Energy storage converter product model and description:
The energy storage converter products are divided into two categories: optical storage integrated machine and non-optical storage integrated machine, as shown in Figure 1.
1.1 Definition of energy storage converter
As one of the important forms of large-scale energy storage system, battery energy storage has many applications such as peak shaving, valley filling, frequency modulation, phase modulation, and accident reserve. Compared with conventional power supplies, large-scale energy storage power plants can adapt to rapid changes in load, play an important role in improving the safe and stable operation level of power systems, power quality and reliability of power grids, and optimize power supply structure to achieve green environmental protection. The overall energy saving of the power system reduces the overall economic benefits.
In a Power Conversion System (PCS) electrochemical energy storage system, a device for bidirectionally converting electrical energy between a battery system and a power grid (and/or load) can control the charging and discharging process of the battery. AC/DC conversion can directly supply AC load without grid.
The PCS is composed of a DC/AC bidirectional converter, a control unit, and the like. The PCS controller receives the background control command through communication, and controls the converter to charge or discharge the battery according to the symbol and size of the power command, thereby realizing the adjustment of the active power and the reactive power of the power grid. At the same time, PCS can obtain the battery pack status information through CAN interface and BMS communication, dry contact transmission, etc., which can realize the protective charging and discharging of the battery and ensure the safe operation of the battery.
1.2 Implementation standards
*** "Technical Regulations for Energy Storage Converter Detection"
*** "Technical Specifications for Energy Storage Converters for Battery Energy Storage Systems"
GB/T14549 power quality utility grid harmonics
GB/T15543 power quality three-phase voltage imbalance
GB/T15945 power quality power system frequency deviation
GB/T12325 power quality supply voltage deviation
1.3 Product Introduction
1.3.1 Working principle
The energy storage bidirectional converter (PCS) is a four-quadrant variable current device that can be controlled on the AC/DC side to realize AC-DC bidirectional conversion of electric energy. PCS can realize the bidirectional energy transfer between the DC battery of the battery energy storage system and the AC grid, and realize the charge and discharge management of the battery system, the tracking of the load power on the grid side, and the control of the charge and discharge power of the battery energy storage system through the control strategy. Control of the network side voltage under the off-grid operation mode.
Figure 2: Energy storage converter system topology
The main function of the energy storage converter is that under the condition of grid connection, the energy storage system performs constant power or constant current control according to the microgrid monitoring command to charge or discharge the battery, and smooth the output of the fluctuating power source such as wind power and solar energy; Under the condition, the energy storage system provides the voltage and frequency support (V/F control) of the microgrid as the main power source, and the load in the microgrid works on the basis of the voltage and frequency. PCS uses dual closed-loop control and SPWM pulse modulation to accurately and quickly regulate output voltage, frequency, active and reactive power.
Figure 3: Schematic diagram of the energy storage converter
1.3.3 Basic control functions
l Grid-connected constant power charging and discharging control
l Grid-connected constant voltage current limiting charging
l Off-grid V/F control
l reactive power control
l Grid-off-network smooth switching control
l Anti-island protection function and island detection for mode switching
l Fault ride through control function
1.3.4 Basic protection functions:
l Battery polarity reverse connection protection
l DC overvoltage protection
l DC overcurrent protection
l Network side over/under voltage protection
l Network side overcurrent protection
l Network side over/under frequency protection
l IGBT module overcurrent protection
l IGBT module over temperature protection
l Transformer / reactor over temperature protection
l lightning protection
l Unplanned island protection
1.3.5 Product Advantages
The unique mode switching smoothing control technology ensures that the grid-off-off mode can be switched without impact to ensure reliable operation of the converter. Ensure that the converter is increased or decreased according to the required active power and reactive power when it is connected to the grid; the load voltage and frequency are stabilized during independent operation.
