Research On Control Strategy Of Two Stage Matrix Converter Under Abnormal Conditions

Two stage matrix converter(TSMC) is a state-of-the-art direct power converter. Because it provides good input/output waveforms, adjustable input power factor, bi-directional power flow, simple commutation, it has been one of the most potential power converters. The voltage transfer ratio of TSMC is limited to 0.866 due to the restriction of circuit topology and modulation strategy. It also has a low immunity to power-grid disturbances and load current distortion since it has no energy storage components. In order to solve the problems, the paper deeply investigates the control strategies, which can enhance the voltage transfer ratio and improve the TSMC's outputs under the abnormal working conditions.The paper divides the modulation zone into linear modulation region and nonlinear modulation region to improve the voltage transfer ratio based on space vector modulation (SVM). The dual SVM is adopted to modulate TSMC in linear region; the two-mode and single-mode over-modulation strategies are employed to increase the voltage transfer ratio and realize smooth transition from linear modulation to nonlinear modulation. The voltage transfer ratio of TSMC can be boost up to 1.0 through above over-modulation strategies.Due to the lack of internal energy storage components, TSMC will also be sensitive to disturbance in the input voltages and distortion in the load currents. The paper introduces two feed forward schemes based on dual SVM-the feed forward scheme based on method of symmetrical components and the feed forward scheme based on 3/2 transformer. These feed forward schemes correct the voltage vector modulation index to gain symmetric output waveforms by calculating the undulation of DC voltage using input three phase voltages. These schemes sacrifice the voltage transfer ratio to get the better waveforms. In order to improve the voltage transfer ratio under abnormal input voltages, the paper proposes a new modified modulation scheme:the over-modulation strategies are adopted to get the max DC voltage at the rectifier, the latter feed forward scheme is also employed to gain symmetric output waveforms.The simulation models have been established by Matlab/Simulink to verify the validity of the control scheme. The results of simulation show that both two mode over-mdulation and single mode over-modulation can effectively improve the voltage transfer ratio.The results also show that the feed forward scheme and its enhanced method can improve the inputs and outputs of TSMC under power grid is under abnormal conditions.