并网逆变器电流控制技术的研究
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南京航空航天大学 硕士学位论文 并网逆变器电流控制技术的研究 姓名：徐志英 申请学位级别：硕士 专业：电力电子与电力传动 指导教师：谢少军 20090201
南京航空航天大学硕士学位论文
摘
要Biblioteka Baidu
并网逆变器是新能源发电系统的重要组成部分。本文以单相全桥并网逆变器为研究对象， 对并网电流控制技术进行了深入研究。 并网逆变器的输出滤波器有 L、LC 和 LCL 三种形式，通过对这三种滤波器的滤波性能进 行对比发现，LCL 滤波器高次谐波衰减效果显著，即使在低开关频率和较小的电感情况下也能 满足电流谐波衰减要求。本文采用了 LCL 滤波器作为输出滤波器，并根据技术指标设计了滤波 器参数。 LCL 滤波器在谐振频率处存在幅值尖峰，对并网电流控制策略要求较高，采用典型的入网 电流直接闭环控制的并网逆变系统是不稳定的。为了抑制谐振尖峰，改善系统稳定性，必须增 加系统阻尼，LCL 滤波并网逆变器的谐振阻尼控制策略可分为无源阻尼方案和有源阻尼方案。 无源阻尼方案简单易于实现，但是，它增加了功耗，降低了滤波器的高次谐波衰减程度，而且 系统稳定性较差。论文从系统稳定性、谐振抑制效果和入网电流相位控制三方面对逆变器输出 电流反馈控制、分裂电容法电流控制与入网电流和电容电流双闭环控制这三种有源阻尼方法进 行了对比分析，综合评估了各种控制策略的性能。研究结果表明，电流双闭环控制策略具有谐 振抑制能力强，入网电流相位直接可控的优点，且系统稳定性也较好。文中对电流双闭环方案 的谐振抑制原理和系统稳定条件进行了具体分析，并给出了闭环控制器的设计方法和外特性的 改善措施。 为了验证本文理论分析的正确性，进行了并网逆变器的仿真研究。最后采用入网电流和电 容电流双闭环控制进行了实验研究。实验结果表明，该控制策略能有效抑制谐振尖峰，实现高 功率因数并网，系统具有优良的动静态性能。 关键词：并网逆变器，并网电流控制，LCL 滤波器，电容电流反馈，双闭环控制
ii
南京航空航天大学硕士学位论文
图、表清单
图 2.1 两级式并网发电系统.................................................................................................................6 图 2.2 单级式并网发电系统.................................................................................................................6 图 2.3 单相全桥并网逆变器.................................................................................................................7 图 2.4 双极性正弦脉宽调制方法及逆变桥输出波形 .........................................................................7 图 2.5 单电感滤波并网逆变器.............................................................................................................8 图 2.6 LC 滤波并网逆变器 ...................................................................................................................8 图 2.7 LCL 滤波并网逆变器 .................................................................................................................9 图 2.8 L 和 LCL 滤波器的幅频特性曲线 ............................................................................................9 图 2.9 单电感滤波并网逆变器滤波电感电流波形 ...........................................................................11 图 2.10 单电感滤波并网逆变器滤波电感电流的谐波分布 .............................................................11 图 3.1 LCL 滤波并网逆变器电路 .......................................................................................................13 图 3.2 LCL 滤波并网逆变器数学模型 ...............................................................................................14 图 3.3 入网电流反馈控制框图...........................................................................................................14 图 3.4 入网电流反馈控制系统开环伯德图 .......................................................................................14 图 3.5 入网电流反馈控制系统闭环根轨迹 .......................................................................................15 图 3.6 LCL 滤波并网逆变器串联阻尼电阻的电路图 ......................................................................15 图 3.7 添加阻尼电阻后入网电流反馈控制框图 ...............................................................................16 图 3.8 带阻尼电阻和不带阻尼电阻时 LCL 滤波器的幅频特性曲线 .............................................16 图 3.9 添加阻尼电阻后入网电流反馈控制系统闭环根轨迹 ...........................................................16 图 3.10 逆变器输出电流反馈控制结构框图 .....................................................................................17 图 3.11 分裂电容法电容中间电流反馈控制结构框图 .....................................................................18 图 3.12 入网电流和电容电流双闭环控制结构框图 .........................................................................18 图 3.13 分裂电容法电流控制输出量闭环系统幅频特性曲线 .........................................................19 图 3.14 逆变器输出电流反馈控制输出量系统和入网电流和电容电流双闭环控制系统的幅频特 性曲线 ..................................................................................................................................................20 图 3.15 电容电流内环控制框图.........................................................................................................21 图 3.16 幅频特性曲线.........................................................................................................................21 图 3.17 入网电流和电容电流双闭环控制等效结构框图 .................................................................22 图 3.18 典型Ⅱ型系统的开环对数幅频特性和中频宽 .....................................................................23 图 3.19 加入电网电压前馈后，电流双闭环控制等效结构框图 .....................................................24 图 4.1 并网逆变器仿真模型...............................................................................................................25 图 4.2 单电感滤波并网逆变器仿真波形 ...........................................................................................26 图 4.3 LC 滤波并网逆变器仿真波形..................................................................................................26
i
并网逆变器电流控制技术的研究
ABSTRACT
