World Electric Vehicle Journal Vol.

7 - ISSN 2032-6653 - ©2015 WEVA Page WEVJ7-0518

EVS28
KINTEX, Korea, May 3-6, 2015

IMPACT OF PENETRATION OF ELECTRIC VEHICLES

ON INDIAN POWER GRID
Kashyap L Mokariya1, Varsha A Shah2, Makarand M Lokhande3
Kashyapmokariya2000@yahoo.com 1
vas@eed.svnit.ac.in2,
mml@eed.svnit.ac.in3
Department of Electrical Engineering
Sardar Vallabhbhai National Institute of Technology,
Surat, Gujarat, India

Abstract
The research on impacts of electric vehicles on Indian power grid is motivated to enhance development of
electric vehicle in India against the burning issues of rising fuel demand and the nation’s dependency on
other countries for fuel which largely affects the GDP of nation. India has declared E-mobility mission
plan to deploy 4,00,000 passenger electric vehicles by 2020. If this target is achieved India can avoid
importing 120 million barrels of oil and avoid 4 million tonnes of CO2 emissions by 2020. In future, as
demand of electric vehicles increases, charging issues while connecting electric vehicle to grid also
increases. This paper presents various aspects in terms of challenges and issues when electric vehicle is
charged from grid and also the benefits, potential services and applications of electric vehicle in V2G
mode. Effect of electric vehicle penetration on distribution grid is carried out in matlab simulink
environment to observe effects on different electrical parameters like dc bus voltage, current, active power,
reactive power, harmonics and power factor. Concept of vector control technique for voltage source
converter is developed for stabilizing grid against penetration of electric vehicle. Control technique
implemented here gives fast dynamic response, reduces harmonics and improves power factor with
constant dc bus voltage. Concept shown here will be very useful for fast dc charging of electric vehicle
batteries. Battery modelling described with the concept of extracting parameters from manufacturers
discharge characteristics gives fast and effective solution and will be useful for not only Li-Ion batteries but
also for Ni-Mh and Lead-acid batteries.

Keywords: vectorcontrol,grossdomesticproduct,phaselocked loop,voltage source converter,mobility mission plan

1 INTRODUCTION emissions. Today’s energy policies lean strongly

towards diversification of transportation fuels,
Globally the transportation systems are almost improving energy efficiency and reducing
completely oil dependent and they are a emissions [1]. The use of grid connected vehicles
significant source of green house gases and other offer great potential to fulfill these challenging

