Energy and Power E ngineering, 2013, 5, 1503-1507
doi:10.4236/epe.2013.54B284 Published Online July 2013 (http://www.scirp.org/journal/epe)
Copyright © 2013 S ciRes. EPE
Research on C on t rol Method of Inverters for Large-scale
Grid Connected Photovoltaic Power System
Zhuo Zhang, Hongwei Li
Power Supply Company of Zhengzhou, Henan, China
Email: zhang-zhuo@msn.com, lihongwei-6@163.com
Received 2013
ABSTRACT
A grid-connected inverter controlling method to analyze dynamic process of large-scale and grid-connected photo-
voltaic power station is proposed. The reference values of control variables are composed of maximum power wh ich i s
the output of the photovoltaic ar ray of t he photo voltaic p o wer plant, and power factor specified by dispatching, the con-
trol strategy of dynamic feedback linearization is adopted. Nonlinear decoupling controller is designed for realizing
decoupling control of active and reactive power. The cascade PI regulation is proposed to avoid inaccurate parameter
estimation which ge nerates the s ystem static err or. Simulation is carr ied out based on the simplified po wer syste m with
large-scale photo voltaic plan t modellin g, and the po wer factor, solar rad iation strength, and bus fault are considered for
the further research. It’s demonstrated that the parameter adjustment of PI controller is simple and convenient, dynamic
response of s ystem is transient , a nd the stab ility of the inverter control is verified .
Keywords: Large-scale Photovoltaic Grid-connected; Dynamic Feedback Linearization; Nonlinear Decoupling;
Cascade Connection PI Control
1. Introduction
The safety and economy of power system are affected
directly by transformer running states, which play an
i mp ortant role in network. According to the survey, the
total transformer loss of about 8% of electricity genera-
tion, and distribution transformer loss is accounted to
about 60~80% of the entire distribution grid [1, 2]. No-
wadays, a large number of frequency electrical ap-
pliances and devices sorted as non-linear loads in indus-
trial and lives have become increasingly universal, which
have led to harmonic pollution to system and brought
about adverse effects including increased wear and tear,
abnormal temperature rise, insulation reduced life ex-
pectancy shortened to transformers and other electro-
magnetic equipments[3]. Therefore, non-linear load loss
calculation and analysis for transformer has been con-
cerned by the ve ry important.
Traditional transformer loss calculation includes theo-
retical analysis and experimental measurements. In ref-
erence [4], curve fitting method applied, and the har-
monics equivalent parameters are calculated with large
number of experimental information as to harmonic loss
by superposition principle. Co re saturatio n is not put into
consideration, and THD for different parameters can be
corrected. IEEE standards with experimental measure-
ments and operating experience data to calculate the
harmonic losses [5], but DC resistance loss is obtained
roughly, and the eddy current and stray losses are not
distributed considerably. Besides, the conservation is
mentioned [6]. The document [7] studie d the curve fitti ng,
and brought out better method when dealing with high
freq uency harmonic problem.
As studied above, equivalent parameter model has
bee n built , and har monic loss is analyzed in this paper by
considering the winding conductor frequency-dependent
characteristics with model parameters and the non-linear
superposition.
2. Winding Harmonic Model
Transformer total loss includes the copper loss, iron loss
and other stray loss, and copper loss of windings is di-
vided into dc loss and winding eddy loss. The total loss is
consisted of dc transformer winding loss, winding eddy
current loss and other stray loss since iron loss has been
ignored in load operation [8].
The harmonic equivalent circ uit of transformer has
been shown in Figure 1. In which, Rh(1), Rh(2), Xh(1), Xh(2)
is winding equivalent resistance values and reactance
values at order h respectively; Rh(m) and Xh(m) is magnetic
resistance and reactance.
Witho ut regar d t o co r e sa tur at i o n, gr o ups o f e quivalent
parameters information are acquired through no-load,