l Integrated charging and discharging design to realize two-way flow of energy between AC system and DC system;
l Efficient vector control algorithm to achieve decoupling control of active and reactive power;
l The power factor can be adjusted arbitrarily, and it can be fully reactive in the capacity range to realize reactive power compensation;
l Under the dispatch of MEMS (microgrid energy management system), actively participate in the peak shaving of the power grid, effectively alleviating the pressure on the large power grid;
l Supports grid-connected operation and off-grid operation; and can realize smooth and seamless switching between grid-connected and off-grid;
l Support micro-grid operation, providing stable voltage and frequency support for the microgrid;
l Active and passive island detection methods are combined to meet the UL1741 standard;
l Perfect relay protection function to effectively prevent abnormal damage of the inverter;
l Support a variety of energy storage batteries, different models only the software of the controller is different;
l Provide CAN and 485 to communicate with battery management system (BMS) and upper monitoring system;
l Multiple PCSs can realize parallel operation of multiple machines;
l Support short-time short-circuit operation mode on the AC side;
l Support self-synchronization function;
l High reliability cabinet design to meet the needs of different operating areas.
l The main power circuit uses a high reliability power module.
1.4 Main technical parameters table
Table 2.1 Technical parameters
Energy storage converters are widely used in power systems, rail transit, military, petroleum machinery, new energy vehicles, wind power generation, solar photovoltaic and other fields. Energy is realized in the grid cutting peaks and valleys, smoothing new energy fluctuations, energy recycling and other occasions. Two-way flow, active support of the grid voltage frequency, improve the quality of power supply.
Figure 2.4 Energy storage smoothing PV fluctuations
Figure 2.5 Storage peaks and valleys (using peak and valley electricity prices)
Figure 2.6 Energy storage participation in grid frequency modulation
l It can be used in distributed power generation systems such as wind energy and solar energy to ensure the balance and continuity of distributed power supply, effectively improve its power output quality and improve the ability to access the power grid.
l It can be used in the stability of power system. It can respond to load fluctuations through fast energy storage, absorb excess energy or supplement the lack of energy, realize high-power dynamic adjustment, and adapt well to frequency adjustment and voltage power factor correction. Thereby improving the stability of the system operation.
l It can be used as emergency power supply to provide power to users during power failure of large power grids or other power sources to improve the reliability of power supply.
l It can be used for power grid clipping and valley filling, which can alleviate the contradiction between supply and demand on the user side, reduce the investment of power generation equipment, improve the utilization rate of power equipment and reduce line loss.
l It can be used in the microgrid as the main power source to provide the voltage and frequency support of the microgrid, so that wind power and photovoltaic can contribute to the regional load.
l It can be used in various types of energy storage components to realize flexible interfaces between energy storage and power grid, which can meet the requirements of independent or grid-connected operation.
1.6 Quick selection calculation method
The energy storage converter configuration is generally based on the actual load in the microgrid and the distributed generation energy capacity. The load is divided into importance load (computer room, office, monitoring and other loads), non-important load (air conditioning, lighting, boiler, door and other loads). The load data generally needs on-site measurement. Generally, the time-sharing data of working days and holidays are measured. And comprehensive analysis of the data of the typical time of the four seasons.
1.6.1 Energy storage converter capacity matching
The energy storage capacity configuration is configured at 1.2 times the load capacity. If the importance load is 200 kW, it is recommended to configure a 250 kW energy storage converter. If other loads need to be operated off-grid, the storage power ratio will be increased accordingly.
1.6.2 Energy storage converter transformer ratio
The energy storage converter transformer ratio is determined by the DC voltage input range (ie, the battery voltage range). The calculation method is as follows: transformer ratio = U l (battery minimum voltage) / 1.414. If the voltage range of the iron-lithium battery is 360~480VDC, 360/1.414=254, the transformer ratio can be determined as 200.
If the configuration without transformer is selected, the minimum voltage of the battery needs to reach 540V or more to access the 400V grid.
1.6.3 Energy storage converter additional function configuration
Self-synchronizing function (S): The energy storage converter can realize seamless and off-grid switching without other devices. Under the premise that the grid-connected switch can be remotely controlled, the energy-storing converter is commanded when it is connected from the grid to the network. The grid-connected switch is opened, and when the off-grid is connected to the grid, the command is issued to close the grid-connected switch (the closing condition is judged by the converter, and cannot be manually closed);
Supercapacitor "charger" function (C): When the energy storage converter is connected to the super capacitor product, it can charge the super capacitor from 0 voltage and charge and discharge when the super capacitor voltage reaches the operating voltage, replacing the traditional charger. effect.