The Research On Some Key Technologies Of Active Power Filter Based On FPGA

With the proliferation of nonlinear loads such as rectifiers and inverters, harmonics and reactive power in power systems are becoming a serious problem. Active power filters have proved to be an important and flexible alternative to compensate harmonics and reactive power. The idea of active filters is relatively old, but their practical development was made possible with the new improvements in power electronics and microelectronics. Shunt active power filter (SAPF) has been becoming the mainstream of practical applications owing to its convenient in installation and maintenance. At present, the research on SAPF mainly concentrates on real time current reference signal detection and current controlling strategies. The dissertation does systemic and deep research on shunt active power filter applied in elevator industry, including related theories and application issues.The instantaneous reactive power theory or "p-q theory." has played a significant role in prototyping of SAPF. Classical power definitions in time domain are reviewed, and the p-q theory and its physical meaning are discussed in detail in this paper. To overcome the shortcoming of p-q theory in dynamic performance under unbalanced and non-sinusoidal AC voltages, a new current reference detection algorithm based on Selective Band Pass Filter (SBPF) is applied. The frequency and dynamic responses of the SBPF are mathematically analyzed and discussed. The extraction method can simultaneously determinate the current reference signal without needing the additional phase locked loop (PLL) and low pass filter (LPF).The mathematic model of three-phase three-wire SAPF is established. After establishing the mathematic model, the spectrum of switching function and AC side voltage are analyzed. Then, based on the practical case, the value of DC side voltage and AC side inductor are derived. What's more, in order to suppress the high frequency harmonic related to the switching frequency, the selection of ac side high frequency filter capacitor is discussed.Real-time and accurate current reference signal extraction method and current track controlling algorithm are the key for SAPF implementation. A field-programmable gate-array (FPGA)-based digital controller of SAPF is designed. The digital controller consists of three parts:analog-to-digital converter control module, current reference signal calculation module and current track controlling module.The designed digital controller implementation is experimentally validated by "FPGA in the loop" prototyping using a Cyclone III DK-DSP-3C120N-0D development platform.