Application and Operation
6.2 The Control Modes
Product User Manual
Operating Instructions, Version AE 12/2009, A5E01454341C
109
frame). A phase-locked loop (PLL) within the motor model tracks the (stator) frequency and
angle of the flux vector.
Motor flux amplitude is controlled by the flux regulator; its output forms the command for the
magnetizing (or flux producing) component. Motor speed is determined from stator
frequency, and is controlled by the speed regulator. Its output is the command for the torque
(producing) current regulator.
The flux angle is used to decompose the measured motor current into magnetizing and
torque producing components. It is this decomposition that allows independent control of flux
and torque, similar to DC motor control. These current components are regulated to their
commanded values by the current regulators. Outputs of the current regulators are combined
to produce three-phase voltage commands that get modified with signals from various other
control routines before being passed on to the modulator. These control routines include: (1)
dead-time compensation (to compensate for dead-time in the switching of the upper and
lower IGBTS of each pole in a power cell), (2) peak reduction for third-harmonic injection (to
maximize drive output voltage, and for drive neutral-shift (during transparent cell-bypass),
and (3) voltage commands to produce losses for dual-frequency braking. Transient response
of the torque regulators is improved with the use of feed-forward compensation (FF) as
shown in Figure "Block Diagram of Vector Control Algorithms for Induction and Synchronous
Motor Control". The following table describes the symbols used to represent various
quantities in the control diagram.
Table 6- 2 List of Symbols Used in Figure "Block Diagram of Vectors Control Algorithmus for Induction and Synchronous
Motor Control"
Symbol Description
FluxDS D-component of motor flux; also equal to the motor flux, since Q-component is zero. Motor Flux is defined as:
Motor_Voltage / Stator_Frequency (rad/s). Flux (which has units of Volt-seconds) is also proportional (but not
equal) to Volts-per-Hertz ratio.
r For an induction motor: Motor_Speed = Stator_Frequency / Pole_Pairs – Slip_Speed
This is the rotor (mechanical) frequency, which is equivalent to the motor speed.
For a synchronous motor: Motor _Speed = Stator_Frequency / Pole_Pairs
I
ds
Magnetizing component of motor current
I
qs
Torque component of motor current
V
ds
,
ref
Output of magnetizing current regulator used in the D-Q transformation to produce 3-phase voltages
V
qs
,
ref
Output of torque current regulator used in the inverse D-Q transformation to produce 3-phase voltages
s Stator frequency or output frequency of the drive. This is motorspeed (r) + Slip.
S Flux angle. This is the instantaneous position of the rotating Slip vector.
I
a
I
b
, I
c
Motor phase currents.
Motor torque (in Newton-meters) and shaft power can be calculated as:
Torque (Nm) = 3* Pole_Pairs * Flux (Vs)* Iqs (A)
≈ 3* Pole_Pairs * Motor_Voltage (V) * Iqs (A) / (2π * Frequency (Hz)),
Shaft Power (W) = Torque (Nm) * Speed (rad/s) = Torque (Nm) * Speed (rpm) / 9.55
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