Inverter drive device and electrically driven vehicle system using the same

This is to reduce electromagnetic noise while reducing a calculation load of a microcomputer. An inverter drive device according to the present invention switches a first control mode, a second control mode, and a third control mode on the basis of vehicle speed information in a motor control device that controls a power converter that drives a polyphase motor by a PWM pulse signal based on a carrier signal, the first control mode being for updating a command voltage signal to the power converter only on a ridge side or a trough side of the carrier signal, the second control mode being for updating a command voltage signal to the power converter both on a ridge side and a trough side of the carrier signal, and the third control mode being for updating a command voltage signal to the power converter only once of ridge-trough-ridge or trough-ridge-trough of the carrier signal.

TECHNICAL FIELD

The present invention relates to an inverter drive device, and more particularly to an inverter drive device used in an electrically driven vehicle system.

BACKGROUND ART

An inverter drive device, which performs pulse width modulation (PWM) control and drives a motor, converts a direct current power supply into an alternating current voltage having an arbitrary frequency to realize variable speed driving.

Since the PWM control compares a sinusoidal modulation signal with a carrier signal such as sawtooth wave or triangular wave to generate a pulse voltage, noise due to electromagnetic exciting force (hereinafter abbreviated as electromagnetic noise) caused by a frequency of the carrier wave occurs.

In particular, when a frequency f of the electromagnetic exciting force coincides with a frequency fm of natural vibration of a mechanism, resonance occurs and large electromagnetic noise is generated. PTL 1 describes a technique of causing the frequency fc of the carrier signal to coincide with the frequency fm of the natural vibration of the mechanism in order to reduce the electromagnetic noise due to resonance.

CITATION LIST

Patent Literature

SUMMARY OF INVENTION

Technical Problem

In PTL 1, update timing of the sinusoidal modulation signal is set to twice of “ridge” and “trough” of the carrier signal of the triangular wave so that no electromagnetic noise due to the frequency fc of the carrier signal occurs (seeFIG. 1).

However, if the voltage update timing is set to “ridge” and “trough” (hereinafter abbreviated as ridge-trough update), a three-phase voltage to be applied to an inverter needs to be updated at a frequency 2fc that is twice the carrier signal and a processing load of a microcomputer increases.

In the case of using the ridge-trough update, the frequency of the voltage update timing needs to be increased. Therefore, it is difficult to increase the frequency of the carrier signal of the inverter. In contrast, if the voltage update timing is set to only “ridge” (hereinafter abbreviated as ridge update), the three-phase voltage to be applied to the inverter can be updated at the frequency fc of the carrier signal and the processing load of a microcomputer decreases (seeFIG. 2). Meanwhile, since the number of times of the voltage update timing is halved in the ridge update, a harmonic voltage other than a basic waveform voltage increases as a waveform of an output voltage becomes coarser than the ridge-trough update.

An object of the present invention is to reduce electromagnetic noise while reducing a calculation load of a microcomputer.

Solution to Problem

To solve the above-described problems, an inverter drive device according to the present invention switches a first control mode, a second control mode, and a third control mode on the basis of vehicle speed information in a motor control device that controls a power converter that drives a polyphase motor by a PWM pulse signal based on a carrier signal, the first control mode being for updating a command voltage signal to the power converter only on a ridge side or a trough side of the carrier signal, the second control mode being for updating a command voltage signal to the power converter both on a ridge side and a trough side of the carrier signal, and the third control mode being for updating a command voltage signal to the power converter only once of ridge-trough-ridge or trough-ridge-trough of the carrier signal.

Advantageous Effects of Invention

According to the present invention, electromagnetic noise can be reduced while a calculation load of a microcomputer is reduced.

DESCRIPTION OF EMBODIMENTS

Hereinafter, a first embodiment of the present invention will be described with reference to the drawings.

FIG. 3is a block diagram illustrating a configuration of a motor drive apparatus6including an inverter drive device according to the present embodiment.FIG. 4is a block diagram of an inside of a control unit1illustrated inFIG. 3.

The motor drive apparatus6includes a motor2and an inverter3.

The inverter3includes an inverter circuit31that mutually converting a direct current into an alternating current, a pulse width modulation signal output means32that outputs a PWM signal to the inverter circuit31, and a smoothing capacitor33that smooths direct current power.

