JPH0746888B2 - Control device for voltage fluctuation compensator - Google Patents

Description

The present invention relates to a control device for a voltage fluctuation compensating device of a constant voltage control system.

[Prior Art and Problems] For example, a control device as shown in FIG. 2 is adopted in order to perform constant voltage compensation for a voltage fluctuation of a bus bar having a fluctuating load such as an arc furnace. The figure shows one phase. A variable load 11 such as an arc furnace is connected to the power bus 1. On the contrary,
A reactor, or a high-impedance transformer 12 and an antiparallel connection thyristor switch 10 as shown in the figure are connected in series to the bus bar 1, and a filter 13 composed of a capacitor and a reactor is arranged in parallel with the reactor 13. Compensation circuit (TQC) is configured to control the energization of the high impedance transformer 12 by applying a phase control ignition pulse to the control pole of the thyristor switch 10 to generate reactive power, which is generated by the variable load 11. The voltage fluctuation is compensated. In this way, in order to compensate the voltage fluctuation, a ΔV detection circuit for detecting the voltage fluctuation of the bus bar 1 is connected. Reference numeral 4 denotes a ΔV detection circuit, a voltage detector 41 is connected to the secondary side of PT2, and its output side has a low-pass filter 42.
, And directly through the comparator 43, the difference voltage output is
The output ΔV is input to the adder 7 via the PI controller 44. The current generated by the fluctuating load 11 is input from the CT3 to the adder 7 via the steady value setting device 5 (for example, 50%).
The timing signal from the synchronous detector 6 which is the output from the adder 7 is input to the pulse generation circuit 8, where the firing phase control pulse of the thyristor 10 is generated, and the pulse amplifier 9
The firing control of the thyristor 10 is performed via the control circuit to control the constant voltage of the busbar.

Since this ΔV detection circuit 4 is in a closed loop, it means that the control error due to the main control is constantly corrected.

Now consider voltage compensation of 1% of the bus voltage. Stationary deviation: ε,
Loop gain: G _L , loop time constant: τ _L.

However, ΔVin: change in voltage input, ΔVo: change in reactive power due to change in thyristor control signal, Ko: gain of ΔV detection circuit, To: time constant of the same circuit.

Here, consider concrete equipment.

Condition ε = 5%, Vin = 10V × 1% = 0.1V, ΔVo = 10V, τ _L =
50mS, G _L = 20 (times).

From equation (1) From equation (2), To = τ _L · G _L = 0.05 × 20 = 1 (S) From the above, the controller 44 in FIG. 2 has a high gain, and the adjustment of the initial setting, the temperature drift of the amplifier, etc. significantly affect. Therefore, not only the use of high-grade parts is required, but also a stable operation control device cannot be expected. For example, PI controller 44 in Fig. 2
Assuming that the zero offset (V _OF ) of the operational amplifier (hereinafter abbreviated as OP amplifier) used for is about 2 mV, the output ΔV of PI controller 44 is ΔV = V _OF × K ₁ = 0.002v × 2000 = 4V On the other hand, the linear region of a normal OP amplifier is ± 10V, so ε = 4/10 = 40 (%) error occurs, and bias adjustment is required.

This becomes a problem in the early stage of operation, and fine adjustment is performed on site, but
Adjustment of mV is quite difficult.

[Means for Solving the Problem] In the present invention, when suppressing voltage fluctuation of several% in a voltage system,
With the conventional method, the open gain of the PI controller becomes 1000 times or more, and it was made for the purpose of solving the difficulty in offset adjustment especially at the initial stage of operation. In the voltage fluctuation compensator of the constant voltage control system, the PI fluctuation can be detected in the preceding stage of the PI control system and amplified, so that PI control can be performed in a minor loop configuration.

FIG. 1 shows the control system of the present invention. The same parts as those in FIG. In the figure, the portion surrounded by the dotted line is the ΔV detection circuit.

PT2 is coupled to the bus 1, its output side is connected to the V detector 41, and its output ΔVin is input to the first comparator 43.
On the other hand, V _S is input to the comparator 43 by the specified voltage setting device 45,
The output of the comparator 43 is input to the comparator 43 ′ via the coefficient unit 46, the output side of the comparator 43 ′ is connected to the PI controller 47, and the output side of the PI controller 47 is the voltage divider 48 and the adder. Connected to 7.

