A control method for a parallel array system of energy storage flywheels

Abstract

The present invention relates to a control method for a parallel array system of energy storage flywheels, which is to connect a plurality of large-capacity and high-power energy storage flywheels in parallel into a flywheel array. In the three different stages of charging, standby, and discharging, the power information fed back by each flywheel is detected, and different control algorithms are used to reasonably allocate the charge / discharge power to each flywheel, so that the power storage capacity of each flywheel in the array tends to be consistent, thereby achieving the optimal state of dynamic performance of each flywheel. The system includes an energy storage flywheel, an integrated flywheel energy storage inverter, a grid-connected switch, and an EtherCAT bus. The integrated flywheel energy storage inverter is based on the ZYNQ platform, and realizes the integrated design of single flywheel charge and discharge control, magnetic suspension bearing control, and main control system, which simplifies the complex communication design between flywheel control systems, reduces hardware costs, and improves the reliability of the system.

Description

Technical Field

[0001] The invention belongs to the field of electric power and relates to an array control method for parallel connection of large-capacity and high-power energy storage flywheels. Background Art

[0002] Traditional energy storage frequency regulation can no longer meet the system requirements of high-power and high-frequency charging and discharging in areas such as power system frequency regulation. Energy storage flywheels rely on their significant features such as high single power, long charging and discharging life, maintenance-free, safe and explosion-free, and low supporting environmental requirements. They are gradually welcomed and recognized in the fields of power system frequency regulation, rail transit, special equipment, etc.

[0003] In order to meet the user's needs for both storage capacity and power, the application of energy storage flywheel systems in the industrial field is mostly in the form of a flywheel array composed of multiple flywheels in parallel. Each energy storage flywheel is a large inertia, high-speed rotating energy storage body, and the amount of stored energy is represented by the linear speed of the rotating shaft connected to the energy storage body. Due to the existence of time accumulation errors and the differences in single-unit power consumption, during the charging and discharging process, the storage capacity of each flywheel will be slightly different, or a flywheel in the flywheel array will fail and shut down, causing the flywheel array as a whole to fail to work normally. At present, the existing patents issue charging and discharging indicators to each flywheel in the array, and most of them assume that the flywheel state is consistent. However, under actual working conditions, frequent charging and discharging will inevitably lead to inconsistent states of each flywheel. The method of average power distribution is obviously unreasonable, and the energy storage flywheel array cannot achieve the optimal dynamic performance state. Over time, the characteristics of each flywheel in the flywheel array will become increasingly different, affecting the service life of the flywheel array. Summary of the invention

[0004] The purpose of the present invention is to overcome the shortcomings of existing control methods in the power distribution problem of parallel arrays of energy storage flywheels. In the three working states of the flywheel: charging state, discharging state, and holding state, the condition of each flywheel in the array is judged according to feedback data, and the control method is reasonably adjusted so that each flywheel can achieve optimal dynamic performance and power balance under the premise of completing the system command action.

[0005] The technical solution proposed in the present invention is: a control method for an energy storage flywheel parallel array system, wherein the energy storage flywheel parallel array system includes an energy storage flywheel, an integrated flywheel energy storage converter, a grid-connected switch, an EtherCAT bus and a public AC bus; the energy storage flywheel is connected to the public AC bus through the integrated flywheel energy storage converter and the grid-connected switch, the energy storage flywheel array is a plurality of energy storage flywheels connected in parallel to the public AC bus, each integrated flywheel energy storage converter of the flywheel array is connected through the EtherCAT bus to form a communication network; each integrated flywheel energy storage converter simultaneously receives instructions issued by an upper system through the EtherCAT bus, and after power-on, the integrated flywheel energy storage converter of each flywheel self-detects the health status of the system and automatically suspends.

[0006] Furthermore, after the integrated flywheel energy storage inverter of each energy storage flywheel receives the charge and discharge command from the upper system through the EtherCAT bus, it judges the overall condition of the current flywheel array based on the system-level diagnosis. The judged status includes the storage capacity of each flywheel, the status of the charge and discharge control system, the status of the magnetic levitation bearing, the status of the vacuum system, the ambient temperature and humidity, the status of the AC and DC bus, and the status of the grid-connected switch. When the status conditions are met, the flywheel array realizes charge and discharge control according to the charge and discharge instructions of the upper level or realizes automatic charge and discharge control by detecting the bus voltage.

