Super Capacitor Energy Storage Unit Research Articles

Power Advance Prediction to Improve the Energy Utilization Efficiency of Motor-Driven System Considering Multilink Time-Delay

In the motor-driven system, the utilization of a supercapacitor energy storage unit contributes to energy saving. However, the multi-link time-delay in the system makes the supercapacitor unable to immediately track and respond to the sharp change of motor power. This will cause the large DC bus voltage fluctuation, the peak current at the power grid side, and unnecessary energy loss. In this paper, a power advance prediction control strategy considering multi-link time-delay is proposed. The multi-link time-delay mechanism in the system is analyzed, in particular for the different conditions of motor power change. Afterward, with the motor speed, torque, and the inverter acceleration/deceleration rate obtained in advance, the motor steady power and power change rate are predicted. In the dynamic process, by adjusting the tracking rate in real time, the motor reference power function is derived. The reference current of the supercapacitor is given online, so as to match the power between the motor and the energy storage unit. Both simulation and experimental results verify the rationality and validity of the proposed control strategy. In the dynamic process, the system stability and energy utilization are successfully improved in comparison with multi-parameter collaborative power prediction control and double closed-loop control.

Multi-Time scale control framework of hybrid energy storage system via robust control and virtual impedance

Aiming at the problems of the strong randomness and fluctuation of the output power in photovoltaic power generation system, a multi-time scale control framework of hybrid energy storage system is proposed. Firstly, the complementary characteristics of charge/discharge between lithium battery and supercapacitor is analyzed. Then, The models of lithium battery energy storage unit and supercapacitor energy storage unit are established, respectively. Considering the different time scales of the output power response of lithium battery and supercapacitor, a short-time scale control framework is designed for supercapacitor energy storage unit based on the robust control, so that the bus voltage of system can be stable when the output power of photovoltaic power generation system changes or the load changes rapidly. At the same time, a long-time scale control framework is designed for lithium battery energy storage unit based on the virtual impedance, so that the voltage of the supercapacitor can be maintained within set value when the output power of the photovoltaic power generation system is stable. Therefore, the multi-time scale control framework can not only realize the large current charging/discharging for lithium battery and the power tracking at low frequency, but also realize the small current charging/discharging for supercapacitor and the power tracking at high frequency. Finally, the effectiveness of the proposed framework is verified by the simulation platform of photovoltaic power generation system.

High Voltage Ride through Control of PMSG-Based Wind Turbine Generation System Using Supercapacitor

Regarding PMSG-based wind turbine generation system, this paper proposes a supercapacitor energy storage unit (SCESU) which is connected in parallel with the DC-link of the back-to-back converter to enhance its high voltage ride through performance. The analysis of the operation and control for the grid-side converter and SCESU are conducted. Based on real time digital simulators (RTDS), a model and a Hardware-in-the-Loop (HiL) platform of PMSG-based wind turbine with SCESU is developed, and the simulation results show that the SCESU absorbs the imbalanced energy and the grid-side converter absorbs inductive reactive power during the period of voltage swell and verify the correctness and feasibility of the high voltage ride through control strategy.

Study on high voltage ride through control strategy of PMSG‐based wind turbine generation system with SCESU

Regarding PMSG-based wind turbine generation system, this study proposes a super-capacitor energy storage unit (SCECU) connected parallel to the DC-link of the back-to-back converter to enhance its high voltage ride through performance. The analysis of the operation and control for the grid-side converter and SCECU are conducted. Based on real-time digital simulators (RTDS), a model of PMSG-based wind turbine with SCECU is developed, and the simulation results show that the SCECU absorbs the imbalanced energy and the grid-side converter absorbs inductive reactive power during the period of voltage swell. The simulation results based on RTDS verify the correctness and feasibility of the high voltage ride through control strategy.