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requirements. Electric vehicles are gaining problems and even collapses the system network
worldwide interest and acceptance as a [5], [6].These issues can be reduced by charging
promising potential long term solution to of electric vehicles during off peak periods by
sustainable personal mobility [1].Transportation coordinated or programmed charging of multiple
sector is responsible for 70% consumption of EV’s in distribution grids [8] or by proper
petroleum products in India [2]. Nation is largely demand management of grid connected PHEV’s
dependent on other countries for rising demand [10].If coordinated charging is implemented for
of fuel which affects GDP (Gross Domestic multiple PHEVs, grid enhancements or
Product) of the nation. Hence in near future it is modifications will be significantly reduced.
expected that the adoption of electric vehicles Proper energy management system along with
will increase significantly. As penetration of the coordinated charging will help to perform
electric vehicle increases there will be some demand response based EV charging. In other
serious challenges due to vehicle charging on words, the EMS (Energy Management System)
power grid. The feasibility analysis of should be able to disconnect the EVs charger
penetration of electric vehicles on grid is prime from the grid in case of overload [7].Regarding
concern among the various issues. In 2007 control techniques researchers have done their
PNNL (Pacific Northwest National Laboratory) work from proportional integral controllers and
has conducted research on impacts of PHEV hysteresis controllers to fuzzy controllers.
deployment in US grid for light duty vehicles Researchers have used various fuzzy techniques
that could be supported by existing electrical for traffic management, forecasting of electrical
infrastructure. The study covered 12 main load, control of dc-dc converters etc[11].As
regions of the U.S with an estimated 213 million nation is concerned regarding obstacles towards
LDVs (Light Duty Vehicles) converted to electric vehicle development, major concern in
PHEVs with an all-electric range of 33 miles India at present is the feasibility of penetration of
(PHEV33).For the electrical grid data, statistics electric vehicle on Indian power grid. Comparing
were gathered for two 24-hour periods for penetration of electric vehicles in US grid to the
summer day and winter day (for each of the 12 Indian grid then India is not even in a position at
regions.)[3].Study revealed that with the existing present to penetrate more than 10% of total
infrastructure approximately 73% of the vehicles if considered as electric vehicles. In
estimated PHEV could be charged. An many parts of India still generation is not
assumption is made for 24-hour charging. For matching the demand. Many distribution systems
above 73% of PHEV out of 213 million LDVs in India were designed decades ago considering
(Light Duty Vehicles) annual U.S generation will the load levels and load characteristics of that
increase by 910 billion kWh (+24%). Some other time. Many of these power system networks do
factors that affects the charging behavior of the not have monitoring and automation capability
EVs are type of connection i.e., unidirectional or and even enough spare capacity [7].So sudden
bidirectional, number of vehicles charging in a EV penetration in Indian power grid needs lot of
given area, geographical location, levels of thinking regarding redesigning power system
current and charging voltage, status of battery networks [7].
and its capacity, charging duration and slow or Obstacles faced in development of electric
fast charging[3]. Fast charging has a great impact vehicles in India can be eliminated by adopting
on grid distribution network because of high following methods.
power i.e. typically more than double of an I. Increasing generation capacity and strengthen
average household load [4].Apart from the grid non renewable generation in country.
feasibility issues there are some other serious Region wise installed capacity of India as on
issues to be considered while charging of electric 28th February 2014 is 237742.94 MW. Many
vehicles on power grid. These charging effects generation and transmission projects are
might result in power quality issues, increase in sanctioned and will be executed in near future.
harmonics, increased transformer losses, [12].
increased line losses, line heating issues and II. Co-ordinate charging
increased reactive power consumption. Coordinated charging means that vehicle
Summarizing all these effects it might result in charging is scheduled to occur at moments of
potential damage to the customer devices and low demand. Daily load curves should be studied
power system equipments. These issues may carefully and from that off peak period should be
cause overall power system and voltage stability identified for penetration of electric vehicles[12].

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III. Energy conservation principles voltage source converter. Section 7 is for results
To enhance penetration of electric vehicles on and discussion.
Indian grid the country has to focus on energy 2 VEHICLE TO GRID
conservation practices not only in Industries but When electric vehicles are charging from grid
also in villages where major chances of energy then that mode of operation is known as grid to
saving potential lies. Author was a part of vehicles and when electric vehicles are delivering
Vishvakarma yojna in which energy losses were energy to grid than that mode of operation is
measured in 255 villages of Gujarat a state of known as vehicle to grid. In these section four
India and solutions were suggested to mitigate quadrant operations along with benefits, potential
them and corresponding reports were submitted services and applications of V2G is discussed.
to the authorities of Gujarat government [12].
In this paper vector control technique for fast 2.1 Four Quadrant operation
dc charging of electric vehicle batteries is
shown.Battery modelling described with the
concept of extracting parameters from
manufacturers discharge characteristics gives fast
and effective solution and will be useful for not
only Li-Ion batteries but also for Ni-Mh and
Lead-acid batteries.Voltage source converter
with battery algorithm based on extracting
parameters from discharging characteristics
stands true for reducing filter size while charging
vehicles and gives fast and effective solution.
Control technique with proper selection of dc bus
capacitor reduces the size of filter. Vector control
technique provides fast response to give constant
dc bus voltage with unity power factor against
the penetration of electric vehicle on fast Figure 1 Modes of operation of charger
charging mode. Alignment to a dq synchronous
The idea of V2G helps to build a whole set of
reference frame orientation with PI regulators is
instantly available distributed energy storage
used in the control topology for decoupling
devices [11]. In V2G services vehicle operation is
purposes. In this voltage source converter
divided into four quadrants. When active and
synchronously rotating dq reference frame is
reactive powers both are positive then it is
used. Very important and necessary feature of
quadrant I operation and it refers to charging and
grid side converter control is grid
inductive operation of charger. When real power
synchronization and for that PLL (Phase locked
is positive and reactive power is negative, it is
loop) is used. Vector control technique used here
quadrant IV operation charging and capacitive.
is based on inner and outer control loops. The
When real power is negative and reactive power
inner loop controls power between dc link and
is positive it is quadrant II operation which is
grid while outer loop controls the dc voltage of
discharging and inductive and if real and reactive
the load. So the control technique implemented
powers both is negative then it is quadrant III
here gives fast dynamic response, reduces
operation, discharging and capacitive. In this
harmonics and improves the power factor with
paper to study the effects of charging and to
constant dc bus voltage. Concept shown here will
mitigate it, quadrant one operation is simulated.
be very useful for fast dc charging of electric
vehicle batteries. Work carried out is explained
2.2 V2G benefits, potential services and
in various sections. Section2 consists of benefits,
applications
potential services and applications of V2G with
quadrant operation of charger. Section3 shows The active power markets of V2G can be
system configuration for proposed work divided into four general groups [13].These four
done.Section4 explains various power levels for groups are base load, peak, spinning reserves, and
battery charging and battery model. Section 5 regulation. Bulk power generation that is running
explains basics of voltage source converter and most of the time it is defined as base load. As
section 6 explains vector control technique for V2G for base load applications requires large
amount of power and large amount of batteries, it

