JP2020137263A - Power conversion device, drive device and power steering device - Google Patents

Abstract

To suppress capacitance of a capacitor to miniaturize a power conversion device.SOLUTION: A power conversion device, which converts power from a power source to supply to a motor including n-phase windings (where n is an integer of 3 or larger) mutually not connected, includes: a first inverter, including switch elements of the n phases and connected to one end of the above windings; and a second inverter, including switch elements of the n phases and connected to the other end of the above windings. Each switch element of each phase in the first inverter and the second inverter performs switching at the same period among the phases, and becomes ON at mutually different timing among the phases.SELECTED DRAWING: Figure 8

Description

The present invention relates to a power converter, a drive device and a power steering device.

Conventionally, there is known a drive system in which inverters are connected to both ends of a winding of a motor and the motor is driven by two inverters.

For example, in Patent Document 1, the first inverter unit is connected between one end of the U-phase coil, the V-phase coil, and the W-phase coil and the first power supply source. Further, the second inverter unit is connected between the other ends of the U-phase coil, the V-phase coil and the W-phase coil and the second power supply source. Further, a smoothing capacitor for smoothing the current supplied from the first power supply source to the SW element is connected in parallel with the first power supply source to smooth the current supplied from the second power supply source to the SW element. A smoothing capacitor is connected in parallel with the second power source.

Japanese Unexamined Patent Publication No. 2014-192950

Since the capacitor has a large volume among the elements, it is preferable that the capacitor has a small volume as a substrate design. However, in the past, there has been no proposal to reduce the size of the power conversion device or drive system by focusing on the capacity of the capacitor.
Therefore, one of the objects of the present invention is to reduce the size of the power conversion device by suppressing the capacity of the capacitor.

One aspect of the power conversion device according to the present invention is a power conversion device that converts power from a power source and supplies it to a motor having n-phase (n is an integer of 3 or more) unconnected windings. A first inverter having each of the n-phase switch elements connected to one end of the winding, and a second inverter having each of the n-phase switch elements connected to the other end of the winding. The switch elements of the respective phases in the first inverter and the second inverter switch each other in the same cycle, and the phases are turned on at different timings.
Further, one aspect of the drive device according to the present invention includes the power conversion device and a motor to which the power converted by the power conversion device is supplied.

Further, one aspect of the power steering device according to the present invention includes the power conversion device, a motor to which the power converted by the power conversion device is supplied, and a power steering mechanism driven by the motor.

According to the present invention, the capacity of the capacitor can be suppressed and the power conversion device can be miniaturized.

FIG. 1 is a diagram schematically showing a circuit configuration of a motor drive unit according to the present embodiment. FIG. 2 is a diagram showing an example of a current value flowing through each coil of each phase of the motor. FIG. 3 is a diagram showing a state of voltage application in a switching operation under PWM control. FIG. 4 is a diagram showing a state in which application is stopped in a switching operation under PWM control. FIG. 5 is a diagram showing a PWM signal. FIG. 6 is a diagram showing switching timing in each phase of the comparative example. FIG. 7 is a diagram showing changes in the amount of charge in the capacitor of the comparative example. FIG. 8 is a diagram showing switching timing in each phase of the present embodiment. FIG. 9 is a diagram showing a change in the amount of charge in the capacitor of the present embodiment. FIG. 10 is a diagram schematically showing a configuration of an electric power steering device according to the present embodiment.

Hereinafter, embodiments of the power conversion device, drive device, and power steering device of the present disclosure will be described in detail with reference to the accompanying drawings. However, in order to avoid unnecessarily redundant explanations below and facilitate understanding by those skilled in the art, unnecessarily detailed explanations may be omitted. For example, detailed explanations of already well-known matters and duplicate explanations for substantially the same configuration may be omitted.

