直流配电网中DC/AC中间变换器建模及直流电压稳定控制

Negative incremental input impedance of DC/AC middle converters will destabilize the DC distributed power system. If DC/AC middle converters are considered as constant power loads with zero-order module, the stability criteria may be conservative. To solve this problem, a more accurate module of the input impedance will be built and reduced to first-order module with the time constant of converters as characteristic parameter. The principle how the DC voltage stability is affected by the dynamic performance will further be exploited. Then the prerequisite of applying the zero-order module of the input impedance to small-signal stability analysis can be derived. Thereby less conservative stability conditions and theoretic basis for simplifying stability analysis can be obtained. In order to improve stability, an input impedance self-adjust method will be proposed. This method on-line identifies if there is oscillation in DC network. The time constant of converters will be adjusted when oscillation occurs to degrade the negative damping effect produced by the converters. The time constant of converters will be adjusted back when voltage is stable to enhance power quality supplied by the converters. As a result, higher power quality can be provided to AC loads on the premise of stabilized DC voltage. Finally, this project can be expected to degrade the conversation of small-signal stability conditions and improve voltage stability.

直流配网中DC/AC中间变换器的负阻抗特性影响直流电压的小信号稳定，其输入阻抗若采用零阶的恒功率负荷模型描述，可能使得稳定性约束趋于保守。为此，本项目拟精确建立DC/AC中间变换器的输入阻抗模型，通过模型降阶获得以变换器时间常数为特征参数的输入阻抗一阶模型，进而探寻变换器动态特性影响直流电压稳定性的机理，由此求取零阶的恒功率负荷模型应用于小信号稳定性分析的前提条件，为简化稳定性分析提供相关理论依据，以降低稳定性约束的保守性。在此基础上，本项目拟提出DC/AC中间变换器输入阻抗的自调整方法，通过在线辨识直流电压振荡与否，振荡时在可行区内调整变换器时间常数，减弱变换器所产生的负阻尼作用，稳定时将时间常数在可行区内往回调整，以提高变换器输出的电压质量，从而实现保证直流电压稳定的前提下，交流负荷区的供电质量接近最优。本项目有望降低直流配网小信号稳定性约束的保守性和提高直流电压的稳定性。

本项目建立DC/AC中间变换器的输入阻抗模型，通过模型降阶获得以变换器时间常数为特征参数的输入阻抗一阶模型，揭示变换器动态特性影响直流电压稳定性的机理，由此求取零阶的恒功率负荷模型应用于小信号稳定性分析的前提条件，为简化稳定性分析提供相关理论依据，降低了稳定性约束的保守性。在此基础上，提出DC/AC中间变换器输入阻抗的自调整方法，通过在线辨识直流电压振荡与否，振荡时在可行区内调整变换器时间常数，减弱变换器所产生的负阻尼作用，稳定时将时间常数在可行区内往回调整，以提高变换器输出的电压质量，从而实现保证直流电压稳定的前提下，交流负荷区的供电质量接近最优。本项目降低了直流配网小信号稳定性约束的保守性和提高直流电压的稳定性。