JPH0675016U - Reactive power compensator - Google Patents

Abstract

(57) [Abstract] [Purpose] A drawback in the case where the initial charge of the phase advancing capacitor SC of the thyristor control capacitor is limited by the current limiting resistor, that is, the power supply is likely to be affected at the time of turning on. A relatively large charging current flows and a current limiting resistor or the like with a large capacity is required. It is necessary to turn on and off the current limiting resistor, and the operability is poor. To eliminate the drawbacks. [Structure] A thyristor connected in anti-parallel is used as an opening / closing switch of a phase advancing capacitor, and thyristor Th1 having one polarity is used for initial charging. After completion of charging, the thyristor functions as a diode. In this initial charging, by detecting the capacitor current, direct current charging is performed up to the maximum value of the power supply by constant current control, and this constant current reference value is provided with an integral element to soft start the charging.

Description

[Detailed description of the device]

[0001]

[Industrial applications]

 The present invention relates to a reactive power compensator installed in a system to suppress voltage fluctuations due to load fluctuations, and in particular, a thyristor control capacitor (hereinafter referred to as TSC (Thyristor Switched Capacitor)) that controls opening / closing of a plurality of phase advancing capacitors. ] Regarding the initial charging method.

[0002]

[Prior art]

As reactive power compensator for suppressing the fluctuation of the system voltage V _l by a reactor load fluctuation of the power system, there are cases where the TSC is installed. An example of this conventional installation, particularly its initial charging method, is shown in FIG. 6 and will be described below.

In FIG. 6, reference numeral 1 denotes a system bus, which is supplied with power from a substation power supply E _S through a power supply impedance X _S and supplies power to a load 2.

Reference numeral 3 denotes a plurality of thyristor control capacitors (TSCs) installed on the system bus 1. Each of the thyristor switch 4 and the thyristor switch 4 and the phase advancing capacitor SC has a small impedance of about several percent. It consists of reactor SR connected in series.

The thyristor switch 4 is formed by connecting a diode D and a thyristor T _h in parallel with their polarities reversed, and turns on the phase advancing capacitor SC depending on whether or not the thyristor T _h is turned on in the forward direction. Take control. During this non-conduction, the phase-advancing capacitor SC is charged in the forward direction of the diode D and stands by.

CB ₁ and CB ₂ are switches provided in two stages in order to perform initial charging of the phase advancing capacitor SC, and a current limiting resistor R is connected in parallel to CB ₂ .

[0007] 5 the input control circuit of phase advancing capacitor SC, in this example, a fast power counteract fluctuating (late phase) of the reactive power Q _L of the detected load, so as to provide a phase advance capacitor SC, the introduced The Q control method that determines the number is adopted.

The closing control circuit 5 includes a reactive power detection circuit 6, an SC control group number determination circuit 7, a synchronization detection circuit 8, a thyristor firing pulse generation circuit 9, and an overcurrent detection circuit 10.

[0009] reactive power detection circuit 6, the system voltage V _L detected by the PT, the load current I _L which receives through to the meter relay Electric circuit 11 detected by CT, and calculates the reactive power Q _L of the load. SC control group number determining circuit 7 determines the number of inserted phase advance capacitor SC required to counteract the variation of this Q _L. Thyristor firing pulse generating circuit 9, to the thyristor T _h corresponding to phase advancing capacitor SC which is turned is determined to a conductive state by supplying a firing pulse. The firing pulse is output at a predetermined timing for each half-wave period by using the power supply synchronization signal generated by the synchronization detection circuit 8. The overcurrent detection circuit 10 limits the ignition of the thyristor T _h when the current I _C of each phase advancing capacitor SC detected by the CT _TSC provided in the TSC circuit becomes excessive. The operating power of the closing control circuit 5 is supplied through the input transformer _Ax TR and the circuit breaker 12.

Each phase advancing capacitor SC of the thyristor control capacitor 3 is initially charged in the forward direction of the diode D before starting. This synchronizes the opening and closing control by thyristors T _h from the time of start-is to prevent the occurrence of an abnormal voltage due to the insertion.

This initial charging is performed by closing CB ₁ with CB ₂ open. At this time, the charging current I _C flows through the current limiting resistor R, the phase advancing capacitor SC, the small capacity reactor SR and the diode D, and charges the phase advancing capacitor SC in a direct current manner.

When CB ₂ is closed a few seconds after the charging is completed, the thyristor control capacitor 3 is connected to the system bus 1 in a state where each phase advancing capacitor SC is initially charged. Accordingly, the closing control of the phase advancing capacitor SC by the closing control circuit 5 can be started in synchronization with the number of closings 0.

[0013]

[Problems to be solved by the device]

 Consider the required size of the current limiting resistor R in the initial charging method.

In order to eliminate the vibration due to the inrush current at the time of closing and to maintain the condition of overbraking

[Equation 1]

At this time, the electric power consumed by the current limiting resistor R becomes P (R) = (I _C ) ² · R.

Therefore, as the TSC has a larger capacity, it is necessary to increase the capacity of the current limiting resistor R including the radiator and simultaneously increase the capacity of the switch CB ₁ for supplying the initial charging current. The problem of large size and high cost arises.

