JP2002300800A - Power converter - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a power converter for suppressing ripple current flowing in a current smoothing capacitor. SOLUTION: Three-phase bridge circuits 1A, 1B are connected to a power source comprising a battery Vb and the current smoothing capacitor C in parallel. Each bridge circuit operates in accordance with a PWM signal from drive circuits 11A, 11B, and power-converts to drive a first motor 25A and a second motor 25B. Triangular wave generators 7, 8 generate triangular waves TR1, TR2 having a phase difference of 90 degrees. When both the motors are during power running or regenerative operation, the PWM signal driving the first motor is generated on the basis of the triangular wave TR1, and the PWM signal driving the second motor is generated on the basis of the triangular wave TR2. The phase of the ripple current generated in each bridge circuit by the phase difference between both the triangular wave signals is shifted to 180 degrees to be canceled so as to suppress the ripple current flowing in the current smoothing capacitor C small.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a power conversion device in which generation of ripple current flowing through a current smoothing capacitor is suppressed.

[0002]

2. Description of the Related Art Hybrid electric vehicles having both a drive motor and an engine are commercially available. In this electric vehicle, the mounted power converter includes two bridge circuits, and drives a first motor that drives the vehicle and a second motor that starts the engine, respectively.

FIG. 8 is a diagram showing a power conversion device used in a conventional electric vehicle. The power converter includes a three-phase bridge circuit 50 for the first motor 25A and a second motor 25B.
And a three-phase bridge circuit 60 for each DC terminal.
It is connected in parallel to a power supply consisting of a vehicle-mounted battery Vb and a current smoothing capacitor 70. A drive signal for each motor created by the control unit 300 according to the driving state of the vehicle is output to the signal processing unit 400. The signal processing unit 400 generates a PWM signal for driving each motor in accordance with the drive signal, and outputs the generated PWM signal to the three-phase bridge circuit 50 and the three-phase bridge circuit 60, so that the first motor 25A and the second motor 2
5B is driven. The ripple current generated when each three-phase bridge circuit operates is absorbed by the current smoothing capacitor 70.

[0004] The ripple current of a power converter having one three-phase bridge circuit was introduced in the literature "Theoretical analysis of DC capacitor effective value current of voltage-type PWM bridge circuit (1995 IEEJ National Convention)". When calculated by the calculation method, the maximum value is about 0.7 times the effective value of the one-phase current of the motor.

In a power converter in which two three-phase bridge circuits as described above are connected in parallel to a power supply, the ripple current flowing through the current smoothing capacitor is equal to the combined value of the ripple current generated by each of the three-phase bridge circuits. Become. The ripple current at this time can be obtained by the following calculation using the equivalent electric circuit diagram shown in FIG.

(Equation 1) Here, ic is a ripple current flowing through the current smoothing capacitor 70. ica is a ripple current generated in the three-phase bridge circuit 50, and icb is a ripple current generated in the three-phase bridge circuit 60. i
a is the phase current of the first motor 25A, and ib is the phase current of the second motor 25B. Ia and Ib are the effective values of the phase current of each motor. T is the period of the current. That is, in a power converter having two three-phase bridge circuits, the magnitude of the ripple current flowing through the current smoothing capacitor is 0.7 times the sum of the phase currents of the two motors.

[0006]

However, in order to absorb such a large ripple current, a capacitor having a large ripple resistance must be used, and a capacitor having a large ripple resistance generally has a large capacitance. . In general, a large-capacity capacitor is large and expensive, so that a large and expensive capacitor must be used as a current smoothing capacitor. The present invention has been made in view of the above-described conventional problems, and has as its object to provide a power conversion device that suppresses a ripple current flowing through a current smoothing capacitor.

[0007]

According to the present invention, a first three-phase bridge circuit and a second three-phase bridge circuit respectively connected to a load have their DC terminals connected to a power source in parallel. In a power converter that is connected and performs power conversion with a PWM signal for operating a first three-phase bridge circuit and a second three-phase bridge circuit, a triangular wave generating means for generating a triangular wave is provided. Is capable of outputting two triangular waves having a predetermined phase difference to the PWM signal generating means of the first three-phase bridge circuit and the second three-phase bridge circuit.

