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Residential Voltage Dip and Swell Mitigation Using. Plug-in Hybrid Electric Vehicle in Smart Grid. Andisheh Ashourpouri. Electrical and Computer Engineering.
Australasian Universities Power Engineering Conference, AUPEC 2013, Hobart, TAS, Australia, 29 September – 3 October 2013

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Residential Voltage Dip and Swell Mitigation Using Plug-in Hybrid Electric Vehicle in Smart Grid Andisheh Ashourpouri

Mahdi Dargahi

S. A. Nabavi Niaki

Electrical and Computer Engineering Department Babol Noshirvani University of Technology Babol, Iran [email protected]

School of Electrical Engineering and Computer Science Queensland University of Technology Brisbane, Australia [email protected]

Department of Electrical and Computer University of Toronto, Toronto, Canada [email protected]

Abstract - Solutions to remedy the voltage disturbances have been mostly suggested only for industrial customers. However, not much research has been done on the impact of the voltage problems on residential facilities. This paper proposes a new method to reduce the effect of voltage dip and swell in smart grids equipped by communication systems. To reach this purpose, a voltage source inverter and the corresponding control system are employed. The behavior of a power system during voltage dip and swell are analyzed. The results demonstrate reasonable improvement in terms of voltage dip and swell mitigation. All simulations are implemented in MATLAB/Simulink environment. Keywords- Voltage Dip; Voltage Swell; Smart grid; Voltage Source Inverter.

I.

INTRODUCTION

Voltage dip is among the most important problems for electronic equipments. It is defined as a decrease between 0.1 and 0.9 P.U. in the RMS voltage magnitude at the power frequency with duration about from 0.5 cycles to one minute [1, 2]. Voltage dips do not tend to necessarily damage the equipment. Equipment performance may be degraded, but the duration is typically quite short for the types of residential voltage dips. Thus, for residential customers, the cost emerged from such voltage problem is probably negligible. More significant costs would be incurred if a power service outage occurs subsequent to the voltage dip, such as if a feeder, on which the dip occurred, goes out of service [3]. Voltage dips pose a serious power quality issue for the electric power industry. Much work has been done assessing the effects of voltage dips on power system operation, as well as the industrial and commercial loads. However, more research is needed on the effects of voltage dips on residential loads. For example, for air conditioners, the compressor motors stalled for dips greater than 50% and durations greater than 10 cycles. The initiation point of the voltage dip in the voltage cycle does not

noticeably affect the motor performance. However, as expected, motor speed decreases and current increases during the dips [3]. In [1] the proposed control strategy applied to a single-phase multilevel active rectifier to attain a fast compensation and reduce ripple in the DC bus during voltage sag. The Unified Power Flow Controller (UPFC) was used to reduce the effect of voltage sag in [2] as a utility side solution. [3] conducted a project to survey the impact of voltage dip on different residential loads. This paper is engaged with the voltage disturbances in residential motor loads (air conditioner compressor). When the air conditioner starts working, it draws high current even more than the current which the utility can supply. So, this may lead to voltage drop. To compensate this voltage dip, this paper suggests using Voltage Source Inverter (VSI). VSI can inject or absorb reactive power to make up for voltage dip. The objective of this paper is to propose a control strategy for VSI in order to compensate voltage drop for household loads in a smart grid. A smart grid is collection of devices and technologies that makes the grid more intelligent and flexible than its current state [4]. One of the essential components in a smart grid is energy storage. A Plug-in Hybrid Electric Vehicle (PHEV) can be used as a smart storage in smart grids. PHEV is a vehicle that provides its forward propulsion from a rechargeable storage to save fuel [5, 6]. A smart grid provides facilities essential for both grid and vehicle, i.e. in peak time it defers the vehicle charge process and on the other hand, to help the peak shaving, the vehicle that has been fully charged, could provide energy for houses. The grid can supply charge for the vehicle while the vehicle provides distributed spinning reserve capacity for the grid. Basically, PHEV can operate as both controllable load and distributed energy resource [4, 7]. II.

REACTIVE POWER CONTROL

Reactive power affects power system operation in numerous ways. For example, loads and delivery system consume reactive power. On the other hand, flow of reactive power from the

Australasian Universities Power Engineering Conference, AUPEC 2013, Hobart, TAS, Australia, 29 September – 3 October 2013

supplies to loads causes additional overheating in lines and voltage drop in networks. Besides that, generating reactive power can limit the source ability to generate active power. So, a sufficient quantity of reactive power needs to provide the loads and losses in the network, but having too much reactive power flowing around in the network causes excessive heating and undesirable voltage drops. The normal solution to this dilemma is to provide reactive power sources exactly at the location where the reactive power is consumed [8]. To this end, Distributed Energy Resources (DER) such as PHEVs can be used to provide reactive power and also active power for residential loads. By increase in PHEV penetration and development of smart grid, the energy stored in PHEV’s battery can be utilized to mitigate voltage dip especially in residential loads. Active power control depends on frequency control while reactive power can be controlled by changing voltage magnitude. Thus, constancy of voltage and frequency are vital factors in power quality. As it is better to avoid transmitting reactive power over long distances, it should be absorbed or generated by special devices dispersed throughout the power system [9]. PROPSED CONTROL SYSTEM

III.