In the present specification, power from a power source is converted into power supplied to a three-phase motor having three-phase (U-phase, V-phase, W-phase) windings (sometimes referred to as "coils"). An embodiment of the present disclosure will be described by taking a power conversion device as an example. However, a power conversion device that converts power from a power source into power supplied to an n-phase motor having n-phase (n is an integer of 4 or more) windings such as four-phase or five-phase is also within the scope of the present disclosure. ..
(Circuit configuration of motor drive unit 1000)
FIG. 1 is a diagram schematically showing a circuit configuration of the motor drive unit 1000 according to the present embodiment.
The motor drive unit 1000 includes inverters 101 and 102, a motor 200, and a control circuit 300.

In this specification, the motor drive unit 1000 including the motor 200 as a component will be described. The motor drive unit 1000 including 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, in which the motor 200 is omitted as a component. The motor drive unit 1000 from which the motor 200 is omitted corresponds to an example of the power conversion device of the present invention.

The motor 200 is, for example, a three-phase AC motor. The motor 200 has U-phase, V-phase, and W-phase coils, and the coils are unconnected to each other. The winding method of the coil is, for example, concentrated winding or distributed winding.

The motor drive unit 1000 is connected to the power supplies 410 and 420. In the present embodiment, the power supply 410 for the first inverter 101 and the power supply 420 for the second inverter 102 are used as the power supplies. That is, the first inverter 101 is connected to the first power supply 410, and the second inverter 102 is connected to the second power supply 420 independent of the first power supply 410.

The power supplies 410 and 420 generate a predetermined power supply voltage (for example, 12V). As the power supplies 410 and 420, for example, a DC power supply is used. However, the power supplies 410 and 420 may be an AC-DC converter or a DC-DC converter, or may be a battery (storage battery). In FIG. 1, as an example, a power supply 410 for the first inverter 101 and a power supply 420 for the second inverter 102 are shown, but the motor drive unit 1000 is connected to a power supply common to the first inverter 101 and the second inverter 102. May be done. Further, the motor drive unit 1000 may have a power supply inside.

The motor drive unit 1000 includes capacitors 105 and 106. The capacitors 105 and 106 are so-called smoothing capacitors, which stabilize the power supply voltage and suppress torque ripple by absorbing the recirculation current generated by the motor 200. The capacitors 105 and 106 are, for example, electrolytic capacitors, and the capacitance and the number of capacitors to be used are appropriately determined according to design specifications and the like. The first capacitor 105 of the two capacitors 105 and 106 is connected to the first inverter 101 in parallel with the power supply 410 for the first inverter 101. Of the two capacitors 105 and 106, the second capacitor 106 is connected to the second inverter 102 in parallel with the power supply 420 for the second inverter 102.

The motor drive unit 1000 can convert the electric power from the power supplies 410 and 420 into the electric power supplied to the motor 200 by the two inverters 101 and 102. For example, the motor drive unit 1000 can convert DC power into three-phase AC power, which is a pseudo sine wave of U-phase, V-phase, and W-phase.

Of the two inverters 101 and 102, the first inverter 101 is connected to one end 210 of the coil of the motor 200, and the second inverter 102 is connected to the other end 220 of the coil of the motor 200. That is, the motor drive unit 1000 includes a first inverter 101 having three-phase switch elements of U-phase, V-phase, and W-phase connected to one end 210 of the coil of the motor 200, and the other end 220 with respect to one end 210. A second inverter 102 having switch elements for each of the three phases of U-phase, V-phase, and W-phase, which are connected to the U-phase, is provided.

Further, the first inverter 101 and the second inverter 102 include a bridge circuit having three legs, and each leg has three high-side switch elements connected to the coil of the motor 200 and the power supply end, and the motor 200. The coil and the three low-side switch elements connected to the ground end are provided.

Specifically, the U-phase high-side switch elements 113H and 116H and the low-side switch elements 113L and 116L are connected to one end 210 and the other end 220 of the U-phase coil, respectively. The V-phase high-side switch elements 114H and 117H and the low-side switch elements 114L and 117L are connected to one end 210 and the other end 220 of the V-phase coil, respectively. The W-phase high-side switch elements 115H and 118H and the low-side switch elements 115L and 118L are connected to one end 210 and the other end 220 of the W-phase coil, respectively. As the switch element, for example, a field effect transistor (MOSFET or the like) or an insulated gate bipolar transistor (IGBT) is used. When the switch element is an IGBT, a diode (freewheel) is connected in antiparallel to the switch element.

