Abstract — Due to global warming, the electric vehicle reappears as a clean transportation solution.
Unfortunately, this substitution/adoption by the consumers presents some problems, namely the high price, the low ability to travel long distances between charges (autonomy) and the charging time.
The goal of this paper is to propose a novel modular compact three phase charger, which uses three single phase systems and high frequency transformers. The charger allows a fast charging, but still decreasing the impact in the connection to the grid: minimizing the currents supplied by the electrical grid, reducing their harmonic content and guaranteeing three phase balanced currents.
To guarantee a realistic simulation of the charging system, the parameters of the battery model were sized, based on the characteristics of a Battery Electrical Vehicle (BEV). Also, all the necessary filters were sized and controllers were designed.
Index Terms — Fast charger, Single phase modular system, Lithium battery, Voltage control, Current control.
I. INTRODUCTION
ue to the large increase in carbon dioxide (CO2) caused by the growth of industry and transport, the Kyoto treaty arose in 1997. This treaty aimed to drastically reduce the level of CO2 and has encouraged the search for new cleaner energy solutions. Thereby, Electrical Vehicles (EV) reappeared as a solution in transportation, as clean vehicles powered by electricity, but its adoption has not increased much due to the following conditions [1]:
1. The acquisition cost, although there are incentives, electric vehicles are still considered expensive in comparison to the combustion vehicles;
2. The difficulty in traveling long distances because of the relatively small capacity of the batteries;
3. Reduced number of charging stations in and outside the cities;
4. Life span of the battery (about 8 years);
5. Charging time is much higher than the combustion engine vehicles.
Table 1 demonstrates the autonomy of some Plug-in Electrical Vehicles (PEV’s), where the Plug-in Hybrid Electric Vehicle (PHEV) and the BEV are included.
Table 1. Models, types and battery capacity of PEV’s by autonomy [2], [3]
Model EV
Type
Battery Capacity
[kW]
Catalogue Autonomy
Electric [km]
Fossil Fuel [km]
Total [km]
BMW i3 BEV 18.8 130 - 130
Volkswagen e-Golf BEV 24 134 - 134
Nissan Leaf BEV 24 135 - 135
Citroën C-Zero BEV 16 150 - 150
Renault Zoe BEV 22 170 - 170
Fiat 500e BEV 24 186 - 186
Kia soul EV BEV 27 193 - 193
Tesla Model S 85D BEV 85 434 - 434
Chevy Volt PHEV 16 61 483 544
Audi A3 E-Tron PHEV 8.8 48 757 805
Toyota Prius
Plugin Hybrid PHEV 4.4 18 852 870
Nowadays, PEVs use lithium batteries because they present:
a relatively low auto-discharge, nearly no memory, high durability and the possibility to reduce the charging time, until 80%, with high charging currents (fast charge).
The battery is the most important component of a BEV.
With the advent of lithium-air batteries, which can store more energy, thus being able to reduce the battery size and consequently their weight, the acquisition of BEVs will become more attractive [4], [5].
Table 2. Charging voltages, type, power and time [6]
Voltage Charge Type
Location of the Charge
Power [kW]
Charging Time [hour]
EV Type
230V On-board Home or office
1.4 4-11 PHEVs
AC 1 phase 1.9 11-36 BEVs
400V AC
On-board 1/3 phases
Private or public
4 1-6 PHEVs
8 2-6 BEVs
19.2 2-3 BEVs
208-600V Off-board Analogous to a filing
station
50 0.4-1
BEVs
AC or DC 3 phases 100 0.2-0.5
There are two ways to charge a PEV: on-board and off- board [table 2 [6]]. Also, depending on the charging time, can be defined three types of chargers:
1) Type 1, slow chargers, normally used at home, taking around 8 hours to fully charge the battery (20% to 100% of the
State of Charge (SOC));
2) Type 2, normal chargers, typically located in parking lots, with a charging duration of about 4 hours (20% to 100%
Modular Fast Battery Charger for Electric Vehicles
Ricardo Guerreiro Gago
Instituto Superior Técnico, University of Lisbon, Portugal Email: Ricardo.gago@tecnico.ulisboa.pt
D
of the SOC);
3) Type 3, fast chargers, typically located in service stations, which require higher power and usually take less than 30 minutes to fully charge the battery (20% to 80% of the SOC).
