JPS5936511B2 - Auxiliary charging control method for forced commutation rectifier - Google Patents

Description

[Detailed description of the invention] The present invention relates to a supplementary charging control method for a forced commutation rectifier.

Generally, in a forced commutation rectifier, it is necessary to charge the commutation capacitor of the forced commutation circuit more quickly in order to quickly extinguish the main thyristor and perform commutation at a faster cycle.

For this reason, it is common to have an auxiliary charging circuit that not only charges the commutating capacitor only with the load current during commutation but also forcibly supplements the commutating capacitor from the outside. Conventionally, in forced commutation rectifiers that include a forced commutation circuit and an auxiliary charging circuit, the auxiliary charging circuit is generally a series circuit of a thyristor and an impedance, and this thyristor is activated at a predetermined timing regardless of the magnitude of the load current. It is being operated.

For this reason, losses are always occurring due to supplementary charging of the commutating capacitor. Originally, auxiliary charging of commutating capacitors is necessary because the load current during commutation is small, so commutation cannot be guaranteed against the transient large current of the next cycle, or the commutation time becomes long and the load current during commutation is small. This is necessary when fast ignition is not possible, and is unnecessary if the load current during commutation is sufficiently large. For this reason, if the auxiliary charging circuit continues to operate and generate losses even when a large load current is flowing, the rectification efficiency of the forced commutation rectifier will be reduced. SUMMARY OF THE INVENTION An object of the present invention is to provide a supplementary charging control system for a forced commutation rectifier that can eliminate the above-mentioned drawbacks and reduce unnecessary loss associated with supplementary charging of a commutating capacitor in a forced commutation circuit.

The present invention will be explained in detail below with reference to the drawings.

FIG. 1 is a diagram showing an example of the main circuit configuration of a rectifier equipped with a forced commutation circuit used in the present invention.

UM, VM, WM; XM, YM, ZM are main thyristors,
Pu and PL are arc-extinguishing thyristors, and PUX and PLX are supplementary charging thyristors. A rectifier consisting of three-phase bridge-connected main thyristors UM, VM, WM, XM, YM, and ZM applies a three-phase AC input voltage, rectifies it, and supplies it to the load.

The forced commutation circuit for this rectifier consists of diode bridges D1 to D6, commutation capacitors CU, Cl) commutation reactors Lu, LL, inverting thyristors PU, PL, reverse current prevention diodes DU, DL) for auxiliary charging. Thyristor PL
X, PUX) consists of braking resistances Rx and RL. First, the operation of a rectifier having a forced commutation circuit will be briefly explained.

Let us take as an example a process in which the main thyristor WM is turned off and the main thyristor UM takes over the load current id from a state in which the main thyristors WM and YM are passing the load current id. The reversing thyristor Pu fires to forcibly extinguish the main thyristor WM.This forms an oscillating circuit of Cu-+Lu-+Pu-+Cu, and the voltage polarity of the commutating capacitor Cu is reversed from the polarity shown in the first diagram. do. When the voltage of the commutating capacitor Cu completes inversion and returns to the original polarity shown in the figure, the inverting thyristor Pu receives a reverse bias and is extinguished, and at the same time, the voltage of the commutating capacitor Cu changes Cu-+Du→W.
Main thyristor WM via the path M-+D3→Lu-+Cu
is reverse biased, so the load current 1d is the main thyristor w
From Hibiki, the commutation circuit starts from D3→Lu-+Cu→Du. When the current in this commutation circuit becomes equal to the load current 1d, the main thyristor WM has no current, and then the load current 1d changes from load→YM→Ls−+1s→IIT−+
The current flows through the path Ls-+D3→Lu-+Cu-+Du→load, and the commutating capacitor Cu is thereby charged to the illustrated polarity by the load current Id. Main thyristor UM
The charging voltage of the commutating capacitor at the time when the load current 1d completely takes over the load current 1d is the path YM-+LS-
+1S-+JT-+L8→D3→Lu-+Cu→Du to route YM-+L8→18→IR-+LS-+UM→It depends on the line voltage IT-1s at the time when commutation starts, and the Load current 1 during overlap period
Depends on the value of d. The former voltage-dependent charge component approaches zero as the firing angle α approaches zero, and the latter current-dependent charge component becomes smaller as the load current becomes smaller. Therefore, if the firing angle is close to zero and the load current is small, the charging voltage of the commutating capacitor will be insufficient, and in the opposite case, the charging voltage of the commutating capacitor will be excessive. Next, the supplementary charging operation of the commutating capacitor will be explained.

If the charging voltage of the commutating capacitor is insufficient, auxiliary charging is performed by firing the auxiliary charging thyristor PLX. This auxiliary charging thyristor PLX is turned on after the inversion thyristor Pu is turned off. For example, the auxiliary charging thyristor PLX may be ignited around the time when the main thyristor UM begins to conduct. By firing the auxiliary charging thyristor PLX, a series circuit consisting of a commutating reactor Lu and a commutating capacitor Cu is connected between the DC side terminals of the diode bridges D1 to D6 via the braking resistor Rx and the auxiliary charging thyristor PLX. Supplementary charging of the connected commutation capacitor is performed. Therefore, the diode bridges D, -D6 are used not only to form a commutation circuit but also as an auxiliary charging power source. FIG. 2 is a diagram showing operating waveforms of commutating capacitor Cu or CL for explaining the basic principle of the present invention.

