JPH08223940A - Voltage-fed self-excited multiple conversion apparatus and its power conversion method - Google Patents

Abstract

PURPOSE: To connect DC circuits in series and to increase a DC voltage in a voltage-fed self-excited multiple conversion apparatus which uses a plurality of voltage-fed self-excited converters and in which AC windings for a transformer for the conversion apparatus are connected in series so as to be multiple. CONSTITUTION: DC voltages of respective converters 41, 42 are detected by detectors 71, 72, their difference voltage is found by a control circuit 11, and a voltage share is controlled so as to be uniform. The phase and the amplitude of an AC current are detected by a detector 30. On the basis of the control output of the control circuit 11, a sine-wave correction signal whose phase is equal to that of the AC current and whose amplitude is in inverse proportion to the amplitude of the AC current is generated from a correction signal generator 12, the signal is added to, or subtracted from, input signals of PWM phase generators 21, 22 for the respective converters 41, 42, and AC voltages of the respective converters 41, 42 are corrected. Thereby, in a constitution in which DC circuits are connected in series, a voltage share can be controlled so as to be uniform, and a DC voltage can be increased.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a semiconductor power converter, and more particularly, to a method of connecting AC voltages of a plurality of voltage source self-exciting converters in series with AC windings of a converter transformer and adding the AC voltages. The present invention relates to a multiplexed voltage type self-excited multiplex converter and its power conversion method.

[0002]

2. Description of the Related Art FIG. 9 is a block diagram of a voltage type self-excited multiplex converter which is multiplexed by using a plurality of voltage type self-excited converters.
That is, the DC circuits of the converters 41, 42 are connected in parallel, while the AC side of each converter is connected to the transformers 51, 52 for the converter, and the transformer 51, 52 for the converter is connected. The 52 AC windings are connected in series. Therefore, the AC voltage is added.

In the configuration of the conventional converter shown in FIG. 9, since the DC circuits of the converters 41 and 42 are connected in parallel, it is difficult to increase the DC voltage. For this reason,
When it is necessary to increase the DC voltage, a configuration in which DC circuits are connected in series can be considered as shown in FIG. 8 or 7. However, according to these configurations, the converted powers of the converter 41 and the converter 42 are not necessarily equal due to the influence of a control error or the like, which causes a problem that the DC voltage cannot be shared. In order to solve this problem, it is necessary to control the DC voltage distribution to be uniform.

In the case of the configuration of FIG. 8, the two converters can be independently controlled because the AC side of the transformer for the converter is connected in parallel, and the voltage sharing can be easily controlled by each converter. Is. However, since the AC side is connected in parallel, there is a drawback that a cross current is generated between the two converters via the transformers 51 and 52 for the converter. Particularly in a high-power converter, since the number of pulses is reduced, it is difficult to suppress the cross current, and there are many problems in its adoption.

In the case of the configuration shown in FIG. 7, the transformer 5 for the conversion device is used.
Since the AC windings of 1,52 are connected in series and the AC current is common, the two converters cannot be controlled independently,
It is difficult to perform voltage sharing control. For this reason, for example, there is a structure shown in S.7-5 New Energy and Power Electronics in the 1988 National Congress of the Institute of Electrical Engineers of Japan,
There is a problem that the circuit becomes complicated. There is also a problem that it cannot be adopted when the number of series is three or more.

[0006]

In order to handle a high DC voltage, it is necessary to connect three or more DC circuits in series. However, in order to apply it to an actual machine, the circuit configuration is simplified and the DC voltage sharing is uniform. There is a problem that it has to be realized. This problem cannot be solved by the above-mentioned conventional technique, and a new technique needs to be developed.

An object of the present invention is to provide a uniform DC voltage with a simple circuit configuration in a multiple voltage type self-excited multiplex converter in which DC circuits are connected in series and AC windings of a transformer for a converter are connected in series. To provide a voltage-type self-excited multiplex conversion device that can be realized and a power conversion method thereof.

[0008]

The object of the above is to connect the AC voltages of a plurality of converters in series on the AC winding side of a transformer for a converter and to multiplex the DC voltage of each converter in series. In the connected voltage type self-exciting multiplex converter, a correction signal for correcting the AC voltage of each converter is generated from the difference voltage between the DC voltage of each converter and the average value of the DC voltage of all converters. This is achieved by adding the correction signal to the control signal of the converter, correcting the AC voltage of each converter by the addition, adjusting the DC voltage, and matching the DC voltage to the average value.

The above-mentioned object is preferably achieved by detecting the phase of the alternating current and making the phase of the correction signal the same as the detected phase.

The above object is preferably accomplished by detecting the amplitude of the alternating current and making the amplitude of the correction signal inversely proportional to the detected amplitude.

