Topology and method for multiplexing motor driver for dual-power transmission function of direct-current micro-grid

Abstract

The invention provides a solution for assisting voltage balance and energy storage of a bipolar direct-current micro-grid by using a non-running open-winding motor driving system, which comprises the following steps of: based on a common-bus open-winding permanent magnet synchronous motor structure, respectively connecting u +, v + and w + of a motor winding with neutral points of the bipolar direct-current micro-grid through connectors; therefore, the voltage balancing task can be reused; and u-, v-and w-of the motor winding are respectively connected with the positive electrode of the energy storage unit through a connector so as to be reused for a voltage balance task. Through voltage and current double closed-loop control, a preset power transmission target is achieved. The invention further provides an algorithm for assisting commutation and assisting power migration tasks by using the residual phases, and a more efficient power transmission task is realized while rotor jitter is avoided. The power requirements of the voltage balancer and the energy storage system are reduced, no extra power element is added, the economic cost and the occupied space are reduced, and system oscillation can be avoided in the starting and running process.

Description

Technical Field

[0001] The present invention relates to the field of power electronics, and in particular to a topology and method for dual-function power migration, and in particular to a topology and method for realizing voltage balance and energy storage of a bipolar direct current microgrid based on an open-winding motor driver. Background Art

[0002] With the increase in the types of renewable energy generation, the development of energy storage technology, and the obvious trend of DC load for end-users, DC microgrids have shown significant advantages in reducing energy conversion, improving energy utilization and system reliability. Compared with the unipolar DC microgrid architecture, the bipolar DC microgrid architecture has a higher output level and higher power transmission efficiency, and has received more extensive attention in recent years. However, the intermittent and asymmetric nature of distributed generation and the volatility and imbalance of loads will result in unstable voltage and unbalanced voltage between the two poles of the bipolar DC microgrid. Unstable and unbalanced voltage will damage the electrical equipment in the system and increase losses.

[0003] In order to ensure voltage stability and balance, energy storage systems and voltage balancers are indispensable. However, since additional voltage balancers increase the complexity and cost of the system, they have gradually been replaced. Reference 1 [Reference 1 is GVdBroeck, W.Martinez, M.Dalla Vecchia, S.Ravyts and J.Driesen,"Conversion efficiency ofthe buck three-level DC–DC converter in unbalanced bipolar DC microgrids,"IEEE Trans.Power Electron., vol.35, no.9, pp.9306-9319, Sept.2020. (Journal article)] proposed a full-bridge three-level DC / DC converter to replace the converter on the power generation side, which can simultaneously stabilize and balance the voltage. However, the converter is often integrated on the power generation side and has a limited adjustment range. In addition, in order to improve system reliability, redundant power switches or converters are often required, which increases the cost and complexity of the system. In order to adjust the load side voltage more accurately, a method based on a power grid model is proposed. Reference 2 [Reference 2 is J.-O.Lee, Y.-S.Kim and S.-I.Moon, "Current injection power flow analysis and optimal generation dispatch for bipolar DC microgrids," IEEE Trans. Smart Grid, vol. 12, no. 3, pp. 1918-1928, May 2021. (Journal article)] proposed a new bipolar DC microgrid injection current and generation dispatch optimization method to reduce operating costs and voltage imbalance. However, the initial investment of such methods is significantly increased.

[0004] Integrating the power transmission function into the system that often appears on the load side, replacing or partially replacing the voltage balancer or energy storage device in the power grid, can effectively solve the problem of high cost and avoid the risk of single point failure. Reference 3 [Reference 3 is Y.Xuan, X.Yang, W.Chen, T.Liu and X.Hao, "A novel three-level CLLC resonant DC–DC converter for bidirectional EV charger in DC microgrids," IEEE Trans. Ind. Electron., vol.68, no.3, pp.2334-2344, March 2021. (Journal article)] designs the electric vehicle charging port as a bidirectional DC / DC converter, and the idle electric vehicle energy storage system is used as the energy storage system of the DC microgrid. However, such a design increases the power devices of the original system, which undoubtedly increases the manufacturing cost and difficulty. In addition, the multiplexing method is limited in function and cannot integrate the voltage balancing function.

