There is a big potential of wide application of power electronic-based embedded converter systems (e.g. static synchronous compensator, battery energy storage system, active power filter). An optimized integration of aforementioned features can provide extensive functionality covering the following areas:
- Grid connection of renewable energy sources
Wind power plants (especially offshore) are nowadays connected to the grid at remote locations, far from the main consumption centers. Active and reactive power control in battery energy storage systems assures robust operation and grid stability dynamically contributing to voltage and frequency control. It supports simultaneously the grid as well as the wind power plant, partially decoupling the dynamics of both.
- Wind fluctuation balancing and Load support
Wind power is stochastic in nature. Active power from wind turbines, when set to maximum power point tracking, can therefore only be predicted subject to the accuracy of the forecasted wind. Likewise, there is continuous variation of the load demand. Any power system unbalance resulting from the variation of generation and/or load affects the system operation and leads as frequency variations. Battery energy storage systems can store energy from wind when there is excess generation and low demand and release the stored energy during periods of low generation and high demand. Moreover, battery energy storage systems can smoothen out fast ramping up/down of the wind power generation due to sudden fluctuations in the wind velocity. Thus, battery energy storage systems enable to optimize the mission profile and enable more predictable and reliable operation of the whole power system, including the wind power plant.
- Reserve capacity
Battery energy storage systems can reduce the number of on-line generators in the system. It can provide the grid with the reserve capacity that is normally subject to limitations on power plant utilization. Battery energy storage systems serves as a dynamic power source. It can continuously support the grid with reactive power, and in the event of loss of generation, battery energy storage systems can supply active power into the grid until the grid is reconfigured (limited by the energy capacity and state of charge of the battery energy storage system).
- Ancillary services
With higher and higher penetration of renewable energy sources, ancillary services to support the power system are becoming increasingly important, e.g. fast frequency response, virtual/synthetic inertia response, power oscillation damping. Frequency regulation service is often provided by generators having the spinning reserve when they are dispatched below their maximum output level. Battery energy storage system installation providing continuous grid support, such as for voltage control, supplies short-time real power at the lowest cost, thus making it the most attractive supplier.
- Emergency power
In the event of a blackout, wind power plant internal/local loads and power system sensitive loads such as hospitals or power distribution areas, can be fed by a battery energy storage installation until emergency generators are started.
- Black start
As the penetration of renewable energy sources increases, and as old thermal generation plants are phased out, there is an obvious need for new black start equipment in the power system grid. Battery energy storage systems can support generators that lack inherent black start capability. Battery energy storage systems can supply the power needed for safely controlled black starts. It keeps the frequency within range and controls the voltage throughout start-up.
- Active filtering
Many modern industrial processes are, by nature, detrimental to power quality. At the same time, grid code requirements are becoming more stringent to address sensitive power electronic-based plants/loads. The modular multilevel converters have a high effective control bandwidth. This property can be used for active filtering of harmonics that are already present in the grid to compensate non-linear plants and improve the quality of power, as the power electronic interface in battery energy storage systems can inject harmonic currents into the grid with proper phase and amplitude to counteract the harmonic voltages. Furthermore, harmonic propagating through the system can be utilized to charge a battery energy storage system and consequently convert harmonics into the fundamental frequency.