[0007] Furthermore, the working process of the energy storage flywheel parallel array system is divided into three states: state one, charging mode; state two, discharging mode; state three, standby mode. The integrated flywheel energy storage inverter detects the current speed of each flywheel to determine the current working state.

[0008] Furthermore, the state of the energy storage flywheel parallel array system is a charging mode. When the flywheel array receives a charging command issued by the superior system or detects that the bus voltage is higher than the charging threshold, the integrated flywheel energy storage inverter will detect the current speed of each flywheel to learn the current power of each flywheel. If the current speed of each flywheel is the same, it means that the current power of each flywheel is the same, then the integrated flywheel energy storage inverter of each flywheel will charge the flywheel to the rated speed according to the rated power, that is, the fully charged state; otherwise, if it is detected that the current speed of each flywheel is different, it means that the current power of each flywheel is different. According to the actual power of each flywheel, the system weightedly distributes the charging power to each flywheel, so that the power of each flywheel is quickly balanced, and synchronously accelerated to the rated speed to complete the charging.

[0009] Furthermore, the second state of the energy storage flywheel parallel array system is the discharge mode. When the flywheel array receives a discharge command issued by the upper system or detects that the bus voltage is lower than the discharge threshold, the integrated flywheel energy storage inverter will detect the current speed of each flywheel and determine the speed of each flywheel in the array. If the speed of each flywheel is the same, it means that the power of each flywheel is consistent, and each flywheel is discharged at equal power until the discharge is completed.

[0010] Furthermore, assuming that the speed of each flywheel is different, it means that the current power of each flywheel is different. The maximum speed ω of all flywheels in the array is obtained by the bubble algorithm. max and the minimum speed ω min After making the difference, compare it with the rated speed ω 额定 If the calculated result is greater than or equal to the set value A, it means that one of the flywheels has a too low speed, and the array cannot complete the discharge work normally. The system fault is reported and the array is shut down for maintenance. Otherwise, if there is a flywheel with the maximum speed ω in the array max and the minimum speed ω min After making the difference, compare it with the rated speed ω 额定 The value of the division is between the set values ​​A and B, indicating that one of the flywheels has a lower speed than other flywheels in the system. To meet the system discharge requirements, the flywheel array operates at a reduced rating, and the integrated flywheel energy storage converter distributes the discharge power according to the actual power weight until the discharge is completed. The values ​​of A and B are set thresholds, which are used to represent the upper and lower limits of the flywheel body fault threshold, respectively.

[0011] Furthermore, the state three of the energy storage flywheel parallel array system is the standby mode. After charging is completed, the flywheel enters the standby mode when it does not receive a discharge command or detects that the bus voltage is lower than the threshold value; when entering the standby mode, it is detected whether the speed of each flywheel is the same. If not, the power is weighted and allocated according to the actual power of each flywheel, so that the power of each flywheel is quickly balanced and synchronously accelerated to the rated speed; if it is detected that the speed of each flywheel is the same, it is determined whether the speed value is less than the rated speed ω 额定 If it is less than the rated speed, each flywheel is charged to the rated speed according to the rated power ω 额定 And maintain the speed at the rated speed ω with the minimum current 额定 .

[0012] Furthermore, the integrated flywheel energy storage converter detects the current speed of each flywheel to determine the current working state, specifically by performing detection and calculation according to the following formula:

[0013] P i =T i ω i

[0014] and formula

[0015]

[0016] Where: P i represents the instantaneous power of the i-th flywheel, T i represents the torque of the i-th flywheel, ω i represents the speed of the i-th machine, E i represents the storage capacity of the i-th flywheel, J i represents the moment of inertia of the i-th flywheel, i represents the i-th flywheel in the flywheel array, 1≤i≤n, n represents the total number of flywheel arrays, and t represents the charge and discharge time.

[0017] The array of large-capacity and high-power energy storage flywheels in parallel of the present invention receives charging and discharging commands and power indicators, and synchronously sends them to the integrated flywheel energy storage inverter of each flywheel in the flywheel array. The integrated flywheel energy storage inverter is developed based on the ZYNQ platform. Since ZYNQ adopts a dual-core ARM-A9+FPGA architecture, it has the characteristics of high performance and low power consumption, and can be embedded in a real-time operating system, which saves the resources of the control system to the greatest extent. Therefore, the integrated flywheel energy storage inverter integrates the charging and discharging control logic and control method of the energy storage flywheel, the magnetic suspension bearing control logic and control method, the overall scheduling and protection logic of the main control system and other functions. The array control method of large-capacity and high-power energy storage flywheels in parallel of the present invention is also implemented on the integrated flywheel energy storage inverter. The integrated flywheel energy storage inverter judges its own power and other flywheel conditions, adjusts the control method in real time, and reasonably distributes the power size to achieve the optimization of the dynamic performance of the entire flywheel array.

