JPS5851741A - Controller for ac/dc converter - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a constant current control method in an AC-DC converter such as DC power transmission.

In DC power transmission, it is common to use constant current control on the forward converter side (REC) and constant voltage control or constant margin angle control on the inverse converter side (INV). FIG. 1 shows a block diagram of such a constant current control system.

In Figure 1, (1) is the main transformer for the converter, (2) is the forward conversion device using a thyristor valve, and (3) is the main transformer for the converter.
) is a DC reactor (DOL) that smoothes the DC current,
(5) is an inversion device using a thyristor valve that converts direct current into alternating current, (6) is the main transformer for the inverter, and next, the operation of the constant current control system will be explained. The direct current flowing through the direct current system is detected by a direct current transformer (DCOT) (7), and is converted by a signal converter (8) into a value Ido corresponding to the direct current. (9) is a comparison amplifier that adds Idc and current set value Idp with the polarity shown. Ql is a comparison amplifier (9)
A is an automatic pulse phase shifter (PPB) for controlling the firing angle of the thyristor valve from the control signal of aΦ.

Figure 2 shows a case where the DC current detection is installed on the DC winding side of the transformer.
This is done from the old Tv, and in the figure, the same reference numerals have the same functions. (b) is a filter that smoothes the current waveform of CT (2). Although only the forward converter side has been described above, the inverse converter is also provided with a constant current control system, and the structure and operation of the control system are the same as those of the forward converter, so in the following discussion, Let us consider the operation of a forward converter.

Now, the following problem occurs in the constant current control device as shown in FIGS. 1 and 2. In other words, in the control system shown in Figure 1, the time constant of the constant current control loop is small, so although the response is fast, ripples in the DC current may occur, and furthermore, failures such as arm short circuits may occur in the converter. Even if
Since no current flows through DC (5T (7)), the fault current cannot be suppressed by current control.
In the constant current control system shown in the figure, the current waveform on the DC winding side of the transformer is a normal 120e width rectangular wave current, as shown in Figure 8, and a resistor (not shown here) attached in parallel to the valve. , a ripple occurs in the charging/discharging current of the capacitor, and therefore a smoothing filter as shown in FIG. 2 111 is required. Therefore, an arm short circuit fault can be detected, but because of the control delay caused by the fill ζ, there is a drawback that fault current suppression is delayed not only in arm short circuits but also in DC transmission line faults.

Generally, the magnitude of the fault current differs depending on whether it is inside the DC reactor DCL, ie, the converter side, or outside, ie, the power transmission line side. An example of an accident inside DCL! In the case of an arm short circuit or DC bus fault, an excessive fault current flows, so high-speed constant current control is required.

On the other hand, in an accident outside the DCL, such as a DC transmission line accident, although an excessive current does not flow as in an accident inside the DCL, fast current control is required. On the other hand, it is desirable to respond slowly and reliably to DC current fluctuations caused by disturbances in the AC system.

The present invention was made in order to eliminate these two drawbacks of the conventional constant current control system, and eliminates the blind spot of current detection. In the event of an accident, the speed of suppression of the fault current is changed depending on the nature of the accident, and constant current control is performed.

Hereinafter, one embodiment of the present invention will be described with reference to the drawings.

