Method and apparatus for direct regulation of output currents of

Details Method and apparatus for direct regulation of output currents of Method and apparatus for direct regulation of output currents of

1990-12-18

1992-03-17

Smith, Jr., David

Electricity: motive power systems

Induction motor systems

Primary circuit control

318809, H02P 540

Patent

active

050971930

ABSTRACT:
A method and apparatus directly regulate the output currents (i.sub.RX, i.sub.SX, i.sub.TX) of an inverter that feeds a predetermined number of induction machines. This method and apparatus is applicable to an inverter feeding one or more induction machines without rotational speed actual value sensors. The regulation is achieved by means of a secondary current control to which is supplied a current command variable system (i.sub.RW, i.sub.SW, i.sub.TW). According to the invention the current command variable system (i.sub.RW, i.sub.SW, i.sub.TW) is determined from the inverter output currents (i.sub.RX, i.sub.SX, i.sub.TX) and the state signals (S.sub.R, S.sub.S, S.sub.T) of the current switches of the inverter, from a calculation of the actual values of the active and reactive powers (P/U.sub.d, P.sub.q /U.sub.d) supplied to the motor, and a given rotational speed setpoint (n.sub.set), using field-oriented variables and simulating the actual rotational speed (n.sub.act). The actual values of the active and reactive powers (P/U.sub.d, P.sub.q /U.sub.d) are converted into the actual values of the active and reactive currents (i.sub.Wact, i.sub.Bact), which are then converted into field-oriented actual values. From an actual value of a fundamental-r.m.s. of the inverter output voltage (U.sub.X), the command value of the flux-forming current component (i.sub.dW) is determined. Consequently the frequency converter output currents (i.sub.RX, i.sub.SX, i.sub.TX) can be regulated directly achieving very good concentricity characteristics even at low output frequencies.

REFERENCES:
patent: 4609983 (1986-09-01), Braun
patent: 4792741 (1988-12-01), Matsuo et al.
patent: 4906912 (1990-03-01), Trauth et al.

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