Electricity: motive power systems – Induction motor systems – Primary circuit control
Patent
1993-10-01
1996-01-09
Martin, David S.
Electricity: motive power systems
Induction motor systems
Primary circuit control
318722, 318807, 363 34, H02P 534
Patent
active
054831407
ABSTRACT:
A power conversion system for driving a three phase synchronous or induction motor receives power from AC power lines and rectifies the power to provide DC current on DC link lines through a link inductor. An inverter connected to the DC link lines is composed of three sets of two thyristors connected in series across the DC link lines. Three output lines extend from connections between each of the three sets of thyristors to the motor. Capacitors are connected across each of the three phase output lines. A controller controls the switching of the thyristors in two modes. In a first mode, used from start-up to low speed operation, a high frequency switching cycle is produced in three steps during which pairs of thyristors in different ones of the three sets are triggered. The relative length of time spent in each one of the three periods during the switching cycle is varied to obtain a desired change in the average output voltage on the three phase output lines at a fundamental frequency. The first mode provides power to drive the motor between standstill and an intermediate speed, with the phase voltages being controlled so that commutation of the thyristors is obtained during each switching cycle. While operating at any speed in the first mode, the system can transfer to a second mode having a four step switching cycle to generate a fundamental voltage component on the three phase output lines by changing the switching cycle in a six step sequence. The motor can be driven in the second mode to a desired speed, while control of the torque is obtained.
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Divan Deepakraj M.
Hess Herbert L.
Martin David S.
Wisconsin Alumni Research Foundation
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