Vcmin indicates the minimum voltage value of the commutating capacitor voltage Vc required to extinguish the main thyristor. Time T. is the point in time when the arc-extinguishing thyristor fires and the commutating capacitor voltage starts to reverse; at time t1, the main thyristor is completely extinguished and the commutating capacitor begins to be recharged by the load current 1d. Time T
At time T2, the auxiliary charging thyristor is fired, and at time T3, the next extinguishing thyristor is fired. The commutating capacitor voltage Vc reaches the minimum voltage value Vcmi at the next ignition time point T3 of the extinguishing thyristor.
It must be recharged to a level of n. Straight line b is at time T when the load current 1d is equal to the predetermined load current value 1.
By 3, the commutating capacitor voltage Vc is exactly the minimum voltage value Vc
The straight line C shows the case where the load current 1d reaches i
This shows a case where the commutating capacitor voltage Vc is smaller than ♂ and has not been recharged to the minimum voltage value VOmin at time T3. Conversely, the straight line a shows that the load current 1d is equal to the predetermined load current value 1 (
The commutating capacitor voltage c is greater than r+′ and before time T3.
is sufficiently recharged above the level of the minimum voltage value Vcmin. In this way, since the commutating capacitor is recharged by the load current 1d during the commutation period,
Whether supplementary charging is necessary or not is determined after the predetermined load current value 1♂. Therefore, by comparing the predetermined load current value 1d* and the actual load current value 1d at time T2 and determining whether or not to fire the auxiliary charging thyristor to perform auxiliary charging, unnecessary auxiliary charging can be avoided reliably. The main thyristor can be extinguished at the same time, eliminating losses associated with supplementary charging.

The straight line d shows that the load current 1d<Id* is determined at time T2, supplementary charging is performed, and the commutating capacitor voltage Vc reaches the minimum voltage value Vcmin before time T3. Third
The figure shows an embodiment of a control block for implementing the invention.

1 is a current or voltage regulator, 2 is a phase shifter, 3 is a pulse amplifier, 4 is a forced commutation circuit firing signal forming and distributing device, 5 and 6 are pulse amplifiers, 7 is a comparator, 8 and 9 are function generators It is a vessel.

Inputs I and of the firing signal forming and distributing device 4 are the positive group thyristor firing signal input and the negative group thyristor firing signal input, respectively. The output of the pulse amplifier 3 is supplied to each gate of the main thyristor group. PU of ignition signal formation and distributor 4
, PL output is sent from the pulse amplifier 5 to the arc-extinguishing thyristor Pu,
Similarly, the PUX and PLX outputs are supplied to the auxiliary charging thyristors Pux and PL via a pulse amplifier 6.
Given to the gate of X. In implementations a) and (b) of the control program of the invention, the load current 1d is detected. Vcmin is also related to the value of the AC input voltage from the grid, and it is possible that this input voltage is not constant, so in Example (b), this AC input voltage Es is detected to determine whether supplementary charging is necessary or not. This is the standard. Example (a
), a predetermined load current 1d* serving as a fixed reference is given, and in the embodiment (b), the AC input voltage Es to the rectifier is received, and the function generator 8 generates a predetermined load current 1♂ corresponding to this.
is generated and compared with the actual load current 1d in the comparator 7, and if Id>Id*, a firing pulse off command for the auxiliary charging thyristors Pux and PLX is output, and unnecessary auxiliary charging of the commutation capacitor is not performed. That's what I do.
This predetermined load current 1♂ is the minimum voltage value of the commutating capacitor V
It is determined in consideration of parameters such as cmin, the next extinguishing thyristor firing time T3, and the supplementary charging thyristor firing time T2. As described above, the present invention can determine whether supplementary charging of the commutation capacitor is necessary by adding a simple control block to the existing control circuit, and can reliably operate the main thyristor without performing unnecessary supplementary charging. The arc can be quickly extinguished, thereby reducing losses associated with supplementary charging.

The present invention is applicable not only to the collective commutation type forced commutation rectifier as shown in FIG. 1, but also to a general forced arc-extinguishing type auxiliary charging circuit using a commutating capacitor.

[Brief explanation of drawings]

FIG. 1 is a diagram showing an example of the main circuit configuration of a rectifier equipped with a forced commutation circuit used in the present invention. FIG. 2 is a diagram showing operating waveforms of a commutating capacitor for explaining the basic principle of the present invention. FIG. 3 is a diagram showing an embodiment of a control block for implementing the present invention. Symbol explanation, UM, VM, WM, XM, YM, ZM: Main thyristor, Cu, CO: Commutation capacitor, PU, PL: Arc extinguishing thyristor, Lu, LL: Commutation reactor, Du, D
L: Reverse current prevention diode, PUX, PLX: Auxiliary charging thyristor, Rx, RL: Braking resistor, 1: Current or voltage regulator, 2: Phase shifter, 3: Pulse amplifier, 4: Forced commutation circuit ignition Signal shaper and distributor, 5, 6: pulse amplifier, 7 recomparator, 8: function generator.

Claims (1)

[Claims] 1. In a forced commutation rectifier equipped with a forced commutation circuit having a commutating capacitor and an auxiliary charging circuit, supplementary charging of the commutating capacitor is performed by detecting the load current during commutation and comparing it with a set reference value. A supplementary charging control method for a forced commutation rectifier, characterized in that it determines whether or not to perform charging.