Covariance Matrix Adapted Evolution Strategy (CMAES)
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View metadata, citation and similar papers at core.ac.uk brought to you by CORE provided by Directory of Open Access Journals ISSN: 2229-6956(ONLINE) ICTACT JOURNAL ON SOFT COMPUTING, OCTOBER 2012, VOLUME: 03, ISSUE: 01 APPLICATION OF RESTART COVARIANCE MATRIX ADAPTATION EVOLUTION STRATEGY (RCMA-ES) TO GENERATION EXPANSION PLANNING PROBLEM K. Karthikeyan1, S. Kannan2, S. Baskar3, and C. Thangaraj4 1,2Department of Electrical and Electronics Engineering, Kalasalingam University, India E-mail: [email protected] and [email protected] 3Department of Electrical and Electronics Engineering, Thiagarajar College of Engineering, India E-mail: [email protected] 4Anna University of Technology Chennai, India E-mail: [email protected] Abstract The Covariance Matrix Adaptation Evolution Strategy This paper describes the application of an evolutionary algorithm, (CMA-ES) is a robust stochastic evolutionary algorithm for Restart Covariance Matrix Adaptation Evolution Strategy (RCMA- difficult non-linear non-convex optimization problems [15]. The ES) to the Generation Expansion Planning (GEP) problem. RCMA- CMA-ES is typically applied to unconstrained or bounded ES is a class of continuous Evolutionary Algorithm (EA) derived from constraint optimization problems, and it efficiently minimizes the concept of self-adaptation in evolution strategies, which adapts the unimodal objective functions and is in particularly superior for covariance matrix of a multivariate normal search distribution. The ill-conditioned and non-separable problems [15], [16]. Anne original GEP problem is modified by incorporating Virtual Mapping Procedure (VMP). The GEP problem of a synthetic test systems for 6- Auger and Nikolaus Hansen showed that increasing the year, 14-year and 24-year planning horizons having five types of population size improves the performance of the CMA-ES on candidate units is considered. Two different constraint-handling multi-modal functions [17]. They suggest a CMA-ES restart methods are incorporated and impact of each method has been strategy with successively increasing population size. In this compared. In addition, comparison and validation has also made with paper, CMA-ES with restart strategy is applied for solving GEP dynamic programming method. Problem with two different constraint handling schemes namely Penalty factor less constraint handling scheme (PFL) and Self- Keywords: Adaptive Penalty scheme (SAP). The paper is organized as Constraint Handling, Dynamic Programming, Generation Expansion follows: Section 2 describes the GEP problem formulation. Planning, Restart Covariance Matrix Adaptation Evolution Strategy Section 3 describes RCMA-ES implementation to the GEP and Virtual Mapping Procedure problem. Section 4 explains two different constraint-handling methods; Section 5 provides test results and section 6 concludes. 1. INTRODUCTION 2. GENERATION EXPANSION PLANNING The Generation Expansion Planning (GEP) problem seeks to PROBLEM FORMULATION identify which generating units should be commissioned and when they should become available over the long-term planning The GEP problem is equivalent to finding a set of best horizon [1], [2]. This GEP model is applicable for developing decision vectors over a planning horizon that minimizes the countries like India, where planning is coordinated by central or investment and operating costs under relevant constraints. state government owned utilities for capacity addition. The major objectives of GEP are to minimize the total investment 2.1 COST OBJECTIVE and the operating cost of the generating units, and to meet the The cost objective is represented by the following demand criteria, fuel-mix ratio, and the reliability criteria. GEP expression: is a constrained, nonlinear, discrete optimization problem. The solution for the GEP problem can be obtained, through complete T min Cost IUt M X t OX t SUt (1) enumeration in the entire planning horizon. Linear programming t1 and Dynamic Programming (DP) were applied to solve the GEP problem [3], [4]. The emerging techniques applied to solve GEP where, were reviewed in [5]. The improved Genetic Algorithm (GA) Xt Xt1 Ut , t 1,2,...T (2) was used to solve the GEP problem in [6]. The Evolutionary N 2t Programming (EP) technique with Gaussian mutation and IUt 1 d CIi Ut,i (3) quadratic approximation technique was applied to solve the GEP i1 problem [7]. The comprehensive survey of the GEP models can N T be found in [8]. Nine different meta-heuristic techniques were SUt 1 d CIi i Ut,i (4) applied to solve the GEP problem [9]. The Elitist Non- i1 1 dominated Sorting Genetic Algorithm version II (NSGA-II) is 1.5t's' applied to multi-objective GEP problem [10], [11]. The M X t 1 d X t FC MC (5) ' environmental constraints and impact of various incentive s 0 mechanisms are considered in [12], [13] and [14]. 