2.5 Result analysis
Figure 2.12 shows the comparison of node voltage before and after performing G2V operation during off-peak hour period using P, Q and P Q power support from the grid. In this case, all the EVs in the CS are considered to have low value of SOCs and have arrived to charge their batteries for G2V operation. The node voltage is initially high above 1.043p.u before G2V operation. It has been observed from Figure 2.12; the node voltage is high around 1.1p.u before supporting the CS. When the CS has drawn the power from the grid, the voltage rise in the DN has been reduced and regulated to the nominal voltage level of the distribution network.
04 : 00 04 : 30 05 : 00 05 : 30 06 : 00 06 : 30 07 : 00
0.85 0.9 0.95 1 1.05 1.1
Time (hrs)
Node voltage (p.u)
P injection
Q injection PQ injection
during off−peak hours (before G2V operation)
Figure 2.12: Comparison of node voltage using P, Q and PQ control (G2V).
It has also been observed P and Q support has almost similar performance with small difference in voltage drop. The combined P Q power support is found to have better voltage regulation than individualP and Qpower transfer.
Figure 2.13 shows the comparison of node voltage before and after performing V2G operation usingP,Q and combined P Qsupport during peak hour. In this case, all the EVs arrived at the CS is considered to have high value of SOCs. In Figure 2.13 during peak-hours, initially their is a drop in the node voltage of around 0.86p.u. After injecting power from EVs, the node voltage got raised to 0.99p.u. It has been observed amongP,Qand P Qsupport, the voltage regulation achieved using combinedP Qsupport is better than individualP andQsupport. The voltage is regulated within the specified nominal voltage of the distribution network.
Figure 2.14 shows the comparison of node voltage before and after performing both G2V and V2G operation during normal hour period. In this case, the EVs arrived at the CS is considered to have high and low value of SOCs. In Figure 2.14 during normal hours, the node voltage is around 1.0045p.u TH-1345_TPERJOY
17 : 00 17 : 30 18 : 00 18 : 30 19 : 00 19 : 30 20 : 00 0.85
0.9 0.95 1 1.05 1.1
Time (hrs)
Node voltage (p.u)
Q support PQ support P support
during peak hours (before V2G operation)
Figure 2.13: Comparison of node voltage using P, Q and PQ control (V2G).
during peak hour. After performing charge/discharge operation with the CS, the node voltage has reduced to 0.96p.u. While comparing to individual P and Q control the voltage regulation provided by combined P Qseems to be better.
11 : 00 11 : 30 12 : 00 12 : 30 13 : 00 13 : 30 14 : 00
0.85 0.9 0.95 1 1.05 1.1
Time (hrs)
Node voltage (p.u)
PQ injection P injection
Q injection during normal hours
Figure 2.14: Comparison of node voltage using P, Q and PQ control (both G2V and V2G).
Figure 2.15 shows the dc link voltage acrossCdc1 at the terminals of the three-phase converter. The dc link capacitor helps to maintain the voltage level during its power transfer in both the direction.
The dc link voltage is rectified from three-phase ac input and is about 1.35 times the ac input voltage for G2V operation. During V2G operation, the voltage across the coupling capacitor is regulated and maintained by the dc-dc converter. The transients in the dc link voltage is smoothed with this large
2.5 Result analysis
11 : 00 11 : 30 12 : 00 12 : 30 13 : 00 13 : 30 14 : 00
−800
−600
−400
−200 0 200 400 600 800
Time (hrs)
DC−link voltage (V)
EV1
AA
Figure 2.15: DC link voltage (across Cdc1).
capacitor.
11 : 00 11 : 30 12 : 00 12 : 30 13 : 00 13 : 30 14 : 00
0.8 0.85 0.9 0.95 1
Time (hrs)
Power factor
CP1
CP29
CP22
CP8
CP15
Figure 2.16: Power factor of the charging system.
Figure 2.16 shows the power factor of the charging system at five different charging points (CP) of the CS. It has been noticed the power factor of the charging system is maintained near to unity. This shows the most efficient loading of the charging systems at the distribution network. High power factor achieved in the system is the result of minimum phase difference between the voltage and the current.
The controllers used in the charging systems has controlled the voltage and current to maintain the power factor of the system close to unity.
The state of charge (SOC) characteristics of the EV batteries are shown in Figure 2.17. For EV1, TH-1345_TPERJOY
11 : 0020 11 : 30 12 : 00 12 : 30 13 : 00 13 : 30 14 : 00 30
40 50 60
Time (hrs)
State−of−charge (%)
EV1
EV8
EV22
EV15
EV29
Figure 2.17: State of charge of EVs batteries.
EV15andEV29, the SOC of the battery has increasing characteristics during G2V operation. ForEV8 and EV22, the SOC of the battery has decreased while supporting the grid.
In Figure 2.18, the total battery power drawn and the total power injected by 5 EVs at the charging points (CP) of the CS is shown to demonstrate the response of the regulation signal. As explained above, positive power indicates that the EVs in the CS have low SOC value and have come for charge operation. While other two group EVs have drawn power from the grid.
13:00 13:30 14:00 14:30 15:00 15:30 16:00
−15
−10
−5 0 5 10 15 20
Time (hrs)
Battery power (kVA)
EV1 EV
15
EV29
EV8 EV
22
Figure 2.18: Battery power.
