1-12 Functional Description
7000-TD002A-EN-P – September 2007
Current Control The function of the current control block (Figure 1.7) is to determine
the firing angles for the converters Alpha Rectifer (327) and Alpha
Inverter (328). The inputs are the torque (InvTorque CurCmd) and
flux producing (Inv Flux CurCmd) components of the dc link current
command from the speed control and flux control blocks respectively,
and the measured dc link current Idc Feedback (322).
The square root of the sum of the squares of Inv Flux CurCmd and
InvTorque CurCmd determines the dc link current reference Idc
Reference (321). This is subtracted from the measured dc current
feedback is subtracted to determine Idc Error (323). This is
processed by the current regulator to produce Vdc Error (332). To
effectively control the dc link current an estimate of the motor side
dc link voltage is done to calculate Vdc Feedfwd (333) which is
added to Vdc Error to produce the reference voltage for the line side
converter Vdc Reference (326). The line converter firing angle is the
inverse cosine of Vdc Reference. The machine converter firing angle
is determined by taking the inverse tangent of the ratio of Inv Flux
CurCmd to the InvTorque CurCmd. The quadrant of operation is
adjusted based on the signs of the current commands.
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