组串型逆变器的并网控制策略研究及实现
发布时间：2019-03-27 18:28
【摘要】：并网逆变器广泛应用于光伏、风力等可再生能源发电领域,作为分布式电源和电网的接口,其谐波抑制能力和进网电流波形质量是重要的性能指标。本文主要研究了单相LCL型并网逆变器的并网电流控制策略,基于DSP和PV-IPM设计了3kW组串型并网逆变器,并完成了相关仿真和实验验证。 本文选用两级式并网逆变器系统结构,前级DC/DC主要用于满足最大功率点跟踪和直流电压输入范围的要求,DC/AC级则进行逆变和并网的控制。首先研究了常见的DC/DC变换器、DC/AC变换器的拓扑电路,分析每种拓扑的优缺点及应用场合。进一步研究了Boost电路实现MPPT的调制原理,双极性、单极性、单极性倍频式SPWM的调制特点和谐波特性。 LCL型滤波器在高频段以-60dB/十倍频衰减,比纯电感滤波器具有更好的高次谐波衰减特性,但其控制模型为三阶系统,在谐振频率处存在很高的谐振峰,这往往会引起电流波形畸变,因此需要采用适当的控制策略提高系统阻尼,增强控制系统稳定性。传统的无源阻尼方案是在滤波器中串联或并联电阻,但相应的阻尼损耗以及高频谐波抑制能力的削弱并不令人满意,典型的有源阻尼技术有分裂电容法,电容电流内环反馈,无差拍控制等。本文围绕LCL型并网滤波器,对其参数设计的约束条件和计算方法,从系统的控制特性、滤波特性、阻尼特性等方面对无源阻尼和有源阻尼控制策略进行了研究和分析。 理想状态下调制只产生了高频谐波,且易被滤波器消除,但实际的非理想状态和外部扰动会注入低次谐波,因此需要对电流控制器进一步优化,来补偿或消除低次谐波污染。本文建立了单相LCL型并网逆变器的系统模型,量化分析了开关管固有特性和死区效应,直流电压二次脉动及电网谐波扰动的低次谐波注入。故而针对性提出了谐波补偿和抑制策略,最后采用一种重复控制与状态反馈相结合,并加入直流电压前馈解耦和电网电压前馈补偿的方案。 本文开发了基于DSP和PV-IPM的3kW单相组串型并网逆变器,完成主功率电路、控制电路及控制部分软件程序的设计,并通过Matlab/Simulink仿真和逆变器样机实验,验证了谐波分析的合理性和复合控制策略的有效性。
[Abstract]:Grid-connected inverters are widely used in the field of photovoltaic, wind and other renewable energy generation. As the interface between distributed power supply and power grid, the harmonic suppression ability and the quality of input current waveform are important performance indexes of grid-connected inverters. In this paper, the current control strategy of single-phase LCL grid-connected inverter is studied. Based on DSP and PV-IPM, the 3kW cascade inverter is designed, and the simulation and experimental verification are completed. In this paper, the two-stage grid-connected inverter system structure is selected. The former DC/DC is mainly used to meet the requirements of maximum power point tracking and DC voltage input range, while the DC/AC stage is used for inverter and grid-connected control. Firstly, the topology circuits of common DC/DC converter and DC/AC converter are studied, and the advantages and disadvantages of each topology are analyzed. The modulation principle, the modulation characteristics and harmonic characteristics of the bipolar and unipolar double frequency SPWM are further studied in this paper. The modulation principle of the Boost circuit to realize the SPWM is also studied. The LCL filter attenuates at the high frequency by-60dB/ ten-fold frequency, which is better than the pure inductor filter. However, its control model is a third-order system, and there is a very high resonance peak at the resonant frequency. This often causes the distortion of current waveform, so it is necessary to adopt appropriate control strategy to improve the damping of the system and enhance the stability of the control system. The traditional passive damping scheme is the series or parallel resistance in the filter, but the corresponding damping loss and the weakening of the high frequency harmonic suppression ability are not satisfactory. The typical active damping techniques include split capacitance method, capacitance current internal loop feedback, and so on. No beat control, etc. In this paper, the control strategies of passive damping and active damping are studied and analyzed from the aspects of system control characteristics, filtering characteristics, damping characteristics and so on. The constraint conditions and calculation methods for the design of LCL type grid-connected filters are discussed in this paper. The modulation only produces high-frequency harmonics in ideal state and is easy to be eliminated by filter, but the actual non-ideal state and external disturbance will inject low-order harmonics, so it is necessary to further optimize the current controller to compensate or eliminate the low-order harmonic pollution. In this paper, the system model of single-phase LCL grid-connected inverter is established, and the inherent characteristics and dead-time effect of switch tube, the second pulsation of DC voltage and the low-order harmonic injection of harmonic disturbance in power network are quantitatively analyzed. Therefore, the strategy of harmonic compensation and suppression is put forward. At last, a scheme of DC voltage feedforward decoupling and grid voltage feedforward compensation is adopted, which combines repetitive control with state feedback. In this paper, a 3kW single-phase series grid-connected inverter based on DSP and PV-IPM is developed. The main power circuit, control circuit and some software programs of the inverter are designed. The simulation of Matlab/Simulink and the prototype experiment of the inverter are carried out. The rationality of harmonic analysis and the effectiveness of compound control strategy are verified.