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is generally not preferable. Peak shaving occurs sized capacitors. The size of these capacitors
during predictable highest power demand hours. depends on the required dc voltage. The primary
Ultra capacitors having high amount of power objective of the dc capacitor is to provide low
density is more suitable for meeting these peak inductive path for the turn-off current and it also
demands in short time. Spinning reserves are works as energy storage device to control the
supplied by generators having fast response time power flow. Capacitor also reduces the voltage
and ready to respond in case of equipment or ripple on dc side. Voltage source converters on
power supply failures. Spinning reserves should the ac side act as a constant current source and
be included in system power design to meet therefore require an inductor as its energy storage.
contract requirements and are typically called On the dc side voltage source converter acts as a
around 20 times a year[14].The duration of constant voltage source and it requires capacitor
supply by a spin reserve is typically around 10 as energy storage device. Loads are put on both
min but the source must be able to last up to 1 ac and dc sides to study the battery charging
hour. Active regulation is used to keep the impacts as it is in general practise. Model
frequency and voltage steady. Regulation is specification for the system configuration is
called for only a few minutes at a time, but the shown in table 1.
number of times can be up to 400–500 times per Table 1: Model specifications
day.The utility pays spinning reserves and
regulation sources in part for just being available, Descriptions Value
per hour availability; however, base load and Voltage source 500 Volts DC, 500 kW
peak shaving are paid per kWh generated[13]. converter rating
AC Supply: 500 V, 30 MVA, 50 Hz
3 SYSTEM CONFIGURATION three-phase system
Load Ac side 1MW,dc side
400kw including electric
vehicle
DcLink:2 25000 mF
capacitors
Switching 1620 Hz
Frequency

4 CHARGING POWER LEVELS WITH

Figure 2: System configuration for proposed work BATTERY MODEL
Figure 2 shows the system configuration for Various power level chargers and infrastructure
analysing vehicle charging impacts. A 30 MVA configurations are classified based on the amount
generator is connected to 3-phase 3 level voltage of power required, charging time location and
source converter via transformer and grid filter. component ratings etc [9].
Function of filter is to reduce harmonics. In
Table 2: Charging power levels [9]
voltage source converter dc side ripples and
harmonics in the system can be taken care by Power Typical Expecte Char Vehicle
effective selection of dc capacitor. Specifications Level use d power ging technolo
for proposed model are shown in table 1. types level time gy
As shown in Figure 2 voltage source Level 1 Chargin 1.4 4-11 PHEVs(
converters are connected to the ac system by US g at kW(12 hours 5-
means of transformers. The function of the 120Vac home A) 11-36 15kWh)
transformer is to transform the ac voltage level to EU230 or 1.9kW( hours EVs(16-
required ac voltage level for dc charging of Vac office 20A) 50kWh)
vehicles. The phase reactors are used for Level 2 Chargin 4kW(1 1-4 PHEVs(
controlling active and reactive power flow by 240Vac g at 7A) hours 5-
regulating currents through them. Reactors also (US) private 8kW(3 2-6 15kWh)
serve as filters and therefore reduce the high 400Vac or 2A) hours EVs(16-
frequency harmonic contents of the ac currents (EU) public 19.2kW 2-3 30kWh)
which are caused by the switching operation of outlet (80A) hours EVs(3-
the IGBTs. The dc side contains two equally 50kWh)

