Modelling and allocation planning for open unified power quality conditioner to improve operational performance of radial distribution networks

𝑃𝑆ℎ1𝑊𝑂𝑃 Active power supplied by shunt inverter of UPQC-WOP 𝑃𝑆ℎ1𝑊 𝑃𝑆ℎ𝐷𝐺 Active power injected through DC link of shunt inverter to PV array 𝑃𝑆ℎ𝑊𝑃 Active power supplied by shunt inverter of UPQC-O-WP.

Introduction

Thus, ADN planning is an involved multi-objective optimization process with a number of objectives, such as, (i) minimizing installation/reinforcement/replacement cost for DP units and storage units (if any), (ii) minimizing operation cost (cost of energy loss and maintenance cost), (iii) maximization of reliability, (iv) maximization of DG capacity, (v) minimization of carbon emission, (vi) determination of the optimal operational strategy for the units of DG, (vii) PQ mitigation etc. The Level #3 classification is based on the different solution strategies reported in solving the ADN scheduling optimization problem.

Table 1.1: The planning cost and decision/optimizing variables for PDN and ADN planning Types of cost/

Literature review on ADN planning

47] SGP (O) Economic benefit from load and plug-in EV (PEV), OC of DG units, and cost of energy purchase from the grid. 55] MGP (I) IC and OMC of DG units, cost of energy sales and cost of purchased energy from the network.

Table 1.2: Different features of different ADN planning approaches Ref.

Motivation behind this thesis

The optimal separation of UPQC-O series and shunt inverters for improving PVHC, energy efficiency and PQ of distribution networks has not been studied. The active power compensation capability of UPQC-O integrated PV-BESS (PV-BESS-UPQC-O) for reducing the peak load of distribution networks has not been investigated.

Organization of this thesis

24. In period '𝑡4', the improvement in minimum bus voltage magnitude in case A is observed with the increase in total PV generation capacity of the network.

Fig. 2.1: A 6-bus radial distribution network with (a) UPQC (b) UPQC-O {symbols used in bracket are for the model with active power injection}

Contribution of this thesis

UPQC and UPQC-O modelling without and with active power injection

Model A: UPQC-WOP
Model B: UPQC-WP
Model C: UPQC-O-WOP
Model D: UPQC-O-WP
Incorporation of UPQC/UPQC-O models into FBSLF algorithm

The active and reactive power provided by the shunt inverter on the UPQC-WP is calculated as:. The reactive power provided by the series inverter of UPQC-O-WOP is equal to 𝑆𝑆𝑒𝑊𝑂𝑃.

Planning model for the allocation of UPQC/UPQC-O in distribution network

𝑁] (2.89) where,⁡𝑃𝐹(𝑜𝑒) and 𝑄𝐹(𝑜𝑒) are the active and reactive power current in line "𝑜𝑒"; 𝜎 is the set of input lines connected to bus ‘𝑒’; ℵ is the set of all downstream buses that are located beyond bus '𝑒'; 𝜏 is set by all downstream lines which are beyond the bus. Minimum Reactive Power Compensation Constraint: A portion (𝐾𝑐𝑜𝑚𝑝) of the total reactive power demand of the network must be provided by UPQC/UPQC-O.

Planning algorithm for the allocation of UPQC/UPQC-O in radial distribution

PSO: Basics

PVSML constraint: 𝑃𝑉𝑆𝑀𝐿 is the percentage of the load protected against a given value of voltage drop by the series inverter. This constraint is incorporated to maintain a given desired PQ level for a distribution network in terms of voltage breakdown with UPQC/UPQC-O placement.

Planning algorithm

Simulation results and discussion

Comparison of the optimal locations as obtained with PSO
Comparison in view of power loss and minimum bus voltage
Comparison among the VA-rating
Comparison among planning cost of UPQC models
The charging schemes for the battery

However, the VA rating for models A and B appears to be higher than that of models C and D in the 33-bus network. The percentage annual energy loss reduction obtained with UPQC-O placement (i.e., models C and D) is found to be significantly higher than that of the UPQC placement (models A and B).

Table 2.2: Different planning parameters

Conclusion

Open-UPQC Integrated PV Generation System Modeling and Allocation to Improve Energy Efficiency and Power Quality of Radial Distribution Networks. Optimal placement of the DG unit in distribution networks improves energy efficiency and bus voltages by providing active power compensation.

Modelling of UPQC-O with PV array for distribution networks

UPQC-O with battery and PV array (UPQC-O-WB) (ii) UPQC-O with PV array without battery (UPQC-O-WOB). Development of UPQC-O model with PV array and battery to act as active and reactive power compensator of radial distribution networks.

Placement strategy for UPQC-O in radial distribution networks

The series and shunt inverters placed at different locations of distribution networks communicate the reactive power compensation sharing information with each other through a communication channel.