According to a second aspect of the present invention, the load of the first three-phase bridge circuit and the load of the second three-phase bridge circuit are respectively the first three-phase bridge circuit.
A motor and a second motor, comprising: operating state detecting means for detecting an operating state of the first motor and the second motor; and a triangular wave generating means for detecting an operating state of the first motor and the second motor. , The phase difference of the triangular wave is switched.

According to a third aspect of the present invention, the operating state detecting means includes:
The operation states of the first motor and the second motor are detected based on the comparison of the torque current instruction values for controlling the respective motors.

According to a fourth aspect of the present invention, the first motor and the second motor
When both motors are in power running operation or regenerative operation, the phase difference is 45 ° to 135 °. When one motor is in power running operation and the other motor is in regenerative operation, the phase difference is 0 °. According to a fifth aspect of the present invention, when both the first motor and the second motor are in a power running operation or a regenerative operation, the phase difference is particularly set to 90 °.

[0011]

According to the first aspect of the present invention, since the triangular wave generating means generates two triangular waves having a predetermined phase difference, the first three-phase bridge circuit and the second three-phase bridge circuit respectively have a phase difference of three. A PWM signal is generated based on different triangular waves, and the phases of ripple current generated when the switching circuits of the respective bridge circuits operate can be shifted. Thereby, each ripple current is canceled by the current smoothing capacitor, and the ripple current flowing through the current smoothing capacitor is reduced. Therefore, a capacitor having a small ripple resistance can be used, and the size and cost of the device can be reduced.

According to the second aspect of the present invention, the phase difference of the triangular wave used for generating the PWM signal is switched according to the operating state of the first motor and the second motor. , The phase difference of the ripple current can be appropriately shifted, and the same effect as in the first aspect can be obtained without narrowing the operation range.

According to the third aspect of the present invention, since the operating states of the first motor and the second motor are determined by comparing the torque current command values for controlling the respective motors, no special circuit such as a sensor is required. In addition, the operating state of each motor can be easily determined with little noise.

According to the present invention, the phase of the triangular wave is set to 45.
Ripple current can be effectively reduced by shifting the angle by 135 ° to 135 °. In particular, by setting the phase difference of the triangular wave to 90 degrees as in claim 5, the phase difference of the ripple current can be set to 180 degrees, and the ripple current can be reduced to the maximum. As a result, a capacitor having a very small ripple resistance can be used as a current smoothing capacitor, and the size and cost of the device can be reduced.

[0015]

Embodiments of the present invention will be described below in detail. In the present embodiment, a description will be given assuming that the power conversion device is applied to an electric vehicle. FIG.
FIG. 1 is a configuration diagram illustrating a configuration of an embodiment. In-vehicle battery V
The DC terminals of the three-phase bridge circuit 1A and the three-phase bridge circuit 1B are connected in parallel to a power supply consisting of b and a current smoothing capacitor C. Each of the three-phase bridge circuits 1A and 1B is a bridge circuit including switching elements Q1a to Q6a and Q1b to Q6b. The AC terminals of each three-phase bridge circuit are connected to a first motor 25A and a second motor 25B, respectively.
Is connected to The first motor 25A is a motor for driving the vehicle, and the second motor 25B is a motor for starting and generating power, each of which is a three-phase synchronous motor. The two three-phase bridge circuits are controlled by the control unit 20. Further, the phase currents when the motors 25A and 25B are driven are detected by the respective current sensors and input to the control unit 20.
Here, the phase current of the first motor 25A is represented by iua, iv
a, iwa, and the phase current of the second motor 25B is iub,
ivb and iwb.

Next, the control section 20 will be described. 3
The phase currents ua, iva, and iwa of the phases are output from the A / D converter 2
A converts it into a digital signal and outputs it to the 3-2 converter 3A. The three phase currents are converted here as current signals ida and iqa on the d-axis and the q-axis and output to the current control unit 4A. Current instruction values ida * (excitation current) and iqa * (torque current) for controlling the first motor 25A are input to the current control unit 4A, and the current signals ida and iqa are ida *, iqa * and voltage signals vda * and v for performing PI control, respectively.
qa * is created. This voltage signal is output from the 2-3 conversion unit 5A.
Where the three-phase voltage indication values vua *, vv
It is converted to a *, vwa *.

