Multi-stage control method, system and equipment for high-power-density modular B2G converter and medium

Abstract

The invention discloses a multi-stage control method, system and device for a high-power-density modular B2G converter and a medium, and belongs to the technical field of converter control, and the method comprises the steps: constructing a two-stage converter topology of a double-ring controller structure comprising a voltage outer ring and a current inner ring; carrying out soft start on the two-stage type converter topology; judging an energy transfer direction, selecting a closed-loop control strategy according to the energy transfer direction, and generating a given value of a current inner loop; according to the given value of the current inner loop and the operation state information of the two-stage converter topology, generating a carrier phase angle and executing voltage and current sharing; soft switching control operation is executed in the two-stage converter topology; according to the invention, the design of the bidirectional symmetric CLLLC resonant topology is combined with hierarchical progressive soft start, and according to a constant power or constant voltage master control strategy of energy direction switching, the adaptation between photovoltaic discharge energy storage discharge and power grid interaction is realized, and the system is ensured to efficiently and stably operate under a wide transformation ratio working condition.

Description

Technical Field

[0001] This invention relates to the field of converter control technology, specifically to a multi-stage control method, system, device, and medium for a high power density modular B2G converter. Background Technology

[0002] To promote the green and high-quality development of the construction industry, strengthening the integration of photovoltaic, energy storage, direct current, and flexible technologies with zero-carbon buildings is beneficial for transforming buildings into energy hubs and promoting sustainable development in the construction sector. In the current context of deepening dual-carbon goals and the vigorous development of new productive forces, the construction industry, as a key energy-consuming sector and one of the largest end-users of the power system, plays a crucial role in the overall energy transition through its green and low-carbon development. In this process, accelerating the construction of a new building power distribution system with renewable energy consumption as its primary objective and innovative technologies such as microgrids and photovoltaic-energy storage direct current and flexible technologies as its features, to achieve low-carbon electricity, flexible load, high-efficiency power consumption, and intelligent operation and maintenance, will become a key lever for promoting the high-quality development of the construction industry.

[0003] However, existing AC / DC converters still have many shortcomings in terms of efficiency, power density, light-load performance, and dynamic response. Especially in energy exchange between medium-voltage and low-voltage DC systems, traditional converters often suffer from large size, low efficiency, and complex control. Existing research indicates that while AC / DC converter structures based on cascaded H-bridges (CHBs) and isolated DC / DC converters can achieve medium-voltage access, their hard-switching operation leads to high switching losses, especially a significant drop in efficiency under light loads. After a unified comparison of various isolated DC / DC soft-switching topologies, the following defects are identified: DAB converters suffer from narrow soft-switching range, high return power, excessive turn-off losses, and overvoltage of the switching transistors; series LC resonant converters have a small output voltage range, making them unsuitable for applications with a large voltage gain range; and LLLC resonant converters have high switching transistor losses and a narrow voltage gain range in frequency conversion boost mode. Summary of the Invention

[0004] In view of the above-mentioned problems, the present invention is proposed.

[0005] Therefore, the technical problem solved by this invention is that existing converters still have significant shortcomings in terms of efficiency, power density, and dynamic response. Especially in energy exchange between medium-voltage and low-voltage DC systems, traditional solutions generally suffer from problems such as large size, low efficiency, and complex control.

[0006] To solve the above-mentioned technical problems, the present invention provides the following technical solution: a multi-stage control method for a high power density modular B2G converter, comprising the following steps, Construct a two-stage converter topology with a dual-loop controller structure including an outer voltage loop and an inner current loop; Perform soft-start control to soft-start the two-stage converter topology; After the two-stage converter topology is soft-started, the current signal of the two-stage converter topology is collected in real time and the energy transfer direction is determined. Based on the energy transfer direction, a closed-loop control strategy is selected and a setpoint value for the inner current loop is generated. Based on the given value of the inner current loop and the operating status information of the two-stage converter topology, the carrier phase angle is generated and voltage and current equalization are performed. When the drive signal determined by the carrier phase angle needs to turn on the high-frequency bridge arm switch, a soft-switching control operation is performed in the two-stage converter topology.

[0007] As a preferred embodiment of the high power density modular B2G converter multi-stage control method described in this invention, the step of constructing a two-stage converter topology including a dual-loop controller structure with an outer voltage loop and an inner current loop includes: A front-end AC / DC unit is constructed as the front-end unit of a two-stage converter topology, and an auxiliary resonant circuit is integrated on the bridge arm of the front-end unit. The subsequent DC / DC unit is constructed as the subsequent unit of the two-stage converter topology, and the subsequent unit is designed as an isolated bidirectional symmetrical CLLLC resonant converter topology. Connecting the DC output terminal of the front-end unit to the input terminal of the rear-end unit forms a two-stage converter topology. A dual-loop controller structure consisting of a preset voltage outer loop and a current inner loop.

[0008] The beneficial effects of this preferred technical solution are as follows: by combining the design of a bidirectional symmetrical CLLLC resonant topology with a hierarchical progressive soft start, zero-voltage or zero-current soft switching and shock-free smooth start-up are achieved across the entire load range.

[0009] As a preferred embodiment of the multi-stage control method for a high power density modular B2G converter described in this invention, the step of performing soft-start control to soft-start the two-stage converter topology includes: Construct an effective duty cycle variation curve that increases linearly with time; During the soft start process of the two-stage converter topology, phase shift control is performed. The phase shift control includes adjusting the phase shift angle of the pulses of the two bridge arms on the input side of the full-bridge converter in the two-stage converter according to the effective duty cycle change curve, thereby changing the equivalent output voltage of the full-bridge converter. When the effective duty cycle rises to the rated duty cycle, it is determined that the system has stably established the required voltage and current, and at this time the two-stage converter topology completes the soft start.

[0010] As a preferred embodiment of the multi-stage control method for a high power density modular B2G converter described in this invention, the steps of: after the two-stage converter topology undergoes soft start, real-time acquisition of the current signal of the two-stage converter topology and determination of the energy transfer direction, and selection of a closed-loop control strategy and generation of the setpoint value for the inner current loop based on the energy transfer direction include: Acquire the current signal between the DC and AC sides of the two-stage converter topology; If the detected current signal flows from the AC side to the DC side, it is determined to be forward transmission. At this time, constant power control is used as the voltage outer loop to generate the current setpoint value of the current inner loop. If the detected current signal flows from the DC side to the AC side, it is determined to be reverse transmission. At this time, constant voltage control is used as the voltage outer loop to generate the current setpoint value of the current inner loop. With the given value of the inner current loop as the target, the switching frequency of the subsequent DC / DC unit is adjusted by the PI controller so that the actual output current approaches the given value.

[0011] The beneficial effects of this preferred technical solution are as follows: Based on the constant power or constant voltage main control strategy of energy direction switching, the adaptation between photovoltaic discharge, energy storage discharge and grid interaction is realized, overcoming the defects of narrow voltage gain range and asymmetrical bidirectional control, and ensuring efficient and stable operation of the system under wide transformation ratio conditions.

[0012] As a preferred embodiment of the multi-stage control method for a high power density modular B2G converter described in this invention, the step of generating a carrier phase angle and performing voltage and current equalization based on the given value of the inner current loop and the operating status information of the two-stage converter topology includes: Collect the output voltage and output current of the subsequent DC / DC unit; The current setpoint is corrected based on the deviation between the output voltage and the average voltage of each subsequent DC / DC unit to obtain the corrected current. The carrier phase angle adjustment is generated based on the deviation between the output current and the correction current of each subsequent DC / DC unit. Adjusting the carrier phase angle of each subsequent DC / DC unit according to the carrier phase angle adjustment amount achieves voltage and current equalization.

[0013] The beneficial effects of this preferred technical solution are as follows: through inter-module carrier phase shifting voltage and current equalization control and underlying soft switching operation, the current distribution command is corrected in real time based on the output voltage and current of each downstream DC / DC unit, and the carrier phase angle is dynamically adjusted, thereby achieving power balance of multiple modules.

[0014] As a preferred embodiment of the multi-stage control method for a high-power-density modular B2G converter described in this invention, when the drive signal determined by the carrier phase angle needs to turn on the high-frequency bridge arm switch, the steps for performing soft-switching control in the two-stage converter topology include: When the drive signal determined by the carrier phase angle needs to turn on the high-frequency bridge arm switch, it triggers the auxiliary switch and uses the resonant cavity to perform the first resonance, resonating the voltage across the bridge arm where the main switch is located to zero. The auxiliary switch is turned off, and a second resonance is achieved using the resonance process, so that the voltage across the auxiliary switch is also resonated to zero, thereby realizing zero-voltage turn-on of the auxiliary switch.

[0015] The beneficial effects of this preferred technical solution are as follows: by integrating an auxiliary resonant circuit into the front-end bridge arm and performing two resonant operations before the high-frequency bridge arm switch is turned on by the PWM drive signal, zero-voltage turn-on of the main switch and the auxiliary switch is achieved, thereby improving the power density and operating efficiency of the converter.

[0016] As a preferred embodiment of the multi-stage control method for a high power density modular B2G converter described in this invention, the formula for the effective duty cycle variation curve that increases linearly with time is: ; in, For an effective duty cycle, This is the rated duty cycle of the converter. The preset converter startup time, This is the current startup time.

[0017] This invention provides a multi-stage control system for a high power density modular B2G converter.

[0018] To address the aforementioned technical problems, the present invention further provides the following technical solution: a multi-stage control system for a high power density modular B2G converter, comprising: Topology building module: Constructs a two-stage converter topology with a dual-loop controller structure including an outer voltage loop and an inner current loop; Soft-start module: Performs soft-start control to soft-start the two-stage converter topology; Control strategy selection module: Real-time acquisition of current signals of the two-stage converter topology and determination of energy transfer direction, selection of closed-loop control strategy based on the energy transfer direction and generation of current inner loop setpoint; Voltage and current equalization module: Based on the given value of the inner current loop and the operating status information of the two-stage converter topology, it generates the carrier phase angle and performs voltage and current equalization. Soft-switching control module: When the drive signal determined by the carrier phase angle needs to turn on the high-frequency bridge arm switch, it performs soft-switching control operation in the two-stage converter topology.

[0019] The present invention provides a computer device, including a memory and a processor, wherein the memory stores a computer program, characterized in that the processor executes the computer program to implement the steps of the multi-stage control method for a high power density modular B2G converter.

[0020] The present invention provides a computer-readable storage medium having a computer program stored thereon, characterized in that, when the computer program is executed by a processor, it implements the steps of the multi-stage control method for a high power density modular B2G converter.

[0021] The beneficial effects of this invention are as follows: By combining a bidirectional symmetrical CLLLC resonant topology design with a hierarchical progressive soft-start, this invention achieves zero-voltage or zero-current soft switching and shock-free smooth startup across the entire load range; based on a constant power or constant voltage main control strategy with energy direction switching, it achieves adaptation between photovoltaic discharge, energy storage discharge, and grid interaction, overcoming the defects of narrow voltage gain range and asymmetrical bidirectional control, ensuring efficient and stable operation of the system under wide transformer ratio conditions; through inter-module carrier phase shift voltage and current equalization control and underlying soft-switching operation, based on the output voltage and current of each downstream DC / DC unit, it corrects the current distribution command in real time and dynamically adjusts the carrier phase angle, achieving power balance among multiple modules; by integrating an auxiliary resonant circuit in the front-end bridge arm and performing two resonant operations before the high-frequency bridge arm switch is turned on by the PWM drive signal, it achieves zero-voltage turn-on of the main switch and auxiliary switch, improving the power density and operating efficiency of the converter. Attached Figure Description

[0022] To more clearly illustrate the technical solutions of the embodiments of the present invention, the accompanying drawings used in the description of the embodiments will be briefly introduced below. Obviously, the accompanying drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0023] Figure 1 The above is a flowchart of a multi-stage control method for a high power density modular B2G converter, provided as an embodiment of the present invention. Detailed Implementation

[0024] To make the above-mentioned objects, features, and advantages of the present invention more apparent and understandable, specific embodiments of the present invention will be described in detail below with reference to the accompanying drawings. Obviously, the described embodiments are only a part of the embodiments of the present invention, and not all of them. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort should fall within the protection scope of the present invention.

[0025] Example 1, referring to Figure 1 This is the first embodiment of the present invention, which provides a multi-stage control method for a high power density modular B2G converter, including: S100: Construct a two-stage converter topology with a dual-loop controller structure including an outer voltage loop and an inner current loop; S200: Perform soft-start control to soft-start the two-stage converter topology; S300: After the two-stage converter topology is soft-started, the current signal of the two-stage converter topology is collected in real time and the energy transfer direction is determined. Based on the energy transfer direction, a closed-loop control strategy is selected and a setpoint value for the inner current loop is generated. S400: Based on the given value of the inner current loop and the operating status information of the two-stage converter topology, generate the carrier phase angle and perform voltage and current equalization. S500: When the drive signal determined by the carrier phase angle needs to turn on the high-frequency bridge arm switch, a soft-switching control operation is performed in the two-stage converter topology.

[0026] It should be noted that existing AC / DC converters still have significant shortcomings in terms of efficiency, power density, and dynamic response. Especially in energy exchange between medium-voltage and low-voltage DC systems, traditional solutions generally suffer from large size, low efficiency, and complex control. While structures based on cascaded H-bridges (CHBs) and isolated DC / DC converters can achieve medium-voltage access, hard switching leads to high switching losses and a significant decrease in efficiency under light loads. DAB converters employ soft switching, but their range is narrow, return power is high, and there is a risk of overvoltage in the switching transistors. Series LC resonant converters have a small voltage gain range, making them unsuitable for wide transformation ratio applications. LLLC resonant converters suffer from high switching losses, and their gain is limited in frequency conversion boost mode. Therefore, it is crucial to propose a multi-stage control method for converters that can reduce switching losses and is applicable to medium- and high-power applications.

[0027] Therefore, to address the existing problems in the use of existing converters, a multi-stage control method for a high-power-density modular B2G converter is constructed through steps S100~S500. By designing a bidirectional symmetrical CLLLC resonant topology combined with a hierarchical progressive soft-start, zero-voltage or zero-current soft switching and shock-free smooth startup are achieved across the entire load range. Based on a constant power or constant voltage main control strategy for energy direction switching, adaptation to photovoltaic discharge, energy storage discharge, and grid interaction is achieved, overcoming the shortcomings of narrow voltage gain range and asymmetrical bidirectional control, ensuring efficient and stable system operation under wide transformation ratio conditions. Through inter-module carrier phase shift voltage and current equalization control and underlying soft-switching operation, current distribution commands are corrected in real time based on the output voltage and current of each downstream DC / DC unit, and the carrier phase angle is dynamically adjusted, achieving power balance among multiple modules. By integrating an auxiliary resonant circuit into the front-stage bridge arm and performing two resonant operations before the high-frequency bridge arm switch is turned on by the PWM drive signal, zero-voltage turn-on of the main switch and auxiliary switch is achieved, improving the power density and operating efficiency of the converter.

[0028] Example 2, refer to Figure 1 This is the second embodiment of the present invention, which provides a multi-stage control method for a high power density modular B2G converter.

[0029] In this embodiment of the application, the two-stage converter topology in step S100, which includes a dual-loop controller structure comprising an outer voltage loop and an inner current loop, includes the following steps A1-A4: A1: Construct a front-stage AC / DC unit as the front-stage unit of a two-stage converter topology, and integrate an auxiliary resonant circuit on the bridge arm of the front-stage unit; In this embodiment, a multi-module cascaded structure is selected to construct the front-end AC / DC unit for connection to a 380V medium-voltage power grid. A half-bridge or full-bridge circuit is used as the basic power unit. On the high-frequency bridge arm of each module, an auxiliary resonant circuit consisting of an auxiliary switching transistor, a resonant inductor, and a resonant capacitor is additionally integrated. It should be noted that the purpose of constructing the front-end AC / DC unit is to create zero-voltage turn-on conditions for the high-frequency bridge arm switch and the auxiliary switch through two resonances during the switching process. The modules adopt a carrier horizontal phase shift modulation method to obtain high-level output and reduce the equivalent switching frequency, thereby reducing the overall switching loss.

[0030] A2: Construct the subsequent DC / DC unit as the subsequent unit of the two-stage converter topology, and design the subsequent unit as an isolated bidirectional symmetrical CLLLC resonant converter topology; In this embodiment, the downstream DC / DC unit adopts a full-bridge structure, with resonant inductors, resonant capacitors, and magnetizing inductors configured on both the primary and secondary sides, forming a bidirectional symmetrical CLLLC resonant converter topology. The forward and reverse operating principles of the bidirectional symmetrical CLLLC resonant converter topology are the same as those of the unidirectional LLC converter. The power flow direction can be switched simply by changing the pulse direction, making control simple and enabling soft switching across the entire load range. The transformer of the downstream DC / DC unit adopts a high-frequency isolation design to meet safety regulations and achieve electrical isolation.

[0031] A3: Connect the DC output terminal of the front-end unit to the input terminal of the rear-end unit to form a two-stage converter topology.

[0032] In this embodiment, the DC bus output terminal of the front-stage AC / DC unit is directly connected to the input terminal of the rear-stage DC / DC unit to form a complete physical path for a two-stage converter. The AC side is connected to a 380V three-phase power grid through a voltage regulator, and the DC side can be connected to a resistive load or a DC source to simulate actual operating conditions. It should be noted that the connection method adopted in the embodiments of this application ensures that energy can flow from the AC side to the DC side and from the DC side to the AC side, realizing the function of bidirectional energy transmission; the two-stage converter topology adopts an ISOP architecture with series input and parallel output, including multiple functional modules. Each functional module consists of a front-stage AC / DC unit and a rear-stage DC / DC unit. The front-stage AC / DC units of multiple functional modules are connected in series on the AC side or DC bus side, and the output terminals of the rear-stage DC / DC units of multiple functional modules are connected in parallel.

[0033] A4: Preset dual-loop controller structure consisting of an outer voltage loop and an inner current loop; In this embodiment, the dual-loop controller structure is deployed in the digital control unit to achieve closed-loop regulation of the downstream DC / DC unit. The outer voltage loop uses the DC bus voltage or the transmission power of the two-stage converter topology as the control target: during reverse transmission, the measured DC bus voltage is compared with a given reference voltage, and the error is output by a PI regulator as the setpoint for the inner current loop; during forward transmission, the measured DC power is compared with a power reference value, and the same setpoint for the inner current loop is generated after PI regulation. The inner current loop uses the actual output current of each module's downstream DC / DC unit as a feedback signal, compares it with the current setpoint output by the outer voltage loop, and the resulting error is calculated by the PI controller to dynamically adjust the switching frequency of the CLLLC converter, ensuring the actual output current tracks the setpoint, thereby achieving stable control of the system power or voltage.

[0034] In one alternative implementation, a two-stage converter topology can be constructed using a matrix converter structure. The front-stage AC / DC unit adopts a matrix converter structure, forming a three-phase matrix topology with nine bidirectional switches, eliminating the power frequency rectification stage. A passive auxiliary resonant network is connected in parallel next to the matrix converter bridge arm, enabling zero-voltage turn-on of the main switch without additional auxiliary switches. The rear-stage DC / DC unit is an isolated bidirectional symmetrical CLLLC resonant topology, with an adjustable capacitor array connected in series in the primary and secondary resonant branches. The resonant parameters can be dynamically adjusted according to voltage changes. Both the primary and secondary sides of the topology are equipped with a full-bridge switching structure, which, together with dead-time control, enables the charging and discharging of parasitic capacitors.

[0035] In another alternative implementation, a two-stage converter topology can be constructed using a modular multilevel and synchronous rectification CLLLC topology. The front-stage AC / DC unit adopts a modular multilevel structure, with each sub-module consisting of a half-bridge switching circuit, an auxiliary resonant capacitor, and a buffer resistor. The sub-modules are cascaded and connected to a 380V medium-voltage power grid. Carrier phase-shift modulation is used between modules. By increasing the number of sub-modules, the number of output levels is increased, and the voltage harmonic distortion rate is reduced. The rear-stage DC / DC unit is designed as a two-phase symmetrical CLLLC resonant topology with synchronous rectification. A synchronous rectification switch is used on the secondary side to reduce reverse recovery losses. The original symmetrical resonant inductor, resonant capacitor, and magnetizing inductor configuration on the secondary side is retained, and voltage gain regulation is achieved through frequency conversion control.

[0036] In this embodiment of the application, step S200 introduces a frequency conversion phase-shift hybrid soft-start strategy to perform soft-start on the two-stage converter topology, including the following steps B1-B3: B1: Construct an effective duty cycle variation curve that increases linearly with time; In this embodiment of the application, the formula for constructing the effective duty cycle variation curve that increases linearly with time is: ; in, For an effective duty cycle, This is the rated duty cycle of the converter. The preset converter startup time, This is the current startup time; It should be noted that by constructing an effective duty cycle variation curve that increases linearly with time to guide the phase-shift control process, and by making the effective duty cycle increase linearly from zero to the rated value, the equivalent output voltage of the full-bridge converter can be smoothly adjusted, thereby avoiding the current surge caused by the low impedance of the resonant cavity during the soft-start phase and ensuring that the system safely establishes initial energy.

[0037] B2: During the soft start process of the two-stage converter topology, phase shift control is performed; the phase shift control includes: adjusting the phase shift angle of the pulses of the two bridge arms on the input side of the full-bridge converter in the two-stage converter according to the effective duty cycle change curve, thereby changing the equivalent output voltage of the full-bridge converter; In this embodiment, during the soft-start phase, phase-shift control is used instead of the main control frequency conversion strategy. The phase shift angle of the two bridge arm pulses on the input side of the full-bridge converter of the front-stage AC / DC unit in the two-stage converter is adjusted according to the effective duty cycle change curve. By changing the phase shift angle, the equivalent output voltage of the full-bridge converter is adjusted so that it slowly increases from zero until it reaches the rated value. The phase-shift control suppresses the starting current spike caused by the near-zero resonant cavity impedance.

[0038] B3: When the effective duty cycle rises to the rated duty cycle, it is determined that the system has stably established the required voltage and current, and at this time the two-stage converter topology completes the soft start.

[0039] In this embodiment of the application, when the current startup time t reaches the preset converter startup time... At this point, according to the formula for the effective duty cycle change curve that rises linearly with time, the effective duty cycle rises to the rated duty cycle, indicating that the system voltage and current have been established stably, and that the soft start process has ended.

[0040] In one optional implementation, soft starting of the two-stage converter topology can also be achieved through a three-stage soft start using current-limiting, phase-shifting, and frequency conversion. The three-stage control logic achieves soft starting in three stages: First, current-limiting start, where a temporary current-limiting resistor is connected in series at the AC / DC unit input, setting the starting current threshold to not exceed a set multiple of the rated current. Simultaneously, the front-stage auxiliary resonant circuit initiates its first resonance, pre-charging the bridge arm voltage to a preset value to avoid large currents caused by zero resonant cavity impedance. Second, phase-shifting control is switched to, removing the current-limiting resistor and constructing a piecewise linear duty cycle curve. The phase shift angle of the two bridge arms is adjusted according to the curve, gradually increasing the DC bus voltage to a set ratio of the rated value. Third, frequency conversion control is transitioned to, when the voltage reaches the preset value, frequency conversion adjustment is initiated. The switching frequency is dynamically adjusted via a PI controller to match the output current to the given value, completing the soft start.

[0041] In another alternative implementation, soft-start of the two-stage converter topology can also be achieved through bidirectional adaptive soft-start. Initially, the voltage difference between the AC and DC sides is detected to determine the potential power transmission direction: if the DC voltage is higher than the AC voltage, it is determined to be reverse transmission startup, and a reverse-adaptive duty cycle curve is constructed, while the subsequent unit adopts synchronous hybrid control; if the AC voltage is higher, it is determined to be forward transmission startup, and a standard linear duty cycle curve is adopted, with the subsequent topology enabling frequency conversion control. During soft-start, the front-end unit always executes phase-shift control, adjusting the bridge arm pulse phase-shift angle according to the duty cycle curve, and the auxiliary resonant circuit ensures zero-voltage turn-on of the switching transistor through two resonances. The subsequent unit matches the resonant parameters based on the power direction prediction result, and switches to a conventional control strategy when the duty cycle reaches the rated value and the current transmission direction stabilizes.

[0042] In this embodiment of the application, after the two-stage converter topology is soft-started in step S300, the current signal of the two-stage converter topology is collected in real time and the energy transfer direction is determined. The closed-loop control strategy is selected according to the energy transfer direction and the setpoint of the inner current loop is generated, including the following steps C1-C4: C1: Acquire the current signal between the DC and AC sides of the two-stage converter topology; In this embodiment of the application, after the soft start is completed and the system enters a stable operating state in step S200, the actual current signal between the DC side and the AC side is collected in real time by Hall current sensors installed at the DC bus and AC input line. The Hall current sensor is installed on the positive or negative path of the DC bus and can measure the magnitude and direction of the current between the AC grid side and the DC energy storage side. The analog current signal collected by the Hall current sensor is filtered, amplified and isolated by the signal conditioning circuit and then converted into a digital signal that can be judged by the processor, thereby obtaining the current signal. This current signal is the physical basis for subsequent determination of power transmission direction and selection of control strategy.

[0043] C2: If the detected current signal flows from the AC side to the DC side, it is determined to be forward transmission. At this time, constant power control is used as the voltage outer loop to generate the current setpoint of the current inner loop. In this embodiment of the application, the direction from the AC side to the DC side is defined as the positive direction. The digital controller analyzes the current signal collected in step C1 in real time. When the value of the current signal collected in step C1 is continuously positive, it is determined that the detected current signal flows from the AC side to the DC side, and there is a current demand for charging the energy storage device from the grid. This is considered positive transmission, and the control objective is to achieve constant power charging to avoid impacting the grid and to meet the preset charging plan. At this time, the voltage outer loop adopts a constant power control strategy to generate the current setpoint value for the current inner loop. The formula for generating the current setpoint value for the current inner loop is: ; in, The current setpoint for the inner current loop. For a given active power, The DC bus voltage is obtained through measurement; the current command for generating the current inner loop is calculated based on the DC bus voltage using the formula for generating the current setpoint value, and then output as the current setpoint value for the current inner loop.

[0044] C3: If the detected current signal flows from the DC side to the AC side, it is determined to be reverse transmission. At this time, constant voltage control is used as the voltage outer loop to generate the current setpoint value of the current inner loop. In this embodiment, the direction from the AC side to the DC side is defined as the positive direction. The digital controller analyzes the current signal collected in step C1 in real time. When the value of the current signal collected in step C1 is continuously negative, it is determined that the detected current signal is flowing from the DC side to the AC side. At this time, the energy storage device is feeding power to the grid, which is determined to be reverse transmission. The control objective is to maintain the stability of the DC bus voltage and provide a stable DC voltage source for the upstream AC / DC unit. At this time, the voltage outer loop adopts a constant DC voltage control strategy to generate the current setpoint value of the current inner loop. The formula for generating the current setpoint value of the current inner loop is: ; ; in, The current setpoint for the inner current loop. For a given active power, This is the DC bus voltage. Set the DC voltage value; This is the voltage outer loop proportionality coefficient. The voltage outer loop integral coefficient; the current setpoint of the current inner loop is calculated using the formula for generating the current setpoint of the current inner loop and outputs a current command to eliminate this deviation.

[0045] C4: Using the given value of the inner current loop as the target, the switching frequency of the subsequent DC / DC unit is adjusted by the PI controller so that the actual output current approaches the given value.

[0046] In this embodiment, the control target current of the downstream DC / DC unit is acquired in real time, and the current error is calculated by combining the current setpoint obtained in step C2 or step C3. The formula for calculating the current error is: ; in, For current error, Given a current value, To control the target current; The current error calculated by the current error is input to the PI controller. The PI controller performs proportional amplification and integral accumulation on the error signal using pre-set proportional and integral coefficients, and outputs the target current control signal. The target current control signal generates a PWM wave through pulse width modulation, thereby adjusting the switching frequency of the subsequent DC / DC unit.

[0047] In one alternative implementation, the control strategy based on the current transmission direction can also be achieved through voltage prediction and parameter self-tuning. The difference between the AC side grid voltage and the DC side voltage is measured. If the AC side voltage is higher than the DC side voltage and the current signal is positive, it is determined to be forward transmission. In this case, frequency conversion control and PI parameter self-tuning strategy are adopted. The controller automatically adjusts the PI parameters according to the load changes, so that the switching frequency can quickly adapt to the resonance requirement and reduce switching losses. If the DC side voltage is higher than the AC side voltage and the current signal is negative, it is determined to be reverse transmission, and the system switches to synchronous hybrid control.

[0048] In another optional implementation, the control strategy based on the current transmission direction can also be achieved through phase-assisted determination and resonant tracking control. When determining the direction, the polarity of the current and the phase of the voltage are combined: the AC side current and the grid voltage are set to be in phase as the positive reference. When the current signal collected by the sensor is positive and the phase difference with the AC side voltage is less than 30°, it is determined to be positive transmission, and frequency conversion control and resonant frequency tracking strategy are adopted. When the current signal is negative and the phase difference with the AC side voltage is greater than 150°, it is determined to be reverse transmission, and synchronous hybrid control is enabled.

[0049] In this embodiment of the application, step S400, which generates the carrier phase angle and performs voltage and current equalization based on the given value of the inner current loop and the operating status information of the two-stage converter topology, includes the following steps D1-D4: D1: Collects the output voltage and output current of the subsequent DC / DC unit; In this embodiment, the two-stage converter topology includes multiple parallel-connected downstream DC / DC units. Each downstream DC / DC unit has a voltage sensor and a current sensor at its DC output terminal to collect the voltage and current signals of each downstream DC / DC unit in real time. The collected voltage and current signals are filtered and isolated by a signal conditioning circuit and then sent to an analog-to-digital converter to be converted into digital quantities to obtain the output voltage and output current. At the same time, the average value of the output voltage of all downstream DC / DC units is calculated to obtain the average output voltage.

[0050] D2: Correct the current setpoint based on the deviation between the output voltage and the average voltage of each subsequent DC / DC unit to obtain the corrected current; In this embodiment, the current command obtained in step C2 or C3 is evenly distributed according to the total number of subsequent DC / DC units to obtain the initial current command. The formula for calculating the initial current command is as follows: ; in, This is the initial current command. Given a current value, This refers to the number of subsequent DC / DC units; To achieve voltage balance, a voltage deviation correction is introduced. The voltage deviation correction rule is as follows: if the output voltage of the subsequent DC / DC unit is lower than the average output voltage, it indicates that the load is heavy or the output capability is weak, and the current command should be increased appropriately to obtain the correction current; if the output voltage of the subsequent DC / DC unit is higher than the average output voltage, it indicates that the load is light or the output capability is strong, and the current command should be decreased appropriately to obtain the correction current. The formula for obtaining the corrected current is: ; in, To correct the current, This is the initial current command. The average output voltage. This is the output voltage of the subsequent DC / DC unit. This is the voltage equalization gain coefficient; D3: Generates carrier phase angle adjustment based on the deviation between the output current and the correction current of each subsequent DC / DC unit; In this embodiment of the application, the unit current error is calculated based on the output current of each subsequent DC / DC unit and the correction current obtained in step D2. The formula for calculating the unit current error is as follows: ; in, To correct the current, For the output current of the subsequent DC / DC unit, This refers to the unit current error; The calculated unit current error is input to the current equalization PI regulator, which then outputs the corresponding carrier phase angle adjustment. The formula for the output carrier phase angle adjustment is: ; in, This is the carrier phase angle adjustment amount. For unit current error, The proportional coefficient of the current-balancing PI regulator. The integral coefficient of the current-balanced PI regulator; It should be noted that the current balancing PI regulator belongs to the inter-module coordination control layer. Under the premise that the total current command has been determined in the constant power or constant voltage control in step S300, it realizes the dynamic load balancing distribution among each parallel downstream DC / DC unit. The current balancing PI regulator is used to generate the phase offset of the PWM carrier in each parallel downstream DC / DC unit, thereby changing the equivalent output impedance of each parallel downstream DC / DC unit by horizontal phase shifting of the carrier, and actively guiding the current to be distributed as needed.

[0051] D4: Adjust the carrier phase angle of each subsequent DC / DC unit according to the carrier phase angle adjustment amount to achieve voltage and current equalization.

[0052] In this embodiment, the calculated carrier phase angle adjustment is superimposed on the original carrier phase of the subsequent DC / DC unit to generate a final phase-shifted carrier signal. Drive pulses for the full-bridge switching transistors of the subsequent DC / DC unit are then generated based on this final phase-shifted carrier signal. By modulating the harmonic components of the output current through horizontal phase shifting of the carrier, the harmonic components are offset along the time axis, achieving harmonic cancellation and ripple cancellation on the parallel DC bus. This is equivalent to increasing the switching frequency to N times that of a single subsequent DC / DC unit, where N is the number of parallel subsequent DC / DC units. To reduce the total output current ripple, the equivalent output impedance of each module can be changed by adjusting the carrier phase angle, thereby actively guiding the current to be distributed as needed: when the output voltage of a certain downstream DC / DC unit is too low, steps D2-D3 will automatically increase its current command, and step D4 will reduce its carrier phase to make the downstream DC / DC unit bear more output current, thereby raising the output voltage of the downstream DC / DC unit; the same applies to the opposite, forming a closed-loop feedback mechanism of voltage, current and phase, ultimately achieving voltage and current sharing among the downstream DC / DC units.

[0053] It should be noted that steps D1-D4 avoid current imbalance between modules caused by component parameter dispersion or thermal drift, ensuring that the system can maintain reliable operation in long-term operation, load change or single module failure scenarios, supports plug and play and has redundant operation capability.

[0054] In this embodiment of the application, when the drive signal determined by the carrier phase angle in step S500 needs to turn on the high-frequency bridge arm switch, the soft-switching control operation in the two-stage converter topology includes the following steps E1-E2: E1: When the drive signal determined by the carrier phase angle needs to turn on the high-frequency bridge arm switch, it triggers the auxiliary switch and uses the resonant cavity to resonate for the first time, bringing the voltage across the bridge arm where the main switch is located to zero. In this embodiment of the application, when the drive signal determined by the carrier phase angle generated in step S400 drives the high-frequency bridge arm switch in the front-end AC / DC unit to be about to be turned on, a drive signal is sent to the auxiliary switch to make it conduct. At this time, the auxiliary resonant circuit composed of the auxiliary switch, the auxiliary resonant inductor and the auxiliary resonant capacitor starts to work. Through the LC resonance process, the voltage across the bridge arm where the switch to be turned on is located is resonated from the initial value to zero. The voltage across the bridge arm where the switch to be turned on is located is temporarily borne by the auxiliary switch which is still in the conducting state, thereby creating a zero-voltage turn-on condition for the high-frequency bridge arm switch.

[0055] E2: Turn off the auxiliary switch and use the resonance process to achieve a second resonance, so that the voltage across the auxiliary switch is also resonated to zero, thereby achieving zero-voltage turn-on of the auxiliary switch.

[0056] In this embodiment, after the voltage across the bridge arm containing the switch to be turned on in step E1 resonates from its initial value to zero, a turn-off command is sent to the auxiliary switch. The auxiliary resonant circuit then undergoes LC resonance again, bringing the voltage across the auxiliary switch to zero. When the voltage across the auxiliary switch drops to zero, the auxiliary switch is in a zero-voltage turn-off state, thus achieving zero-voltage turn-on for the auxiliary switch itself. Through these two LC resonance processes, not only are zero-voltage turn-on conditions created for the high-frequency bridge arm switch, but also zero-voltage turn-on for the auxiliary switch itself is achieved. This reduces the overall switching losses of the front-stage AC / DC unit, enables soft-switching control of the front-stage unit in the two-stage converter topology, and improves system operating efficiency.

[0057] In one alternative implementation, soft-switching control can also be achieved through modular cross-resonance. When the target module's high-frequency bridge arm switch is turned on, the auxiliary switch of this module is first triggered to initiate the first resonance, bringing the bridge arm voltage of this module to zero. At the same time, the cross-resonance branch couples the resonant energy of adjacent modules, enhancing the resonance effect and ensuring that the bridge arm voltage returns to zero stably, thus providing a guarantee for the zero-voltage turn-on of the target switch. After the turn-on is completed, the auxiliary switch of this module is turned off. At this time, the auxiliary resonant circuit of this module and the cross-resonance branch of the adjacent module work together to initiate the second resonance. The shared capacitor and the coupling inductor work together to resonate the voltage across the auxiliary switch to zero, achieving zero-voltage turn-on.

[0058] In another alternative implementation, soft-switching control can also be achieved through segmented resonance and voltage feedback. Before turning on the high-frequency bridge arm switch, the voltage across the bridge arm is collected in real time by a voltage sensor. The capacitance of the adjustable resonant capacitor is adjusted according to the voltage amplitude, and then the auxiliary switch is triggered to turn on, initiating the first segmented resonance: when the voltage is higher than the set threshold, a long-period resonance is used to gradually lower the voltage; when the voltage is close to the set threshold, it switches to a short-period resonance until it resonates to zero. The bridge arm voltage is temporarily carried by the auxiliary switch to ensure zero-voltage turn-on of the main switch. When the auxiliary switch is turned off, the second resonance is initiated based on the voltage feedback signal. The adjustable resonant capacitor automatically matches the voltage characteristics across the auxiliary switch and quickly returns the voltage to zero through LC resonance. After the voltage stabilizes at zero, the drive signal is reapplied to turn on the auxiliary switch, achieving zero-voltage turn-on.

[0059] Example 3, referring to Figure 1 This is a third embodiment of the present invention, which provides a multi-stage control system for a high power density modular B2G converter, comprising: Topology building module: Constructs a two-stage converter topology with a dual-loop controller structure including an outer voltage loop and an inner current loop; Soft-start module: Performs soft-start control to soft-start the two-stage converter topology; Control strategy selection module: Real-time acquisition of current signals of the two-stage converter topology and determination of energy transfer direction, selection of closed-loop control strategy based on the energy transfer direction and generation of current inner loop setpoint; Voltage and current equalization module: Based on the given value of the inner current loop and the operating status information of the two-stage converter topology, it generates the carrier phase angle and performs voltage and current equalization. Soft-switching control module: When the drive signal determined by the carrier phase angle needs to turn on the high-frequency bridge arm switch, it performs soft-switching control operation in the two-stage converter topology.

[0060] Example 4, the fourth embodiment of the present invention, differs from the previous three embodiments in that: if the function is implemented as a software functional unit and sold or used as an independent product, it can be stored in a computer-readable storage medium. Based on this understanding, the technical solution of the present invention, or the part that contributes to the prior art, or a part of the technical solution, can be embodied in the form of a software product. This computer software product is stored in a storage medium and includes several instructions to cause a computer device (which may be a personal computer, server, or network device, etc.) to execute all or part of the steps of the methods described in the various embodiments of the present invention. The aforementioned storage medium includes various media capable of storing program code, such as USB flash drives, portable hard drives, read-only memory (ROM), random access memory (RAM), magnetic disks, or optical disks.

[0061] The logic and / or steps represented in the flowchart or otherwise described herein, for example, can be considered as a sequenced list of executable instructions for implementing logical functions, and can be embodied in any computer-readable medium for use by, or in conjunction with, an instruction execution system, apparatus, or device (such as a computer-based system, a processor-including system, or other system that can fetch and execute instructions from, an instruction execution system, apparatus, or device). For the purposes of this specification, "computer-readable medium" can be any means that can contain, store, communicate, propagate, or transmit programs for use by, or in conjunction with, an instruction execution system, apparatus, or device.

[0062] More specific examples of computer-readable media (a non-exhaustive list) include: electrical connections (electronic devices) having one or more wires, portable computer disk drives (magnetic devices), random access memory (RAM), read-only memory (ROM), erasable and editable read-only memory (EPROM or flash memory), fiber optic devices, and portable optical disc read-only memory (CDROM). Furthermore, computer-readable media can even be paper or other suitable media on which the program can be printed, because the program can be obtained electronically, for example, by optically scanning the paper or other medium, followed by editing, interpreting, or otherwise processing as necessary, and then stored in computer memory.

[0063] It should be understood that various parts of the present invention can be implemented in hardware, software, firmware, or a combination thereof. In the above embodiments, multiple steps or methods can be implemented in software or firmware stored in memory and executed by a suitable instruction execution system. For example, if implemented in hardware, as in another embodiment, it can be implemented using any one or a combination of the following techniques known in the art: discrete logic circuits having logic gates for implementing logical functions on data signals, application-specific integrated circuits (ASICs) having suitable combinational logic gates, programmable gate arrays (PGAs), field-programmable gate arrays (FPGAs), etc.

[0064] It should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and not to limit it. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can be made to the technical solutions of the present invention without departing from the spirit and scope of the technical solutions of the present invention, and all such modifications or substitutions should be covered within the scope of the claims of the present invention.

Claims

1. A high power density modular B2G converter multilevel control method, characterized in that, include, Construct a two-stage converter topology with a dual-loop controller structure including an outer voltage loop and an inner current loop; Perform soft-start control to soft-start the two-stage converter topology; After the two-stage converter topology is soft-started, the current signal of the two-stage converter topology is collected in real time and the energy transfer direction is determined. Based on the energy transfer direction, a closed-loop control strategy is selected and a setpoint value for the inner current loop is generated. Based on the given value of the inner current loop and the operating status information of the two-stage converter topology, the carrier phase angle is generated and voltage and current equalization are performed. When the drive signal determined by the carrier phase angle needs to turn on the high-frequency bridge arm switch, a soft-switching control operation is performed in the two-stage converter topology.

2. The multi-stage control method for a high power density modular B2G converter as described in claim 1, characterized in that, The steps for constructing a two-stage converter topology with a dual-loop controller structure including an outer voltage loop and an inner current loop include: A front-end AC / DC unit is constructed as the front-end unit of a two-stage converter topology, and an auxiliary resonant circuit is integrated on the bridge arm of the front-end unit. The subsequent DC / DC unit is constructed as the subsequent unit of the two-stage converter topology, and the subsequent unit is designed as an isolated two-phase symmetrical CLLLC resonant converter topology. Connecting the DC output terminal of the front-end unit to the input terminal of the rear-end unit forms a two-stage converter topology. A dual-loop controller structure consisting of a preset voltage outer loop and a current inner loop.

3. The multi-stage control method for a high power density modular B2G converter as described in claim 2, characterized in that, The steps for performing soft-start control to soft-start the two-stage converter topology include: Construct an effective duty cycle variation curve that increases linearly with time; During the soft start process of the two-stage converter topology, phase shift control is performed. The phase shift control includes adjusting the phase shift angle of the pulses of the two bridge arms on the input side of the full-bridge converter in the two-stage converter according to the effective duty cycle change curve, thereby changing the equivalent output voltage of the full-bridge converter. When the effective duty cycle rises to the rated duty cycle, it is determined that the system has stably established the required voltage and current, and at this time the two-stage converter topology completes the soft start.

4. The multi-stage control method for a high power density modular B2G converter as described in claim 3, characterized in that, After a soft start is performed on the two-stage converter topology, the steps of acquiring the current signal of the two-stage converter topology in real time, determining the energy transfer direction, selecting a closed-loop control strategy based on the energy transfer direction, and generating the setpoint value for the inner current loop include: Acquire the current signal between the DC and AC sides of the two-stage converter topology; If the detected current signal flows from the AC side to the DC side, it is determined to be forward transmission. At this time, constant power control is used as the voltage outer loop to generate the current setpoint value of the current inner loop. If the detected current signal flows from the DC side to the AC side, it is determined to be reverse transmission. At this time, constant voltage control is used as the voltage outer loop to generate the current setpoint value of the current inner loop. With the given value of the inner current loop as the target, the switching frequency of the subsequent DC / DC unit is adjusted by the PI controller so that the actual output current approaches the given value.

5. The multi-stage control method for a high power density modular B2G converter as described in claim 4, characterized in that, Based on the given value of the inner current loop and the operating status information of the two-stage converter topology, the steps for generating the carrier phase angle and performing voltage and current equalization include: Collect the output voltage and output current of the subsequent DC / DC unit; The current setpoint is corrected based on the deviation between the output voltage and the average voltage of each subsequent DC / DC unit to obtain the corrected current. The carrier phase angle adjustment is generated based on the deviation between the output current and the correction current of each subsequent DC / DC unit. Adjusting the carrier phase angle of each subsequent DC / DC unit according to the carrier phase angle adjustment amount achieves voltage and current equalization.

6. The multi-stage control method for a high power density modular B2G converter as described in claim 5, characterized in that, When the drive signal determined by the carrier phase angle needs to turn on the high-frequency bridge arm switch, the steps for performing soft-switching control in a two-stage converter topology include: When the drive signal determined by the carrier phase angle needs to turn on the high-frequency bridge arm switch, it triggers the auxiliary switch and uses the resonant cavity to perform the first resonance, resonating the voltage across the bridge arm where the main switch is located to zero. The auxiliary switch is turned off, and a second resonance is achieved using the resonance process, so that the voltage across the auxiliary switch is also resonated to zero, thereby realizing zero-voltage turn-on of the auxiliary switch.

7. The multi-stage control method for a high power density modular B2G converter as described in claim 3, characterized in that, The formula for the effective duty cycle changing linearly with time is: ； in, For an effective duty cycle, This is the rated duty cycle of the converter. The preset converter startup time, This is the current startup time.

8. A multi-stage control system for a high power density modular B2G converter, employing the multi-stage control method for a high power density modular B2G converter as described in any one of claims 1 to 7, characterized in that, include: Topology building module: Constructs a two-stage converter topology with a dual-loop controller structure including an outer voltage loop and an inner current loop; Soft-start module: Performs soft-start control to soft-start the two-stage converter topology; Control strategy selection module: Real-time acquisition of current signals of the two-stage converter topology and determination of energy transfer direction, selection of closed-loop control strategy based on the energy transfer direction and generation of current inner loop setpoint; Voltage and current equalization module: Based on the given value of the inner current loop and the operating status information of the two-stage converter topology, it generates the carrier phase angle and performs voltage and current equalization. Soft-switching control module: When the drive signal determined by the carrier phase angle needs to turn on the high-frequency bridge arm switch, it performs soft-switching control operation in the two-stage converter topology.

9. A computer device comprising a memory and a processor, wherein the memory stores a computer program, characterized in that, When the processor executes the computer program, it implements the steps of the multi-stage control method for a high power density modular B2G converter as described in any one of claims 1 to 7.

10. A computer-readable storage medium having a computer program stored thereon, characterized in that, When the computer program is executed by the processor, it implements the steps of the multi-stage control method for a high power density modular B2G converter as described in any one of claims 1 to 7.

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