A simple smart grid system, including a house which is equipped with a PHEV, a VSI, and the required communication system as the one presented in Fig. 1 and Fig. 2 is considered. The PHEV is connected to the Point of Common Coupling (PCC) through the VSI and load of the house supplied with grid and the PHEV. Zs and ZL in Fig. 2, are the impedance of grid and load respectively and VPCC is the voltage of PCC.

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To reduce the effect of voltage dip and swell on this house a hybrid control strategy of the VSI is employed. As mentioned before active and reactive power can be controlled by the voltage frequency and magnitude control respectively. In the proposed hybrid control scheme, reactive power is controlled by droop method while a Central Power Management (CPM) unit decides about the active power. CPM has all the required information about the load and power of PHEV and according to the information, determines some set points. The set points can be adjusted based on an economic load flow same as what proposed in [4], and then be sent to the inverter of the PHEV using the communication system. During the interval of sudden changes in load, an Auxiliary Power Unit (APU) provides the additional load demand until the control system updates its data. Indeed, APU, which in this paper the utility grid plays its role, keeps the voltage and frequency of the grid fixed by providing the additional power demand. We assume that each PHEV is fully charged and 100% available and also PHEV, APU, house and CPM are interconnected with each other through communication. Fig. 3 shows a schematic of the inverter with the feedback system. Ld

Lf 1Φ Inverter

Battery of PHEV

Cf

AC Grid

Load

rg Lg

io

Φ Vref

vo

P&Q calculation

Droop &Pset

IvI

Grid

Inverter’s Control Section

Comparison

Fig. 3. The inverter with feedback system.

Load Battery Fig. 1. Connection of PHEV’s battery, house and grid. ZL

Zs

In Fig. 3, Lf, Cf, Ld, rg, and Lg are filter’s inductance, filter’s capacitance, decoupling impedance, grid’s resistance, and grid’s inductance respectively. As shown in Fig. 3, after calculating active and reactive power in P&Q calculation block, Droop & Pset block calculates angle and magnitude of the reference voltage, denoted by φ and ‫׀‬v‫ ׀‬respectively. Fig. 4 illustrates Droop & Pset block in details and is designed based on (1) and (2) [10, 11].

AC Load Pm

VPCC

-

PID

Φ

Power injection

|v|

Voltage droop

+ Pset E

-

PHEV PHEV

Vm

House

Fig. 2. Schematic connection of PHEV’s battery, house, and grid.

+ E*

Fig. 4. Droop & Pset block in details.

Q

Australasian Universities Power Engineering Conference, AUPEC 2013, Hobart, TAS, Australia, 29 September – 3 October 2013

t

  m  pd  m p p  md 

E  E *  n p Q  nd

dp dt

(1)

dQ dt

(2)

where φ is difference angle between PCC voltage and inverter output voltage, P is active power, Q is reactive power, E* is voltage reference, m , mp, and md are PID coefficients for the control of φ, and np, nd are PID coefficients for voltage control. As both power injection and droop methods are used, this control strategy is named as hybrid control. The values of these parameters as well as control system parameters used in the simulations are listed in Table І.

Fig. 5. Voltage waveform of load during voltage dip without controller.

TABLE І. VALUES OF THE SYSTEM’S PARAMETERS Parameter

Value

symbol

Grid voltage

311* sin(ωt)

vg

V

Frequency Grid’s resistance Grid’s inductance Decoupling Impedance Filter’s Inductance Filter’s Capacitance Switching Frequency Integral Coefficient of Phase Controller Proportional Coefficient of Phase Controller Integral Coefficient of Magnitude Controller Proportional Coefficient of Magnitude Controller

50

f

Hz

0.0035

rg

Ω

0.001

Lg

H

3.0812*10-4

Ld

H

1.5458*10-3

Lf

H

0.97*10-3

Cf

F

7000

Fs

Hz

10-4

m

10-6

mp

IV.

Unit

Fig. 6. RMS Voltage of load during voltage dip without controller.

 rd

 rd.s Fig. 7. Voltage waveform of load during voltage dip with controller.

1

n

var v

0.01

np

var v

TEST RESULTS

To verify the proposed control system ability to mitigate voltage dip and swell on residential loads, let us consider a house which is supplied with grid and PHEV’s battery. A sudden increase in house’s load occurs at t= 2.5 s by imposing an air condition load. The results with and without controller are shown in Figs. 5 to 13.

