In today's society to the energy and power supply quality and safety and reliability requirements more and more high, the traditional large power supply because of its defect itself cannot have satisfied the requirements. Can integrate the new grid of distributed generation micro grid arises at the historic moment, it can save investment, reduce energy consumption, improve the system security and flexibility, is the development direction of the future. Capacitance as essential in micro grid energy storage system, plays a very important role. Super capacitor as a new type of energy storage device, with its irreplaceable advantage, become a micro grid (Microgrid) one of the energy storage device of choice.

What is a super capacitor?

Super capacitor (super capacitor), also called the electric Double Layer capacitor (Electrical Double Layer capacitor), gold capacitance, farah capacitance. Is between conventional capacitors and rechargeable batteries of a new type of energy storage element. Its capacity can reach hundreds to thousands of law. More than l0 times that of battery power, storage capacity is higher than normal capacitors, has a wide working temperature range, can fast charge and discharge, long cycle life, no pollution, zero emissions, etc.

Super capacitor for electric double layer structure, the activated carbon electrodes and the electrolyte is a space between the distributed structure, can be used multiple capacitor series parallel description of the characteristics of super capacitor.

In super capacitor Banks charge and discharge process, voltage range change is big, usually DC/DC converter as an interface circuit must be used to adjust the super capacitor energy storage and release can. DC/AC converter can adopt the bidirectional DC/AC inverter, or the use of AC/DC rectifier and DC/AC inverter. Super capacitor energy storage system in parallel on bus or feeder in micro grid.

Super capacitor energy storage system using multiple sets of super capacitor energy in the form of electric field can be stored, when energy emergency lack or need to. To release the energy will be stored by the control unit, a fast the active and reactive power compensation system, so as to realize the balance and stability of power control. The advantages of super capacitor itself makes it when applied in the distributed generation, in with the rest of the way of competing with each other.

The composition of the super capacitor

Common super capacitor is composed of three ways: series mode, parallel mode and string and hybrid mode. Series of super capacitor component: due to the working voltage of capacitor monomer is not high, can't cover demand scope, the operating mode of the applied voltage in series to meet the application needs to be more monomer working voltage requirement, but because of the inherent differences between monomer capacitor in series on the components of total voltage is not evenly distributed to different capacitors, it can lead to voltage distribution asymmetry.

In parallel of ultracapacitors: construction of the super capacitor component can output in parallel way or accept a large current. In the process of charging, the charging series resistance ensure monomer, the voltage distribution between the intrinsic to the super capacitor charging the amount of resistance is a dynamic, have certain dispersion, to adjust the resistance change control circuit is extremely complex, difficult point control. Control in the process of discharge, discharge resistance, can obtain very high output power, but in order to avoid excessive discharge current, ensure licensing power output, to appropriate control component of energy storage.

String and hybrid super capacitor component: the advantages of the combination of series and parallel way, avoid their deficiency in one of two ways. Each capacitor are specified a resistance voltage control the charging process. In the new hybrid system of crane is described in this article, the combination of the super capacitor used using series and parallel hybrid way of connection form.

The super capacitor in the application of the micro grid

Micro power grid by micro power supply, load, energy storage and energy manager, etc. Energy storage in the form of a micro power grid works are: on the micro power dc bus, contain important load on the feeder or micro power grid communication on the bus. Among them, the first two can be called a distributed energy storage, finally called the central storage.

When parallel operation, micro grid power fluctuations by large power grid in balance, energy storage in charge standby state at this time. When micro power grid by the parallel operation to switch to the isolated net running, the central storage started immediately, make up for the power gap. Micro power grid of the isolated net running load fluctuations or micro power source can be determined by the central storage or distributed energy storage balance. Among them, there are two kinds of micro power source power fluctuation in the balance, will need a distributed energy storage and energy storage of micro power supply and connection on a feeder, or direct access to energy storage on the micro power dc bus.

1. To provide short-term power supply

Micro grid, there are two kinds of typical operation modes: under normal circumstances, the micro grid with conventional parallel operation of distribution network is called parallel operation mode; When they tested the grid fault or power quality does not meet the requirements, the micro grid will promptly with grid disconnection to run independently, referred to as the isolated net running mode. Micro grid often need to absorb part of the active power from the normal distribution, and micro power grid from the grid pattern to the isolated net pattern transformation, there will be a power gap, installation of energy storage equipment to help the smooth transition of the two models.

2. Used as energy buffer device

Due to the smaller micro power grid, the system of inertia is not big, often happens for network and load fluctuation is very serious, affect the stability of the whole micro power grid operation. We always expect micro power grid efficient generator (such as fuel cells) always work under its rated capacity. But not all of micro power grid load remains the same, on the contrary, it can change with the change of the weather, and so on and so forth. In order to meet the peak load of power supply, must use the peak load of fuel, gas peak shaving plant for adjustment, because of the high fuel prices, this way of operation cost is too expensive. Super capacitor energy storage system can effectively solve the problem, it can be stored in the load is low excess electricity power supply, and during the peak load back to the grid to adjust power demand. The super capacitor characteristics of large power density, high energy density makes it the best choice for dealing with peak load, and using the super capacitor storage and peak load considerable energy.

3. Improve the micro grid power quality

Energy storage system to improve the micro grid power quality has played a very important role. Through the inverter control unit, can adjust the super capacitor energy storage system to the user and network to provide reactive power and active, so as to achieve the aim of improving power quality. Due to super capacitor can be rapidly absorbed, release the power electricity, very suitable for the application to the micro grid power quality control device, is used to solve some transient problems in system, such as for system failure caused by instantaneous power, voltage surge, the problem such as voltage sag, the use of super capacitor provides a quick power buffer, absorb or supply power, provide active power support for active or reactive power compensation, at a steady, smooth power grid voltage fluctuations.

4. Optimization of micro power supply operation

Green energy such as solar energy, wind energy, often with non-uniformity, power output is easy to change. It will need to use a buffer to store energy. As a result of these energy to produce electricity output may not be able to meet the demand of micro power grid peak power, therefore, energy storage device can be used in a short period of time for peak power, until the output increases, reduced demand. The right amount of energy storage in DG unit can not be normal operation under the condition of transition role. Such as the use of solar power at night, the wind power in the case of no wind, or other types of DG units are in the maintenance period, then the system energy storage can transition role.

In the process of energy generation is stable while demand is constantly changing circumstances, also need to use energy storage device. By moving the excess energy stored in the storage device, can in a short period of time through the peak value of energy storage device to provide the required energy.