[0005] Considering that the AC motor drive is an important part of the bipolar DC microgrid and consumes a lot of electricity. At the same time, modern AC drive systems usually use variable voltage and frequency control, which is the same as the power conversion components, energy storage components, voltage stabilization components and other components of the power conversion module; the essence of the motor drive system is also the process of power conversion, which is the same as the function of the power conversion module. This means that the AC motor drive has high power density and power sharing potential. Therefore, in order to fully utilize the power density and power transmission capability of the AC motor drive to complete the voltage balance and voltage stability tasks of the bipolar DC microgrid, the method of reusing the motor drive system for the voltage balancing device and the bidirectional DC / DC converter needs to be studied. Summary of the invention

[0006] In order to solve the voltage imbalance and instability problems faced by bipolar DC microgrids, voltage balancing devices and energy storage systems are usually used to control the power flow between the two levels of the bipolar DC microgrid and between the grid and the energy storage system to obtain balanced and stable voltage, or to readjust the distributed generation interface or load on the bipolar DC microgrid. However, this will increase the size and manufacturing cost of the device, or cause unnecessary losses and reduced reliability.

[0007] The present invention makes full use of the power density and power transmission capability of the open-winding motor driver to complete the voltage balancing and stabilization tasks of the bipolar DC microgrid, and provides a solution for using a non-operating motor driver to assist dual power transmission. When the motor is in a non-operating state, the two power transmission tasks of voltage balancing and energy storage can be completed separately or simultaneously by closing the connector to change the topology. When the motor operation instruction is received or the power migration task is completed, all connections can be disconnected and the traditional topology can be restored. The strategy and corresponding topology adopted by the present invention do not require additional power switching devices and do not affect the normal operation of the motor driver, because the topology will be the same as the traditional one after the connector is disconnected. From the perspective of the entire bipolar DC microgrid system, the present invention will not significantly increase the cost and floor space. On the contrary, by applying the present invention to reduce the power requirements of the voltage balancer and the bidirectional DC / DC converter, cost and volume can be saved to a certain extent.

[0008] The topology and technical solution adopted by the present invention to solve its technical problem are:

[0009] The present invention uses a non-operating open-winding permanent magnet synchronous motor to complete the power migration task. The topological structure of the circuit is as follows Figure 1 As shown, P, O, and N are the positive pole, neutral line, and negative pole of the bipolar DC microgrid, respectively; "+" is the positive pole of the energy storage system, and "-" is the positive pole of the energy storage system; S1-S6 are the 6 power switches of inverter 1, U1, V1, and W1 are the three output interfaces of inverter 1, S1'-S6' are the 6 power switches of inverter 2, and U2, V2, and W2 are the three output interfaces of inverter 2; current sensors and voltage sensors are as shown in Figure 1 As shown, the arrow direction represents the positive direction of the current. The U1, V1, and W1 ports of the inverter 1 are connected to the u+, v+, and w+ windings of the open-winding motor, and are also connected to the inverter through the connector K. B1 , K B2 , K B3 Connected to the neutral point O of the bipolar DC microgrid through the control connector K B1 , K B2 , K B3 The U2, V2, and W2 ports of inverter 2 are connected to the u-, v-, and w-windings of the open-winding motor, and are also connected to the open-winding motor through connector K. S1 , K S2 , K S3 Connected to the positive pole of the energy storage system through the control connector K S1 , K S2 , K S3 The on and off of the device determines whether to perform the energy storage task.

[0010] The specific steps of power migration are as follows:

[0011] Step 1: Determine the task type of the dual power transmission multiplexing system.

[0012] According to the upper and lower pole voltage U of the bipolar DC microgrid P , U N The sampling result and the total voltage of the bipolar DC microgrid are equal to the target control voltage U Target The type of task is determined by the method shown in formula (1).

[0013]

[0014] And according to whether the direction of the current is consistent with the Figure 1 Whether the specified positive direction is consistent determines the polarity of the task, where the consistent direction is a positive task and the opposite direction is a negative task. The specific judgment method is shown in formula (2).

[0015]

[0016] If the system performs a mixed task of voltage balancing and energy storage, proceed to step 2; if it only performs a single task, jump to step 3.

[0017] Step 2: Determine how to allocate initial tasks.