[0018] The array of large-capacity and high-power energy storage flywheels in parallel includes energy storage flywheels, integrated flywheel energy storage inverters, grid-connected switches, EtherCAT buses and common AC busbars. All system components with the same parameters and indicators are connected in parallel to form a flywheel array. The capacity and power of the flywheel array depend on the number of energy storage flywheels in parallel. The control mode of the flywheel array system adopts a control mode of the same level. The integrated flywheel energy storage inverters in the array are connected through the EtherCAT bus, and broadcast to other integrated flywheel energy storage inverters in the flywheel array through the EtherCAT bus to diagnose the status of the entire flywheel array system. Charging and discharging actions, magnetic levitation actions, vacuum system control actions, and environmental system control actions are performed according to the general scheduling instructions.

[0019] Beneficial Effects

[0020] The present invention overcomes the deficiency of existing control methods in considering the real-time status of a single flywheel in a flywheel array. By obtaining the status of the flywheel itself and the status of other flywheels in the flywheel array, the method proposes a charging and discharging strategy for the flywheel array under different speeds, realizes the reasonable distribution of the power shared by each flywheel and makes timely adjustments through the algorithm to ensure the balance of power of each flywheel in the flywheel array, so that each flywheel achieves an ideal configuration. The integrated flywheel energy storage inverter reduces the risks brought by the communication between complex control systems and ensures the long-term stable and efficient operation of the system. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 It is a system structure block diagram of the present invention;

[0022] Figure 2 is a flow chart of the charging mode of the present invention;

[0023] Figure 3 is a flow chart of the discharge mode of the present invention;

[0024] Figure 4 It is a flow chart of the standby mode of the present invention. DETAILED DESCRIPTION

[0025] The technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, rather than all the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the protection scope of the present invention.

[0026] like Figure 1 As shown, the array system of large-capacity and high-power energy storage flywheels in parallel of the present invention includes an energy storage flywheel 1, an integrated flywheel energy storage converter 2, a grid-connected switch 3, an EtherCAT bus 4 and a public AC bus 5. The energy storage flywheel 1 is connected to the public AC bus 5 through the integrated flywheel energy storage converter 2 and the grid-connected switch 3. The energy storage flywheel array is a plurality of energy storage flywheels 1 connected in parallel to the public AC bus 5. The communication network of the flywheel array is each based on the ZYNQ platform (Xilinx's new generation of dual ARMCortex-A9 MPCore processors + 28nm7 series FPGA scalable processing platform, developed by Zynq). The integrated flywheel energy storage converter 2 is connected through the EtherCAT bus 4. Each integrated flywheel energy storage converter 2 simultaneously receives instructions issued by the upper system through the EtherCAT bus 4. After power-on, the integrated flywheel energy storage converter 2 of each flywheel self-detects the health status of the system and automatically suspends.

[0027] After the integrated flywheel energy storage converter 2 of each energy storage flywheel 1 receives the charge and discharge command from the upper system through the EtherCAT bus 4, the overall condition of the current flywheel array is judged according to the system-level diagnosis. The judged status includes the storage capacity of each flywheel, the status of the charge and discharge control system, the status of the magnetic suspension bearing, the status of the vacuum system, the status of the ambient temperature and humidity, the status of the AC and DC bus, and the status of the grid-connected switch. When the status conditions are met, the flywheel array realizes charge and discharge control according to the charge and discharge command of the upper level or realizes automatic charge and discharge control by detecting the bus voltage.

[0028] The working process can be divided into the following three states: Figure 2 , 3 , as shown in 4:

[0029] State 1: Charging mode. When the flywheel array receives a charging command from the upper system or detects that the bus voltage is higher than the charging threshold, the integrated flywheel energy storage converter will detect the current speed of each flywheel according to the formula:

[0030] P i =T i ω i

[0031] and formula

[0032]

[0033] Where: P i represents the instantaneous power of the i-th flywheel, T i represents the torque of the i-th flywheel, ω i represents the speed of the i-th machine, E i represents the storage capacity of the i-th flywheel, J i represents the moment of inertia of the i-th flywheel, i represents the i-th flywheel in the flywheel array, 1≤i≤n, n represents the total number of flywheel arrays, and t represents the charge and discharge time.

