一种基于非线性扰动观测器的飞轮储能系统优化充电控制策略

An Optimized Charging Control Strategy for Flywheel Energy Storage System Based on Nonlinear Disturbance Observer

飞轮储能系统的工作模式要求在最短的时间内对飞轮进行可靠地充电。该文在分析传统充电控制策略的基础上,结合飞轮储能系统的工作特性,提出了一种基于非线性扰动观测器的优化充电控制策略。外环采用转速控制和能量控制相结合的方式,转速环实现恒转矩控制,能量环实现恒功率控制;引入过渡控制环节实现恒转矩控制和恒功率控制的切换;利用非线性扰动观测器估计电机损耗功率和负载功率并进行前馈补偿;基于控制系统稳态、动态和抗扰动性能的要求,给出一种控制器参数设计方法。与传统控制策略相比,所提充电控制策略恒功率控制灵活,恒转矩控制至恒功率控制切换平滑,且有效抑制了电机损耗功率和负载功率的影响,满足了飞轮储能系统的工作特性要求。最后,仿真和实验结果验证了所提策略的可行性和实用性。

The operating mode of the flywheel energy storage system(FESS)requires the flywheel to be charged reliably in the shortest time.The traditional charging control strategy adopts vector control with the speed loop or voltage loop as the outer loop,which has low charging efficiency and poor dynamic performance.Moreover,it is separate from the operating mode of FESS,which cannot realize the energy control and speed stability of the flywheel motor at the same time.The traditional implementation of the operating mode of FESS needs to be more flexible,and the electromagnetic torque will jump,which affects the system’s stability.Besides,the power loss and load power of the flywheel motor can cause the charging power to drop and affect the system’s robustness.Therefore,this paper proposes an optimized charging control strategy(OCCS)based on a nonlinear disturbance observer(NDOB).Firstly,the outer loop adopts the combination of speed control and energy control,the speed loop realizes constant torque control,and the energy loop uses flywheel kinetic energy as a control variable to realize constant power control.Secondly,the transition control unit is proposed to realize the smooth switching between constant torque control and constant power control.Thirdly,the NDOB estimates motor power loss and load power to perform feedforward compensation.Moreover,the transfer function of the energy-current double closed-loop system considering NDOB is derived.Finally,based on the steady-state,dynamic,and anti-disturbance performance requirements of the control system,a controller parameter design method is given.The experimental results show that in the charging process,the maximum peak-to-peak value of phase currents of OCCS is 480 A.The sudden change of the phase currents is avoided,but the charging time is still sacrificed.OCCS+NDOB applies the NDOB to estimate motor power loss and load power,reducing the charging time.The proposed charging control strategy has no torque jump in the switching process from constant torque control to constant power control,and the switching process is smooth.The maximum torque of OCCS+NDOB is 188.5 N·m,which is 18.5%lower than 231.3 N·m of the improved charge control strategy 1(ICCS1).In addition,compared with the improved charge control strategy 2(ICCS2)and OCCS,OCCS+NDOB has significantly shorter charging time and higher charging efficiency.The charging time of OCCS+NDOB from 4000 r/min to 10000 r/min is about 21.13 s,which is consistent with ICCS1,while the charging times of ICCS2 and OCCS are 26.01 s and 24.36 s,respectively.Compared with OCCS,the charging time of OCCS+NDOB is reduced by 13.3%.Therefore,although introducing a transition control unit increases the charging time,the charging efficiency can be improved by NDOB.In the constant power control unit,the actual power of OCCS+NDOB can reach 100 kW,while other strategies cannot reach 100 kW due to the motor power loss and load power.The total power loss observed by NDOB in the experiment is 2.15 kW.The conclusions can be drawn as follows:(1)the feasibility of combining speed control and energy control in the outer loop of FESS is verified.The speed loop realizes constant torque control,and the energy loop realizes constant power control.(2)The transition control unit is introduced to realize the smooth switching from constant torque control to constant power control,and the jump of electromagnetic torque is avoided.(3)The NDOB is used to estimate the motor power loss and load power,and the feedforward compensation control is carried out,which improves the anti-disturbance ability and dynamic performance of the system,further reducing the charging time.