Architecture Design And Control Strategy Of DC Charger Considering Unbalance Control

New energy vehicles are widely used for their environmental friendliness and high efficiency,and chargers,as the core supporting facilities,are developing rapidly.However,behind the comprehensive promotion of the construction of DC chargers,there are many challenges,such as low utilization rate and difficult profitability.To realize the diversified application of chargers and develop value-added services has become an innovative measure in the field of distribution network.Taking the technical requirement of one DC charger with multiple functions as an opportunity,this paper deeply researches the DC charger architecture design and multi-scenario control strategies that take into account the unbalance control.First of all,the DC charger to participate in the unbalance control must have the topology of bi-directional energy flow,and a two-stage topology with a full-control PWM converter at the front stage and a full-bridge DC-DC converter at the back stage is selected.The mathematical models of front and back stage topology are constructed respectively,and the working principle of DC charger is expounded.Secondly,for the former topology,a flexible switching control strategy is proposed to achieve energy transfer through constant power control.After the compensation current is extracted by the improved ip-iq method,the upper limit of compensation is determined according to the power margin of the charger,and the multi resonance PR control is used to track the comprehensive command current,so as to achieve the charging and unbalance control.For the latter topology,the double closed-loop control is used to ensure stable charging.Run a variety of working conditions in the form of simulation,and the charging and governance effects are good;at the same time,combining with the specific equipment in the laboratory,the NI real-time simulation platform is built to verify the effectiveness of the front-end topology and control strategy.Finally,the capacity of a single unit is "negligible" for the global unbalance component of the distribution network,and for multiple flexible DC chargers,they coordinate and participate in the control of unbalances in the form of scheduling.Comprehensively considering the benefits of distribution network and chargers,a multi-objective function with minimum network loss and minimum value-added service cost of DC chargers is constructed under the constraints of node unbalance,reliable operation of chargers and power grid.An improved forward-backward substitution method is proposed to calculate three-phase unbalanced power flow calculation,and Non-dominated Sorting Genetic Algorithm-Ⅱ(NAGA-Ⅱ)with elite strategy is used to solve the multi-objective optimization model and realize the governance of power grid unbalance;Combined with the 33 bus power grid example and Monte Carlo simulation,the effect of multi machine coordinated unbalance governance control strategy is verified.