V2G Operation

Modeling and Control of Contactless based Smart Charging Station in V2G Scenario

3.3 Modeling of Smart Charging Station

3.3.3 Multi-Point BCCS Unit

3.3.3.2 V2G Operation

AND

0 NOT High frequency

S₇ S₈

I_pc

. Figure 3.14: Energy injection control.

The block diagram of energy injection control is given in Fig. 3.14. The primary side current is compared with the zero, then the gate pulse is generated for switches S₇ and S₈ which converts dc current to high-frequency ac current.

ModelingandControlofContactlessbasedSmartChargingStationinV2GSce

EV Battery

Pack Grid

L

S₂ S1 S3

S₄

S₅

S₆

S8

S₇ S₉

S10

S₁₁

S12

S₁₃

D₂ D1 D3

D4

D5

D6

D₈ D₇

D₉

D₁₀ D₁₁

D12

D13

S14

D₁₄ C1 C₂

Cdc Cb1 Lb C_b2

PrimaryCoil

CB

Vdcmeaa

3Φ ac to dc converter dc to high frequency ac converter

1Φ ac to dc

converter dc to dc converter Ipc

SecondaryCoil

Transformer L

C

Contactless coil Lr

Load angle control 1ΦSPWM DC Voltage

control

Primary Side Secondary Side

Control signal

L_r I_sc

Vconv

Vnode

Ic/d

/

i i

C c d

V Power flow

Figure 3.15: Circuit topology for V2G operating mode.

80

LPF

LPF

25 kHz p.u

DLV−FLC

Delay Signal

Carrier LPF − Low pass filter

S₁₄ V_dc^{re f}

∆E^′_r E^′_r

R^′′

V_dc^mea

Figure 3.16: DC link voltage control.

−1 −0.5 0 0.5 1

NB NS Z PS PB

0 1

0.25 0.5 0.75

0

VS S M B VB

1 0

1

(b)

(a) E^′_rand∆E^′_r R^′′

Figure 3.17: Fuzzy membership function for DLV-FLC (a) inputs: E^′′_r and∆E_r^′′(b) output: D^′′. Table 3.6: Rule base for DLV-FLC.

E^′′_r ∆E_r^′′ D^′′ E^′′_r ∆E^′′_r D^′′

PB NB M Z PS B

PB NS B Z PB B

PB Z B NS NB VS

PB PS VB NS NS S

PB BP VB NS Z S

PS NB S NS PS M

PS NS M NS PB B

PS Z B NB NB VS

PS PS B NB NS VS

PS PB VB NB Z S

Z NB S NB PS S

Z NS S NB PB M

Z Z M - - -

the BB converter ton has been increased. This information will be updated every instant of time and the DLV-FLC maintain the V_dc^meais equal to the V_dc^{re f} by increasing the D^′′.

3.3.4 C_rateand SOC Calculation

As it is not desired to deplete or overcharge the battery, the C_rateand SOC (in this Chapter SOC de- notes both S OCcrand DODcrfor simplicity) of the batteries are monitored. The capacity fading of the EVs’ batteries is not considered in this work. An algorithm is used to control the charging/discharging of EVs’ batteries by changing the C_rateof EVs’ batteries. The C_rate of BCCS unit is calculated from Eq. (3.9).

C^BCCS_rate = Pmax

V_c^C

i/d_iQ (3.9)

where, P_max is the maximum peak power handling capability of charging point. The algorithm has also taken into account of user defined C_rate(C_rate^user) and the current C_rate(C_rate^crt ) of the battery. The C^crt_ratecalculated from the equation given below.

C^crt_rate= Pbn

V_c^C

i/d_iQ (3.10)

V Filter Calculation for battery power calculation

Energy

Switch

Polynomial coefficients

Controlled Voltage Source Calculation for

Calculation for

for charging Battery model

for discharging Battery model Q

Sign Q

Polynomial coefficients C^user_rate

C_rate^BCCS C^crt_rate

I^∗>0

I^∗<0

for discharging (a1−a31) I_c, t_c, C_r, S OC

I_d, t_d, D_r, DOD Pmax

V_c^C

i/di

V_c^C_i/di Pⁿ_{re f}

Ebn Pc/d

tc/d

Ic/d

I^∗

R I_c/d Pbn

V^C_c

i/di

User defined DOD limits

User defined SOC limits for charging (a1−a31)

V^C_c

i/di

Crate

min(C_rate^BCCS,C^user_rate,C^crt_rate)

Figure 3.18: Crateand SOC calculation.

The control algorithm chooses the minimum of the C_rate (C_rate^BCCS,C^crt_rate and C_rate^user) to regulate the current flows of individual EV battery. The minimum of the C_rate (C^min_rate) will be the processed C_rate of the charging point. Besides, the SOC limits of vehicle owners are also considered in this work.

When the SOC is near to full (empty), a high power charging or discharging should not be allowed for preventing over charge (over discharge). Therefore, S OCminand S OCmax of the EVs’ batteries are taken into account. Based on these limits, the control algorithm is implemented using Eq. (2.13) and Eq. (2.14). Fig. 3.18 shows the block diagram of C_rate and SOC evaluation used in EV batteries of SCS.

The main features of the charge rate control is given below:

• Control the minimum C_rateto regulate the battery current based on the user define C_rate, BCCS unit C_rateand current C_rateof the battery.

Bidirectional Contactless Chraging System (BCCS) CB=1

CB=0

If

SPWM generate gate pulse for

dc to high frequency ac converter dc to high frequency ac converter EIC generate gate pulse for

FLC based SC Syn−G2V

No Yes

No

Yes

Unsyn−G2V Syn−V2G

Power flow If

voltage, phase and freq−

uency are equal

FLC based dc link voltage control

FLC based SC

FLC based charging current control

DN

CS aggregator calculate

Pbn≥0

control the load angle (δ) DN and BCCS

based on ET, Vnodeand D V_node, V_prim, I_prim, V_dc^mea, I_c/I_d, P_max

V_c^C

idi, E_bnand E_T

CCU calculate Pgrid

Pgrid, ET, Ebn

control the load angle (δ)

Pbn

P_bn Distribute the Pbn

Figure 3.19: Flow chart for energy transfer in V2G and G2V operations based on DNC command.

• Estimate the I_c, t_c, S OC and V_c^C

i for charging scenario and I_d, t_dand V_d^C

i for discharging scenario.

• Calculate the battery power and availability/required energy of the individual EVs.

• The battery model work based on the reference current I^⋆. If I^⋆ > 0 for charging scenario and I^⋆ <0 for discharging scenario.

For example, let as consider that P_max is 50kW, Q_r is 32Ah, V_c^C_i is 258V, P_b1 is 9.81kW and the C^user_rate is 2.5. The C_rate of the BCCS is 6.056. The C^crt_rateof the battery is 1.188. The control algorithm chooses the minimum of the Crateto regulate the battery charging current flow to the EV battery. The

minimum C_rate is 1.188. For the ease of analysis, the flow chart for V2G, G2V with synchronization operation is given in Fig. 3.19. The detail explanation is already discussed in the previous section.