A DC side control method for a static synchronous condenser

Abstract

The present application provides a DC side control method for a static synchronous condenser, including: starting the SSC DC side unlocking and enabling, calculating the number of energy storage modules N that need to be put into use plugin and the number of energy storage modules N that require electronic bypass bypass ; Calculate the current voltage balance degree k of each energy storage module and sample the branch current, and determine whether to switch the energy storage module in active voltage balancing mode or select the energy storage module in order of numbering according to the voltage balance degree k and the branch current. The DC side control method of the static synchronous phase condenser provided by the present invention can achieve balanced control of the voltage between the energy storage modules on the DC side of the SSC under the premise that the equivalent switching frequency is basically controllable; in addition, if there are multiple parallel branches on the DC side, the circulating current between the branches can be effectively reduced, thereby reducing system losses and improving operating efficiency.

Description

Technical Field

[0001] The present application relates to the field of power electronic control technology, and in particular to a DC side control method of a static synchronous phase condenser. Background Art

[0002] New energy stations are usually equipped with static var generators (SVG) to provide reactive power and voltage support for the system. Most of these devices operate in the grid-following (GFL) mode, which is equivalent to a controlled current source based on a phase-locked loop. Under weak grid conditions, they are prone to resonance with grid impedance and other problems, which can cause system instability in severe cases. In this context, two main technical routes have been derived: one is to add a grid-forming (GFM) control algorithm to the control strategy of traditional SVG, so that SVG simulates the operating characteristics of a synchronous generator and operates in a self-synchronous voltage source mode to improve its adaptability to weak grids; Figure 1 This is a schematic diagram of the main circuit topology of a static synchronous condenser. Figure 1 The valve side adopts MMC (modular multilevel converter, MMC) rectifier topology, including two SVGs, #1SVG and #2SVG, and an energy storage device is connected between the positive and negative poles of the DC side. This is the main topology of the static self-synchronous compensator (SSC). Figure 2 This is a schematic diagram of the DC side energy storage module structure of a static synchronous condenser. Figure 2 , (a) lithium battery half-bridge module, (b) supercapacitor half-bridge module, (c) lithium battery full-bridge module, (d) supercapacitor full-bridge module; a single energy storage module is a half-bridge structure or a full-bridge structure, and the DC side can be a supercapacitor cluster, a lithium battery cluster, or a hybrid of the two. Therefore, SSC has the voltage and reactive power support capabilities of conventional SVG, and can also provide frequency and inertia support to the power grid with the help of DC side energy storage devices.

[0003] In order to improve the operational reliability of SSC equipment, the number of modules in each branch of the SSC DC side is usually configured according to a certain degree of redundancy, so it is necessary to control the switching of the energy storage module to ensure voltage balance between the modules; when there are multiple branches in parallel on the DC side, if there is a circulating current between the branches, it will cause unnecessary charging and discharging of the energy storage module and increase system losses. Therefore, how to design a suitable switching control method for the DC side energy storage unit to achieve voltage balancing between modules while reducing the circulating current between parallel branches is a key issue that needs to be solved for SSC to achieve large-scale engineering applications. Summary of the invention

[0004] The present application provides a DC side control method for a static synchronous condenser to solve the problem of how to balance the voltage between DC side energy storage units and how to reduce the circulating current between parallel branches.

[0005] In order to solve the above technical problems, the present application provides a DC side control method for a static synchronous condenser, comprising: identifying all available DC side energy storage module voltages and module numbers, calculating the maximum value U of the available energy storage module voltages max , minimum value U min and the average value U avg ; SSC DC side starts unlocking and enables, and calculates the number of energy storage modules N that need to be put into use plugin and the number of energy storage modules N that require electronic bypass bypass ; Calculate the voltage balance degree k of each energy storage module at present, k = MAX[(U max -U avg ) / U avg , (U avg -U min ) / U avg ], MAX means to take the maximum value function, U max Indicates the maximum voltage of the energy storage module, U avg Indicates the average voltage of the energy storage module, U min Indicates the minimum voltage of the energy storage module. When k> k set When there is current in the branch, k set The voltage balance setting value of the energy storage module is used to switch the energy storage module in the active voltage balancing mode: when the branch current causes the energy storage module to charge, the available energy storage module voltages are sorted in ascending order; when the branch current causes the energy storage module to discharge, the available energy storage module voltages are sorted in descending order; and energy storage modules are selected according to the sorting order until the number of energy storage modules N required to be put into operation plugin , the remaining energy storage modules perform electronic bypass; when k < k set When there is no current in the branch, the switching is performed in a sequential rolling mode: the energy storage modules in the unsorted available energy storage module queue are switched in a front-to-back order until the number of energy storage modules N required to be switched is reached. plugin , the remaining energy storage modules perform electronic bypass; after the rolling cycle delay, take the queue No. 2~N plugin +1 energy storage module is put into operation, and the other energy storage modules are electronically bypassed; after the rolling cycle delay, the queue No. 3~N is selected plugin Energy storage module No. +2 is put into operation, and the remaining energy storage modules perform electronic bypass. The cycle is executed until the end of the queue is reached and then returns to the starting position of the queue.