A high-voltage battery5is a direct current voltage source of the motor drive apparatus6. A direct current voltage VB of the high-voltage battery5is converted into a pulsed three-phase alternating current voltage having a variable voltage and a variable frequency by the inverter circuit31and the pulse width modulation signal output means32of the inverter3and applied to the motor2.

The motor2is a synchronous motor rotationally driven by supplying the three-phase alternating current voltage. A rotational position sensor4is attached to the motor2in order to control a phase of an applied voltage of a three-phase alternating current according to a phase of an induced voltage of the motor2, and a rotational position detector41calculates a rotational position8from an input signal of the rotational position sensor4and calculates a motor rotational speed or.

Here, as the rotational position sensor4, a resolver constituted by an iron core and winding is favorable. However, a magnetic resistance element such as a GMR sensor or a sensor using a Hall element is also acceptable.

A current detection means7detects a U-phase alternating current Iu, a V-phase alternating current Iv and a W-phase alternating current Iw that are three-phase alternating currents flowing in the motor2. Here, the current detection means7provided with three current detectors is illustrated. However, two current detectors are provided and a remaining one phase may be calculated according to a fact that a sum of three-phase currents is zero. Further, a pulsed direct current bus current flowing into the inverter3is detected as a voltage (current detection value Idc) between both ends of a shunt resistor Rsh inserted between the smoothing capacitor33and the inverter3, and a direct current may be reproduced as a three-phase current according to the applied voltage.

As illustrated inFIG. 4, the control unit1includes a three-phase/dq conversion current control unit11, a current control unit12, and a voltage command generation unit13, and drives the inverter circuit31of the inverter3according to the detected U-phase alternating current Iu, V-phase alternating current Iv, and W-phase alternating current Iw, and a d-axis current command Id* and a q-axis current command Iq* of the motor2.

The three-phase/dq conversion current control unit11calculates dq-converted d-axis current value Id and q-axis current value Iq from the detected U-phase alternating current Iu, V-phase alternating current Iv, W-phase alternating current Iw, and rotational position8. The current control unit12calculates a d-axis voltage command Vd* and a q-axis voltage command Vq* such that the d-axis current value Id and the q-axis current value Iq match the d-axis current command Id* and the q-axis current command Iq* created according to target torque.

The voltage command generation unit13calculates a U-phase voltage command value Vu*, a V-phase voltage command value Vv*, and a UW-phase voltage command value Vw* that are three-phase voltage command values UVW-converted from the d-axis voltage command Vd*, the q-axis voltage command Vq*, and the rotational position8, and PWM-outputs a PWM pulse that is obtained by modulating a pulse width of the three-phase voltage command values. The PWM pulse controls ON/OFF of a semiconductor switch element of the inverter circuit31via a drive circuit to adjust an output voltage.

Note that, in a case of controlling a rotational speed of the motor2in the motor drive apparatus6, the motor rotational speed or is calculated from time change in the rotational position8, and a voltage command or a current command is created to coincide with a speed command from a host controller. Further, in a case of controlling motor output torque, the d-axis current command Id* and the q-axis current command Iq* are created using a relational expression or a map among the d-axis current value Id, the q-axis current value Iq, and motor torque.

Next, a voltage command generation unit13according to the present embodiment will be described with reference toFIG. 5.FIG. 5is a block diagram of the voltage command generation unit13. The voltage command generation unit13includes a voltage update timing generation unit131, a dq/three-phase voltage command conversion unit132, a triangular wave generation unit133, and a gate signal generation unit134.

The voltage update timing generation unit131determines voltage update timing according to a calculation load of a microcomputer.FIG. 6is a voltage update timing generation flow in the first embodiment.

The voltage update timing generation unit131changes an update cycle T1according to a processing load factor of the microcomputer on the basis of the voltage update timing generation flow inFIG. 6. A processing load factor of the microcomputer varies according to the calculation load. For example, a case of using rectangular wave control or torque pulsation suppression control for improving a voltage utilization factor is dealt with. A frequency of a carrier signal is fc. In this case, since current estimation calculation or control in which 6-times pulsation is superimposed on dq-axis currents is performed, a calculation amount is increased as compared with normal current control. In such a case, by extending the update cycle T1from 1/(2fc) used in the normal current control to 1/(fc) or 3/(2fc), calculation time necessary for the rectangular wave control or the torque pulsation suppression control can be secured.

