| New energy represented by wind power and photovoltaic power has achieved notable results in the progress towards carbon peaking and carbon neutrality goals and energy transition.Switched Reluctance Generator(SRG),with its high reliability and excellent fault-tolerance performance,can be well applied to off-grid wind power systems.Furthermore,parallel operation of multiple generators can enhance the power supply reliability and capacity of the system in many application fields.Therefore,for the purpose of widening the range of the power generation and improving the power generation efficiency of the parallel power generation system,the phase current modulation,busbar current control and power generation efficiency optimization were investigated.Firstly,in the hope of improving the power generation capacity of the power generation system when operating at low speed and expanding the speed operation range of power generation systems,a new two-step phase current modulation strategy based on voltage balance was proposed.In accordance with the analysis on the relationship between motional electromotive force(MEMF)and demagnetization voltage in the traditional three-step phase current modulation strategy,the electric circuit equations of the balance between MEMF and demagnetization voltage under different working conditions was educed.Moreover,the functional relationship between MEMF of each SRG in the parallel power generation system and the reference magnitude of current as well as speed was put forward.The judgment criteria for phase current mode switching in different speed ranges were presented in the form of mathematical expressions.The simulation and experiment results indicated that the proposed control strategy effectively reduced the rate of phase current decay during power generation and enhanced the power generation capacity at low speed.Besides,the controller can switch the phase current modulation strategy in line with accurate mathematical models,widening the speed operation range.Secondly,in the light of the shortcomings of traditional current sharing control and double closed-loop current sharing control based on the feedback-type two-degree-offreedom PID,a busbar current control strategy in accordance with double closed-loop decoupling of voltage and current was proposed.In addition,the decoupling equations of busbar voltage variation,current distribution ratio variation,and busbar current variation of each SRG were derived by the analysis on the circuit models of both steady and dynamic parallel power generation systems,reducing parameters set by the controller.The simulation and experiment results indicated that the presented control strategy can allocate power to each SRG by changing the reference voltage and the distribution ratio of reference current,which makes the control strategy applicable to more working conditions and provides a control basis for the efficiency optimization of parallel power generation systems.Finally,on the basis of the proposed phase current and busbar current control strategy,an efficiency optimization strategy based on predicting method was presented.The turn-on angle was optimized with fitting formulas,and the turn-off angle was selected in the optimal interval by comprehensively considering the power generation efficiency and power generation capacity.Based on the analysis of the influence of power distribution on parallel power generation system,the speed ratio between SRGs was taken as the initial current distribution ratio,and four optimization intervals and three optimization stages were designed based on the ratio.In the optimization interval,iterative adjustment of current distribution ratio was conducted by means of interpolation for online efficiency optimization.The simulation and experiment results demonstrated that the optimal current distribution ratio can be obtained by only one interpolation when the inserting point of the current distribution ratio is selected appropriately,and thus the optimal efficiency of parallel power generation systems can be achieved.This thesis has 61 figures,5 tables and 85 references. |
PDF Full Text Request