[0018] When the system performs mixed tasks, it is stipulated that two windings are selected to undertake different power transmission tasks in the initial stage. The tasks to be performed by the windings are determined according to the polarity and rotor position of the two tasks. The regional division is as follows: Figure 2 If both tasks are positive tasks, the task allocation division area is as follows Figure 2 As shown in (a), when the rotor falls into the three regions [A+, B+), [B+, C+), and [C+, A+), the voltage balancing task is undertaken by the A, B, and C windings respectively, and the energy storage function is undertaken by the B, C, and A windings respectively; if both tasks are negative tasks, the task allocation division area is as follows Figure 2 As shown in (b), when the rotor falls into the three regions [B-, C-), [C-, A-), and [A-, B-), the voltage balancing task is undertaken by the B, C, and A windings respectively, and the energy storage function is undertaken by the C, A, and B windings respectively; when the polarities of the two tasks are opposite, the initial task allocation method is as follows Figure 2 (c) shows that the positive and negative of the task correspond to the positive and negative of the winding. After determining the initial task allocation method, execute step 3.

[0019] Step 3: Topology switching

[0020] When the system only needs to perform a single task, the topology switching method for different tasks is as follows: When performing the voltage balancing task, disconnect KS1 , K S2 , K S3 And turn on K B1 , K B2 , K B3 , transform the topology into Figure 3 As shown; when performing voltage balancing tasks, disconnect K B1 , K B2 , K B3 And turn on K S1 , K S2 , K S3 , transform the topology into Figure 4 and proceed to step 4.

[0021] When the system performs a composite task, the composite system topology is switched according to the initial task allocation method in step 2: if the phase performs a voltage balancing task, the K of the corresponding phase needs to be disconnected. S1 , K S2 or K S3 , open the corresponding K B1 , K B2 or K B3 If the phase performs energy storage task, the K of the corresponding phase needs to be disconnected. B1 , K B2 or K B3 , open the corresponding K S1 , K S2 or K S3 . After the switch is complete, skip to step 5.

[0022] Step 4: Single task control method.

[0023] When performing voltage balancing tasks, the control target is U N -U P =0; when performing energy storage tasks, the control target is U N +U P =U Target The feedback value U sampled by the voltage sensor is used N , U P Perform voltage PI regulation and calculate the required target current value i Target At the same time, the three-phase winding adopts current sharing control, distributes the target current according to formula (3), and obtains the target current of each phase. The target current is compared with the actual phase current feedback value, and then the duty cycle of each phase winding is obtained through PI adjustment.

[0024]

[0025] When the multiplexing system only performs the positive task of voltage balance, the corresponding duty ratios of A, B, and C are allocated to the power switches S2', S4', and S6' of the inverter 2, so that the power transmission from the lower pole to the upper pole of the bipolar DC microgrid can be realized; when the multiplexing system performs the negative task of voltage balance, the corresponding duty ratios of A, B, and C are allocated to the power switches S1', S3', and S5' of the inverter 2, so that the power transmission from the lower pole to the upper pole of the bipolar DC microgrid can be realized;

[0026] When the multiplexing system only performs the positive task of energy storage, the corresponding duty ratios of A, B, and C are allocated to the power switches S1, S3, and S5 of inverter 1, so that the bipolar DC microgrid can charge the energy storage system; when the multiplexing system performs the negative task of energy storage, the corresponding duty ratios of A, B, and C are allocated to the power switches S2, S4, and S6 of inverter 1, so that the energy storage system can discharge to the bipolar DC microgrid.

[0027] If the power transfer task is to be continued, this step is executed in a loop; if the system task type needs to be changed or an instruction to end the power transfer task is received, jump to step 9;

[0028] Step 5: Initial hybrid mission control approach.

[0029] When performing voltage balancing tasks, the control target is U N -U P =0; when performing energy storage tasks, the control target is U N +U P =U Target The U obtained by sampling the voltage sensor N , U P Calculate the control voltage of different tasks, and calculate the target current value i of different tasks through voltage PI adjustment Target , compare the target current with the actual phase current feedback value of the corresponding phase, and then obtain the duty cycle of the voltage balance task and the energy storage task through PI adjustment.

[0030] If the phase performs a positive voltage balancing task, the duty cycle of the voltage balancing task is assigned to the corresponding S2', S4' or S6'; if the phase performs a negative voltage balancing task, the duty cycle of the voltage balancing task is assigned to the corresponding S1', S3' or S5'. If the phase performs a positive energy storage task, the duty cycle of the energy storage task is assigned to the corresponding S1, S3 or S5; if the phase performs a negative energy storage task, the duty cycle of the energy storage task is assigned to the corresponding S2, S4 or S6. At the same time, the auxiliary commutation flag is set to 0 and the auxiliary power transmission flag is set to 0.

