Research On Constant Voltage And Constant Frequency Control Strategy Of Brushless Doubly Fed Generator

Brushless doubly-fed Machine（BDFM）became the mainstream in market application and academic research,and was specifically applied in wind power,hydropower and diesel power generation.More advanced than conventional motors,it can be used not only as a motor but also as a generator.Because of the cancellation of brush and brush ring: in the structure has the characteristics of simple structure,reliable operation;In terms of performance,its frequency converter capacity is smaller,so the cost is lower.Corresponding to different power supply modes,different control terminals have four operating modes: synchronous operation,sub-synchronous operation,asynchronous operation and super synchronous operation mode.The sub-synchronous and super-synchronous operation is also called double-fed operation mode.Its control power because only a small part of the total power,and can do in the absorption of power grid energy at the same time can also be sent to the grid advantage,so it will effectively reduce its capacity in the speed control system.BDFM with its superior structure and performance and gradually in the VSCF and fan pump field shine and get widespread attention.First of all,a Brushless doubly-fed Generator（BDFG）with a magnetoresistive rotor structure was taken as the research object in this paper.Through reading a large number of relevant literature as a knowledge reserve,the purpose is to improve the stability of output voltage amplitude and frequency under variable load and variable speed conditions faced by wind power generation operation.After deducing the voltage and flux equation,the mathematical model is established.Secondly,the control goal of this paper is to keep the output of BDFG as constant voltage and constant frequency,and derive the output voltage frequency expression of the power winding in the rotation coordinate system of slip frequency.The model of voltage and frequency output by power winding in this coordinate system is studied and analyzed and the influencing factors are found out.Vector decomposition of BDFG in this coordinate system,the control strategy is proposed to Orient the induced potential of the power winding,and then the control relationship between the current of the control winding,the voltage of the power winding and the frequency is deduced.To ensure fast calculation of the actual input current of the control winding,the corresponding target current model should be established to ensure that it can quickly and correctly track the target current.Finally,the tracking control model is established by combining sliding mode and SVPWM control strategy.The voltage and frequency control model of BDFG output is simulated and compared under the condition of constant speed variable load and constant load variable speed.The simulation results verify the rationality and accuracy of this control strategy.