Performance Analysis and Application of Superconducting Magnetic Energy Storage in a Power System

Abstract

Delivering an adequate amount of power to electrical equipment is being a tough job due to the continuous upgradation and technological advancement in the equipment. One of such familiar challenging technology adapted nowadays in power system for some specific applications is termed as pulsed power technology. The electrical grid with pulsed power loads is of the significant interest in aerospace and marine applications. Keeping in the mind of pulsed power applications, especially in defence sectors, the Superconducting Magnetic Energy Storage (SMES) system is proposed for a smooth and reliable power flow in the grid. In SMES system, the PCU interfaces the SMES magnet and the AC system in order to give an efficient power exchange and high quality power flow. Power Converter Unit (PCU) of the SMES system consists of a bidirectional DC-DC converter and a three-phase Voltage Source Inverter (VSI) coupled with a common DC-link capacitor. The control schemes employed for both the VSI and DC-DC converter is intended to maintain a constant DC-link voltage. Particularly, the voltage across the DC-link capacitor is tightly regulated using a Dynamic Evolution Control (DEC) strategy instead of a PI controller for the DC-DC converter. Consequently, the DC-link voltage is maintained almost constant with a voltage regulation well below ±10% during a Pulsed Power Load (PPL) condition.
Initially, the performance of the SMES system using a Leaky Least Mean Square (LLMS) control algorithm is compared with that using a Synchronous Reference Frame (SRF) control technique. The comparison is presented to show the effectiveness of the SMES system for power quality improvement. Henceforth, the control scheme for the VSI is proposed based on the Modified SRF (MSRF). Similarly, DEC or PI control strategy is employed to generate appropriate switching pulses for the DC-DC converter. It has been observed that the PI in the inner loop of MSRF is found sluggish during the PPL. Thus, PI is replaced by the DEC scheme to provide a fast response to the PPL. Also, the DC-DC converter employs the DEC instead of a PI in order to achieve a less rippled coil current and uniform voltage distribution across the SMES coil irrespective of load profile. Consequently, it ensures a reduced and acceptable AC loss across the SMES system, and a symmetric voltage distribution across the coil. Moreover, the control performance of the DEC scheme is compared with that of the Proportional-Integral (PI) control technique.
A uniform source current and power with minimum variations is maintained irrespective of the pulsed power load. A detrimental high rating stress on the system due to the load is substantially reduced by the proposed system. The DEC scheme is implemented for tight error regulation of the controlling parameters. The system supply current is found almost balanced, and its Total Harmonic Distortion (THD) is found well below 5%. An effective PPL compensation and a symmetric and uniform voltage distribution across the SMES coil, are achieved due to the precise solid-state control. Nevertheless, it has been seen that the SAPF is incompetent under high PPL demands whereas the SMES system has shown excellent performance under such load conditions. Moreover, a comparative analysis has been made between the conventional SAPF and the SMES system under PPL and Nonlinear Load (NL) conditions, to check the effectiveness of the SMES system. The performance of the proposed system is presented by using Sim Power System (SPS)/MATLAB Simulink, and real-time digital simulator (i.e. Opal RT-Lab/ dSPACE-1104).