Reactive power optimization method for multi-port power spring

Abstract

The invention discloses a reactive power optimization method for a multi-port power spring, and belongs to the technical field of power spring control. The defects of large key load voltage fluctuation, large circuit reactive power and poor dynamic performance in the existing power spring control process are overcome. The topology of the three-port power spring system comprises a direct current input source, voltage stabilizing capacitors C1-C4 of all ports, a primary inversion full bridge, a secondary modulation full bridge, a tertiary rectification full bridge, a power coupling inductor L, a critical load, a non-critical load, a bidirectional DC-DC conversion module and an energy storage unit. The invention constructs a reactive power optimization control method, and the method comprises the steps: building four working modes according to the interaction characteristics of a voltage regulation ratio and transmission power, then dividing the transmission power into three regulation and control regions, and building a Lagrange optimization model; constructing a dynamic voltage control strategy method; and constructing a direct power control lifting dynamic response. According to the invention, optimal solutions of different power regions are obtained.

Description

Technical Field

[0001] The present invention belongs to the technical field of power spring control, and particularly relates to a reactive power optimization method for a multi-port power spring. Background Art

[0002] With the continuous development of renewable energy power generation systems, it is particularly important to integrate various energy forms such as energy storage batteries and photovoltaic modules. These systems need to be interconnected with loads and backup batteries to improve overall efficiency and reliability. Three-port converters have been widely used in these fields due to their advantages in reducing power transmission links, integrating high-frequency links, multi-winding transformers, and centralized control. They are applied in multiple scenarios such as fuel cell systems, automotive electronics, and power supply for single-family houses. To overcome the deficiencies of traditional converters, researchers have proposed the concept of three-port power springs and continuously expanded their applications.

[0003] Currently, the three-port power spring control system mainly consists of a three-active-bridge converter and an energy storage battery modulation unit. As an extension of the dual-active-bridge structure, the three-active-bridge converter inherits similar control logics, mainly including three control modes: single-phase-shift, double-phase-shift, and triple-phase-shift. Researchers are now focusing on the decoupling optimization of single-phase-shift control, hoping to achieve better power regulation and efficiency improvement in this way. However, this control method still has some problems, such as low control freedom, high reactive power loss, and limited soft-switching range under high-voltage gain conditions. When power fluctuations occur in the microgrid, the three-active bridge can direct the fluctuating power to non-critical loads, thus ensuring the power supply quality of critical loads. If the output-side fluctuations exceed the absorption capacity of non-critical loads, the energy storage device needs to be activated to discharge to maintain power balance.

[0004] Existing power spring systems have the following deficiencies: complex system architecture, low energy interaction efficiency; limited power transmission range, difficult to meet the requirements of multi-load scenarios; single control strategy, slow dynamic response speed, unable to meet the requirements of high-precision energy regulation; system efficiency needs to be improved, large power loss. Therefore, in-depth research on the topology optimization of three-port power springs and their advanced control strategies has important theoretical and practical values. Summary of the Invention

[0005] The problem to be solved by the present invention is to overcome the defects of large voltage fluctuations of critical loads, large reactive power of the circuit, and poor dynamic performance in the existing power spring control process, and propose a reactive power optimization method for a multi-port power spring.

[0006] To achieve the above object, the present invention is realized through the following technical solutions:

[0007] A reactive power optimization method for a multi-port power spring, which is implemented based on a three-port power spring system. The topology of the three-port power spring system includes a DC input source, voltage stabilizing capacitors C1 to C4 at each port, a primary inverter full bridge, a secondary modulation full bridge, a tertiary rectification full bridge, a power coupling inductor L, a critical load and a non-critical load, a bidirectional DC-DC conversion module, and an energy storage unit;

[0008] The method includes the following steps:

[0009] S1. Construct a reactive power optimization control method, including establishing four working modes according to the interaction characteristics between the voltage regulation ratio and the transmission power, then dividing the transmission power into three regulation regions, and establishing a Lagrangian optimization model;

[0010] S2. Construct a dynamic voltage control strategy method;

[0011] S3. Construct a direct power control method to improve the dynamic response.

