JPS6056069B2 - power converter - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a power conversion device that converts an AC power supply voltage to a DC voltage or an AC voltage having a lower frequency than the AC power supply voltage, and particularly relates to a power conversion device that can reduce reactive power taken from an AC power supply. Regarding equipment.

Figure 1 is a configuration diagram of a conventional power conversion device, where 1 is an AC power supply, 2A and 2B are power transformers, and for example, 2A and 2B are Δ-Δ connections, and the output voltages of 2A and 2B are in phase. Configure it so that 3A and 3B are power converters each configured as a bridge with six arms of semiconductor switching elements, and a forced commutation circuit using a well-known series diode type capacitor commutation method is provided on the positive side of 3A and the negative side of 3B. There is.

4 is a DC reactor for smoothing the output current ID, and 5 is a load.

FIG. 2 shows operating waveforms of the power converter having the configuration shown in FIG. 1) R-phase, S-phase, T-phase currents and IR supplied to Figure 3A).

, IS. , IT, are each the second bridge (Fig. 1 3B)
R-phase, S-phase, and T-phase currents supplied to IR, 15,
IT represents the R-phase, S-phase, and T-phase primary side composite currents of the power transformers (FIG. 1, 2A, 2B), respectively. In Fig. 1 and Fig. 2, thyristors RP2, SP2, 'IP2, RN3
, SN3, and TN3 are controlled to fire at a control angle -α, and thyristors RH2, SN2, RP3, and SP3 are controlled to fire at a control angle α.

That is, at timing t1, RP2, Shide SN2, Chide SP
2. TN2 in T4, TP2 in T5, RN2 in T6, T7
RN3 in T8, SP3 in T8, SN3 in T. TP3 with O
, IR2, IS2, IT2, IR3, IS3, IT by firing TN3 at Tll and RP3 at Tl2, respectively.
3 has a waveform as shown in FIG. As can be seen from Figure 2, the fundamental wave phases of IR2 and IR3 are in phase with ER, and IS
2, The fundamental wave phase of IS3 is in phase with ES, IT2, IT3
The fundamental wave phase of is in phase with ET. Currents 1R1, IS1, IT1 flowing into the power transformer (Fig. 1, 2A, 2B)
are IR2 and 1R3, IS2 and IS3, IT2 and IT, respectively.
Since there is a composite value of 3, the waveform will be as shown in Figure 2,
Even harmonics cancel and become zero. IRl, ISl, IT
The fundamental wave phase of l is in phase with ER, ES, and ET, respectively.
In this way, the fundamental wave power factor is always 1, making it possible to operate with a good power factor. In the configuration shown in FIG. 1, six commutation capacitors are required. Furthermore, as is well known, in the configuration shown in Figure 1, the voltage value and commutation time that are recharged to the commutation capacitor during commutation are the instantaneous value of the power supply voltage during the commutation period and the voltage on the power supply side. It depends on the inductance and commutation current value 1D. Therefore, the commutation conditions change due to α control and ID control, and the α control range and ID control range are restricted from the commutation possible conditions. In order to accommodate this change in commutation conditions, it is sufficient to switch the values of the commutation capacitors according to changes in the α control amount and ID. It is almost impossible to switch depending on the situation. An object of the present invention was to eliminate the drawbacks of the above-mentioned conventional system, and to simplify the commutation circuit by using only one commutation capacitor, and to control the firing timing of the thyristor. An object of the present invention is to provide a power conversion device that can expand the α control range and the control range of the output current 1D by controlling the recharging voltage. The present invention will be described below with reference to the drawings.

FIG. 3 is a circuit configuration diagram showing an embodiment of the present invention.
, 2B are both Δ-Δ connected, and the output voltages of 2A and 2B are configured to be in phase. Reference numerals 3A and 3B each represent a power conversion device configured as a bridge by six-arm thyristor elements.

4 is a DC reactor that smoothes the output current 1D, 5 is a load, and 6 is six commutating auxiliary thyristors RC2, SC2, TC.
2. There is a forced commutation circuit consisting of RC3, SC3, TC3 and commutation capacitor C.

