Abstract
This paper presents a clock phase-shifting (CPS) energy balance control (EBC) method for cascaded half-bridge multilevel inverters in standalone solar photovoltaic (PV) systems. It is based on the conservation of energy in each cascaded unit. By shifting the phase of the clock pulse of each cascaded unit, a staircase-like output voltage is obtained. The CPS EBC not only regulates the staircase-like output voltage of the cascaded multilevel inverters accurately under static conditions, but also suppresses the fluctuations of DC sources and improves its dynamic responses to load steps. Thus, the problems existing in solar PV systems using the cascaded multilevel inverters are avoided. Results obtained from simulations and experiments are presented to verify the feasibility and advantages of the proposed control method.
Highlights
Renewable energy sources are becoming increasingly important for electricity generation, since non-renewable energy sources such as fossil fuels are facing serious problems, e.g., pollutions, uncertain future of fossil-fuel prices, being unsustainable and CO2 emissions [1]
The overall control strategy is implemented on a DS1104 system, where the proposed clock phase-shifting (CPS) energy balance control (EBC) controller was programmed for the five-level half-bridge cascaded multilevel inverter
To evaluate the ability of the CPS EBC to suppress the fluctuations of DC sources, DC sources (u1, u2, · · ·, un ) are designed by DC voltage mixed with low frequency interferences
Summary
Renewable energy sources are becoming increasingly important for electricity generation, since non-renewable energy sources such as fossil fuels are facing serious problems, e.g., pollutions, uncertain future of fossil-fuel prices, being unsustainable and CO2 emissions [1]. The existence of these problems cause distortions or bring lots of low harmonics to the output voltages of the cascaded multilevel inverters using basic modulation techniques, which leads great hazards to electrical equipment. New control methods [19,20] or converter topology [21] have been proposed to deal with the interphase power imbalance problem of CHB converters in PV systems. A continuous time-domain power balancing control algorithm was presented to solve the interbridge imbalance of a single-phase CHB converter [22] This method can improve but not completely suppress fluctuations of the DC supply of the multilevel inverter. The objective of this paper is to verify the ability of the proposed CPS EBC method to deal with the problems of a multilevel inverter in standalone solar PV applications.
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