Further, the above-mentioned initial charging method has a problem that the rush current at the time of turning on CB ₁ adversely affects the power supply. Further, the operation of the switch requires that CB ₁ and CB ₂ are charged in two steps at a predetermined interval, and the operation is complicated.

Therefore, in the present invention, the above-mentioned current limiting resistor R and the CB ₂ for turning it on and off are not necessary, and the capacity of CB ₁ is reduced, and the initial charging is performed with the influence on the power supply being minimized. The purpose is to

[0019]

[Means for Solving the Problems]

The reactive power compensator provided by this device is a reactive power compensator (TSC) that suppresses voltage fluctuations by increasing / decreasing and controlling the number of inputs of multiple phase-advancing capacitors SC installed in the system according to load fluctuations. in, are configured in a pair of thyristors connected in parallel polarities reversed by T _h1, T _h2, are one by one connected in series with each of said phase advancing capacitor SC, a direct current while the polarity of the thyristor T _h1 It is used for the current control of the initial charging of the phase advancing capacitor SC that is performed, and after the end of charging it has a diode action, and by controlling the conduction of the thyristor T _h2 of the other polarity, it controls the closing of this phase advancing capacitor. a thyristor switch 14 which has an integral element, in a state in which gradually reached the rising predetermined constant current reference value V _S with start current target of the initial charge of holding the A reference circuit 16 of V _C, to detect the current i _C of phase advancing capacitor to be controlled, the feedback control, which is to follow the said current target value V _C, the thyristor T _h1 for the corresponding initial charge An initial charging control circuit 17 for supplying a gate pulse is provided.

[0020]

[Action]

The thyristor T _{h1 having the} above configuration is feedback-controlled so that the current i _{C of the} phase-advancing capacitor follows the current target value V _C during initial charging. The target current value V _C gradually rises with the start-up, reaches a predetermined constant current reference value V _S, and enters a holding state. Therefore, the charging current at the time of startup gradually rises as shown in FIG. 4 (a) and reaches a predetermined constant current value (b). At this time, the conduction period of each control cycle of the thyristor T _h1 gradually increases. When the phase-advancing capacitor SC is fully charged, it enters a diode state in which it is conductive for the entire half cycle (270 ° to 90 °) in the forward direction.

When the initial charging is completed, the thyristor T _h1 is kept in a diode state, and the conduction control of the thyristor T _h2 is performed to control the closing of each phase advancing capacitor SC.

[0022]

【Example】

 One embodiment of this invention is shown in FIG. 1 and will be described below.

In this embodiment, an improvement is made to the conventional configuration shown in FIG. 6, and the improved portion uses a thyristor switch 14 in which the diode D of the conventional thyristor switch 4 is replaced with a thyristor T _h1. This is the addition of the capacitor soft charging circuit 15 for controlling the initial charging current with the thyristor T _h1 . In addition, the current limiting resistor R and the CB ₂ for turning it on and off, which were required in the past, have been eliminated, and the capacity of the main switch CB ₁ has been reduced.

Since the other components are common to those in FIG. 6, the same reference numerals are given and the description thereof is omitted, and the improved portion will be described.

The changed thyristor switch 14 is formed by connecting thyristors T _h1 and T _h2 in parallel with opposite polarities, and the thyristor T _h1 having one polarity is used for current control at the time of initial charging. It will function as a diode later. The thyristor T _h2 of the other polarity is used for closing and tripping of the phase advancing capacitor SC by its conduction control, and its control is performed by the closing control circuit 5 as in the conventional case.

FIG. 2 shows a specific example of the capacitor soft charging circuit 15 that controls the thyristor T _h1 .

The capacitor soft charging circuit 15 shown in FIG. 2 comprises a current target value reference circuit 16 and an initial current control circuit 17.

The current target value reference circuit 16 has a generator 18 of a variably adjustable reference voltage V _S, an integrating circuit composed of a resistor 19, a capacitor 20 and an operational amplifier 21, and a start switch SW ₁ Immediately after turning on, the current target value V _C that rises according to a predetermined time constant 1 / _CR is output toward the constant current reference value V _S.

The initial charge control circuit 17 includes a subtractor 22, a controller 23, a sawtooth wave generator 24, a comparator 25, and a gate pulse generation circuit 26.

The subtractor 22 outputs a difference between the charging current i _C of the phase advancing capacitor input from the overcurrent detection circuit 10 and the current target value V _C. The input charging current i _C is a DC signal detected by CT _TSC and smoothed in the overcurrent detection circuit 10, and the output of the subtractor 22 is the current target value of the phase advance capacitor current i _C at each time point. It represents the difference with respect to V _C.

The controller 23 proportionally integrates the output of the subtractor 22, and adjusts the characteristics of the feedback control by variably adjusting the amplification factor and the response speed. The maximum output of the controller 23 is limited by the limiter 27 so as to correspond to a predetermined ignition phase angle for causing the thyristor T _h1 to operate as a diode.

The sawtooth wave generator 24 receives the power supply synchronization signal from the synchronization detection circuit 8 and generates a sawtooth wave V _SAW that serves as a reference for determining the firing phase angle.