[0012] Furthermore, in the topology of the three-port power spring system, the primary inverter full bridge adopts a full bridge structure of four switching tubes S1 to S4; the positive pole of the DC input source is connected to the common end of S1 and S3, and the negative pole is connected to the common end of S2 and S4; the output ends of S1 and S2 are connected to the input end of the power coupling inductor; the output ends of S3 and S4 are connected to the other end of the primary winding of the transformer; the secondary modulation full bridge is composed of eight switching tubes S5 to S 12 constitute; the two leads of the secondary winding of the transformer are respectively connected to the midpoints of the bridge arms of the secondary modulation full bridge; the switching tubes of the secondary modulation full bridge adopt a common source topology configuration to optimize the drive circuit; the tertiary rectification full bridge is composed of four switching tubes S 13 ~S 16 constitute, and the output end is connected to the energy storage unit through a bidirectional DC-DC conversion module.

[0013] Furthermore, the specific implementation method of step S1 includes the following steps:

[0014] S1.1. Establish four working modes according to the interaction characteristics between the voltage regulation ratio and the transmission power;

[0015] Set D 12 as the external shift ratio between the primary inverter full bridge and the secondary modulation full bridge, and D 22 as the internal shift ratio between the primary inverter full bridge and the secondary modulation full bridge. According to the interaction characteristics between the voltage regulation ratio M and the transmission power P as follows:

[0016] The first working mode is D 12 < D 22 and D 12 + D 22 > 1;

[0017] The second working mode is D12 <D 22 and D 12 +D 22 <1;

[0018] The third working mode is D 12 >D 22 and D 12 +D 22 <1;

[0019] The fourth working mode is D 12 >D 22 and D 12 +D 22 >1

[0020] The voltage regulation ratio M = u1 / nu2, where u1 is the input voltage of the primary inverter full bridge, and nu2 is the voltage of the output voltage at the critical load end converted to the primary side of the transformer;

[0021] S1.2. Divide the transmission power into three regulation regions, including region I corresponding to 0 ≤ P ≤ 0.5, which is compatible with all four working modes; region II corresponding to 0.5 < P ≤ 0.67, where the first to third working modes are enabled; and region III corresponding to 0.67 < P ≤ 1, where the second working mode is enabled;

[0022] S1.3. Establish the Lagrangian optimization model L(D 12 ,D 22 ,λ), and the expression is:

[0023] L(D 12 ,D 22 ,λ) = P bf (D 12 ,D 22 ) + λ[P(D 12 ,D 22 ) - P * (1)

[0024] where λ is the Lagrangian multiplier, P bf is the reactive power, and P * is the transmission power reference value.

[0025] Furthermore, the specific implementation method of step S2 includes the following steps: The non-critical load end uses the voltage u3 across the non-critical load as the control quantity, subtracts it from the reference voltage u 3ref of the non-critical load end. After the calculated difference is input to the PI controller for adjustment, the external shift ratio D 13 between the primary inverter full bridge and the three-phase rectifier full bridge is generated; the voltage u C4After being adjusted by the PI controller, the duty cycle D for regulating the energy storage unit is generated to regulate the switch S of the bidirectional DC-DC conversion module. 17 and S 18 .

[0026] Furthermore, the specific implementation method of step S3 includes the following steps:

[0027] S3.1. According to the working principle of the power spring, the output power P of the secondary modulation full bridge o is expressed as:

[0028] P o = u2i2 = u2(i c + i o ) (2)

[0029] where u2 is the output voltage at the critical load end, i2 is the output current at the critical load end, i c is the current passing through the capacitor C2, and i o is the output current of the secondary modulation full bridge;

[0030] S3.2. Considering the energy loss in the actual circuit, the energy transfer efficiency η is introduced, and with the maximum transmission power as the normalization benchmark, the expression of the improved transmission power is obtained:

[0031]

[0032] where u 2ref is the voltage reference value of u2, p is the normalized transmission power, P N is the transmission power reference value, and f is the switching frequency;

[0033] Through the analytical formula of the normalized power p and the output power P of the secondary modulation full bridge o , the dynamic response process is optimized; through the minimum reactive power optimization algorithm, combined with the reactive power optimization control method obtained in step S1, the optimal phase shift parameter is solved based on p and M, and the power switch device is driven to minimize the reactive power.

[0034] Advantages of the present invention:

[0035] The reactive power optimization method of a multi-port power spring described in the present invention uses double phase shift control for the provided three-port power spring topology to expand the degree of freedom of the power spring control method, thereby making the control more flexible.

