无变压器并网H桥逆变系统直流链电流传感技术的自动校准资源-CSDN文库

需积分: 5 120 浏览量 2021-07-07 09:29:59 上传评论收藏 1.25MB PDF 举报

资源推荐

资源详情

资源评论

IEEE TRANSACTIONS ON POWER ELECTRONICS, VOL. 21, NO. 5, SEPTEMBER 2006 1385

Auto-Calibrating DC Link Current Sensing Technique

for Transformerless, Grid Connected,

H-Bridge Inverter Systems

Matthew Armstrong, David. J. Atkinson, C. Mark Johnson, Member, IEEE, and Tusitha. D. Abeyasekera

Abstract—Power electronic inverters are commonly used for

the interfacing of distributed generation systems to the electrical

power network. These electronic inverters operate in a current

controlled mode to inject unity power factor sinusoidal current

into the network. To prevent possible dc current injection, a mains

frequency isolation transformer is often employed at the inverter

output. This isolation transformer is a costly component. An alter-

native approach is to use current sensing and control techniques

to eliminate the dc current component. One method is to use a

current controller to force the output dc current to zero. Current

controllers are prone to errors associated with nonlinearity and

offsets in the current transducers. This paper considers a novel

auto-calibrating dc link current sensing technique that eliminates

the errors associated with the current transducer, and helps avoid

dc current injection into the grid when using a transformerless

grid connect inverter system.

Index Terms—Current controllers, power electronic inverters.

I. INTRODUCTION

ANY DISTRIBUTED generation systems, such as pho-

tovoltaic arrays, use a current controlled dc to ac inverter

to inject unity power factor sinusoidal current into the grid (see

Fig. 1). In general, electricity supply companies do not allow

grid connection of such inverter systems unless they provide

adequate means of eliminating the possibility of unwanted dc

current being injected into the grid [1], [2]. This is due to con-

cerns over substation transformer saturation [3], [4]. dc current

in the network has also been linked to increased corrosion of net-

work cabling [5]. Typically, inverter systems which have semi-

conductor circuits directly connected to the mains cannot be

designed in such a way that guarantees unwanted dc current

components will not ﬂow into the network. Such dc compo-

nents can be attributed to several factors including asymmetry

in the switching of the semiconductor devices. This is caused

by imbalance in the turn-on and turn-off times of the semicon-

ductor switches, pulse width imbalance in the pulsewidth mod-

ulation (PWM) process, or possible mismatch in the alignment

Manuscript received April 4, 2005; revised November 18, 2005. This work

was supported by the Engineering and Physical Sciences Research Council

(EPSRC) of UK, Intelligent Power Systems, Ltd. (IPS), Gateshead, UK, and

Scottish Power Plc, UK. Recommended by Associate Editor F. Z. Peng.

M. Armstrong, D. J. Atkinson, and T. D. Abeyasekera are with the School

of Electrical, Electronic and Computer Engineering, University of Newcastle

upon Tyne, Newcastle upon Tyne NE1 7RU, U.K. (e-mail: matthew.arm-

strong@ncl.ac.uk).

C. M. Johnson is with the Department of Electronic and Electrical Engi-

neering, University of Shefﬁeld, Shefﬁeld S1 3JD, U.K.

Digital Object Identiﬁer 10.1109/TPEL.2006.880267

of the gate drive signals. Current controller errors also create

unwanted dc components in the inverter output current, a major

cause being the error in the actual current measurement. A mains

frequency isolation transformer is therefore typically employed

at the inverter output to eliminate the possibility of unwanted dc

currents being injected into the grid. This isolation transformer

is large, heavy, and forms a substantial cost in a grid connected

system [6]. Furthermore, it contributes signiﬁcantly to the in-

verter system losses [7]. By removing the need for this isola-

tion transformer the market for grid connected inverter systems

would be strengthened, leading to more widespread application.