II. FAST CHARGER
The proposed fast charger system (figure 1) will consist in three single phase modules in order to reduce the current demand in each phase, allowing bidirectional power flow. The transformers are used to ensure galvanic isolation, with unitary turn ratio. However, they are not conventional low frequency transformers (50Hz) but high frequency transformers (10 kHz), allowing the volume and weight reduction of the whole charger [7]. The proposed system should be able to guarantee the charge (Grid to Vehicle - G2V) and the discharge of the battery (Vehicle to Grid - V2G), must ensure fast charge, respect the battery limits, reduce harmonic contents in the battery charging/discharging current and minimize Power Quality disturbances in the connection to the grid. Also, the proposed system must guarantee the compliance with international standards: standard IEC 61851-23: 2014 [8] in G2V operation mode and standard IEEE 1547 [9] in V2G operation mode.
A. Converters topology
The topology used is a single-phase converter, as shown in figure 2, containing Insulated Gate Bipolar Transistors (IGBT) with antiparallel diodes, to guarantee bidirectional power flow.
Thus, it may operate as a rectifier, performing AC to DC conversion, or it may operate as an inverter, performing DC to AC conversion.
Using a three level PWM and respecting the topological constraints, 𝑉𝑃𝑊𝑀 is obtained from (1):
𝑉𝑃𝑊𝑀= {
𝑈𝐷𝐶1→ 𝑆11 𝑎𝑛𝑑 𝑆22 𝑂𝑁 0 → 𝑆11 𝑎𝑛𝑑 𝑆21 𝑜𝑟 𝑆12 𝑎𝑛𝑑 𝑆22
−𝑈𝐷𝐶1→ 𝑆12 𝑎𝑛𝑑 𝑆21 𝑂𝑁 𝑂𝑁 (1)
Fig. 2. Single phase full bridge converter
B. Modulation of the Converters that Interconnect to the Grid In order to guaranty a nearly unitary power factor in the connection to the grid, a three level Pulse Width Modulation (PWM) strategy (figure 3) is used in the converter that connects to the grid.
Fig. 3. Three level PWM
Considering the modulator amplitude, 𝐴𝑚, and the carrier amplitude, 𝐴𝑝, the Root Mean Square (RMS) value of the 1st harmonic of voltage 𝑉𝑃𝑊𝑀 will be given by [10]:
Lx L2
Lx L2
Lx L2
Lr
Lr
Lr
Converter 1 AC/DC
Converter 2 DC/AC
Converter 3 AC/DC High Frequency
Transformer Electric
Grid
Battery UDC2
UDC2
UDC2
C2
C2
C2
C1
C1
C1
VPWM
VPWM
VPWM
UDC1
UDC1
UDC1 a
b
c
a
b
c
a
b
c
VPa
b
c
VXN
VXN
VXN a
b
c
VP
VP
VS
VS
VS a
b
c
VBAT
SBAT
Fig. 1. Full schematic of the proposed modular fast charger
𝑉𝑃𝑊𝑀𝑅𝑀𝑆= 𝑈𝐷𝐶1√∑𝛼𝑘+1− 𝛼𝑘
𝜋
𝑃−1
𝑘=1
(2)
𝑉𝑃𝑊𝑀1𝑅𝑀𝑆=2√2𝑈𝐷𝐶1
𝜋 ∑(−1)𝑘
𝑃
𝑘=1
sen 𝛼𝑘≈𝐴𝑚 𝐴𝑝
𝑈𝐷𝐶1
√2 (3)
C. Modulation of the converters connected to the HFT For the converters connected to the HFTs, high frequency single pulse modulation was chosen to ensure nearly zero average value in the voltages applied to the transformers in each switching period, avoiding their saturation.
Fig. 4. Command PWM with phase shift
As shown in figure 4, the approach used in the modulation of single phase inverter is to use one carrier in each arm of the converter, guaranteeing a phase shift 𝛼 between each carrier.
This phase shift defines the pulse width in AC voltages. So, the RMS values of these AC voltages of the converters that interconnect to the high frequency transformers (converter 2) is given by [10]:
𝑉𝑝𝑅𝑀𝑆= 𝑈𝐷𝐶1√𝛼
𝜋 (4)
𝑉𝑝1𝑅𝑀𝑆=2√2𝑈𝐷𝐶1
𝜋 sen (𝛼
2) (5)
Considering that, for the converters connect to the HFTs, the pulse width is 𝛼, then, the RMS value of the voltages in AC side and the RMS value of their 1st harmonics will be:
𝑉𝑥𝑛𝑅𝑀𝑆= 𝑈𝐷𝐶2√𝛼
𝜋 (6)
𝑉𝑥𝑛1𝑅𝑀𝑆=2√2𝑈𝐷𝐶2
𝜋 sen (𝛼
2) (7)
D. Model of the Battery
From a BEV catalogue [11] and a lithium cell datasheet, some calculations were done to obtain the values of an equivalent EV battery, including the number of necessary cells and the values used in the simulation model.