[0036] The reactive power optimization method of a multi-port power spring described in the present invention can actively suppress the output power fluctuation when the battery is not working or transmitting a small amount of power during specific operations, thereby reducing the battery loss under normal working conditions.

[0037] A reactive power optimization method for a multi-port power spring according to the present invention partitions power for different working modes, analyzes the optimization trajectory of reactive power under each working mode, and obtains the optimal solutions for different power regions. BRIEF DESCRIPTION OF THE DRAWINGS

[0038] Figure 1 It is the circuit structure diagram of the multi-port power spring of the present invention;

[0039] Figure 2 It is the power transmission range area diagram of the three-port power spring described in the present invention;

[0040] Figure 3 It is the modulation waveform diagram of the reactive power optimization method for the multi-port power spring of the present invention;

[0041] Figure 4 It is the schematic diagram of the principle for generating the PWM modulation signal of the multi-port power spring of the present invention;

[0042] Figure 5 It is the schematic diagram of the key load voltage control method for the multi-port power spring of the present invention without energy storage battery regulation;

[0043] Figure 6 It is the experimental waveform diagram of the reactive power optimization for the multi-port power spring of the present invention, where (a) is the comparison experimental diagram under single phase-shift control; (b) is the voltage and current experimental diagram under the optimized control mode I; (c) is the voltage and current experimental diagram under the optimized control mode II; (d) is the voltage and current experimental diagram under the optimized control mode III; (e) is the voltage and current experimental diagram under the optimized control mode IV. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0044] In order to make the objectives, technical solutions and advantages of the present invention clearer, the present invention will be further described in detail below in conjunction with the accompanying drawings and specific embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not used to limit the present invention, that is, the specific embodiments described are only a part of the embodiments of the present invention, rather than all of the specific embodiments. Usually, the components of the specific embodiments of the present invention described and shown in the accompanying drawings herein can be arranged and designed in various different configurations, and the present invention can also have other embodiments.

[0045] Therefore, the detailed description of the specific embodiments of the present invention provided in the accompanying drawings below is not intended to limit the scope of the claimed present invention, but only represents the selected specific embodiments of the present invention. All other specific embodiments obtained by those skilled in the art based on the specific embodiments of the present invention without creative efforts fall within the scope of protection of the present invention.

[0046] To further understand the content, features and effects of the present invention, the following specific embodiments are exemplified and are accompanied by the attached Figure 1 - Attachment Figure 6 The detailed description is as follows:

[0047] Embodiment 1:

[0048] A reactive power optimization method for a multi-port power spring is implemented based on a three-port power spring system. The topology of the three-port power spring system includes a DC input source, voltage stabilizing capacitors C1 to C4 at each port, a primary inverter full bridge, a secondary modulation full bridge, a tertiary rectification full bridge, a power coupling inductor L, a critical load and a non-critical load, a bidirectional DC-DC conversion module, and an energy storage unit;

[0049] It includes the following steps:

[0050] S1. Construct a reactive power optimization control method, including establishing four working modes according to the interaction characteristics of the voltage regulation ratio and the transmission power, then dividing the transmission power into three regulation regions, and establishing a Lagrangian optimization model;

[0051] Further, in the topology of the three-port power spring system, the primary inverter full bridge adopts a full bridge structure of four switching tubes S1 to S4; the positive pole of the DC input source is connected to the common end of S1 and S3, and the negative pole is connected to the common end of S2 and S4; the output ends of S1 and S2 are connected to the input end of the power coupling inductor; the output ends of S3 and S4 are connected to the other end of the primary winding of the transformer; the secondary modulation full bridge is composed of eight switching tubes S5 to S 12 constitute; the two lead-out ends of the secondary winding of the transformer are respectively connected to the midpoints of the bridge arms of the secondary modulation full bridge; the switching tubes of the secondary modulation full bridge adopt a common-source topology configuration to optimize the drive circuit; the tertiary rectification full bridge is composed of four switching tubes S 13 ~S 16 constitute, and the output end is connected to the energy storage unit through a bidirectional DC-DC conversion module;

[0052] Further, all power devices are selected as SiC MOSFETs to improve the switching characteristics;

