JP3316860B2 - 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 suitable for supplying power to two sets of variable loads, such as a power supply system for an overhead wire for a train.

[0002]

2. Description of the Related Art Various conventional techniques for stabilizing a system against a fluctuating load are known. In recent years, a reactive power of a load has been compensated by a self-excited converter using a self-extinguishing semiconductor device. The means for stabilizing is attracting attention. 111
It has been reported in the study of 100 MVA class GTO-SVG for stabilization of zero system.

[0003] In these conventional devices, voltage fluctuations in the system are mainly caused by reactive power of the load. Therefore, it has been attempted to stabilize the voltage of the system by compensating the reactive power.

[0004]

The above prior art mainly deals with three-phase balanced loads, and converts this technology into two sets of single-phase loads by converting three-phase power into two sets of single-phase power using a transformer. When applied to a supply system, if the active power of each single-phase load is different, phase imbalance occurs on the three-phase power side, so that there has been a problem that voltage fluctuation cannot be sufficiently suppressed only by reactive power compensation.

It is an object of the present invention to provide a power converter for stabilizing two sets of systems in which both active power and reactive power vary independently.

Another object of the present invention is to provide a power converter that compensates for unbalance of three-phase power due to single-phase load operation and further suppresses the amount of generated harmonics.

[0007]

In order to achieve the above object, the present invention focuses on the fact that a self-excited power converter can control active power and reactive power independently, and power between two sets of power converters. The power is balanced to balance the power of the two sets of loads.

Further, the respective power converters also compensate for the reactive power, so that a high power factor operation can be performed.

The above object can also be achieved by using a self-excited power converter connected between the three phases to exchange power between the respective power converters and balance the power of the two sets of loads. Can be achieved.

[0010] Another object of the present invention is to provide, in addition to the above means,
This can be achieved by providing each self-excited power converter with harmonic generation means for canceling the harmonic component generated by the load.

[0011]

The three-phase power is converted into two sets of single-phase power by a transformer and supplied to two sets of loads. The active power and the reactive power of each load are obtained from the measurement results of the load voltage and current. A self-excited power converter connected in parallel to each load uses a PWM inverter or the like, but since it is self-excited, active power and reactive power can be controlled independently. If the DC side of this self-excited power converter is commonly connected, the active power can be exchanged between the self-excited power converters, and at the same time, the reactive power can be compensated. Furthermore, since the active powers of the two sets of systems can be controlled equally, the system can be stabilized.

If the operation on the single-phase side is converted to the three-phase side, the self-excited power converter connected to at least two phases on the three-phase side can exchange power between the respective power converters. And the power of the two sets of loads can be similarly balanced, so that the system can be stabilized.

[0013] Further, if each self-excited power converter is controlled such that a harmonic generated by the load is detected and a harmonic for canceling the harmonic is generated from each self-excited power converter, the imbalance of three-phase power is compensated. In addition, it is possible to provide a high-quality load system in which the amount of generated harmonics is suppressed.

[0014]

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a block diagram of a power converter according to the present invention.

FIG. 1 shows an embodiment of the power converter of the present invention. In the figure, reference numeral 1 denotes a transformer whose primary side is connected to a three-phase AC power supply AC and whose secondary side is connected to loads 21 and 22 of a single-phase two-system, and converts three-phase power into single-phase two-system power by Scott connection. It is configured to be. On the secondary side of the transformer 1, self-excited power converters 31 and 32 are provided for each system.
Are connected, and their DC sides are commonly connected to a capacitor 4 as a DC power supply. Reference numerals 51 and 52 denote voltage detectors for detecting the voltages of the single-phase two-system, respectively.
And 62 are current detectors for detecting the current of each of the single-phase two systems, and 7 is a voltage detector 51, 52 and a current detector 61,
A control device that gives a control command to the self-excited power converters 31 and 32 based on the voltage, current, and their phase relationship detected by 62. Examples of the single-phase two-system loads 21 and 22 include a train. When the load is a train, the load power greatly fluctuates in both the active power and the reactive power, and the loads of the two systems change independently. Therefore, the respective system voltages greatly change independently due to the impedance drop of the system. Self-excited power converters 31 and 32 are controlled to stabilize this voltage fluctuation. That is, the loads 21 and 2 detected by the voltage detectors 51 and 52 and the current detectors 61 and 62
2, the active power P21, P22 and the reactive power Q21, Q22 of the loads 21 and 22 are calculated by the control device 7 from the phase relationship thereof, and the output invalidity of the self-excited power converters 31 and 32 is calculated therefrom. Power Q11, Q12
And the active powers P11 and P12, and gives command values to the self-excited power converters 31 and 32. The calculation in the control device 7 is performed by the following equation.

Q11 = −Q21 (1) Q12 = −Q22 (2) P11 = (P22−P21) / 2 (3) P12 = (P21−P22) / 2 = −P11 (4) The self-excited power converters 31 and 32 are composed of self-extinguishing type semiconductor elements, and the output power can be independently controlled for the effective component and the reactive component by pulse width modulation (PWM) control or the like.

FIG. 2 shows the details of the control device 7. In the figure, reference numerals 71 and 72 denote load voltages V1 and V2 and a current I
A first calculating unit 73 for calculating the active powers P21, P22 and the reactive powers Q21, Q22 of the load from I1, I2; and 73 the output reactive power of the self-excited power converter from the active powers P21, P22 and the reactive powers Q21, Q22 of the load. The second calculation units 74 and 75 for calculating Q11, Q12 and active powers P11, P12 are output reactive powers Q11, Q of the self-excited power converter.
12 is a modulation unit that converts the active power command and the reactive power command from the active powers P11 and P12 into command values for the self-excited power converter. The second operation unit 73 includes a subtractor and a half.
Equations (1), (2), (3) using a coefficient unit and a -1 coefficient unit
And a circuit configured to execute the operation of (4). According to this, the outputs of the self-excited power converters 31 and 32 and the active power and the reactive power of the loads 21 and 22 are combined as seen from the power supply side as follows.