[0031] Step 6: Determine whether the remaining phases are required to assist in commutation

[0032] The feedback voltage value is obtained through the voltage sensor, and the i of the two tasks is calculated again according to the feedback voltage. Target .

[0033] If the auxiliary commutation flag is 0, according to the last i Target The value determines whether the polarity of the two tasks changes at the same time: if not, execute step 7; if they change at the same time, it is necessary to determine whether the auxiliary power transmission flag is 0. If the auxiliary power transmission flag is 1, it is necessary to stop the auxiliary task of the phase first, set the target current of the remaining phase to 0, return the auxiliary work, and after the auxiliary task of the remaining phase is completed, set the auxiliary power transmission flag to 0, and then continue the auxiliary commutation process of the remaining phase. According to the two tasks i Target The size of the phase with the heavier task is determined as the replaced phase, and the task of the replaced phase is assigned to the remaining phases. The specific process is: switch the remaining phase topology to be the same as the replaced phase, set the reference voltage of the replaced phase to 0, and the reference voltage of the remaining phase to i Target , set the auxiliary commutation flag to 1 and jump to step 8.

[0034] If the auxiliary commutation flag is 1, continue to set the reference voltage of the replaced phase to 0, and the reference voltage of the remaining phases to i Target , skip to step 8.

[0035] Step 7: Determine whether the remaining phase auxiliary power transmission task is required.

[0036] According to the two tasks in step 6, Target Determine whether the remaining phases are needed to assist power transmission. Target_Max Greater than the i of another task Target_Min , then it is called a larger i Target_Max The winding is the heavy phase. Set the shunt threshold i Shunt , at this time, if i Target_Max ≤i Shunt , then the remaining phase auxiliary power transmission task is not required, jump to step 5; if i Target_Max >i Shunt , the remaining phase is needed to assist the power transmission task.

[0037] If the auxiliary power transmission flag is 0 at this time, the steps of the auxiliary power transmission task are: switch the topology of the remaining phases to the heavy phase topology, and perform i according to formula (4). Target_Max reallocation and sets the auxiliary power transfer flag to 1.

[0038]

[0039] If the auxiliary power transmission flag is 1, it is necessary to determine whether the task of the auxiliary phase has changed. If it has changed, the topology of the auxiliary phase needs to be switched, and then the auxiliary power transmission flag is set according to formula (4). Target_Max redistribution.

[0040] Step 8: Hybrid mission control approach.

[0041] The feedback current of each phase is obtained through the current sensor, the required duty cycle is calculated according to the target current of each phase, and is allocated to the corresponding power switch.

[0042] If the auxiliary commutation flag is set to 1, position sampling is performed to determine whether the position is turned to Figure 2 In the divided area: if the rotor does not rotate to the corresponding area, the commutation flag remains at 1; if the rotor rotates to the corresponding area, the task of the auxiliary phase needs to be assigned to the replaced phase, and the reference voltage of the replaced phase is set to i Target , the reference voltage of the remaining phases is 0, and the auxiliary commutation flag is cleared.

[0043] If the power transfer task is to be continued, jump to step 6; if the system task type needs to be changed or an instruction to end the power transfer task is received, jump to step 9.

[0044] Step 9: Stop the power migration task.

[0045] Setting Target = 0, sample the motor phase current, then calculate the duty cycle that each phase should generate and allocate it to the corresponding power switch. When the motor phase current is small to a certain range, turn off all power switches and open all connectors. At this time, you can execute step 1 to continue the new power migration task, or stop the power transmission work.

[0046] The beneficial effects of the present invention are:

[0047] (1) The present invention can reduce the power requirements of the voltage balancer and the energy storage device in the power grid, and reduce the economic cost and space occupied: The strategy proposed in the present invention makes full use of the non-operating open-winding motor drive belonging to the bipolar DC microgrid, thereby sharing part of the power transmission and energy storage burden of the voltage balancer and the energy storage device. In addition, considering that there are many motor drives attached to the bipolar DC microgrid, it is possible to reduce the power requirements of the voltage balancer, thereby reducing the cost, volume and weight.

[0048] (2) The present invention can realize voltage balancing and energy storage functions separately or simultaneously, and can flexibly change the topology according to the needs of the power grid to ensure voltage balance and stability on the load side.