For each phase, an H-bridge is composed of a high-side switch element and a low-side switch element connected to one end 210 and the other end 220 of the coil. That is, the motor drive unit 1000 includes three H bridges corresponding to the U phase, the V phase, and the W phase. The motor drive unit 1000 can individually supply electric power to each of the U-phase, V-phase, and W-phase coils that are not connected to each other by these three H bridges.

In the control circuit 300, the target torque of the motor 200 and the like are input from an external device such as a control computer of the power steering device. The control circuit 300 sets a target current value based on the output information of the motor 200 detected by an angle sensor or a current sensor (not shown) and the target torque or the like, and drives the motor 200 by the inverters 101 and 102. Control. Specifically, the control circuit 300 PWM-controls the on / off operation of each switch element provided in the inverters 101 and 102.
As the control circuit, two control circuits individually corresponding to the two inverters 101 and 102 may be provided.
FIG. 2 is a diagram showing an example of a current value flowing through each coil of each phase of the motor 200.

FIG. 2 shows the current obtained by plotting the current values flowing through the U-phase, V-phase, and W-phase coils of the motor 200 when the first inverter 101 and the second inverter 102 are controlled according to the three-phase energization control. A waveform (sine wave) is exemplified. The horizontal axis of FIG. 2 shows the motor electric angle (deg), and the vertical axis shows the current value (A). I _pk represents the maximum current value (peak current value) of each phase.
The motor drive unit 1000 can also drive the motor 200 by using two inverters 101 and 102 using a waveform other than a sine wave.

The current waveform as illustrated in FIG. 2 is generated when a voltage having a waveform corresponding to such a current waveform is applied to the motor 200. Then, such a voltage is generated by switching the switch element of the first inverter 101 and the switch element of the second inverter 102 at a high speed such as 20 kHz by PWM control.
3 and 4 are diagrams schematically showing a switching operation under PWM control, FIG. 3 shows a state of voltage application, and FIG. 4 shows a state of application stop.

3 and 4 show, for example, a U-phase leg among the legs of the inverters 101 and 102. As described above, the U-phase leg includes a high-side switch element 113H and a low-side switch element 113L on the first inverter 101 side, and a high-side switch element 116H and a low-side switch element 116L on the second inverter 102 side.

The high-side switch element 113H and the low-side switch element 113L on the first inverter 101 side are not turned on at the same time, and when one is turned on, the other is turned off. Similarly, the high-side switch element 116H and the low-side switch element 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, one of the two inverters 101 and 102 (the second inverter 102 in the case of FIG. 3) turns on the high side switch elements 113H and 116H, and the other (FIG. 3). In the case of 3, the low-side switch elements 113L and 116L are turned on by the first inverter 101). As a result, a current flows from the one side to the other side as shown by an arrow in FIG.

When the application is stopped, all the switch elements are turned off. Immediately after the power is turned off, the recirculation current from the motor 200 flows through one of the two capacitors 105 and 106 (the first capacitor 105 in the case of FIG. 4) as shown by the arrow in FIG. 4 to the capacitor. Be absorbed. This recirculation current does not contribute to the torque of the motor 200. As for the control of the switch element when the application is stopped, in addition to the control that both the two inverters 101 and 102 are turned off as shown in FIG. 4, only one side of the two inverters 101 and 102 is turned off. It is also possible to adopt the control.

In the two inverters 101 and 102, the voltage application state shown in FIG. 3 and the application stop state shown in FIG. 4 are repeated at high speed. The repetition of voltage application and application stop in the inverters 101 and 102 is executed according to the PWM signal generated by the control circuit 300.
FIG. 5 is a diagram showing a PWM signal.

The PWM signal is a binary pulse signal, and a first value indicating voltage application and a second value indicating application stop occur alternately. The pulse of the PWM signal is repeated in the period T0, and the period T0 is divided into a first value duration T1 and a second value duration T2.