Further, 8 is a voltage detection circuit that detects the voltage of the commutating capacitor C, 10 is a thyristor firing timing control circuit, and 11
is thyristor RN29SN29TN29RP39SP3
9ll) This is the ignition command signal for 3. Hereinafter, the present invention having the above configuration will be explained in detail.

FIG. 4 shows the operating waveforms of the power converter of the present invention having the configuration shown in FIG. R phase, S phase, T phase current, IR supplied to Figure 3, 3A)
3, lS3, and IT3 are the second bridges (Fig. 3, 3
B) R phase, S phase, T phase currents, IRl, IS supplied to
1, ITl are the R-phase, S-phase, and T-phase primary side composite currents of the power transformers (FIG. 3, 2A, 2B), respectively. In Fig. 3 and Fig. 4, thyristors RN2, SN2, TN2, RP3
, SP3, TP3 are controlled to fire at a control angle of -α, and thyristors RP2, SP2, TP2, RN3, SN3, TN3
It is assumed that firing is controlled by a control angle α. That is, commutation auxiliary thyristor TC3 is fired at timing t1. At this time, if the charge on the commutating capacitor C has the polarity shown in FIG. 3, a reverse voltage is applied to the thyristor TP3 and the thyristor TP3 is turned off. The current flowing through the thyristor TP3 flows through the commutation capacitor C, so the voltage at C is reversed, and by turning on the thyristor RP3 at an appropriate timing, T
Forced commutation from P3 to RP3 is completed. Next is the timing! If the thyristor SN3 is turned on at this time, since the potential of the S-phase voltage ES is lower than the R-phase voltage ER, natural commutation occurs from the thyristor RN3 to the thyristor SN3.
Similarly, if commutating auxiliary thyristor SC2 is turned on at timing Tll, since the electric charge of commutating capacitor C has the opposite polarity to that shown in FIG. 3, a reverse voltage is applied to thyristor SN2 and thyristor SN2 is turned off. . Since the current flowing through the thyristor SN2 flows through the commutation capacitor C, the voltage at C is inverted again, and by turning on the thyristor TN2 at an appropriate timing, the forced commutation from SN2 to TN2 is completed. Similarly, 1 at timing Tl2.
Commutation timing from P2 to RP2 From RP3 to SP
Commutation from SN3 to TN3 at timing T4, commutation from TN2 to RN2 at timing T8, commutation from RP2 to SP2 at timing T8, commutation from SP3 to TP3 at timing T5, timing ! I hesitate.

commutation from RN2 to RN3, from RN2 to SN at timing T9
The commutation from SP2 to TP2 is performed at timing TlO, and the commutation from SP2 to TP2 is performed at timing TlO. With the above commutation control, IR2
, IS2, IT2, IR3, IS3, and IT3 have waveforms as shown in FIG. Also, IRl, ISl, and ITl are IR2 and IR3, IS2 and IS3, and IT2 and IT3, respectively.
Since it is a composite value of , it has a waveform as shown in FIG. 4, and its fundamental wave phase is in phase with ER, ES, and ET, respectively. In this way, the fundamental wave power factor is always 1, making it possible to operate with a good power factor. Next, the commutation operation will be explained in more detail by taking the commutation at timing t1 as an example.

In Fig. 5, immediately before timing t1, the thyristor RN
3, lT) 3, SN2 is on. Assuming that the voltage of commutating capacitor C is 1 EC, if commutating auxiliary thyristor TC3 is turned on at timing t1, the reverse voltage of upper C is applied to thyristor TP3, and the current flowing through thyristor 'IP3 is transferred to commutating auxiliary thyristor TC3. and commutation capacitor C
Let's move on to the circuit. Therefore, the current of thyristor TP3 becomes zero. The voltage of the commutating capacitor C is reversed from the value of the upper C as shown in FIG. 7, and a reverse voltage is applied to the thyristor 'IP3 during the period T1. ID during the commutation period when the output current is D
If the change in is ignored, T1 is expressed by the following formula. Here, the values of C and EC for ID are chosen so that T1 is longer than the turn-off time of thyristor TP3.