The comparator 25 compares the integrated output V _I output from the controller 23 with the sawtooth wave V _SAW and generates a trigger pulse for the thyristor T _h1 at the crossing timing. This trigger pulse is amplified by the pulse amplifier 26 and output to the gate of the corresponding thyristor T _h1 .

The operation of the capacitor soft charging circuit 15 will be described with reference to FIGS.

Initial charging is started by closing CB ₁ of FIG. 1 and turning on the start switch SW ₁ of the current target value reference circuit 16 of FIG. The output V _C of the current target value reference circuit 16 gradually increases toward the constant current reference value V _S , and the difference from the capacitor current i _C is input to the controller 23. The proportional-integral output V _I of the controller 23 is input to the comparator 25, a gate pulse G ₁ is generated at the timing when it crosses the sawtooth wave V _SAW, and is output to each thyristor T _h1 for initial charging through the pulse amplifier 26. To be done.

[0036] The initial charging control circuit 15, since the feedback control Ru to follow the capacitor current i _C to a current target value V _C, with increasing current target value V _C, proportional integral output V _I is It gradually rises as shown in FIG. Along with this, the capacitor current I _C slowly rises, and the capacitor voltage V _SC also rises with a small inclination, as shown in FIG. Such soft start suppresses the generation of abnormal voltage due to inrush current.

After that, when the current target value V _C reaches the constant current reference value V _S , the constant current control shown in FIG. 4B is performed. The capacitor voltage V _SC during this period increases at a constant rate.

At this time, the proportional-integral output V _I increases in accordance with the rise of the charging voltage V _SC of the phase advancing capacitor, the phase angle of the gate pulse is gradually advanced, and the current in each control cycle period is stabilized. There is.

As a result of the constant current charging, when the phase advancing capacitor SC is in the fully charged state [FIG. 4 (c)], the capacitor current I _C becomes only a minute capacitor leakage current [FIG. 4 (d)]. As a result, the output of the subtractor 22 reaches the maximum value, and thereafter, the controller 23 is fixed to the maximum output state determined by the limiter 27, and the thyristor T _h1 for initial charging is conducted for a period of 270 ° to 90 °, Functions as a diode.

In the state where the initial charging is completed in this way, the thyristor _Th2 starts the closing control of the phase advancing capacitor. At this time, each phase advancing capacitor SC is charged in the forward direction of the thyristor T _h1 for initial charging. Therefore, as shown in FIG. 5, the control of the number of inputs can be started in a synchronous state.

[0041]

[Effect of device]

According to the present invention, since the initial charging of the TSC is performed by the constant current control of the thyristor T _{h1 which is} soft-started, the influence on the power supply system during the initial charging can be reduced.

Further, the current limiting resistor R for initial charging and the switch CB ₂ for turning the switch on and off which are conventionally required are not required, and the main switch CB ₁ can have a low capacity, thereby reducing the equipment cost. It can be reduced.

Further, since the switch CB ₂ which has been conventionally required is eliminated and the operation thereof is eliminated, the operation and maintenance becomes easy.

[Brief description of drawings]

FIG. 1 is a system diagram showing a thyristor control capacitor provided with an initial charging circuit of the present invention.

FIG. 2 is a block diagram showing an embodiment of a capacitor soft charging circuit.

FIG. 3 is a diagram showing waveforms of respective parts at soft start.

FIG. 4 is a diagram showing changes in the charging current I _C and the charging voltage V _SC during initial charging when the circuit of FIG. 2 is used.

FIG. 5 is a phase relationship diagram showing that the initial charge of the phase-advancing capacitor enables synchronous closing.

FIG. 6 is a power supply system diagram showing an initial charging circuit for a conventional thyristor control capacitor.

[Explanation of symbols]

1 system bus 2 load 5 lead-phase capacitor closing control circuit 13 thyristor control capacitor (TSC) 14 thyristor switch 15 capacitor soft charging circuit 16 current target value reference circuit 17 initial charging control circuit T _h1 initial charging thyristor T _h2 charging control Thyristor V _S Voltage for reference of constant current V _C Current target value V _C i _C Charge current of phase-advancing capacitor

Claims (1)

[Scope of utility model registration request] 1. A reactive power compensator that suppresses voltage fluctuations by increasing / decreasing / controlling the number of phase-advancing capacitors installed in the system according to load fluctuations, and connecting a pair of reverse polarity parallel connections. It is composed of thyristors, and is connected in series to each of the above-mentioned phase advancing capacitors, and the thyristor of one polarity is used for the current control of the initial charging of the phase advancing capacitors performed by DC, and the diode is connected to this after the end of charging. A thyristor switch that operates and controls the conduction of the thyristor of the other polarity to control the turning on of this phase-advancing capacitor, has an integral element, and gradually rises at startup and reaches a predetermined constant current reference value. Then, the current target value reference circuit of the initial charge that holds this and the current of the phase-advancing capacitor to be controlled are detected, and feedback control A reactive power compensating device, comprising: an initial charge control circuit for supplying a gate pulse to a corresponding initial charge thyristor so that this follows the current target value.