[0053] Further, the DC input source provides a stable DC power supply for the system. The voltage stabilizing capacitors C1 to C4 are used for voltage stabilization at each port. The primary inverter full bridge converts DC electrical energy into AC electrical energy. The secondary modulation full bridge performs secondary modulation on the energy. The power coupling inductor L realizes efficient energy interaction. The high-frequency isolation transformer ensures the safety of energy transmission. The three-stage rectifier full bridge converts AC electrical energy into DC electrical energy. The critical load port and the non-critical load port respectively provide power for the critical load and the non-critical load. The bidirectional DC-DC conversion module realizes bidirectional energy flow. The energy storage unit is used for suppressing power fluctuations and storing energy. After the DC source undergoes energy conversion through the primary inverter bridge, energy interaction is achieved with the secondary full bridge and the three-stage rectifier bridge through the inductor L respectively. The output end of the three-stage rectifier is connected to the critical load, and the output end of the secondary full bridge is connected to the non-critical load. The voltages across the voltage stabilizing capacitors C1, C2, C3, and C4 at each port are: u C1 、u C2 、u C3 、u C4 , where C4 is connected to the energy storage unit. v p is the voltage at the midpoint of the primary side bridge arm, v s is the voltage at the midpoint of the secondary side bridge arm, v s2 is the voltage at the midpoint of the three-stage side bridge arm;

[0054] Further, the specific implementation method of step S1 includes the following steps:

[0055] S1.1. Establish four working modes according to the interaction characteristics of the voltage regulation ratio and the transmission power;

[0056] Set D 12 as the external shift ratio between the primary inverter full bridge and the secondary modulation full bridge, and D 22 as the internal shift ratio between the primary inverter full bridge and the secondary modulation full bridge. According to the interaction characteristics of the voltage regulation ratio M and the transmission power P as follows:

[0057] The first working mode is D 12 < D 22 and D 12 + D 22 > 1;

[0058] The second working mode is D 12 < D 22 and D 12 + D 22 < 1;

[0059] The third working mode is D 12 > D 22 and D 12 + D 22 < 1;

[0060] The fourth working mode is D12 >D 22 and D 12 +D 22 >1

[0061] The voltage regulation ratio M = u1 / nu2, where u1 is the input voltage of the primary inverter full bridge, and nu2 is the voltage of the output voltage at the critical load end converted to the primary side of the transformer;

[0062] S1.2. Divide the transmission power into three regulation regions, including Region I corresponding to 0 ≤ P ≤ 0.5, which is compatible with all four operating modes; Region II corresponding to 0.5 < P ≤ 0.67, where the first to third operating modes are enabled; Region III corresponding to 0.67 < P ≤ 1, where the second operating mode is enabled;

[0063] S1.3. Establish a Lagrangian optimization model L(D 12 , D 22 , λ), and the expression is:

[0064] L(D 12 , D 22 , λ) = P bf (D 12 , D 22 ) + λ[P(D 12 , D 22 ) - P * (1)

[0065] where λ is the Lagrange multiplier, P bf is the reactive power, and P * is the transmission power reference value.

[0066] Figure 3 This is the modulation waveform diagram of the reactive power optimization method of the multi-port power spring in this embodiment. i 13 is the equivalent current between the primary side and the tertiary side, i 12 is the equivalent current between the primary side and the secondary side, i 23 is the equivalent current between the secondary side and the tertiary side, v p is the midpoint voltage of the primary side bridge arm, v s is the midpoint voltage of the secondary side bridge arm, v s2 is the midpoint voltage of the tertiary side bridge arm, T s is the switching period.

[0067] S2. Construct a dynamic voltage control strategy method;

[0068] Furthermore, the specific implementation method of step S2 includes the following steps: The non-critical load end uses the voltage u3 across the non-critical load as the control quantity, the same as the reference voltage u of the non-critical load end 3refPerform subtraction, and after the calculated difference is input to the PI controller for adjustment, an external shift ratio D between the primary inverter full-bridge and the tertiary rectifier full-bridge is generated 13 ; the voltage u corresponding to the fourth voltage-stabilizing capacitor in the energy storage unit C4 After being adjusted by the PI controller, the duty cycle D of the energy storage unit is generated, which is used to adjust the switch S of the bidirectional DC-DC conversion module 17 and S 18 .