FIGS. 7 to 9illustrate the voltage update timings in the update cycle T1. InFIGS. 7 to 9, a ratio between f1and fc is 15 when a motor electrical angular frequency is f1and the frequency of the carrier signal is fc.

FIG. 7illustrates the voltage update timing of when the update cycle T1is 3/(2fc). InFIG. 7, the voltage update timing is 3/2 times the one cycle (1/fc) of the carrier signal, and “ridge side/trough side/ridge side” and “trough side/ridge side/trough side” of the carrier signal that is a triangular wave alternately appear.

FIG. 8illustrates the voltage update timing of when the update cycle T1is 1/fc. InFIG. 8, the voltage update timing is one time the one cycle (1/fc) of the carrier signal, and “ridge side/trough side” of the carrier signal that is a triangular wave continuously appears. Hereinafter, the above voltage update timing is abbreviated as update timing of “ridge”.

FIG. 9illustrates the voltage update timing of when the update cycle T1is 1/(2fc). InFIG. 9, the voltage update timing is ½ times the one cycle (1/fc) of the carrier signal, and “ridge side” and “trough side” of the carrier signal that is a triangular wave alternately appear. Hereinafter, the above voltage update timing is abbreviated as update timing of “ridge-trough”.

The dq/three-phase voltage conversion unit132performs fixed coordinate conversion and two-phase three-phase conversion from the d-axis voltage command Vd* and the q-axis voltage command Vq* that are the outputs of the current control unit12, the rotational position8that is the output of the rotational position detector41, and the update cycle T1that is the output of the voltage update timing generation unit131to generate a U-phase voltage command value Vu*, a V-phase voltage command value Vv*, and a W-phase voltage command value Vw*.

The triangular wave generation unit133generates a triangular wave of the frequency fc of the carrier signal on the basis of the frequency fc of the carrier signal.

The gate signal generation unit134compares the U-phase voltage command value Vu*, the V-phase voltage command value Vv*, and the W-phase voltage command value Vw* that are the outputs of the dq/three-phase voltage conversion unit132with the triangular wave that is the output of the triangular wave generation unit133to generate a pulsed voltage. At that time, gate signals Gup, Gvp, and Gwp of an upper arm are logically inverted to generate lower arm gate signals Gun, Gvn, and Gwn.

By thinning the voltage update timing using the voltage update timing generation flow in the first embodiment illustrated inFIG. 6in this manner, the dq-axis voltage commands are calculated to the three-phase voltage commands, and the processing load of the microcomputer of the voltage command generation unit13to be compared with the triangular wave can be reduced.

Next, a second embodiment of the present invention will be described with reference to the drawings.

FIG. 10is a graph illustrating harmonic components of a voltage caused by a difference in voltage update timing illustrated inFIGS. 7 to 9of when a ratio of f1and fc is 15, where a motor electrical angular frequency is f1and a frequency of a carrier signal is fc.

At any voltage update timing, frequencies fc±2f1(13th order component and 17th order component inFIG. 10), fc±4f1(11th order component and 19th order component inFIG. 10), and 2fc±f1(29th order component and 31st order component inFIG. 10) occur.

Interference occurs between a rotating magnetic field of a stator and a magnetic field of a rotor due to the harmonic components of the voltage, resulting in occurrence of electromagnetic noise of frequencies fc±3f1and 2fc.

The above-described frequencies will be described in detail using actually measured electromagnetic noise of the motor as an example.FIG. 11is a graph of a measurement result of noise of the motor2driven by the inverter drive device. The voltage update timing T1of the voltage update timing generation unit131in this inverter drive device is (1/fc). At this time, the harmonic voltage output from the inverter31of the motor drive apparatus6is the harmonic voltage of when the voltage update timing T1inFIG. 10is (1/fc). When the voltage update timing T1is (1/fc), the harmonic voltage of a frequency fc±f1(14th order component and 16th order component inFIG. 10) occurs in addition to the harmonic voltages of the frequencies fc±2f1(13th order component and 17th order component inFIG. 10), fc±4f1(11th order component and 19th order component inFIG. 10), and 2fc±f1(29th order component and 31st order component in FIG.10).