[0049] (3) The present invention avoids system oscillation during the entire power transmission process: To prevent the motor from rotating or swinging when the power transmission is started, the task polarity and the motor rotor position are used to determine the allocation of winding tasks during the initial task allocation stage; during the power transmission process, a hybrid method of residual phase auxiliary commutation and auxiliary power transmission is used to avoid system oscillation problems caused by changes in system tasks.

[0050] (4) The present invention can achieve precise control of the voltage value of the bipolar DC bus: the proposed strategy can implement dual closed-loop control of voltage and current based on the feedback values ​​of the upper and lower pole voltages and phase currents of the bipolar DC bus, thereby achieving precise control of the DC bus. BRIEF DESCRIPTION OF THE DRAWINGS

[0051] Figure 1 This is the topological structure proposed by the present invention.

[0052] Figure 2 is the allocation method of the initial tasks in the hybrid mode, Figure 2 (a) The allocation method when all tasks are positive. Figure 2 (b) The allocation method when all tasks are negative. Figure 2 (c) Task allocation method when the tasks have different polarities.

[0053] Figure 3 It is a topology and process of single-function power transmission that only performs voltage balancing. Figure 3 (a) is the charging process of the polar winding in a bipolar DC microgrid. Figure 3 (b) is the process of the winding discharging to the upper pole through the diode. Figure 3 (c) is the charging process of the polar winding on the bipolar DC microgrid. Figure 3 (d) is the process of the winding discharging to the lower pole through the diode.

[0054] Figure 4 It is a topology and process of single-function power transmission that only performs energy storage. Figure 4 (a) is the process of bipolar DC microgrid charging the winding. Figure 4 (b) is the process of the winding discharging to the energy storage system through the diode freewheeling. Figure 4 (c) is the process of energy storage system charging the winding. Figure 4 (d) is the process of the winding discharging to the bipolar DC microgrid through the diode.

[0055] Figure 5 It is a dual-function multiplexed power topology and transmission process in hybrid mode. The A-phase winding performs voltage balancing tasks, the B-phase winding performs energy storage work, and the C-phase winding serves as the remaining phase auxiliary power migration task. Figure 5(a) and (b) are the winding charging process of the C winding assisting the B phase energy storage task and the winding discharging process through the diode, respectively. Figure 5 (c) and (d) respectively show the winding charging process in which the C winding assists in completing the voltage balancing task of phase A and the winding discharging process through the diode.

[0056] In the figure, P, O, and N are the three-terminal interfaces of the bipolar DC microgrid; + and - are the interfaces of the energy storage unit; S1, S2, S3, S4, S5, S6, S1', S2', S3', S4', S5', and S6' are the power switches of the inverter; K B1 , K B2 , K B3 , K S1 , K S2 , K S3 is a connector; U1, V1, W1 are the outlets of inverter 1, and U2, V2, W2 are the outlets of inverter 2; u+, v+, w+, u-, v-, w- are the interfaces of the motor windings respectively; i A 、i B 、i C are the currents of the three-phase windings of the motor; i DC is the bus current of the motor; the arrow direction represents the positive direction of the specified current; U P , U N , U S They are the positive voltage of the bipolar DC microgrid, the negative voltage of the bipolar DC microgrid and the terminal voltage of the energy storage system. DETAILED DESCRIPTION

[0057] The present invention is further described below in conjunction with embodiments.

[0058] The present invention uses a non-operating open-winding permanent magnet synchronous motor drive system to complete the power migration task. The output end of the inverter 1 is connected to the motor winding and is also connected to the motor winding through the connector K. B1 , K B2 , K B3 Connected to the neutral point O of the bipolar DC microgrid, the output end of inverter 2 is connected to the motor winding and connected to the output end of inverter 2 through connector K. S1 , K S2 , K S3 Connected to the + pole of the energy storage system. By controlling the switch closure of the connector, the topology is changed and the idle motor drive system is reused for different power transmission functions. When the motor is idle and the upper and lower loads of the bipolar DC microgrid system are not equal, that is, the upper pole is loaded with 40Ω and the lower pole is loaded with 80Ω, U Target =200V,i Shunt=0.5A, and the bipolar DC microgrid voltage is higher than the set value, at this time the motor rotor position is 29.8°. During the operation of the motor, reduce the input U N +U P , simulating the scenario where the power generation decreases, that is, using the method of the present invention, the specific implementation method is as follows:

[0059] (1) Perform step 1: According to the load imbalance, grid voltage excess and other conditions, the voltage sampling result U P , U N The condition in formula (1) is satisfied: the system performs a voltage balancing and energy storage hybrid task. And according to formula (2), it can be determined that both voltage balancing and energy storage perform positive tasks. Since the system performs a voltage balancing and energy storage hybrid task, step 2 is performed.

