The pursuit of new energy and low-carbon economy has led countries around
the world to vigorously develop green energy such as wind energy and solar
energy. However, the power generation process of wind energy, solar energy and
other renewable energy sources is unstable and discontinuous, resulting in a
decline in the power quality of the power grid, resulting in waste of electrical
energy and Equipment failure. Therefore, before wind energy and solar energy are
input into the grid, it is extremely important to add a new environmentally
friendly vanadium redox flow battery (VRB) energy storage system for smooth
energy conversion.
1How vanadium batteries work
The vanadium flow energy storage battery system is a system that converts
and stores wind energy, solar energy and other energy with chemical energy. The
main unit of the energy storage system is the vanadium battery. Compared with
traditional batteries such as lead-acid batteries and nickel-cadmium batteries,
the battery has its own unique internal and external structures and operating
modes. In terms of performance, it is more suitable for large-scale energy
storage power stations such as wind energy and solar energy and smart grid peak
shaving. and other applications. Its main components are: stack system,
electrolyte and electrolyte storage and transportation system, and energy
conversion and control system, as shown in Figure 1.
The battery stack is assembled from a different number of single cells
arranged in sequence according to the required electrical power. The positive
and negative electrolyte solutions are stored in two storage barrels
respectively, and chemical pumps are used to drive the electrolyte to flow
through the positive and negative electrodes of the battery stack. An
electrochemical reaction occurs in the battery stack to realize the conversion
of electrical energy and chemical energy. The output power of the battery stack
is determined by the total area of the battery electrodes; the battery capacity
is determined by the total capacity of the electrolyte solution.
2 Energy storage system structure and functions of each module
The vanadium flow battery energy storage system involves multiple
components such as new energy power generation, battery stack and electrolyte
transportation management, power electronic conversion system, power load or
power system, etc. It is a coupling of electrochemistry, chemical industry,
electrical and network information. It is a complex dynamic system, and its
operating characteristics are related to various factors such as the combination
method and capacity of the flow energy storage battery system, as well as the
power converter, power load, and control method. How to improve the energy
efficiency, economy and reliability of the entire system while ensuring safe and
stable system operation is a key issue that must be solved in the practical
process of large-scale flow battery energy storage systems. Therefore, it is
necessary to combine high-efficiency power conversion technology, battery charge
and discharge control and management, advanced sensing and communication
technology and modern optimal control theory to establish a high-performance
vanadium battery energy storage management and control system, which will
greatly improve the development of all-vanadium redox flow energy storage
systems. High performance and normal operation play a very important role.
The energy storage management and control system consists of a central
control module, a power conversion control module, an electrolyte flow and
transportation control module, a battery charge and discharge management module,
and a system security protection monitoring and management module.
2.1 Management control system structure
The energy storage system inputs energy such as wind energy and solar
energy into the vanadium battery through the charging control module. Through an
electrochemical reaction in the electrolyte, the wind energy and solar energy
are converted into chemical energy, completing the first step of energy
conversion. The chemical energy stored in the electrolyte is converted into DC
power through electrochemical reaction, and the AC power is transmitted to the
power grid and the client through the inverter power supply to complete the
second step of energy conversion. This charging and discharging process requires
orderly cooperation between the central control module, power conversion control
module, electrolyte flow and transportation control module, battery charge and
discharge control management module, and safety protection monitoring and
management module for energy optimization and management control to be
effective. Various performances of the energy storage system ensure that the
energy storage system functions efficiently. The structural block diagram of the
control system is shown in Figure 2.
2.2 System center control module
The system uses a high-performance CPU to collect signals and monitor the
data variables of control information points when the working conditions of each
module in operation of the energy storage system change. It is the center for
information data exchange and control of the system.
2.3 Power conversion control module
In order to avoid large fluctuations in the voltage and frequency of the
grid caused by direct connection of wind and solar energy to the grid, and
further improve power quality and safety, the system adopts advanced
multi-quadrant current control technology, allowing output power phase control,
voltage drift compensation, low harmonics Wave distortion, reactive current
compensation (PFC), and instantaneous high load capacity to enhance system
stability and reliability.
2.4 Electrolyte flow and transportation control module
The system uses high-performance detection and automatic control technology
to measure and control through high-precision chemical pumps and control valves
to ensure the accuracy of electrolyte delivery.