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Level3( Analog 50 kW 0.4-1 EVs(20- better represent the open circuit voltage behavior
Fast) ous to 100kW hour 50kWh) and the term concerning the polarization
filling 0.2- resistance [22],[23]was slightly modified. The
station 0.5 battery voltage obtained was given by
hour (1)

Table 2 shows charging power levels. Typical use term refers to polarization voltage
of level 1 charging is at home or office. Level 2 term refers to polarization resistance
charging is used at private or public outlets. Level
Where
3 is analogous to commercial filling station. Fast
=battery voltage V
dc charging can be used for greater than 100kw
E0 = battery constant voltage (V)
power level and vehicle can be charged within 30
K=polarization resistance (Ω) or polarization
minutes. Level 1 and level 2 are onboard chargers
constant(V/AH)
and level 3 and dc chargers or charging stations
Q = battery capacity (Ah)
are off board chargers.
Analysis is done to study effect of various =ɭ idt=Actual battery charge (Ah)
electrical parameters while charging battery from A =exponential zone amplitude (V)
B = exponential zone time constant inverse
the grid. To analyze the grid impact battery model
used is free from algebraic loop problems. R =battery internal resistance (Ω)
i=battery current (A)
=filtered current
Particularity of this model was use of a filtered
current flowing through the polarization
resistance. This filtered current solves issue of
algebraic loop problem due to the simulation of
electrical systems in simulink. Finally, the OCV
varies non-linearly with the SOC. This
phenomenon was modeled by the polarization
voltage term. Equation (1) is valid for the Li-Ion
battery. For the other batteries (Lead-Acid,
Figure 3: Discharge characteristic of Li-Ion battery NiMH and NiCD), hysteresis phenomenon
Figure 3 shows discharge characteristic of Li-Ion between the charge and the discharge should be
battery.Discharge characteristic can be simplified taken into account irrespective of the SOC of the
as shown in Figure 4 below. battery [22], [24]. It is very necessary to extract
the parameters for the given battery while doing
modeling in matlab, hence equation 1 should be
simplified in steady state condition to reproduce
manufacturers discharge curves. Generalized
equation will be as under.
(2)
Comparing equation 1 with 2, the filtered
current will be equal to i because current is in
steady state.
Vehicle battery manufacturer provides
datasheet which includes discharge
characteristics. From the discharge characteristics
it is possible to extract fully charged voltage
Figure 4: Typical discharge curve (Vfull),end of the exponential zone(Qexp,Vexp),end
Figure 4 shows a typical discharge characteristic. of the nominal zone(Qnom,Vnom),Maximum
Shepherd model can represent accurately the capacity(Q) and the internal resistance R. With
voltage dynamics when the current varies and these 3 points calculation becomes much easier.
takes into account the open circuit voltage (OCV) The capacity Qnom is extracted from the battery
as a function of SOC (State of charge). A term until the voltage drops under the nominal voltage.
concerning the polarization voltage is added to Value should be between Qexp and Q as shown in
figure. The voltage Vexp and the capacity Qexp

