Inter national J our nal of A pplied P o wer Engineering (IJ APE) V ol. 14, No. 2, June 2025, pp. 319 ∼ 327 ISSN: 2252-8792, DOI: 10.11591/ijape.v14.i2.pp319-327 ❒ 319 Optimal placement of DGs in a multi-feed radial distrib ution system using actor -critic lear ning algorithm Neelakanteshwar Rao Battu 1 , Sur ender Reddy Salkuti 2 1 Department of Electrical and Electronics Engineering, V allurupalli Nagesw ara Rao V ignana Jyothi Institute of Engineering and T echnology (VNR VJIET), Hyderabad, India 2 Department of Railroad and Electrical Engineering, W oosong Uni v ersity , Daejeon, Republic of K orea Article Inf o Article history: Recei v ed Jan 3, 2023 Re vised No v 6, 2024 Accepted No v 28, 2024 K eyw ords: Actor -critic learning Distrib uted generation Distrib ution system Netw ork reconguration Reinforcement learning ABSTRA CT Multi-feed radial distrib ution systems are used to reduce the losses in the sys- tem using reconguration techniques. Reconguration can reduce the losses in the system only to a certain e xtent. Introduction of distri b ut ed generators has v astly impro v ed the performance of distrib ution systems. Distrib uted generators can be used for reduction of loss, the impro v ement of the v oltage prole, and reliability enhancement. Distrib ution generators play a vital role in reducing the losses in the distrib ution system. Placement of distrib uted generators in a multi- feed system is a comple x task to be solv ed using classical optimization methods. Classical optimization techniques may sometimes f ail to pro vide a con v er ged so- lution. Installation of distrib uted generators at suitable locations in a multi-feed system is found in this pape r using the actor -critic learning algorithm. Actor - critic learning approach uses temporal dif ference error as a signal in making judgements re g arding actions to be tak en for future states in ac cordance with re w ards that ha v e been obtained by applying the present polic y . The approach is applied to a standard 16-b us distrib ution system for reduction of system losses, and the results are discussed. This is an open access article under the CC BY -SA license . Corresponding A uthor: Surender Reddy Salkuti Department of Railroad and Electrical Engineering, W oosong Uni v ersity Jayang-dong, Dong-gu, Daejeon 34606, Republic of K orea Email: surender@wsu.ac.kr 1. INTR ODUCTION Distrib uted generation (DG) has been playing a vital role in the electric po wer system for the pas t fe w years [1]. It has led to se v eral benets lik e en vironmenta l protection in case of rene w able DG, deferment of feeder upgradation under load gro wth, v oltage prole enhancement, reduction in losses, and in reliability enhancement of the system [2]. An e xtensi v e research has been made till no w for single DG placement , and relati v ely little w ork has been done in the case of multiple DG placement. DG placement using a fuzzy logic approach has been done in [3]. Pre vious study [4], the optimal placement of DGs in a microgrid has been performed. Probabilistic placement of DG has been performed in [5] considering uncertainties. DG planning using the enhanced search group algorithm is done in [6]. DG planning using a Monte Carlo simulation has been done in [7]. Distrib ution system planning to minimize the cost of operation, considering reliability aspects, has been proposed in this w ork. A mix ed inte ger linear programming (MILP) model for optimal placement of DGs along with switches and tie-lines is proposed in [8]. An algorithm for the enhancement of netw ork resilience has been introduced in [9]. An articial hum- mingbird algorithm for optimal placement of rene w able sources is presented in [10]. Netw ork reconguration J ournal homepage: http://ijape .iaescor e .com Evaluation Warning : The document was created with Spire.PDF for Python.