[0006] Further, the number of energy storage modules that need to be put into use and the number of energy storage modules that need electronic bypass are calculated: the number of energy storage modules that need electronic bypass N bypass Initialized to 0; the number of energy storage modules required is N plugin Equal to the number of available energy storage modules N avail Subtract the number of energy storage modules N that require electronic bypass bypass , until the number of energy storage modules N required to be invested plugin Equal to the number of energy storage modules N1 required for the rated operation of the system; maintain the current number of energy storage modules N required to be invested plugin and the number of energy storage modules N that require electronic bypass bypass .

[0007] Furthermore, if the number of available energy storage modules N avail The number of energy storage modules N1 required for rated operation of the system is greater than or equal to the number of energy storage modules N1 required for electronic bypass. bypass Initialized to 0; if the number of available energy storage modules N avail The number of energy storage modules N1 required for rated operation of the system is less than that required, the DC side is blocked, and the number of energy storage modules N required to be put into operation is terminated. plugin and the number of energy storage modules N that require electronic bypass bypass Calculation.

[0008] Furthermore, if the number of energy storage modules N required to be invested plugin The number of energy storage modules N1 that is not equal to the rated operation of the system is N1. After the step-by-step electronic bypass delay time, the number of energy storage modules that need electronic bypass is N bypass =N bypass +1 into N plugin =N avail -N bypass , until the number of energy storage modules N required to be invested plugin Equal to the number of energy storage modules N1 required for rated operation of the system.

[0009] Furthermore, the on / off status of the bypass switch of each energy storage module is received through communication, and the voltage and module number of each energy storage module on all available DC sides are identified.

[0010] Furthermore, the absolute value of the sampled branch current is calculated and compared with the dead zone setting value. I set For comparison, when the absolute value of the sampled branch current is greater than I set When the absolute value of the sampled branch current is less than or equal to I set When , it is determined that there is no current in the branch.

[0011] Furthermore, if the active voltage balancing mode is currently in operation, when the voltage balance degree k of each energy storage module calculated in real time is less than 0.9× k set Or when there is no current in the branch, it switches to the sequential rolling mode, otherwise it always maintains the active voltage balancing mode; if it is currently working in the sequential rolling mode, when the voltage balance degree k of each energy storage module calculated in real time >1.1× k set Only when there is current in the branch will it switch to active voltage equalization mode, otherwise it will always maintain sequential rolling mode.

[0012] Furthermore, a single energy storage module includes a first semiconductor device and a second semiconductor device, wherein the second semiconductor device is connected in parallel with a bypass switch to open the N plugin The first semiconductor device of the number of energy storage modules is turned off. plugin The second semiconductor device of the number of energy storage modules is turned on by N bypass The second semiconductor device of the energy storage module is used to turn off the N bypass A first semiconductor device of an energy storage module.

[0013] Furthermore, the power supply of the driving control part of each energy storage module is obtained from the DC side of the energy storage module. When the SSC DC side starts charging from zero voltage, the first semiconductor device and the second semiconductor device are both in the off state, and each energy storage module is charged by an anti-parallel diode in an uncontrolled rectification manner.

[0014] Furthermore, if the SSC DC side is configured with multiple parallel branches, each branch is controlled according to the DC side control method of the static synchronous phase condenser, and through the drive synchronization mechanism between the branches, each branch always updates the drive signal of each energy storage module at the same time.

