Soft switching multi-port converter control method for distributed optical storage configuration

Abstract

The invention belongs to the technical field of distributed optical storage, and particularly relates to a soft switching multi-port converter control method for distributed optical storage configuration. The FPC model provided by the method is subjected to loss analysis and efficiency calculation and is compared with other two models, and the comparison model comprises a traditional double-converter model and a traditional three-converter model. The FPC model provided by the invention has stable high efficiency, can reach a peak value of about 95.37% during full load, and can maintain the peak value of about 94.07% during no load. Compared with a traditional model, the method has obvious advantages in switching mechanism and efficiency. In conclusion, the method can meet the technical requirements of optimizing MPPT performance, adapting to PV wide voltage change, efficient differential power processing and reducing the cost and complexity of a single packaging device at the same time, and provides powerful support for efficient and reliable operation of the distributed optical storage system.

Description

Technical Field

[0001] The present invention belongs to the technical field of distributed photovoltaic storage, and in particular relates to a soft-switching multi-port converter control method for distributed photovoltaic storage configuration. Background Art

[0002] In distributed solar-storage configurations, photovoltaic (PV) modules are the main power generation units, and their performance directly affects the power generation efficiency and stability of the entire system. However, due to problems such as uneven illumination, errors in the maximum power point tracking (MPPT) algorithm, and the drop in PV module voltage, PV power generation is often significantly affected. These problems not only reduce the efficiency of the DC converter, but also pose higher challenges to power density and stability reliability.

[0003] In order to solve these problems, existing research has adopted a variety of solutions. One mainstream solution is to integrate the photovoltaic system and the energy storage system into an independent DC-DC level DC link, but this method has obvious defects. It increases the number of converters, resulting in increased system complexity and reduced power density. Another solution is to directly couple the photovoltaic array or energy storage battery to the main DC link. Although this method solves the problem of low power density to a certain extent, the frequency oscillation of the photovoltaic terminal and the battery voltage requirements have become new trade-offs.

[0004] In addition, although the use of distributed energy storage and series cascade photovoltaic architecture, as well as centralized energy storage and parallel cascade photovoltaic architecture, can to a certain extent deal with the problem of uneven illumination and improve the performance of PV under uneven illumination conditions, these architectures also require multiple isolated high-gain converters to allow flexible and variable PV low voltages. This not only increases the complexity and cost of the system, but also limits the flexibility and scalability of the system. At present, there is a lack of a technology on the market that can simultaneously meet the requirements of optimizing MPPT performance under uneven illumination, adapting to wide PV voltage changes, efficient differential power processing, and minimizing the cost and complexity of a single packaged device. These performance requirements often have a mutually restrictive relationship, which further increases the difficulty of solving these problems.

[0005] Therefore, how to achieve a distributed photovoltaic storage configuration that can not only optimize MPPT performance, adapt to wide PV voltage changes, and efficiently process differential power while minimizing the cost and complexity of individual packaged devices has become a technical problem that needs to be solved urgently. Summary of the invention

[0006] In view of the above-mentioned deficiencies in the prior art, the present invention provides a soft-switching multi-port converter control method for distributed photovoltaic storage configuration, which can simultaneously meet the technical requirements of optimizing MPPT performance, adapting to wide PV voltage changes, efficient differential power processing, and reducing the cost and complexity of single packaged devices, thereby providing strong support for the efficient and reliable operation of distributed photovoltaic storage systems.

[0007] In order to solve the above technical problems, the present invention adopts the following technical solutions:

[0008] A soft-switching multi-port converter control method for distributed photovoltaic storage configuration comprises the following steps:

[0009] S1. construct a four-port converter FPC; the four-port converter FPC has three input ports and one common DC link port; the three input ports are respectively connected in series with respective power sources and finally converged to the common DC link port;

[0010] Among them, the three input ports represent two photovoltaic modules and one energy storage unit respectively; the three input ports are connected to the public DC link through their own inductors and capacitors respectively; the inductors and capacitors on the circuits of each input port constitute the filtering part of the circuit, which is used to smooth the fluctuations of current and voltage; the circuits of each input port are also provided with soft switches, which are used to drive through PWM control signals to realize the transformation and energy transmission of the corresponding circuit;

[0011] The common DC link port is provided with a soft switch for controlling the on and off of the DC link, and is also provided with a capacitor connected to the common DC link for further smoothing the voltage of the DC link;

[0012] S2, setting component parameters of the four-port converter FPC; the component parameters include inductance parameters and capacitance parameters;

[0013] S3, setting a control scheme of the four-port converter FPC, for generating and optimizing each soft switch control signal of the four-port converter FPC according to the system state and the upper logic;

[0014] S4. Control the four-port converter FPC according to the set control scheme.

[0015] Compared with the prior art, the present invention has the following beneficial effects:

[0016] 1. Optimize the photovoltaic maximum power point tracking (MPPT) performance. By constructing a four-port converter FPC with three input ports, this method can connect two photovoltaic modules and an energy storage unit respectively to achieve independent and flexible MPPT control. The inductor and capacitor filtering parts equipped on each input port, as well as the soft-switching PWM control signal, can smooth current and voltage fluctuations, thereby improving the accuracy and stability of MPPT, especially under uneven lighting conditions.

[0017] 2. Meet the requirements of low voltage gain. Through reasonable circuit design and component parameter setting, this method enables the four-port converter FPC to operate efficiently under low voltage gain conditions. This helps reduce the system's dependence on high-gain converters, reduce the number and complexity of converters, thereby improving power density and reducing costs.

[0018] 3. Adapt to wide PV voltage changes. Since each input port is connected to the public DC link through inductors and capacitors and equipped with soft switches for PWM control, this method can adapt to the wide voltage changes generated by the photovoltaic module under different light and temperature conditions. This enables the system to operate stably over a wider voltage range, improving the adaptability and reliability of the system.

[0019] 4. Efficient differential power processing. The design of the four-port converter FPC allows the simultaneous processing of differential power from different input ports, achieving efficient transmission and distribution of energy. By optimizing the control scheme, the power balance between the input ports can be ensured to avoid power waste and energy loss.

[0020] 5. Reduce the cost and complexity of a single packaged device. This method reduces the number of required converters by integrating multiple functions into a four-port converter, thereby reducing the cost of a single packaged device. At the same time, due to the use of soft switching technology, energy loss and electromagnetic interference during the switching process are reduced, further simplifying the system structure and reducing complexity.

[0021] 6. Perform loss analysis and efficiency calculation on the FPC model proposed by this method, and compare it with the other two models. The comparison models include the traditional dual-converter model (one photovoltaic module is connected in series with one energy storage unit) and the traditional three-converter model (two photovoltaic modules are connected in series with one energy storage unit). The FPC model proposed by the present invention has a stable high efficiency, which can reach a peak value of about 95.37% at full load and maintain nearly 94.07% at no load. Compared with the traditional model, the proposed model has obvious advantages in switching mechanism and efficiency.

[0022] In summary, this soft-switching multi-port converter control method for distributed photovoltaic storage configuration can simultaneously meet the technical requirements of optimizing MPPT performance, adapting to wide PV voltage changes, efficient differential power processing, and reducing the cost and complexity of single packaged devices, providing strong support for the efficient and reliable operation of distributed photovoltaic storage systems.

[0023] Preferably, the three input ports are respectively a first photovoltaic port pv1, a second photovoltaic port pv2 and a battery port bat which are arranged in descending order.

[0024] Such a setting, 1. Optimize energy management. By configuring the first photovoltaic port pv1, the second photovoltaic port pv2 and the battery port bat in sequence, this technical content realizes the effective management and integration of multiple energy inputs (photovoltaic and energy storage). This configuration enables the system to flexibly adjust the power output of each port according to the lighting conditions and energy storage status, thereby optimizing energy utilization efficiency and system stability.

[0025] 2. Enhanced MPPT performance. For the first photovoltaic port pv1 and the second photovoltaic port pv2, since they are connected to different photovoltaic modules respectively, they can perform maximum power point tracking (MPPT) independently. This configuration helps to maximize the power generation efficiency of each photovoltaic module under uneven lighting conditions, thereby improving the power generation capacity of the entire system.

[0026] 3. Improve system flexibility. The introduction of the battery port BAT provides the system with additional energy storage and regulation capabilities. When there is insufficient light or the grid demand changes, the battery can release or absorb energy to maintain the stable operation of the system. At the same time, the battery can also serve as a backup power source to provide power support for the system in an emergency.

[0027] Preferably, in S2, when setting the inductance parameters, the following requirements are met:

[0028]

[0029] In the formula, the subscript pv1 Denotes the first photovoltaic, subscript pv2 Indicates the second photovoltaic; subscript bat represents battery; the subscript dc represents direct current; Δi represents the change in current; F sw Indicates the switching frequency; V dc Indicates the DC port voltage; Indicates that the flow through L pv1 The nominal current; I critical Indicates the minimum current flowing through the capacitor; Indicates that the flow through L pv2 The nominal current.

[0030] Such a setting, by properly setting the inductance value, can limit current fluctuations, reduce voltage ripple, adapt the switching frequency and meet the DC voltage requirements, thereby optimizing the performance and stability of the four-port converter FPC.

[0031] Preferably, in S2, when setting the capacitance parameters, the following requirements are met:

[0032]

[0033] In the formula, Δi Lpv1 Indicates that the flow through L pv1 The change in current; Δi Lpv2 Indicates that the flow through L pv2 The change in current; Δi bat Indicates flow through Z b The change in current; Represents capacitance C pv2 The time differential interval of the change is 1; Indicates the capacitance C pv2 The time differential interval of the change is 2; Represents capacitance C bat The time differential interval of the change is 1; Represents capacitance C bat The time differential interval of the change is 2; Indicates the nominal value of DC current; F sw Indicates the switching frequency.

[0034] Such a setting, by reasonably setting the capacitance value and other related parameters, can limit the voltage ripple, adapt to the current change, meet the switching frequency, consider the capacitance characteristics, and optimize the overall performance of the system.

[0035] Preferably, in S3, the control scheme includes a reference signal generation layer, an implementation and execution layer, and a phase modulation switch layer;

[0036] The reference signal generation layer is used to generate an initial reference signal according to the system state and the upper control logic; wherein the system state includes the battery SOC and the DC link voltage error; the reference signal includes the battery reference current input to the battery port and the reference voltage input to the two photovoltaic ports;

[0037] The implementation and execution layer is used to process the reference signal of the reference signal generation layer through the PI controller algorithm, generate control signals for driving the soft switches corresponding to the three input ports, adjust the duty cycle of each soft switch, and optimize the PWM technology of each soft switch;

[0038] The phase modulation switch layer is used to convert the control signal generated by the implementation and execution layer module into a pulse signal suitable for driving the power electronic device; the power electronic device includes various soft switches.

[0039] Such a setting can achieve accurate system status monitoring and response. The signal generation layer can accurately capture changes in system requirements by real-time monitoring of system status (such as battery SOC and DC link voltage error). Based on this system status information, the generation layer can generate an initial reference signal that meets the current system requirements and provide accurate input for subsequent control processes.

[0040] 2. Efficient energy transmission and regulation. The implementation and execution layer uses the PI controller algorithm to process the reference signal and generate the control signal for driving the soft switch. By accurately adjusting the duty cycle of each soft switch and optimizing the PWM technology, efficient energy transmission and precise regulation can be achieved. This helps to reduce energy loss and improve the overall efficiency of the system.

[0041] 3. Stable power electronic device drive. The phase modulation switch layer converts the control signal into a pulse signal suitable for driving the power electronic device (soft switching). This conversion ensures stable and reliable driving of the power electronic device, thereby ensuring the stable operation of the four-port converter.

[0042] 4. Flexible system adaptability. The entire control scheme can flexibly adapt to different system states and upper-level control logic. Whether it is a change in battery SOC or a fluctuation in DC link voltage, the control scheme can respond quickly to ensure stable system operation and efficient use of energy.

[0043] Preferably, the upper control logic includes: when the state signal Flag curt =0, when the battery is operating normally, the battery reference current Ibat Ref Follow Iref PI The reference current value;

[0044] During the discharge process, if the remaining battery power is 0 or reaches the maximum discharge current Ibat Max , the system cuts off part of the load. If there is no response or the DC link is unstable, the system disconnects the entire load and charges the battery through the available PV port. During the charging process, if the battery is full or reaches the peak value, the status signal Flag curt Set to 1 to reduce the power of the PV port and reset the integrator of the PI controller of the PV port to 0; if the battery is full, the battery reference current Ibat Ref Set to 0 or the default Ibat Min , while reducing the power of the PV port to regulate the DC link;

[0045] In the power abandonment mode, the load demand exceeding the power generation is sensed by the drop of DC link voltage, and the status signal Flag curt= 0, reset the integrator of the PI controller of the battery port and initialize it to the battery reference current Ibat Ref The system then transfers the DC link regulation back to the battery.

[0046] Such a setting, 1. Accurate control of normal battery operation. When the state signal Flagcurt = 0, it means that the battery is in normal operation. At this time, the battery reference current IbatRef follows the reference current value of IrefPI, ensuring accurate control of the battery in normal operation.

[0047] 2. Battery discharge protection mechanism. During the discharge process, if the remaining battery power is 0 or reaches the maximum discharge current IbatMax, the system can quickly cut off part of the load to prevent the battery from over-discharging. If the system still does not respond or the DC link is unstable after cutting off part of the load, the system disconnects the entire load and charges the battery through the available photovoltaic port to ensure the safety of the battery and the stability of the system.

[0048] 3. Battery charging management. During the charging process, if the battery is full or reaches the peak value, the system sets the status signal Flagcurt to 1 to reduce the power output of the photovoltaic port to avoid overcharging the battery. At the same time, resetting the integrator of the PI controller of the photovoltaic port to 0 helps to quickly adjust the output power of the photovoltaic port to adapt to changes in the battery charging state. If the battery is full, the battery reference current IbatRef is set to 0 or the preset IbatMin, and the power of the photovoltaic port is reduced to adjust the DC link voltage to maintain stable operation of the system.

[0049] 4. Intelligent regulation in power abandonment mode. In power abandonment mode, the system senses the load demand that exceeds power generation by monitoring the drop in DC link voltage. At this time, the status signal Flagcurt = 0, and the integrator of the PI controller of the battery port is reset and initialized to the current value of the battery reference current IbatRef, which helps to quickly adjust the output power of the battery port to adapt to changes in load demand. The system then transmits the DC link regulation back to the battery, using the battery's energy storage capacity to balance the load demand and power generation capacity to ensure stable operation of the system.

[0050] 5. Improve overall system performance: The above control logic improves the overall performance of the four-port converter through precise battery charge and discharge management, photovoltaic port power regulation, and intelligent regulation in power abandonment mode. This helps to ensure stable operation of the system under various working conditions, improve energy utilization efficiency, and reduce energy waste.

[0051] Preferably, the outputs of the PI controllers of the three input ports always comply with the requirement that the duty cycle of one soft switch is smaller than the duty cycle of the downstream soft switch.

[0052] Such a setting, 1. Ensure the orderliness of energy flow. In a multi-port converter, the energy of each input port needs to be transferred to the output end or the common DC link through the switching of soft switches. By ensuring that the duty cycle of a soft switch is less than the duty cycle of its downstream soft switch, the energy can be controlled to flow from each input port to the output end or the common DC link in an orderly manner, avoiding confusion and conflict in energy flow.

[0053] 2. Optimize PWM waveform and reduce harmonics. The size of the duty cycle directly affects the shape and frequency of the PWM (pulse width modulation) waveform. By accurately controlling the duty cycle of the soft switch and following the above constraints, the PWM waveform can be optimized, the generation of harmonics and noise can be reduced, thereby improving the efficiency and stability of the system.

[0054] 3. Protect power electronic devices. Soft switches will generate a certain amount of heat and stress during the switching process. By setting the duty cycle reasonably and following the above constraints, it is possible to ensure that the load of each soft switch is balanced during the switching process and avoid damage to a soft switch due to excessive work.

[0055] 4. Improve the flexibility and response speed of the system. Following the above constraints, the flexibility and response speed of the system can be improved while ensuring the stability of the system. For example, when the power of a certain input port needs to be adjusted quickly, it can be achieved by adjusting the duty cycle of the corresponding soft switch without making major adjustments to the entire system.

[0056] 5. Optimize energy distribution and efficiency. By precisely controlling the duty cycle of each soft switch and following the above constraints, the energy distribution and transmission path can be optimized, thereby improving the overall efficiency of the system. For example, in a system with hybrid photovoltaic and battery power supply, the power output of the photovoltaic port and the battery port can be dynamically adjusted according to the light intensity and battery status to achieve optimal energy utilization and efficiency. BRIEF DESCRIPTION OF THE DRAWINGS

[0057] In order to make the purpose, technical solution and advantages of the invention more clear, the present invention will be further described in detail below with reference to the accompanying drawings, in which:

[0058] Figure 1 A flowchart of the method is shown in FIG.

[0059] Figure 2 A topological structure diagram of a four-port converter FPC in an embodiment;

[0060] Figure 3 This is a switching sequence diagram for optimizing the PWM technology in the embodiment. DETAILED DESCRIPTION

[0061] The following is a further detailed description through specific implementation methods:

[0062] Embodiment 1

[0063] like Figure 1 As shown, this embodiment discloses a soft-switching multi-port converter control method for distributed photovoltaic storage configuration, comprising the following steps:

[0064] S1. Build a four-port converter FPC.

[0065] The topology of the four-port converter FPC is as follows: Figure 2 As shown, the four-port converter FPC has three input ports and one common DC link port; the three input ports are respectively connected in series with respective power sources and finally converged to the common DC link port;

[0066] Among them, the three input ports represent two photovoltaic modules and one energy storage unit respectively; the three input ports are connected to the public DC link through their own inductors and capacitors respectively; the inductors and capacitors on the circuits of each input port constitute the filtering part of the circuit, which is used to smooth the fluctuations of current and voltage; a soft switch is also provided on the circuit of each input port, which is used to drive through a PWM control signal to realize the transformation and energy transmission of the corresponding circuit.

[0067] The common DC link port part is provided with a soft switch for controlling the on and off of the DC link, and is also provided with a capacitor connected to the common DC link for further smoothing the voltage of the DC link.

[0068] In the specific implementation, the three input ports are the first photovoltaic port pv1, the second photovoltaic port pv2 and the battery port bat, which are sequentially downstream. In this way, by configuring the first photovoltaic port pv1, the second photovoltaic port pv2 and the battery port bat in sequence, the technical content realizes the effective management and integration of multiple energy inputs (photovoltaic and energy storage). This configuration enables the system to flexibly adjust the power output of each port according to the lighting conditions and energy storage status, thereby optimizing energy utilization efficiency and system stability. In addition, for the first photovoltaic port pv1 and the second photovoltaic port pv2, since they are connected to different photovoltaic modules respectively, the maximum power point tracking (MPPT) can be performed independently. This configuration helps to maximize the power generation efficiency of each photovoltaic module under uneven lighting conditions, thereby improving the power generation capacity of the entire system. It can also improve system flexibility. The introduction of the battery port bat provides the system with additional energy storage and regulation capabilities. When the light is insufficient or the grid demand changes, the battery can release or absorb energy to maintain the stable operation of the system. At the same time, the battery can also serve as a backup power supply to provide power support for the system in an emergency.

[0069] S2. Setting component parameters of the four-port converter FPC; the component parameters include inductance parameters and capacitance parameters.

[0070] In specific implementation, when setting the inductance parameters, the following requirements must be met:

[0071]

[0072] In the formula, the subscript pv1 Denotes the first photovoltaic, subscript pv2 Indicates the second photovoltaic; subscript bat represents battery; the subscript dc represents direct current; Δi represents the change in current; F sw Indicates the switching frequency; V dc Indicates the DC port voltage; Indicates that the flow through L pv1 The nominal current; I critical Indicates the minimum current flowing through the capacitor; Indicates that the flow through L pv2 The nominal current.

[0073] When setting the capacitance parameters, meet the following requirements:

[0074]

[0075] In the formula, Δi Lpv1 Indicates that the flow through L pv1 The change in current; Δi Lpv2 Indicates that the flow through L pv2 The change in current; Δi bat Indicates flow through Z b The change in current; Represents capacitance C pv2 The time differential interval of the change is 1; Indicates the capacitance C pv2 The time differential interval of the change is 2; Represents capacitance C bat The time differential interval of the change is 1; Represents capacitance C bat The time differential interval of the change is 2; Indicates the nominal value of DC current; F sw Indicates the switching frequency.

[0076] By properly setting the inductance value, capacitance value and other related parameters, it is possible to limit voltage ripple, adapt to current changes, meet switching frequency, consider capacitance characteristics, and optimize the overall performance of the system.

[0077] S3. Setting a control scheme for the four-port converter FPC to generate and optimize each soft switch control signal of the four-port converter FPC according to the system state and upper-layer logic.

[0078] Wherein, the control scheme includes a reference signal generation layer, an implementation and execution layer, and a phase modulation switch layer;

[0079] The reference signal generation layer is used to generate an initial reference signal according to the system state and the upper control logic; wherein the system state includes the battery SOC and the DC link voltage error; the reference signal includes the battery reference current input to the battery port and the reference voltage input to the two photovoltaic ports;

[0080] The implementation and execution layer is used to process the reference signal of the reference signal generation layer through the PI controller algorithm, generate control signals for driving the soft switches corresponding to the three input ports, adjust the duty cycle of each soft switch, and optimize the PWM technology of each soft switch;

[0081] The phase modulation switch layer is used to convert the control signal generated by the implementation and execution layer module into a pulse signal suitable for driving the power electronic device; the power electronic device includes various soft switches.

[0082] In this way, accurate system status monitoring and response can be achieved. The signal generation layer can accurately capture changes in system requirements by monitoring the system status (such as battery SOC and DC link voltage error) in real time. Based on these system status information, the generation layer can generate an initial reference signal that meets the current system requirements and provide accurate input for the subsequent control process. In addition, the implementation and execution layer uses the PI controller algorithm to process the reference signal and generate a control signal for driving the soft switch. By accurately adjusting the duty cycle of each soft switch, the PWM technology is optimized to achieve efficient transmission and precise regulation of energy. This helps to reduce energy losses and improve the overall efficiency of the system. In addition, the phase modulation switch layer converts the control signal into a pulse signal suitable for driving power electronic devices (soft switches). This conversion ensures stable and reliable driving of power electronic devices, thereby ensuring the stable operation of the four-port converter. In addition, the entire control scheme can flexibly adapt to different system states and upper-level control logic. Whether it is a change in battery SOC or a fluctuation in DC link voltage, the control scheme can respond quickly to ensure stable operation of the system and efficient use of energy.

[0083] In specific implementation, the upper control logic includes: when the state signal Flag curt =0, when the battery is operating normally, the battery reference current Ibat Ref Follow Iref PI The reference current value;

[0084] During the discharge process, if the remaining battery power is 0 or reaches the maximum discharge current Ibat Max, the system cuts off part of the load. If there is no response or the DC link is unstable, the system disconnects the entire load and charges the battery through the available PV port. During the charging process, if the battery is full or reaches the peak value, the status signal Flag curt Set to 1 to reduce the power of the PV port and reset the integrator of the PI controller of the PV port to 0; if the battery is full, the battery reference current Ibat Ref Set to 0 or the default Ibat Min , while reducing the power of the PV port to regulate the DC link;

[0085] In the power abandonment mode, the load demand exceeding the power generation is sensed by the drop of DC link voltage, and the status signal Flag curt = 0, reset the integrator of the PI controller of the battery port and initialize it to the battery reference current Ibat Ref The system then transfers the DC link regulation back to the battery.

[0086] Thus, when the status signal Flagcurt=0, it indicates that the battery is in normal operation. At this time, the battery reference current IbatRef follows the reference current value of IrefPI, ensuring the precise control of the battery in normal operation. During the discharge process, if the remaining battery power is 0 or reaches the maximum discharge current IbatMax, the system can quickly cut off part of the load to prevent the battery from over-discharging. If the system still does not respond or the DC link is unstable after cutting off part of the load, the system disconnects the entire load and charges the battery through the available photovoltaic port to ensure the safety of the battery and the stability of the system. During the charging process, if the battery is full or reaches the peak, the system sets the status signal Flagcurt to 1 to reduce the power output of the photovoltaic port to avoid overcharging the battery. At the same time, resetting the integrator of the PI controller of the photovoltaic port to 0 helps to quickly adjust the output power of the photovoltaic port to adapt to changes in the battery charging state. If the battery is full, the battery reference current IbatRef is set to 0 or the preset IbatMin, and the power of the photovoltaic port is reduced to adjust the DC link voltage to maintain the stable operation of the system. In the power abandonment mode, the system senses the load demand that exceeds the power generation by monitoring the drop in the DC link voltage. At this time, the state signal Flagcurt = 0, the integrator of the PI controller of the battery port is reset and initialized to the current value of the battery reference current IbatRef, which helps to quickly adjust the output power of the battery port to adapt to changes in load demand. The system then transmits the DC link regulation back to the battery, using the battery's energy storage capacity to balance load demand and power generation capacity to ensure stable operation of the system. The above control logic improves the overall performance of the four-port converter through precise battery charge and discharge management, photovoltaic port power regulation, and intelligent regulation in power abandonment mode. This helps to ensure stable operation of the system under various operating conditions, improve energy utilization efficiency, and reduce energy waste.

[0087] In specific implementation, in order to reduce the duration of body diode conduction, reduce device power loss, and improve overall system efficiency, an optimized PWM switching technology is proposed to create a phase-controlled gate pulse sequence by adjusting the system to generate non-phase-shifted pulses. The switching sequence is as follows Figure 3 As shown. At this time, the volt-second balance of the inductor is completely decoupled. No matter what working mode it is in, the output of the PI controller always follows the same order. The duty cycle of one soft switch is smaller than the duty cycle of the downstream soft switch. That is, d pv1 <d pv2 <d bat .

[0088] Thus, in a multi-port converter, the energy of each input port needs to be transferred to the output end or the common DC link through the switching of the soft switch. By ensuring that the duty cycle of a soft switch is less than the duty cycle of its downstream soft switch, the energy can be orderly controlled to flow from each input port to the output end or the common DC link, avoiding the chaos and conflict of energy flow. In addition, the PWM waveform can be optimized and harmonics can be reduced. The size of the duty cycle directly affects the shape and frequency of the PWM (pulse width modulation) waveform. By accurately controlling the duty cycle of the soft switch and following the above constraints, the PWM waveform can be optimized, the generation of harmonics and noise can be reduced, thereby improving the efficiency and stability of the system. In addition, power electronic devices can be protected. The soft switch will generate a certain amount of heat and stress during the switching process. By reasonably setting the duty cycle and following the above constraints, the load balance of each soft switch during the switching process can be ensured, and a certain soft switch can be avoided from being damaged due to excessive work. The flexibility and response speed of the system can also be improved. Following the above constraints, the flexibility and response speed of the system can be improved while ensuring the stability of the system. For example, when the power of a certain input port needs to be adjusted quickly, it can be achieved by adjusting the duty cycle of the corresponding soft switch without making major adjustments to the entire system. In addition, energy distribution and efficiency can be optimized. By accurately controlling the duty cycle of each soft switch and following the above constraints, the energy distribution and transmission path can be optimized, thereby improving the overall efficiency of the system. For example, in a system with hybrid photovoltaic and battery power supply, the power output of the photovoltaic port and the battery port can be dynamically adjusted according to the light intensity and battery status to achieve optimal energy utilization and efficiency.

[0089] S4. Control the four-port converter FPC according to the set control scheme.

[0090] Compared with the prior art, the present invention optimizes the photovoltaic maximum power point tracking (MPPT) performance. By constructing a four-port converter FPC with three input ports, the method can be connected to two photovoltaic modules and an energy storage unit respectively to achieve independent and flexible MPPT control. The inductor and capacitor filtering parts equipped on each input port, as well as the PWM control signal of the soft switch, can smooth the current and voltage fluctuations, thereby improving the accuracy and stability of MPPT, especially under uneven lighting conditions. It also meets the requirements of low voltage gain. Through reasonable circuit design and component parameter setting, the method enables the four-port converter FPC to operate efficiently under low voltage gain conditions. This helps to reduce the system's dependence on high-gain converters, reduce the number and complexity of converters, thereby improving power density and reducing costs.

[0091] In addition, this method is adaptable to wide PV voltage changes. Since each input port is connected to the common DC link through an inductor and a capacitor, and is equipped with a soft switch for PWM control, this method can adapt to the wide voltage changes generated by the photovoltaic module under different light and temperature conditions. This enables the system to operate stably within a wider voltage range, improving the adaptability and reliability of the system. It can also efficiently process differential power. The design of the four-port converter FPC allows the differential power from different input ports to be processed simultaneously, achieving efficient transmission and distribution of energy. By optimizing the control scheme, the power balance between the input ports can be ensured to avoid power waste and energy loss. In addition, this method can reduce the cost and complexity of a single packaged device. This method reduces the number of required converters by integrating multiple functions into a four-port converter, thereby reducing the cost of a single packaged device. At the same time, due to the use of soft switching technology, energy loss and electromagnetic interference during the switching process are reduced, further simplifying the system structure and reducing complexity.

[0092] In summary, this method can simultaneously meet the technical requirements of optimizing MPPT performance, adapting to wide PV voltage changes, efficient differential power processing, and reducing the cost and complexity of a single packaged device, providing strong support for the efficient and reliable operation of distributed photovoltaic storage systems.

[0093] Embodiment 2

[0094] In order to better illustrate the effect of this method.

[0095] The FPC model proposed in this method is subjected to loss analysis and efficiency calculation, and is compared with the other two models. The comparison models include: ① the traditional dual-converter model (one photovoltaic module is connected in series with one energy storage unit); ② the traditional three-converter model (two photovoltaic modules are connected in series with one energy storage unit).

[0096] During the specific implementation, a detailed comparison of the efficiency of the three schemes from no-load to full-load is carried out from the switching mechanism.

[0097] The FPC model can reach a peak value of about 95.37% at full load and maintain nearly 94.07% at no load, with stable high efficiency. During system operation, the switch S bat , S pv1 , S dc For ZVS-ON, switch S pv2 , S pv1 and S dcThe body diode of the conventional dual converter solution is SCBD-OFF. In contrast, the efficiency from no-load to full-load is between 86.7% and 88.2% only when the switch on the converter is ZVS-ON. The conventional three-converter solution is the least efficient of the three solutions. Its low efficiency is due to the fact that PV1 and PV2 are hard-switched throughout the load spectrum, and the efficiency is between 0.52-0.72pu (i.e. -0.5ΔI Lbat <I bat <0.5ΔI Lbat ) in the load range, the efficiency is improved (about 82.7%), where both switches of the energy storage converter are in ZVS-ON state. bat <-0.5ΔI Lbat ) and above 0.72 pu (i.e. I bat >0.5ΔI Lbat ) load, the upper and lower switches of the energy storage converter experience the ZVS-ON state respectively.

[0098] Regarding the power loss of the three solutions, the reverse blocking loss of the two conventional solutions is large, and the inductance loss in the conventional solution is also higher than that of the FPC solution. The inductance loss of conventional solution 1 and conventional solution 2 is 1.78 times and 2.29 times that of the FPC solution, respectively. However, due to the smaller inductance number of conventional solution 2, its inductance copper loss is the lowest.

[0099] In summary, the present invention proposes a soft-switching multi-port converter control method for distributed photovoltaic storage configuration, which integrates two groups of cascaded PV modules and energy storage systems using only two half-bridge modules and three inductors, thereby improving power density and achieving full-range voltage operation. The proposed optimized phase modulation PWM technology achieves ZVS-ON of the switch and soft switching of the body diode without an additional resonant circuit, significantly reduces the reverse blocking loss of the system, and further improves the efficiency of the system. The above characteristics and control methods enable the FPC model to provide higher power density and energy conversion efficiency for photovoltaic power generation parks with distributed photovoltaic storage.

[0100] Embodiment 3

[0101] In order to allow those skilled in the art to better understand the principle and process of setting component parameters in the present method S2, the following description is given.

[0102] First, the dynamic response of the system is studied, and the mathematical model of FPC is analyzed by small signal AC. In the specific implementation, in order to be close to the actual model, a series of DC cable line resistances are added to each series-connected photovoltaic module. A single PV substring is modeled as a current source in parallel with a resistor. In steady state, the inductor voltage satisfies the KVL equation:

[0103]

[0104] Simplifying, we get:

[0105]

[0106] In steady state, the capacitor current satisfies the KCL equation:

[0107]

[0108] The DC link satisfies the equation in steady state:

[0109]

[0110] Make a small signal equivalent circuit, and the required inductor voltage is:

[0111]

[0112] The capacitor current is:

[0113]

[0114] When designing the component parameters of the FPC model (including inductance parameters and capacitance parameters), let L pv1 and L bat Half of the ripple current is greater than the critical value to ensure that the switch S dc and S dc in I Lpv1 and I Lbat When it is greater than zero, the zero voltage switch is in the on state (ZVS-ON), and the constraint requires that the upper limit of the current ripple does not exceed 30% of the respective nominal rated current. pv1 and L bat The value range of is:

[0115]

[0116] L pv2 The differential characteristic allows for a larger ripple current, so L pv2 The value range can be calculated by the following formula:

[0117]

[0118] The filter capacitor is selected by the maximum current and voltage ripple method in the boost dc-dc converter. pv1 Connect directly through PV port 1, considering 2% voltage ripple, C pv1 The value range of is as follows:

[0119]

[0120] By Cpv2 The ripple current is i Cpv2 , for the L pv1 and L pv2 Negative value of ripple current, considering 2% voltage ripple, C pv2 The value range of is as follows:

[0121]

[0122] in and It can be expressed as:

[0123]

[0124] Similarly, considering a 2% voltage ripple, C can be calculated. bat The minimum value of:

[0125]

[0126] in and It can be expressed as:

[0127]

[0128] C dc In d pv1 Supports DC loads during continuous operation. dc In the off state, under the 2% voltage ripple requirement, only The area of ​​the region can be calculated as C dc Minimum value range:

[0129]

[0130] Finally, it should be noted that the above embodiments are only used to illustrate the technical solution of the present invention rather than to limit the technical solution. Those skilled in the art should understand that those modifications or equivalent substitutions of the technical solution of the present invention that do not depart from the purpose and scope of the technical solution should be included in the scope of the claims of the present invention.

Claims

1. A soft-switching multi-port converter control method for distributed photovoltaic storage configuration, characterized in that: The following steps are involved: S1. construct a four-port converter FPC; the four-port converter FPC has three input ports and one common DC link port; the three input ports are respectively connected in series with respective power sources and finally converged to the common DC link port; Among them, the three input ports represent two photovoltaic modules and one energy storage unit respectively; the three input ports are connected to the public DC link through their own inductors and capacitors respectively; the inductors and capacitors on the circuits of each input port constitute the filtering part of the circuit, which is used to smooth the fluctuations of current and voltage; the circuits of each input port are also provided with soft switches, which are used to drive through PWM control signals to realize the transformation and energy transmission of the corresponding circuit; The common DC link port is provided with a soft switch for controlling the on and off of the DC link, and is also provided with a capacitor connected to the common DC link for further smoothing the voltage of the DC link; S2, setting component parameters of the four-port converter FPC; the component parameters include inductance parameters and capacitance parameters; S3, setting a control scheme of the four-port converter FPC, for generating and optimizing each soft switch control signal of the four-port converter FPC according to the system state and the upper logic; S4. Control the four-port converter FPC according to the set control scheme.

2. The soft-switching multi-port converter control method for distributed photovoltaic storage configuration according to claim 1, characterized in that: The three input ports are respectively the first photovoltaic port pv1, the second photovoltaic port pv2 and the battery port bat in descending order.

3. The soft-switching multi-port converter control method for distributed photovoltaic storage configuration according to claim 2, characterized in that: In S2, when setting the inductance parameters, the following requirements must be met: In the formula, the subscript pv1 Denotes the first photovoltaic, subscript pv2 Indicates the second photovoltaic; subscript bat represents battery; the subscript dc represents direct current; Δi represents the change in current; F sw Indicates the switching frequency; V dc Indicates the DC port voltage; Indicates that the flow through L pv1 The nominal current; I critical Indicates the minimum current flowing through the capacitor; Indicates that the flow through L pv2 The nominal current.

4. The soft-switching multi-port converter control method for distributed photovoltaic storage configuration according to claim 3, characterized in that: In S2, when setting the capacitance parameters, the following requirements must be met: In the formula, Δi Lpv1 Indicates that the flow through L pv1 The change in current; Δi Lpv2 Indicates that the flow through L pv2 The change in current; Δi bat Indicates flow through Z b The change in current; Represents capacitance C pv2 The time differential interval of the change is 1; Indicates the capacitance C pv2 The time differential interval of the change is 2; Represents capacitance C bat The time differential interval of the change is 1; Represents capacitance C bat The time differential interval of the change is 2; Indicates the nominal value of DC current; F sw Indicates the switching frequency.

5. The soft-switching multi-port converter control method for distributed photovoltaic storage configuration according to claim 4, characterized in that: In S3, the control scheme includes a reference signal generation layer, an implementation and execution layer, and a phase modulation switch layer; The reference signal generation layer is used to generate an initial reference signal according to the system state and the upper control logic; wherein the system state includes the battery SOC and the DC link voltage error; the reference signal includes the battery reference current input to the battery port and the reference voltage input to the two photovoltaic ports; The implementation and execution layer is used to process the reference signal of the reference signal generation layer through the PI controller algorithm, generate control signals for driving the soft switches corresponding to the three input ports, adjust the duty cycle of each soft switch, and optimize the PWM technology of each soft switch; The phase modulation switch layer is used to convert the control signal generated by the implementation and execution layer module into a pulse signal suitable for driving the power electronic device; the power electronic device includes various soft switches.

6. The soft-switching multi-port converter control method for distributed photovoltaic storage configuration according to claim 5, characterized in that: The upper control logic includes: when the state signal Flag curt =0, when the battery is operating normally, the battery reference current Ibat Ref Follow Iref PI The reference current value; During the discharge process, if the remaining battery power is 0 or reaches the maximum discharge current Ibat Max , the system cuts off part of the load. If there is no response or the DC link is unstable, the system disconnects the entire load and charges the battery through the available PV port. During the charging process, if the battery is full or reaches the peak value, the status signal Flag curt Set to 1 to reduce the power of the PV port and reset the integrator of the PI controller of the PV port to 0; if the battery is full, the battery reference current Ibat Ref Set to 0 or the default Ibat Min , while reducing the power of the PV port to regulate the DC link; In the power abandonment mode, the load demand exceeding the power generation is sensed by the drop of DC link voltage, and the status signal Flag curt = 0, reset the integrator of the PI controller of the battery port and initialize it to the battery reference current Ibat Ref The system then transfers the DC link regulation back to the battery.

7. The soft-switching multi-port converter control method for distributed photovoltaic storage configuration according to claim 6, characterized in that: The outputs of the PI controllers of the three input ports always follow that the duty cycle of one soft switch is smaller than the duty cycle of the downstream soft switch.

Images