320 ❒ ISSN: 2252-8792 of radial distrib ution systems for the enhancement of v oltage has been discussed in [11]. An optimal placement of DGs for the enhancement of reliability has been discussed in [12]. Optimal placement of DGs considering the CIGRE benchmark has been e xplained in [13]. Optimal placement of DG considering netw ork recon- guration for reliability impro v ement is dis cussed in [14]. Optimal placement of a wind f arm for reliability enhancement is sho wn in [15]. Optimal placement of DG for stability impro v ement is discussed in [16]. Optimal placement of tie-lines and DGs to minimize post-outage operations is disc ussed [17]. Opti- mal placement of rene w able sources in a microgrid is discussed in [18]. The result in [19], a method to impro v e distrib ution system reliability , has been discussed using the distr ib uted generators a v ailable in the system. A multi-objecti v e planning of DGs and rene w ables in a microgrid is proposed in [20]. A mix ed inte ger linear programming (MILP) technique for optimal placement of char ging stations is proposed in [21]. Dynamic net- w ork reconguration in coordinat ion with switchable capacitor banks has been discussed in [22]. Simultaneous placement of shunt capacitors and DG units has been proposed in [23]. Harris Ha wks’ optimization for optimal placement of DGs is discussed in [24]. Rene w able DG inte gration to grid has been discussed in [25]. DG place- ment considering a lar ge scale disturbance is discussed in [26]. Optimal sizing and placement of rene w ables using metaheuristic technique has been discussed in [27]. Most of the w ork a v ailable in the literature is on single DG placement, and mostly heuristic techniques ha v e been used. No v elty in this paper is multiple DG placement in a multi-feed system and solving the problem using a no v el approach called actor -critic (A C) learning algorithm. A C is an e xtension to the reinforcement learning (RL) algorithm, which is based on the Mark o v decision process (MDP) [28]. RL can be e xpected to gi v e gratifying re sults in the case of a comple x problem ha ving a lar ge number of states. The remaining content of the paper is di vided into the follo wing s ections: i) Section 2 brief about the proposed methodology; ii) Section 3 deals with problem formulation; iii) Section 4 describes the solution methodology; i v) Section 5 follo wed by a discussion on the results; v) Section 6 gi v es the conclusion of the w ork. 2. REINFORCEMENT LEARNING Reinforcement learning (RL) is a goal-directed method that tackles a problematic situation through interaction. It basically consists of an agent and an en vironment. The learner and decision mak er is kno wn as the agent, and e v erything outside it is kno wn as the en vironment. RL maps the situations to actions to enhance the re w ard signal. During the learning process, the agent gets information about the present en vironment’ s state, s t ∈ S at time step ‘ t ’. On the basis of this state agent decides the action, a t ∈ A ( s t ) to be tak en and recei v es a re w ard, r t +1 one time step later and enters into a ne w state s t +1 . This is sho wn in Figure 1. Figure 1. Architecture of reinforcement learning This process of the agent deciding the action to be tak en, the en vironment reciprocating to these actions and presenting ne w re w ards and states tak es place for each time step and during each time step, the agent does mapping between the present state and the probability of deciding each possible action when the agent is in this state. This mapping i s kno wn as Agent’ s Polic y , represented as π ( s t , a t ) . Agent, based on the e xperience changes its polic y . The objecti v e of the RL agent is to maximize the sum of re w ards o v er the long run. These reinforcement learning algorithms use the v alue function, V π ( s ) , to estimate “ho w good it is for the agent to tak e a particular action for a present state”. V π ( s ) represents the e xpected v alue of return when the system be gins in state s and then follo ws a polic y π . Mathematically , this can be represented as (1). V π ( s ) = E π { R t | s t = s } = E π { ∞ X j =0 γ k r t + j +1 | s t = s } (1) Int J Appl Po wer Eng, V ol. 14, No. 2, June 2025: 319–327 Evaluation Warning : The document was created with Spire.PDF for Python.
Int J Appl Po wer Eng ISSN: 2252-8792 ❒ 321 Where, V π ( s ) is the v alue function of a polic y π , E π is the e xpected v alue for a gi v en polic y , γ is the discount f actor , and r t + j +1 is the re w ard g ained when agent mo v es from state s t + j to state s t + j +1 . Solving a problem using reinforcement learning in v olv es nding an optimal v alue function, which is e xpressed as (2). V ∗ ( s ) = max ( V π ( s )) , ∀ s ∈ S (2) Where, V ∗ ( s ) is the optimal v alue function. 3. PR OPOSED METHODOLOGY The DG placement problem in this w ork is solv ed using the actor -critic (A C) learning method. A C learning method is an e xtension to the reinforcement learning problem. A C learning embeds reinforcement learning in it. In actor -critic architecture, the polic y selects acti ons, hence, it is termed as an actor , and the estimated v alue function i s termed as the critic, as it criticizes the actions tak en by the polic y . Learning is done in an on-polic y manner , the critic must learn about and must criticize the polic y that is presently follo wed by the actor . The criticism made is in the form of temporal dif ference (TD) error , hence, this method comes under temporal dif ference methods. TD error acts as a scalar signal for the output gi v en by critic and helps in learning process that tak es place between actor and critic as sho wn in Figure 2. Figure 2. Architecture of actor -critic learning Mathematically TD error , δ t is gi v en as (3). δ t = r t +1 + γ V ( s t +1 ) − V ( s t ) (3) Where, δ t is temporal dif ference and r t +1 is the re w ard g ained when agent mo v es from s t to s t +1 state. If TD error is positi v e, the tendenc y to select an action a t in future should be strengthened and if it is ne g ati v e the tendenc y to select an action a t in future should be weak ened. This is done by updating the tendenc y as (4). p ( s t , a t ) ← p ( s t , a t ) + β δ t (4) Where, p ( s t , a t ) is the tendenc y to select an action a t in future when state is s t and β is the step size parameter . Polic y is e v aluated using Gibbs softmax method as (5). π t ( s, a ) = e p ( s,a ) B X b =1 e p ( s,b ) (5) Where, π t ( s, a ) is the polic y corresponding to state s t and action a t . The state v alues are updated as (6). Optimal placement of DGs in a multi-feed r adial distrib ution system ... (Neelakanteshwar Rao Battu) Evaluation Warning : The document was created with Spire.PDF for Python.
