Reactive power compensation device in the application

With the development of power electronic technology and the use of various nonlinear load and large power equipment start-stop, will produce a large number of harmonic current and reactive power, so that the quality of power supply are badly affected. As big iron and steel enterprise, electric arc furnace, rolling mill as a nonlinear load and irregular grid people, such as a series of adverse impact on power grid and other loads. Is the main method to solve these problems in interference load access points connect static dynamic reactive　50 kvar capacitor power compensation type I Pi Bei now of intermediate frequency furnace and medium frequency power rectifier filter circuit, the device is mainly include thyristor for capacitors, thyristor controlled reactor, which is the TSC mixing device three kinds of structure, the TCR type structure generally parallel capacitor, a fixed capacitor thyristor controlled reactor structure [1, 21. Through the thyristor control dynamic reactive power compensation, adjust the bus voltage and line reactive power at the required level, to improve power system stability, and expand the line transport capacity.
Through the comprehensive comparison of the above three kinds of structure SVC, from the dynamic response time is short, can be divided into phase to control and adjust the continuity of the consideration, FC TCR type SVC can have very good 50 kvar power capacitor compensation effect. Therefore, this article selects the structure to realize rolling mills are reactive power compensation, and focus from hardware implementation, software algorithm and the characteristics of the controller, and implements the rolling with static reactive compensation device the implementation scheme of the controller.
1 system composition and working principle
1.1 which is the basic structure and principle
Which is the basic structure of single-phase as shown in figure 1, two of the parallel thyristor with a reactor in series, and more than three phase using triangle connection. This circuit is on the grid, is equal to the inductance load of the ac voltage regulation circuit structure mockery. With thyristor series reactor as the energy storage component, absorb the inductive reactive power, by adjusting the equivalent susceptance trigger delay Angle change system, so as to adjust the equivalent reactance of compensator, reach the role of perceptual reactive power regulation.
1.2 the composition and the principle of FC TCR type SVC
FC TCR type SVC is mainly composed of three parts: FC filter, which is the thyristor controlled reactor control and protection system, as shown in figure 2. FC filter is used to provide a capacitive reactive power compensation and harmonic filter, which is the thyristor controlled reactor is used to balance in the system due to the fluctuation of the load produced by the inductive reactive power.
Adjust the size of the thyristor trigger Angle, the current through the reactor can be controlled, so as to achieve the purpose of reactive power control. According to the change of load reactive power Q, changes the reactive power of the reactor 9 T-shirt tara reactive power), namely, no matter how the load reactive power make the sum  capacitor 50 kvar of both constant is constant, the constant is equal to the capacitor Banks issued a capacitive reactive power Q value of the reactive power from the power grid is constant or zero, namely the Q = Qc_ lifted up) and (Q Q = constant (or zero), led to the power factor of power grid in a set value, voltage fluctuations, hardly to achieve the purpose of reactive power compensation, to restrain the load fluctuation caused by the system voltage fluctuation and flicker.
2 the implementation of the controller
TCR type SVC FC mainly includes the main circuit and controller of two parts, as shown in figure 3 below. This article focuses on the controller, the system block diagram as shown in figure 4 shows, the controller through the acquisition of three-phase voltage, three-phase current signal, after the instantaneous reactive power theory calculate algorithms, such as the triggering Angle and output signals to control thyristor conduction, which is the realization of dynamic reactive power compensation.
2.1 hardware implementation
The hardware of the controller according to the modular design concept design, as shown in figure 5 shows, mainly composed of signal conditioning module, power supply module, voltage current signal conditioning module, DSP module, CPLD module. Power supply module for power supply, the controller voltage signal conditioning module, current signal conditioning module, respectively, three phase current of three-phase voltage signal conditioning, sampling and filtering. In addition to containing the minimum system, DsP module also contains external AD sampling circuit, etc. In addition to containing the minimum system, CPLD module also contains a trigger pulse transmission circuit, return signal receiving circuit, frequency multiplication phase-locked circuit and so on.
2.2 software implementation
Controller software process as shown in figure 6 shows, software implementation mainly includes to regulate three-phase voltage, current signal after the AD sampling, calculation of the effective value of voltage and frequency values, DsP module according to 7.5 kvar power capacitor the algorithm to calculate the trigger Angle, CPLD module trigger pulse signal, etc. This article focuses on based on instantaneous reactive power theory of three-phase voltage, three-phase current calculation algorithm implementation of compensation Angle, as shown in figure 7, specific algorithm including:
[41 (1) based on instantaneous reactive power theory of three-phase voltage signals were collected by three phase current, signal extraction of 7.5 kvar capacitor fundamental positive sequence active component, reactive component of the fundamental positive sequence and fundamental negative sequence power component and fundamental negative sequence reactive component; the positive and negative sequence current detection using instantaneous reactive power theory is one of the algorithms, the detection principle of positive sequence current as shown in figure 8. In this method, need to use with the voltage phase one eostot sintot sine and cosine signal, which consists of a phase-locked loop (PLL) and the circuit is a sine, cosine signal. According to the definition can be calculated, IQ, via IJPF filter to obtain the dc component.
3 summary
People power grid for nonlinear load such as rolling mill, seriously affect the quality of power supply problem, put forward the TCR type FC compensate static reactive compensation device, improve the quality of power supply. This paper mainly based on DSP and CPLD device was developed with static reactive compensation device of steel rolling controller, this paper introduces the hardware implementation and software algorithm of the controller, and has carried on the thorough analysis to the characteristics of the controller. Finally, the development of steel rolling by static reactive compensation device controller has carried on the experiment, the experimental results show that the controller can according to the change of the three-phase voltage, three-phase current, real-time, split phase control thyristor conduction, reactive power compensation.