JP3463169B2 - Power converter - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a power converter for converting direct current into alternating current or alternating current into direct current, and more particularly to PW.
The present invention relates to control of an M (pulse width modulation) inverter.

[0002]

[Prior Art] Electric Vehicle Research Society "Science of Electric Vehicles" 199
An example of an inverter modulation method is given in Fig. 1 on page 14 of the April 3 issue, "Evaluating Recent Inverter Control Technology". In an inverter for an electric railway vehicle, as shown in FIG. 2, when the output voltage fundamental frequency is low, control is performed to keep the ratio of the output voltage magnitude and the fundamental frequency constant (the region in which this control is performed is variable voltage). When the output voltage fundamental frequency rises and the output voltage reaches its maximum value, frequency control is performed while maintaining the maximum value voltage (the region where this control is performed is a constant voltage variable). We will call it the frequency domain). In the variable voltage variable frequency region, since the output voltage is adjusted by pulse width modulation control, a multi-pulse mode in which a half cycle of the output voltage is composed of a plurality of voltage pulses is used. On the other hand, in the constant voltage variable frequency region, the one-pulse mode in which a half cycle of the output voltage is configured by a single pulse is used in order to maximize the voltage utilization rate and downsize the device.

[0003]

A conventional inverter using a GTO thyristor as a switching element (hereinafter, referred to as
As shown in FIG. 3, the GTO inverter uses a multi-pulse mode of a pulse number switching method in which the number of pulses included in one cycle of the output voltage is switched and gradually reduced as the output voltage fundamental frequency increases. It was This is because the upper limit of the switching frequency of the GTO thyristor is several hundred Hz. In this method, since the switching frequency becomes discontinuous when the number of pulses is switched, there is a problem that the tone color change of the magnetic noise occurs due to the switching of the number of pulses, which is annoying. Further, in the GTO inverter, between the output voltage in the 3-pulse mode and the 1-pulse mode in which three voltage pulses are included in a half cycle of the output voltage, the output voltage of about 10% depends on the limitation of the minimum off time of the GTO thyristor. There is a problem of jumping, and there is a problem that the torque generated by the electric motor fluctuates when switching between the 3-pulse mode and the 1-pulse mode.

An object of the present invention is to prevent a large discontinuity in the switching frequency in a two-level inverter device which controls the magnitude of the output voltage from zero to the maximum voltage by a combination of the multi-pulse mode and the one-pulse mode, which is annoying. Eliminates the change in the timbre of magnetic noise, and multi-pulse mode 1
The purpose is to reduce the output voltage gap in the pulse mode and control the entire output voltage range almost continuously.

[0005]

In order to solve the above problems, a plurality of switching elements are controlled by a plurality of control modes to convert a DC voltage into a three-phase AC phase voltage of a variable voltage and a variable frequency, and the phase voltage thereof is changed. In a two-level power converter that outputs positive and negative binary pulses as a control mode, the control mode includes a pulse width modulation control mode in which a plurality of voltage pulses are output in a half cycle of the output voltage fundamental wave, and a half of the output voltage fundamental wave. The overmodulation control mode is interposed between the 1-pulse control mode that outputs a single voltage pulse in a cycle, and the overmodulation control mode moves from the peak of the output voltage fundamental wave to the zero crossing as the output voltage increases. The switching frequency is continuously changed by gradually increasing the voltage pulse cycle and controlling the switching asynchronously with the cycle of the output voltage fundamental wave. It is allowed, so that gradually lowers the switching frequency in accordance with the output frequency is increased.

[0006]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT An embodiment of the present invention will be described with reference to FIGS.
This will be described using 7. The PWM mode configuration of the inverter of the present invention is as shown in FIG. It operates in the bipolar mode (pulse width modulation control mode) in the low output voltage range, in the overmodulation mode (overmodulation control mode) in the high output voltage range, and in the 1 pulse mode (1 pulse control mode) in the maximum output voltage range. Here, the multi-pulse mode has a bipolar mode and an overmodulation mode. FIG. 1 is a configuration diagram showing an embodiment of the present invention, which is an example in which a voltage type two-level inverter is used as a control converter of an induction motor for driving an electric vehicle. In the figure, 6 is an induction motor, 5 is a two-level three-phase PWM inverter that drives the induction motor, 9 is a DC overhead wire that serves as a power source for the inverter, and 7 and 8 are a filter reactor and a capacitor on the DC input side of the inverter. The multi-pulse generation means 2, the 1-pulse generation means 3, and the PWM mode selection means 4 of FIG. 1 have the output voltage command E * of the inverter and the frequency command Fi * of each phase obtained by integrating the frequency command Fi * by the integrator 1. A control signal for the inverter is generated based on the phase θx of the output voltage fundamental wave (the subscript x is a general term for subscripts indicating the phase, that is, any one of u, v, and w phases). Of the control signals of the inverter, S1x, S2x, S
x is called a switching function and is defined as 1 when the positive arm of the inverter is on and 0 when the negative arm of the inverter is on.