322 ❒ ISSN: 2252-8792 V ( s t ) ← V ( s t ) + α δ t (6) Where, α is the step size parameter . 4. PR OBLEM FORMULA TION It is assumed that the distrib ution system and the DGs to be placed in the system are o wned by the same utility . This paper focuses on nding the suitable locations ( D G l oc ) and si zes ( D G siz e ) of DGs in each feeder that reduce the total system real po wer loss (TPL). Mathematically , it can be e xpressed as (7). M in { T P L ( D G l oc , D G siz e ) } (7) Subject to belo w mentioned constraints. 4.1. V oltage constraints Installation of DG, though reduces real po wer loss compared to the base case, sometimes it may result in v oltage violations at some b uses. Hence, there is a need to put a constraint on the node v oltages. Substation b uses are tak en as r eference, and v oltages at thes e b uses are maintained at 1 p.u. In accordance with ANSI C84.1, v oltages at remaining b uses are constrained amid 0.95 p.u. and 1.05 p.u. [29], [30]. That can be e xpressed as (8). 0 . 95 ≤ V n ≤ 1 . 05 (8) Where, V n is the v oltage at load b us n . 4.2. Real and r eacti v e po wer balance According to IEEE Std 1547-2003 [31], DG connected in the distrib ution system should operate at unity po wer f actor . Therefore, the real po wer consumed by load and losses in each feeder is fed from grid and DG, connected to the respecti v e feeder , whereas reacti v e po wer load and associated losses are supplied by the grid alone. Hence, the po wer balance equations for real and reacti v e po wers can be e xpressed as (9)-(10). P g r id m + P D G m,n = P l oad m + P l oss m (9) and Q g r id m = Q l oad m + Q l oss m (10) Where, P g r id m is the r eal po wer supplied by the grid to feeder m , P D G m,n is MW capacity of DG placed at b us n in feeder m , P l oad m is the real po wer load connected to feeder m , P l oss m is the real po wer loss in feeder m , Q g r id m is the reacti v e po wer supplied by the grid to feeder m , Q l oad m is the reacti v e po wer load connected to feeder m , and Q l oss m is reacti v e po wer loss in feeder m . 4.3. DG po wer constraints DG solution resulted from the optimization algorithm should be a positi v e v alue and it should be a less than a maximum v alue. Hence, this condition can be e xpressed as (11). 0 ≤ P D G m,n ≤ P D G max (11) Where, P D G max is the maximum limit of P D G . 5. SOLUTION METHODOLOGY This paper discusses multiple DG placements in a multi -feed system. The objecti v e is to place a DG in each fe eder at an optimal location with an optimal size that minimizes the total system losses. In case of a multi-feed system, the situations, possible load in each feeder , and the actions to be tak en, a combination of DG locations and sizes of it in each feeder , will increase with the increase in the size of the system. In such a situation, it w ould be better to use a technique that decides on the solution by mapping e xisting states with possible act ions. The reinforcement algorithm m aps the s tates to actions and maximizes the v alues of a polic y that leads to maximum e xpected return. A C algorithm is an impro v ement to reinforcement learning, and since it embeds the features of both dynamic programming and Mont e-Carlo methods. This method has been adopted to solv e the problem of DG installation. Int J Appl Po wer Eng, V ol. 14, No. 2, June 2025: 319–327 Evaluation Warning : The document was created with Spire.PDF for Python.
