JP2007288968A - Capacitor charging device for rectifier circuit - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To prevent an initial charging current to two capacitors, which are connected in series between DC output terminals P, N of a positive electrode and negative electrode of a rectifier circuit, from becoming excessive. <P>SOLUTION: A series circuit of two thyristors (TR1-TT2), whose conduction directions are aligned with each other, and a series circuit of two switching elements (SR1-ST2), whose conduction directions are aligned with each other, are connected in parallel so as to constitute a two-way switch circuit for one phase. The two-way switch for one phase is provided corresponding to the number of phases (figure shows an example of three phases). Firing-angle control of the thyristors (TR1-TT2) is executed via a thyristor control circuit 102 during starting. Consequently, it is possible to limit the initial charging current. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a rectifier circuit that converts an AC voltage of N (N is a natural number of 2 or more) phase into a DC voltage, and more particularly to its control.

2. Description of the Related Art Conventionally, a system that converts an N-phase AC voltage into a DC voltage using an AC / DC conversion circuit composed of a semiconductor power conversion element and supplies the converted voltage to a load is well known. FIG. 8 shows an example of a three-phase rectifier circuit and its control circuit disclosed in Patent Document 1, for example.
In FIG. 8, R, S, and T are AC input terminals, P and N are DC output terminals, LR, LS, and LT are reactors, and SR1, SR2, SS1, SS2, ST1, and ST2 are IGBTs (insulated gate bipolar transistors). And switching elements such as MOSFET (metal oxide field effect transistor), DR1-4, DS1-4, DT1-4 are diodes, C1, C2 are capacitors connected in series between P and N, 4R, 4S, 4T Is a bidirectional switch circuit.

  For example, the bidirectional switch circuit 4R is configured by connecting in parallel a series circuit of switching elements SR1 and SR2 and a series circuit of diodes DR1 and DR2. A connection point between the diodes DR1 and DR2 is connected to one end of the reactor LR, and a connection point between the switching elements SR1 and SR2 is connected to a connection point between the capacitors C1 and C2. Both ends of the series circuit of switching elements SR1 and SR2 are connected to both ends of the series circuit of capacitors C1 and C2 via diodes DR3 and DR4. The bidirectional switch circuits 4S and 4T are configured in the same manner as described above.

The operation of the control circuit will be described.
The input line voltages VRS, VST detected by the voltage detectors 2RS, 2ST are converted into phase voltages VR, VS, VT by the phase voltage converter 10, and synchronized with the polarity of the converted input phase voltages VR, VS, VT. Signals R +, R−, S +, S−, T +, T− are created by the polarity discriminator 11. Further, the capacitor voltage VC1 detected by the voltage detector 5C1 is fed back to the command value 12, and is multiplied by the input phase voltages VR, VS, and VT through the voltage regulator 13b. Further, the DC output voltage VC2 detected by the voltage detector 5C2 is fed back to the command value 12 and multiplied by the input phase voltages VR, VS, and VT via the voltage regulator 13a.

  In response to these multiplication results, the respective phase input currents IR, IS, IT detected by the current detectors 3R, 3S, 3T are fed back, and the comparators 17R, 17S, 17T via the current regulators 16R, 16S, 16T. By comparing with the carrier signal 20, the PWM signal for the switching elements SR1, SS1, ST1 of the upper arm is obtained and compared with the carrier signal 20 by the comparators 17Ra, 17Sa, 17Ta via the current regulators 16Ra, 16Sa, 16Ta. As a result, a PWM signal for the switching elements SR2, SS2, ST2 of the lower arm is obtained. Further, a logical product of the signals R +, R-, S +, S-, T +, T- synchronized with the polarities of the input phase voltages VR, VS, VT and the PWM signal is obtained by AND gates 18R-18Ta to drive the gate. Control signals for the switching elements SR1, SR2, SS1, SS2, ST1, and ST2 are created through the circuits 19R to 19Ta.

  Here, when the capacitor voltage VC1 decreases, the pulse width of the switching element SS2 increases, and when the capacitor voltage VC1 increases, the control circuit 101 operates so that the pulse width of the switching element SS2 decreases. As a result, the charging current of the capacitor C1 flowing through the path of R → LR → DR1 → DR3 → C1 → SS2 → DS2 → LS → S → R changes, and the capacitor voltage VC1 is kept constant. On the other hand, the control circuit 101 operates such that when the capacitor voltage VC2 decreases, the pulse width of the switching element SR1 increases, and when the capacitor voltage VC2 increases, the pulse width of the switching element SR1 decreases. As a result, the charging current of the capacitor C2 flowing through the path of R → LR → DR1 → SR1 → C2 → DS4 → DS2 → LS → S → R changes, and the capacitor voltage VC2 is kept constant.