[0069] Figure 4 This is a schematic diagram of the PWM modulation signal generation principle of the multi-port power spring in the present invention. The key load end uses u3 as the control quantity, and the phase shift signal D is generated through the PI regulator 13 ; in the energy storage unit, u C4 generates the duty cycle D through PI regulation

[0070] S3. Construct a direct power control method to improve the dynamic response;

[0071] Through real-time power closed-loop adjustment and combined with the minimum reactive power optimization algorithm, fast and stable control is achieved. During the closed-loop regulation process of the power spring, the dynamic adjustment of the converter operating parameters is inevitable. The response rate of restoring the steady state after its state switching is the core parameter to measure the performance of the control system. In view of the characteristics of the closed-loop control system, the direct power control strategy can significantly improve the dynamic response performance of the circuit under load fluctuation and voltage disturbance conditions

[0072] Furthermore, the specific implementation method of step S3 includes the following steps:

[0073] S3.1. According to the working principle of the power spring, express the output power P of the secondary modulation full-bridge o as:

[0074] P o = u2i2 = u2(i c + i o ) (2)

[0075] where u2 is the output voltage of the key load end, i2 is the output current of the key load end, i c is the current passing through the capacitor C2, and i o is the output current of the secondary modulation full-bridge

[0076] S3.2. Considering the energy loss in the actual circuit, introduce the energy transfer efficiency η, and use the maximum transmission power as the normalization benchmark to obtain the expression of the improved transmission power:

[0077]

[0078] where u 2refis the voltage reference value of u2, p is the normalized transmission power, and P N is the transmission power reference value, and f is the switching frequency;

[0079] Through the analytical formula of the normalized power p and the output power P of the secondary modulation full-bridge o to optimize the dynamic response process; through the minimum reactive power optimization algorithm, combined with the reactive power optimization control method obtained in step S1, the optimal phase-shift parameter is solved based on p and M, and the power switch device is driven to minimize the reactive power.

[0080] Compared with the traditional optimization scheme, the introduction of the capacitor current i c significantly improves the model accuracy. It can be seen from the circuit structure that the voltage fluctuation on the output side is due to the charge and discharge process of the support capacitor. Therefore, the dynamic characteristics of the system can be effectively enhanced by regulating the capacitor current. Based on this theory, the present invention combines the minimum reactive power algorithm with direct power control. The specific implementation process is as follows: u1 is collected in real time and subtracted from the reference value u 1ref , and the output capacitor current i c is output through the PI regulator. The measured output current i0 is superimposed to deduce i2, and then the actual power P o is calculated. Combining the efficiency parameter η and the reference power P N to complete the power normalization process. Finally, through the minimum reactive power optimization algorithm, the optimal phase-shift parameter is solved based on the real-time power p and the voltage ratio M, and the power switch device is driven to minimize the reactive power. For the key load end, D 13 phase shift is generated through PI regulation with u3 as the control variable, and the energy storage unit generates a pulse width modulation signal D through the PI operation of u C4 .

[0081] u 2ref is the reference voltage. By establishing a conversion relationship between the transmission power p and the power p o at the output end of the power spring, a fast dynamic response effect is achieved. Compared with the traditional dynamic performance optimization scheme, the introduction of the capacitor current i c can make the transmission model more accurate, and the output side voltage of the power spring is stabilized by the support capacitor on the output side. The change of the output side voltage is actually caused by the charge and discharge of the support capacitor. Therefore, in actual control, the capacitor current is introduced to control to accelerate the response speed, which is beneficial to improving the dynamic performance of the power spring. Based on the above control theory, a method combining the minimum reactive power and the direct power method under double-phase shift control is proposed, which is abbreviated as the direct power method. First, the photovoltaic input voltage u1 sampled in real time is subtracted from the reference voltage u 1ref . After the calculated difference enters the PI controller, the output capacitor current i c is obtained. The output capacitor current i cIt is used to compensate the output current i2, so the obtained capacitor current i c After adding the output current i0 obtained by real-time sampling, the output current i2 can be obtained, and further the output power p required at the output end can be obtained o , and then divided by the efficiency η and the base value P N The per-unit transmission power p is obtained. Finally, through the minimum reactive power optimization control algorithm for the transmission power and voltage transmission ratio, the optimal phase shift ratio coordinates at the transmission power p and voltage transmission ratio M are obtained, so as to control the main circuit switching tubes of the power spring, and finally minimize the reactive power of the power spring.