Fig. 8. RMS voltage of load during voltage dip with controller.

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Australasian Universities Power Engineering Conference, AUPEC 2013, Hobart, TAS, Australia, 29 September – 3 October 2013

Fig. 9. Current waveform of load during voltage dip with controller.

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Fig. 13. Active and reactive power of inverter voltage dip with controller.

To investigate the impact of the control strategy on voltage swell we consider a load which can generate reactive power. Figs. 14 to 21 show the test results and demonstrate that the control system is capable of absorbing reactive power to prevent voltage swell.

Fig. 10. Voltage waveform of inverter during voltage dip with controller.

Fig. 14. Voltage waveform of load during voltage swell without controller.

Fig. 11. Active and reactive power of load during voltage dip with controller.

Fig. 15. RMS voltage of load during voltage swell without controller.

Fig. 12. Active and reactive power of grid voltage dip with controller.

As can be seen in Fig. 5 to 13, when load increase happens and as a consequence voltage drop occurs, inverter with the help of its control system can counteract the voltage dip. Fig. 16. Voltage waveform of load during voltage swell with controller.

Australasian Universities Power Engineering Conference, AUPEC 2013, Hobart, TAS, Australia, 29 September – 3 October 2013

Fig. 17. RMS voltage of load during voltage swell with controller.

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Fig. 20. Active and reactive power of grid with controller.

Fig. 21. Active and reactive power of inverter with controller. Fig. 18. Voltage waveform of inverter during voltage swell with controller.

Fig. 19. Active and reactive power of load with controller.

As Figs. 14 to 21 have shown, the hybrid strategy is designed in such a way that the inverter can absorb the required amount of reactive power as well. V.

CONCLUSION

In this paper, the impact of voltage dip and swell on residential loads is analyzed. In order to reduce the effects of these voltage disturbances, a VSI and a hybrid control strategy is deployed. The control theory developed based on the fact that the active and reactive powers can be controlled by controlling frequency and voltage magnitude, respectively. So, the proposed control strategy adjusts reactive power based on droop method and active power is controlled by set points which are commanded from a CPM unit. The CPM calculates these set points and sends them to the inverter of each PHEV using the communication system. As can be inferred from the presented results, adequate operation of the proposed control system leads to controlling the active and reactive powers in a way that the entire system remains stable.

REFRENCES [1] J. Lira, C. Núñez, M. Flota, R. Álvarez, “A Control Strategy to Improve Voltage Dip Ride-Through in Single-Phase Multilevel Active Rectifier”, Electrical and Electronics Engineering, 3rd International Conference, 6-8 Sept. 2006, Veracruz. [2] MahdiM. EI-Arini, YoussefM.T., Hamed H. Hendawy, “Voltage Sag Analysis and Its Reduction to Improve Power System Performance”, The 11th International Middle East Power Systems Conference, 2006. [3] George G. Karady, Saurabh Saksena, Baozhuang Shi, Nilanjan Senroy, “Effects of Voltage Dips on Loads in a Distribution System”, Power Systems Engineering Research Center, Arizona State University, October 2005. [4] Ashourpouri, A; Sheikholeslami, A; Shahabi, M; Niaki, A.S.N , “Active Power Control of Smart Grids Using Plug-in Hybrid Electric Vehicle” Smart Grids (ICSG), 2012 2nd Iranian Conference, 24-25 May 2012. [5] Palo Alto, “Comparing the Benefits and Impacts of Hybrid Electric Vehicle Options”, EPRI, CA: 2001. 1000349. [6] Palo Alto, :Comparing the Benefits and Impacts of Hybrid Electric Vehicle Options for Compact Sedan and Sport Utility Vehicles”, EPRI, CA: 2002. 1006892. [7] A. Godarzi, S.A. Nabavi Niaki,F. Ahmadkhanlou, and R. Iravani, “Local and Global Optimization of Exportable Vehicle Power based Smart Micro grid,” IEEE-PES Innovative Smart Grid Technologies Conference, 17 - 19 January 2011 in Anaheim, CA, USA. [8] Peter W. Sauer, “Applied Mathematics for Power Systems”, University of Illinois at Urbana-Champaign, Chapter 2. [9] P.Kundur, “Power System Stability And Control, Handbook”, Second Edition, University of Toronto Ontario, 581-695. [10] Josep M. Guerrero, Luis García de Vicuña, José Matas, Miguel Castilla, Jaume Miret, “A Wireless Controller to Enhance Dynamic Performance of Parallel Inverters in Distributed Generation Systems,” IEEE Transaction On Power Electronics, Vol. 19, No. 5, September 2004. [11] Suratsavadee Koonlaboon Korkua, Rasool Kenarangui, “Control Strategy for Load Sharing in Distributed Generation System in Parallel Operation,” IEEE Green Technologies Conference, 22 April 2010.