[0034] It can be known that the current power of each flywheel, if the current speed of each flywheel is the same, it means that the current power of each flywheel is the same, then the integrated flywheel energy storage converter of each flywheel will charge the flywheel to the rated speed according to the rated power, that is, the full power state. Otherwise, if it is detected that the current speed of each flywheel is different, it means that the current power of each flywheel is different. According to the actual power of each flywheel, the system weightedly distributes the charging power to each flywheel, so that the power of each flywheel is quickly balanced, and synchronously accelerates to the rated speed to complete the charging.

[0035] State 2: Discharge mode. When the flywheel array receives a discharge command from the upper system or detects that the bus voltage is lower than the discharge threshold, the integrated flywheel energy storage converter will detect the current speed of each flywheel. Similarly, according to the formula:

[0036] P i =T i ω i

[0037] and formula

[0038]

[0039] Determine the speed of each flywheel in the array. If the speed of each flywheel is the same, it means that the charge of each flywheel is consistent. Each flywheel is discharged at equal power until the discharge is completed. In the prior art, it is assumed that the speed of each flywheel remains the same. In fact, due to the differences between each flywheel itself, there will inevitably be differences in charge during the charging and discharging process. If it is still discharged at equal power, the current of the flywheel with low charge will increase, which will cause the loss of a single flywheel to increase, affecting the service life of the flywheel, increasing maintenance costs, and reducing the safety and reliability of the flywheel array. Therefore, from this aspect, the present invention proposes the following control method when the speed is different in the flywheel discharge mode: Assuming that the speed of each flywheel is different, indicating that the current charge of each flywheel is different, the bubbling algorithm is used to find the maximum speed ω of all flywheels in the array. max and the minimum speed ω min After making the difference, compare it with the rated speed ω 额定 If the calculated result is greater than or equal to the set value A (the values ​​of A and B are set thresholds, which are used to represent the upper and lower limits of the flywheel body fault threshold respectively), it means that one of the flywheels has a low speed and the array cannot complete the discharge work normally, so the system fault is reported and the machine is shut down for maintenance. Otherwise, if there is a flywheel with the maximum speed ω in the array max and the minimum speed ω min After making the difference, compare it with the rated speed ω 额定 The compared value is between the set values ​​A and B, indicating that the speed of one of the flywheels is slightly lower than that of other flywheels in the system. In order to meet the system discharge requirements, the flywheel array adopts a derated operation, and the integrated flywheel energy storage inverter distributes the discharge power according to the actual power weight until the discharge is completed.

[0040] State 3: Standby mode. After charging is completed, the flywheel enters standby mode when it does not receive a discharge command or detects that the bus voltage is lower than the threshold. When entering standby mode, it detects whether the speed of each flywheel is the same. If not, the power is weighted and allocated according to the actual power of each flywheel, so that the power of each flywheel is quickly balanced and accelerated to the rated speed synchronously. If it is detected that the speed of each flywheel is the same, it is determined whether the speed value is less than the rated speed ω 额定 If it is less than the rated speed, each flywheel is charged to the rated speed according to the rated power ω 额定 And maintain the speed at the rated speed ω with the minimum current 额定 .

[0041] The technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, rather than all the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the protection scope of the present invention.