A triangular wave generator 7 is connected to the minus end of the comparator 6A.
, And voltage indication values vua *, vva *, and vwa * from the 2-3 conversion unit 5A.
Here, by comparing the amplitude with the triangular wave, the PWM
Signals pua, pva, and pwa are generated. The PWM signals pua, pva, and pwa are output through the drive circuit 11A,
The three-phase bridge circuit 1A is operated.

Similarly, on the second motor 25B side, the phase currents iub, ivb, iwb of the second motor 25B are converted into digital signals by the A / D converter 2B and output to the 3-2 converter 3B. . The three-phase current is calculated by the 3-2 conversion unit 3
After being converted as current signals idb and iqb on the d-axis and q-axis by B, the current control unit 4B compares the current instruction values idb * and iqb * for controlling the second motor 25B by Voltage signal vdb for performing PI control
*, Vqb * are created. This voltage signal is converted by the 2-3 converter 5b into three-phase voltage indication values vub *, vvb *, vw.
b *.

The minus end of the comparing section 6B is switched to and connected to triangular wave generators 7 and 8 via a switch circuit 10. The voltage instruction values vub *, vvb *, vwb * from the 2-3 conversion unit 5B are compared in amplitude with the input triangular wave in the comparison unit 6B to generate PWM signals pub, pvb, pwb. PWM signal p
ub, pvb, and pwb are transmitted through the drive circuit 11B to 3
The phase bridge circuit 1B is operated.

The triangular wave generator 8 generates a triangular wave having a phase difference of 90 ° with respect to the output of the triangular wave generator 7 in synchronization with the triangular wave generator 7. First motor 25A
The current instruction value iqa * of the second motor 25B and the current instruction value iqb * of the second motor 25B are input to the phase determination unit 9, and the phase determination unit 9 determines the first motor 25A and the second motor 25A based on the input signal.
The operation state of the motor 25B is determined. The switch 10 is switched based on the result of the determination.

That is, when both the first motor 25A and the second motor 25B are in the power running operation or the regenerative operation, a triangular wave generated by the triangular wave generator 8 is output to the comparison unit 6B. When one is a power running operation and the other is a regenerative operation, a triangular wave generated by the triangular wave generator 7 is output. Thereby, the first motor 25A and the second motor 25B have a phase difference of 90 in the same operation state.
° Each PWM signal will be created based on different triangular waves. In the case of different operating states, the PWM signal is generated based on the same triangular wave, that is, a triangular wave having a phase difference of 0 °. Here, the triangular wave generator 7
And 8 and the switch 10 constitute the triangular wave generating means of the present invention, and the phase judging section 9 constitutes the operating state detecting means.

The control unit 20 described above may be constituted by a discrete circuit or the A / D converter 2
Except for A and 2B, a microcomputer may be used. FIG. 2 is a flowchart illustrating a control flow when the control unit 20 is configured by a microcomputer. First, in steps 100 and 101,
The current control units 4A and 4B read the current instruction values ida * and idq * of the first motor 25A and the current instruction values idb * and iqb * of the second motor 25B, respectively.

In steps 102 and 103, the 3-2 converters 3A and 3B output the phase currents iua, iva and iwa of the first motor 25A detected by the current sensor.
a and the phase currents iub, ivb, iw of the second motor 25B.
b are read via the A / D converters 2A and 2B, respectively, and the phase currents iua, iva and iwa of the first motor 25A read by the 3-2 conversion units 3A and 3B, and the phase current iub of the second motor 25B are read. , Ivb, iwb, the d-axis,
They are converted into current signals ida, iqa and idb, iqb on the q-axis, respectively, and output to the current controllers 4A, 4B.

In Steps 104 and 105, the current controllers 4A and 4B compare the phase current with the current instruction value to obtain the voltage signals vda *, vqa * and vdb *, v
qb * is calculated and output to the 2-3 conversion units 5A and 5B, and the 2-3 conversion units 5A and 5B output the voltage signal vda
*, Vqa *, vdb *, and vqb * are designated as voltage instruction values vua *, vva *, vwa * of the first motor 25A,
Voltage indication values vub *, vvb *, v of second motor 25B
wb *, and convert them into comparison units 6A and 6B.
Output to The above control is the same as the conventional vector control.

