Active Damping Control Strategy For Constant Power Load Of Ship's DC Microgrid

With the rapid development of new energy generation technology,DC/DC power conversion technology and energy storage technology,DC microgrid technology has gradually become the main research direction of ship integrated power system.In ship DC microgrid,in order to ensure stable voltage on the input side of constant power load,LC input filter is usually cascade between DC bus and constant power load to filter out high frequency interference in bus voltage.If the filter capacitance value of LC input filter is small,the negative impedance characteristic of constant power load will reduce the stability margin of cascade system,cause the resonance phenomenon of the system,and cause the fluctuation of input voltage and output voltage.In view of the above problems,this paper takes the constant power load cascade system in ship DC microgrid as the research object,and the main research contents are as follows:First of all,the research background,significance and research status at home and abroad are summarized.Then the structure of constant power load cascade system in ship DC microgrid is introduced,the DC/DC converter in the system is modeled,the voltage closed-loop controller is designed,and the mathematical model of constant power load cascade system is established.On this basis,based on the Middlebrook impedance ratio criterion,the stability of cascade system is analyzed,the stability constraint condition of cascade system is derived,and the reason of resonance phenomenon is explained.To suppress resonance phenomenon,first adopted a passive damping control strategy based on damping resistance method,the strategy by the constant power load on both ends of the damping resistor in parallel to increase the system damping coefficient,effectively restrain the resonance phenomenon,but the introduction of damping resistance increase lead to the consumption of power system,so its efficiency is low;Aiming at the existence of passive damping control strategy for the problem of low efficiency is put forward based on the virtual resistance capacity of feed-forward loop active damping control strategy,by introducing virtual resistance capacity is constructed with constant power load in parallel feed-forward loop of virtual impedance,the impedance can be regarded as the combination of virtual resistance and capacitance,including virtual resistance is partly offset by negative impedance characteristic of constant power load,effectively restrain the resonance phenomenon,but the virtual part capacitance reduces the system's dynamic characteristics,so this strategy did not achieve the best control effect;To solve these problems,a feed-forward loop resistance capacity was improved,put forward a kind of optimization strategy based on virtual pure feed-forward loop resistance,through the introduction of feed-forward loop first order low-pass filter is offset by virtual part capacitance,makes constructing virtual impedance at the resonant frequency of pure resistance,effectively restrain the resonance phenomenon of cascade system,control of the system to achieve the best effect.Finally,the model of constant power load cascade system is built on Matlab/Simulink for simulation experiment,and the simulation results of two active damping control strategies are compared and analyzed.The experimental results show that both strategies can effectively suppress the generation of resonance phenomenon and improve the stability of cascade system.Compared with the active damping control strategy based on the virtual resistance capacity feedforward,the virtual pure resistance optimization strategy has shorter adjustment time,faster dynamic response,better dynamic characteristics and steady state performance.