The voltage of the commutating capacitor is reversed to the positive side, and the power supply R3-
When the voltage becomes larger than the line voltage between T3, the anode voltage of thyristor RP3 becomes positive with respect to the cathode, so that ignition of thyristor RP3 becomes possible. The line voltage between R3 and T3 is zero when commutation is performed with α = 0, and when commutation is performed between α = -90, it is equal to the peak value of the line voltage and changes as a sine function with respect to α. do. Therefore, in the case of the conventional device shown in Fig. 1, when the commutation capacitor voltage becomes larger than the line voltage between R3 and T3, the commutation operation starts, and the recharging voltage of the commutation capacitor is determined by the α control angle. , there was a problem that changed drastically. According to the circuit configuration according to the present invention, it is possible to control the recharging voltage according to the firing timing of the thyristor RP3 at this time.

For example, if the seventh line voltage is higher than the maximum value of the line voltage between R3 and T3,
If the thyristor RP3 is fired until the commutating capacitor is recharged at point 5 in Fig. 5, the current change shown by the dotted line in Fig. 6 occurs, and at point 5 in Fig. 7, the commutating auxiliary thyristor TC3
The current flowing through becomes zero and commutation is completed. Therefore, regardless of α control, the recharging voltage of the commutation capacitor can be maintained at a value necessary for the next commutation. One way to detect when the commutating capacitor voltage has reached E1 in Fig. 7 in order to determine the firing timing of thyristor RP3 is to detect the voltage of the commutating capacitor C using the voltage detection circuit shown in Fig. 38. There is a method of detecting that the commutating capacitor voltage has reached E1 using FIG. 3 and FIG. Also the 7th
In the figure, T2 is expressed by the following formula. Therefore, the five points in FIG. 7 may be detected by detecting the ID and calculating T2 using equation (2).

Furthermore, in FIG. 7, since E2 depends on the power source inductances I and ID and the α control angle, it is also possible to optimally control EC by varying E1 based on these quantities. As described above, according to the circuit configuration of the present invention shown in FIG. 3, commutation auxiliary thyristors RC2, SC2, TC2, RC3,
After firing C3 and TC3, the main thyristor RN2,
By controlling the timing of firing SN2, RP3, SP3, and TP3, the recharging voltage EC of the commutating capacitor JC can be controlled arbitrarily, so stable transfer can be achieved regardless of changes in the control angle α and ID. flow becomes possible. Next, FIG. 8 is a circuit configuration diagram showing another embodiment of the present invention,
1 to 6 in the figure are the same as those in FIG. 3. 7 is two thyristors S connected in anti-parallel with inductance L.
A charge inversion circuit for commutating capacitor C composed of CRl and SCR2, 8 a voltage detection circuit for detecting the voltage of commutating capacitor C, 9 a current detection circuit for detecting output current 1D,
10 are thyristors SCRl, SCR2, RN2, 7SN
2, a firing timing control circuit that controls the firing timing of RP3, SP3, SP3, 'IP3; 11 is a thyristor SCRl, SCR2, RN2, SN2, TN2, RP;
3, SP3, and TP3 are ignition command signals.

The main difference between FIG. 8 and FIG. 3 is the addition of a charge inversion circuit 7 for commutating capacitor C, the purpose of which will now be explained. In the commutation operation in the circuit configuration shown in Fig. 3, as shown in Fig. 7, the charge in the commutation capacitor C is discharged in proportion to the output current 1D, and a reverse voltage is applied to the thyristor to be extinguished for a period of T1. is applied. Therefore,
Since T1 is inversely proportional to ID as expressed by equation (1), it is necessary to select C and EC so as to ensure T1 that is longer than the turn-off time of the thyristor with respect to the maximum value of ID. On the other hand, from the relationship in equation (1), T1 is the output current 1D
decreases, it becomes longer than necessary and limits the maximum value of the output frequency. Therefore, it is not possible to control the output current 1D below a certain value. For this reason, in the configuration example shown in FIG. 8, a charge inversion circuit 7 for the commutating capacitor C is added. Fig. 9 is a diagram explaining the commutation operation using the circuit configuration shown in Fig. 8. When the output current 1D is small, the commutation operation takes a long time and it takes T1'' for the electric charge on the commutation capacitor to become zero. At this time, if the thyristor SCR2 is fired at 6 points, the commutating capacitor charge is quickly reversed by the circuit formed by commutating capacitor C-SCR2 → inductance. By controlling the back pressure time T1 applied to the thyristor to extinguish the arc, it is possible to control the back pressure time T1 applied to the thyristor to extinguish the arc to the necessary minimum value, which is longer than the turn-off time of the thyristor, without affecting the change in the output current 1D. When the thyristor RP3 is ignited at point (lower), the current change shown by the dotted line in Figure 6 occurs in the same way as explained for the commutation operation in Figure 3, and the commutation operation is completed at point 8 in Figure 9. .

