Parallel multi-inverter systems can be designed to have the advantages of expandable output power, improved reliability, and easy N+X redundancy operation. However, a current-sharing control scheme has to be employed to enable the inverters to share the load current equally. The concept of circulating impedance is proposed in the paper, and introduced into current-sharing control scheme in parallel multi-inverter systems. The mathematical model of circulating impedance is set up. By introducing circulating-impedance control regulator, the characteristic of circulating-impedance is controlled to be similar to that of the pure resistance or inductance. Then the relationship between the circulating-current phasor and the amplitude, the phase of inverter module's output voltage reference is decoupled. Experimental 220Vac/3KVA inverter modules are built and parallel operated. The results of experiment verify that the current-sharing scheme based on circulating impedance is available and efficient.
In this work, we sequentially doped poly(3-hexylthiophene) (P3HT) films with 2,3,5,6-tetrafluoro-7,7,8,8-tetracyanoquinodimethane (F4TCNQ) from multiple good solvent/orthogonal solvent blends with different ratios. Combining UV-visible (UV-vis) spectroscopy, grazing-incidence wide-angle X-ray diffraction (GIXRD),...
Standalone photovoltaic systems have solved power supply in the many remote areas. Inverter is the key component of photovoltaic system. By paralleling several mid/low-power inverter units to compose a large power supply system, both the capability and the reliability of power supply system can be enhanced. The circumfluence among parallel inverter in PV is the key reason for preventing the parallel operating system from running normally. In order to share the load and restrain circumfluence, it is described that a digital current sharing control technique for inverter parallel operation in detail in this paper. The parallel system structure of the stand-alone photovoltaic inverter on distributed-logical-control is presented. Based on the analysis of circumfluence of paralleled system, characteristic of the power regulation, a novel digital power detection technique is deduced. With measuring and analyzing the instantaneous average current of all inverters and the output current of each inverter, both of the current components are used to control and regulate the amplitude and the phase of the output voltage. In this way, the control of current sharing in the inverter paralleling system is realized. The proposed control technique has been verified the good characteristic of restraining circumfluence by the results of the experiment. The control strategy has advantages of brevity, high practicality.
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