【学位授予单位】：东华大学
【学位级别】：硕士
【学位授予年份】：2014
【分类号】：TM464
本文编号：2448440
[Abstract]:Grid-connected inverters are widely used in the field of photovoltaic, wind and other renewable energy generation. As the interface between distributed power supply and power grid, the harmonic suppression ability and the quality of input current waveform are important performance indexes of grid-connected inverters. In this paper, the current control strategy of single-phase LCL grid-connected inverter is studied. Based on DSP and PV-IPM, the 3kW cascade inverter is designed, and the simulation and experimental verification are completed. In this paper, the two-stage grid-connected inverter system structure is selected. The former DC/DC is mainly used to meet the requirements of maximum power point tracking and DC voltage input range, while the DC/AC stage is used for inverter and grid-connected control. Firstly, the topology circuits of common DC/DC converter and DC/AC converter are studied, and the advantages and disadvantages of each topology are analyzed. The modulation principle, the modulation characteristics and harmonic characteristics of the bipolar and unipolar double frequency SPWM are further studied in this paper. The modulation principle of the Boost circuit to realize the SPWM is also studied. The LCL filter attenuates at the high frequency by-60dB/ ten-fold frequency, which is better than the pure inductor filter. However, its control model is a third-order system, and there is a very high resonance peak at the resonant frequency. This often causes the distortion of current waveform, so it is necessary to adopt appropriate control strategy to improve the damping of the system and enhance the stability of the control system. The traditional passive damping scheme is the series or parallel resistance in the filter, but the corresponding damping loss and the weakening of the high frequency harmonic suppression ability are not satisfactory. The typical active damping techniques include split capacitance method, capacitance current internal loop feedback, and so on. No beat control, etc. In this paper, the control strategies of passive damping and active damping are studied and analyzed from the aspects of system control characteristics, filtering characteristics, damping characteristics and so on. The constraint conditions and calculation methods for the design of LCL type grid-connected filters are discussed in this paper. The modulation only produces high-frequency harmonics in ideal state and is easy to be eliminated by filter, but the actual non-ideal state and external disturbance will inject low-order harmonics, so it is necessary to further optimize the current controller to compensate or eliminate the low-order harmonic pollution. In this paper, the system model of single-phase LCL grid-connected inverter is established, and the inherent characteristics and dead-time effect of switch tube, the second pulsation of DC voltage and the low-order harmonic injection of harmonic disturbance in power network are quantitatively analyzed. Therefore, the strategy of harmonic compensation and suppression is put forward. At last, a scheme of DC voltage feedforward decoupling and grid voltage feedforward compensation is adopted, which combines repetitive control with state feedback. In this paper, a 3kW single-phase series grid-connected inverter based on DSP and PV-IPM is developed. The main power circuit, control circuit and some software programs of the inverter are designed. The simulation of Matlab/Simulink and the prototype experiment of the inverter are carried out. The rationality of harmonic analysis and the effectiveness of compound control strategy are verified.
【学位授予单位】：东华大学
【学位级别】：硕士
【学位授予年份】：2014
【分类号】：TM464
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