Problem formulation

The mathematical expressions for active and reactive power balance constraints, bus voltage constraint, thermal constraint, and PVSML constraint are given in Eqs. Limitation of DG Penetration: DG penetration is defined as the ratio of the energy supplied by the DG unit (in one day) to the total energy required by the loads (in one day). 𝑡1𝑃𝑡𝑜𝑡𝑎𝑙𝑃𝑒𝑎𝑘 )+{(𝑡3+𝑡4)𝑃𝑡𝑜𝑡𝑎𝑙𝑂𝑓𝑓−𝑝𝑒𝑎𝑘} (3.6) According to the limit of DG penetration, the amount of DG penetration must be higher than the set value.

Solution algorithm

Simulation results and discussion

Impact on energy loss and bus voltages
Locations of the series and shunt inverters
Ratings of the series and shunt inverters
Size of the battery and PV array
Comparison of the planning costs of two cases
Relative merits and demerits for the deployment of Cases A and B
Performance comparison with similar approaches

It is found that the locations of the series inverter are the same in all the cases. But the ratings of the shunt converters are found to vary with the planning cases depending on their locations in the network.

Fig. 3.3: The variations of: (a) mean fitness value and (b) percentage of particles violating constraints in the PSO population with iterations as obtained with 69-bus network Case A (1-Se, 2-Sh)

Conclusion

Minimum bus voltage as obtained by the proposed approach is also comparable to that of the combined DSTATCOM allocation and reconfiguration approach. The UPQC-O rating requirement is higher than DSTATCOM [117] because it is designed to improve power dissipation by maintaining a desired PQ level.

Introduction

The various combinations of BSS and converter unit sizes are used to maximize PVHC. Formulation of a mono-objective scheduling problem to maximize the PVHC of a distribution network, considering the network power loss as one of the operational constraints.

Mono-objective planning for the maximization of PVHC

Determination of the DGHC
Modelling of series and shunt inverters

Modelling of the series inverter
Modelling of the shunt inverter

Incorporation of PV generation and inverters models into FBSLF
Mono-objective optimization problem for the maximization of PVHC…
Solution approach for mono-objective planning
Simulation results of mono-objective planning

PVHC
Bus voltages of the network
Maximum line current flow
VA-rating of inverters of UPQC-O
Effect of placement of inverters of UPQC-O on network power loss
The optimal PV generation capacities as obtained with PSO
Impact of placement of single series and single shunt inverter on
Comparison of proposed mono-objective planning approach with

This section describes the mathematical modeling of the series and shunt inverters for distribution networks. The VA rating requirement for the series inverter is found to be less compared to the shunt inverter.

Fig. 4.1: Plot of operational performance of a distribution network with respect to amount of DG injection used for the determination of DGHC

Multi-objective planning for simultaneous optimization of PVHC and energy loss of

Multi-objective optimization problem

Pareto-dominance principle

Modelling of UPQC-O
SPEA2-MOPSO based solution approach

Assumptions
SPEA2-MOPSO
MOPSO based planning algorithm

Simulation results of multi-objective planning

Impact of maximum PV capacity on PAF
Impact of placement of UPQC-O on PAF

The energy loss corresponding to Case B solution 3 is 25-30% less than that of Case A. For the same amount of PVHC, the network energy loss corresponding to Case B solution is lower than that of Case A.

Fig. 4.9: Flow chart for the SPEA2-MOPSO-based multi-objective planning algorithm

Conclusion

Multi-objective scheduling for the allocation of PV-BESS integrated open UPQC for peak class shearing of radial distribution networks. Multi-Objective Planning for Allocation of PV-BESS Integrated Open UPQC for Peak Load Restraint….

Fig. 4.12: Bar chart for the PV generation capacities in each bus for solutions 1, 2, and 3 of the 69-bus network in Case B

Modelling of PV-BESS-UPQC-O for peak load shaving of distribution networks…

PV and BESS rating requirements

The depth of discharge (DOD) of the BESS at any instant of time is complementary to the state of charge (SOC) of the BESS. The BESS rating associated with the shunt inverter is determined based on the amount of active power to be supplied during peak hours and the inverter loss to be compensated.

Assumptions/consideration

Multi-objective optimization problem

Maximizing peak load shaving requires a larger amount of active power supply through the PV-BESS-UPQC-O. Therefore, maximizing peak load shaving and the cost of PV-BESS-UPQC-O placement are two conflicting objectives.

SPEA2-MOPSO based solution approach

MOPSO-based planning algorithm

Simulation results and discussion

PAF obtained with MOPSO

The PAFs together with the Pareto approximation surface obtained with MOPSO are shown in Fig. These figures show that the total power loss when installing PV-BESS-UPQC-O initially decreases with the increasing value of peak load shedding.