The above object is preferably achieved by making the correction signal a sine wave.

[0012]

The alternating current of each converter is common, and by correcting the alternating voltage of each converter, it is possible to correct the conversion power of each converter and make the voltage sharing uniform. At that time, the correction voltage can be set to 0 in total for all converters, so that there is no interference between the voltage sharing control and the control of the converter.

Further, when the correction voltage is synchronized with the AC current phase, the correction can be performed regardless of the direction of the conversion power of each converter.

Further, by making the magnitude of the correction voltage inversely proportional to the magnitude of the alternating current, the correction control is not affected by the magnitude of the current, and the voltage sharing can be equalized.

Furthermore, by making the correction voltage waveform a sine wave, it is possible to make the voltage distribution uniform without causing distortion of the output voltage.

[0016]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to the drawings. First, before describing the embodiments, the problem of voltage sharing will be examined in detail. For simplification, consider a case where two converters are connected in series as shown in FIG. The configuration including the control device is shown in FIG. The entire device is the control device 2
It is controlled by the signal Vc from 0. PWM (pulse width modulation) control is usually used for the pulse control of each converter. That is, Vc is the PWM pulse generator 2 of each converter
1, 22 to generate ON / OFF pulses of the converters, and the converters 41, 42 operate accordingly.

As a result, the converters 41 and 42 generate AC voltages v1 and v2 in the DC windings of the converter transformers 51 and 52, respectively. Only the fundamental wave component is extracted and defined as v1 = √2 · V1 · sin (ωt) (1) v2 = √2 · V2 · sin (ωt) (2). V1 and V2 are effective values of AC voltage, ω is angular frequency,
t is time. In the figure, a three-phase converter is used, but in that case, the above voltage may be considered as its positive phase component.

The AC windings of the converter transformers are connected in series, and the AC current i of each converter has a common value i = √2 · I · sin (ωt + φ) (3). I is the effective value of the alternating current, and φ is the phase with respect to the voltage. The output power of each converter is: converter 41 P1 = V1 · I · cosφ (4) converter 42 P2 = V2 · I · cosφ (5)

By the way, the output voltage of the converter is generally controlled by PWM as described above. DC voltage of each converter is E
When d1 and Ed2 are set and the PWM modulation rate is k, the AC voltage effective value of each converter is V1 = A · k · Ed1 (6) V2 = A · k · Ed2 (7). However, A is a proportional constant. Substituting this into Eqs. (4) and (5), P1 = A · k · Ed1 · I · cosφ (8) P2 = A · k · Ed2 · I · cosφ (9) The DC current of each converter is Id1 = P1 / Ed1 = A · k · I · cosφ (10) Id2 = P2 / Ed2 = A · k · I · cosφ (11) From this, it can be seen that Id1 and Id2 are basically the same even if the DC voltage is different.

In practice, the converter is affected by PWM error and the like, and differs from the above ideal value. As a result, a difference occurs between Id1 and Id2, causing an imbalance in voltage sharing. Even if an imbalance occurs, the higher voltage does not have the function of reducing the current and correcting the voltage sharing as in the above result, and the imbalance expands without being corrected.

As another method, as shown in FIG.
There is a method of normalizing the control signal Vc to the reference DC voltage Ed at the PWM pulse generator input so that the AC voltage of each converter is not affected by the DC voltage. This is to detect the DC voltage of each converter with the DC voltage detectors 71 and 72,
This is a method of multiplying Vc by (Ed / Edn) times (n = 1, 2) in the arithmetic units 26 and 27. In this case, the modulation factor of each converter is k (Ed /
Since Ed1) and k (Ed / Ed2), V1 = A · k · Ed (12) V2 = A · k · Ed (13) Id1 = P1 / Ed1 = A · k (Ed / Ed1) I · cosφ ( 14) Id2 = P2 / Ed2 = A · k (Ed / Ed2) I · cosφ (15), the absolute value of the current becomes smaller as the DC voltage becomes higher, and in the case of forward conversion (cosφ is positive), the voltage becomes rather It increases the sharing imbalance.

Therefore, in the first embodiment of the present invention, the configuration shown in FIG. 1 is used to balance the voltage sharing.
In FIG. 1, the DC circuits of the two converters 41, 42 are connected in series, and the AC windings of the converter transformers 51, 52 connected to the converters 41, 42 are also connected in series. There is.

The entire converter is controlled by the controller 20. Examples of this control include active / reactive power control of the converter and direct-current voltage control with total series. The control pulse of each converter 41, 42 is generated by the PWM pulse generator 2
1 and 22 occur. The DC voltage of each converter 41, 42 is made uniform by the DC voltage sharing control device 10.
In order to detect the DC voltage, the DC voltage detectors 71, 72
Is used. The alternating current phase detector 30 calculates the phase and amplitude of the alternating current detected by the alternating current detectors 81, 82 and 83.

