交直流混合微网接口变换器广义直流电动势控制策略

Generalized DC electromotive force control strategy for AC/DC hybrid microgrid interface converter

随着“双高”特征日趋明显,农村交直流混合微电网的源荷呈现多电力电子化,双向接口变换器(bidirectional interface converter,BIC)的低惯性和阻尼问题较为突出。针对此问题,该研究提出一种基于广义直流电动势(generalized direct current electromotive force,G-DCEMF)的BIC控制策略。采用虚拟电阻对直流和交流子网间有功功率的缺额或盈余状态进行判定,根据判定结果通过BIC对功率进行分配控制,在多BIC并联运行时也更易实现功率分配。通过虚拟电感来提高惯性,以减少交流母线频率或交直流子网电压波动的影响,有效地提高了交直流混合微电网的抗干扰特性和动态性能。分析虚拟电阻和虚拟电感的取值,讨论电阻和电感参数影响控制效果的规律。最后通过PSCAD/EMTDC仿真研究验证了所提出的G-DCEMF控制策略的有效性,混合微电网初始状态:直流母线电压为0.75 kV,交流母线频率为50 Hz,系统在额定状态下运行。在运行时间t=1.5 s时,投入0.1 MW的交流负载。分别取虚拟电感为0、0.02、0.05 H,但随着虚拟电感增大,BIC的抗扰动能力增强,结果证明了G-DCEMF控制在可以实现BIC的功率双向流动的同时,提高系统惯性,改善动态响应和抗扰性能,提高微电网的稳定性。

Bidirectional Interface Converter(BIC)connecting the AC and DC buses is the hub of the hybrid microgrid in the energy interaction between the AC and DC subnets.Therefore,the research on the control strategy of BIC is of great significance for the stable operation of the microgrid.Rural distributed power supply and power load are complex and decentralized.AC/DC hybrid microgrid is very suitable for the rural distributed energy consumption and power supply.However,the access of a high proportion of new energy and power electronic equipment has made the power supply and load of rural AC/DC hybrid microgrid appear the multi-power electronics,leading to the low inertia and damping problems of BIC.In this study,Generalized Direct Current Electromotive Force(G-DCEMF)control strategy was proposed to effectively solve the problem of low inertia and damping in hybrid microgrids.Power sharing was also realized in the AC-DC side of the hybrid microgrid for better inertia and dynamic performance.Firstly,a connection was established between the AC bus frequency and the DC motor angular velocity,where the terminal voltage was equivalent to the DC bus voltage,while the BIC transmission power was expressed by the DC side voltage and current.Then,the electromotive force balance equation of the DC motor was incorporated into the BIC control to derive the G-DCEMF control equation.Secondly,the relationship was obtained between the virtual resistance value and the rated capacity of BIC in the generalized DC electromotive force control strategy.The virtual resistance was used to determine the active power deficit or surplus state between DC and AC subnets.The judgment results show that the BIC was used to control the power distribution,in order to verify the autonomous bidirectional power regulation of generalized DC electromotive force control.The power distribution was also achieved in the multi-BIC parallel operation.Thirdly,the stability of the system was evaluated using a small signal model.The improved control strategy was simple in structure and easy to model.Only the external control loop of BIC was modified without switching between control modes,thereby reducing power loss and instability caused by mode switching.Then,the dynamic response of BIC was analyzed under the control of generalized DC electromotive force.The value of the virtual inductance was obtained during this time.The virtual inductance was adjusted to improve the inertia of the system.The power distribution and dynamic response between subnets were adjusted to reduce the influence of the frequency of the AC bus or the voltage fluctuation of the AC/DC subnets.The anti-interference characteristics and dynamic performance of the AC/DC hybrid microgrid were improved effectively for better stability of the hybrid microgrid operation.Finally,compared with the traditional bidirectional droop control,the generalized DC electromotive force control can be expected to better adjust the power transmission,according to the load fluctuation of the AC/DC subnet.The finding can provide the inertia for the entire microgrid system,and then weaken the impact of unilateral microgrid power disturbance on other microgrids in the system.The AC/DC hybrid microgrid was established in the PSCAD/EMTDC simulation software.The effectiveness of the G-DCEMF control strategy was also verified.The G-DCEMF control can be expected to realize the bidirectional power flow of BIC for better system inertia,dynamic response and anti-disturbance performance in the stability of the microgrid.