[0015] The DC side control method of the static synchronous condenser provided by the present invention can realize balanced control of the voltage between the energy storage modules on the SSC DC side under the premise that the equivalent switching frequency is basically controllable; in addition, if there are multiple parallel branches on the DC side, the circulating current between the branches can be effectively reduced, thereby reducing system losses and improving operating efficiency. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] In order to more clearly illustrate the specific implementation methods of the present application or the technical solutions in the prior art, the drawings required for use in the specific implementation methods or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are some implementation methods of the present application. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative work.

[0017] Figure 1 It is a schematic diagram of the main circuit topology of a static synchronous condenser;

[0018] Figure 2 This is a schematic diagram of the DC side energy storage module structure of a static synchronous condenser;

[0019] Figure 3 A schematic diagram of a flow chart for calculating the number of energy storage modules required to be put into operation in each branch and the number of energy storage modules required to be electronically bypassed on the DC side of a static synchronous condenser provided in an embodiment of the present invention;

[0020] Figure 4 A schematic diagram of the switching strategy of each energy storage module in the active voltage balancing mode on the DC side of a static synchronous condenser provided by an embodiment of the present invention;

[0021] Figure 5 A schematic diagram of the switching strategy of each energy storage module in the DC side sequential rolling mode of the static synchronous phase condenser provided in an embodiment of the present invention. DETAILED DESCRIPTION

[0022] The following will be combined with the accompanying drawings to clearly and completely describe the technical solutions in this application. Obviously, the described embodiments are part of the embodiments of this application, not all of them. Based on the embodiments in this application, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of this application.

[0023] In the description of the present application, it should be noted that the terms "center", "up", "down", "left", "right", "vertical", "horizontal", "inside", "outside", etc., indicating orientations or positional relationships, are based on the orientations or positional relationships shown in the accompanying drawings, and are only for the convenience of describing the present application and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore should not be understood as a limitation on the present application.

[0024] In the description of this application, it should be noted that, unless otherwise clearly specified and limited, the terms "installed", "connected", and "connected" should be understood in a broad sense, for example, it can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection or an electrical connection; it can be a direct connection, or it can be indirectly connected through an intermediate medium, it can also be the internal connection of two components, it can be a wireless connection, or it can be a wired connection. For ordinary technicians in this field, the specific meanings of the above terms in this application can be understood according to specific circumstances.

[0025] In addition, the technical features involved in the different embodiments of the present application described below can be combined with each other as long as they do not conflict with each other.

[0026] An embodiment of the present invention provides a DC side control method of a static synchronous condenser, comprising:

[0027] Identify all available DC side energy storage module voltages and module numbers, and calculate the maximum value of the available energy storage module voltage U max , minimum value U min and the average value U avg ;

[0028] SSC DC side startup unlocking enable, calculate the number of energy storage modules N that need to be put into use plugin and the number of energy storage modules N that require electronic bypass bypass ;

[0029] Calculate the voltage balance degree k of each energy storage module at present, k = MAX[(U max -U avg ) / U avg , (U avg -U min ) / U avg ], MAX means to take the maximum value function, U max Indicates the maximum voltage of the energy storage module, U avg Indicates the average voltage of the energy storage module, U min Indicates the minimum voltage of the energy storage module. When k> k set When there is current in the branch, k set Set the voltage balance value for the energy storage module and switch the energy storage module in active voltage balancing mode:

[0030] When the branch current charges the energy storage module, the available energy storage module voltages are sorted in ascending order; when the branch current discharges the energy storage module, the available energy storage module voltages are sorted in descending order; and energy storage modules are selected according to the sorting order until the number of energy storage modules N required to be invested is reached. plugin , the remaining energy storage modules perform electronic bypass;

[0031] When k < k set Or when there is no current in the branch, switching is performed in sequential rolling mode:

[0032] The energy storage modules in the unsorted available energy storage module queue are put into use in a sequential order until the number of energy storage modules N required to be put into use is reached. plugin , the remaining energy storage modules perform electronic bypass;

[0033] After the rolling cycle delay, take queues 2 to N plugin + Energy storage module No. 1 is put into operation, and the remaining energy storage modules perform electronic bypass;

[0034] After the rolling cycle delay, take the queue No. 3 to N plugin Energy storage module No. +2 is put into operation, and the remaining energy storage modules perform electronic bypass. The cycle is executed until the end of the queue is reached and then returns to the starting position of the queue.