Next, the operation of the voltage type self-excited multiplex converter shown in FIG. 1 will be described. The output signal Vc of the control device has a magnitude proportional to the modulation factor k and synchronized with the AC voltage phase,
In sinusoidal modulation, Vc = k · sin (ωt) (16).

The DC voltage sharing control device 10 receives DC voltages Ed1 and Ed2 of the converters from the DC voltage detectors 71 and 72, respectively. The difference voltage control circuit 11 detects the difference in DC voltage Ed1.
-Ed2 is obtained, a control operation for making the deviation zero is performed, and the operation output ΔU is output.

The AC current phase detector 30 uses the reference phase signal ωt of the AC voltage to detect the AC current detectors 81, 82,
The phase φ and amplitude (effective value) I of the alternating current are obtained by, for example, Fourier transforming the alternating current detected at 83.

The correction signal generator 12 generates a correction signal of C = (ΔU / I) sin (ωt + φ) (17) from ΔU, φ, and I, which is output signal Vc of the controller.
Add or subtract to. In the PWM control device 21, Vc + C is P
Vc-C is input to the WM control device 22. That is, each input signal is Vc1 = k.sin (ωt) + (ΔU / I) sin (ωt + φ) (18) Vc2 = k · sin (ωt)-(ΔU / I) sin (ωt + φ) (19) When the AC voltage of each converter is extracted by the fundamental wave, the amplitude is √2 · A · Edn with respect to the input of the PWM control device.
(n = 1, 2) times, and the fundamental wave component is v1 = √2 · A · Ed1 {k · sin (ωt) + (ΔU / I) sin (ωt + φ)} (20) v2 = √ 2 · A · Ed2 {k · sin (ωt) − (ΔU / I) sin (ωt + φ)} (21) The total voltage is v1 + v2 = 2√2 ・ A ・ (Ed1 + Ed2) ・ k ・ sin (ωt) + √2 ・ A ・ (Ed1-Ed2) ・ (ΔU / I) ・ sin (ωt + φ) (22), and Ed1 ≒ Since it is Ed2, the total voltage is hardly affected by the correction signal.

Since the alternating current is i = √2 · I · sin (ωt + φ) (23), the converted power is P1 = A · Ed1 (k · I · cosφ + ΔU) (24) P2 = A · Ed2 (k)・ I · cosφ-ΔU) (25) The direct current of each converter is Id1 = P1 / Ed1 = A (k.I.cos.phi. +. DELTA.U) (26) Id2 = P2 / Ed2 = A (k.I.cos.phi .-. DELTA.U) (27). From this, the DC current of each converter can be corrected by ΔU, and ΔU can be calculated from the differential voltage of the DC voltage by the differential voltage control circuit 1
Since it is controlled by 1, the voltage sharing can be made uniform.

In this embodiment, even if correction is performed, the total voltage is hardly affected by the correction. Since the correction signal is synchronized with the phase of the alternating current, the correction can be performed with the same polarity regardless of the phase of the alternating current, that is, the direction of power conversion and the status of active / reactive power. Since the correction signal is inversely proportional to the amplitude of the current, constant correction is possible regardless of the magnitude of the current. Since the correction signal is a sine wave, the output voltage is not distorted.

As the alternating current, a set value may be used instead of the detected value. When the AC current is 0, control cannot be performed, so the limiter is set to the minimum current. In this case, if the power factor is set to 0, it is possible to prevent the active power from being output.

In the present embodiment, the control is performed from the differential voltage of the DC voltage, but the average DC voltage EdAV = (Ed1 + Ed2) / 2 (28) is calculated and the DC voltage and the average voltage are calculated for each converter. It is the same even if controlled from the voltage difference between For example, in the proportional control of the gain K, the control calculation result of each converter is ΔU1 = K (Ed1-EdAV) = K (Ed1-Ed2) / 2 (29) ΔU2 = K (Ed2-EdAV) = K (Ed2- Ed1) / 2 = -ΔU1 (30), which is the same as the above except that the gain is halved.

FIG. 2 is a block diagram of a voltage type self-excited multiplex converter according to a second embodiment of the present invention. In this embodiment, the average DC voltage is calculated by the average DC voltage detector 13 and the control signal is normalized by the average DC voltage, so that the polarity of power conversion is not affected as in the conventional example of FIG. Correction control is possible and a normalization function is also possible.