For sustainable energy generation system, grid-connected inverter is one of the most important parts. In this thesis, grid current control strategies are studied for single-phase grid-connected inverter using full-bridge power topology. There are three candidates for the output filter of grid-connected inverter, which are L, LC and LCL filters. By comparing the filtering performance of these three filters, it is clear that the LCL-filter can reduce high frequency harmonics current greatly at lower switching frequency and with small inductors. In this paper, LCL-filter is adopted as the filter interface between the inverter and the grid. The filter parameters have been designed based on technical indexes. However, there is resonant peak in the system incorporating LCL-filter, so more complex control strategies are needed. The grid current feedback control system is unstable. In order to restrain resonate peak and improve the system stability, passive damping or active damping methods must be adopted. Passive damping solutions are simple and easy to implement, but the damping resistor increases the system losses and decreases switching harmonic attenuation of LCL filter, furthermore, the stability of the system is poor. In this thesis, inverter output current feedback control scheme, the method of splitting the filter capacitor and dual-loop control strategy with grid current and capacitor current feedback, the three active damping methods have been evaluated in stability, resonance restraint and grid current phase control. The evaluation results verify that dual-loop current control strategy has the advantage of good damping performance, and the grid current phase can be controlled directly, moreover its stability is acceptable. The study for dual-loop current control scheme is present in this paper. Its damping principle and stable condition have been analyzed. The regulator parameters selection and the measure for output characteristics improving of dual-loop control strategy are also detailed in the thesis. In order to validate the correctness of the theory analysis, grid-connected inverter simulation has been done. Finally, dual-loop current control strategy has been experimentally tested, and the experiment results prove that the resonant peak can be restrained effectively and high power factor can be achieved by dual-loop current control strategy, and also the system has a good dynamic response. Key Words: grid-connected inverter, grid current control, LCL filter, capacitor current feedback, dual-loop current control
南京航空航天大学硕士学位论文
摘
要Biblioteka Baidu
并网逆变器是新能源发电系统的重要组成部分。本文以单相全桥并网逆变器为研究对象， 对并网电流控制技术进行了深入研究。 并网逆变器的输出滤波器有 L、LC 和 LCL 三种形式，通过对这三种滤波器的滤波性能进 行对比发现，LCL 滤波器高次谐波衰减效果显著，即使在低开关频率和较小的电感情况下也能 满足电流谐波衰减要求。本文采用了 LCL 滤波器作为输出滤波器，并根据技术指标设计了滤波 器参数。 LCL 滤波器在谐振频率处存在幅值尖峰，对并网电流控制策略要求较高，采用典型的入网 电流直接闭环控制的并网逆变系统是不稳定的。为了抑制谐振尖峰，改善系统稳定性，必须增 加系统阻尼，LCL 滤波并网逆变器的谐振阻尼控制策略可分为无源阻尼方案和有源阻尼方案。 无源阻尼方案简单易于实现，但是，它增加了功耗，降低了滤波器的高次谐波衰减程度，而且 系统稳定性较差。论文从系统稳定性、谐振抑制效果和入网电流相位控制三方面对逆变器输出 电流反馈控制、分裂电容法电流控制与入网电流和电容电流双闭环控制这三种有源阻尼方法进 行了对比分析，综合评估了各种控制策略的性能。研究结果表明，电流双闭环控制策略具有谐 振抑制能力强，入网电流相位直接可控的优点，且系统稳定性也较好。文中对电流双闭环方案 的谐振抑制原理和系统稳定条件进行了具体分析，并给出了闭环控制器的设计方法和外特性的 改善措施。 为了验证本文理论分析的正确性，进行了并网逆变器的仿真研究。最后采用入网电流和电 容电流双闭环控制进行了实验研究。实验结果表明，该控制策略能有效抑制谐振尖峰，实现高 功率因数并网，系统具有优良的动静态性能。 关键词：并网逆变器，并网电流控制，LCL 滤波器，电容电流反馈，双闭环控制
ii
南京航空航天大学硕士学位论文
图、表清单
图 2.1 两级式并网发电系统.................................................................................................................6 图 2.2 单级式并网发电系统.................................................................................................................6 图 2.3 单相全桥并网逆变器.................................................................................................................7 图 2.4 双极性正弦脉宽调制方法及逆变桥输出波形 .........................................................................7 图 2.5 单电感滤波并网逆变器.............................................................................................................8 图 2.6 LC 滤波并网逆变器 ...................................................................................................................8 图 2.7 LCL 滤波并网逆变器 .................................................................................................................9 图 2.8 L 和 LCL 滤波器的幅频特性曲线 ............................................................................................9 图 2.9 单电感滤波并网逆变器滤波电感电流波形 ...........................................................................11 图 2.10 单电感滤波并网逆变器滤波电感电流的谐波分布 .............................................................11 图 3.1 LCL 滤波并网逆变器电路 .......................................................................................................13 图 3.2 LCL 滤波并网逆变器数学模型 ...............................................................................................14 图 3.3 入网电流反馈控制框图...........................................................................................................14 