Research On The Control Strategy Of Two Level Inverter

Two level inverter is widely used in batteries,photovoltaic arrays and fuel cells and other new energy power grid or off grid system.In the aspect of circuit structure,the boost circuit is used in the former circuit,and the whole circuit is used in the latter stage.In the control aspect,due to the large intermediate storage capacitor can support the bus voltage,pre-stage circuit and circuit realizes decoupling model,the controller first stage circuit and the second stage circuit can each design.Due to the instantaneous output power of the two-stage inverter,the output voltage of the inverter is increased by a factor of two times,which makes the DC converter and the input source generate a ripple current of the order of two times.In most of the DC source system,the ripple current of the DC side is strictly limited,so that the cutoff frequency of the external voltage loop is very low.The low voltage outer loop cutoff frequency will make the dynamic characteristic of bus voltage worse.For the traditional control of two level inverters,the problem of restraining the ripple current of the two time and improving the dynamic characteristics of the intermediate bus voltage can not be considered.In this paper,the control strategy of the front-end circuit of the two-stage inverter is studied.Firstly,the development of the two-stage inverter is introduced.This paper introduces the working principle of the Boost circuit and the single-phase inverter circuit,the parameter design of the main circuit,the modeling and the digital control.The rationality and effectiveness of the design are verified by S function simulation and experiment.Secondly,the problems of the two-stage inverter are introduced.This paper analyzes the generation mechanism and suppression method of the two ripple,analyzes the causes of the fluctuation of the bus voltage in the load transformation and the reasons for the poor dynamic characteristics.Finally,three improved control methods of the former circuit are presented.such as add trap in voltage feedback,Instantaneous power feedforward of a post inverter,a variable structure control method for charge balance control of the pre circuit.To verify the validity and effectiveness of the proposed method in this paper,the inhibition,verified by the two-level inverter prototype S function and a 500 W simulation,simulation results and experimental results verify the correctness and effectiveness of proposed suppression methods.