Figure 2.19 shows the estimated frequency, sine component, amplitude (v′),ωt, cosine component, power angle (δ′) using enhanced PLL control. Fast and accurate extraction of the frequency (f) is
2.5 Result analysis
Table 2.3: Summary of injected and drawn power from/to the CS during several hours in a day.
Time Mode of S′ S Et Pbat Active Reactive pf
(hrs) operation (kV A) (kV A) (kWh) (kW) power (kW) power (kVar)
S1= 4.901 Pb1= 4.881 P1= 4.692 Q1= 1.385 pf1= 0.9589
at G2V S2= 6.576 101.781 Pb2= 6.533 P2= 6.384 Q2= 1.434 pf2= 0.9756
0530 off- 240.702 S3= 5.119 (required) Pb3= 5.013 P3= 4.979 Q3= 1.095 pf3= 0.9758
hrs peak S4= 11.395 Pb4= 11.201 p4= 10.971 Q4= 2.771 pf4= 0.9689
hours S5= 6.395 Pb5= 6.305 P5= 6.311 Q5= 0.911 pf5= 0.9895
240.702 7
P5 i=1
Si×7 101.781×7
P5 i=1
Pbi
P5 i=1
Pi×7
P5 i=1
Qi Avg. pf
= 34.386 = 240.702 = 712.467 = 237.531 = 233.359 = 53.172 = 0.974
S1= -4.476 Pb1= -4.402 P1= -4.229 Q1= -1.248 pf1= 0.9789
at V2G S2= -8.778 106.052 Pb2= -8.750 P2= -8.546 Q2= -1.921 pf2= 0.9761
1730 peak -250.593 S3= -6.812 (available) Pb3= -6.613 P3= -6.556 Q3= -1.445 pf3= 0.9651
hrs hours S4= -8.611 Pb4= -8.587 p4= -8.331 Q4= -2.125 pf4= 0.9874
S5= -7.122 Pb5= -7.102 P5= -7.019 Q5= -1.012 pf5= 0.9784
−250.593 7
P5 i=1
Si×7 106.052×7
P5 i=1
Pbi
P5 i=1
Pi×7
P5 i=1
Qi Avg. pf
=−35.799 =−250.593 = 742.364 =−248.178 =−242.767 =−54.257 = 0.977 S1= 5.287 70.461 Pb1= 5.176 P1= 5.006 Q1= 1.639 pf1= 0.9504
at both 162.141 S2= -8.812 (required) Pb1= -8.894 P2= -8.379 Q2= -2.481 pf2= 0.9589 0300 normal -141.498 S3= 7.982 59.851 Pb1= 7.857 P3= 7.621 Q3= 2.089 pf3= 0.9644 hrs hours S4= -11.402 (available) Pb1= -11.589 P4= -10.923 Q4= -2.783 pf4= 0.9690
S5= 9.894 Pb1= 9.567 p5= 9.351 Q5= 2.652 pf5= 0.9621
162.141 7
P i=1,3,5
Si×7 70.461×7 P i=1,3,5
Pbati×7 P i=1,3,5
Pcpi×7 P i=1,3,5
Qcpi×7 Avg. pf
= 23.163 = 162.141 = 493.227 = 158.2 = 153.846 = 44.660 = 0.962
x
−141.498 P i=2,4
Si×7 59.851×7 P i=2,4
Pbati×7 P i=2,4
Pcpi×7 P i=2,4
Qcpi×7 Avg. pf
=−20.214 =−141.498 = 418.95 =−143.381 =−135.114 =−36.848 = 0.962
obtained by three-phase PLL. The result of angular frequency (ωt) is given when the natural frequency is (314rad/sec). It is also shown that the sine and cosine component are tracked faithfully using the PLL. The modulation index (v) is calculated using M-FLC, which is then passed through a limiter to obtainv′. The value of MI ranges from 0 to 1. The PLL calculates the phase angle (δ′) using PA-FLC control. The phase angle calculated PA-FLC is found to be unaffected by oscillations in the system.
The detected phase angle (δ′) shifted by 4◦ phase angle.
Figure 2.20 shows the apparent of 5 group of EVs in the CS which shows the power drawn or injected at the charging point by EVs arrived in the CS.
Table 2.3 shows the summary of power division at the FLC (S), aggregator (S′), total battery energy (Et), battery power (Pbat), active and reactive power and power factor (pf) at certain hours in the CS during off-peak, peak and normal hours. Five group of EVs are shown in the Table 2.3, where TH-1345_TPERJOY
13:00 1 2 3 49.5
50 50.5
Time (sec)
f (Hz)
0 0.02 0.04 0.06 0.08 0.1
0 5
Time (sec)
ωt (rad/sec)
0 0.02 0.04 0.06 0.08 0.1
−1 0 1
Time (sec)
sinθ
0 0.02 0.04 0.06 0.08 0.1
−1 0 1
Time (sec)
cosθ
0 1 2 3
0 1 2
Time (sec)
v’
0 0.5 1 1.5 2 2.5 3
0 4 8
Time (sec)
δ’ (deg)
Figure 2.19: Estimated grid components using enhanced PLL method.
11 : 00 11 : 30 12 : 00 12 : 30 13 : 00 13 : 30 14 : 00
−15
−10
−5 0 5 10 15
Time (hrs)
Apparent power (kVA)
CP1
CP15
CP29
CP8
CP22
Figure 2.20: Apparent power injected/drawn by the CS.
each group denotes seven sets of EVs in the CS as mentioned in Table 2.2 (example: S1 denotes 7 group of EVs).