Single-phase power conversion system such as PWM rectifier, grid connected PV inverter system, static synchronous compensator (STATCOM) can be implemented by an H-bridge inverter with a large electrolytic DC capacitor to absorb the ripple power pulsating at twice the line frequency (2ω ripple power). In order to reduce the capacitor size and to achieve high power density, a single phase DC-capacitor-less inverter with SVPWM control is proposed. The DC-capacitor-less inverter consists of an H-bridge and an additional phase leg connected to an AC capacitor to absorb the 2ω ripple power. The H-bridge and the additional phase leg can be analyzed together as an unbalanced three phase system. By adopting SVPWM control and choosing the optimal AC capacitance and the voltage reference, the voltage and current stress of the switches can be minimized to the same as H-bridge circuit. Among the existing methods, the proposed method has the minimal energy storage capacitor and total device power rating (TDPR), resulting in small capacitor size and low cost, for unity power factor inverter, PWM rectifier and STATCOM applications. The size of capacitor can be reduced by 10 times with only 1.5 times TDPR of H-bridge circuit.One important application of the single phase DC-capacitor-less inverter with SVPWM control is solid state variable capacitor (SSVC) for flexible AC transmission systems (FACTS) devices. SSVC based on the DC-capacitor-less inverter shows special benefit of TDPR, which is minimal among all applications. In order to reduce the DC capacitor to minimal value, a novel control system directly based on ripple power is proposed for fast dynamic response and good steady state performance. In addition, the proposed control system can be extended for other single phase applications and can compensate not only 2ω ripple power, but also other even order frequency ripple power caused by the harmonics of grid voltage. As a result, the capacitor size is reduced by 13 times with only 1.125 times TDPR of H-bridge circuit.Another important application is high power density and high efficiency inverter system. An interleaved DC-capacitor-less inverter with SiC devices is proposed for inverter application with different power factors. In order to improve THD performance for output voltage, an enhanced phase-shift interleaved PWM scheme is extended to unbalanced three phase system with different power factors. In order to further reduce the filter size, a new structure of integrated coupled inductors is proposed to suppress circulating current between the two parallel inverters and to filter output current at the same time. As a result, the total capacitor size is reduced by 16 times and power density of 45 W/in3 is achieved.In conclusion, the proposed DC-capacitor-less inverter with SVPWM is a competitive candidate for high power density, high efficiency and low cost single phase power conversion applications.
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