[0060] (2) Perform step 2: Both tasks are positive tasks, and the rotor position is 29.8°. The partition is as follows Figure 2 (a) When the rotor falls in the interval [A+, B+), phase A performs voltage balancing and phase B performs energy storage.

[0061] (3) Perform step 3: Ensure that K is disconnected S1 , K B2 Under the premise of connecting K B1 , K S2 , after the switch is completed, jump to step 5.

[0062] (4) Perform step 5: Read the sampled value U of the voltage sensor N , U P , using the sampling value and the target value U N -U P =0, U N +U P =U Target Compare and perform PI calculation to get the target current value. Feedback the current values ​​of phase A and phase B, and then perform PI adjustment to get the duty cycle of power switches S2' and S3. At the same time, set the auxiliary commutation flag to 0.

[0063] (5) Perform step 6: If the task polarity does not change, proceed to step 7.

[0064] (6) Perform steps 7 and 8: At this time, the target current for voltage balance is calculated to be 2.2A through the voltage PI loop, and the target current for energy storage is 5A. Therefore, the C-phase winding is required to assist the B-phase in energy storage, and the circuit topology is switched to ensure that K is disconnected. B3 Under the premise of turning on K S3, and help phase B share 50% of the target current, obtain the feedback current of each phase through the current sensor, calculate the required duty cycle of each phase according to the target current of phases A, B, and C 2.2A, 2.5A, and 2.5A, and distribute the duty cycle to power switches S2', S3, and S5. The power transmission process is as follows Figure 5 As shown in (a) and (b).

[0065] (8) At this time, the total voltage is reduced and step 6 is executed: the task polarity does not change at the same time.

[0066] (9) Perform steps 7 and 8: At this time, the target current for voltage balance is calculated to be 2.2A through the voltage PI loop, and the target current for energy storage is 2A. Therefore, the C-phase winding is still required to assist the A-phase in energy storage tasks, and to help the B-phase share 30% of the target current. At this time, A and B complete their tasks separately, and then set the target current of the C-phase to 0, wait for the C-phase auxiliary power transmission task to be completed, and then switch the topology to ensure that the K S3 Under the premise of turning on K B3 Then, the feedback current of each phase is obtained through the current sensor, and the required duty cycle of each phase is calculated according to the target current of phases A, B, and C (1.54A, 2A, and 0.66A), and the duty cycle is allocated to the power switches S2', S3, and S5. The power transmission process is as follows: Figure 5 As shown in (c) and (d).

[0067] (10) Perform step 9: Set the target current of each phase to 0, sample the phase current of the motor, calculate the duty cycle that each phase should generate, and allocate it to the corresponding power switch. When the phase current of the motor is small to a certain range, turn off all power switches and open all connectors.

Claims

1. A topology and method for reusing a motor driver for dual power transmission function in a DC microgrid, characterized in that: The voltage balancing system for bipolar DC microgrid power migration using an open-winding motor and its driver changes the topology of the three-phase open-winding motor driver connected to the P and N poles of the bipolar DC bus: the u+, v+, and w+ interfaces of the open winding are connected to the O pole of the bipolar DC bus, and the connectors K are used to connect the open-winding motor and the N poles of the bipolar DC bus. B1 , K B2 , K B3 Control its on and off to determine whether the phase performs the voltage balancing function; connect the open winding u-, v-, w- to the positive pole of the energy storage system, and use connector K S1 , K S2 , K S3 Control its on and off to determine whether the phase performs the energy storage task; the negative pole of the energy storage system is connected to the N pole of the bipolar DC microgrid; if the system receives a power transmission command, the type, polarity and distribution method of the task are determined according to the actual situation and target value of the system, and then the topology is switched according to the task characteristics of each phase winding, and dual closed-loop control is used to calculate the duty cycle of the corresponding power device to realize power migration. When the size or direction of the task changes, the remaining phases are flexibly used to complete the auxiliary power transmission and commutation.

