Research on Harmonic Characteristics of Nonlinear Loads in PEMFC Generator

doi:10.4236/epe.2013.54B013

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Energy and Power Engineering, 2013, 5, 68-71

doi:10.4236/epe.2013.54B013 Published Online July 2013 (http://www.scirp.org/journal/epe)

Research on Harmonic Characteristics of Nonlinear

Loads in PEMFC Generator

Jinquan Wang, Jianke Li, Shuhua Qian, Jingjing Chen, Jianhua Fang, Yachao Hu

PLA University of Science & Technology, College of National Defense, Nanjing, China

Email: [email protected]

Received April, 2013

ABSTRACT

Hydrogen as a clean energy source is made full use, this paper researches the electrical model of PEMFC generator,

analyzes the harmonic trend and its hazards when the generator operates with linear load and nonlinear load running

synchronously, comparatively analyzes the commonly used harmonic suppression technology. Simulate and analyze the

filter performance when APF is used. The results illustrate that as a filter device, APF can absorb the harmonic properly

in PEMFC power system.

Keywords: PEMFC Generator; Nonlinear Load; Harmonic Flow; Filter Device

1. Introduction

Because of the advantages of non-polluting, high effi-

ciency, no noise, Hydrogen PEMFC generator has very

broad application prospects in the civilian spheres, with-

out “Carnot” cycle limit, with low working temperature,

small heat radiation. Due to the need for energy conser-

vation or engineering practice, the load contains a lot of

power electronics, such as controlled rectifier, inverter,

which resulting in harmonics and increasing the nonlin-

ear components of the power supply system. The har-

monic current and voltage were coupled to each other,

thus increasing the difficulty of suppression of harmonic

currents. This grid is often low tension and close trans-

mission. It is usually chosen cable to reduce the possibil-

ity of to suffer lightning and external damage. However,

the high-order harmonics may not only result in resonant,

causing overvoltage on the line, but also make the volt-

age waveform spikes appear to accelerate the aging of

the cable insulation. The harmonic pollution even affects

the stability and usage of the power supply[1-2].

2. PEMFC Generator Model

2.1. Dynamic Output Characteristics of the

PEMFC Generator

Due to the limited capacity of the PEMFC generator, a

sudden change of the load has greater impact on the

operating state of generator. In order to describe the

characteristics of the generator accurately, we researched

the electrical characteristics of the PEMFC generator when

the load has a sudden increase and sudden reduction.

The PEMFC generator dynamic characteristic curves

are shown in Figure 1 and Figure 2 by the experiment.

According to the PEMFC hydrogen generator output

voltage waveform, due to the influence of changes in the

external load, the generator output voltage amplitude

variation is large. Especially, when the load is increased

suddenly, the instantaneous voltage drop is very serious.

Such changes usually greatly exceeded the allowed range

of variation of the input voltage of the power conversion

apparatus. When a sudden increase in load, the in-

stantaneous voltage drop instantaneously, and the DC /

AC converter is self-protecting and stop working.

2.2. PEMFC Generator Electrical Model

The PEMFC generator as a power source, three electrical

models, start-up model, running the model, and downtime

model are considered. Studies made in this article are a

dynamic process, and here is running the model. The

012345

Time(s)

Figure 1. DC load operating sudde nly (0 to 4.7 kw).

J. Q. WANG ET AL. 69

first-order RC model is shown in Figure 3 when the load

is reduced and the first-order RL model is shown in

Figure 4 when the load is increased. Here is 5 kW level

PEMFC generator. In Figure 3, R1 = 0.1605 Ω, R2 =

0.2130 Ω, C = 0.703 F. In Figure 4, R1 = 0.3870 Ω, R2 =

0.3981 Ω, L = 22.31 mH.

3. Harmonic Load Flow and the Hazard

Analysis

PEMFC power supply system includes various types of

load. They are divided into two types, linear load and

nonlinear load. There is no power conversion apparatus

such as the inverter or rectifier in the linear load. It

contains the core loss that depends on the physical

characteristics of the iron or copper, such as motors,

current limiting reactance, etc. The nonlinear load is that

its current and voltage waveforms are not similar because

of certain reasons, such as rectifying devices, UPS, EPS

etc. Typically, PEMFC generator output voltage changes

based on the load’ changes. In order to stabilize the

voltage in the circuit, DC/DC link is added. The system

block diagram is shown in Figure 5.

To simply analysis, they will not consider the

impedance of the DC/DC converter and power supply

system can be equivalent to:

Figure 2. DC load exiting suddenly (0 to 4.7 kw).

Figure 3. The first-order RC model.

Figrue 4. The first-order RL model.

In Figure 6, Rs+jXs represent internal impedance of

the PEMFC generator; Rd+jXd represent the impedance

of the DC/AC inverter; RLand RNL represent the im-

pedance of the linear load and the nonlinear load re-

spectively.

ssdd

IRR

RjXRjXRR



 





(1)

LLNL









(2)

NL LNL









(3)

when considering harmonic and ignoring the superimposed

effect of the harmonic currents, assume the harmonic

current of the nonlinear load is h



. So the power supply

system can be equivalent to:

ssddL

RjXRjXR





 



(4)

ssdd

ssddL

RjXRjX

RjXRjXR







 



(5)

Figure 5. The block diagram of P EMFC power supply.







Figure 6. Equivalent circuit diagram.







Figure 7. Equivalent circuit with harmonic.