When the harmonic voltage is applied to the motor, the current becomes a harmonic current having the same frequency as the voltage. Interfere occurs between the rotating magnetic field of the stator and the magnetic field of the rotor due to the frequencies fc±2f1(13th order component and 17th order component inFIG. 10) and fc±4f1(11th order component and 19th order component ofFIG. 10), resulting in occurrence of electromagnetic force of the frequency fc±3f1. Similarly, electromagnetic force of the frequencies fc±3f1and 2fc occurs. This electromagnetic force vibrates a motor case and a housing, resulting in the electromagnetic noise.

Meanwhile, when the voltage update timing T1inFIG. 10is (½fc), the harmonic voltage of the frequency fc±f1(14th order component and 16th order component inFIG. 10) does not occur. Therefore, frequencies of the electromagnetic force generated by the harmonic voltage are frequencies fc±3f1and 2fc. Further, when the voltage update timing T1inFIG. 10is (3/2fc), the harmonic voltage of the frequency fc±f1(14th order component and 16th order component inFIG. 10) does not occur and the harmonic voltage of frequencies (2fc)/3±f1and (2fc)/3±f1occur. Therefore, electromagnetic noise of a frequency (2fc)/3±2f1generated by the harmonic voltage occurs.

When a rotation speed of the motor changes, the motor electrical angular frequency f1changes accordingly. The frequency fc±3f1of the electromagnetic noise that changes according to the rotation speed of the motor, a natural frequency fm of a case housing (mechanism) of the motor2, and a frequency caused by electromagnetic exciting force generated in proportion to the rotational speed inherent to the magnetic design of the motor2resonate, so that the noise becomes large. As an example, in the measurement result of the electromagnetic noise of the motor2inFIG. 11, the noise of the frequency fc−3f1caused by the voltage harmonic of the inverter3coincides with the natural frequency fm of the motor structure system, and the noise becomes large due to the resonance.

Next, the noise due to the magnetic design of the motor will be described. The noise due to the magnetic design of the motor occurs depending on the number of poles of the rotor and the number of slots of the stator of the motor, a magnetic gap, a winding method of the stator, and the like, and generally occurs at N times the motor electrical angular frequency f1. For example, in the measurement result of the motor inFIG. 11, large noise occurs in the motor2at 12 times and 24 times the electrical angular frequency f1.

FIG. 12illustrates a table of frequencies of the electromagnetic noise generated by the motor2and the inverter3. When the electromagnetic force generated at these frequencies coincides with the natural frequency (fm1, fm2, fm3, or the like) of the case housing, vibration and noise due to the electromagnetic force become large.

In the second embodiment of the present invention, voltage command update timing and a frequency of a carrier signal are changed to avoid the resonance to minimize the electromagnetic noise, unlike the actually measured electromagnetic noise illustrated inFIG. 11.

Generally, a calculation load of a microcomputer increases as the voltage command update timing is set to ridge-trough update while increasing the frequency of the carrier signal. Therefore, in a case of increasing the frequency of the carrier signal, the voltage command update timing needs to be set to ridge update. In a case of using the same carrier frequency when switching the ridge-trough update and the ridge update, the carrier frequency coincides with natural frequencies fm1and fm2of the case housing as illustrated inFIG. 13, and the carrier electromagnetic noise becomes large.

FIG. 14illustrates an example of a method of changing the carrier frequency and the voltage update timing according to the second embodiment of the present invention. In the second embodiment of the present invention, two carrier frequencies: a first carrier frequency fc1and a second carrier frequency fc2are provided. When the rotation speed of the motor is low, the carrier frequency is set to the carrier frequency rather than to the natural frequencies fm1and fm2of the case housing. When the processing load of the microcomputer becomes high and the voltage update timing is set to the ridge update, the carrier frequency fc1is set to between the natural frequencies fm1and fm2of the case housing so as not to coincide with the frequency fc±3f1of the electromagnetic noise that radially spreads. With the setting, the resonance with the case housing is avoided, and the electromagnetic noise occurring in the motor drive system6can be reduced.

