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Comparison of Metro Energy Storage Methods - Super Capacitor Energy Storage

Author: Source: Datetime: 2016-11-24 15:19:07
Urban rail transit system, its operating conditions are characterized by frequent start and braking, start consuming a lot of power grid, while the brake will generate considerable regenerative power and energy storage batteries. In general, the subway vehicle braking energy generated when the traction energy consumption accounts for about 40% to 50%. This part of the energy feedback back to the grid, about 30% to 50% (with the departure interval and other factors related to the use of adjacent trains). As the traction substation rectifier diodes do not control the rectifier, the energy can only flow in one direction, not being the use of temporary vehicles will lead to increased traction power network pressure, endangering the safety of electrical equipment.
Super Capacitor Energy Storage
At present, regenerative braking energy recovery technology mainly includes resistance dissipation type, inverter feedback type and energy storage type. Among them, the dissipation type is the regenerative braking energy in the form of thermal energy through the braking resistor is consumed, which is commonly used at home and abroad, this braking method in the vehicle braking, the locomotive kinetic energy into electrical energy Consumption in the resistor, the heat dissipation into the atmosphere caused the temperature energy storage batteries inside the tunnel and the station, the regenerative braking energy is not re-used, resulting in energy waste, and low-speed braking effect is poor, need to ensure that the locomotive has enough Ventilation, so do not make a detailed comparison.
Comparison of Metro Energy Storagepng
Inverter feedback type is the braking energy inverter through the inverter and the grid, the power supply network to use other electrical equipment. Energy storage is the braking energy stored through the bi-directional converter in the energy storage batteries devices, including batteries, flywheels and super capacitors.

Inverter feedback type

Regenerative braking energy inverter feedback system mainly uses the power electronic power module IGBT to constitute the high-power three-phase inverter, the DC side of the device is connected with the DC busbar of the traction power grid, and the AC side is connected with the AC grid. When the train braking energy causes the DC voltage of the traction power grid to exceed the set value, the regenerative braking energy regenerating solar power generator starts and absorbs the electric energy from the traction grid and feeds the electric energy back to the alternating current network for use by other loads.

Regenerative braking energy inverter feedback device using high frequency power electronic switching device IGBT inverter has a harmonic content of small, flexible control method and dynamic performance advantages. Regenerative braking energy feedback scheme based on PWM grid-connected inverter can stabilize the DC-side voltage in regenerative braking of locomotives.

Specific advantages are as follows

1, AC grid side using inductive filter, there is no commutation voltage distortion, and the AC current harmonic content is small, light pollution on the grid. Network power factor is high, and not because of changes in power feedback, can reduce the reactive power compensation equipment investment.

2, the power transistor switching frequency is relatively high, the filter volume capacity can be designed to be smaller, the filter loss is small, and fast dynamic response.

3, make full use of the regenerative braking energy of the subway train, improve the regenerative braking energy utilization efficiency, energy saving effect, but also reduce the locomotive braking resistor capacity. Solar power generator energy directly back to the grid, not to configure the energy storage components, and do not absorb the resistance, so a small impact on the ambient temperature.
Supercapacitor Project for Renewable Eneergy Storage
Specific shortcomings are as follows

1, the feedback to the grid of the alternating current although the harmonic content is small, but the existence of the harmonics of other electrical equipment will have a certain impact.

2, back to the grid of electricity, although the effect can be achieved by repeated use, but because there are losses in the transmission line, solar power generator can not reach the maximum energy conservation.

3, inverter feedback device circuit structure is complex, high maintenance costs.

4, the inverter feedback device in the transformer is always connected to the grid, resulting in a larger no-load loss.

5, power back to the grid, should the coordination with the grid side properly, will generate a second tariff calculation, making the subway side to bear more electricity costs.

Super capacitor energy storage type

Super capacitor energy storage regenerative braking energy absorption utilization system includes two-way DC converter and super capacitor energy storage system in two parts, and then connected to the subway train DC power supply bus.

When the subway train braking, the DC bus voltage increases, the bi-directional DC converter to the super capacitor array charging, super capacitor array to absorb the braking energy;

When the subway train starts, the DC bus voltage drops and the energy stored in the supercapacitor array discharges energy through the bi-directional DC-converter.

Working principle:

1, when the subway vehicle regenerative braking, the DC traction power grid voltage, control circuit control bi-directional DC / DC converter main circuit work in the Buck circuit mode, DC traction power grid and super capacitor solar energy storage system connected to charge . The super capacitor group absorbs regenerative braking energy while reducing the DC traction grid voltage.

2, when the subway vehicle is in acceleration or start conditions, the DC traction power grid voltage will be pulled down, this time the controller to control the two-way DC / DC converter work in Boost circuit mode, super capacitor solar energy storage system and DC traction power grid , The super capacitor group through the boost inductor to the energy feedback network. Under this condition, the super capacitor energy storage system put into use, reducing the peak solar power generator of the power supply system requirements, so that the DC voltage drop traction network has been eased.

3, when the subway vehicle idle line, the controller can be super-capacitor group capacity, control bi-directional DC / DC converter main circuit of the super-capacitor group to adjust the energy storage state.

Supercapacitor array consists of a large number of supercapacitor cells connected in series and parallel, which is the energy storage unit of the super capacitor solar energy storage system, realizing the dual purpose of energy storage and stabilizing the DC traction power grid voltage. As the DC traction grid voltage is raised, the supercapacitor array carries out energy storage; when the DC traction grid voltage is pulled low, the supercapacitor array feeds back energy to the traction grid.

The specific advantages of super capacitor energy storage device

1, super capacitor energy storage device, simple structure, no additional transformer and other devices, less energy consumption components, energy consumption, easy installation and maintenance costs less.

2, the use of super-capacitor energy storage device, the brake energy conversion of energy stored directly in the super capacitor, no energy back to the grid, will not cause pollution or shock to the grid.

3, the power stored directly in the super capacitor, the subway starts, the super capacitor full discharge, the stored energy can be all released, to achieve the greatest energy saving effect.

4, the use of super-capacitor solar energy storage system devices, can enhance the contact voltage, to reduce the contact voltage fluctuations, reducing the DC bus energy loss.

In the beginning of the super capacitor energy storage device, because of the high price of super capacitor, resulting in higher cost, but with the super capacitor research and production, super capacitor cost is declining, so this shortcoming is not And then become a super capacitor solar energy storage system device defects.
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