Technical details of three extreme solutions of PAFs

It is found that the cost of placing PV-BESS-UPQC-O and total power loss with the placement of PV-BESS-UPQC-O are more in solution 1 compared to solutions 2 and 3 because the higher value of peak shear required placement of higher-rated converters, BESS and PV. Similarly, the implementation of solution 3 will provide moderate values of peak shear and cost of placement of PV-BESS-UPQC-O along with the least total power loss among all the solutions in PAF.

Fig. 5.3: PAFs along with Pareto-approximation surface obtained with (a) 33-bus and (b) 69-bus networks with the placement of PV-BESS-UPQC-O

Qualitative comparison of proposed work with other similar works

Cost of investment in DS unit, arbitrage profit, economic profit due to reduction of working power loss and limitation of renewable energy, improvement of voltage profile and system resilience and postponement of system upgrade. Number, location, rated power and capacity of DS units and charge and discharge strategy for DS units.

Table 5.2: The selected solutions obtained with the 33-bus and 69-bus distribution networks

Conclusion

The optimal operation of power systems under time-varying load demand and PV generation is a challenging research problem. Determining the optimal set points of these devices under time-varying load demand and PV generation requires the formulation of an online optimization approach.

Steady-state models of radial distribution network and UPQC-O

Steady-state model of radial distribution network

Various operational parameters of the distribution network such as bus voltage magnitude, electric current flow, network power loss can be calculated using Eqs.

Steady-state model of UPQC-O

A typical 5-bus radial distribution network with PV generation sources and UPQC-O is shown in Fig.

Operation of UPQC-O during time varying load demand and PV generation

Time varying load demand PV generation

Operation of UPQC-O during time varying load demand and PV

Since both inverters of the UPQC-O are designed to inject only reactive power into a grid, the phase angle between 𝑉𝑆𝑒𝐻𝑒𝑙(𝑡) and 𝐼𝑆(𝑡) is maintained exactly at 90° for the series inverter under all conditions. One of the functions of the series inverter is to smooth out the voltage drop that occurs in the overhead network.

Optimization problem

Stage 1: Determination of PV capacity in each bus

For the shunt inverter, the phase angle between 𝑉𝐿(𝑡) and 𝐼𝑆ℎ′ (𝑡) is also kept at 90° for the same reason. The maximum amount of series injected voltage is limited by the series inverter rating as shown in Eq. Operation optimization approach for open UPQC with time-varying load demand and PV generation.

Stage 2: Operational optimization problem for energy loss minimization…

is used for active and reactive power balance at each bus of a network, except the substation bus. 6.16) and (6.17) are used for calculating bus voltage magnitude in each bus and line current flow in each line of a network respectively. 6.18) and (6.19) represent the bus voltage magnitude limitation and thermal capacity limitation respectively. represents the steady-state operational constraints of a radial distribution network with UPQC-O and PV generation is used for active and reactive power balance at each bus of a network, except the substation bus. 6.25) is used for calculating bus voltage magnitude in each bus of a network. 6.26) is used for the calculation of line current flow in each line of a network. 6.27) and (6.28) represent the bus voltage magnitude limitation and thermal capacity limitation respectively.

Infrastructure for the real-time implementation of proposed methodology and

This information is transferred to the computer for determining the optimal VAR injection setpoints for the UPQC-O inverters. The determination of set points for UPQC-O inverters using GAMS is shown in Fig.

Simulation results and discussion

Simulation results with planning Case A

Optimal VAr injection set point obtained for the inverters of UPQC-
Minimum bus voltage magnitude
Cost benefit analysis
Comparison of annual energy losses obtained with variable and
Comparison among different compensation approaches for the

In cases 1(a) and 2(a), energy loss is minimized by variable VAr injection settings UPQC-O. In cases 1(b) and 2(b), energy loss is minimized by injecting UPQC-O with constant/nominal VAr.

Fig. 6.10. Flow chart for the determination of locations and sizes of shunt inverters for single-point and multi-point

Simulation results with planning Case B

PV capacity of each bus
Hourly energy loss and minimum bus voltage magnitude
VAr injection set points for the inverters of UPQC-O

The energy loss reduction in Case B(2) is only observed in PV generation hours compared to Case B(1). However, the reduction of the energy loss in case B(3) is observed during the day compared to cases B(1) and B(2).

Fig. 6.15: Bar chart for the PV capacities in each bus of 33-bus radial distribution network

Conclusion

Akagi, “Unified Power Quality Conditioner: Integration of Series and Shunt-Active Filters,” IEEE Trans. Taylor, “Potential for peak reduction on low-voltage distribution networks using electrical energy storage,” Journal of Energy Storage, vol.