[0082] As Figure 5 shown Figure 5 This is a simulation waveform diagram of the output power of each port of a three-port power spring in this embodiment when the energy storage battery is not working. The simulation data shows that when the energy storage system is in the state of not charging or discharging, the DC bus voltage deviation can be stably maintained within the tolerance range of ±10%. To verify the dynamic performance of the system, we set the working conditions of photovoltaic power mutation at two time points of 0.2 s and 0.4 s for testing. At the moment of 0.2 s, the output power of the photovoltaic unit had a step increase of 11 W (from 176 W to 187 W). At the same time, the non-critical load power also increased by 11 W correspondingly (from 96 W to 107 W). This dynamic adjustment mechanism reflects the control advantages of the system in two aspects: on the one hand, it ensures that the critical load always obtains a stable power supply of 100 W; on the other hand, through the intelligent power distribution strategy, the energy disturbance is guided to the non-critical load end. This control logic makes full use of the flexible adjustment ability of the load and realizes the reasonable distribution of energy without the intervention of the energy storage system. When the experiment reached 0.4 s, the photovoltaic output had a negative step of 21 W (from 187 W to 166 W). In this transient process, the power supply of the critical load always remained unchanged at the reference value of 100 W, while the non-critical load power decreased by 21 W correspondingly (from 107 W to 86 W). This control process fully demonstrates the two core advantages of the system: first, it can ensure the power supply quality of the critical load is not affected by disturbances under any working conditions; second, through the adaptive adjustment function of the load-side power, a new power fluctuation buffer path is successfully constructed.

[0083] From the above analysis, it can be seen that the control system shows excellent dynamic response performance when dealing with photovoltaic power mutation. It can not only ensure the stability of the critical load power supply, but also realize the efficient distribution and management of energy through a flexible load adjustment mechanism. This design idea provides a new solution for the stable operation of the power system.

[0084] Figure 6This is the waveform diagram of the reactive power optimization experiment of the multi-port power spring in this embodiment. The experimental parameters are: the input voltage u1 is 180V, the output voltage u2 is 150V, and the switching frequency is 100kHz. Figure 6 (a) is the comparison experimental diagram under single-phase shift control; Figure 6 (b) is the voltage and current experimental diagram under optimized control mode I; Figure 6 (c) is the voltage and current experimental diagram under optimized control mode II; Figure 6 (d) is the voltage and current experimental diagram under optimized control mode III; Figure 6 (e) is the voltage and current experimental diagram under optimized control mode IV. It can be seen from the figure that compared with the traditional single-phase shift control, the reactive power under the optimized control in different modes can be effectively reduced, significantly improving the energy regulation ability and operation efficiency of the system.

[0085] It should be noted that relational terms such as "first" and "second" are only used to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply any actual relationship or order between these entities or operations. Moreover, the terms "comprising", "including" or any other variant thereof are intended to cover non-exclusive inclusion, so that a process, method, article or device including a series of elements not only includes those elements, but also includes other elements not expressly listed, or elements inherent to such process, method, article or device. Without further limitation, an element defined by the statement "including a..." does not exclude the existence of additional identical elements in the process, method, article or device including the element.

[0086] Although the present application has been described above with reference to specific embodiments, various improvements can be made to it and components can be replaced with equivalents without departing from the scope of the present application. In particular, as long as there is no structural conflict, the various features in the specific embodiments disclosed in the present application can be combined with each other in any way, and the exhaustive description of these combinations is omitted in this specification only for the sake of saving space and resources. Therefore, the present application is not limited to the specific embodiments disclosed herein, but includes all technical solutions falling within the scope of the claims.

Claims

1. A reactive power optimization method for a multi-port power spring, implemented based on a three-port power spring system. The topology of the three-port power spring system includes a DC input source, voltage stabilizing capacitors C1 to C4 at each port, a primary inverter full bridge, a secondary modulation full bridge, a tertiary rectification full bridge, a power coupling inductor L, a critical load and a non-critical load, a bidirectional DC-DC conversion module, and an energy storage unit; It is characterized in that It includes the following steps: S1. Construct a reactive power optimization control method, including establishing four working modes according to the interaction characteristics of the voltage regulation ratio and the transmission power, then dividing the transmission power into three regulation regions, and establishing a Lagrangian optimization model; S2. Construct a dynamic voltage control strategy method; S3. Construct a direct power control method to improve the dynamic response.