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corresponds to end of exponential zone. The The VSC system incorporates advanced power
voltage should be between Vnom and Vfull and the electronics technology used in electric power
capacity should be between 0 and Qnom as shown systems and has the capability of transmitting
in the figure. large amount of power over long distances. Fast
For the fully charged voltage extracted charge is and decoupled active and reactive power control
0(it=0) and the filtered current ( because can be achieved by voltage source converters
current step has just begin. [16].The drawback of VSC’s is the bulky
(3) dimensions of dc-link capacitors, which is the
For the end of the exponential zone the factor B main limiting factor. By reducing the dc-link
capacitor size a reduction in cost and volume of
can be approximated to since the energy of
the converter can be achieved. However, a small
the exponential term is almost 0 after 3 time dc-link capacitance leads to large fluctuation in
constants. the dc-link voltage, and hence can cause
(4) semiconductor switch breakdown. The proposed
(5) work involves the control of converter dynamics.
The idea is to control the exact amount of
The filtered current ( is equal to i because the required current in the converter, to force the
current is in steady state hence equation 1 can be power balance. Hence, the dc-link voltage does
modified as. not fluctuate even though a fairly small
Li-Ion discharge model capacitance is utilized.
(6)
VSCs utilize self-commutating switches, e.g.
gate turn-off thyristors (GTOs) or insulated gate
Where C=A (7) bipolar transistors (IGBTs), which can be turned
Li-Ion Charge model on or off in a controlled manner. VSCs operate at
(8) switching frequency utilizing Pulse-Width
Modulation (PWM) technique. Advantages of
Where C=A same as 7. implementing such a scheme is.
Equation 6 and 8 suggests that the discharging (1) Active and reactive power can be controlled
characteristics used for parameter extraction independently (to or from the Converter) without
stands true for evaluating charging impacts. any needs for extra compensating equipment.
From the manufactures discharge curve it (2) Little risk of commutation failures in the
becomes easy and effective to find E0. converter.
Assumption made here is the internal resistance (3) Faster dynamic response and reduced need for
is constant during the charge and discharge filtering and hence smaller filter size [15].
cycles and does not vary with the amplitude of (4) Minimal environmental impact.
the current. (5)Current smoothing is done by dc capacitor so
small amount of filter size is required.
5 VOLTAGE SOURCE CONVERTER In an attempt to improve the poor harmonic
Thyristors can only be turned on (not off) by performance of the two-level converter, some
control action, and rely on the external ac system systems have been built with three level
to affect the turn-off process. Control system only converters. Three-level converters can synthesize
has one degree of freedom. With some other three (instead of only two) discrete voltage levels
types of semiconductor device such as at the AC terminal of each phase: +½ Ud, 0 and -
the insulated-gate bipolar transistor (IGBT), both ½ Ud. A common type of three-level converter is
the diode-clamped (or neutral-point-clamped)
turn-on and turn-off can be controlled, giving a
second degree of freedom. As a result self converter, where each phase contains four IGBT
commutated converters can be made by IGBTs valves, each rated at half of the dc line to line
that can be turned on and off many times per voltage, along with two clamping diode valves
cycle in order to improve the harmonic [16].The dc capacitor is split into two series-
performance. Voltage-source converters are connected branches, with the clamping diode
compact as compared to line-commutated valves connected between the capacitor midpoint
converters (mainly because much less harmonic and the one-quarter and three-quarter points on
filtering is needed). So VSC’s are preferred where each phase. To obtain a positive output voltage
space is prime consideration. (+½ Ud) the top two IGBT valves are turned on,

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to obtain a negative output voltage (-½ Ud) the harmonics elimination is also required on the ac
bottom two IGBT valves are turned on and to side. On the dc side VSC acts as a constant
obtain zero output voltage the middle two IGBT voltage source and it requires a capacitor as its
valves are turned on. In this latter state, the two energy storage device. Energy storage capacitor
clamping diode valves complete the current path here provides dc filtering capability.
through the phase. The control system of VSC has a fast inner
current control loop that controls the ac currents.
The ac current references are provided by the
outercontrollers [19].The slower outer controllers
can be the dc voltage controller, the ac voltage
controller, the active power controller, the
reactive power controller and the frequency
controller. Thus, the reference of the active
current can be obtained from the dc voltage
controller, from the active power controller or
from the frequency controller [17].