One possibility is to replace the transformer with a dc

blocking capacitor in the inverter output. However, this ca-

pacitor would need to have a low reactance at 50 Hz mains

frequency. Therefore a large and expensive capacitor is re-

quired. An alternative approach is to use an inverter topology

that is naturally capable of preventing dc current components

arising at the inverter output. Very few inverter topologies

exist which possess this property, although the half-bridge [8]

inverter is one example. Regardless of the switching state of

the inverter, one capacitor is always present in the current path,

hence blocking any dc current components. Unfortunately,

twice the dc link voltage of a typical H-bridge inverter is re-

quired to achieve the same rated output. The H-bridge requires

a 380 V dc link to synthesize 230 Vac at the inverter output,

hence a 760 V dc link would be needed by the half bridge to

synthesize the same output voltage level. This impacts on the

semiconductor devices used in the inverter; 1200 V IGBTs

would be needed, as opposed to 600 V IGBT devices in the

H-Bridge. Compared to 600 V IGBTs, higher voltage devices

cannot be switched as fast, have greater switching losses and

are undesirable on cost grounds. A further approach is to use

current sensing and control techniques to eliminate the dc

current component. One method would be to use a current

controller to force the output dc current to zero. However, the

main problem with this approach is that it depends upon an

accurate current sensor. A number of different types of cur-

rent sensor are available in power electronic applications [9],

including Hall Effect current transducers, current transformers

and resistive shunts. Resistive shunts are cost effective, but it

is often difﬁcult to achieve high common mode rejection with

resistive shunt ampliﬁers. They also offer no natural isolation

between the power circuit and measurement equipment. Hall

Effect current sensors are widely used due to their good perfor-

mance, relatively low cost and galvanically isolated principle

of operation. Unfortunately these devices are prone to linearity

1386 IEEE TRANSACTIONS ON POWER ELECTRONICS, VOL. 21, NO. 5, SEPTEMBER 2006

Fig. 1. Typical topology of a grid connected inverter system.

errors and offset drift [10], [11]. In current control applications,

offset drift affects the controller accuracy at dc and nonlinearity

may result in harmonic distortion which itself may produce a dc

component in the system output. It is impossible to limit, with

any level of certainty, the dc component in the inverter output

with better accuracy than that of the current measurement

device. This makes it very difﬁcult to meet present electricity

supply regulations concerning dc current injection [1], [2] using

conventional current sensing and control methods. This paper

therefore considers an alternative current sensing technique to

help eliminate dc current components in the inverter output

current. The proposed technique auto-calibrates the current

sensor to compensate for any dc offsets in the current sensor.

The scheme also minimizes the effect of dc components caused

by current sensor nonlinearity by ensuring a symmetrical

nonlinearity in the current sensor measurement. This results in

a fully compensated, dc accurate, current sensor from which it

is possible to accurately limit the dc component in the inverter

output via current sensing and control techniques.

II. D

ESCRIPTION OF DC LINK CURRENT SENSING TECHNIQUE

The proposed current sensing scheme considers current con-

trol of a single-phase inverter using dc link current sensing tech-

niques. dc link current sensing itself is not a new concept. For a

long time it has been used in many applications to detect inverter

shoot-through and other over-current conditions. More recently

however, knowledge of the dc link current has been put to further

use. In 1986, Evans and Hill-Cottingham [12] published work

detailing the dc link current behaviour of a general poly-phase

inverter. By determining the dc link current wave shape, it was

shown that the ripple current rating of the dc link ﬁlter capac-

itor could be speciﬁed with greater precision. Boys [13] took

the concept a step further, by using dc link current analysis to

derive signals for induction motor control. By sampling prefer-

ential portions of the dc link current, the current magnitudes of

the inverter output current could be determined. The technique

was shown to be accurate at high-power factors, but tended to

underestimate the motor current at low-power factors. Further-

more, the signals derived from the dc link current provided no

phase information about the output current. Green and Williams

[14] went on to describe techniques for faithful reconstruction

of the motor line currents at the output of a three-phase inverter

from a single dc link current sensor. The reconstruction of the

line currents included both current magnitude and phase infor-

mation. Through identiﬁcation of the inverter switching state,

it was shown that the three line currents in the inverter output

could be determined via the condition of the dc link current.

