Reduction of Energy Storage Requirements in Future Smart Grid Using Electric Springs



The electric spring is an emerging technology proven to be effective in i) stabilizing smart grid with substantial penetration of intermittent renewable energy sources and ii) enabling load demand to follow power generation. The subtle change from output voltage control to input voltage control of a reactive power controller offers the electric spring new features suitable for future smart grid applications. In this project, the effects of such subtle control change are highlighted, and the use of the electric springs in reducing energy storage requirements in power grid is theoretically proven and practically demonstrated in an experimental setup of a 90 kVApower grid.Unlike traditional Statcom and StaticVar Compensation technologies, the electric spring offers not only reactive power compensation but also automatic power variation in non-critical loads. Such an advantageous feature enables noncritical loads with embedded electric springs to be adaptive to future power grid. Consequently, the load demand can follow power generation, and the energy buffer and therefore energy storage requirements can be reduced.


  1. Distributed power systems
  2. Energy storage
  3. Smart grid
  4. Stability




Fig. 1. Experimental setup based on the 90 kVA Smart Grid Hardware Simulation System at the Maurice Hancock Smart Energy Laboratory.


Fig. 2. Measured rms power line voltage (vs) and non-critical load voltage (vo)

Fig. 3. Measured average powers of the wind power simulator (PG+PR), battery storage (PS) and non-critical load(P1)

Fig. 4. Measured power (Ps) and energy change (Es) of the battery storage.

Fig. 5. Measured electric spring reactive power (QES), critical load voltage (VR2) and power (P2).


In this paper, the differences between the output voltage control and the input voltage control of a reactive power controller are highlighted. While energy storage is an effective but expensive means to balance power supply and demand, an analysis and practical confirmation are presented to show that electric springs can reduce energy storage requirements in a power grid. Electric springs allow the non-critical load power to vary with the renewable energy profile. By reducing the instantaneous power imbalance of power supply and demand, electric springs allow the non-critical load demand profile to follow the power generation profile and reduce the energy storage requirements in power grid. This important point has been theoretically proved and practically verified in an experimental setup. Due to the advantageous features such as enabling the load demand to follow the power generation, the reduction of energy storage requirements, the reactive power compensation for voltage regulation, and the possibility of both active and reactive power control [28], electric springs open a door to distributed stability control for future smart grid with substantial penetration of intermittent renewable energy sources.


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Grid-Connected PV Array with Supercapacitor Energy Storage System for Fault Ride Through


A fault ride through, power management and control strategy for grid integrated photovoltaic (PV) system with supercapacitor energy storage system (SCESS) is presented in this paper. During normal operation the SCESS will be used to minimize the short term fluctuation as it has high power density and during fault at the grid side it will be used to store the generated power from the PV array for later use and for fault ride through. To capture the maximum available solar power, Incremental Conductance (IC) method is used for maximum power point tracking (MPPT). An independent P-Q control is implemented to transfer the generated power to the grid using a Voltage source inverter (VSI). The SCESS is connected to the system using a bi-directional buck boost converter. The system model has been developed that consists of PV module, buck converter for MPPT, buck-boost converter to connect the SCESS to the DC link. Three independent controllers are implemented for each power electronics block. The effectiveness of the proposed controller is examined on Real Time Digital Simulator (RTDS) and the results verify the superiority of the proposed approach.


  1. Active and reactive power control
  2. Fault ride through
  3. MPPT
  4. Photovoltaic system
  5. RTDS Supercapacitor
  6. Energy storage




Fig.1. Grid connected PV system with energy storage



Fig.2. Grid voltage after three phase fault is applied


Fig.3. PV array power PPV with SCESS and with no energy storage


Fig.4. Grid active power Pg for a three phase fault with and without energy storage


Fig.5.SCESS power PSC for the applied fault on the grid side


Fig.6. Grid reactive power Qg during three phase fault


Fig.7. DC link voltage for the applied fault


Fig.8. PV array voltage VPV during three phase fault


Fig.9. MPPT output voltage Vref for the applied fault


This paper presents grid connected PV system with supercapacitor energy storage system (SCESS) for fault ride through and to minimize the power fluctuation. Incremental conductance based MPPT is implemented to track the maximum power from the PV array. The generated DC power is connected to the grid using a buck converter, VSI, buck-boost converter with SCESS. The SCESS which is connected to the DC link controls the DC link voltage by charging and discharging process. A P-Q controller is implemented to transfer the DC link power to the grid. During normal operation the SCESS minimizes the fluctuation caused by change in irradiation and temperature. During a grid fault the power generated from the PV array will be stored in the SCESS. The SCESS supplies both active and reactive power to ride through the fault. RTDS based results have shown the validity of the proposed controller.


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