6 CONTROL ALGORITHM FOR

PROPOSED SCHEME
Vector current control is the most popular control
Figure5: Three phase three level voltage source method used for VSC. Dc-link voltage regulation
converter is achieved by implementing a control based on
the energy stored in the dc-link capacitor.
Figure 5 shows three phase three level voltage Alignment to a dq synchronous reference frame
source converter. It is also called as neutral orientation with PI regulators is used in the
clamped converter. In a refinement of the diode- control topology for decoupling purposes. In
clamped converter, the so-called active neutral- voltage source converter synchronously rotating
point clamped converter, the clamping diode dq reference frame is used and active and
valves are replaced by IGBT valves, giving reactive power can be independently controlled.
additional controllability. Normally, converters Very important and necessary feature of grid side
are connected to the ac system by means of converter control is grid synchronization and for
transformers. The most important function of that PLL (Phase locked loop) is used. Vector
transformers is to transform the ac voltage level control technique used here is based on inner and
to the dc voltage level. Usually, they are single- outer control loops. The inner loop controls
phase three-winding type, but depending on the power between dc link and grid while outer loop
transportation requirements and the rated power, controls the dc voltage of the load. So the control
they can be arranged in other ways [18].The technique implemented here gives fast dynamic
phase reactors are used for controlling active and response, reduces harmonics and improves the
reactive power flow by regulating currents power factor with constant dc bus voltage.
through them. The reactors also serve as ac filters Concept shown here will be very useful for fast
and therefore reduce the high frequency dc charging of electric vehicle batteries. Voltage
harmonic contents of the ac currents which are source converter with proposed control technique
caused by the switching operation of the IGBTs. can be utilized in all four quadrants for effective
The dc side contains two equally-sized capacitors. V2G operation. Vector control scheme is shown
Size of these capacitors depends on the required in Figure6.
dc voltage.The primary objective of the dc
Vdc*
capacitor is to provide a low inductive path for
the turned-off current [18] and also works as DC VOLTAGE CURRENT
KP=0.3,KI=20, KD=0
Id* PWMd
DC VOLTAGE CONTROLLER CONTROLLER
energy storage device to be able to control the CONTROL Vdc (REGULAR OUTER (INNER CONTROL
PWM
CONTROL LOOP) LOOP)
power flow. The capacitor also reduces the
PWMq
voltage ripple on the dc side. Ac filters prevent Iq*
Idq
the voltage harmonics entering the ac system. AC
CURRENT
ABC TO DQ
TRANSFORM

VSC on the ac side acts as a constant current

source and therefore requires an inductor as its PLL MEASURENT
Cosθ,Sinθ

energy storage device. A small ac filter for Figure6: Vector current principle

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By utilizing synchronously rotating dq reference 6.1 Phase locked Loop

frame, independent active and reactive power The phase locked loop measures the system
control is possible. Initially, system currents and frequency and provides the phase synchronous
voltages are described as vectors in a stationary angle θ (more precisely [sinθ,cosθ] for dq
αβ reference frame and then they are transformed transformation block[21].Very important and
to the rotating dq coordinate system. The necessary feature of grid side converter control is
transformation to dq coordinates is done as the grid synchronization. The synchronization
follows. Three-phase components xa(t), xb(t) and algorithm is able to detect the phase angle of grid
xc(t) are first described as two vectors in the αβ voltage in order to synchronize the delivered
reference frame. power. The purpose of this method is to
synchronize the converter output current with the
grid voltage in order to obtain a unity power
factor .The inputs of the PLL model are the three
phase voltages measured on the grid side and the
output is the tracked phase angle. The PLL
model is implemented in synchronous dq
reference frame, where a park transformation is
used. The phase-locking of the system is realized
Figure7: stationary abc and αβ reference frames
by adjusting the q-axis voltage to zero. A PI
Using a park transformation, the transformation controller is used for this purpose. The grid angle
from αβ frame to dq can be written as is obtained by integration of the angular
Xdq=Xαβ θ (9) frequency. The grid angle is introduced in the
The vectors xα(t) and xβ(t) are rotating with the park transform to calculate the dq voltage
angular frequency ω(t), which is the angular components.
frequency of the grid voltage in rad/s. Let θ(t) be
the angle defined by integrating ω(t).Then the 6.2 Control strategy
expanded matrix form of park transformation is The control strategy of voltage source
obtained as converter as discussed has its base level and a
(10) fast inner current control loop that controls ac
currents. The ac current references are provided
Vectors xd(t) and xq(t) represent currents, by the outer controllers. The outer controller is
where xd(t) is the current which gives required dc voltage controller. Thus the reference of
power to the dc bus and xq(t) is the current active current can be obtained from the dc
which defines the reactive power condition. voltage controller. The inner loop controls power
Excellent controlling is achieved with this between dc link and grid while outer loop
transformation and it is shown in vector control controls the dc voltage of the load.
block of figure 6 as Idq. A correct transformation
requires an exact value of the angle θ(t) to 6.2.1 Inner current loop
decouple the components for independent power Vd
Id*
control. The angle θ is given as:
) (11) + +
V d*
PI
Where Vα and Vβ are voltage components in the - +
id
αβ reference frame. Synchronization technique ωL
phase locked loop is utilized to compute value of Iabc abc
the angle θ [20].The phase-locked loop is used to dq