First, a method of generating a control signal for the inverter will be described. FIG. 5 shows an example (for one phase) of the multi-pulse generation means 2 of FIG. Here, the switching functions of the bipolar mode and the overmodulation mode are generated by the same means. The output voltage command → modulation rate conversion means 21 obtains the modulation rate A, that is, the amplitude of the modulated wave from the output voltage command E *. If carrier wave amplitude is 1, 0 ≦ A ≦ in bipolar mode
1, A> 1 in the overmodulation mode. In order to match the magnitude of the output voltage fundamental wave with the voltage command, E * and A are made to correspond by (Equation 1) in the bipolar mode and (Equation 2) in the overmodulation mode.

[Equation 1]

[Equation 2] In the function y = sin (x) 22, the sin of the phase (equivalent to the phase of the modulating wave) θx of the output voltage fundamental wave is obtained. The product of this and the modulation factor A is the modulated wave ax. The modulated wave ax and the carrier frequency (equivalent to the switching frequency in the bipolar mode) Fc are given to the switching function calculating means 24 to obtain the switching function S1x. The switching function calculating means 24 generates a carrier wave which is a triangular wave having an amplitude of 1 and a frequency Fc, and compares it with the value of the modulated wave to generate a switching function. Further, the switching function may be obtained by calculation from the modulated wave ax and the pulse interval without using the triangular wave.

An example of the waveform of the switching function in the bipolar mode and the overmodulation mode obtained by the triangular wave comparison is shown in FIGS. 6 and 7, respectively. In the inverter device of the present invention, a device capable of switching at several kHz, such as an IGBT or a large-capacity power transistor, is used as a switching element (hereinafter, generically referred to as an IGBT inverter), and a modulated wave is used in the multi-pulse mode. And the carrier wave are asynchronous. In the bipolar mode shown in FIG. 6, since 0 ≦ A ≦ 1, the carrier 242 corresponds to the switching function 243, and the carrier 242 and the modulated wave 241 are not synchronized. Further, since A> 1 in the overmodulation mode shown in FIG. 7, a switching function 246 of a wide pulse is obtained in a portion where A exceeds 1, and a comparison is made between the carrier wave 245 and the modulated wave 244 in other portions. A switching function 246 is obtained. Also in this overmodulation mode, the carrier wave 245 and the modulated wave 244 are generated asynchronously. As described above, in the figure, for the sake of understanding, the method of obtaining the switching function by comparing the carrier wave and the modulation wave is shown, but the switching function can be obtained by calculation from the modulation wave ax and the pulse interval.

As a result, the switching frequency becomes constant in the bipolar mode and can gradually approach the switching frequency in the one-pulse mode described below in the overmodulation mode. In this multi-pulse mode, since the modulated wave and the carrier wave are asynchronous, the carrier wave frequency needs to be sufficiently higher than the modulated wave frequency.
It is desirable to be higher than 0 times.

FIG. 8 shows an example of the waveform of the switching function generated by the one-pulse generating means shown in FIG. The value of the switching function S2x is 1 when the sign of the fundamental wave 31 of the output voltage (the amplitude may be any value) is positive, and S when the sign is negative.
The value of 2x is 0.