Int J Appl Po wer Eng ISSN: 2252-8792 ❒ 323 5.1. Ev aluation of states A standard 16-b us distrib ution system with 3 feeders, sho wn in Figure 3, is used to apply the actor - critic learning approach for minimization of t otal system real po wer losses. In this gure, solid lines encircled with number s 1-13 are sectionalizing branches, and the dashed lines encircled with numbers 14-16 are tie branches of the system for the base case. T otal po wer losses produced in the system for each possible DG location and quantum represent states. Location set { b 1 , b 2 , b 3 } represents a state in this paper , where: b 1 = { n ∀ n = 4 , 5 , 6 , 7 } (12) b 2 = { n ∀ n = 8 , 9 , 10 , 11 , 12 } (13) b 3 = { n ∀ n = 13 , 14 , 15 , 16 } (14) Figure 3. Single line diagram of a 16-b us radial distrib ution system 5.2. Ev aluation of actions In this paper , DG-connected b us beha v es lik e a PQ b us. The minimum v alue of DG capacity is tak en as 0 MW . 0 MW indicat es a case of no DG placement. The maximum capacity of DG in each feeder is limited to 30% of the load in the feeder to mak e proper utilization of the present substation sunk cost [32]. DG sizes are chosen to be positi v e inte gers from a practical point of vie w . The Cartesian product of location set { b 1 , b 2 , b 3 } and DG capacity set { c 1 , c 2 , c 3 } represents the possible actions in this paper . Real po wer load on feeder 1, feeder 2, and feeder 3 are 8.5 MW , 15.1 MW , and 5.1 MW , respecti v ely . 5.3. Ev aluation of r ewards F or each state-action pair , real po wer losses are e v aluated for the best congurati o n of the sys tem. Reciprocal of total system real po wer losses is tak en as a re w ard for a particular state-action pair . r t +1 = 1 T P L (15) The mathematical procedure of agent making transition between dif ferent states, by taking actions according to the polic y (actor) and correction of thes e actions by v alue function (critic) is gi v en in o wchart in Figure 4. F or the policies and v alues obtained using the actor -critic algorithm, the optimum v alue is obtained using (2). State-action pair corresponding to this optimal v alue, kno wn as optimal polic y , π ∗ gi v es the DG solution for each feeder . Optimal placement of DGs in a multi-feed r adial distrib ution system ... (Neelakanteshwar Rao Battu) Evaluation Warning : The document was created with Spire.PDF for Python.
324 ❒ ISSN: 2252-8792 Is  ? Sele ct a n   in iti al  ac tio n   ran dom ly No Yes Read the input  data Initially selec t a state randomly   from se t of possible states Select an  ac ti on Set time  count, t  = 1 Evalua te  the  r ewa rd Evaluate the temp or al di ffere nce  Eva l uate the tendenc y  to  s e lect  the pres ent  action in  futur e Evalua te  Policy  matrix Evaluate V a lue matrix Set tendenc y  of  s e lecting any  actio n to be eq ual   in it iall y. Selet Va lues of each  state to zero  initia lly  tt + 1 |V ( s ) - V ( s ) | < 0 Stop the  e xecution  of pro g r am E n te r in to   t h e new   s t a t e Figure 4. Flo wchart for actor -critic learning method 6. RESUL TS The information obtained for DG soluti on in each feeder using A C approach is sho wn in T able 1. The v oltage proles at v arious b uses before and after the placement of DG is sho wn as a plot in Figure 5. V oltages at substation b uses are maintained at 1 p.u. Apart from the substation b uses, there is a signicant impro v ement in v oltages at other b uses. Real po wer loss in the system and minimum node v oltage in the system, with and with- out DG, are sho wn in T able 2. Percentage reduction in losses compared to the base case without DG is found to be 48.35% and the minimum node v oltage has impro v ed from 0.9568 p.u. to 0.9710 p.u. after placement of DG. Int J Appl Po wer Eng, V ol. 14, No. 2, June 2025: 319–327 Evaluation Warning : The document was created with Spire.PDF for Python.
