Control Strategy Of Cascade SVG And The Controller Based On FPGA

The power quality at the end of the existing electric power system is so poorthat cannot satisfy the requirement of people. However, the demands for electricityand power quality have becoming more and more high. To solve the problem ofelectric power quality is imminent. Achieving the reactive compensation andsuppressing the harmonic with active filter at the load-side is mainly used to solvethese problems. Cascaded H-bridge SVG is the main topology of the active filterwith compact topology and less switching devices, compared to the other kinds ofconverters. Its capacity is also easy to enlarge and the controller is simple to design.These advantages make the type of reactive power compensation device can be themost widely used engineering application. Researching and improving controlstrategy for the cascaded H-bridge SVG has an important significance.In this paper, the cascaded H-bridge SVG was the object of study. First of all,its domestic and international status and background were reviewed; then this paperintroduced the design of the experiment platform, presenting the main circuitstructure of the power unit module and the commonly used modulation of thecascade H-bridge SVG CPS-PWM in more detail.Then this paper recommended three commonly used current controllingmethods, including their principles and simulation results. And summarized that thedecouple control technology would low the dynamic response of the SVG speedwhen surpressing the harmonic current; current hysteresis control technique was ofgood real-time performance. However, it’s more difficult to realize in the cascadeSVG; Dead-beat technique used with CPS-PWM mode can be in combined withcascade SVG, and response fast. Finally, the paper selected the dead-beattechnology to control the current directly.Meanwhile, on the basis of the analysis for phase-in-phase voltage imbalancefactors, this paper compared two commonly used DC voltage balancing controlstrategies in phase: controlling the reference voltage for the unit; changing thePWM. Based on the analyses, this paper concluded that the first method was notstable and the latter regulation was complex which will lead the power units work atdifferent frequency. The paper proposed one new strategy to realize the balance forDC voltage in each phase by controlling the duty cycle for each unit in every halfcycle. At last, the paper proposed a set of control strategy for the cascade SVG bycombining the balance algorithm with the dead-beat technique.Finally, the proposed strategy was verified by experimental results. There were6units in each phase. The experimental results show that SVG responds fast under the control of the proposed strategy when it suppressed the harmonic current and theDC side capacitor voltage was stability.