Next, the combination of the multi-pulse mode and the one-pulse mode for controlling the high output voltage range will be described. Proceedings of the 1st Annual Meeting of the Institute of Electrical Engineers of Japan, Applied Industry, No. 1
06 "Overmodulation control system of voltage type three-phase PWM inverter"
There is. According to this, the operation with the extremely large modulation rate in the overmodulation mode is the operation of the 6-step inverter, namely, 1
It is said to be in pulsed mode of operation. However, if the 1-pulse mode is realized by extending the overmodulation mode (the 1-pulse mode is realized by making the modulation rate extremely large), the following inconvenience occurs. First, the point at which the overmodulation mode and the 1-pulse mode are switched depends on the switching frequency and cannot be set arbitrarily. Second, when the modulated wave in the overmodulation mode and the carrier are asynchronous (hereinafter referred to as asynchronous PWM), the modulated wave near the boundary between the overmodulation mode and the 1-pulse mode is affected by the turn-on and turn-off times of the element. The pulse near the zero cross may or may not come out. As a result, an imbalance occurs between the positive and negative output voltages, and a beat phenomenon occurs in which low-frequency pulsation is superimposed on the load current of the inverter.
Third, in the overmodulation mode, as shown in FIG. 7, the output voltage waveform (equivalent to the waveform of the switching function described later) has a uniform pulse interval near the zero cross of the modulation wave (equivalent to the output voltage fundamental wave). That is, it is divided into a portion where the pulse generation period is uniform (equal interval pulse) and a wide pulse portion centered on the peak of the modulation wave. Switching can occur. In this case, the load current of the inverter is disturbed,
The switching element may be destroyed or the torque generated by the motor may significantly change due to overcurrent.

To solve these problems, the voltage for switching the overmodulation mode and the one-pulse mode (hereinafter referred to as transition voltage) and the phase of the output voltage fundamental wave for switching (hereinafter referred to as transition phase) Manage. First, the management of the transition voltage will be described. When the transition voltage is set and the overmodulation mode and the 1-pulse mode are switched with the transition voltage as the boundary, it is desirable that the set value of the transition voltage is as close to the output voltage of the 1-pulse mode as possible, that is, 100%. This is because the smaller the difference from the maximum value of the output voltage in the overmodulation mode, the smaller the fluctuation in the torque generated by the electric motor during switching. However, in asynchronous PWM, the width of each voltage pulse included in one cycle of the fundamental of the output voltage becomes different for each cycle, and as the output voltage approaches 100% in the overmodulation mode, the zero crossing of the fundamental of the output voltage occurs. When the number of pulses in the vicinity decreases, this effect becomes apparent and an imbalance occurs between the positive and negative of the output voltage, and a beat phenomenon occurs in the load current of the inverter. An example of this state is shown in FIG.

FIG. 10 shows an example of the relationship between the average pulse number in the vicinity of the output voltage fundamental wave zero cross and the current pulsation due to the beat phenomenon. As shown in FIG. 7, the absolute value of the modulated wave is 1.0
Since the following portions correspond to equidistant pulses, the average pulse number is given by the formula shown in (Equation 3). The current pulsation rate is defined by (Equation 4).

[Equation 3]

[Equation 4] From FIG. 10, if at least one pulse is not secured near the zero cross of the output voltage fundamental wave, the low frequency pulsation of the load current of the inverter due to the beat phenomenon becomes extremely large. Therefore, the set value of the transition voltage is set to a value that secures at least one voltage pulse in the vicinity of the output voltage fundamental wave zero cross. Since this value depends on the output voltage fundamental wave frequency Fi * and the carrier frequency Fc in the multi-pulse mode, means for calculating from these values may be provided.
It may be set in advance by calculation from the upper limit of the output voltage fundamental wave frequency Fi *.

Next, the management of the transition phase will be described. Depending on the phase of the output voltage fundamental wave when switching between the overmodulation mode and the 1-pulse mode, the transient changes in the load current of the inverter and the torque generated by the motor immediately after switching differ. An example of current fluctuation is shown in FIG. The same figure (a)
As shown in FIG. 12, when the three phases are collectively switched at 0 ° in the phase of the U-phase output voltage fundamental wave, a transient fluctuation in the current is observed immediately after the switching. On the other hand, FIG.
As shown in FIG. 13, the phase of the output voltage fundamental wave of the U phase is 9
This is a case where the three phases are collectively switched at 0 °, and there is almost no transient fluctuation of the current.

FIG. 14 shows an example of the relationship between the phase of the output voltage fundamental wave (U phase reference) and the transient fluctuation of the current when the overmodulation mode is switched to the one-pulse mode in three phases at once.
Here, the current fluctuation rate is defined by (Equation 5).

[Equation 5] In FIG. 14, the current fluctuation rate increases every 60 ° in the phase of the output voltage fundamental wave. This is a case where the overmodulation mode and the 1-pulse mode are switched when any one of the three phases has equal-interval pulses in the overmodulation mode. Since the imbalance becomes large, the transient current fluctuation also becomes large.
Therefore, as shown in FIG. 15, by setting the transition phase in a portion where all the phases are wide pulses in the overmodulation mode, transient current and torque fluctuations can be suppressed.