Further, when the rotation speed of the motor is low, the frequency fc2of the carrier electromagnetic noise occurring as the voltage update timing is set to T1may be caused to coincide with the natural frequency fm1or fm2of the case housing to generate sound with a small harmonic voltage.

Next, another embodiment in which the inverter drive device according to the present invention is applied to a vehicle will be described with reference toFIG. 15.

FIG. 15is a configuration diagram of a hybrid automobile system to which the inverter drive device of the present embodiment is applied. As illustrated inFIG. 15, the hybrid automobile system includes a power train in which the motor2is applied as a motor/generator.

In the automobile illustrated inFIG. 15, the reference numeral700represents a vehicle body. A front wheel axle701is rotatably supported on a front portion of the vehicle body700, and front wheels702and703are provided at both ends of the front wheel axle701. A rear wheel axle704is rotatably supported on a rear portion of the vehicle body700, and rear wheels705and706are provided at both ends of the rear wheel axle704.

A differential gear711that is a power distribution mechanism is provided in a central portion of the front wheel axle701and distributes rotational driving force transmitted from an engine710via a transmission712to the right and left front wheel axles701.

A pulley710aprovided on a crankshaft of the engine710and a pulley720aprovided on a rotation shaft of the motor2are mechanically coupled via a belt730between the engine710and the motor2.

As a result, the rotational driving force of the motor2can be transmitted to the engine710, and the rotational driving force of the engine710can be transmitted to the motor2. In the motor2, the rotor rotates as three-phase alternating current power controlled by the inverter3is supplied to a stator coil of the stator, and the rotational driving force according to the three-phase alternating current power is generated.

That is, the motor2operates as an electric motor under the control of the inverter3while operating as a generator that generates the three-phase alternating current power when electromotive force is induced in the stator coil of the stator as the rotor rotates by receiving the rotational driving force of the engine710.

The inverter3is a power conversion device that converts the direct current power supplied from the high-voltage battery5, which is a high-voltage (42 V or 300 V) system power supply, into the three-phase alternating current power, and controls the three-phase alternating current flowing in the stator coil of the motor2according to a magnetic pole position of the rotor according to an operation command value.

The three-phase alternating current power generated by the motor2is converted into the direct current power by the inverter3to charge the high-voltage battery5. The high-voltage battery5is electrically connected to a low-voltage battery723via a DC-DC converter724. The low-voltage battery723constitutes a low-voltage (14 V) power supply of the automobile, and is used as a power supply for a starter725for initial start (cold start) of the engine710, a radio, light, and the like.

When the engine710is stopped when the vehicle is stopped (idle stop mode) such as waiting for a traffic light, and when the engine710is restarted (hot start) at the time of re-departure, the inverter3drives the motor2to rotate the engine710. Note that, in a case where a charge amount of the high-voltage battery5is insufficient or a case where the engine710is not sufficiently warmed in the idle stop mode, the engine710is not stopped and the driving is continued. Further, during the idle stop mode, a drive source for auxiliary machinery that uses the engine710as a driving source, such as an air conditioner compressor, needs to be secured. In this case, the auxiliary machine is driven by driving the motor2.

Even in an acceleration mode or a high-load operation mode, the motor2is driven to assist driving of the engine710. Conversely, in a charging mode where the high-voltage battery5requires charging, the engine710causes the motor2to generate power to charge the high-voltage battery5. That is, a regeneration mode at the time of braking or deceleration of the vehicle is performed.

The electrically driven vehicle using the inverter drive device of the present embodiment reduces the electromagnetic noise while reducing the calculation load of the microcomputer, thereby reducing vibration-proof material, sound-proof material, and sound insulation material to be affixed to the vehicle body. Further, fuel economy can be improved by reducing these materials.

In the above-described embodiments, the case in which the motor drive apparatus6of the present embodiment is applied to the hybrid automobile system has been described. However, similar effects can be obtained in electric automobiles.

Further, in the above-described embodiment, the single inverter device has been described. However, it goes without saying that the present invention can also be applied to a motor drive system in which an inverter unit and a motor are integrated as long as the system has the above-described functions.

Note that the present invention is not limited to the above-described embodiments, and various modifications can be made without departing from the spirit of the present invention.

REFERENCE SIGNS LIST