Claims

1. A control method for a parallel array system of energy storage flywheels, characterized in that: The energy storage flywheel parallel array system includes an energy storage flywheel, an integrated flywheel energy storage converter, a grid-connected switch, an EtherCAT bus and a public AC bus; the energy storage flywheel is connected to the public AC bus through the integrated flywheel energy storage converter and the grid-connected switch, the energy storage flywheel array is a plurality of energy storage flywheels connected in parallel to the public AC bus, each integrated flywheel energy storage converter of the flywheel array is connected through the EtherCAT bus to form a communication network; each integrated flywheel energy storage converter simultaneously receives instructions issued by the upper system through the EtherCAT bus, and after power-on, the integrated flywheel energy storage converter of each flywheel self-detects the health status of the system and automatically suspends; After the integrated flywheel energy storage converter of each energy storage flywheel receives the charge and discharge command from the upper system through the EtherCAT bus, it determines the overall status of the current flywheel array based on the system-level diagnosis. The determined status includes the storage capacity of each flywheel, the status of the charge and discharge control system, the status of the magnetic suspension bearing, the status of the vacuum system, the status of the ambient temperature and humidity, the status of the AC and DC bus, and the status of the grid-connected switch. When the status conditions are met, the flywheel array implements charge and discharge control according to the upper-level charge and discharge command or realizes automatic charge and discharge control by detecting the bus voltage; The working process of the energy storage flywheel parallel array system is divided into three states: state one, charging mode; state two, discharging mode; state three, standby mode, according to the integrated flywheel energy storage converter, the current speed of each flywheel is detected to determine the current working state; The state one of the energy storage flywheel parallel array system is the charging mode. When the flywheel array receives a charging command issued by the superior system or detects that the bus voltage is higher than the charging threshold, the integrated flywheel energy storage inverter will detect the current speed of each flywheel to learn the current power of each flywheel. If the current speed of each flywheel is the same, it means that the current power of each flywheel is the same, then the integrated flywheel energy storage inverter of each flywheel will charge the flywheel to the rated speed according to the rated power, that is, the full power state; otherwise, if it is detected that the current speed of each flywheel is different, it means that the current power of each flywheel is different. According to the actual power of each flywheel, the system weightedly distributes the charging power to each flywheel, so that the power of each flywheel is quickly balanced, and synchronously accelerates to the rated speed to complete the charging.

2. The control method of a parallel array system of energy storage flywheels according to claim 1, characterized in that: State 2 of the energy storage flywheel parallel array system is the discharge mode. When the flywheel array receives a discharge command from the superior system or detects that the bus voltage is lower than the discharge threshold, the integrated flywheel energy storage inverter detects the current speed of each flywheel and determines the speed of each flywheel in the array. If the speed of each flywheel is the same, it means that the power of each flywheel is consistent, and each flywheel discharges at equal power until the discharge is completed.

3. The control method of a parallel array system of energy storage flywheels according to claim 1, characterized in that: Assuming that the speed of each flywheel is different, it means that the current power of each flywheel is different. Using the bubble algorithm, find the maximum speed of all flywheels in the array. and speed minimum After the difference is made, compare it with the rated speed If the calculated result is greater than or equal to the set value A, it means that one of the flywheels has a too low speed, and the array cannot complete the discharge work normally. The system fault is reported and the system is shut down for maintenance. Otherwise, if there is a flywheel with the maximum speed in the array, and speed minimum After the difference is made, compare it with the rated speed The value of the division is between the set values ​​A and B, indicating that one of the flywheels has a lower speed than other flywheels in the system. To meet the system discharge requirements, the flywheel array operates at a reduced rating, and the integrated flywheel energy storage converter distributes the discharge power according to the actual power weight until the discharge is completed. The values ​​of A and B are set thresholds, which are used to represent the upper and lower limits of the flywheel body fault threshold, respectively.

4. The control method of a parallel array system of energy storage flywheels according to claim 1, characterized in that: The state three of the energy storage flywheel parallel array system is the standby mode. After charging is completed, the flywheel enters the standby mode when it does not receive a discharge command or does not detect that the bus voltage is lower than the threshold value; When entering standby mode, check whether the speed of each flywheel is the same. If not, weight the power distribution according to the actual power of each flywheel, so that the power of each flywheel is quickly balanced and synchronously accelerated to the rated speed; If it is detected that the speed of each flywheel is the same, determine whether the speed value is less than the rated speed If it is less than the rated speed, each flywheel is charged to the rated speed according to the rated power. And maintain the speed at the rated speed with the minimum current .

5. The control method of a parallel array system of energy storage flywheels according to claim 1, characterized in that: The integrated flywheel energy storage converter detects the current speed of each flywheel to determine the current working state, specifically, the flywheel parameters are detected and calculated according to the following formula: ， and formula ， in: Indicates The instantaneous power of a flywheel, Indicates Flywheel torque, Indicates Table speed, Indicates The amount of energy stored in a flywheel, Indicates The moment of inertia of the flywheel, Indicates the first Flywheel, 1 , represents the total number of flywheel arrays, and t represents the charging and discharging time.

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