Battery storage systems can act as a buffer between multiple power sources and stable power demand, increasing the capacity and legal quality of unstable power sources such as wind and solar. Can also be used for general grid peak power distribution of the user and the valley when the price of electricity in the form of direct current (dc) stored in the battery matrix (pile), time to peak electricity price, again with power frequency (50 hz) to all electrical appliances and electricity output, high prices on time using the time electricity at a lower price, the price difference is poor peak valley energy storage power saving benefits.
Transformer and high voltage switchgear
Convert the grid voltage (10KV, 6KV or other levels) from the grid to the voltage level required by the user's electrical appliances and power consumption (such as 0.4kV)
Low voltage switch and control cabinet
Used for charge and discharge and power output control and management
Control system
The battery energy storage system is controlled by programmable logic controller (PLC) and man-machine interface (HMI). One of the key functions of PLC system is to control the charging time and rate of energy storage system. For example: PLC can receive the real time data of electricity price, and according to the maximum allowed electricity demand, charging state and peak/off-peak price comparison, decide how to quickly recharge the battery system. This decision is dynamic and can be optimized on a case-by-case basis. It is integrated with the rest of the system through standardized communication inputs, control signals, and power supply. It can be accessed by dial-up or the Internet. It has multiple layers of defense to limit access to its various functions and provides customized reporting and alerting capabilities for remote monitoring.
Power Conversion System (PCS)
The power conversion system functions to charge and discharge batteries and provide improved supply quality, voltage support and frequency control to the local grid. It has a complex and fast action, multi-quadrant, dynamic controller (DSP) with a dedicated control algorithm that can convert the output over the entire range of the device, i.e. from full power absorption to full power output in cycles. At present, bi-directional inverters are usually used.
Battery matrix (stack)
A battery matrix (stack) is composed of a number of single cells.
Battery energy storage system can be used to save the fixed equipment investment of power grid system. Improve the utilization rate of power grid equipment and reduce the use cost of end users.
Other important advantages that an energy storage system can achieve in a TD system include:
Service reliability and power quality are improved by reactive power compensation and voltage regulation.
Peak cutting, storage, and storage Power is sold at peak times, thereby reducing the market risk of peak price fluctuations and controlling the high cost of energy imbalances;
Reduce line loss by local power supply, power factor correction and voltage adjustment;
Reduce line congestion and provide smooth passage in the bottleneck part of energy supply;
Basic users can realize the use of valley power during peak demand, increasing the use value of equipment and capacity expansion.
Peak peel
The energy storage system can reduce the peak energy load of users at the distribution end, which will promote the utilization of grid equipment and meet the end customer demand. The load coefficient of power grid is improved.
The smart grid
Smart grid is an important part of future developed power grid management system, and energy storage technology has a huge market space in it.
In terms of investment and power quality, there are generally two modes:
1, all adopt during peak power output, the model of cell matrix size and output inverter is large, the storage energy is also the largest, the electrical energy stored in batteries matrix to meet the peak period of all the electricity, energy storage power station system during peak to use all appliances and electricity output of electricity shall be borne by the valley of stored energy, The power frequency electric energy connected by the grid is only used as charging power and backup power. This mode has the largest peak-valley difference energy saving benefit, but the investment is also the largest, and because of all the output to electrical appliances and electricity is PWM waveform, so the power quality management requirements are the highest. This is called A mode.
2. The electric energy output at peak time is jointly undertaken by the electric energy stored at peak time and the power frequency electric energy connected to the power grid, that is, the power frequency electric energy connected to the energy storage power station system and the power grid is connected in parallel to output the required electric energy to the electrical appliance and power consumption during peak time. In this mode, the battery matrix size and output inverter are smaller than that of mode A (e.g. 50%), and the energy storage is also relatively small (e.g. 50%). The energy stored in the battery matrix only needs to meet the part of the peak power consumption (e.g. 50%). The peak-valley difference energy saving benefit of this mode is smaller than that of MODE A, but the investment is also small, and because all the electric energy output to electrical appliances and power consumption is the superposition of PWM waveform and power frequency of the grid, so the requirements for power quality management are relatively low. This is called B mode.
In addition, there are also two sub-models in terms of investment and battery matrix scale:
3, a charge pattern, the pattern of the battery matrix size is larger, the storage energy is also big, the electrical energy stored in batteries matrix can satisfy all the time except at valley when the electricity, energy storage power station system in the valley of a stored energy, enough during peak hours when peace time to use electrical output power and power consumption. In this mode, the peak-valley difference energy saving benefits are relatively large, but the investment is also relatively large. Here, the combination of the seed mode and A mode is called A1 mode, and the combination of the seed mode and B mode is called B1 mode.
4, secondary charging mode, the model of the relatively small size battery matrix, the energy storage energy is also small, the electrical energy stored in batteries matrix only meet in the morning peak period of electricity can, energy storage power station system in the valley of stored energy, for the first time in the morning peak hours can be to use the electrical output power and power consumption. At noon and afternoon, the energy storage station system is charged again, and the energy storage station system uses the energy stored in the second charge to output energy to electrical appliances and power consumption during peak periods in the evening and evening. Since the electricity price in normal time period is higher than that in valley time period, the peak-valley difference energy saving benefit of this mode is relatively small, but the investment is also relatively small. Here, the combination of the seed mode and A mode is called A2 mode, and the combination of the seed mode and B mode is called B2 mode.
The energy storage power station uses batteries as energy storage devices to store energy during valley hours, and uses inverters to generate PWM waves to output power to electrical appliances and electricity during peak hours. Although its technology is basically mature, there are almost no barriers, and the overall technical content is not very high. However, considering the requirements of power consumption and power grid for power quality, it is necessary to make the power output to the electric appliance and power consumption, as well as the relevant provisions of power quality feedback to the power grid. Not only to ensure the quality of the power output to the electrical appliances and power consumption, but also to meet the requirements of the power quality feedback to the grid.
If the current common construction scheme of battery energy storage power station is adopted, it is necessary not only to control the power quality of electrical appliances and electricity consumption, so as to eliminate the adverse impact on the power quality, but also to control the power quality of the power feedback to the power grid, so as to meet the requirements of the state on the power quality of the power grid. Therefore, it is necessary to design and install high-voltage and high-power energy management devices (such as SVG, etc.) in energy storage power stations, which inevitably leads to the following three main problems: 1. Greatly increasing construction costs; 2. 2. As the treatment of waveform malformation by power management equipment such as SVG will eliminate some electric energy such as harmonics. Harmonics are also electric energy, and the elimination of some will be less, so the energy saving benefit will be reduced to some extent. 3. SVG and other power management devices are power electronic devices in dynamic operation, with large failure rate and operation and maintenance workload. Increased operation and maintenance costs will also reduce energy saving benefits.
If the three-phase balanced transformer with special connection is used to replace the ordinary transformer, and then the stored electric energy is output to the electric appliance and the power consumption side through the three-phase balanced transformer, the influence of the waveform malformation such as harmonics on the power consumption quality of the user and the power grid can be greatly reduced. For the battery storage power stations in B1 and B2 modes, it can completely meet the requirements of users' power consumption quality and the requirements of the state on the power quality of the power grid without using any power management equipment. Accordingly, there are the following three main advantages: 1, reduce the construction cost; 2. Reduce the elimination of electric energy such as harmonics by power management equipment such as SVG for waveform malformation management, which increases the energy saving income; 3, three-phase balance transformer and three-phase balancer is static operation, will not produce any failure, no operation and maintenance costs.