The output side of the voltage divider 48 is connected to a perfect integrator 49, whose output is V _ref via the second comparator 43 '.
To enter.

On the other hand, the output ΔV of the PI controller 47 is added to V ₅₀ from the steady value setting device (50%) 50 in the adder 7 and input to the thyristor pulse generation circuit 8. The thyristor pulse generating circuit 8 receives a sync signal from the sync detector 6 connected to PT2.

In the above configuration, unlike the conventional ΔV detection circuit of FIG. 2, basically, the change amount is first detected by the specified voltage V _S , and this signal is multiplied by a coefficient to obtain a PI controller. 47,
The gain of the controller 47 is reduced by performing minor loop control including the voltage divider 48, the perfect integrator 49, and the comparator 43 ', and a stable voltage feedback control configuration is formed.

Specifically, consider the equipment. However, the equipment has the same specifications as the equipment described above, G _L = 20 (times), ε = 5%, τ _L = 50 ms
And

The specified voltage V _{S is set} to 100% and the coefficient (-K
₂ ) = 20 (times).

The second first relationship Fig K _2, K ₃ of FIG K _1, since a K ₁ = K ₂ · K _3, from K ₁ = 2000 (times), K ₃ = 100
(Double) is fine. Further, if T ₃ = T _o = 1 (S), then from the above equation (1) From equation (2), since τ _L = T ₃ / G _L = 50 ms or more, and K ₃ = 100 (times), there is no need to perform initial setting of operation and use of high-grade parts. It can be considered that the influence of the offset will be 1/20 of the conventional one.

Further, the voltage divider 48 and the perfect integrator 49 form V _ref , and the time constant τ ₄ is τ ₄ = T ₄ / K ₃ (3) where n = 1 / K ₃ (n is a voltage division ratio) Consider the zero offset of the control system.

Since K ₂ = 20 (times), the zero offset ΔV _{K of the} coefficient unit 46
Is ΔV _K = 2 mV × 20 (times) = 40 mV The output ΔV ′ of the next stage PI controller 47 is ΔV = K ₃ (if the zero offset voltage of the OP amplifier of PI controller 47 is ΔV _KOF = 2 mV). ΔV _K + ΔV _KOF ) = 100 × (40mV + 2mV) = 4.2V By making V _ref with the voltage divider 48 and the perfect integrator 49 and applying the feedback, the output of the perfect integrator 49 becomes 4.2V, and the PI controller 47 outputs The output is ΔV = ΔV ′ + V _ref = 4.2 + 4.2 = 0 (V). That is, the offset of the control system can be removed by the minor loop.

[Effects of the Invention] (1) In the present invention, the voltage change is detected in the preceding stage of the PI control system,
By amplifying, the PI control may have a minor loop configuration, and the voltage change amount can be accurately controlled.

(2) The gain of the PI control system can be apparently reduced, resulting in a stable control configuration.

(3) The zero offset of the OP amplifier can be ignored, and a stable control circuit that does not require adjustment can be expected.

[Brief description of drawings]

FIG. 1 shows a control circuit of the voltage fluctuation suppressing device of the present invention. FIG. 2 shows a conventional control circuit of the voltage fluctuation device. 41 …… Voltage detector, 42 …… Low pass filter, 43,43 ′
…… Comparator, 44,47 …… PI controller, 45 …… Specified voltage, 46
…… Coefficient unit, 48 …… Voltage divider, 49 …… Complete integrator, 50…
… Steady value setter (50%).

Claims (1)

[Claims] 1. A voltage fluctuation of a bus bar to which a variable load is connected is ΔV.
In the control device of the voltage fluctuation compensating device for detecting the thyristor of the reactive power compensating circuit by detecting by the detecting circuit,
The detection circuit is a V detector connected to the bus through PT,
The output of this V detector and the specified voltage of the specified voltage setting device are input, and a first comparator that compares the two and outputs the voltage fluctuation change amount, and the output of the comparator are input and multiplied by a coefficient-coefficient , A second comparator that receives the coefficient-multiplied output of the coefficient multiplier, a PI controller that receives the output of the comparator, and a thyristor control signal line and the PI controller on the output side of the PI controller. A controller for a voltage fluctuation compensating device, comprising a minor loop including a controller, a voltage divider, a perfect integrator, and the second comparator.