[0035] Specifically, firstly, the number N of all available energy storage modules is identified by the on / off state of each module bypass switch S0 received through communication. avail , record the available energy storage module voltage and energy storage module number. According to the normal startup process, after the SSC system is started, the AC side MMC module is connected to the grid for charging. After charging is completed, the MMC module begins to unlock and run. When the DC side needs to be put into use, the DC side circuit breaker is closed to connect the AC side and the DC side, and the DC side energy storage module begins to charge. The power supply for the drive control part of each energy storage module is taken from the DC side of the module. When the SSC DC side starts charging from zero voltage, the module voltage is low and the control pulse cannot be sent normally. Figure 2 First Semiconductor Devices T 1 and the first semiconductor device T 2 are both in the off state, at which time each energy storage module is charged by an anti-parallel diode in an uncontrolled rectification manner.

[0036] When the voltage of each energy storage module rises to meet the normal operation requirements of the drive control, the SSC DC side starts unlocking and enables, and calculates the number of energy storage modules that need to be put into use and the number of modules that require electronic bypass.

[0037] Figure 3 A schematic diagram of a flow chart of calculating the number of energy storage modules required to be put into operation in each branch and the number of energy storage modules required to be electronically bypassed on the DC side of a static synchronous condenser provided by an embodiment of the present invention. Figure 3 , the number of energy storage modules that need electronic bypass is N bypass Initialized to 0;

[0038] The number of energy storage modules N required plugin Equal to the number of available energy storage modules N avail Subtract the number of energy storage modules N that require electronic bypass bypass , until the number of energy storage modules N required to be invested plugin Equal to the number of energy storage modules N1 required for rated operation of the system;

[0039] Maintain the current number of energy storage modules N that need to be invested plugin and the number of energy storage modules N that require electronic bypass bypass .

[0040] If the number of available energy storage modules N avail The number of energy storage modules N1 required for rated operation of the system is greater than or equal to the number of energy storage modules N1 required for electronic bypass. bypass Initialized to 0; if the number of available energy storage modules Navail If the number of energy storage modules N1 required for the rated operation of the system is less than that required, that is, the system does not meet the normal operating conditions, the DC side will be blocked and the number of energy storage modules N required to be put into operation will be terminated. plugin and the number of energy storage modules N that require electronic bypass bypass Calculation.

[0041] If the number of energy storage modules N required plugin Not equal to the number of energy storage modules N1 required for rated operation of the system, after the step-by-step electronic bypass delay time T step , the number of energy storage modules that need electronic bypass is N bypass =N bypass +1 into N plugin =N avail -N bypass , until the number of energy storage modules N required to be invested plugin Equal to the number of energy storage modules N1 required for rated operation of the system.

[0042] In the embodiment of the present invention, the number of energy storage modules that need electronic bypass is firstly bypass Initialized to 0, the number of energy storage modules required is N plugin =N avail -0, after the step-by-step electronic bypass delay time, the number of energy storage modules that will need electronic bypass N bypass Increase to 1, then the number of energy storage modules N required to be invested plugin =N avail -1; after the step-by-step electronic bypass delay time, the number of energy storage modules that need electronic bypass is N bypass Increase to 2, the number of modules put into operation is the number of energy storage modules that need to be put into operation N plugin =N avail -2.....Repeat this operation until the number of energy storage modules required is N. plugin The number of energy storage modules required to achieve the rated operation of the system is N1, that is, N plugin =N1.

[0043] A single energy storage module uses Figure 2 In the half-bridge structure shown in (a) and (b), the first semiconductor device T 1 and second semiconductor devices T 2. The second semiconductor device is connected in parallel with the bypass switch to open the N plugin The first semiconductor device of the energy storage module is turned off. plugin The second semiconductor device of the energy storage module is turned on by the N bypass The second semiconductor device of the energy storage module is used to turn off the N bypassA first semiconductor device of an energy storage module.

[0044] In the embodiment of the present invention, the absolute value of the sampled branch current is calculated and compared with the dead zone setting value. I set For comparison, when the absolute value of the sampled branch current is greater than I set When the absolute value of the sampled branch current is less than or equal to I set When , it is determined that there is no current in the branch.

