A Novel Approach for Multiple DG Allocation in Real Distribution System

Abstract: A novel approach has been proposed in this paper for optimal placement of DG units in radial distribution system. An objective function is formulated to find out the optimal size, quantity and position of DG units for real power loss reduction and voltage profile enhancement. A new mathematical expression, Power Voltage Sensitivity Constant (PVSC), has been proposed to solve the allocation problem. The total size of DG units is also restricted up to 50% of total load of system. A novel index is also proposed which incorporates level of DG penetration and % reduction in real power losses. The results of the proposed technique are validated on standard IEEE 33 bus system and 130 bus real distribution system of Jamawaramgarh, Jaipur city. The obtained results are compared with latest optimization techniques to show the effectiveness and robustness of the proposed approach.

In this paper, a novel approach to solve allocation of multiple DG units problem is presented for active power loss minimization and voltage profile enhancement. A new mathematical expression is formulated that is called PVSC (Power Voltage Sensitivity Constant). This constant evaluate size and location of DG units at the same time. The total size of DG units is also restricted up to 50% of total load of system, so that less size of DG units produce maximum loss reduction. A new index, DG penetration index (DGPI), is also introduced here. This index gives the value of percentage loss reduction for unit DG size. This index is used to show the superiority of the proposed approach over other ones. Standard 33 bus distribution system and 130 bus practical system of Jamawaramgarh area of Jaipur city are used to validate the above mentioned approach. The obtain results showed that proposed approach gives better outcome than other approaches mentioned in this paper.

II. PROBLEM FORMULATION
The objective of the paper is the minimization in active power loss of radial distribution system to its lowest value. This is achieved by installing the DG units of appropriate size at optimal location. The operating constraints of the problem are divided into equality and inequality constraints. Mathematically, the DG placement problem can be formulated as a constrained nonlinear optimization model [12]: k2(x,z) ≤ 0 k1(x,z) and k2(x,z) are the set of equality and inequality constraints, respectively. Where, x is the state variables and z is the control variables. The control variables are power outputs of DG (P and Q). The state variables are bus voltage and line power flows. The figure 1 shows the line diagram of two bus system. The DG unit is connected at bus j. The distribution network power loss of above system for n bus is calculated by using: (a) Equality Constraints: The arithmetical summation of all incoming and outgoing powers together with power losses for distribution system and power generated by DG units should be equal to zero. (b) Inequality Constraints: (i) The injected power by each DG units is restricted by its maximum and minimum limits as, The feeder should not go beyond the thermal limit of the line. Where, R : Line resistance between bus i and j; X : Line reactance between bus i and j; Z : Line impedance; V i : Magnitude of voltage at bus i ; V j : Magnitude of voltage at bus j; V min : Minimum bus voltage δ i : Angle of voltage at bus i; δ j : Angle of voltage at bus j ; P and Q: Active and reactive power flow from bus i to j

III. PROPOSED APPROACH A. Power Voltage Sensitivity Constant (PVSC)
In this paper allocation of DG unit problem is done by analytical technique. The Power Voltage Sensitivity Constant (PVSC) is proposed to determine the size and position of DG units. This constant takes active power loss and voltage limits in account and suggest the optimal location of the DG.

3)
Where, P realloss is the base case real power loss. P dgloss is the real power loss after DG placement at i th bus. V max is maximum bus voltage in pu after DG placement at i th bus. (Always 1pu) V min is minimum bus voltage in pu after DG placement at i th bus. For optimal placement of DG units the value of PVSC should be minimum. Computational procedure for proposed analytical method is explained below.
Step 1: Run the load flow program calculate value of P realloss .
Step 2: Set 5% DG penetration level and run load flow program.
Step 3: Compute P dgloss of the system and "PVSC" values for each bus using eq. 3.
Step 4: Now vary DG penetration in small step and compute P dgloss .
Step 5: Store the size of DGs which gives least amount of P dgloss .
Step 6: The bus, which has least "PVSC" value, will be the optimal position of DG unit.
Step 7: Repeat Steps 4 to 6 to find more location of DGs.

B. DG penetration Index (DGPI)
Most of the researchers did not consider DG penetration in their research. In many practical cases along with economic constraints the size of DG units are not pragmatic. In their paper the size of DG unit is very high. But the high size of DG unit will lead to high cost of the system. In this paper a novel index, called DG penetration index, is proposed. The DGPI gives the % power loss reduction for unit size of DG.
Hence, for optimal allocation of DG units the value of DGPI should be maximum.

IV. RESULTS
The proposed technique has been tested on standard 33 test distribution system and 130 bus real distribution system of Jamwaramgarh area of Jaipur city. Three different loading conditions i.e. light load (50%), nominal load (100%) & heavy load (160%) have also been considered to validate the results. Test system-II The IEEE 33 bus radial distribution has total load of 3.715 MW and 2.30 MVAr. The base network power loss is 202.68 kW [13]. The base values are 12.66 kV and 100 MVA. Before and after DG placement results at different load levels are shown in table I. The results of proposed analytical approach for 33 bus system at nominal load level is compared with Mixed Integer Non-Linear Programming (MINLP) [14], hybridization of analytical method and heuristic search method [15], BAT algorithm [16] and Bacterial Foraging Optimization Algorithm (BFOA) [17]. It is observed from table II, that the proposed approach has maximum value of DGPI than other techniques. This shows the credibility of proposed method.  Figure 2 shows the voltage profile before and after DG placement at different bus for 33 bus distribution system (at nominal load). The bus voltages are improved in proposed method.

B. Test system-II
The system under consideration is 11 kV, 130 bus radial distribution system of Jamwaramgarh area, Jaipur city as shown in figure 2. The system load is 1878 kW and 1415 kVAr. The line and load data are given in appendix.
The real power loss of the system is 335 kW and minimum bus voltage is 0.825 pu without any compensation.   Table 3 shows the result of practical system with and without DG allocation at different load. The percentage power loss reductions are 54%, 57.7% and 62.2% at light, nominal and heavy load level. The voltage profile before and after DG placement at nominal load level is shown in figure 4. V. CONCLUSION In this paper a novel technique has been proposed to find out optimal site and size of multiple DG units in order to reduce distribution losses. A Power Voltage Sensitivity Constant (PVSC) has been formulated to solve the problem. The level of DG penetration is also considered in a range of 0-50% of total system load. A novel index (DGPI) is also proposed which incorporates level of DG penetration and % reduction in real power losses. The proposed technique is experienced on IEEE 33 bus standard system and 130 bus real distribution systems. The test results are compared with latest proposed algorithm and found better in terms of DGPI value. The results of real system are also promising.