2. The reactive power optimization method of a multi-port electric spring according to claim 1, characterized in that: In the topology of the three-port power spring system, the primary inverter full bridge adopts a full bridge structure of four switch tubes S1~S4; the positive pole of the DC input source is connected to the common end of S1 and S3, and the negative pole is connected to the common end of S2 and S4; the output ends of S1 and S2 are connected to the input end of the power coupling inductor; the output ends of S3 and S4 are connected to the other end of the primary winding of the transformer; the secondary modulation full bridge consists of eight switch tubes S5~S 12 The two leads of the transformer secondary winding are connected to the midpoint of the bridge arm of the secondary modulation full bridge respectively; the secondary modulation full bridge switch tube adopts the common source topology configuration to optimize the drive circuit; the tertiary rectifier full bridge consists of four switch tubes S 13 ~S 16 The output end is connected to the energy storage unit via a bidirectional DC-DC conversion module.

3. The reactive power optimization method of a multi-port electric spring according to claim 1 or 2, characterized in that: The specific implementation method of step S1 includes the following steps: S1.

1. Establish four working modes according to the interaction characteristics of the voltage regulation ratio and the transmission power; Setting D 12 Compared with the external shift between the primary inverter full bridge and the secondary modulation full bridge, D 22 Compared with the inward shift of the primary inverter full bridge and the secondary modulation full bridge, the interactive characteristics of the voltage regulation ratio M and the transmission power P are as follows: The first working mode is D 12 <D 22 And D 12 +D 22 >1; The second working mode is D 12 <D 22 And D 12 +D 22 <1; The third working mode is D 12 >D 22 And D 12 +D 22 <1; The fourth working mode is D 12 >D 22 And D 12 +D 22 >1 The voltage regulation ratio M = u1 / nu2, where u1 is the input voltage of the primary inverter full bridge, and nu2 is the voltage of the output of the critical load terminal折算 to the primary side of the transformer; S1.

2. Divide the transmission power into three regulation regions, including region I corresponding to 0 ≤ P ≤ 0.5, which is compatible with all four working modes; region II corresponding to 0.5 < P ≤ 0.67, where the first working mode - the third working mode are enabled; region III corresponding to 0.67 < P ≤ 1, where the second working mode is enabled; S1.

3. Establishing Lagrangian optimization model L(D 12 ,D 22 ,λ), the expression is: L(D 12 ,D 22 ,λ)LP bf (D 12 ,D 22 )+λ[P(D 12 ,D 22 )-P * ] (1) Where λ is the Lagrange multiplier, P bf is the reactive power, P * is the transmission power reference value.

4. The reactive power optimization method of a multi-port electric spring according to claim 3, characterized in that: The specific implementation method of step S2 includes the following steps: the non-critical load end uses the voltage u3 across the non-critical load as the control quantity, and the non-critical load end reference voltage u 3ref The difference is calculated and input into the PI controller for adjustment to generate the external shift comparison D between the primary inverter full bridge and the tertiary rectifier full bridge. 13 ; The voltage u corresponding to the fourth voltage-stabilizing capacitor in the energy storage unit C4 After being adjusted by the PI controller, the energy storage unit adjustment duty cycle D is generated, which is used to adjust the switch S of the bidirectional DC-DC conversion module. 17 and S 18 .

5. The reactive power optimization method of a multi-port electric spring according to claim 4, characterized in that: The specific implementation method of step S3 includes the following steps: S3.

1. According to the working principle of the electric spring, the output power P of the secondary modulated full bridge o It is expressed as: P o =u2i2=u2(i c +i o ) (2) Among them, u2 is the output voltage of the key load end, i2 is the output current of the key load end, i c is the current passing through capacitor C2, i o is the secondary modulated full-bridge output current; S3.

2. Considering that there are energy losses in the actual circuit, introduce the energy transfer efficiency η, and use the maximum transmission power as the normalization benchmark to obtain the improved expression of the transmission power: Among them, u 2ref is the voltage reference value of u2, p is the normalized transmission power, P N is the transmission power reference value, f is the switching frequency; By normalizing the power p and the output power P of the secondary modulated full bridge o The analytical expression of is used to optimize the dynamic response process; through the minimum reactive power optimization algorithm, combined with the reactive power optimization control method obtained in step S1, the optimal phase shift parameters are solved according to p and M, and the power switching device is driven to minimize the reactive power.

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