Table 3. Sized battery
Sized battery
Maximum capacity 73.5 Ah Nominal capacity 70 Ah Total number cells 444
Nominal voltage 355.2 V Maximum charge voltage 405.15 V Discharge cut-off voltage 222 V
Internal resistance 87.21 mΩ Nominal discharge current 14 A E. Filters sizing
To guarantee the correct operation of the system, minimizing harmonic components resulting from the semiconductors switching, it is necessary to use some filters:
a) in the connection of inverters to the grid; b) in the interconnection between DC converters; and c) in connection to the battery.
a) To ensure that the voltage and the current in the grid are in phase, it is required that VPWM voltage has the right amplitude and phase. To guarantee this, the vector diagram shown in figure 5 was obtained, where 𝑉𝐿𝑟 represents the voltage in one of the main coils, 𝐼𝑟 the current in the grid, 𝑉𝑟 the voltage in the grid and 𝑉𝑃𝑊𝑀 the voltage at the converter input.
Fig. 5. Vector diagram of the grid side voltages and current, in order to obtain nearly unitary power factor
Based on the vector diagram of figure 5, it is possible to establish:
𝑉𝑃𝑊𝑀> √2 𝑉𝑟𝑅𝑀𝑆 (8) As the voltage 𝑉𝑃𝑊𝑀 is switched at high frequency, the connection between the grid and the converter should be done using a filtering inductance, 𝐿𝑟. This inductance also allows the minimization of the current ripple, ∆𝑖𝑟 which is related to the current and to the 𝑇𝐻𝐷𝑖[12]:
∆𝑖𝑟= 2√3𝐼𝑟1𝑅𝑀𝑆𝑇𝐻𝐷𝑖 (9) Knowing the values of the DC voltage, 𝑈𝐷𝐶1, switching frequency, 𝑓𝑐, and 𝑇𝐻𝐷𝑖, which is assumed to be 1%, it is possible to calculate the filtering inductance 𝐿𝑟 [13]:
𝐿𝑟= 𝑈𝐷𝐶1
4∆𝑖𝑟𝑓𝑐 (10)
In order to assure the correct operation of the converters that connect to the grid or the ones that interconnect to the high frequency transformers, it is necessary to introduce a filtering capacitor, 𝐶1, which objective is to obtain a nearly
constant voltage, 𝑈𝐷𝐶1.
From the energy stored in the capacitor it is possible to calculate the capacitor value, where 𝑃0 represents the power flow, ∆𝑡 the stabilization time and 𝑈𝐷𝐶1𝑚𝑎𝑥 and 𝑈𝐷𝐶1𝑚𝑖𝑛 the maximum and minimum voltage allowed, respectively:
𝐶1= 2𝑃0∆𝑡
𝑈𝐷𝐶1𝑚𝑎𝑥2− 𝑈𝐷𝐶1𝑚𝑖𝑛2 (11)
b) The power flow, 𝑃𝐿𝑥
,
to/from the battery, can be calculated from (12):𝑃𝐿𝑋=𝑉𝑠1𝑅𝑀𝑆𝑉𝑥𝑛1𝑅𝑀𝑆
2𝜋𝑓𝑐𝐿𝑥 sen 𝛿 (12) Neglecting the converter losses and considering the DC power in the battery, the filtering inductance 𝐿𝑥 can be calculated from:
𝐿𝑥=𝑉𝑠1𝑅𝑀𝑆 𝑉𝑥𝑛1𝑅𝑀𝑆
2𝜋 𝑓𝑐 𝑈𝐷𝐶2 𝐼2𝐷𝐶 sin 𝛿 (13) c) The battery must be charged with constant voltage and current, so the filters that connect the converter to the battery are mainly intended to ensure this condition.
The capacitors guarantee nearly constant voltage, but they also filter the current AC component in the DC link, leaving only the current DC component to charge and discharge the battery. Capacitors 𝐶2 can be calculated from (11).