The ignition timing at points 5 and b in Fig. 9 can be controlled according to the commutation capacitor voltage and output current 1D by the voltage detection circuit 8, current detection circuit 9, and ignition timing control circuit 10 in Fig. 8. , simply starts commutation operation (Fig. 4 t1
At the point of , roll! The time from flow auxiliary thyristor TC3 on) to point 5 (SCR2 on in Figure 8) is equal to the thyristor turn-off time. If the thyristor RP3 is controlled to be turned on, the point where the commutating capacitor voltage is reversed and E1 reaches a value E1 larger than the maximum value of the power line voltage is set as 5 points, and the change in the α control angle and The commutation condition is always satisfied with respect to changes in the output current 1D, and T1 becomes T. It does not increase that much. As explained above, according to the present invention, commutation is performed by a common commutation capacitor for the minus side of the positive side bridge and the plus side of the negative side bridge, so the commutation circuit is simplified. In addition, by controlling the firing timing of the inverting thyristor after firing the commutating auxiliary thyristor, the commutation time and recharging voltage of the commutating capacitor can be adjusted arbitrarily, regardless of changes in output current and α control negative changes. Since the recharging voltage is controlled every 60 voltages of the power supply voltage phase, the light current voltage can be controlled in response to rapid changes in commutation conditions.

[Brief explanation of drawings]

FIG. 1 is a circuit configuration diagram of a conventional device, FIG. 2 is an operation waveform diagram of FIG. 1, and FIG. 3 is a circuit configuration diagram showing an embodiment of the present invention.
Figure 4 is the operation waveform diagram of Figure 3, Figures 5 and 6 are the operation waveform diagram of Figure 3.
7 is a diagram showing the commutation operation waveform of FIG. 3, FIG. 8 is a diagram showing another embodiment of the present invention, and FIG. 9 is a commutation operation waveform of FIG. 8. It is a diagram. 1... AC power supply, 2A, 2B... power transformer, 3A, 3B... power converter, 4...
...DC reactor, 5...Load, 6...
...Forced commutation circuit, 7...Charge inversion circuit,
8...Voltage detection circuit, 9...Current detection circuit, 10...Ignition timing control circuit, 11
・・・・・・Ignition command signal.

Claims (1)

[Claims] 1 Consists of a positive side thyristor bridge, a negative side thyristor bridge, a commutation capacitor, and a commutation thyristor, each of which is supplied with power from an isolated AC power supply, and the negative terminal of the positive side thyristor bridge and the negative side thyristor bridge A commutating thyristor having a common anode side and a cathode, the positive terminals of which are connected in common, one end of a commutating capacitor being connected to the common connection point, and an anode being common to the other end of the commutating capacitor. The cathodes of the commutating thyristors having the anode in common are connected to the AC power terminal of the positive side thyristor bridge, and the anodes of the commutating thyristors having the cathode in common are connected to the negative side. A power conversion device characterized in that it is connected to an AC power terminal of a thyristor bridge. 2 Consisting of a positive side thyristor bridge, a commutation capacitor, a commutation thyristor and a reactor, each supplied with power from an insulated AC power supply, the negative terminal of the positive side thyristor bridge and the positive terminal of the negative side thyristor bridge are commonly connected, and the One end of a commutation capacitor is connected to the common connection point, and the anode side of a commutation thyristor having a common anode and the cathode side of a commutation thyristor having a common cathode are connected to the other end of the commutation capacitor. Connect the cathodes of the commutating thyristors having a common thyristor to the AC power terminal of the positive thyristor bridge,
The anodes of the commutating thyristors having a common cathode side are each connected to the AC power terminal of the negative side thyristor bridge, and further a series circuit of the thyristors and reactors connected in antiparallel is connected in parallel with the commutating capacitor. A power conversion device characterized by: