Research On Control Strategies And Raising The Voltage Transfer Ratio Of AC-AC Matrix Converter

Regarding the topic " research on control strategies and raising the voltage transfer ratio of AC-AC matrix converter " as a main subject, this paper has studied the basic principle and advantages of matrix converter as well as the feasibility of space vector modulation strategy; analyzed the properties, basic algorithms and rules of control strategy for double input line-to-line voltage composition; developed the DSP-based prototype system and control software for matrix converter based on space vector modulation; set up the equivalent circuit model of matrix converter by PARK transformation; proposed novel modulation strategies to raise the voltage transfer ratio of matrix converter. Main contents of this paper are as follows:The formula of voltage transfer ratio for matrix converter was derived from its operating principle and it has been pointed out that its maximum is 0.866 under normal linear modulation; two simulation models for matrix converter were set up in MATLAB/SIMULINK, that is simplified simulation model and complex simulation model. The simplified simulation model would have considered bi-directional switches as ideal ones, and its simulated speed was faster, by which the reasonability of control algorithm has been verified; the complex simulation model designed four step commutation strategy and thought of effects of actual switch devices on matrix converter, which is almost the same as the actual system and can simulate the actual operation of matrix converter.The control strategy for double input line-to-line voltage composition was theoretically analyzed in detail; the related theorem and inference conclusions were gotten on the basis of analysis of composing local averages of output line-to-line voltages and input line-to-line currents, and it was deeply analyzed that the control strategy has a self-adjustable rule for output line-to-line voltages; the algorithm was simplified according to the concept 'source key'; finally, the simulated model was set up in MATLAB language, and simulation was done in four cases respectively, the results verified the feasibility and self-adjustabilityof this modulation strategy; further, so did for various abnormal things of input supply, and rules were gotten that the abnormal input supply affects input line-to-line currents, so the method was put forward to reject harmonics that filtering measures should be taken on input port.The four step commutation strategy for matrix converter was programmed in VHDL language, and the program tested by MAXPLUS II 10.2 and MAX7000, then the correctness of four step commutation has been verified by simulation; the control software was developed in DSP 2000 assembly language according to the space vector modulation algorithm, and four step commutation strategy successfully was applied to the commutation process of matrix converter together with the programmable logic device; the control system frame of matrix converter was given out; the success of software design and feasibility of space vector modulation and correctness of hardware making scheme have been verified by experiments, having laid a good foundation for further expanding hardware circuits and software functions.Three-phase to three-phase matrix converter was divided into five parts, PARK transformation was respectively applied to them to derive the corresponding equivalent circuits then based on Venturini direct transformation method, they was comprehended into linear constant circuit model of matrix converter; the mathematical models of input power factor, output voltage gain, input current, input active power and input reactive power have been achieved; the feasibility of PARK transformation has been verified in the study of matrix converter by simulation; a foundation was laid for research on properties and other equivalent circuit models of matrix converter under other modulation strategies; important conclusions have been concluded: in order to raise the voltage transfer ratio of matrix converter, the input current or output voltage waveform qualities must be sacrificed or modulation strategies improved.The current research situation and necessity of voltage transfer ratio for matrix converter was briefly summarized, and three novel modulation strategies have been put forward faced with the low voltage transfer ratio: 1.combine input current space vector modulation with output voltagespace vector over-modulation method mode I; 2.combine input current space vector modulation with output voltage space vector over-modulation method mode II; 3.combine input current space vector over-modulation method mode I with output voltage space vector over-modulation method mode I. The former two novel modulation strategies were mainly analyzed and the third was also analyzed on basis of the former two; for these three novel modulation strategies, the concrete control algorithms have been put forward; the total cycle ratio formulas have been derived; so has been the functional formula of output line to neutral voltage for imaginary inverter. By means of application of Fourier series theory and calculus, etc. the basic wave amplitude of line to neutral output voltage has been derived, then the imaginary rectifying and inverting have been comprehended to get the total basic wave amplitude of output line to line voltage, finally the voltage transfer ratio formulas have been derived for matrix converter. Voltage transfer ratios can reach up to 0.91 and 0.955 respectively for the former two novel modulation strategies by theoretical calculation; it is periodically variable-time in every sector and can reach maximum 1.05. The variable-time curves and three dimensional curve surfaces were drawn, which have reference values to decide and analyze control strategies of raising voltage transfer ratios; three dimensional curve surface indicates voltage transfer ratio can be raised by combinational control of input power factor angle and over-modulation index. At last, the control algorithm software was programmed in MATLAB language, which did simulated experiments respectively for these three novel modulation strategies. The results indicate the three novel modulation strategies are feasible and can effectively raise the voltage transfer ratio of matrix converter, but increase harmonics pollution. Increase in harmonic contents follows the over-modulation index going up. Filtering measures must be taken in order to improve waveform qualities of input currents and output voltages.