Since the PWM signal is a high frequency signal such as 20 kHz as described above, the period T0 is a short period such as 50 μsec. Therefore, the effective voltage (effective voltage) applied to the motor 200 is a voltage averaged by the period T0, and the ratio (duty) of the period T0 to the duration T1 of the first value is the power supply voltage and the effective voltage. Is equal to the ratio of. The effective voltage is a voltage that changes with time in response to a changing current value, such as the current waveform shown in FIG. Such a time change of the effective voltage is realized by controlling the duty of the PWM signal by the control circuit 300.

When the duty of the PWM signal changes in order to change the effective voltage, the on-timing of the switch element (that is, the rising timing of the PWM signal) is fixed to the period T0 for ease of control and the like. Then, the off timing of the switch element (that is, the falling timing of the PWM signal) changes, and the duration T1 of the first value corresponding to the effective voltage is realized. In other words, when the ratio of the on state changes by PWM control, the switching off timing changes, and the switching on timing is fixed.

Here, FIG. 1 is referred to again. Capacitors 105 and 106 are connected to the inverters 101 and 102 in parallel with the power supplies 410 and 420. The capacitors 105 and 106 absorb the recirculation current generated in each of the n-phase (here, three-phase) coils of the motor 200. That is, one capacitor repeats charging and discharging due to the recirculation current of n phases. Charging and discharging of the capacitors 105 and 106 will occur at each off-timing of switching associated with PWM control.

As the capacitors 105 and 106, capacitors having a sufficient capacity for absorbing the recirculation current are required. Further, in the present embodiment, since the power supplies 410 and 420 are independent of the two inverters 101 and 102, capacitors 105 and 106 for each of the inverters 101 and 102 are required. Therefore, the capacitance suppression of the capacitors 105 and 106 greatly contributes to the miniaturization of the motor drive unit 1000.

6 and 7 are diagrams showing the charging / discharging of the capacitor in the comparative example, FIG. 6 shows the switching timing in each phase, and FIG. 7 shows the change in the charge amount in the capacitor. The horizontal axis of FIGS. 6 and 7 represents time, and the vertical axis of FIG. 7 represents the amount of electric charge accumulated in the capacitor.

In the comparative example, the on-timing is the same between the UVW phases in the switching operation. In the case of the current waveform as shown in FIG. 2, since the effective voltage is generally different between the phases, the duty is different between the phases at many points on the current waveform. As a result, the off-timing differs between the phases at many times, but if the on-timing is the same between the phases, the off-timing is often close to each other. Further, when the on-timing is the same, the smaller the output of the motor, the closer the off-timing is. As a result, the circulating currents generated in each phase flow into the capacitor at timings close to each other. As shown in FIG. 7, the capacitor rapidly absorbs the recirculation current during charging and then gradually discharges. For this reason, if the off-timing is close to each other, charging by the recirculation current of each phase will be overlapped one after another before the discharge proceeds, and a large capacity C1 is required as the capacity of the capacitor. As a result, a large capacitor is required, which hinders the miniaturization of the motor drive unit 1000.
Even if the charging overlap does not always occur as shown in FIG. 7, for example, when it is assumed that the charging overlap occurs repeatedly in a specific phase on the current waveform as shown in FIG. 2, the instantaneous maximum charging is performed. In order to correspond to the amount, a capacitor having a large capacity C1 is required as a capacitor.

In contrast to such a comparative example, in the present embodiment, the on-timing differs between the UVW phases in the switching operation. That is, the switch elements of each phase in the first inverter 101 and the second inverter 102 switch between the phases at the same cycle and turn on at different timings between the phases. Here, "turning on at different timings" means that the timing at which the switch in the off state is switched to the on state is different. As the switching control, the length and timing of the on state may be controlled based on the off state, or the length and timing of the off state may be controlled based on the on state.
In the present embodiment, this switching is switching by PWM control, but it may be applied to switching other than PWM control. Further, switching operations having different on-timing can be realized because the coils of the motor 200 are not connected to each other in phases. This is because if the phases are not connected to each other, the currents in each phase are not linked.

