Power Electronics Loads Considering Response Cost
In an islanded microgrid where the distributed generators (DGs) capacities are not very large and their output powers are fluctuating, a large capacity installation of energy storage system (ESS) is not ideal method due to its high price. Load control is a preferred control for supply and demand balance. At present, many load controls based on central management system have been proposed to achieve supply and demand balance according to the load capacities or price. However, these existing schemes are not suited for islanded microgrids without central controller. This paper proposes an autonomous control of flexible power electronics loads (FPELs), whose objective is to make the FPELs to automatically participate in supply and demand balance and reduce the response cost with various response prices taken into consideration. Therefore, the proposed control scheme can retain advantages of the traditional distributed load control schemes, while can keep in lower response cost. The effectiveness of the proposed control has been validated via Matlab simulations in islanded microgrid.
SIMULATION VERIFICATIONS
MATLAB/Simulink simulation was used to verify the performance of the proposed control scheme. The microgrid is assumed to be composed of two DG units, one ESS, two fixed loads and two FPELs. The power ratings of two DGs, ESS and two FPELs are 1.5kW, 3kW and 0.725kW, respectively. The detailed circuit and control parameters of simulated system are listed in Table I. With this setup, two cases were considered to test the effectiveness of the proposed control scheme: FPELs participate in the supply-demand balance based on their response capacity and their response cost. Code Shoppy
A. Based on response capacity In this case, the fixed loads and FPELs were connected to PCC at first, where the FPELs were under the traditional load control scheme based on the response capacity. Since the DG units and ESS power generation capacity are more than the loads demand, it can be seen that the DGs and ESS can share the loads, and the FPELs can maintain their normal operation from Fig. 5. At t = 0.4s, fixed load2 was turned on. The total load demands were more than the DGs power generation capacities, the microgrid was therefore in heavy load condition and the ESS must output more power to meet the loads demand, as shown in Fig.5 (a) and (b). Click Here In this case, the FPELs were switched to autonomous control scheme along with the frequency declining and autonomously participated in the supply-demand balance based their response capacity, as shown in Fig. 5 (c). From Fig. 5 (c)-(e), it can be seen that the FPELs can equally share the supply-demand imbalance due to the same response capacity. The microgrid can maintain stable, as shown in Fig. 5 (f)-(g). In this case, the total response cost is 320 units.
B. Based on response cost The simulation was tested again to verified the proposed control scheme, where the FPELs were under the autonomous control based on the response cost. Before t = 0.4s, the simulation results shown in Fig. 6 are same as the case A as shown in Fig. 5. After t = 0.4s, with the connection of fixed load2, the frequency was lower than the preset threshold fLower, as shown in Fig.6 (f). With the local frequency measurement, FPELs were switched to autonomous control scheme and autonomously reduce their power consumption to participated in the supply-demand balance based their response cost, as shown in Fig. 6 (c)-(e). From Fig. 6 (c), it can be seen that the FPEL2 reduced more power consumption than the FPEL1 due to the lower response cost. Therefore, the total is 270 units, which is lower than the response cost in the case A.
Power Electronics 