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B-2 ControlSystem MN1942

B.1.1 Servo configu ration
The servo configuration is the default configuration for the drive, allowing the motorc ontrol
system to operate as a torque controller, a velocity controller or a position controller. This
configurationcompris es 3 nested control loops; a current c ontrol loop, a velocity control loop and
aposition c ontrol loop, as shown in Figure 51.
The universal encoder interface reads rotor position from the enc oder and estimates velocity.
Thecommutation block us es the position to calculate the electrical angle of the rotor. Thecurrent
sensorsystemmeasures U andV phas e currents. These are fed into a current conversionblock
thatconv erts them into quantities representing torque producing andmagnet izing currents (the
’vector’ currents which are locked to the rotor).
In the current control loop, a current demand and the final measured current values form the
inputs to a PI (Proportional, Integral) control system. This control system generates a set of
voltagedemands that ar e fed into aPW M (pulse-width modulation) block. TheP WM block uses
thespace -vector modulation method to convert these volt age demands into a sequence of U, V
and W phase switching signals, whic h are applied to the output bridge of the drive. The PWM
block uses the measured DC bus voltage to compensate for variations in supply voltage.
The torque controller converts a torque demand into a current demand and compensates for
various load non-linearities. A 2-stage notch or low-pass filter allow s the effects of load
complianceto be reduced. To avoid motor damage, a user-defined application current limit is also
applied,as w ell as individual positive and negative torque limits.
In the velocity control loop, a velocity demand and measured velocity form the inputs to a PI
controlsystem. The outputof the control systemis a torque demandwhich, when the driveis
operatingas a v elocity controller, forms the input to the current control loop.
Finally,in the position cont rol loop, a position demand and measured position form the inputs to
a PID (Proportional, Integral, Differential) control system incorporating v elocity feedback,
velocity feed-forward and acceleration feed-forward. The output of the position c ontrols ystem
isa v elocity demand which, when the drive is operating as a position controller, forms the input
tothe veloc ity control loop.