8 and 9 are diagrams showing the charging / discharging of the capacitor in the present embodiment, FIG. 8 shows the switching timing in each phase, and FIG. 9 shows the change in the charge amount in the capacitor. The horizontal axis of FIGS. 8 and 9 represents time, and the vertical axis of FIG. 9 represents the amount of electric charge accumulated in the capacitor.

As shown in FIG. 8, in the present embodiment, the cycle of the switching operation is the cycle T0 for each phase, but the on-timing is different between the phases. Specifically, the period T0 is turned on at each timing divided into n (n is the number of phases, here divided into 3). Here, the n division does not have to be divided into n equal parts, but in the case of three divisions, it is desirable that the n divisions cause a timing difference of, for example, 30% or more of the period T0 between the phases. When the switch elements of each phase are turned on at such a division timing, the switch-off timings are sufficiently separated from each other. Further, when the on-timing is different between the phases, the smaller the output of the motor, the more the off-timing is separated from each other.

When the switch-off timings are sufficiently separated from each other, as shown in FIG. 9, the inflow (that is, charging) of the recirculating current to the capacitor is sufficiently spaced between the phases to be a single charge for each phase. , The next charge will occur after the discharge has progressed sufficiently. As a result, the maximum value of the electric charge accumulated in the capacitor is suppressed, so that the capacitors 105 and 106 can be small capacitors having a small capacity C2, and the motor drive unit 1000 can be miniaturized (that is, the power converter and the drive device can be miniaturized. ) Contributes to.
(Embodiment of Power Steering Device)

Vehicles such as automobiles are generally equipped with a power steering device. The power steering device generates an auxiliary torque for assisting the steering torque of the steering system generated by the driver operating the steering handle. The auxiliary torque is generated by the auxiliary torque mechanism, and the burden on the driver's operation can be reduced. For example, the auxiliary torque mechanism includes a steering torque sensor, an ECU, a motor, a deceleration mechanism, and the like. The steering torque sensor detects the steering torque in the steering system. The ECU generates a drive signal based on the detection signal of the steering torque sensor. The motor generates an auxiliary torque according to the steering torque based on the drive signal, and transmits the auxiliary torque to the steering system via the reduction mechanism.

The motor drive unit 1000 of the above embodiment is suitably used for a power steering device. FIG. 10 is a diagram schematically showing the configuration of the electric power steering device 2000 according to the present embodiment.
The electric power steering device 2000 includes a steering system 520 and an auxiliary torque mechanism 540.

The steering system 520 is, for example, a steering handle 521, a steering shaft 522 (also referred to as a "steering column"), universal shaft joints 523A, 523B, and a rotary shaft 524 (also referred to as a "pinion shaft" or "input shaft"). ) Is provided.

Further, 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 steering wheels (for example, left and right front wheels) 529A. It is equipped with 529B.

The steering handle 521 is connected to the rotating 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 the right end of the rack shaft 526 via a ball joint 552A, a tie rod 527A, and a knuckle 528A in this order. Similar to the right side, the left steering 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 side and the left side correspond to the right side and the left side as seen from the driver sitting in the seat, respectively.

According to the steering system 520, steering torque is generated when the driver operates the steering handle 521, and is transmitted to the left and right steering wheels 529A and 259B via the rack and pinion mechanism 525. As a result, the driver can operate the left and right steering wheels 529A and 529B.

The auxiliary torque mechanism 540 includes, for example, a steering torque sensor 541, an ECU 542, a motor 543, a speed reduction mechanism 544, and a power supply device 545. The auxiliary torque mechanism 540 applies auxiliary torque to the steering system 520 from the steering handle 521 to the left and right steering wheels 529A and 259B. The auxiliary torque is sometimes referred to as "additional torque".

