A novel transformerless boost inverter for standalone photovoltaic generation systems is proposed in this paper. The proposed inverter combines the boost converter with the traditional bridge inverter. The switch S 1 not only realizes the boost function but also participates in inverting process. The inverter has a higher voltage gain and good characteristics when the inductor L 1 is operated in discontinuous mode (DCM) and the nonpolarized capacitor can be chosen as bus capacitor, which makes the volume smaller and the service life of the inverter is increased. The inverter consists of five switches in which only two switches are operated at high frequency state and a monopole sinusoidal pulse width modulation (SPWM) strategy is used. Therefore, the modulation strategy of switches is very simple and the switching loss is reduced. The principle of inverter is described in detail and mathematical models are built by small-signal analysis. Finally, the correctness of the theoretical analysis is verified by simulation and experiment.Index Terms-Boost inverter, discontinuous mode (DCM), monopole sinusoidal pulse width modulation (SPWM), nonpolarized capacitor, photovoltaic generation systems, transformerless.
The concepts of dual coupled inductors and voltage multiplier cell are integrated to derive a novel non-isolated interleaved high step-up boost converter in this paper. At the input, due to the interleaved dual coupled inductors and voltage multiplier cell, the converter inhibits current ripple and reduced voltage stress for the power devices; At the output, the secondary sides of the two coupled inductors are connected in series to achieve the purpose of much higher voltage gain and lower voltage stress on the power devices. Therefore, lower voltage rating MOSFETs and diodes can be selected to reduce both switching and conduction losses. In addition, the leakage inductance energy of two coupled inductors can be absorbed and recycled to the output, and the reverse-recovery problem of diodes can be effectively suppressed. Zero current switching (ZCS) turn-on is realized for the power switches to reduce the switching loss. The working principle and steady-state characteristics of the converter are analyzed in detail. The voltage balance of the output capacitors and input current sharing by two interleaved phases are realized through the double closed-loop control of voltage and current. Finally, a 400 W laboratory prototype with 25~30 V input and 400 V output is built to verify the significant improvements of the proposed converter.Index Terms-Coupled inductor, high voltage gain, interleaved, voltage multiplier cell.
The configuration and principle of shunt active power filter is introduced briefly in this paper. A digitally controlled shunt active power filter based on double DSP is designed for the three-phase four-wire system. The main circuit of the shunt active power filter selects a four-leg voltage-source inverter, and a dynamic hysteresis-band current control is used to track the current. A control strategy based on the instantaneous reactive power theory is given in consideration of the source voltage becoming distorted and unbalanced. The facility can compensate harmonic and reactive power completely for three-phase four-wire system. The hardware configuration, flow chart of software, derivation of compensating signal and derivation of PWM waves are analyzed. The validity and correctness of the filter are proved in experiment.
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