不对称故障下两级式光伏逆变器的LVRT策略
|
摘要
为提升基于Boost电路的两级式光伏逆变器的并网运行稳定性,研究了不对称故障下光伏逆变器的运行特性,提出了以Boost调节直流母线电压配合负序电压前馈的电流控制策略,来实现低电压穿越(Low Voltage Ride Through,LVRT)。首先,分析了两级式光伏逆变器的常规Boost电压控制模式和电流控制策略。在电网故障时通过引入基于故障前光伏阵列最大功率点电压前馈的母线电压控制外环改变Boost电压控制模式,以稳定直流母线电压和防止逆变器过流。接着,为在不对称故障期间控制并网电流三相对称,提出了基于电网负序电压前馈的电流控制策略;结合根据电压跌落深度直接给定参考值的方式调节输出电流,为电网提供无功功率支撑;为实现前述电流控制,设计了基于二阶广义积分器(Second Order Generalized Integrator,SOGI)的正负序分离锁相模块。最后,利用PSCAD/EMTDC仿真软件搭建100 kW光伏逆变器模型进行控制策略验证,结果表明该策略在单相电压跌落至0.2 p.u时仍能快速有效地抑制直流母线电压升高,使光伏逆变器安全地实现低电压穿越。
In order to improve the grid-connected stability of two stage PV inverter based on boost circuit, the operation character-istic of PV inverter under unbalanced fault is studied. Combining with boost circuit regulating the DC bus voltage, a current control strategy based on negative sequence voltage feed forward is proposed to achieve LVRT. The conventional boost circuit voltage con-trol mode and output current control strategy are analyzed. A DC bus voltage control outer loop based on PV array maximum power point voltage feed forward is introduced to change the boost circuit voltage control mode. By this way, the purpose of making the DC bus voltage stable and preventing over current of the inverter can be achieved. Then, a current control strategy based on nega-tive sequence voltage feed forward is designed to ensure the output current three-phase symmetry under unbalanced fault. To pro-vide a certain reactive power support to the grid, the current reference value is provided directly according to the voltage sage. In order to achieve the aforementioned current control method, a positive and negative sequence separation function module based on SOGI is designed. Finally, a 100 kW PV inverter PSCAD simulation model is built to verify the proposed control strategy. The re-sult shows that the method not only can suppress the DC bus voltage rise rapidly and effectively, but also can make the inverter provide more dynamic reactive power support for the grid even when the single-phase voltage falls to 0. 2 p. u.
In order to improve the grid-connected stability of two stage PV inverter based on boost circuit, the operation character-istic of PV inverter under unbalanced fault is studied. Combining with boost circuit regulating the DC bus voltage, a current control strategy based on negative sequence voltage feed forward is proposed to achieve LVRT. The conventional boost circuit voltage con-trol mode and output current control strategy are analyzed. A DC bus voltage control outer loop based on PV array maximum power point voltage feed forward is introduced to change the boost circuit voltage control mode. By this way, the purpose of making the DC bus voltage stable and preventing over current of the inverter can be achieved. Then, a current control strategy based on nega-tive sequence voltage feed forward is designed to ensure the output current three-phase symmetry under unbalanced fault. To pro-vide a certain reactive power support to the grid, the current reference value is provided directly according to the voltage sage. In order to achieve the aforementioned current control method, a positive and negative sequence separation function module based on SOGI is designed. Finally, a 100 kW PV inverter PSCAD simulation model is built to verify the proposed control strategy. The re-sult shows that the method not only can suppress the DC bus voltage rise rapidly and effectively, but also can make the inverter provide more dynamic reactive power support for the grid even when the single-phase voltage falls to 0. 2 p. u.
引文
[1]国家电网公司. Q/GDW 617—2011光伏电站接入电网技术规定[S].北京:中国电力出版社,2011.
[2]周京华,刘劲东,陈亚爱,等.大功率光伏逆变器的低电压穿越控制[J].电网技术,2013,37(7):1799-1807.
[3]韩贤岁,刘其辉.对称和不对称故障下的并网光伏逆变器低电压穿越研究[J].电测与仪表,2015,52(9):113-118.
[4]王巨波,鲍伟,徐文丽,等.不平衡故障下光伏逆变器LVRT无功控制策略[J].华东电力,2014,42(8):1527-1533.
[5]王京保,曾国宏,荆龙.电压不对称故障下光伏逆变器低电压穿越技术[J].电气传动,2013,43(12):24-27.
[6]张明光,陈晓婧.光伏并网发电系统的低电压穿越控制策略[J].电力系统保护与控制,2014,42(11):28-33.
[7]安志龙.光伏并网控制策略与低电压穿越技术研究[D].北京:华北电力大学,2012.
[8]刘耀远,曾成碧,李庭敏,等.基于超级电容的光伏并网低电压穿越控制策略研究[J].电力系统保护与控制,2014(13):77-82.
[9]舒大松,黄挚雄,康伦,等.基于超级电容储能的光伏并网低电压穿越研究[J].湖南大学学报(自然科学版),2014,41(8):60-64.
[10]张兴,曹仁贤.太阳能光伏并网发电及其逆变控制[M].北京:机械工业出版社,2011.
[2]周京华,刘劲东,陈亚爱,等.大功率光伏逆变器的低电压穿越控制[J].电网技术,2013,37(7):1799-1807.
[3]韩贤岁,刘其辉.对称和不对称故障下的并网光伏逆变器低电压穿越研究[J].电测与仪表,2015,52(9):113-118.
[4]王巨波,鲍伟,徐文丽,等.不平衡故障下光伏逆变器LVRT无功控制策略[J].华东电力,2014,42(8):1527-1533.
[5]王京保,曾国宏,荆龙.电压不对称故障下光伏逆变器低电压穿越技术[J].电气传动,2013,43(12):24-27.
[6]张明光,陈晓婧.光伏并网发电系统的低电压穿越控制策略[J].电力系统保护与控制,2014,42(11):28-33.
[7]安志龙.光伏并网控制策略与低电压穿越技术研究[D].北京:华北电力大学,2012.
[8]刘耀远,曾成碧,李庭敏,等.基于超级电容的光伏并网低电压穿越控制策略研究[J].电力系统保护与控制,2014(13):77-82.
[9]舒大松,黄挚雄,康伦,等.基于超级电容储能的光伏并网低电压穿越研究[J].湖南大学学报(自然科学版),2014,41(8):60-64.
[10]张兴,曹仁贤.太阳能光伏并网发电及其逆变控制[M].北京:机械工业出版社,2011.