The inductors L2 will adjust the voltage levels in the DC link capacitors and in the battery. They are sized to minimize the current ripple, preventing them to exceed a pre-set value [14]:
𝐿2= 𝐼2𝐷𝐶
32𝑓𝑐2∆𝐼𝐿2𝐶2 (14)
III. CONVERTERS CONTROL
In order to ensure a null static error and an acceptable rise time, Proportional-Integral (PI) compensators were used, except for the battery current controller, where an integral compensator was used.
A. Current control of the converter that interconnect to the grid
The grid current control is represented in figure 6, where 𝑖𝑟𝑟𝑒𝑓_𝑠𝑖𝑛𝑐 is the reference current and 𝑖𝑟the current on the grid.
Both are multiplied by 𝛼𝑖𝑟 (current sensor gain) and the difference between them gives the error that is applied to the compensator 𝐶𝑖𝑟(𝑠).
Fig. 6. Block diagram of the current regulator in the converter that interconnect to the grid
Considering that the zero of the PI compensator cancels the pole introduced by the grid filter, the PI zero 𝑇𝑧𝑟 may be
calculated according to (15), where 𝐿𝑟 represents the value of the filtering inductance and 𝑅𝑇 the results from the association of the resistance of the inductance with the equivalent resistance in the connection point to the grid.
𝑇𝑧𝑟=𝐿𝑟
𝑅𝑇 (15)
To size the current controller, the association of the modulator and the converter is represented as a first order model with a gain, 𝐾𝑑𝑟, and an average delay, 𝑇𝑑𝑖𝑟, usually assumed as one half of the switching period [12].
𝐺(𝑠) = 𝐾𝑑𝑟
1 + 𝑠𝑇𝑑𝑖𝑟 (16)
The gain can be calculated from (17), where 𝑢𝑐𝑚𝑎𝑥
represents the maximum amplitude of the modulator.
𝐾𝑑𝑟= 𝑈𝐷𝐶1
𝑢𝑐𝑚𝑎𝑥 (17)
From figure 6 and considering null disturbances, the transfer function of the closed loop current controller is obtained.
𝑖𝑟(𝑠) 𝑖𝑟𝑟𝑒𝑓_𝑠𝑖𝑛𝑐(𝑠)=
𝛼𝑖𝑟 𝐾𝑑𝑟
𝑇𝑑𝑖𝑟𝑇𝑝𝑟𝑅𝑇 𝑠2+ 𝑠 1
𝑇𝑑𝑖𝑟+ 𝛼𝑖𝑟 𝐾𝑑𝑟 𝑇𝑑𝑖𝑟𝑇𝑝𝑟𝑅𝑇
(18)
Comparing the denominator of the transfer function (18) with the denominator of the transfer function of a 2nd order system written in canonical form (19), it is possible to obtain 𝑇𝑝𝑟 (20).
𝐺2(𝑠) = 1 (𝑠
𝜔𝑛)2+2𝜉 𝜔𝑛𝑠 + 1
= 𝜔𝑛2
𝑠2+ 2𝜉𝜔𝑛𝑠 + 𝜔𝑛2 (19)
𝑇𝑝𝑟=4𝜉2𝑇𝑑𝑖𝑟𝐾𝑑𝑟∝𝑖𝑟
𝑅𝑇 (20)
The gains of proportional and integral compensator are:
{
𝐾𝑝𝑖𝑟=𝑇𝑧𝑟
𝑇𝑝𝑟= 𝐿𝑟 4𝜉2𝑇𝑑𝑖𝑟𝐾𝑑𝑟∝𝑖𝑟
𝐾𝑖𝑖𝑟= 1
𝑇𝑝𝑟= 𝑅𝑇
4𝜉2𝑇𝑑𝑖𝑟𝐾𝑑𝑟∝𝑖𝑟
(21)
B. Voltage control of the converter that interconnects to the grid
To ensure proper operation of the system it is also necessary to control the capacitor voltage.
The block diagram of the voltage regulator with internal control of the current is represented in figure 7, where 𝛼𝑣𝑟
represents the voltage sensor gain:
Fig. 7. Block diagram of the voltage regulator in the converter that interconnects to the grid
The current controlled converter can be represented by the following transfer function:
𝑖𝑟(𝑠) 𝑖𝑟𝑟𝑒𝑓_𝑠𝑖𝑛𝑐(𝑠)≅
𝐺𝑖
𝛼𝑖𝑟
⁄
1 + 𝑠𝑇𝑑𝑣𝑟 (22)
The gain of the current controller 𝐺𝑖 is obtained from the relation between the AC active power and the DC power, where 𝑉𝑟𝑚𝑎𝑥 is the grid voltage amplitude.