J. Q. WANG ET AL.

Learn from the harmonic load flow, the harmonic,

which sends out by the nonlinear load, may flow to the

linear slip and the power bus. When harmonic flowing

through the line, for the frequency characteristic, the line

resistance may increase with the frequency. Acting under

the skin effect, the harmonic current increases the addi-

tional loss in the line. The harmonics can also make harm

to the rotary electric machine through the additional loss

and torque, due to the affection of skin effect, hysteresis

and eddy, the additional loss in the iron and windings of

the rotary electric machine would increase with the in-

crease of the frequency [3-5] .

4. Method for Harmonic Suppression

4.1. Method for Harmonic Suppression

Currently, filter is the main method to suppress the har-

monic in power system. Filter which immediately ab-

sorbs the generated harmonic current produced by har-

monic sources is the effective method for harmonic sup-

pression. Usually, the power filter can be divided into

two kinds, passive and active power filter.

Passive Power Filter(PPF) is configured in accordance

with certain elements such as capacitance, inductance

and resistance, and connected in a certain topology. It is

simple in structure, low in price, and high reliability

when operating. What’s more, it may also compensate

reactive power and improve power factor on the basis of

absorb harmonics. The PPF is widely used as a harmonic

suppression device for its easy maintenance and its

mature technology design and manufacture experience. A

typical single tunable filter is shown in Figure 8(a).

Active power filter (APF) is based on the principle of

instantaneous power theory which dynamically track load

harmonic changes and are real-time filtering technology

[6], and the principle is shown in Figure 8(b). As one of

the strategies used for harmonic suppression in the large

grid or small capacity one, the APF has some unparalleled

advantages. The following advantages are concluded by

theoretical study and widely use in practice [7]:

1) It can not only compensate for all the harmonics,

but also inhabit the flicker and compensate reactive.



(a) (b)

Figure 8. Schematic diagram of filter.

2) Its filter characteristic does not matter with the sys-

tem impedance, and it can eliminate the risk of series or

parallel syntony with the system impedance or load.

3) It has not overload problem.

4) It can automatically tracks harmonic and compen-

sates the changes.

5) It has fast dynamic response.

The novel combines the characteristics of the PEMFC

generator power, and chooses the APF as harmonic filter

device. The schematic diagram of the system is shown as

follows: (Figure 9)

4.2. Simulation Study

We choose MATLAB as simulation platform, and use

the first-order RC model of PEMFC. Then we choose

three-phase motor and rectifier as linear and nonlinear

load separately. The active power filter is based on the

theory of instantaneous power, then we build the simula-

tion model of PEMFC generator power system, the sim-

ulation results are shown as follows:

As is shown in Figure 10 and Figure 11, the three-

phase nonlinear load sends out the five times, seven

times, 11 times, and 13th times harmonic current, and the

current distortion rate is 28.39%, the current waveform

has a serious distortion. The urrent-wave of compensa-

tion and Current wave after filtering is shown as Figure

12 and F igure 13 respectively.

Seen from Figure 14, after the using of active power

filter in a separate small capacity grid, the current wave-

form has significantly improved, and its harmonic distor-

tion rate is reduced to 4.8%, and each harmonic content

are greatly reduced.

Figure 9. Diagram of APF.

Figure10. Current-wave of load.

J. Q. WANG ET AL.

Figure 12. Current-wave of compensation.

Figure 11. Frequency of load current.

Figure 13. Current wave after filtering.

Figure 14. Frequency of source current after filtering.

5. Conclusions

As a clean energy source, generating electricity by hy-

drogen has attracted broad attention. Accompanying with

the study of PEMFC gradual thorough, this paper studies

the electric model of PEMFC, and analyses the harmonic

load flow and its hazards when the generator running

with linear and nonlinear load, and compares the com-

mon technology used to suppress harmonic. What’s more,

simulate and analyze the filter performance with active

filter. The results show that the using of active filter for

PEMFC generator system can achieve our filter goal.

REFERENCES

[1] Z. Wong and H. Tu, “The Research of Development and

Application about Proton Exchange Membrane Fuel

Cell,” Beijing: Metallurgical Industry Press, 2002

[2] J. Q. Wang and Y. Chu, “The Determination of an Order

Equivalent Circuit about PEMFC Hydrogen Generator,”

Nanjing: Chinese Colleges and Universities and the

Electric Power System and Its Automation Professional's

22nd Annual Conference, Vol. 10, 2006, pp. 16-17.

[3] F. C. De La Rosa and Y. Zhao, “Narmonics and Power

Systems,” Translation, Beijing: Mechanical Industry

Press, 2009.

[4] K. Qian, Y. Yuan and X. Shi, et al., “Environmental

Benefits Analysis of Distributed Generation,” Proceed-

ings of the CSEE, Vol. 28, No. 29, 2008, pp. 11-15.

[5] W. Hu, “Research on Improving Harmonic Detection

Algorithm Based on Instantaneous Power of Idle Work,”

Electrical Measurement & Instrumentation, Vol. 46, No.

3, 2009, pp. 6-10.

[6] J. X. Meng, X. H. Lin and G. H. Shen, “Research on

Power Electronics System Harmonic Interference

Suppression Methods,” The Academic Journal of

Shandong University of Science and Technology (Natural

Science), Vol. 24, No. 2, 2005, pp. 52-56.

[7] X. H. Wang and K. L. Lo, “New Development of Torque

Analysis of Synchronous Machine,” Electric Machines

and Power Systems, Vol. 25, No. 8, 1997, pp. 827-838.

doi:10.1080/07313569708955778