摘要
以并网逆变器为功率接口的新能源发电系统在弱电网条件下易发生振荡失稳问题。该文将并网逆变器的控制回路可视化为电路元件组成的虚拟阻抗,基于该电路模型分析了弱电网条件下电流内环与锁相环交互作用导致并网逆变器振荡失稳的机理,在此基础上,提出了基于有源阻尼的稳定控制设计方法,并对不同有源阻尼控制的电路特性以及稳定性提升能力进行了对比分析。研究结果表明,针对锁相环引入负电阻造成的振荡失稳问题,阻抗-高通滤波器型有源阻尼控制策略具有更优的稳定性提升能力。最后通过PSCAD/EMTDC仿真和远宽StarSim控制器硬件在环实验对比了不同有源阻尼控制策略的振荡抑制效果,并验证了阻抗-高通滤波器型有源阻尼控制的动态性能。结果表明,所设计的稳定控制能够在200 ms内有效抑制系统振荡,并且可实现在短路比为1的极弱电网条件下稳定运行。
The renewable energy power generation systems that utilize grid-connected inverters as the power interface are prone to instability issues when the AC grid is weak.The fundamental reason for the wideband oscillation phenomenon when grid-connected inverters are integrated into AC grids is negative resistance. Firstly, to understand the mechanism of the negative resistance and propose the effective oscillation suppression methods, this paper visualizes the current-inner loop, phase-locked loop, voltage feedforward, and decoupling terms of the grid-connected inverter in to the equivalent circuit model in the dq-domain, modified-sequence domain and positive/negative-sequence domain. By studying the interaction of control dynamics within the sub-/super-synchronous frequency range, the circuit essence of the negative resistance is revealed. Secondly, based on the equivalent circuit model of the grid-connected inverter and the inherent essence of the negative resistance, the design principles of active damping control are proposed. Additionally, the optimal location for implementing active damping control is examined. According to the equivalent circuit among various active damping controls, the investigation is conducted to understand the impact of these controls on the negative resistance characteristics. Finally, the oscillation suppression effects of different active damping control strategies are compared through PSCAD/EMTDC simulations and StarSim controller hardware-in-the-loop experiments. Besides, the dynamic performance of the impedance-high-pass filter type active damping control is validated. It is demonstrated that the system oscillation can be effectively suppressed within 200 ms using the designed control method. Additionally, the grid-connected inverter remains stable under weak grid conditions with SCR=1. The main conclusions of this paper are as follows: (1) The interaction between the current inner loop and the phase-locked loop of the grid-connected inverter is the primary cause for the emergence of the negative resistance in the q-axis equivalent circuit. The negative resistance of the q-axis circuit results in the negative resistance characteristic in the traditional sequential-domain impedance, particularly near the fundamental frequency. Under the weak grid scenarios, the negative resistance characteristic becomes more pronounced, elevating the risk of sub-/super-synchronous oscillations. (2) Based on the circuit model resulting from the interaction between the phase-locked loop and current inner loop, the phase-locked loop determines the existence of negative resistance and its frequency range coverage. The magnitude of the negative resistance is influenced by the integral coefficient of the current inner loop. (3) When designing the active damping control parameters, it is essential to enhance the inductance characteristics of the active damping control to mitigate the impact of negative resistance caused by the integral coefficient of the current inner loop. Thus, the system oscillatory stability can be improved. (4) The band-pass filter and band-rejection filter are beneficial for reducing negative resistance within the specific frequency range. Meanwhile, low-pass filters are advantageous for mitigating the high-frequency oscillations, whereas high-pass filters are useful for suppressing low-frequency oscillations. Under the same parameter conditions, the impedance-high pass filter-based active damping control proposed in this paper demonstrates a better suppression effect on sub-/super-synchronous oscillations, resulting in a notable enhancement of the dynamic performance.
作者
高磊
吕敬
马骏超
刘佳宁
蔡旭
Gao Lei;LüJing;Ma Junchao;Liu Jianing;Cai Xu(Key Laboratory of Control of Power Transmission and Conversion Ministry of Education Shanghai Jiao Tong University,Shanghai 200240 China;State Grid Zhejiang Electric Power Co.Ltd Research Institute,Hangzhou 310000 China)
出处
《电工技术学报》
EI
CSCD
北大核心
2024年第8期2325-2341,共17页
Transactions of China Electrotechnical Society
基金
国家自然科学基金项目(52277195)
国网浙江省电力有限公司科技项目(B3311DS22000K)资助。
关键词
并网逆变器
电路等效
振荡稳定性
有源阻尼
虚拟阻抗
稳定控制
Grid-connected inverter
impedance circuit equivalent
oscillation stability
active damping
virtual impedance
stability control
