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,