FIG. 4 shows only the forward converter side of the constant current control system according to the present invention. In Figure 4, (2) is the maximum value selection circuit that selects the larger of the outputs of D(30T, (to) DOCT (7) and (2) installed on the return line side, @ and - are A signal conversion circuit that converts direct current to Idc or Idc, 04 to O. is an addition that adds , K, to the detected value Idc1.Ida, current setting value Idp, and a constant described later with the polarity shown. Comparator to do, target is comparator 04
018 is a constant current control loop (AOR) with a relatively large time constant that makes the deviation of 0 O, 018 is a constant current control loop (AOR) with a small time constant that makes the deviation of
MACR), (11 is the bias of the comparator Q, the constant current control loop (HACR) whose time constant such that the difference is O is even smaller than the constant current control loop (to), and (e) is the home current control loop. It is a minimum value selection circuit that selects the minimum value among the outputs of Q to DI, and ap is a pulse phase shifter PP8.K, , and are bias values added to the comparators.
l <Kl, and then! is the ripple component of the transformer DC winding current i (usually 2 of the DC current) as shown in Figure 8.
(approximately 0 to 80%). When K1 and Kl are set in this way, the current detection value Idc1 and the set value are always equal, so the constant current control loop α
The force is no output, and the comparator (G) is set with 1 Kl on the bias.
, 0. have a certain finite value, so the constant current control loop M
A(!R (to), the constant current control loop HACRQI is fully saturated, so this is selected because the output of the constant current control loop AORαη is the minimum. On the other hand, when a fault occurs in the DC transmission line, the DC current Transformer (7), σno detection current I
As φ01 increases and approaches Idp0Kl, although HACRO is still saturated on the + side, MAOR (to) enters the operating region and maximum value selection circuit 4 has AORQ71. M.A.
(The smaller one among 3R(to) is selected.Idol
If is almost the same as Idp-)-Kl, the output of MACR(to) will be smaller than the output of A(3RQη, so M
The output of AOR(to) is selected.

However, since MAORoa has a smaller time constant than ACjRQη, MACRQII quickly performs constant current control and suppresses the fault current. In addition, if an arm short circuit occurs and the detected value Idc of DOCT (2) becomes about the same as Idp 10, the output of the constant current control loop (2) will be the minimum, so HAORQ mode will be selected, and the Rapid constant current control is performed. Also, Konoto! If 1 and 2 are set as described above, there is no need to provide a filter, so there is no delay in control caused by providing a filter. In other words, the eight-loop constant current control system allows constant current control to be quickly performed depending on the nature of the accident. In Fig. 4, the DC current transformer (to) and the maximum value detection circuit (to) may be omitted; they are only provided to duplicate the DC current transformer. As described above, this invention uses a constant with the smallest time constant to deal with converter failures such as arm short circuits and DC bus failures, which require the most rapid current control. Can be rapidly controlled by current control loop Q-groan, DC reactor (3)
Failures in DC transmission lines outside of the area can be controlled relatively quickly using the constant current control loop with the second smallest time constant, and DC current fluctuations due to disturbances in the AC system can be controlled relatively quickly. , constant current control loop Q7 with the largest time constant
) can be controlled slowly. In other words, the converter (2) can be controlled at the most appropriate speed for each failure.

Furthermore, in the present invention, high-speed control can be achieved without using a filter by setting the constant added to the comparator when it is 0 to be larger than the ripple of the current on the secondary winding side of the transformer (1).

As described above, according to the present invention, since the time constant of the constant current control system is configured to be switched depending on the magnitude of the fault current, there is an advantage that rapid constant current control is possible depending on the nature of the fault.

[Brief explanation of drawings]

Fig. 1 and Fig. 2 are diagrams showing a conventional constant current control system, Fig. 8 is a diagram showing a waveform of a transformer DC winding current, and Fig. 4 is a diagram showing a constant current control system according to the present invention. . In the figure, (2) is an AC/DC converter, (7), 17υ,
(2) is a current transformer, (2) is a maximum value selection circuit, α◆, (2
), fs comparator, Q21, (to), cap * constant current fl
Hl) h-f, met maximum/lX value selection circuit. Agent Makoto Kuzuno - Figure 1 DP No. 21-21

Claims (1)

[Claims] A first means for detecting a current on the alternating current side of an AC/DC converter equipped with a constant current control system, a second means for detecting a current on the direct current side, and an eighth means for detecting a current on the direct current return side. and when the outputs of the second and eighth means are equal, the first means has the largest time constant. The ignition phase is controlled by a constant current control system, and if the outputs of the second and eighth means are not equal, the firing phase is controlled by the constant current control system whose time constant is smaller than that of the first constant current control system. When the arc phase is controlled and the output by the first means is larger than the output by either the second or eighth means, the timing factor is smaller than that of the second constant current control system. An AC/DC converter control device characterized in that an ignition phase is controlled by a constant current control system.