  With such an operation, the capacitor voltages VC1 and VC2 can be controlled independently. In addition, the input current is controlled to a sinusoidal waveform synchronized with the input voltage by feedback control of the input current, and the output voltage (the voltages of the capacitors C1 and C2) can also be controlled to a constant DC voltage by feedback control. . As a result, the AC voltage can be converted to a DC voltage while controlling the input current at a high power factor.

JP 2002-142458 A

In FIG. 8, when the AC input 1a is turned on when the capacitor voltages VC1 and VC2 are close to zero at the time of starting the apparatus and the two switching elements constituting each bidirectional switch circuit are turned off, R → LR → DR1 A current flows through a route of DR3 → C1 → C2 → DS4 → DS2 → LS → S → R to charge the capacitors C1 and C2. As a result, an excessive current as shown in FIG. 9C flows, and there is a risk of destroying elements such as a reactor and a diode.
In Patent Document 1, one of the two diodes constituting the bidirectional switch circuit is replaced with thyristors TR1, TS1, and TT1 as shown in FIG. 10 and turned on in a state where each interphase voltage is low as shown in FIG. However, depending on the selection of the reactor and the capacitor, a current exceeding the current rating of the diode in the charging current path may flow.

Therefore, for example, the reactor can be increased in size and the impedance of the charging current path can be increased. However, it is inevitable that the device is increased in size and the cost is increased. Of course, if a dedicated initial charging circuit is provided, the above problem can be solved, but the circuit configuration becomes complicated.
Accordingly, an object of the present invention is to allow the charging current of a capacitor to be limited during initial charging, and to prevent destruction of each semiconductor element at low cost.

In order to solve such a problem, in the invention of claim 1, in order to convert an AC voltage of N (N is a natural number of 2 or more) phase into a DC voltage, a series of two thyristors whose flow directions coincide with each other. N bidirectional switch circuits for one phase constituted by connecting a circuit and a series circuit of two switching elements having the same flow direction in parallel are provided, and connection points between thyristors in each bidirectional switch circuit Are connected to the AC input terminal of each phase via the reactor, and the cathode side of the series circuit of the thyristor in each bidirectional switch circuit is connected to the DC output terminal of the positive electrode via the diode, respectively. Connect the anode side of the series circuit of thyristors in the switch circuit to the negative DC output terminal via a diode, and connect between the positive and negative DC output terminals. One of connecting a capacitor in series, in the rectifier circuit the connection point between the switching elements connected collectively to a connection point between the two capacitors in each of the bidirectional switching circuit,
A voltage detecting means for detecting an N-phase AC input voltage; a synchronization signal generating means for generating a signal synchronized with the AC input voltage phase; and a firing angle of the thyristor based on the signal synchronized with the AC input voltage phase. A firing angle control means for controlling is provided, and initial charging of the two capacitors is performed.

In the first aspect of the present invention, the current detection means for detecting the N-phase AC input current is provided, and the firing angle of the thyristor can be controlled so that the AC input current is limited to a constant value. Item 2).
In the first or second aspect of the present invention, one of the two thyristors constituting each of the bidirectional switch circuits is replaced with a diode, and the firing angle of the thyristor is controlled, so that the DC output terminals are connected in series. In addition, initial charging of only two capacitors can be performed (invention of claim 3).

According to the first and second aspects of the present invention, since the charging current of the capacitor is limited by controlling the firing angle of the thyristor during initial charging, a device with a lower current capacity of the diode and a smaller reactor Can be reduced in weight and cost, and destruction of each semiconductor element can be prevented.
According to the invention of claim 3, by replacing one of the two thyristors constituting the bidirectional switch with a diode, the thyristor gate drive circuit can be reduced in size and weight, and the cost can be reduced.

