steering torque of the driver. In particular, by using the motor drive unit 1000 of the above embodiment, it is possible to reduce noise, vibration, and other problems caused by torque ripple, and to achieve smooth power assist.

Here, although the power steering apparatus is given as an example of a method of using the drive control apparatus and the drive apparatus according to the present invention, the method of using the drive control apparatus and the drive apparatus according to the present invention is not limited to the above method, and can be used in a wide range of applications such as pumps and compressors.

The above-described embodiments should be considered in all respects as illustrative and not restrictive. The scope of the present invention is defined by the claims, not by the embodiments described above, and includes all modifications equivalent in meaning and scope to the claims.

Description of the symbols

101. 102: an inverter; 200: a motor; 301. 302: a control circuit; 311. 312: a power supply circuit; 321. 322: an angle sensor; 331. 332: an input circuit; 341. 342: a microcontroller; 351. 352: a drive circuit; 361. 362: a ROM; 371. 372: an internal clock; 401. 402, a step of: a current sensor; 403. 404: a power source; 1000: a motor drive unit; 2000: provided is a power steering device.

Claims

1. A drive control device for controlling the driving of a motor, comprising:

a first inverter connected to one end of a winding of the motor;

a second inverter connected to the other end opposite to the one end;

a first control circuit that performs PWM control on the first inverter; and

a second control circuit that performs PWM control on the second inverter,

in the first control circuit and the second control circuit, a frequency of a carrier signal of PWM control has a frequency difference of more than a product of a maximum rotation speed of the motor and a pole pair number.

2. The drive control apparatus according to claim 1,

the frequency difference is a value obtained by removing 3n times (n is a natural number) of the product from the mechanical angle.

3. The drive control apparatus according to claim 1 or 2,

the first control circuit and the second control circuit frequency-convert a clock signal obtained from an oscillator and generate a carrier signal for PWM control,

the first control circuit performs frequency conversion by a first conversion ratio, and the second control circuit performs frequency conversion by a second conversion ratio different from the first conversion ratio.

4. A motor driving device is provided with:

the drive control apparatus according to any one of claims 1 to 3; and

a motor, the driving of which is controlled by the drive control means.

5. A power steering device is provided with:

the drive control apparatus according to any one of claims 1 to 3;

a motor, the driving of which is controlled by the drive control means; and

a power steering mechanism driven by the motor.