6.6 Simulation results and discussion
6.6.2 Simulation results with planning Case B
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Case 4: In this case, the energy loss is minimized with the allocation of fixed capacitor bank. The size of capacitor bank is also determined through the optimization for energy loss minimization in peak load condition.
The single point compensation is chosen for this case study. The results obtained with these four cases are shown in Table 6.4. The results show that the variable VAr set points of UPQC-O in Case 1(a) and 2(a) provide better compensation to obtain higher energy loss reduction as compared to Cases 1(b) and 2(b), respectively. The solutions obtained with Case 1(a) and Case 2(a) show similar annual energy loss reduction. However, the VA-rating requirement for UPQC-O for solution obtained with Case 2(a) is higher as compared to Case 1(a). The allocation of DSTATCOM in Case 3 provides similar annual energy loss reduction as obtained with the solutions of Cases 1(a) and 2(a). The size of DSTATCOM is also found to be similar as obtained with Case 1. Among all the above mentioned approaches, the allocation of fixed capacitor bank results in comparatively lesser energy loss reduction in network because of the constant VAr injection in Case 4. Although the installation of capacitor bank for VAr compensation is an economical option, it is not skilled to mitigate any of the PQ issues. UPQC-O with its series inverter can protect the downstream load from voltage sag occurring in upstream section. The voltage sag mitigation can be done with a DSTATCOM installed in a similar strategic location.
However, this needs additional DSTATCOM and it will increase the total VA rating.
Table 6.4: Comparison among different compensation approaches of energy loss reduction Solution obtained with
different types compensation approaches
Case A(1) UPQC-O Allocation DSTATCOM
allocation (Case 3)
Capacitor allocation (Case 4)
Case 1 Case 2
Case 1(a) Case 1(b) Case 2(a) Case 2(b)
Annual energy loss (MWh) 1233.2115 943.4183 954.0300 942.5683 963.9156 943.7999 965.0003 VA-rating of shunt
compensator (MVA)
- 1.6078 1.6078 1.778 1.778 1.792 1.792
VA-rating of series compensator (MVA)
- 0.1913 0.1913 0.359 0.359 - -
Total VA-rating - 1.7991 1.7991 2.137 2.137 1.792 1.792
Operation Optimization Approach for Open UPQC with Time Varying Load Demand and PV Generation…
6.6.2.1 PV capacity of each bus
The PV capacity of each bus as obtained with the Stage 1 optimization problem is shown in Fig. 6.15. From the bar chart, it is observed that the buses near to the substation can allow more integration of PV than the buses distant away from the substation. It also provides the information of maximum PV generation that a network can accommodate in each bus during peak generation hour. The allowable maximum PV generation in each bus would be equal to the PV capacities of the respective buses.
6.6.2.2 Hourly energy loss and minimum bus voltage magnitude
The hourly energy loss obtained with Cases B(1)-B(3) are shown in Figs. 6.16 (a)- (c) for the different seasons in a year. The results show that the energy loss of the network is varying with the variations in load demand and PV generation in Cases B(2) and B(3).
The energy loss reduction in Case B(2) is observed only during PV generation hours as compared to Case B(1). However, the energy loss reduction in Case B(3) is observed throughout the day as compared to Cases B(1) and B(2). It is due to the VAr compensation provided by the inverters of UPQC-O in addition to the active power compensation provided by the PV. The numerical values for annual energy loss are provided in Table 6.5 for Cases B(1)-(3).
The minimum bus voltage magnitude obtained with Cases B(1)-(3) are shown in Figs. 6.17 (a)-(c) for different seasons in a year. The results show that the minimum bus voltage magnitude is also varying with the variations in load demand and PV generation in Cases B(2) and B(3). In Case B(2), significant improvement in minimum bus voltage
Fig. 6.15: Bar chart for the PV capacities in each bus of 33-bus radial distribution network
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magnitude is observed during PV generation hours as compared to Case B(1). In Case B(3), the improvement in minimum bus voltage magnitude is observed throughout the day as
(a)
(b)
(c)
Fig. 6.17: Minimum bus voltage magnitude of the network obtained with Cases B(1), B(2), and B(3) for the weekday and
weekend of: (a) winter, (b) summer, and (c) spring seasons Fig. 6.16: Hourly energy loss of the network obtained with
Cases B(1), B(2), and B(3) for the weekday and weekend of:
(a) winter, (b) summer, and (c) spring seasons
(a)
(b)
(c)
Operation Optimization Approach for Open UPQC with Time Varying Load Demand and PV Generation…
compared to Cases B(1) and B(2) due to the VAr compensation provided by the inverters of UPQC-O.
Table 6.5: Annual energy loss obtained for different planning cases of Case B Parameters Case B(1) Case B(2) Case B(3) Annual energy loss (MWh) 1233.2115 878.5402 609.3889
% reduction w.r.t. Case B(1) - 28.7600 50.5852
6.6.2.3 VAr injection set points for the inverters of UPQC-O
The VAr injection set points obtained for the shunt inverter of UPQC-O during hourly load demand and PV generation variations are shown Fig.6.18 for Case B(3). It is observed that the VAr injection set points for the shunt inverter are varying with the variations in load demand and PV generation. It means that different amount of VAr injection is required in different load and PV generation scenario to minimize the energy loss of a distribution network. The results show that the higher amount of VAr injection is required during higher load demand or/and PV generation hours to minimize the energy loss for a distribution network. Thus, the shunt inverter needs to be set at the rated VAr capacity in some of the higher load or/and PV generation hours. The VAr compensation set points obtained for the series inverter of UPQC-O during hourly load demand and PV generation variations are found to be same in the planning Case B(3). These are found to be set at the rated VAr capacity of the series inverter.