Practical Stable Control Scheme Under End Point Equivalence Modulation For DC Power Supply Converters

The DC power supply converter(DCPSC),mainly including DC-AC inverters and DC-DC converters,plays an important role as the interface in industrial applications,such as photovoltaic grid-connected,active filtering,electric vehicles and motor drives.For the research of converters,it is focused on ensuring safety and improving conversion efficiency.And stability research is the basis of safety.Stable controllers are usually designed based on the average model for conventional converters.The disadvantage of this method is that the switching process of the converter is not considered,which leads to fast scale instability,such as bifurcation.The DCPSC can be described as an input limited affine system with limited switching frequency,which is a typical switching system.This study aims to provide a control method that can guarantee practical stability for DC voltage input converters.A practical stability control method for finite control set(FCS)system under duty cycle modulation is proposed.For the traditional control method,which ignores the switching process,this paper proposes an end point equivalent modulation(EPEM)method,which decomposes the practical stability problem of the duty cycle into two sub-problems:the asymptotic stability of the endpoint and the analysis of the intermediate switching process to determine the convergence boundary.Firstly,the model characteristics of different converters are analyzed.A unified affine model is constructed and two common constraints are conceived.The one is the input finite set and the other is the limited switching frequency.Secondly,according to the discrete system without the switching frequency constraints,the Lyapunov function is constructed to meet the asymptotic stability of the endpoint.Then,through EPEM,the constraint of FCS is eliminated.Finally,the actual control law is obtained by solving the endpoint inversely.On account of the method realizing the equivalent of the endpoint,the output of the system under the duty cycle is the same as the result under the discrete control at the next control moment,which indirectly solves the constraint of FCS.And it provides the theoretical support for transplanting the control method of input-independent directly to the traditional FSC system.Moreover,the method considers the switching process,making the process of obtaining the duty cycle more accurate than the PWM method.The mathematical relationship between stability boundairy and topological parameters is derived,and a switching optimization strategy is proposed.Under EPEM,all endpoints approach the equilibrium point and the practical stability boundary(convergence domain)of the real system will be determined by the non-endpoint bias values.Therefore,in the steady state,the mathematical relationship between the convergence domain and the input,sampling frequency and circuit parameters is derived,and verified by theoretical proof,simulation and experiments.In addition,based on the practical stability control,this paper proposes a switching optimization strategy.According to the switch state of the adjacent periodic,the action sequence of the switch is adjusted,which makes the switching loss reduced by half without changing the control effect.Furthermore,it provides a theoretical basis to the optimization of the converter controllers,especially for the control effect optimization and energy loss reduction.The controller is designed for different DC voltage input converters to verify the effectiveness of the proposed method.For DC-AC converters,single-phase inverters and three-phase inverters are selected.For DC-DC converters,Buck chopper circuit and Buck-Boost chopper circuit are selected as research objects.The controllers are designed separately,and the mathematical models between the convergence domain and the circuit parameters are derived.The simulation proves that the method meets the requirements of practical stability.The single-phase inverter and the Buck converter are also experimentally verified.Moreover,the analysis shows that the traditional Sinusoidal Pulse Width Modulation(SPWM)and volt-second balance principle can ensure practical stability control.For the Buck-Boost nonlinear affine system,the method is improved.The continuous average model is used to construct a continuous Lyapunov asymptotically stable virtual controller,which is used to predict the system state at the next moment.And then combined with EPEM,the actual practical stability control law is derived,which provides some new ideas for other types of converters to study the practical stability.