Here, in order to switch the overmodulation mode and the 1-pulse mode collectively for the three phases, there must be a section in which the output voltage of the overmodulation mode for all three phases is a wide pulse. For this purpose, the crossing point (U
Based on the phase of the phase-modulated wave, 30 °, 90 °, 150
(°, 210 °, 270 °, 330 °), the absolute value of the modulated wave must be greater than 1.0. Considering the case of 30 °, au = Asin 30 °> 1.0 from A> 2, and in the overmodulation mode, the correspondence between the modulation rate A and the output voltage E * is given by (Equation 2), so E *> 95. Must be 6%. Therefore, in order to switch overmodulation mode and 1-pulse mode in a three-phase package, the transition voltage is higher than 95.6%, and at least one voltage pulse is secured in the vicinity of the output voltage fundamental zero cross by overmodulation. Becomes

FIG. 16 shows a configuration example of the PWM mode selection means 3 which realizes the management of the transition voltage and transition phase. The mode selection command generation means 32 compares the transition voltage Ec set in the transition voltage means 31 with the voltage command E * and generates a mode selection command Mc indicating which of the multi-pulse mode and the one-pulse mode should be selected. Here, the mode selection command Mc is obtained based on the output voltage command E *, but since the output voltage command E * uniquely corresponds to the modulation factor A, the modulation factor Ac corresponding to the transition voltage is previously set. The mode selection command Mc may be set in advance and the modulation ratio A may be compared to generate the mode selection command Mc. Further, in the variable voltage variable frequency region, the output voltage command and the output voltage fundamental wave frequency also uniquely correspond to each other. Therefore, the output voltage fundamental wave frequency Fic corresponding to the transition voltage is set in advance, and the frequency command Fi *
May be compared to generate the mode selection command Mc. The transitional phase management means 44 refers to Mc, compares the phase θx of the output voltage fundamental wave with the transitional phase θc set in the transitional phase setting means 43 when it is necessary to switch the modes, and θx is θ.
If it has reached c, the mode selection signal M is switched. The mode selection switches 45, 46, 47 select either the output S1x of the multi-pulse generation means or the output S2x of the one-pulse generation means according to the mode selection signal M to determine the switching function Sx.

The transition phase may be managed by the following method. Take the absolute value of the modulated wave of each phase,
If all three phases are greater than 1.0, then all phases are in the overmodulated wide pulse portion.
Therefore, at such a time point, the outputs of the multi-pulse generating means and the 1-pulse generating means are switched.

As described above, the gap between the output voltages in the multi-pulse mode and the one-pulse mode is reduced from about 10% in the conventional GTO inverter to about 1 to 2%, and the magnitude of the output voltage is changed from zero to the maximum voltage. Control almost continuously until
In addition, it is possible to configure a two-level inverter device that can smoothly switch between the multi-pulse mode and the one-pulse mode without changing the current or the torque generated by the electric motor. Further, the relationship between the output voltage fundamental wave frequency and the switching frequency in the present invention is as shown in FIG. 17, and there is no large discontinuity as in the conventional inverter modulation system of FIG. It is possible to eliminate a great change in tone color.

[0020]

INDUSTRIAL APPLICABILITY In an inverter device in which the magnitude of output voltage is controlled from zero to the maximum voltage by the combination of the multi-pulse mode and the one-pulse mode, it is possible to eliminate discontinuous change in magnetic noise and to reduce the entire output voltage range. Can be controlled almost continuously. Further, by adopting the overmodulation mode as the control mode, a two-level inverter device that can be smoothly switched without changing the current or the torque generated by the electric motor when switching between the multi-pulse mode and the one-pulse mode is configured. be able to.

[Brief description of drawings]

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

FIG. 2 is a diagram showing operating characteristics of a vehicle inverter.

FIG. 3 is a diagram showing an example of a conventional inverter modulation method.

FIG. 4 is a diagram showing operating characteristics of the inverter according to the present invention.

FIG. 5 is a diagram showing an example of a configuration of a multi-pulse generation means.

FIG. 6 is a diagram showing a modulated wave, a carrier wave, and a switching function in a bipolar mode.

FIG. 7 is a diagram showing a modulated wave in an overmodulation mode, a carrier wave, and a switching function.