Q21 + Q11 = 0 (5) Q22 + Q12 = 0 (6) P12 + P11 = P22 + P12 = (P21 + P22) / 2 (7) That is, the power factor of the single-phase two-system viewed from the power supply side is 1, The active power will be equal. Therefore, according to the present embodiment, it is possible to realize a power converter for stabilizing two sets of systems in which the active power and the reactive power both independently fluctuate, and there is an effect that no interphase imbalance occurs in the three-phase power. .

In the embodiment of FIG. 1, the voltage and current detection points are on the load side of the connection point of the self-excited power converter.
The same effect can be obtained by transferring this to the power supply side and performing feedback control on the self-excited power converters 31 and 32 so that the reactive power on the power supply side becomes zero and the active powers of the two systems become equal.

FIG. 3 shows another embodiment of the present invention in which the voltage and current detection points are on the load side of the connection point of the self-excited power converter. Since the active power and the reactive power on the single-phase side can be converted into the active power and the reactive power on each of the three-phase sides by a vector operation, the self-excited power converters 31, 32, and 33 connected to each phase of the three-phase power supply. A power converter for stabilizing two sets of systems can be realized as in the above embodiment,
The three-phase power also has the effect that no imbalance between phases occurs.

FIG. 4 is a control block diagram showing details of the control device 7 of FIG. Here, the same portions as those in FIG. 2 are denoted by the same reference numerals. In this figure, a harmonic suppression control unit is added. That is, the harmonic currents included in the load currents I1 and I2 are detected by the harmonic detection circuits 76 and 77 and are detected by the modulation unit 74.
And 75. Modulation unit 7
In steps 4 and 75, control is performed so that the opposite phase currents of the respective harmonic currents are superimposed and supplied to the self-excited power converter. 7
8 is a vector operation circuit. By configuring the control device 7 in this manner, there is an effect that the imbalance of the three-phase power due to the single-phase load operation can be compensated and the generation amount of the harmonic can be suppressed.

FIG. 5 shows still another embodiment of the present invention in which the voltage and current detection points are on the load side of the connection point of the self-excited power converter. Although FIG. 4 illustrates the use of three self-excited power converters, zero-phase components are canceled out in three-phase alternating current, so that the same effect can be obtained with any two units. Therefore, in this embodiment, one of the three self-excited power converters is omitted.

In the above embodiment, the voltage and current are detected on the single-phase load side. However, even if the detection point is on the three-phase side, the calculation of active power and reactive power on the single-phase side is possible. And the same effect can be obtained. The voltage and current detection points are set on the power supply side from the connection point of the self-excited power converter, and the self-excited power converter is feedback-controlled so that the reactive power on the power supply side becomes zero and the active powers of the two systems are equal. The same effect can be obtained even if the same is performed.

In the embodiments of FIGS. 1, 3 and 5, the self-excited power converter is assumed to be of the voltage type, and a capacitor is connected on the DC side, but the self-excited power converter is of the current type. The same effect can be obtained even when the DC side is used as a reactor.

[0025]

According to the present invention, power can be exchanged between the two sets of power converters, and the power of the two sets of loads can be balanced, so that the two sets of systems can be stabilized. Further, since the compensation of the reactive power is also performed in each of the power converters, there is an effect that a high power factor operation can be performed. Furthermore, since the harmonics of the load can be canceled by the self-excited power converter, there is an effect that a high-quality load system can be realized. The above effect is the same in the configuration in which the self-excited power converter is provided on the three-phase side.

[Brief description of the drawings]

FIG. 1 is a single-wire connection diagram illustrating an embodiment of a power converter of the present invention.

FIG. 2 is a block diagram showing details of a control device shown in FIG. 1;

FIG. 3 is a single-line connection diagram showing another embodiment of the power converter of the present invention.

FIG. 4 is a block diagram showing details of a control device shown in FIG. 3;

FIG. 5 is a single-line connection diagram showing still another embodiment of the power converter of the present invention.

FIG. 6 is a block diagram showing details of a control device shown in FIG. 5;

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Transformer, 21, 22 ... Load, 31, 32, 33 ... Self-excited power converter, 4 ... Capacitor, 51, 52 ... Voltage detector, 61, 62 ... Current detector, 7 ... Control device, 7
1, 72: first operation unit, 73: second operation unit, 74, 75
... Modulation unit, 76, 77 ... Harmonic detection circuit.

──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP-A-3-157711 (JP, A) JP-A-60-147952 (JP, U) JP-B-55-26783 (JP, B1) JP-B-63 21411 (JP, B1) JP-B-61-775 (JP, B1) (58) Fields investigated (Int. Cl. ⁷ , DB name) H02J 3/00-5/00

Claims (2)

(57) [Claims] 1. An apparatus for converting three-phase power into two sets of single-phase power via a transformer and supplying the two sets of single-phase loads, wherein an AC side is connected to an input side of the transformer and a DC side is connected to the input side. Three sets of self-excited static power converters connected to a common power supply, means for detecting the voltage and current of each single-phase power, and correction of unbalance between the two sets of single-phase loads from the detected voltages and currents And a control device for controlling the self-excited static power converter. 2. A power converter according to claim 1, wherein the self-commutated static power converter, characterized by generating harmonics to cancel the harmonics load is generated which is connected in parallel.