Circuit Design of Photovoltaic Grid-Connected Inverter Based on LCL Filter

Filter 18.432M

Overview:
1 Introduction In recent years, new energy power generation has risen rapidly, and photovoltaic and wind power integration has become an important research direction. Inverters as grid-connected core devices have become a new hotspot in the field of power electronics.
In order to suppress the high-frequency harmonics generated by the high-frequency power switch in the inverter link, the LCL-type filter is introduced into the grid-connected system, which can eliminate the high-order harmonic components injected into the grid, but it has shortcomings, and it is easy to produce a third-order system. The resonance peak causes oscillation and even affects the stability of the whole system. Therefore, it is necessary to improve the control strategy of the system, effectively suppress the resonance problem, and improve the power quality of the photovoltaic grid connection.
At present, domestic and foreign scholars have proposed a variety of control strategies for LCL filters, which can be divided into three types: current-based control strategies, virtual synchronous motor control strategies, and direct power control strategies (DPC). Based on the research and analysis of the principle based on direct power control strategy (DPC), this paper proposes an improved quasi-DPC control strategy, which not only preserves the LCL filter, but also reduces the harmonic energy in the high frequency band. The advantages of the ability to solve the resonance problem fundamentally.

2 Direct power control strategy is based on current and virtual synchronous motor control strategies. Direct power control has higher power factor, lower THD (total harmonic distortion rate), and excellent dynamic performance and simple structure. In 1991, Tokuo Onhishi proposed to apply direct power control to the control of the converter, the direct power control of the inverter has been widely concerned by scholars at home and abroad.
Direct power control is generally used in the switch vector table query method (L-DPC), the switch vector table is the core of system control, so studying the switch vector table is an important direction to study direct power control. Some scholars have also proposed different spatial division and optimization switch table design methods. This improvement of the switch table greatly improves the dynamic performance of the direct power control system. However, the L-DPC switching frequency is not fixed, which is not conducive to the design of the output filter.
In order to solve the problems mentioned above, people have proposed constant frequency direct power control, based on several methods of constant frequency direct power control, not only taking into account the dynamics of power regulation, but also fixed the switching frequency, but this can not achieve the grid-connected current Direct control. Later, some direct power control methods based on virtual flux linkage and active damping control were proposed, but the two control algorithms are more difficult to implement and the control is more complicated.
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