A resistive shunt with a high slew-rate ampliﬁer was used as

the transducer in the dc link. A digital decoding circuit deter-

mined the state of the inverter, and was used to control a set of

analogue switches in an analogue circuit. By correct control of

these switches, reconstruction of the three inverter line currents

was possible. In 1996, Atkinson [15] described a new technique

of controlling a three-phase motor via a single dc link current

sensor. From dc link measurements alone, this approach deter-

mined the rectangular components of the single current vector

representation of the three-phase currents. Current control was

carried out through comparison of these rectangular compo-

nents with reference values. A current vector error was gener-

ated, which determined the next switching pattern to be applied

to the inverter.

This paper builds upon much of this work to develop a novel

dc link current sensing technique. This technique involves using

a dc link current sensor which can be auto-calibrated at reg-

ular intervals while still being used for the inverter output cur-

rent control. For this application, the topology of interest is the

H-bridge inverter (Fig. 2). If the H-bridge is switched using a

unipolar switching scheme [8] then there are four main bridge

switching states that arise. These are summarized in Table I.

During the ﬁrst two switching states, from here on called current

conducting states, a voltage is applied across the output of the

inverter and current ﬂows via the dc link to the load, in this case

the supply network. During these intervals it is possible to mea-

sure the output current via the dc link sensor. Depending upon

the switching state of the H-bridge, the dc link current will either

be equal to, or inversely equal to, the output current. The third

and fourth switching states are often referred to as free wheeling

states. When the inverter is in one of these states, the inductor

current simply freewheels around a loop in the H-bridge. During

these periods the actual dc link current collapses to zero. If the dc

link current sensor output is monitored during the freewheeling

periods then, due to the described offset errors in the current

sensor, a zero current measurement is unlikely to be made. How-

ever, since the actual current in the dc link is known to be zero,

these periods can be used to calibrate the current sensor and re-

move any offset present. The inverter current controller can then

accurately control the dc current component in spite of drift er-

rors in the sensor.

A. Determining the Switching State of the H-Bridge

It is necessary to know which switching states the H-Bridge

is in at the time of taking a current measurement. This can be

determined by studying the effect of the PWM signals on the dc

link current. Fig. 3 shows a simpliﬁed switching diagram for a

unipolar-switched H-Bridge inverter. In practice, the triangular

switching waveform will be of a much higher frequency than

the sinusoidal waveform. Also shown are the switching states

剩余8页未读，继续阅读

评论收藏

内容反馈

??2050

粉丝: 2
资源: 924

无变压器并网H桥逆变系统直流链电流传感技术的自动校准

基于并网逆变技术的变电站直流系统远程充放电控制策略

离网逆变器和并网逆变器并网逆变器如何离网使用

单相无变压器型光伏并网逆变器的拓扑结构及共模电流分析

关于并网光伏逆变器的基本设计

光伏并网逆变系统的MATLAB仿真研究.pdf

三相光伏并网逆变器仿真

三相光伏并网逆变器.pdf

光伏三相逆变并网、MPPT控制的Matlab/Simulink仿真.rar

三相光伏逆变并网 仿真

并网型光伏发电系统及其逆变器工作原理详述.pdf

电子功用-用于监测无变压器的光伏逆变器的泄漏电流的装置

光伏并网逆变器选型细则.pdf

2020并网逆变器硬件设计.rar

基于直线式移相变压器的多重叠加逆变系统

单相3.5kw无变压器住宅并网光伏系统研究

分布式电源并网逆变器控制策略与仿真研究.pdf

单相两级式非隔离型光伏并网逆变器设计

并网逆变器工作原理.pdf

常熟开关CS1G 组串式并网型光伏逆变器资料下载.pdf

电源类设计逆变器电源开关电源DSP全数字逆变电源设计论文及技术资料155个合集.zip

直驱式风力发电系统并网逆变器控制策略研究

光伏并网逆变器选型细则.doc

光伏并网发电装置中逆变器资料

半桥逆变电路工作原理的分析.docx

基于MATLAB的单相光伏并网逆变系统的设计.pdf

最新资源

三相光伏逆变并网仿真