图 3.4 入网电流反馈控制系统开环伯德图 .......................................................................................14 图 3.5 入网电流反馈控制系统闭环根轨迹 .......................................................................................15 图 3.6 LCL 滤波并网逆变器串联阻尼电阻的电路图 ......................................................................15 图 3.7 添加阻尼电阻后入网电流反馈控制框图 ...............................................................................16 图 3.8 带阻尼电阻和不带阻尼电阻时 LCL 滤波器的幅频特性曲线 .............................................16 图 3.9 添加阻尼电阻后入网电流反馈控制系统闭环根轨迹 ...........................................................16 图 3.10 逆变器输出电流反馈控制结构框图 .....................................................................................17 图 3.11 分裂电容法电容中间电流反馈控制结构框图 .....................................................................18 图 3.12 入网电流和电容电流双闭环控制结构框图 .........................................................................18 图 3.13 分裂电容法电流控制输出量闭环系统幅频特性曲线 .........................................................19 图 3.14 逆变器输出电流反馈控制输出量系统和入网电流和电容电流双闭环控制系统的幅频特 性曲线 ..................................................................................................................................................20 图 3.15 电容电流内环控制框图.........................................................................................................21 图 3.16 幅频特性曲线.........................................................................................................................21 图 3.17 入网电流和电容电流双闭环控制等效结构框图 .................................................................22 图 3.18 典型Ⅱ型系统的开环对数幅频特性和中频宽 .....................................................................23 图 3.19 加入电网电压前馈后，电流双闭环控制等效结构框图 .....................................................24 图 4.1 并网逆变器仿真模型...............................................................................................................25 图 4.2 单电感滤波并网逆变器仿真波形 ...........................................................................................26 图 4.3 LC 滤波并网逆变器仿真波形..................................................................................................26
i
并网逆变器电流控制技术的研究
ABSTRACT
For sustainable energy generation system, grid-connected inverter is one of the most important parts. In this thesis, grid current control strategies are studied for single-phase grid-connected inverter using full-bridge power topology. There are three candidates for the output filter of grid-connected inverter, which are L, LC and LCL filters. By comparing the filtering performance of these three filters, it is clear that the LCL-filter can reduce high frequency harmonics current greatly at lower switching frequency and with small inductors. In this paper, LCL-filter is adopted as the filter interface between the inverter and the grid. The filter parameters have been designed based on technical indexes. However, there is resonant peak in the system incorporating LCL-filter, so more complex control strategies are needed. The grid current feedback control system is unstable. In order to restrain resonate peak and improve the system stability, passive damping or active damping methods must be adopted. Passive damping solutions are simple and easy to implement, but the damping resistor increases the system losses and decreases switching harmonic attenuation of LCL filter, furthermore, the stability of the system is poor. In this thesis, inverter output current feedback control scheme, the method of splitting the filter capacitor and dual-loop control strategy with grid current and capacitor current feedback, the three active damping methods have been evaluated in stability, resonance restraint and grid current phase control. The evaluation results verify that dual-loop current control strategy has the advantage of good damping performance, and the grid current phase can be controlled directly, moreover its stability is acceptable. The study for dual-loop current control scheme is present in this paper. Its damping principle and stable condition have been analyzed. The regulator parameters selection and the measure for output characteristics improving of dual-loop control strategy are also detailed in the thesis. In order to validate the correctness of the theory analysis, grid-connected inverter simulation has been done. Finally, dual-loop current control strategy has been experimentally tested, and the experiment results prove that the resonant peak can be restrained effectively and high power factor can be achieved by dual-loop current control strategy, and also the system has a good dynamic response. Key Words: grid-connected inverter, grid current control, LCL filter, capacitor current feedback, dual-loop current control