Study On The Control Strategies And Digital Control System For Series Voltage Transient Variation Compensators

With the increasing use of the big power electronic equipments and the non-linear loads in power system, the power quality problem is becoming more and more severe. Therefore, how to improve and ensure power quality has been one of the major topics that need to be solved urgently in the electrical engineering.First of all, the basic concept of power quality is introduced. Aiming at transient variations of voltage magnitude, which is one of the power quality issues. Then in this paper, a transformer-less series voltage transient variation compensator topology without energy storage capacitors is analyzed based on the development of its control technology.This topology is cost-effective by eliminating the large injection transformer and energy storage capacitors that are used in conventional series injection devices. This topology can compensate deep transient variations of voltage magnitude and has a good performance In order to conquer the disadvantage of the higher DC link voltage and the higher resistence voltage the switch need. A novel topology is proposed to improve the bad impact. Two-level inverter is replaced by three-level inverter so the resistence voltage of the switch will be relieved and the compensator will be high effective and low voltage harmonics. Then, this paper proposes and illustrates a new compensation control strategy which combines energy optimal control with time optimal control to enlarge the compensating time and draw a minimum amount of energy from the compensator during sags. And then, an asymptotically angle rotation method is proposed to avoid sudden phase jump of the load-side voltage and the detail algorithms is displayed.This paper use FPGA which is the Cyclone II series in Altera company to design the digital control system, such as detecting the transient variations of voltage, creating the rated voltage signal, realizing the control strategy and asymptotically angle rotation. The whole system will have a good performance besause of the fast responding time of the detection method. This paper analyzes the principle of creating the rated voltage signal and converts asymptotically angle rotation to frequency variations. Some simulation and the experiment results are given at last. Simulation and experiment results verify the feasibility of the scheme and the validity of the theory analysis.According to the research results, the proposed transformer-less series voltage variation compensator topology can compensate deep voltage variation and has a good performance. By using the mentioned improved compensation control strategy, a particular disturbance can be corrected much longer compared to that of existing energy optimal control and time optimal control. So, the improved compensation control strategy has its unique advantages and application future.