High-power Grid-connected Inverter Research Articles

Integrated Design of Filter and Controller Parameters for Low-Switching-Frequency Grid-Connected Inverter Based on Harmonic State-Space Model

In high-power grid-connected inverter for new energy power generation system, low switching frequency makes the control loop, <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">LCL</i> -filter resonant peak and sideband harmonics generated by modulation coupled, so that the parameter design of filter and controller affects each other. This increases the difficulty of design of filter parameters and controller parameters. To solve this problem, an accurate current harmonic calculation method based on harmonic state-space model and considering switching frequency and control delay is proposed in this article firstly. Secondly, based on the above model, the parameter optimization process considering current harmonic distortion rate, filter cost and so on is constructed. The integrated optimization design of filter and controller parameters of low-switching-frequency <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">LCL</i> grid-connected inverter is completed through intelligent algorithm. Thus the filter cost is minimized on the premise that inverter performances meet the specific requirements. In addition, considering the non-ideal characteristic of grid, a scheme of integrated parameter design which can adapt to the large-scale change of grid strength is proposed. Finally, the effectiveness of the proposed method and scheme is verified by simulation and experiment.

Study of a Current Control Strategy Based on Multisampling for High-Power Grid-Connected Inverters With an LCL filter

The high-power grid-connected inverters with LCL filters have been widely used. Current control plays a key role in the grid-connected inverter control system. To cope with the inherent resonance of the LCL filter, active damping (AD) methods are usually employed. However, the AD performance is impaired by control delays which are introduced in the digital control implementation process. Besides, the lag phase due to control delays limits the system bandwidth and stability margin. The effects of control delays are more noteworthy in the high-power grid-connected inverter due to its low switching frequency. This paper investigates the current control strategy based on multisampling for the high-power grid-connected inverter with the LCL filter. First, the multisampled AD scheme is studied, which can reduce control delays effectively and improve AD performance. Besides, the multisampled control without additional damping whether passive or active is researched. Through the inverter-side current feedback, the system can realize single-current-loop control based on multisampling. Thus, the control system is simplified and it can be stable, and achieve better dynamic performance. Finally, experimental results show that the proposed control schemes are effective.

Hysteresis Model Predictive Control for High-Power Grid-Connected Inverters With Output LCL Filter

Hysteresis model predictive control (HMPC) is a variant of finite-control-set model predictive control, which is mainly developed for high-power applications. In this paper, the HMPC scheme is proposed to control a high-power grid-connected two-level voltage source inverter with an inductive-capacitive-inductive (LCL) filter. To ensure the stable operation of the control system, the resonance characteristics of the system with an LCL filter based on HMPC are analyzed, and an active damping scheme is then given. On the other hand, the impacts of the modeling error on system stability and average switching frequency are analyzed in detail. Then, a new switching frequency-adaptive control scheme that uses the average switching frequency to adjust the parameter value of the predictive model online is presented. The new control scheme can keep the average switching frequency within an acceptable operational margin, while improving the stability of the control system. For demonstration, the proposed control scheme has been implemented on a small-scale grid-connected inverter system, and the results show that the theoretical analysis is correct and that the proposed control scheme is effective.

Synthesis of Active Damping for Grid-Connected Inverters with an LCL Filter

LCL filter characterized with high harmonic current attenuating and low bulk is preferable for medium and high power grid-connected inverters, but the resonance poles of filter endanger the safety of operation. Active damping (AD) is an effective measure to increase the system stability, but various AD structures were developed with no explanation as to how they were generated. The objective of this paper is to propose a general approach for developing AD technology of grid-connected inverter with LCL-filter. Firstly, the unified analytical model and systematical synthesis method for AD are proposed, the AD structures are listed based on single-state-variable single-compensator (SSVSC), and the effective AD structures are identified by root locus. Accordingly, a family of AD structures included some of the existing AD structures and a new one has been generated systematically. In order to verify the feasibility of the synthesis method, the properties of the deduced new AD structure are analyzed and compared with the existing AD structures by theoretic and simulation. Finally, a 3kw prototype is implemented and tested to show the effectiveness of the deduced AD structures by synthesis method. Furthermore, the AD structures are developed based on multi-state-variables multi-compensators (MSVMC) to deduce another family of AD structures, and an AD table is drew. One of the main contributions of this paper is that a clear picture is made on the systematical synthesis method to generate AD structures