Yu Deqing

The separation of positive and negative sequence component based on SOGI and cascade DSC and its application at unbalanced PWM rectifier

The second-order generalized integrator (SOGI) and cascade delayed signal cancellation (DSC) have been used respectively in the separation of positive and negative component. But they have their own disadvantages. In order to extract grids positive and negative sequence fundamental component from unbalanced power system, the strategy of second-order generalized integrator eliminating higher harmonic and cascade delayed signal cancellation eliminating the specific frequency harmonic has been put forward in this article. It can quickly and accurately separate the positive and negative sequence fundamental component of the grid While grid voltage is distortion, symmetrical fault and asymmetric fault cases. Then, this new method is applied to unbalanced PWM rectifier.

A new modulation strategy of quasi-Z-source inverter in photovoltaic system

A photovoltaic system based on quasi-Z-source inverter (QZSI) is discussed. The QZSI has higher boost capacity and stability than the traditional inverters, but different modulation strategy is needed to realize these characteristics. A new space vector pulse-width amplitude modulation strategy is proposed to reduce the switching loss and the weighted total harmonic distortion of the output voltage of photovoltaic system. Its algorithm and implementation are discussed. The proposed method is validated by simulations and experiments.