Energy is among the crucial basic materials for developing a national economy and improving people’s living standards. Due to both population increases and modern economic development, overall energy demand has increased and caused a depletion of traditional fossil fuel reserves, which can lead to energy shortages. In addition, pollution from the utilization of traditional fossil fuels is also becoming more serious, leading to acid rain, the greenhouse effect, increased concentrations of Particulate Matter (PM
2.5), and haze. Therefore, the development and utilization of renewable energy is imperative. In 2002, CERTS (Consortium for Electric Reliability Technology Solutions) proposed the microgrid (MG) concept, which has been closely examined by governments and laboratories because of its flexible control and high power supply reliability [
1,
2,
3]. MGs cover a variety of Distributed Generation (DG) systems, both uncontrollable power sources (such as wind turbines (WT) and photovoltaics (PVs)) and controllable power supply sources such as diesel generators. MGs are regarded as platforms for clean energy to access the power grid and can also lead to the flexible and economically improved operation of a power system. MGs can make a large power grid become more economical and stable [
4,
5]. Therefore, it is of great significance to optimize the capacity of DG for the sake of safe and stable MG operation [
6]. The common methods to optimize the capacity of MG systems are as follows: using HOMER software Pro Version 3.9.1 (HOMER Energy, Boulder, CO, USA) [
7], using a mixed integer linear programming (MILP) model [
8], or using optimization algorithms, such as particle swarm optimization (PSO), a genetic algorithm (GA), a differential evolution (DE) algorithm, etc. Using HOMER software to solve the problem is simple and convenient but the regional adaptive ability is poor, so it cannot be widely promoted. As a classical programming model, the MILP model is theoretically suitable for solving arbitrary integer programming problems, however, its design is cumbersome and computationally expensive, and it will consume too many computing resources. The various optimization algorithms proposed in recent years have shown good performance in solving complex problems but the defects of the algorithms are inevitable. So it is necessary to improve the algorithms according to different application scenarios. For the operation scenarios of an MG system in different seasons, an improved DE algorithm is proposed in this paper and analyzed according to how different scheduling strategies use it, in order to grasp the internal rules of each device running state in various scenarios.
The optimization of microgrid DG capacity allocation is a typical optimization problem [
9,
10,
11]. According to the parameters and structure of the model, most of the investigations in the literature have used optimization algorithms, which can be roughly divided into genetic algorithms (GA) and particle swarm optimization (PSO) algorithms. The authors in [
12] proposed an improved PSO algorithm: weights and learning factors change with respect to iteration numbers in order to solve the capacity distribution problem of an MG containing wind turbines, PV, diesel generators, diesel generators, and electric vehicles (EV). The EV in the MG of [
12] was used as a portable energy storage device. However, the EV, as an uncontrollable energy storage device, is greatly affected by user behavior and cannot stably supply power like batteries. Reference [
13] established a dynamic multi-objective optimization model to reduce MG costs and pollution emissions and used the PSO algorithm combined with quorum sensing (QS). The influence of climatic conditions on the optimization results was not considered and the calculation of real-time dynamic scheduling was too large. Reference [
3] discussed a real-time energy management system, optimizing MG real-time performance and applied the binary PSO algorithm for optimization. The authors in [
14] used the PSO algorithm to solve the optimal power dispatch problem considering load uncertainties and the probabilistic modeling of generated power. However, the objective function does not take into account environmental costs. Reference [
15] raised a dynamic economy and control method for an islanded microgrid in which a diesel generator and energy storage battery acted as the main power source with respect to the system power fluctuation and a GA was used to solve the problem. The original GA encoding and decoding process takes a lot of time and is not suitable for solving dynamic economic dispatch problems. Reference [
16] combined the GA and bacterial foraging algorithm (BFA) to solve the problem of dynamic economic allocation. The GA was applied in the behavioral tendency stage of the BFA to modify the parameters. The objective was to minimize the overall production cost and verify the effectiveness of the algorithm in different test systems. But this literature does not consider renewable sources and does not fit the current development of energy. However, these methods are not limited to only the PSO algorithm and GA. For example, in order to address the uncertainty of renewable energy and MG demand, a model predictive control (MPC) strategy was proposed in [
17]. However, the existing algorithms are mainly applicable to slow dynamic process and environments, which limits their promotion in a wider range of applications and applications. Hourly planning ahead was formulated according to not only weather forecasting information but also to grid network topology and power flow constraints. As an evolutionary algorithm, the DE algorithm has advantages of less adaptive parameters, easier programming, and a faster convergence rate [
18]. The variation and cross-operation of the standard DE algorithm are all stochastic and easily fall to the local optimal point when the dimension of variable decisions is high. Here, there still exists the potential to improve the DE algorithm in aspects of convergence speed and local optimum avoidance. To overcome these shortcomings, some researchers carried out improvement strategies for the DE algorithm. For example, the authors in [
19] proposed a new crossover strategy based on eigenvector decomposition. They decomposed the correlation coefficient matrix of individuals to obtain the eigenvectors and eigenvalue matrix. The individuals who go through the crossover operation are multiplied by eigenvectors according to the method of probability selection. In [
20], the efficiency of the DE algorithm was improved by monitoring the midpoint of population. In this paper, the improvement of the DE algorithm proceeds mainly from the following aspects: parameter control strategy, new crossover strategy, elite retention strategy [
21], and multi-population strategy. Simulation results showed that the improved DE algorithm not only improved the convergence speed but also greatly improved the precision, minimizing the impact of stochastic factors.
In most of the existing literature, despite so much research having dealt with solutions, there is little research on scheduling strategies, so this paper studies the impact of different scheduling strategies on the capacity optimal allocation of grid-connected MG. There are both energy storage and grid in an existing grid-connected MG. So when the energy generation sources are not enough to meet the demand of power load, giving priority to the grid or energy storage is a problem to be studied. In this paper, the scheduling strategies of wind-PV-energy storage-grid-diesel and wind-PV-grid-energy storage-diesel are proposed in view of the priority of the grid and energy storage and the optimization results of the two strategies under four typical days in four seasons are analyzed. At the same time, a SMG model which considers the total investment cost and environment protective cost as the objective function is established and the constraints of each DG operation in SMG are fully considered to guarantee the proper, safe, and economical operation of SMG. The MPDE with dominant population (DP) was adopted to improve the convergence speed of the algorithm.