2. A topology and method for utilizing a motor driver as claimed in claim 1 for dual power transmission function of a DC microgrid, characterized in that The steps include: Step 1: Determine the task type of the dual power transmission multiplexing system: According to the voltage U P , U N The sampling result and the total voltage of the bipolar DC microgrid are equal to the target control voltage U Target Determine the type of task, and the determination method is shown in formula (1): The polarity of the task is determined based on whether the direction of the current when executing the task is consistent with the direction of the winding positive terminal u+, v+, w+ pointing to u-, v-, w-. The consistent direction is a positive task, and the opposite direction is a negative task. The specific judgment method is shown in formula (2): If the system performs a mixed task of voltage balancing and energy storage, proceed to step 2; if it only performs a single task, jump to step 3; Step 2: Determine the initial task allocation method: When the system performs mixed tasks, it is stipulated that two windings are selected to undertake different power transmission tasks in the initial stage; the execution of the winding tasks is determined according to the polarity of the two tasks and the rotor position: if both tasks are positive tasks, the modulation area is divided into three areas [A+, B+), [B+, C+), and [C+, A+) according to the three directions of the three windings A+, B+, and C+. When the rotor falls into the three areas respectively, the voltage balancing task is undertaken by the A, B, and C windings respectively, and the energy storage function is undertaken by the B, C, and A windings respectively; if both tasks are negative tasks The modulation area is divided into [B-, C-), [C-, A-), [A-, B-) according to the three directions of the three windings A-, B-, and C-. When the rotor falls in the three areas, the voltage balancing task is undertaken by the B, C, and A windings respectively, and the energy storage function is undertaken by the C, A, and B windings respectively; when the two tasks have opposite polarities, the modulation area is divided into [A+, C-), [B+, A-), [C+, B-) according to 90°, 210°, and 330°, and the positive and negative of the tasks correspond to the positive and negative of the windings; after determining the initial task allocation method, execute step 3; Step 3: Topology switching: When the system only needs to perform a single task, the topology switching method for different tasks is as follows: When performing the voltage balancing task, disconnect K S1 , K S2 , K S3 And turn on K B1 , K B2 , K B3 ; When performing voltage balancing tasks, disconnect K B1 , K B2 , K B3 And turn on K S1 , K S2 , K S3 , and proceed to step 4; When the system performs a composite task, the composite system topology is switched according to the initial task allocation method in step 2: if the phase performs a voltage balancing task, the K of the corresponding phase needs to be disconnected. S1 , K S2 , K S3 , open the corresponding K B1 , K B2 , K B3 If the phase performs energy storage task, the K of the corresponding phase needs to be disconnected. B1 , K B2 , K B3 , open the corresponding K S1 , K S2 , K S3 , after the switch is completed, jump to step 5; Step 4: Single task control method: When performing voltage balancing tasks, the control target is U N -U P =0; when performing energy storage tasks, the control target is U N +U P =U Target ; Feedback value U sampled by voltage sensor N , U P Perform voltage PI regulation and calculate the required target current value i Target At the same time, the three-phase windings adopt current sharing control, and the target current is distributed according to formula (3) to obtain the target current of each phase; the target current is compared with the actual phase current feedback value, and the duty cycle of each phase winding is obtained through PI adjustment; When the multiplexing system only performs the positive task of voltage balance, the corresponding duty ratios of A, B, and C are allocated to the power switches S2', S4', and S6' of the inverter 2, so that the power transmission from the lower pole to the upper pole of the bipolar DC microgrid can be realized; when the multiplexing system performs the negative task of voltage balance, the corresponding duty ratios of A, B, and C are allocated to the power switches S1', S3', and S5' of the inverter 2, so that the power transmission from the lower pole to the upper pole of the bipolar DC microgrid can be realized; When the multiplexing system only performs the positive task of energy storage, the corresponding duty ratios of A, B, and C are allocated to the power switches S1, S3, and S5 of inverter 1, so that the bipolar DC microgrid can charge the energy storage system; when the multiplexing system performs the negative task of energy storage, the corresponding duty ratios of A, B, and C are allocated to the power switches S2, S4, and S6 of inverter 1, so that the energy storage system can discharge to the bipolar DC microgrid. If the power transfer task is to be continued, this step is executed in a loop; if the system task type needs to be changed or an instruction to end the power transfer task is received, jump to step 9; Step 5: Initial hybrid mission control method: When performing voltage balancing tasks, the control target is U N -U P =0; when performing