FIG. 1 is an overall configuration diagram showing an embodiment of the present invention.
The difference from FIG. 8 is that the series circuit of two diodes in the bidirectional switch circuit is replaced with a series circuit of thyristors and a thyristor control circuit 102 is added.
The thyristor control circuit 102 inputs the input line voltage detected by the voltage detectors 2RS and 2ST to the phase synchronization circuit 24, and outputs a phase synchronized with each phase. On the other hand, the firing angle command of the thyristor output from the firing angle command generation circuit 21 and the phase of each phase output from the phase synchronization circuit 24 are input to the firing angle control circuit 22, and the thyristor gate drive circuit 23 is A gate signal is output to each thyristor.

A specific example of the firing angle command generation circuit is shown in FIG. 2 (a), and its operation is shown in FIG. 2 (b).
As shown in FIG. 2A, the firing angle command generation circuit 21 includes an integrator 202, a limiter 203, a subtractor, and the like. The integrator 202 operates according to the initial charge command 201, and is limited by 0 to the limiter 203. The firing angle command αref is gradually shifted from 180 ° to 0 °.

Specific examples of the firing angle control circuit 22 are shown in FIGS.
The firing angle command value αref output from the firing angle command generation circuit 21 and the firing angles θR, θS, θT of each phase synchronized with the input voltage output from the firing angle synchronization circuit 24 are compared. Compare at 30R, 30S, and 30T. For the control of the negative thyristor constituting the bidirectional switch, the firing angle shift circuits 31R, 31S, 31T shift the firing angle by 180 °, and then the comparison is made by the comparators 30Ra, 30Sa, 30Ta. . As shown in FIGS. 3B to 3D, the initial charging can be performed by controlling the upper and lower thyristors of the two phases of the three phases, but the initial charging is completed as compared with the case of controlling by the three phases. It takes some time to complete.

With reference to FIG. 4, the firing angle control of the thyristor in FIG. 1 will be mainly described.
FIG. 4 shows the input phase voltage, the phase of R phase, the gate signal of each thyristor, the current (IR) of the reactor LR, and the voltage between PN (capacitor voltage) in this order, as shown in FIG. 3B. An example of controlling the firing angle of the R-phase and S-phase thyristors is shown. When the firing angle command is decreased from the phase of the input phase voltage of 180 °, the gate signal TR1 of the thyristor on the R phase positive side and the gate signal TS2 of the thyristor on the S phase negative side overlap, and at this point, the capacitor is switched from the AC input to the capacitor. A pulsed charging current flows toward the capacitor, and the capacitor voltage rises.

  The same applies to the gate signal TR2 of the R-phase negative thyristor and the gate signal TS1 of the S-phase positive thyristor. When the firing angle command αref reaches 0, the capacitor voltage is √2 times the input voltage. The voltage of the peak value (200 × √2 = 282.8 V when the effective value is 200 V) is reached, and the initial charging is completed. Although the case where two phases are controlled has been described here, the initial charging is possible even when the control is performed using three phases, and the charging current path is increased as compared with the case of two phases, so that the initial charging time can be shortened. Although details are omitted because of the control method similar to the conventional one, the voltage can be boosted from the initial charge value by performing individual control of the upper and lower capacitors by the control circuit 101 after the initial charge.

FIG. 5 shows another embodiment of the firing angle command generation circuit.
This is obtained by adding a block that detects the input current of each phase and adjusts the firing angle command so that the charging current does not exceed the current limit value, as shown in FIG. That is, as shown in FIG. 5A, the current of each phase is detected, the maximum value is calculated from the absolute value by the maximum value calculation circuit 204, and is compared with the current limit value via the first-order lag element 205. As a result, if the detected current is within the limit value, the integrator 202 is operated, and if the detected current is reached, the integrator 202 is stopped. Instead of stopping, a negative command may be given to the integrator 202 to return the firing angle command.

FIG. 6 is an overall configuration diagram showing another embodiment of the present invention.
As is apparent from FIG. 6, one of the two thyristors constituting the bidirectional switch is replaced with a diode (DR2, DS2, DT2), and the control circuit 101 is the same as FIG. The thyristor control circuit 102 is the same as that shown in FIG. 1, but its description is omitted because it is slightly different from that shown in FIG. 1 in that it does not have a negative-side control circuit.

