ABB ACS800-67, System Description And Start-Up Manual

Page: 25 / 120

System description 25
Control of torque and reactive power via grid-side converter
The fundamental theory of grid-side converter can be simplified to be analog to the
synchronous generator. One voltage source is the electrical power network and the other
voltage source is the grid-side converter. The voltages and currents can be presented as
vectors. When the reactive power is zero, the current vector is in the same direction with
the grid voltage vector. In the figure below, the current contains capacitive component, ie,
the current is leading the grid-voltage.
The primary function of the grid-side converter is to control the power transfer between the
network and the DC link. The control system can be divided into two sections:
•
Flux controller and torque controller. The flux controller is controlling the length of the
flux vector (flux vector is an integral of the voltage vector) that has influence on the
reactive power.
•
Torque controller controls the power flow from/to the electrical power network
(basically the power transfer angle is controlled). The DC voltage controller gives the
reference to the torque controller.
Power transfer equation between the network and the grid-side converter is following:
U
1
U
2
I
X = j L
u
1
i
Q
u
L
Symbol Description
U
1
grid voltage
U
2
grid-side converter voltage
angular frequency of the grid
X reactance between U
1
and U
2
P active power
Q reactive power
I grid-side converter current
angle between
U
2
and I
i
i
D
u
2
P =
U
1
U
2
X
sin