𝐺𝑖= 𝑉𝑟𝑚𝑎𝑥
2𝑈𝐷𝐶1 (23)
From figure 7, the closed loop transfer function is obtained:
𝑈𝐷𝐶1(𝑠) 𝑈𝐷𝐶1𝑟𝑒𝑓(𝑠)=
𝛼𝑣𝑟𝐺𝑖
𝛼𝑖𝑟 𝐾𝑝𝑣𝑟+ 𝑠𝐾𝑖𝑣𝑟
𝑇𝑑𝑣𝑟𝐶1 𝑠3+ 𝑠2 1
𝑇𝑑𝑣𝑟+ 𝑠𝛼𝑣𝑟𝐺𝑖𝐾𝑝𝑣𝑟
𝛼𝑖𝑇𝑑𝑣𝑟𝐶1 +𝛼𝑣𝑟𝐺𝑖𝐾𝑖𝑣𝑟
𝛼𝑖𝑟𝑇𝑑𝑣𝑟𝐶1
(24)
Comparing the denominator of (24) with the third order polynomial (25) and solving the resultant equations, the compensator gains (26) can be obtained:
𝑃3(𝑠) = 𝑠3+ 1,75𝜔𝑜𝑠2+ 2,15𝜔𝑜2𝑠 + 𝜔𝑜3 (25)
{
𝐾𝑝𝑣𝑟= 2,15𝐶1𝛼𝑖𝑟
𝛼𝑣𝑟𝐺𝑖𝑇𝑑𝑣𝑟1,752 𝐾𝑖𝑣𝑟= 𝐶1𝛼𝑖𝑟
𝛼𝑣𝑟𝐺𝑖𝑇𝑑𝑣𝑟21,753
(26)
C. Current control of the converter that interconnects to the battery
The block diagram of the battery charging current is represented in figure 8, where 𝛼𝑖 is the current sensor gain:
Fig. 8. Block diagram of the current regulator in converter that interconnects to the battery
From (12), the displacement angle 𝛿 between the fundamental component of voltage 𝑉𝑆1𝑒𝑓 and voltage 𝑉𝑥𝑛1𝑒𝑓 allows the power flow regulation to/from the battery. Then, the gain that will be used in the equivalent model can be determined by [15]:
𝐾𝐷=𝑉𝑠1𝑅𝑀𝑆𝑉𝑥𝑛1𝑅𝑀𝑆
2𝜋𝑓𝑐𝐿𝑥𝑈𝐷𝐶2 (27)
Considering figure 8, the closed loop transfer function is obtained by:
𝑖2(𝑠)
𝑖2𝑟𝑒𝑓(𝑠)= 𝛼𝑖𝐾𝑖𝑖𝐾𝐷 𝑇𝑑𝑖
𝑠2+ 𝑠 1
𝑇𝑑𝑖+ 𝛼𝑖𝐾𝑖𝑖𝐾𝐷 𝑇𝑑𝑖
(28)
Comparing the denominator of (28) with the denominator of (19), the integral gain of the compensator is calculated.
𝐾𝑖𝑖= 1
4𝜉2𝑇𝑑𝑖𝐾𝐷𝛼𝑖 (29)
D. Voltage control of the converter that interconnects to the battery
To guarantee that the maximum voltage limit allowed by the battery is not exceeded, it is necessary to control the voltage in the capacitor.
The block diagram of the voltage regulator with internal current regulator is represented in figure 9, where 𝛼𝑣 is the voltage sensor gain.
Fig. 9. Block diagram of the voltage regulator in the converter that interconnects to the battery
To size the voltage controller, the current controlled system can be represented by the following transfer function:
𝑖2
𝑖2𝑟𝑒𝑓≅ 1 𝛼⁄ 𝑖
1 + 𝑠𝑇𝑑𝑣 (30)
The transfer function of the system in the closed loop is then:
𝑈𝐷𝐶2(𝑠) 𝑈𝐷𝐶2𝑟𝑒𝑓(𝑠)=
𝛼𝑣
𝛼𝑖
𝐾𝑝𝑣+ 𝑠𝐾𝑖𝑣 𝑇𝑑𝑣𝐶2
𝑠3+ 𝑠2 1
𝑇𝑑𝑣+ 𝑠 𝛼𝑣𝐾𝑝𝑣
𝛼𝑖𝑇𝑑𝑣𝐶2+ 𝛼𝑣𝐾𝑖𝑣
𝛼𝑖𝑇𝑑𝑣𝐶2
(31)
Once again, it is necessary to compare the denominator of (31) with the third order polynomial (25). Solving the resultant equations, it is possible to obtain the gains of the PI compensator.