  FIG. 7 illustrates the operation of FIG. 6. From the top of FIG. 7, the input phase voltage, the phase of R phase, the gate signal of each thyristor, the current of the reactor LR (IR), the voltage between PN (capacitor voltage) Here, an example in which the firing angle of each phase thyristor is controlled is shown. When the firing angle command is reduced from the phase of the input phase voltage of 180 °, the negative side of the bidirectional switch is a diode in this example, and therefore, when the firing angle command αref having a positive input voltage is given. (Within 180 °), a pulsed charging current flows from the AC input to the capacitor, and the capacitor voltage rises. The difference from FIG. 4 is that since the thyristor is connected only to the positive side, only the positive side current can be controlled. Note that the input current can be limited in the same manner as in the circuit shown in FIG.

Overall configuration diagram showing an embodiment of the present invention Specific example of firing angle command generation circuit of FIG. Configuration diagram showing a specific example of the firing angle control circuit of FIG. 1 is an explanatory diagram of the operation. Another specific example of the firing angle command generation circuit of FIG. Overall configuration diagram showing another embodiment of the present invention FIG. 6 is an operation explanatory diagram. Overall configuration diagram showing a first conventional rectifier circuit and its control circuit Operation explanatory diagram of FIG. Overall configuration diagram showing a second conventional rectifier circuit and its control circuit Explanation of operation in FIG.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Three-phase alternating current power supply, 2RS, 2ST, 5C1, 5C2 ... Voltage detector, 3R, 3S, 3T ... Current detector, 4R, 4S, 4T ... Bidirectional switch circuit, 6 ... Load, 10 ... Phase voltage conversion circuit 11a, 13b, voltage regulator, 15R, 15Ra, 15S, 15Sa, 15T, 15Ta, multiplier, 16R, 16Ra, 16S, 16Sa, 16T, 16Ta, current regulator, 17R, 17Ra, 17S, 17Sa, 17T, 17Ta ... comparators, 18R, 18Ra, 18S, 18Sa, 18T, 18Ta ... AND gates, 19R, 19Ra, 19S, 19Sa, 19T, 19Ta ... gate drive circuits for switching elements, 21 ... firing angle Command generation circuit, 22 ... firing angle control circuit, 23 ... thyristor gate drive circuit, 24 ... phase synchronization circuit, 101 ... Control circuit 102 ... Thyristor control circuit 202 ... Integrator 203 ... Limiter 204 ... Maximum value calculation circuit 205 ... First-order lag element 31R, 31S, 31T ... Starting angle shift circuit, LR, LS, LT ... Reactor , DR1-4, DS1-4, DT1-4, diode, C1, C2 ... capacitor, R, S, T ... input terminal, P, N ... output terminal, NP ... neutral point terminal, SR1, SR2, SS1, SS2, ST1, ST2 ... switching elements, TR1, TR2, TS1, TS2, TT1, TT2 ... thyristors.

Claims (3)

In order to convert an AC voltage of N (N is a natural number of 2 or more) phase into a DC voltage, a series circuit of two thyristors having the same flow direction and a series of two switching elements having the same flow direction N bidirectional switch circuits for one phase constituted by connecting the circuits in parallel are provided, and the connection points between the thyristors in each bidirectional switch circuit are connected to the AC input terminals of the respective phases through the reactors, Connect the cathode side of the series circuit of the thyristor in each bidirectional switch circuit to the positive DC output terminal via a diode, and connect the anode side of the series circuit of the thyristor in each bidirectional switch circuit via a diode. Connect to the negative DC output terminal at once and connect two capacitors in series between the positive and negative DC output terminals. In the rectifier circuit the connection point between the switching elements connected collectively to a connection point between the two capacitors in,
A voltage detecting means for detecting an N-phase AC input voltage; a synchronization signal generating means for generating a signal synchronized with the AC input voltage phase; and a firing angle of the thyristor based on the signal synchronized with the AC input voltage phase. A capacitor charging device for a rectifier circuit, characterized in that an ignition angle control means for controlling is provided to perform initial charging of the two capacitors.   2. The rectifier circuit according to claim 1, further comprising a current detection unit configured to detect an N-phase AC input current, and controlling an ignition angle of the thyristor so that the AC input current is limited to a constant value. Capacitor charger. By replacing one of the two thyristors constituting each of the bidirectional switch circuits with a diode and controlling the firing angle of the thyristor, initial charging of two capacitors connected in series between the DC output terminals is performed. 3. The capacitor charging device for a rectifier circuit according to claim 1, wherein the capacitor charging device is a rectifier circuit.

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