In step 106, the triangular wave generators 7 and 8 generate a triangular wave signal TR1 and a triangular wave signal TR2 having a phase difference of 90 ° with respect to TR1. In step 107, the phase determination unit 9 determines that the current instruction value i
The operation state of the first motor 25A and the second motor 25B is determined by comparing qa * and iqb *.

When both of the current instruction values are positive or negative, the first motor 25A and the second motor 25B are in the same operation state. At this time, the triangular wave signal TR1 and the second motor 25A are controlled to control the first motor 25A. The switch 10 is set so that the triangular wave signal TR2 is used for controlling the motor 25B. When one of the current instruction values is positive and the other is negative, the first motor 25A and the second motor 25B are in different operation states, and at this time, the switch 10 is switched to
The same triangular wave signal TR1 is set to control both the motor 25A and the second motor 25B.

In step 108, the comparator 6A compares the amplitudes of the specified voltage values vua *, vva *, and vwa * with the triangular wave signal TR1, and outputs the PWM signals pua, pva, pwa for controlling the first motor 25A. Calculate. In step 109, the comparator 6B compares the amplitude of the voltage instruction values vub *, vvb *, and vwb * with the input triangular wave signal TR1 or TR2,
A PWM signal pub for controlling the second motor 25B,
Calculate pvb and pwb. By the above calculation, the obtained PWM signals are output to the respective drive circuits 11A and 11B, and the three-phase bridge circuits 1A and 1B are controlled.

Next, the effect of the above configuration will be described with reference to FIGS. FIG. 3 is a diagram showing the instruction voltage vua * of the first motor 25A, the triangular wave TR1, and the waveform of the PWM signal pua based on these. FIG. 4 shows the first motor 25.
FIG. 7 is a diagram illustrating a DC-terminal (DC) -side current ica of the three-phase bridge circuit 1A when it is assumed that iua flows in the u phase of A.

The current ica is a current having a cycle twice that of the triangular wave shown in FIG. This is because the current becomes 0 at both the positive and negative vertexes of the triangular wave. The effective value of the AC component of the current ica (corresponding to a single ripple current) is about 0.6 · Iua (I
ua is the effective value of iua).

FIGS. 5 and 6 show waveforms on the second motor 25B side. First motor 25A and second motor 25B
5 is a power running operation, the triangular wave shown in FIG. 5 is a waveform of TR2, which is ahead of TR1 shown in FIG. 3 by 90 °. For this reason, the current icb of the three-phase bridge circuit 1B shown in FIG.
It can be seen that it is shifted by °.

Also in this case, the effective value of the AC component of the current icb is about 0.6 · Iub (Iub is i
ub). As described above, the phases of the currents generated on the DC side of the respective three-phase bridge circuits are shifted by 180 °, so that the currents cancel each other out, thereby reducing the ripple current flowing through the current smoothing capacitor C.

FIG. 7 shows a waveform of a ripple current flowing through the smoothing capacitor C. However, the AC components of the currents ica and icb all flow through the capacitor, and Ia = Ib. The phases of the currents ica and icb are
Since the phases of the triangular waves TR1 and TR2 for generating the M signal are shifted by 90 °, they are shifted by 180 °, and merge with each other in a direction to cancel each other. At this time, the effective value of the ripple current ic flowing through the current smoothing capacitor C is
It is about 0.3 · (Ica + Icb), which is equal to the ripple current when one motor is used.

The present embodiment is configured as described above. When the first motor 25A and the second motor 25B are in the same operation state, the respective triangular waves are shifted by 90 °,
Ripple current can be halved. Further, when the first motor 25A and the second motor 25B operate in different operation states, the ripple current is similarly canceled by reducing the phase difference to 0 ° using the same triangular wave.

As a result, as the current smoothing capacitor C, one having a small ripple resistance can be used, and the cost can be reduced. In the present embodiment, the first motor 25A and the second motor 25B are all three-phase synchronous motors. However, the same effects can be obtained with an entirely similar configuration using an induction motor.