401 K KARTHIKEYAN et. al.: APPLICATION OF RESTART COVARIANCE MATRIX ADAPTATION EVOLUTION STRATEGY (RCMA-ES) TO GENERATION EXPANSION PLANNING PROBLEM 1 ' ' 1.5t s Rmin minimum reserve margin OX t EENSOC 1 d (6) ' s 0 Rmax maximum reserve margin The outage cost calculation of Eq.(6), used in Eq.(1), Dt demand at the t-th stage in megawatts (MW) depends on Expected Energy Not Served (EENS). The equivalent energy function method [2] is used to calculate EENS Xt,i cumulative capacity of i-th unit at t-th stage (and also to calculate loss of load probability, LOLP, used in the 3) Fuel Mix Ratio: The GEP has different types of constraint objective). generating units such as coal, liquefied natural gas t' = 2(t – 1) and T' = 2 T – t' (7) (LNG), oil, and nuclear. The selected units along with the and existing units of each type must satisfy the fuel mix ratio, N Cost total cost, $ j j FMmin X t, j X t,i FMmax j 1,2,...., N (10) i1 Ut N-dimensional vector of introduced units in t-th stage (1 stage = 2 years) where, j minimum fuel mix ratio of j-th type Ut,i the number of introduced units of i-th type in t-th stage FMmin X cumulative capacity vector of existing units in t-th t FM j maximum fuel mix ratio of j-th type stage, (MW) max j type of the unit (e.g., oil, LNG, coal, nuclear) I(Ut) is the investment cost of the introduced unit at the t-th stage, $ 4) Reliability Criterion: The introduced units along with the existing units must satisfy a reliability criterion on loss of M(Xt) total operation and maintenance cost of existing and the newly introduced units, $ load probability (LOLP), LOLP(X ) (11) s' variable used to indicate that the maintenance cost is t calculated at the middle of each year where, is the reliability criterion, a fraction, for maximum allowable LOLP. Minimum reserve margin O(Xt) outage cost of the existing and the introduced units, $ constraint avoids the need for a separate demand S(Ut) salvage value of the introduced unit at t-th interval, $ constraint. d discount rate 3. IMPLEMENTATION TO THE GEP CIi capital investment cost of i-th unit, $ PROBLEM δi salvage factor of i-th unit 3.1 VIRTUAL MAPPING PROCEDURE (VMP) [9] T length of the planning horizon (in stages) Convergence problems were encountered when N total number of different types of units implementing the standard RCMA-ES algorithm on the GEP FC fixed operation and maintenance cost of the units, problem. Investigation revealed the reason pertained to the $/MW sensitivity of capacity to changes in the decision vector. To illustrate, consider the range of the decision vector lies between MC variable operation and maintenance cost of the units, $ [0] and Umax,t as given in [6]. The capacity vector is [200 450 EENS Expected energy not served, MWhrs 500 1000 700]. Let a candidate solution be U1= [5 0 1 1 0]; then its corresponding capacity will be 2500 MW (5200 + 0450 + OC value of outage cost constant, $/ MWhrs 1500 + 11000 + 0700). If U1 changes to [5 0 1 2 0] (via mutation operators), then the capacity is increased from 2500 2.2 CONSTRAINTS MW to 3500 MW, a difference of 1000 MW, which is a large deviation. 1) Construction limit: Let Ut represent the units to be committed in the expansion plan at t-th stage that must So VMP is introduced to improve the effectiveness of the satisfy, RCMA-ES in solving the GEP problem. VMP is concerned with the solution representation; it transforms each combination of 0 Ut Umax,t candidate units for every year into a dummy decision variable, where, U is the maximum construction capacity of the max,t referred to as the VMP variable. The value of the VMP variable units at t-th stage. for a specific candidate solution is the rank of that solution when 2) Reserve Margin: The selected units must satisfy the all solutions are sorted in ascending order of capacity. For minimum and maximum reserve margin. example, the solution [5 0 1 1 0] with capacity of 2500 has VMP N value of 190. A change (by mutation) to VMP value of 198 1 Rmin Dt X t,i 1 Rmax Dt (9) would correspond to a solution of [2 1 2 0 1] with capacity of i1 2550, a relatively small change in capacity. Without VMP, to get where, a solution with capacity of 2550 MW, all 5 variable values must 402 ISSN: 2229-6956(ONLINE) ICTACT JOURNAL ON SOFT COMPUTING, OCTOBER 2012, VOLUME: 03, ISSUE: 01 be changed. This may take a very large number of iterations, and Stop if the range of the best objective function values of in general, moving from sub-optimal to optimal may take much the last 10 + [30n / λ] generations is zero. iteration. Stop if the standard deviation of the normal distribution Since five different types of units are assumed to be available is smaller than 10-12 δ(0) in all coordinates.