[0045] Figure 4 This is a schematic diagram of the switching strategy of each energy storage module in the active voltage balancing mode on the DC side of the static synchronous condenser provided by the embodiment of the present invention. Figure 4 , when k> k set When there is current in the branch, k set Set the energy storage module voltage balance value, and perform energy storage module switching in active voltage balancing mode: when the sampled branch current charges the energy storage module, sort the available energy storage modules in ascending order of voltage, that is, the energy storage modules with low voltage are placed in front of the queue, and the energy storage modules with high voltage are placed in the back of the queue; select energy storage modules according to the sorting order until the number of energy storage modules N that need to be put into operation plugin , the remaining energy storage modules perform electronic bypass; when the energy storage modules are charged, they are put into use according to the queue order, that is, they are put into use in order from small to large from the front to the back until the number of energy storage modules N is reached plugin After being put into use, the number of available energy storage modules N avail The remaining energy storage modules in the system perform electronic bypass to ensure that the energy storage modules with lower voltages are charged first and maintain system voltage balance.

[0046] When the branch current direction causes the energy storage module to discharge, the available energy storage modules are sorted in descending order of voltage, that is, the energy storage modules with high voltage are placed in the front of the queue, and the energy storage modules with low voltage are placed in the back of the queue; the energy storage modules are selected in the sorting order until the number of energy storage modules N required to be put into use plugin The remaining energy storage modules perform electronic bypass. When the energy storage modules are discharged, they are put into operation in the order of queue, that is, they are put into operation from the front to the back in the order from the largest to the smallest until the number of energy storage modules N is reached. plugin After being put into use, the number of available energy storage modules N avail The remaining energy storage modules perform electronic bypass to ensure that the energy storage modules with higher voltages are discharged first to maintain system voltage balance.

[0047] For the convenience of explanation, in this embodiment, the number of available energy storage modules N is avail 5, the number of energy storage modules required for normal operation N1 is set to 3, refer to Figure 4 , if the module queue after the system is sorted for the first time is: the second energy storage module, the fourth energy storage module, the third energy storage module, the first energy storage module, and the fifth energy storage module, according to the queue order, the second energy storage module, the fourth energy storage module, and the third energy storage module are put into charging or discharging, and the first energy storage module and the fifth energy storage module perform electronic bypass; after updating the switching drive signals of each energy storage module, the order of the energy storage module queue changes according to the size of the voltage value: the fourth energy storage module, the first energy storage module, the second energy storage module, the fifth energy storage module, and the third energy storage module, according to the queue order, the fourth energy storage module, the first energy storage module, and the second energy storage module are put into charging or discharging, and the fifth energy storage module and the third energy storage module perform electronic bypass; after updating the switching drive signals of each energy storage module again, the order of the energy storage module queue changes according to the size of the voltage value: the third energy storage module, the fifth energy storage module, the first energy storage module, the second energy storage module, and the fourth energy storage module, according to the queue order, the third energy storage module, the fifth energy storage module, and the first energy storage module are put into charging or discharging, and the second energy storage module and the fourth energy storage module perform electronic bypass.

[0048] Figure 5 This is a schematic diagram of the switching strategy of each energy storage module in the DC side sequential rolling mode of the static synchronous condenser provided by the embodiment of the present invention. Figure 5 , when k < k set When there is no current in the branch, the switching is performed in a sequential rolling mode: the energy storage modules in the unsorted available energy storage module queue are switched in a front-to-back order until the number of energy storage modules N required to be switched is reached. plugin , the remaining energy storage modules perform electronic bypass; after the rolling cycle delay, take the queue No. 2~N plugin +1 energy storage module is put into operation, and the other energy storage modules are electronically bypassed; after the rolling cycle delay, the queue No. 3~N is selected plugin Energy storage module No. +2 is put into operation, and the remaining energy storage modules perform electronic bypass. The cycle is executed until the end of the queue is reached and then returns to the starting position of the queue.