As the ECU 542, for example, the control circuit 300 shown in FIG. 1 or the like is used. Further, as the power supply device 545, for example, the inverters 101 and 102 shown in FIG. 1 and the like are used. Further, as the motor 543, for example, the motor 200 shown in FIG. 1 or the like is used. The ECU 542, the motor 543, and the power supply device 545 may form a unit generally referred to as a "mechanical-electric integrated motor".

Among the elements shown in FIG. 10, the mechanism composed of the elements excluding the ECU 542, the motor 543, and the power supply device 545 corresponds to an example of the power steering mechanism driven by the motor 543.

The steering torque sensor 541 detects the steering torque of the steering system 520 applied by the steering handle 521. The ECU 542 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 auxiliary torque according to the steering torque based on the drive signal. The auxiliary torque is transmitted to the rotating shaft 524 of the steering system 520 via the reduction mechanism 544. The reduction mechanism 544 is, for example, a worm gear mechanism. Auxiliary torque is further transmitted from the rotating shaft 524 to the rack and pinion mechanism 525.

The power steering device 2000 is classified into a pinion assist type, a rack assist type, a column assist type, and the like, depending on where the auxiliary torque is applied to the steering system 520. FIG. 10 shows a pinion assist type power steering device 2000. However, the power steering device 2000 is also applied to a rack assist type, a column assist type, and the like.

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

The ECU 542 sets the target current value at least based on the torque signal. It is preferable that the ECU 542 sets the target current value in consideration of the vehicle speed signal detected by the vehicle speed sensor and further in consideration of the rotation signal of the rotor detected by the angle sensor. The ECU 542 can control the drive signal of the motor 543, that is, the drive current so that the actual current value detected by the current sensor (not shown) matches the target current value.

According to the power steering device 2000, the left and right steering wheels 529A and 529B can be operated by the rack shaft 526 by utilizing the combined torque obtained by adding the auxiliary torque of the motor 543 to the steering torque of the driver. Further, by using the motor drive unit 1000 of the above embodiment, the space in the power steering device 2000 can be saved.

Here, a power steering device is mentioned as an example of the usage method in the power conversion device and the drive device of the present invention, but the usage method of the power conversion device and the drive device of the present invention is not limited to the above, and the pump and the compressor It can be used in a wide range.

The embodiments described above should be considered exemplary in all respects and not restrictive. The scope of the present invention is shown not by the above-described embodiment but by the scope of claims, and it is intended that all modifications within the meaning and scope equivalent to the scope of claims are included.

101, 102: Inverter 105, 106: Capacitor 200: Motor 300: Control circuit 410, 420: Power supply 1000: Motor drive unit 2000: Power steering device

Claims (7)

A power conversion device that converts power from a power source and supplies it to a motor having n-phase (n is an integer of 3 or more) unconnected windings.
A first inverter connected to one end of the winding and having each of the n-phase switch elements,
A second inverter having each of the n-phase switch elements connected to the other end with respect to the one end is provided.
A power conversion device in which switch elements of each phase of the first inverter and the second inverter switch between phases at the same cycle and are turned on at different timings between the phases. The first inverter is connected to the first power supply and
The second inverter is connected to a second power source independent of the first power source.
A first capacitor connected to the first inverter in parallel with the first power supply,
A second capacitor connected to the second inverter in parallel with the second power supply,
The power conversion device according to claim 1. The electric power according to claim 1 or 2, wherein the switch elements of the respective phases in the first inverter and the second inverter switch each other in the same cycle, and are turned on at each timing when the cycle is divided into n. Conversion device. Any one of claims 1 to 3 in which the switch elements of the respective phases of the first inverter and the second inverter perform switching by PWM control between the phases at the same cycle and are turned on at different timings between the phases. The power converter according to the section. The power conversion device according to claim 4, wherein when the ratio of the on state changes by the PWM control, the switching off timing changes and the switching on timing is fixed. The power conversion device according to any one of claims 1 to 5.
A motor to which the power converted by the power conversion device is supplied, and
A drive device equipped with. The power conversion device according to any one of claims 1 to 5.
A motor to which the power converted by the power conversion device is supplied, and
The power steering mechanism driven by the motor and
Power steering device equipped with.

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