Design And Optimization Of Digital Controller For The Three-phase Four-wire Shunt Active Power Filter

There is a growing concern about the problems of harmonics in power distributions nowadays, for it may reduce the efficiency of the electrical energy in production and transformation, and the electrical equipment would be overheating, vibrating and making noises, which isolation and life-cycle would be shorten, or even facing the high risk of failure or burned, and also cause serious EMI problems to other power system equipment. Thus, the elimination of harmonics is particularly important. Active power filter(APF, active power filter), which can dynamically compensate harmonics and reactive power for the power distribution, is considered the most effective means to the problem. This paper studies the design and optimization of phase four-wire shunt active power filter digital controller, the work has been done in the following areas,First, the main design targets of the three-phase four-wire shunt active power filter have been reviewed. The main power topology has been analyzed, and the discrete current-loop and voltage-loop mathematic model have been deduced, which are based on synchronous rotating coordinate. Analyzed and designed a load harmonic current detection algorithm based on synchronous rotation transformation. Analyzed and designed a simplified 3D-SVPWM algorithm for the topology, which is extremely saving time and storage space compared to the traditional SVPWM algorithm.Second, the detailed method to design the digital compensator for the control loop of the active power filter has been proposed, including one-zero approach and a combination of one-zero approach and repetitive controller for the current-loop, and one-zero approach for the voltage-loop. As for designing the system, an optimized software structure has been proposed based on the hardware signal connection of the prototype, which implements multi-thread and state-machine to optimize the overall performance. An EDMA-based human-machine communication solutions has been applied to further optimize the overall performance of the digital controller.Third, the relationship between the performance of the active power filter and the DC-side operation voltage has been analyzed. And based on the conclusion, the optimized DC-side operation voltage has been deduced and a phase-II soft-start method has been proposed and analyzed in details. Also, in order to improve the performance of the voltage-loop compensator, the discrete voltage-loop model has been modified and re-designed. All the methods have been validated by simulation.Finally, all the theories and optimization methods have been verified by running the Simulink simulation and experiments on the prototype. The results show that the designed digital controller can effectively utilize the resources of the system to achieve a high performance, which could effectively compensate the load harmonic currents and reactive power. And the methods to optimize DC-side operation voltage can further improve the performance, reducing the THD of compensated source currents.