[0049] Reference Figure 5 , the queue of unqueued energy storage modules is: the first energy storage module, the second energy storage module, the third energy storage module, the fourth energy storage module, and the fifth energy storage module. The first energy storage module, the second energy storage module, and the third energy storage module are charged or discharged in the order of the queue, and the fourth energy storage module and the fifth energy storage module perform electronic bypass; after a rolling cycle T roll After the delay, the first energy storage module at the front of the queue performs electronic bypass, and the fourth energy storage module previously in electronic bypass is put into charging or discharging; after a rolling cycle T rollAfter the delay, the second energy storage module at the second front end of the queue is electronically bypassed, and the fifth energy storage module previously in electronic bypass is put into charging or discharging; after a rolling cycle T roll After the delay, the third energy storage module at the third front of the queue is electronically bypassed, and the first energy storage module that was previously in electronic bypass is put into charging or discharging... According to this rule, after the electronic bypass module reaches the end of the queue, it returns to the beginning of the queue and executes in a loop. For the unsorted module queue, the number of energy storage modules that need to be put into operation is rolled out in order. plugin In the above embodiment, the energy storage module cycle input and output mode ensures that the number of available energy storage modules N avail The time of inputting and exiting each energy storage module is the same, so as to achieve the purpose of equalizing the pressure of the final system. In addition, in the process of cyclic inputting and exiting, the energy storage modules can be selected in the order of the above embodiment or at intervals, as long as the time of inputting and exiting each energy storage module is the same.

[0050] If the current system is already operating in active voltage balancing mode, when the voltage balance degree k of each energy storage module calculated in real time is < 0.9× k set Or when there is no current in the branch, it switches to the sequential rolling mode, otherwise it always maintains the active voltage balancing mode; if the current system is already working in the sequential rolling mode, when the voltage balance degree k of each energy storage module calculated in real time is >1.1× k set Only when there is current in the branch will it switch to active voltage balancing mode, otherwise it will always operate in sequential rolling mode. Dynamically adjust the threshold of mode switching according to the current operating mode to avoid voltage imbalance when the module voltage is unbalanced. k set When the value is close to the upper limit, the system switches frequently between the two modes.

[0051] If the SSC DC side is configured with multiple parallel branches, each branch is controlled according to the DC side control method of the static synchronous condenser, and through the drive synchronization mechanism between the branches, each branch always updates the drive signal of each energy storage module at the same time.

[0052] The DC side control method of the static synchronous condenser provided by the present invention can realize balanced control of the voltage between the energy storage modules on the SSC DC side under the premise that the equivalent switching frequency is basically controllable; in addition, if there are multiple parallel branches on the DC side, the circulating current between the branches can be effectively reduced, thereby reducing system losses and improving operating efficiency.

[0053] Obviously, the above embodiments are merely examples for the purpose of clear explanation, and are not intended to limit the implementation methods. For those skilled in the art, other different forms of changes or modifications can be made based on the above description. It is not necessary and impossible to list all the implementation methods here. The obvious changes or modifications derived therefrom are still within the scope of protection created by this application.