Research on frequency inertia response control strategy of SCESS‐DFIG system considering variable wind speed

The doubly fed induction generator (DFIG) has insufficient capacity to respond to the frequency inertia of the power grid due to the isolation between the rotor kinetic energy and the power grid by the generator-side converter. At the same time, the ‘source’ of the DFIG cannot be as stable as the thermal generator, so sudden changes in the wind speed on the ultra-short time scale can affect the system inertia. In this study, the inertia of a doubly fed wind generator with a super capacitor energy storage system (SCESS-DFIG) is defined from the standpoint of a single machine. Based on fuzzy logic controller, an inertia response control strategy of multi energy coordinated control is proposed. Then the SCESS-DFIG inertia response control strategy under variable wind speed is proposed at the wind field level. Based on the establishment of DFIG, DC bidirectional buck–boost converter, and supercapacitor energy storage unit model, a wind farm with three SCESS-DFIGs is simulated. When the grid frequency is dropped, the effectiveness of the proposed control strategy is verified by simulating their operation under the same rated parameters, different wind speed curves, and different initial voltages of the supercapacitors.

Application of a voltage compensation type active superconducting current controller to current limiting capability of power grid

This paper introduces a laboratory prototype of 800 V/30 A active superconducting current controller (SCC). The SCC has three main components, a series connected superconducting transformer, a controllable compensation voltage source, and a supercapacitor energy storage unit. To solve the issue of transformer magnetic saturation, an air-core superconducting transformer is adopted. The controllable compensation voltage source is composed of voltage source PWM converter and DC chopper, which control the amplitude and phase of the output voltage of SCC. The supercapacitor module is adopted to compensate the dynamic power during current control process. To evaluate the dynamic characteristic of the SCC, a series of experiments are carried out in the laboratory. With the energy storage support, the SCC can control the current level quickly and effectively, which can cooperate with the action of circuit breaker.

Computation of Ancillary Service Requirement Assessment Indices for Load Frequency Control in a Restructured Power System using SMES Unit and SCES Unit

To ensure a quality power supply the power system should not only match the total generation with total load and the associated system losses but also should emphasis better Ancillary Services. Even small disturbances to the power system can result in wide deviation in system frequency and quick restoration process are of prime importance not only based on the time of restoration and also should ensure stability limits. This paper proposes various design procedures for computing Power System Ancillary Service Requirement Assessment Indices (PSASRAI) for a Two-Area Thermal Reheat Interconnected Power System (TATRIPS) in a restructured environment. As simple conventional Proportional plus Integral (PI) controllers are still popular in power industry for frequency regulation as in case of any change in system operating conditions new gain values can be computed easily even for multi-area power systems, this paper focus on the computation of various PSASRAI for Two Area Thermal Reheat Interconnected Power System in restructured environment based on the settling time and peak undershoot concepts of control input deviations of each area. Energy storage is an attractive option to augment demand side management implementation, so storage devices like Super Capacitor Energy Storage (SCES) and Superconducting Magnetic Energy Storage (SMES) unit can be efficiently utilized to meet the peak demand. So the design of the Proportional plus Integral (PI) controller gains for the restructured power system without and with the storage units are carried out using Bacterial Foraging Optimization (BFO) algorithm. These controllers are implemented to achieve a faster restoration time in the output responses of the system when the system experiences with various step load perturbations. In this paper the PSASRAI are calculated for different types of possible transactions and the necessary remedial measures to be adopted are also suggested. If PSARAI based on settling time lies between 1 to 1.5 and if PSARAI based on peak undershoot is less than 0.2 distributed generation has to be incorporated and if the limit exceeds then the system becomes vulnerable and may result to black outs.

Research on Multiple Bi-Directional DC/DC Converter in Wind Power Flow Optimization and Control System

A kind of multiple bi-directional DC/DC converter used in supercapacitor energy storage unit of the wind power flow optimization and control system is analyzed and studied. Based on DSPs, the converter uses a double closed-loop control strategy to stabilize voltage and uses a digital parallel current sharing strategy to eliminate circulation current among each converter unit. In the paper, firstly, the working principle and the working process of the multiple bi-directional converter are analyzed in detail. Then, on the basis of the small signal model, the way to voltage stabilization and current balance are presented. Finally, a low power converter prototype is designed and made to carry on the experiment. The experimental results show that the proposed control strategies are feasible and effective. So the multiple bi-directional DC/DC converter designed in the paper has comparatively high practicable value in the wind power flow optimization and control system.