{
𝐾𝑝𝑣= 2,15𝐶2𝛼𝑖
𝛼𝑣𝑇𝑑𝑣1,752 𝐾𝑖𝑣= 𝐶2𝛼𝑖
𝛼 𝑣𝑇𝑑𝑣21,753
(32)
E. Main battery switch
To guarantee the correct operation of the overall system, additional conditions were considered:
a) In G2V mode, if the SOC of the battery is less than or equal to a predetermined value, the battery charges; if the SOC is higher than that value and the current battery charging is less than 0.1A, the overall controller system gives order to turn off the semiconductors of the converters that interconnect to the battery and also the main battery switch 𝑆𝑏𝑎𝑡.
b) In V2G mode, if the SOC of the battery is higher than a predetermined value, the battery discharges; if the SOC is less than or equal or to that value, the overall controller system gives order to turn off the semiconductors on converters that interconnect to the battery and also the main battery switch 𝑆𝑏𝑎𝑡.
IV. OBTAINED RESULTS
The fast charger here proposed was implemented in MATLAB/Simulink software in order to evaluate and test its performance. To allow full charging and discharging cycles in
the simulation, the battery characteristics were changed so that 1 second in the simulation corresponds to 1 hour in real time.
A. Scenario 1 – G2V
In this scenario, the system operates as a fast charger with a maximum current of 125A. In figure 10, the blue waveform represents the voltage grid, 𝑉𝑟, and the green waveform represents the current supplied by the grid, 𝐼𝑟. It is perceived that they are nearly in phase, ensuring unitary power factor.
Fig. 10. Grid current and voltage in G2V operation The system does not introduce significant harmonic distortion in the grid currents, as the Total Harmonic Distortion of the current is lower than 1%.
From figure 11 a), the voltage at the battery terminals meet the desired requirements. As for the current in the battery, 𝐼𝑏𝑎𝑡, shown in figure 11 b), initially it is 125A but, as the SOC increases (figure 11 c)), the current decreases and the voltage remains constant. Also, it can be observed that the proposed system is operated fulfilling the main goals: fast charging (around 30 minutes) when the battery SOC changes from 20% to 80%.
B. Scenario 2 – V2G
In this scenario, it is assumed that the battery is fully charged when it starts supplying energy to the grid (figure 12 a)) and the current supplied by the battery is 70A (figure 12 b)).
At t ≈ 0,84s the current in the battery becomes zero. This occurs because the system supervisor has established 20% as the minimum SOC value to prevent the battery from discharging completely. From the obtained results, the battery is able to supply the requested current for approximately 50 minutes. Regarding the battery voltage, it decreases while it is discharging with constant current, as would be expected.
When it stops discharging, its value increases, as shown in figure 12 c).
a)
b)
c) Fig. 11. a) Battery voltage b) Battery current c) Battery SOC
a)
b)
c) Fig. 12. a) Battery SOC b) Battery current c) Battery voltage In figure 13, where the voltage waveform is represented in blue and the current waveform is represented in green, it can be seen that they are out of phase, showing that the power factor is nearly unitary.
Fig. 13. Grid current and voltage in V2G operation The harmonic spectrum of the current injected in the grid is THD = 4.14%, which allows to confirm that it is within the
limits imposed by international standards [9], TDD < 5%.
V. CONCLUSIONS
In this paper is proposed a fast charger for electric vehicles, which allows bidirectional power flow (G2V and V2G) and guarantees galvanic isolation using high-frequency transformers. This permits the reduction of the overall system volume, when compared to other solutions based on low- frequency transformers (50 or 60 Hz).
With the purpose to achieve a simulation very close to the reality, it was obtained a battery model with properties very similar to those of a BEV.
The objectives were met, i.e. the battery is charged within the given time for a fast charger (30 minutes from 20% to 80%
of the SOC) and unitary power factor at the connection to the grid is guaranteed (consumption / injection with reactive power approximately equal to zero).
When operating as V2G, the system maintains constant current value supplied by the battery, also ensuring almost unitary power factor. The total harmonic distortion of the current rate is less than 5%, which is within the allowed value for these systems.
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