In the case where the phase difference of the triangular wave is changed by switching between power running and regeneration during the operation of the vehicle, the PWM
Although there is a possibility that one pulse is missing from the signal, such a missing pulse hardly affects the motor current because the period of the triangular wave is usually sufficiently short with respect to the time constant of the motor.

In addition to the determination of the operating state of the motor based on the current instruction value, the determination can be made based on the motor current or the increase in the voltage at the DC terminal of the three-phase bridge circuit. However, the determination based on the current instruction value is particularly advantageous in that separate measurement is unnecessary and noise is reduced. In addition, at the time of switching between powering / regeneration or at the time of indicating the minimum current, it is conceivable that the current instruction value and the actual operation state are different, but at the time of switching between powering / regeneration, only a shift of several tens of milliseconds occurs. In the case of the minimal current instruction, the ripple current does not cause any problem, so that there is no substantial effect.

In the embodiment, the phase difference has been described as 90 °. However, according to the simulation, a substantial ripple reduction effect can be obtained within the range of 45 ° to 135 °. It could be confirmed. In this embodiment, an electric vehicle has been described as an example. However, any electric vehicle having a plurality of bridge circuits and absorbing a ripple current with the same capacitor can be applied. Needless to say.

[Brief description of the drawings]

FIG. 1 is a configuration diagram showing an embodiment of the present invention.

FIG. 2 is a flowchart showing a flow of control in the embodiment.

FIG. 3 is a diagram showing waveforms of a command voltage, a triangular wave, and a PWM signal of a first motor.

FIG. 4 is a diagram showing a phase current of a first motor and a DC terminal side current of a three-phase bridge circuit.

FIG. 5 is a diagram showing waveforms of a command voltage, a triangular wave, and a PWM signal of a second motor.

FIG. 6 is a diagram showing a phase current of a second motor and a DC terminal side current of a three-phase bridge circuit.

FIG. 7 is a diagram showing a waveform of a ripple current flowing through a smoothing capacitor.

FIG. 8 is a diagram showing a conventional example.

FIG. 9 is an equivalent electric circuit diagram for calculating a ripple current.

[Explanation of symbols]

 1A, 1B Three-phase bridge circuit 2A, 2B A / D converter 3A, 3B 3-2 conversion unit 4A, 4B Current control unit 5A, 5B 2-3 conversion unit 6A, 6B Comparison unit 7, 8 Triangular wave generator 9 Phase Judgment unit 10 Switch 11A, 11B Drive circuit 20 Control unit 25A First motor 25B Second motor C Current smoothing capacitor Vb In-vehicle battery

 ──────────────────────────────────────────────────続 き Continuing on the front page F term (reference)

Claims (5)

[Claims] A first three-phase bridge circuit and a second three-phase bridge circuit, each connected to a load, have their DC terminals connected in parallel to a power supply, and the first three-phase bridge circuit and the second three-phase bridge circuit In a power conversion device that performs power conversion with a PWM signal for operating a three-phase bridge circuit, a triangular wave generating means for generating a triangular wave is provided, and the triangular wave generating means includes the first three-phase bridge circuit and the second triangular wave generating means. A power conversion device capable of outputting two triangular waves having a predetermined phase difference to a PWM signal generating means of a three-phase bridge circuit. 2. The first three-phase bridge circuit and a second three-phase bridge circuit.
Wherein the load of the three-phase bridge circuit is a first motor and a second motor, respectively, and has operation state detection means for detecting the operation state of the first motor and the second motor. The power converter according to claim 1, wherein the phase difference of the triangular wave is switched based on the operating states of the first motor and the second motor. 3. The system according to claim 2, wherein the operating state detecting means detects an operating state of the first motor and the second motor based on a comparison of a torque current instruction value for controlling each motor. 3. The power converter according to 2. 4. When both the first motor and the second motor are in power running operation or regenerative operation, the phase difference is set to 45
4. The power converter according to claim 2, wherein the phase difference is set to 0 ° to 135 °, and the phase difference is set to 0 ° when one motor is in power running operation and the other motor is in regenerative operation. 5. 5. When the first motor and the second motor are both in power running operation or regenerative operation, the phase difference is set to 90.
5. The power converter according to claim 4, wherein the angle is set to °.