FIG. 3 is a block diagram of a voltage type self-excited multiplex converter according to a third embodiment of the present invention. Although this embodiment shows the case where four converters are connected in series, it is generally applicable to a case where three or more converters are connected in series. In the present embodiment, the average DC voltage detector 13 calculates the average value of the DC voltage of each converter EdAV = (Ed1 + Ed2 + Ed3 + Ed4) / 4 (31), and each converter is supplied with the DC voltage Edn (n = 1 to 4). And the average value EdAV. Other configurations are similar to those of the above-described embodiment.

FIG. 4 is a block diagram of a voltage type self-excited multiplex converter according to a fourth embodiment of the present invention. In this embodiment, the DC circuits 41 and 42 of the converter are connected in parallel, and the DC circuit 4
3, 44 are connected in parallel, and these two parallel circuits are connected in series. Other configurations are the same as those of the other embodiments described above.

[0035]

According to the present invention, since the voltage sharing among the converters connected in series is controlled, the voltage sharing can be equalized. As a result, the converters can be easily connected in series, and there is an effect that a converter in which the DC voltage is high can be easily provided by the series connection.

[Brief description of drawings]

FIG. 1 is a configuration diagram of a voltage type self-exciting multiplex converter according to a first embodiment of the present invention.

FIG. 2 is a configuration diagram of a voltage type self-excited multiplex converter according to a second embodiment of the present invention.

FIG. 3 is a configuration diagram of a voltage type self-exciting multiplex conversion device according to a third embodiment of the present invention.

FIG. 4 is a configuration diagram of a voltage type self-exciting multiplex converter according to a fourth embodiment of the present invention.

FIG. 5 is a diagram showing a conventional semiconductor power conversion device.

FIG. 6 is a diagram showing another conventional semiconductor power conversion device.

FIG. 7 is a diagram showing another conventional semiconductor power conversion device.

FIG. 8 is a diagram showing another conventional semiconductor power conversion device.

FIG. 9 is a diagram showing another conventional semiconductor power conversion device.

[Explanation of symbols]

10 ... Voltage sharing control device, 11 ... Differential voltage control circuit, 11
1, 112, 113, 114 ... Differential voltage control circuit, 12 ...
Correction signal generator, 121, 122, 123, 124 ... Correction signal generator, 13 ... Average DC voltage detector, 20 ... Control device, 21-24 ... PWM control device, 26, 27 ... Arithmetic unit, 30 ... AC current Amplitude / phase detector, 41-44 ... Converter, 51-54 ... Transformer for transformer, 60-64 ... Capacitor, 70 ... DC power supply, 71-74 ... DC voltage detector, 81-83 ... AC current detection vessel.

Claims (8)

[Claims] 1. A voltage type self-excited multiplex system in which AC voltages of a plurality of converters are connected in series on the AC winding side of a transformer for a converter and multiplexed, and DC circuits of the converters are connected in series. In the converter, a means for generating a correction signal for correcting the AC voltage of each converter from the difference voltage between the DC voltage of each converter and the average value of the DC voltage of all converters, and converting the correction signal. A voltage characterized by comprising means for adding to the control signal of the device, and means for controlling the DC voltage by correcting the AC voltage of each converter by the addition and controlling the DC voltage to match the average value. Self-excited multiplex converter. 2. The voltage type self-excited multiplex converter according to claim 1, further comprising means for detecting the phase of the alternating current and means for making the phase of the correction signal the same phase as the detected phase. . 3. The voltage-type self-excitation according to claim 1, further comprising means for detecting the amplitude of the alternating current and means for making the amplitude of the correction signal inversely proportional to the detected amplitude. Multiplexing device. 4. The voltage type self-excited multiplex conversion device according to claim 1, wherein the means for generating the correction signal outputs the correction signal as a sine wave. 5. A voltage-type self-excited multiplex system in which AC voltages of a plurality of converters are connected in series on an AC winding side of a transformer for a converter and multiplexed, and DC circuits of the converters are connected in series. In the converter, for each converter, a correction signal for correcting the AC voltage of each converter is generated from the difference voltage between the DC voltage and the average value of the DC voltages of all the converters, and the correction signal is used as the converter. Of the voltage-type self-excited multiplex conversion device, characterized in that the control is performed by adding the control signal to the control signal and correcting the AC voltage of each converter by the addition to adjust the DC voltage to match the DC voltage with the average value. Power conversion method. 6. The power conversion method for a voltage type self-excited multiplex converter according to claim 5, wherein the phase of the alternating current is detected and the phase of the correction signal is made the same as the detected phase. 7. The electric power of a voltage type self-excited multiplex converter according to claim 5, wherein the amplitude of the alternating current is detected and the amplitude of the correction signal is made inversely proportional to the detected amplitude. How to convert. 8. The power conversion method for a voltage type self-excited multiplex converter according to claim 5, wherein the correction signal is a sine wave.