A new Improvement Strategy based on hysteresis space vector control of Grid-connected inverter

As a type of renewable energy, photovoltaic system has attracted increasingly great attention recently for its simple topology, control strategy and high efficiency. Grid-connected current control strategy, a key point of photovoltaic system, also becomes a hot research. At present, the current control strategies of photovoltaic inverter are divided into indirect and direct current control. Due to its simple theory and no current feedback, indirect current control strategy is commonly used in the situation that has few requirements on dynamic response. Direct current control, mainly including hysteresis and the space vector (SVPWM) control strategy, has been widely used because of its fast dynamic response and higher grid-connected current quality. Hysteresis control has many advantages, such as simplicity, easy implementation, fast dynamic response and insensitive to load, etc., but its application is limited for unfixed switching frequency and high switching loss. Comparing to hysteresis control, space vector control has low switching frequency and loss. However, its improvement is also restricted by lower dynamic response and higher sensitivity to system parameter. Therefore, A new control method: hysteresis space vector control, which has good dynamic performance and lower switching frequency and loss, have been proposed by some scholars, through combining the advantages of hysteresis with space vector control. But the new problem is that the total harmonic distortion (THD) is large in this method. With the photovoltaic power generation technology widely used, the higher requirements of grid-connected current quality have been proposed in the relevant China and international standards. In order to reduce THD, a new segmentation control strategy is firstly proposed in this paper. In this new strategy, the threshold of the current error vector was pre-set. When the actual current error is greater than the threshold, the pure hysteresis control strategy will be ad- pted to achieve the current fast track; when the current error is less than it, the hysteresis SVPWM will be adopted to reduce the switching frequency and loss. Then, the model of this improved control strategy has been established in this paper. Contrasting these control strategies by matlab/simulink simulation software, the results show that the new segmentation control strategy not only ensures fast dynamic response, lower switching frequency and system loss, but also significantly reduces current total harmonic distortion, and improves the quality of grid-connected current. Finally, a 1kW photovoltaic system has been built in this paper, and the feasibility and the superiority of the new segmentation control strategy have been further verified.