Claims

1. A DC side control method for a static synchronous condenser, characterized in that: include: Identify all available DC side energy storage module voltages and module numbers, and calculate the maximum value of the available energy storage module voltage U max , minimum value U min and the average value U avg ; SSC DC side startup unlocking enable, calculate the number of energy storage modules N that need to be put into use plugin and the number of energy storage modules N that require electronic bypass bypass ; Calculate the voltage balance k of each energy storage module at present, k=MAX[(U max -U avg ) / U avg ,(U avg -U min ) / U avg ], MAX means to take the maximum value function, U max Indicates the maximum voltage of the energy storage module, U avg Indicates the average voltage of the energy storage module, U min Indicates the minimum voltage of the energy storage module. When k>k set When there is current in the branch, k set Set the voltage balance value for the energy storage module and switch the energy storage module in active voltage balancing mode: When the branch current charges the energy storage module, the available energy storage module voltages are sorted in ascending order; when the branch current discharges the energy storage module, the available energy storage module voltages are sorted in descending order; and energy storage modules are selected according to the sorting order until the number of energy storage modules N required to be invested is reached. plugin , the remaining energy storage modules perform electronic bypass; When k <k set When there is no current in the branch, the switching is performed in a sequential rolling mode: The energy storage modules in the unsorted available energy storage module queue are put into use in a sequential order until the number of energy storage modules N required to be put into use is reached. plugin , the remaining energy storage modules perform electronic bypass; After the rolling cycle delay, take queues 2 to N plugin + Energy storage module No. 1 is put into operation, and the remaining energy storage modules perform electronic bypass; After the rolling cycle delay, take queues 3 to N plugin + Energy storage module No. 2 is put into operation, and the remaining energy storage modules are electronically bypassed. This cycle is repeated until the end of the queue is reached and the queue is returned to the beginning. Calculate the number of energy storage modules N required for each branch plugin and the number of energy storage modules N that require electronic bypass bypass : The number of energy storage modules that require electronic bypass is N bypass Initialized to 0; The number of energy storage modules N required plugin Equal to the number of available energy storage modules N avail Subtract the number of energy storage modules N that require electronic bypass bypass , until the number of energy storage modules N required to be invested plugin Equal to the number of energy storage modules N1 required for rated operation of the system; Maintain the current number of energy storage modules N that need to be invested plugin and the number of energy storage modules N that require electronic bypass bypass ; The switching principle between active voltage balancing mode and sequential rolling mode is: if the active voltage balancing mode is currently in operation, when the voltage balance degree k of each energy storage module calculated in real time is less than 0.9*k set Or when there is no current in the branch, it switches to the sequential rolling mode, otherwise it always maintains the active voltage balancing mode; if it is currently working in the sequential rolling mode, when the voltage balance degree of each energy storage module calculated in real time k>1.1*k set Only when there is current in the branch will it switch to active voltage equalization mode, otherwise it will always maintain sequential rolling mode.

2. The DC side control method of a static synchronous condenser according to claim 1, characterized in that: If the number of available energy storage modules N avail The number of energy storage modules N1 required for rated operation of the system is greater than or equal to the number of energy storage modules N1 required for electronic bypass. bypass Initialized to 0, the number of energy storage modules required is N plugin Initialized to N avail ; If the number of available energy storage modules N avail The number of energy storage modules N1 required for rated operation of the system is less than that required, the DC side is blocked, and the number of energy storage modules N required to be put into operation is terminated. plugin and the number of energy storage modules N that require electronic bypass bypass Calculation.

3. The DC side control method of a static synchronous condenser according to claim 1, characterized in that: If the number of energy storage modules N required plugin The number of energy storage modules N1 that is not equal to the rated operation of the system is N1. After the step-by-step electronic bypass delay time, the number of energy storage modules that need electronic bypass is N bypass =N bypass +1 into N plugin =N avail -N bypass , until the number of energy storage modules N required to be invested plugin Equal to the number of energy storage modules N1 required for rated operation of the system.

4. The DC side control method of a static synchronous condenser according to claim 1, characterized in that: The on / off status of the bypass switch of each energy storage module is received through communication, and the voltage and module number of each energy storage module on all available DC sides are identified.

5. The DC side control method of a static synchronous condenser according to claim 1, characterized in that: Calculate the absolute value of the sampled branch current and compare it with the dead zone setting value I set For comparison, when the absolute value of the sampled branch current is greater than I set When the absolute value of the sampled branch current is less than or equal to I set When , it is determined that there is no current in the branch.

6. The DC side control method of a static synchronous condenser according to claim 1, characterized in that: A single energy storage module includes a first semiconductor device and a second semiconductor device, wherein the second semiconductor device is connected in parallel with a bypass switch to open the N plugin The first semiconductor device of the number of energy storage modules is turned off. plugin The second semiconductor device of the number of energy storage modules is turned on by N bypass The second semiconductor device of the energy storage module is used to turn off the N bypass The first semiconductor device of an energy storage module.

7. The DC side control method of a static synchronous condenser according to claim 6, characterized in that: The power supply of the driving control part of each energy storage module is obtained from the DC side of the energy storage module. When the SSC DC side starts charging from zero voltage, the first semiconductor device and the second semiconductor device are both in the off state, and each energy storage module is charged by an anti-parallel diode in an uncontrolled rectification manner.

8. The DC side control method of a static synchronous condenser according to claim 1, characterized in that: If the SSC DC side is configured with multiple parallel branches, each branch is controlled according to the DC side control method of the static synchronous condenser, and through the drive synchronization mechanism between the branches, each branch always updates the drive signal of each energy storage module at the same time.

Images