FIG. 8 is a diagram showing a fundamental wave of an output voltage and a switching function in a 1-pulse mode.

FIG. 9 is a diagram showing how a beat phenomenon occurs.

FIG. 10 is a diagram showing the relationship between the average pulse number near the output voltage fundamental wave zero crossing and the current pulsation.

FIG. 11 is a diagram showing that the state of transient current fluctuation immediately after mode switching differs depending on the transition phase.

FIG. 12 is a diagram showing the switching timing of FIG.

FIG. 13 is a diagram showing the switching timing of FIG. 11 (b).

FIG. 14 is a diagram showing a relationship between a transitional phase and a transient current fluctuation immediately after mode switching.

FIG. 15 is a diagram showing transition phase settable sections.

FIG. 16 is a diagram showing an example of the configuration of PWM mode selection means.

FIG. 17 is a diagram showing the relationship between the output voltage fundamental frequency and the switching frequency of the inverter in the present invention.

[Explanation of symbols]

1 ... Integrator, 2 ... Multi-pulse generation means, 3 ... 1-pulse generation means, 4 ... PWM mode selection means, 5 ... 2-level three-phase P
WM inverter, 6 ... Induction motor, 7 ... Filter reactor, 8 ... Smoothing capacitor, 9 ... DC overhead wire, 21 ... Frequency command → modulation wave amplitude reference conversion means, 22 ... Function y = sin
(x), 23 ... Switching frequency, 24 ... Switching function computing means, 241, 244 ... Modulated wave ax, 24
2, 245 ... Carrier wave c, 243, 246 ... Switching function S1x, 31 ... Output voltage fundamental wave, 41 ... Transition voltage setting means, 42 ... Mode selection command generating means, 43 ... Transition phase setting means, 44 ... Transition phase management means , 45, 46, 4
7 ... Mode selection switch

Front page continuation (72) Inventor Mutsuhiro Terunuma 1070 Ige, Katsuta City, Ibaraki Prefecture Mito Plant, Hitachi, Ltd. (56) References JP-A-5-146160 (JP, A) JP-A-5-161364 (JP) , A) JP-A-3-32391 (JP, A) JP-A-62-163589 (JP, A) JP-A-62-131791 (JP, A) JP-A-63-287372 (JP, A) (58) Fields investigated (Int.Cl. ⁷ , DB name) H02M 7/48 H02M 7/5387 H02P 7/63

Claims (2)

(57) [Claims] 1. A two-level control circuit that controls a plurality of switching elements in a plurality of control modes to convert a DC voltage into a three-phase AC phase voltage having a variable voltage and a variable frequency, and outputs positive and negative binary pulses as the phase voltage. In the power converter, in the control mode, a pulse width modulation control mode for outputting a plurality of voltage pulses in a half cycle of the output voltage fundamental wave, and a single voltage pulse in a half cycle of the output voltage fundamental wave 1 An overmodulation control mode is interposed between the pulse control mode and the overmodulation control mode, in which the cycle of the voltage pulse is gradually increased from the peak of the output voltage fundamental wave toward the zero cross as the output voltage increases. At the same time, the switching frequency is continuously changed by performing switching control asynchronously with the cycle of the output voltage fundamental wave, and the output frequency is increased. Power conversion device is characterized in that the outer switching frequency so gradually lowered. 2. A plurality of switching elements are controlled in a plurality of control modes to convert a direct current voltage into a three-phase alternating current phase voltage having a variable voltage and a variable frequency, and a positive and negative binary pulse is output as the phase voltage. In a control device for an electric vehicle, which is provided with an electric power converter and an AC output from the electric power converter, and includes an electric motor for driving the electric vehicle, the control mode includes a plurality of voltages in a half cycle of an output voltage fundamental wave. An overmodulation control mode is interposed between a pulse width modulation control mode for outputting a pulse and a one-pulse control mode for outputting a single voltage pulse in a half cycle of an output voltage fundamental wave. As the output voltage increases, the cycle of the voltage pulse is gradually lengthened from the peak of the output voltage fundamental wave toward the zero crossing, and the switching voltage is switched asynchronously with the cycle of the output voltage fundamental wave. The switching frequency is continuously changed by controlling so that the switching frequency is gradually decreased as the output frequency increases, and when the electric vehicle is driven from the low speed range to the high speed range, the pulse width modulation control is performed. Mode, the overmodulation control mode,
A control device for an electric vehicle, wherein the one-pulse control mode is sequentially shifted.