synchronize the turning on/off of the power iq

ωL
devices, calculate and control the flow of
active/reactive power by transforming the - -
PI V q*
+ +
feedback variables to a reference frame suitable
for control purposes [20]. Vector control system Iq* Vq
is primarily based on inner and outer control
loops, inner loop controls power between dc link Figure8: structure of inner current loop
and grid while outer loop controls the dc voltage
of the load.

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The inner controller or current controller as rotating at ω speed and the d axis is oriented
input takes the error between the reference along the grid voltage vector. The value of iq ref
current and measured current. Error is carried is set to zero to get unity power factor.
through the PI regulator and the decoupling
terms are compensated by feed-forward. As a 7 SYSTEM DESCRIPTION & RESULTS
result the desired converter voltage in dq
reference frame is obtained. The feed-forward is Uncontrolled rectifier is simulated in Matlab
used to minimize disadvantage of slow dynamic simulink environment under different load
response of cascade control. As the reference condition and reduction in dc bus voltage with
values of the inner loop variables are often ample current harmonics was observed.
available, these are fed forward for a faster and Uncontrolled rectifier was replaced by 12 pulse
safer operation. voltage source converter and disturbance in
The structure of the block of current electrical parameters was stabilized against
controller (inner current loop) of figure6 is increase in load. On this stable grid Li-ion
shown in Figure8. The controller in Figure 8 batteries were connected and again the variation
consists of two PI regulators, for q and d axis in electrical parameters was stabilized by using
respectively. Active current (id) is used to vector control technique for multi pulse
control active power flow or dc voltage level. converter. Initially the proposed matlab model is
Similarly, reactive current (iq) is used to control simulated on uncontrolled rectifier. As the load is
reactive power flow into grid. increased from 200kW to 400kW the dc bus
voltage immediately drops to 270V. Similar
loading was done on controlled rectifier. It can
6.2.2 Outer controller be observed that the dynamic response of the dc
Vdcref
regulator to this sudden load variation is
acceptable. The dc voltage is back to 500 V
+
PI CONTROLLER Id* within 1.5 cycles and the unity power factor on
-
the ac side is maintained. So it is verified that the
KP=0.015 -1<Id<1 system is stable.
KI=0.6
Vdc KD=0 On this stable grid batteries with Li-ion
chemistry were connected and the impact on
Figure9: Outer controller various electrical parameters on grid was
Figure 9 represents the dc voltage controller, observed with battery charged from fully
outer control loop of Figure 6.Output of Id* of discharge condition.While battery charging
output dc voltage regulator block (outer loop) is constant dc bus voltage was achieved at unity
given to current controller (Inner current loop). power factor at source side with vector control
logic. Results obtained from simulation are
6.2.3 Overall control scheme summarized below.
Vd*
Table 3: Results obtained from simulation
converter id
Vq* iq
Iqref=0 Uncontrol Controlle Controlled Controll
+
Kp+kdi/s led d rectifier rectifier ed
-
Rectifier with LI- rectifier
ωL
Ion Battery with LI-
ωL

+
250 Ion
-
Kp+kdi/s
+
Kp+ki/s
+ vdref
volt,6.5 Ah Battery
+ Id*
- 250
vdc
volt,30
Ah
Figure 10: Overall controller for active rectifier Vdc=270 Vdc=500 Vdc=500 V Vdc=500
(converter) V V V
The controller within the AC/DC converter Active Active Active Active
manipulates the q axis current to achieve unity power=1. power=1. power=1.4 power=1
power factor operation, while the d axis current 138× 36× 33× .626×
is being used to regulate dc link voltage as shown W W W
in Figure10. It is assumed that the dq frame is Reactive Reactive Reactive Reactive

