Z-source inverters eliminate the need for front-end DC-DC boost converters in applications with limited DC voltage such as solar PV, fuel cell. Quasi Z-source inverters offer advantages over Z-source inverter, such as continuous source current and lower component ratings. In this paper, switching table based Direct Torque Control (DTC) of induction motor fed by quasi Z-Source Inverter (qZSI) is presented.
In the proposed technique, dc link voltage is boosted by incorporating shoot through state into the switching table. This simplifies the implementation of DTC using qZSI. An additional DC link voltage hysteresis controller is included along with torque and flux hysteresis controllers used in conventional DTC. The results validate the boost capability of qZSI and torque response of the DTC.
Fig. 1: Block Diagram for DTC using qZSI
EXPECTED SIMULATION RESULTS:
Fig.2: Torque vs. Time
Fig. 3: Stator Phase ‘a’ Current
Fig. 4: Speed vs. Time
Fig. 5: DC Link Voltage
Fig. 6: Capacitor Voltage, VC1
In this paper, direct torque control of induction motor fed by qZSI is presented. Dynamic torque response for step change obtained is 3 ms, which is needed for high performance applications. qZSI provides a single stage solution for drives with variable input DC voItage, instead of DC-DC converter cascaded with 3-leg inverter bridge.
This paper presents a solution for drives with lesser DC input voItage availability and also requiring very fast torque response. The results shows that by introducing shoot through state in switching table of direct torque control, DC link voItage in qZSI is boosted. The DC link voItage hysteresis controller uses the input and capacitor voItage for controlling DC link voItage. If there is any disturbance in input voItage, the reference for capacitor voItage will be changed accordingly to maintain the DC link voItage.
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