energy storage tasks, the control target is U N +U P =U Target , U obtained by sampling the voltage sensor N , U P Calculate the control voltage of different tasks, and calculate the target current value i of different tasks through voltage PI adjustment Target , compare the target current with the actual phase current feedback value of the corresponding phase, and obtain the duty cycle of the voltage balance task and the energy storage task through PI regulation; If the phase performs a positive voltage balancing task, the duty cycle of the voltage balancing task is allocated to the corresponding S2', S4' or S6'; if the phase performs a negative voltage balancing task, the duty cycle of the voltage balancing task is allocated to the corresponding S1', S3' or S5'; if the phase performs a positive energy storage task, the duty cycle of the energy storage task is allocated to the corresponding S1, S3 or S5; if the phase performs a negative energy storage task, the duty cycle of the energy storage task is allocated to the corresponding S2, S4 or S6; at the same time, the auxiliary commutation flag is set to 0 and the auxiliary power transmission flag is set to 0; Step 6: Determine whether the remaining phases are required to assist in commutation: The feedback voltage value is obtained through the voltage sensor, and the i of the two tasks is calculated again according to the feedback voltage. Target ; If the auxiliary commutation flag is 0, according to the last i Target The value determines whether the polarity of the two tasks changes at the same time: if not, execute step 7; if they change at the same time, it is necessary to determine whether the auxiliary power transmission flag is 0. If the auxiliary power transmission flag is 1, it is necessary to stop the auxiliary task of the phase first, set the target current of the remaining phase to 0, return the auxiliary work, and after the auxiliary task of the remaining phase is completed, set the auxiliary power transmission flag to 0, and then continue the auxiliary commutation process of the remaining phase; according to the two tasks i Target The size of the phase with the heavier task is determined as the replaced phase, and the task of the replaced phase is assigned to the remaining phases. The specific process is: switch the remaining phase topology to be the same as the replaced phase, set the reference voltage of the replaced phase to 0, and the reference voltage of the remaining phase to i Target , set the auxiliary commutation flag to 1 and jump to step 8; If the auxiliary commutation flag is 1, continue to set the reference voltage of the replaced phase to 0, and the reference voltage of the remaining phases to i Target , skip to step 8; Step 7: Determine whether the remaining phase auxiliary power transmission task is required: According to the two tasks in step 6, i Target Determine whether the remaining phase auxiliary power transmission is needed: If the i of one phase task Target_Max Greater than the i of another task Target_Min , then it is called a larger i Target_Max The winding is the heavy phase, set the shunt threshold i Shunt , at this time, if i Target_Max ≤i Shunt , then the remaining phase auxiliary power transmission task is not required, jump to step 5; if i Target_Max >i Shunt , then the remaining phase is needed to assist the power transmission task; If the auxiliary power transmission flag is 0 at this time, the steps of the auxiliary power transmission task are: switch the topology of the remaining phases to the heavy phase topology, and perform i according to formula (4). Target_Max Redistribution of power and setting the auxiliary power transmission flag to 1; If the auxiliary power transmission flag is 1, it is necessary to determine whether the task of the auxiliary phase has changed. If it has changed, the topology of the auxiliary phase needs to be switched, and then the auxiliary power transmission flag is set according to formula (4). Target_Max redistribution of Step 8: Hybrid Mission Control Method: The feedback current of each phase is obtained through the current sensor, the required duty cycle is calculated according to the target current of each phase, and the duty cycle is allocated to the corresponding power switch; If the auxiliary commutation flag is recorded as 1, position sampling is performed to determine whether the motor position is rotating: if the rotor does not rotate to the corresponding area, the commutation flag is still 1; if the rotor rotates to the corresponding area, the task of the auxiliary phase needs to be assigned to the replaced phase, and the reference voltage of the replaced phase is set to i Target , the reference voltage of the remaining phases is 0, and the auxiliary commutation flag is cleared; If the power transfer task is to be continued, jump to step 6; if the system task type needs to be changed or an instruction to end the power transfer task is received, jump to step 9; Step 9: Stop the power migration task: Setting Target =0, sample the phase current of the motor, then calculate the duty cycle that each phase should generate and allocate it to the corresponding power switch. When the phase current of the motor is small to a certain range, turn off all power switches and open all connectors. At this time, you can execute step 1 to continue the new power migration task or stop the power transmission work.

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