Research On Control Technology Of Multi-Load Matrix Converter

The advantages of the AC–AC direct matrix converter are that it can realize a unity power factor on the input side without a large capacitance capacity.However,direct conversion increases the coupling between the input and output,which affects output side performance under abnormal conditions such as input side imbalance.Similarly,asymmetry in the output load power will also degrade performance on the input side.To solve the above problems,methods to improve the modulation method,optimize the internal and external loop regulator designs,and introduce compensation units can be adopted.These methods are based on the principle of maintaining the average voltage or current of the virtual DC bus to decouple the input and output power and reduce mutual influence,while simultaneously maintaining a high input power factor and low harmonic content.In this study,the improved modulation method,closed-loop control theory,introduction of a compensation unit,and system performance optimizations are investigated extensively as applied to a three-phase input matrix converter under single and double loads,and a set of theoretical methods is formed and subsequently verified by simulation and experiment.Maintaining a constant average voltage or current in the virtual DC bus is the theoretical basis for decoupling input and output power.In this thesis,the components of the virtual bus current for a single-phase output matrix converter with multiple loads under conventional modulation methods are derived,and the influence of existing modulation methods on input and output performance under unbalanced input is analyzed.Then,a double closed-loop control strategy is proposed that involves decoupling the positive and negative sequence components from the network-side current.This strategy not only achieves constant average current in the virtual DC bus,but also takes the weighted composite voltage of the output phase and compensation phase as the control object in the outer loop control,thus avoiding the direct control of the AC output flow.In order to address the problems with linear regulators and the many adjustment parameters for the inner loop,a nonlinear control strategy for a multi-load single-phase output matrix converter with unbalanced input is proposed based on the Lyapunov stability principle.The feedforward decoupling control method for a multi-load symmetrical dual-output matrix converter can improve the dynamic response performance of the system,but it cannot track the negative sequence component of the input current under asymmetric output conditions.In this thesis,a double closed-loop control strategy of a dual load symmetrical output matrix converter is described.Based on the state equation,small and average signal models are established,and the expression of output current weighted synthesis control is analyzed and derived.A decoupling control strategy of positive and negative sequence current components based on a grid-side negative sequence regulator is proposed for independent regulation of two-phase output with the same input and output frequency.This method limits the effect of the AC flow on the amplitude of the three-phase input current without introducing harmonics of triple the output frequency by allocating a reasonable quantity of AC to the pulsating output power.The feedforward decoupling control expression is given for this case,and the influence of the proposed strategy on the input side performance is analyzed in detail.When the orthogonal two-phase output is adjusted independently in the matrix converter with different input and output frequencies,the existing methods focus only on improving the output performance,neglecting input performance;that is,the input current must contain low-frequency harmonics related to both input and output frequencies.In this thesis,a group of bidirectional switches and power compensation units on the output side are introduced,and the process of achieving power compensation is described in detail.According to the topology,a specific modulation method and a double closed-loop control strategy are proposed,including sector division,switch combination mode,calculation of effective vector operation time,selection of input,output control objects,and optimization methods of various parameters in the closed loop regulator.The performance characteristics of the system before and after the introduction of the compensation unit are compared.The low voltage utilization ratio of the matrix converter is one of the main factors limiting its application.The over-modulation method and the introduction of a Z-source network into the topology are two directions of current research.When the two above methods are applied to a multi-load matrix converter,they produce incomplete power decoupling,resulting in a certain amount of low-frequency harmonics on the input side.Therefore,it is necessary to study the linear regulation method to broaden the voltage utilization ratio of the converter.In this thesis,a switch combination optimization modulation method is proposed,in which at least two outputs are co-modulated during the shortest overlap time period of three-phase output modulation to improve the effective vector utilization in unit cycle time.The proposed method not only achieves complete power decoupling,but also effectively improves the voltage utilization ratio of said converter.For this study,an experimental prototype based on a digital signal processor and a complex programmable logic device was constructed.The experimental results show that the proposed method is effective and achievable,and provides an experimental platform for the development and evaluation of modulation methods and control strategies.