ABB ACS 600 User Manual page 36

ACA 635 IGBT Supply Sections
The primary function of the ISU is to control the power transfer
between the network and the DC link. The purpose of the AC choke
(represented by reactance X = j w L) is to smooth the line current and to
act as an energy storage for the switch-mode supply. Power transfer
equation between the network and the ISU is presented below:
U U
P = @
1 2 sin
X
Real power is being transferred only if an angle difference exists
between the two voltage vectors. Reactive power transfer equation is
presented below:
2
U U U
= -
Q 1 1
X X
For the desirable magnitude and the direction of the power and
reactive power flow, the length of the converter voltage vector and its
@
phase angle (with respect to the line voltage vector) must be
controlled. The d.c. voltage is controlled by keeping the power (energy)
equilibrium between the line and the drives in the DC link constant. The
sign of the angle determines the direction of the power flow.
The output a.c.voltage is controlled by setting the length of the flux
reference to correspond to the desired output voltage level producing
cosfii = 1.0.
The ISU control needs measurements of the DC link voltage and two
line currents. The "stator flux" (integral of the voltage vector of the ISU)
is calculated by integrating the voltage vector used to generate the
output voltage of the ISU. This is due to the fact that the existing
voltage in the network can be thought to be generated by a rotating
magnetic flux encircled by coils. Each of these coils is one of the line
voltage phases. The voltage in the coils can be expressed by the
formula below:
O
d
=
U
dt
The virtual torque generated by the ISU is calculated as a cross
product of flux and current vectors:
= O
T x I
Power can also be expressed as a product of torque and angular
velocity:
M
P = T
Chapter 6 – Firmware Description
@
2 cos
6-3