Reactive Compensation And It’s Realization Based On The Variable Capacitor

Electric is one of the most important energy nowadays.The wide application of resistive load in power network increases the loss of power supply and reactive power and causes voltage fluctuation.In order to solve this problem,the traditional method is to use a combination of multiple fixed-value capacitors switching to perform reactive power compensation of the power system.this way can realize the adjustment of the power factor of the power grid and achieve the adjustment of the power factor of the grid,so as to ensure the quality of power.The main drawback of this method is that the fixed-value capacitor combination can only be adjusted stepwise,which may result in incomplete or over-compensation of reactive power compensation.In view of the above problems,this paper conducts the following research:(1)Firstly,the theoretical analysis has been completed.The control technology of variable capacitance based on single-phase H-bridge topology is studied.Since the control object in this paper is AC signal,the conventional PI control has static error and slow control speed.Aiming at this shortcoming of PI control algorithm,this paper studies the PR control algorithm.Theoretical derivation and simulation experiment show that PR control algorithm has the advantage of tracking sinusoidal quantity without static difference.In view of this shortcoming of PI control algorithm,the PR control algorithm is further studied.Theoretical derivation and simulation experiment show PR control algorithm has the advantage of tracking sinusoidal quantity without static difference.Under the same condition,the control speed has a higher control speed compared with the PI control algorithm.However,the passband of PR control algorithm is narrow,even if the power grid frequency is slightly offset,the PR control algorithm may not achieve the desired control effect.On this basis,this paper studies the quasi-pr control algorithm,which has the bandwidth and fast performance to adapt to the frequency fluctuation of power network through parameter selection.(2)Secondly,the simulation analysis has been carried out.In the SIMULINK simulation environment,a single-phase h-bridge inverter circuit model is built.By controlling the phase between the voltage and current on the grid side and the amplitude of the grid side current,the purpose of implementing the device with the circuit is completed.The performance of PI,PR and quasi-PR control algorithms are compared and analyzed in the simulation environment:the analysis shows that the PI control algorithm can not track sinusoidal quantity without static difference;the PR control algorithm has no static tracking for sinusoidal quantity,but the passband is narrow;and its control performance is poor when the power grid is offset;the quasi-PR control algorithm can overcome the shortcoming of PR control algorithm,and meet the requirement of rapidity.The simulation waveform is consistent with the theoretical results,and the final control algorithm in the system adopts the quasi-pr control algorithm.(3)Finally,the experimental analysis of small-capacity prototype has been carried out.In terms of hardware,The power supply module,main control module,sampling module,drive module and main circuit module are designed separately.The ac 6V input,dc +5V,dc 3.3v and dc 1.8v output are realized in the power supply module;the high-performance DSP is used in the main control module to design the core processing system;the pre-processing,capture and sampling circuits are designed in the sampling module;the drive and main circuit modules are designed for isolation,driving and MOS tube single-phase H-bridge.In terms of software,the program is written in C language,which is mainly divided into main program,interrupt program and quasi-PR control algorithm program.On this basis,using P1000 waveform acquisition prototype experiments,the experiment can be achieved when the network voltage is 6 v alternating current(ac),which can realize net side current hysteresis net voltage to 90°,and the amplitude variation range of 0-1 A,equivalent to the change of capacitance value range of 0-0.5 mF variable capacitance.In this paper,theoretical derivation,simulation and small-capacity prototype design have been based on high performance DSP to realize stepless adjustment of capacitance value to ensure smoother reactive compensation.In addition,through the optimization of the control algorithm,the control speed can be greatly improved,so as to provide high-quality electric energy to meet the needs of equipment.Through simulation and prototype experiment,the realization of small capacity variable capacitance provides the possibility for the improvement of reactive power compensation and the improvement of power quality.