To improve the power quality of traction power system, a novel active power quality compensator (APQC) and a new compensating currents detection method are proposed. The APQC consists of a three-phase voltage source converter and a Scott transformer. The Scott transformer, taken as an isolation transformer, not only connects the three-phase converter to the traction power system, but also converts the traction power system to a nearly balanced three-phase power system. Therefore, a general three-phase converter could be used in APQC. Regarding the traction substation as a compensating object, the power quality of a traction substation can be improved integrally. Simulation and prototype experimental results show that the proposed APQC is able to compensate reactive power, harmonic, and negative-sequence currents in two feeders of a traction substation.
A new type of three-phase quasi-Z-source indirect matrix converter (QZS-IMC) is proposed in this paper. It uses a unique impedance network for achieving voltage-boost capability and making the input current in continuous conduction mode (CCM) to eliminate the input filter. The complete modulation strategy is proposed to operate the QZS-IMC. Meanwhile, a closed-loop DC-link peak voltage control strategy is proposed, and the DC-link peak voltage is estimated by measuring both the input and capacitor voltages. With this proposed technique, a high-performance output voltage control can be achieved with an excellent transient performance even if there are input voltage and load current variations. The controller is designed by using the small-signal model. Vector control scheme of the induction motor is combined with the QZS-IMC to achieve the motor drive. A QZS-IMC prototype is built in laboratory, and experimental results verify the operating principle and theoretical analysis of the proposed converter. The simulation tests of QZS-IMC based inductor motor drive are carried out to validate the proposed converter's application in motor drive.
Purpose -The paper aims to propose a new type of three-phase quasi-Z-source indirect matrix converter (QZSIMC) to extend the voltage gain for application in the induction motor drives. Design/methodology/approach -A unique H-shape quasi-Z-source network is connected between the three-phase voltage source and traditional indirect matrix converter to achieve the voltage boost and buck in a single-stage power conversion. The complete space vector modulation (SVM) method is proposed to control the proposed QZSIMC. The output voltage amplitude of quasi-Z-source network can be boosted by the shoot-through of the front-end rectifier, so the whole system's voltage gain is extended. Meanwhile, the QZSIMC modeling and quasi-Z-source impedance parameter design are developed by using the state space averaging method. The design-oriented analysis based on small signal model is used to investigate the quasi-Z-source impedance parameter's impact on the QZSIMC's dynamic performance. A simulated application example employs a 4-kW induction motor drive to verify the proposed QZSIMC, the developed modulation method and parameter design method. Findings -The proposed QZSIMC can achieve high voltage gain larger than one and also can fulfill buck function, which widens the induction motor drive's operation range. The simulation results verify the proposed QZSIMC and SVM and also validate the quality performance of the proposed induction motor drive and all theoretical analysis and parameter design method. Originality/value -The proposed QZSIMC effectively overcomes the limitation of traditional indirect matrix converter, through extending the voltage gain larger than one. The systematic principle, analysis, parameter design, and simulation verification provide the proposed QZSIMC with a feasible approach in practical induction motor drive applications.
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