Subsynchronous resonance and its mitigation for power system with unified power flow controller
J. Mod. Power Syst. Clean Energy (
Subsynchronous resonance and its mitigation for power system with unified power flow controller
Xinyao ZHU 0 1
Meng JIN 0 1
Xiangping KONG 0 1
Jingbo ZHAO 0 1
Jiankun LIU 0 1
Qian ZHOU 0 1
0 State Grid Jiangsu Electric Power Research Institute , Nanjing 211103, Jiangsu , China
1 State Grid Jiangsu Electric Power Maintenance Branch Company , Nanjing 211102, Jiangsu , China
Control strategy of unified power flow controller (UPFC) utilizing dq decoupling control is deduced in this paper, which can closely follow the control orders of the active and reactive power. The subsynchronous resonance (SSR) characteristics of a series compensated system equipped with UPFC are studied, and the results reveal that SSR characteristics of the system may vary significantly with UPFC in service or not. Consequently, supplementary subsynchronous damping controller (SSDC) for UPFC is proposed and investigated, and the effectiveness of the proposed SSDC is verified by damping torque analysis and time domain simulations.
Unified power flow controller (UPFC); Series capacitor compensation; Subsynchronous resonance (SSR); Supplementary subsynchronous damping controller (SSDC); Damping torque analysis
1 Introduction
In recent years, series capacitor compensations have
been widely used in China to enhance the stability and to
increase the transmission capacity of the power system
[
1?3
]. Although series capacitor compensation can provide
good economical profit, the risk of SSR (Subsynchronous
Resonance) could be brought to the power system at the
same time [
4, 5
]. Meanwhile, with the rapid development
of the power electronics, flexible AC transmission system
(FACTS) devices are widely used in the power system
[
6?9
]. With the ability of controlling multi electrical
parameters, e.g. the bus voltage and the active/reactive
power of the transmission line, unified power flow
controller (UPFC) is the most versatile FACTS so far [
7
]. In
China, the first UPFC project has already been put into
service in East China Power Grid in 2015, and other UPFC
projects are being planned or built.
SSR characteristics and its mitigation for series
compensated power system have been adequately studied, and
many research results have been published [
10, 11
].
However, for the problem of SSR characteristics of the
power system with UPFC, very limited studies have been
reported. In [
12, 13
], the impacts of the series voltage
injected by UPFC series converter and the shunt current
injected by UPFC shunt converter on the SSR
characteristics have been studied. UPFC is always used to control
the power flow of the system, whereas the impacts of the
active and reactive power flow controlled by UPFC on the
SSR characteristics have not been studied.
FACTS like static synchronous compensator
(STATCOM) and static synchronous series compensator (SSSC)
have been used to mitigate SSR in previous literatures
[
14?16
]. Equipped with back-to-back voltage source
converters (VSC), proper supplementary control of UPFC can
be used to enhance the stability of the power system [
17
].
In addition, given that no extra expensive electrical
equipment is needed, it is most promising to mitigate SSR
by using UPFC supplementary control for the power
system equipped with UPFC. However, few researches have
been reported on using UPFC to damp SSR. Reference [
18
]
optimized the control parameters of UPFC, and
investigated the SSR damping effect of the UPFC itself.
Reference [
19
] investigated a SSR damping controller for the
shunt converter of UPFC using fuzzy control theory;
however, SSR damping controller for the series converter
has not been designed, and the SSR damping mechanism
has not been deduced.
In this paper, the control strategy of UPFC utilizing dq
decoupling control is deduced which can follow the orders
of the active and reactive power of the transmission line
closely. Then supplementary subsynchronous damping
controllers (SSDC) for UPFC are proposed, and the SSR
damping mechanism is deduced as well. Meanwhile, both
the SSR characteristics of the series compensated system
with UPFC and the effectiveness of the proposed SSDC are
investigated by damping torque analysis and time domain
simulations.
The rest of this paper is organized as follows. Section 2
proposes the control strategy of UPFC. Section 3 describes
the test system used in this paper. Section 4 studies the
SSR characteristics of the test system equipped with UPFC.
The configuration of the SSDC for UPFC, its SSR damping
mechanism as well as its damping effect are given in Sects.
5 and 6. The analysis results of the SSR characteristics and
the effectiveness of the SSDC are verified by time domain
simulations presented in Sect. 7. Conclusion remarks are
given in Sect. 8.
2 Control strategy of UPFC
2.1 Equivalent circuit of UPFC
UPFC device consists of shunt transformer-converter,
series transformer-converter and a DC capacitor. The shun (...truncated)