Int J Appl Po wer Eng ISSN: 2252-8792 ❒ 325 T able 1. Optimum location and size of DGs Feeder no. Optimum location Optimum size (MW) 1 7 3 2 12 5 3 16 2 T able 2. T otal real po wer loss and minimum node v oltage Case T otal real po wer loss in MW Minimum node v oltage (p.u.) W ithout DG 0.5995 0.9568 W ith DG 0.3097 0.9710 Figure 5. V oltages at v arious b uses with and with out DGs in a 16-b us distrib ution system 7. CONCLUSION In case of a multi-feed system, the problem of multiple DG placement comes out with se v eral combi - nations of DG locations and sizes. Reinforcement learning and actor -critic l earning algorithms ha v e a feature of mapping situations with possible actions. These algorithms nd a potential application in case of comple x and uncertain situations. Actor -critic learning algorithm embeds the features of reinforcement learning, dynamic programming, and Monte-Carlo approaches. Hence the problem of optimal placement of DGs in a multi-feed system is solv ed in this paper using act or -critic learning algorithm. In actor -critic learning algorithm, actions tak en by the polic y (actor) are corrected by the v alue function (critic). The approach is applied to a standard 16- b us radial distrib ution system for minimization of system real po wer losses. The results obta ined are discussed for both the cases of with and without DG. FUNDING INFORMA TION This research w ork w as supported by “W oosong Uni v ersity’ s Academic Research Funding - 2024”. A UTHOR CONTRIB UTIONS ST A TEMENT This journal uses the Contrib utor Roles T axonomy (CRediT) to recognize indi vidual author contrib u- tions, reduce authorship disputes, and f acilitate collaboration. Name of A uthor C M So V a F o I R D O E V i Su P Fu Neelakanteshw ar Rao Battu ✓ ✓ ✓ ✓ ✓ ✓ ✓ ✓ ✓ Surender Reddy Salkuti ✓ ✓ ✓ ✓ ✓ ✓ ✓ ✓ ✓ C : C onceptualization I : I n v estig ation V i : V i sualization M : M ethodology R : R esources Su : Su pervision So : So ftw are D : D ata Curation P : P roject Administration V a : V a lidation O : Writing - O riginal Draft Fu : Fu nding Acquisition F o : F o rmal Analysis E : Writing - Re vie w & E diting Optimal placement of DGs in a multi-feed r adial distrib ution system ... (Neelakanteshwar Rao Battu) Evaluation Warning : The document was created with Spire.PDF for Python.
326 ❒ ISSN: 2252-8792 CONFLICT OF INTEREST ST A TEMENT Authors state no conict of interest. INFORMED CONSENT Informed consent is not applicable to t his paper as no personal information of an ybody is used in this w ork. ETHICAL APPR O V AL Ethical appro v al is not applicable to this paper as the proposed w ork doesn’ t use people or animals. D A T A A V AILABILITY The data that support the ndings of this study are a v ailable from the corresponding author , [SRS], upon reasonable request. REFERENCES [1] R . Gautam, S. Khadka, T . B. Malla, A. Bhattarai, A. Shrestha, and F . Gonzalez-Long att, “ Assessing uncertainty in the optimal placement of distrib uted generators in radial distrib ution feeders, ” Electric P o wer Systems Research , v ol. 230, pp. 110249, May 2024, doi: 10.1016/j.epsr .2024.110249. [2] N. R. Battu, P . Krishna, and V . Y arlag adda, Inte gration of Photo v oltaic Distrib uted Generation into Grid . 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He recei v ed M.T ech. de gree from JNTU Anantapur in 2004 and Ph.D. de gree from IIT Delhi in 2016. He is presently w orking as an associate professor at VNR V ignana Jyothi Institute of Engineering and T echnology , Hyderabad, T elang ana, India. His research interests include distrib ution system planning, po wer system protection, and modelling of electrical machines. He can be contacted at email: neelakanteshw arrao b@vnrvjiet.in. Sur ender Reddy Salkuti recei v ed the Ph.D. de gree in Electrical Engineering from the Indian Institute of T echnology , Ne w Delhi, India, in 2013. He w as a postdoctoral researcher with Ho w ard Uni v ersity , W ashington, DC, USA, from 2013 to 2014. He is currently an associate professor with the Departm ent of Railroad and Electrica l Engineering, W oosong Uni v ersity , Daejeon, Republic of K orea. His current research interests include mark et clearing, including rene w able ener gy sources, demand response, smart grid de v elopment with inte gration of wind, and solar photo v oltaic ener gy sources. He can be contacted at email: surender@wsu.ac.kr . Optimal placement of DGs in a multi-feed r adial distrib ution system ... (Neelakanteshwar Rao Battu) Evaluation Warning : The document was created with Spire.PDF for Python.