The selection of electrolyte solution flow rate is related to factors such
as solution concentration, flow rate, temperature, charge and discharge mode,
operating current density, etc. Its size has a great impact on the performance
of the battery stack.
Calculate appropriate current density and flow data based on the amount of
power or charging time required by the system. After the flow data is set, the
delivery volume can remain relatively stable and will not be affected by the
pressure difference caused by the electrolyte storage volume and external load
changes.
2.5 Battery charge and discharge management control module
The combination of high-speed, low-power consumption, multi-function
microcontroller and battery intelligent charging and discharging control process
makes the performance of the battery stack charging and discharging process
stable and reliable. At the same time, the battery operating status data is
transmitted to the system safety monitoring module in a timely manner, which can
be realized The charging and discharging process of the stack is monitored in
real time, so that the charging and discharging of the stack is carried out
according to the set optimal curve.
In view of the randomness and intermittent characteristics of renewable
energy power generation such as solar and wind energy, the system's automatic
control and energy regulation capabilities can be used to smooth the disturbance
of the renewable energy power generation system and maintain the balance and
stability of the output voltage.
2.6 Security protection monitoring module
The system uses safety data fast real-time inspection reminder and alarm
control technology to monitor the normal operating parameters of the battery
such as voltage, current, flow, capacity, temperature and internal resistance of
the energy storage system. Under normal operating conditions of the system, the
working performance and safety performance parameters such as overcurrent,
overvoltage, short circuit, overtemperature protection, leakage, and electrolyte
level height of the battery are detected, and the detection data is saved. At
the same time, according to the data Prompt, warn and control when exceeding the
standard. It can also monitor the working status of the power conversion system
and each control cabinet in real time to prevent premature damage to the energy
storage system.
3 Technical characteristics of the system
①The output is independent. The output power and energy storage capacity
are independent of each other. The power is determined by the effective area of
the stack electrode, and the capacity is determined by the electrolyte capacity.
The system expansion and maintenance are very convenient.
②High density charging. The system can charge with high current density,
and at the same time, it has fast response and strong overload working
capabilities.
③High energy efficiency. The system has high energy efficiency, stable and
reliable discharge performance, and can discharge deeply.
④ Large energy storage. The system has large energy storage and is suitable
for large-scale energy storage power stations such as wind and solar energy. The
system has a lifespan of up to 20 years and is low cost.
⑤High safety. The system is safe and reliable, and the battery has no
potential explosion or fire hazards. Even if the positive and negative
electrolytes are mixed, there will be no danger. The electrolyte can be
recycled, no harmful gases are produced during operation, and there is no
pollution to the environment.
⑥ Fully automatic control. The system can be fully automatically controlled
and can automatically operate, protect, control and manage.
4 Applications and functions of the system
4.1 New energy wind energy and solar power station energy storage
Smooth new energy sources such as wind energy and solar energy, effectively
adjust the changes in grid voltage, frequency and phase caused by new energy
power generation, and improve power quality and stability.
4.2 Smart grid cuts peaks and fills valleys to ensure grid security
Cut peaks and fill valleys in the power grid to make the power grid smart;
reduce the number of peak-shaving power plants, reduce investment, and reduce
environmental pollution; improve power supply quality and reduce power grid line
losses; improve the power supply capacity of the existing power grid and delay
the need for urban power grid transformation.
4.3 Distributed energy storage and power supply
Energy storage of distributed energy can effectively solve the problem of
energy storage and power supply in restricted areas such as ocean islands,
remote mountainous areas, grasslands and desert areas, and promote the
development of remote and poor areas.
4.4 Backup power supply and UPS power supply
Making full use of low-peak power or the remaining power of the grid,
adjusting the rhythm of power consumption and rationally arranging power
consumption can save power and meet backup needs.
5 Conclusion
Vanadium battery energy storage system management and control technology
has functions such as charge and discharge management, flow and transmission
control, power conversion and control, and automatic detection and safety
protection of the energy storage system. It is instrumental in improving the
energy efficiency, economy and reliability of the entire energy storage system.
It plays a key role in ensuring the high performance, stable performance and
normal operation of the all-vanadium flow energy storage system.
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