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World Electric Vehicle Journal Vol. 7 - ISSN 2032-6653 - ©2015 WEVA Page WEVJ7-0527

power=41 power=37 power=37 power=3 for unity power factor. Variation of modulation
830 var 390 var 450 var 9930 var index, Id and Iq are also shown in the figure 13.
Voltage Voltage Voltage Voltage
harmonics harmonic harmonics harmoni
=1.48% s=0.19% =0.21% cs=0.23
%
Current Current Current Current
harmonics harmonic harmonics harmoni
=43.17% s=8.33% =7.28% cs=4.91
%
Power Power Power
factor=0. factor=0.9 factor=0.
997 997 9999

Figure 11 shows dc bus voltage of uncontrolled

rectifier. As load increases the dc bus voltage
drops considerably in uncontrolled rectifier. Figure 13 Variations in Id, Iq and modulation index
Ideally it should remain at 500 volt. So before
connecting EV batteries to grid this drop in Figure 14 shows that constant dc bus voltage is
voltage should be stabilized. achieved with controlled rectifier. Control
strategy is already discussed for achieving
constant voltage at dc bus side and unity power
factor at source side.
900

800

700

600
voltage

500

400

300

200

100

0
0 0.05 0.1 0.15 0.2 0.25 0.3 0.35 0.4 0.45 0.5
time
Figure 11: dc bus voltage waveform of Uncontrolled
rectifier with increase in Load Figure 14: Constant dc bus voltage with controlled
rectifier
Figure 12 shows considerable amount of current
harmonics in the supply system due to Figure 15 shows that as supply voltage
uncontrolled rectifier harmonics are negligible a sinusoidal supply is
obtained with the active converter.

Figure 12: Uncontrolled rectifier with increase in

Figure 15: Supply voltage harmonics of controlled
current harmonics.
rectifier
For implementing control strategy, as discussed Figure 16 shows that in case of controlled
and as shown in the figure 13 Iqref is set to zero converter supply current harmonics are reduced
as compared to the uncontrolled case.

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World Electric Vehicle Journal Vol. 7 - ISSN 2032-6653 - ©2015 WEVA Page WEVJ7-0528

technique harmonics are obtained within the

standards.

Figure 16: Supply current harmonics of controlled

rectifier
Figure 17 shows that even with battery impact Figure 19: Supply current harmonics of 30AH
the terminal voltage can be obtain constant with battery connected to grid
proper selection of dc bus capacitor and control
logic discussed earlier. Once the dc bus voltage 8 CONCLUSION
is stabilized distribution grid is ready to take the
electric vehicle load. The proposed model used for analysing
grid impacts can be used for dynamic conditions.
900
It has certain advantages as compared to basic
800
battery models. Simulation is done in three parts.
700
First the load is increased at the bus with
600
uncontrolled rectifier and voltage reduction at dc
voltage

500
bus and increase in current harmonics are
400
observed. Then this bus is stabilized by control
300
rectifier (Active converter) and constant dc bus
200
voltage at unity power factor at the source side is
100
achieved. On this stable grid Li-ion batteries are
0
0 0.05 0.1 0.15 0.2 0.25 0.3 0.35 0.4 0.45 0.5 charged and impact of vehicle on grid is analysed
time
and again the dc bus voltage is regulated,
Figure 17: Constant dc bus voltage with controlled harmonics are controlled with unity power factor
rectifier and battery at source side.With vector control logic, variation
in electrical parameters can be mitigated when
Figure 18 shows the supply voltage and current
batteries are charged from the grid even from
are in phase irrespective of the loading which
fully discharged condition. Concept shown here
gives excellent power factor.
will be very useful for fast dc charging of electric
vehicle batteries. Battery modelling shown with
the concept of extracting parameters from
manufacturers discharge characteristics gives fast
and effective solution and will be useful for not
only Li-Ion batteries but also for Ni-Mh and
Lead-acid batteries.

Figure 18 source voltage and current

Figure 19 shows that with proper selection of
filter, dc bus capacitor and vector control

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World Electric Vehicle Journal Vol. 7 - ISSN 2032-6653 - ©2015 WEVA Page WEVJ7-0529

vehicles in Indian power grid”,published at

waset,International journal of electrical,computer
and communication engineering vol 9,no2,2015.
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