An efficiency optimization system and method based on modular multilevel solid state transformer

Abstract

The application discloses an efficiency optimization system and method based on a modular multi-level solid-state transformer, and belongs to the technical field of solid-state transformer efficiency optimization. The system comprises an MMSST system-level controller, which internally comprises a main control processor and a single energy efficiency optimization unit. The main loss analysis master module in the energy efficiency optimization unit centrally manages the switching loss and conduction loss model parameters of all sub-modules, and writes a unified parameter set to the exclusive storage area of each sub-module loss regulation module when the system starts or the load suddenly changes, ensuring that all sub-modules independently execute local efficiency optimization based on consistent loss calculation benchmarks. The main loss analysis master module can receive a single configuration instruction, decouple the optimization target vector containing the efficiency priority factor, the ripple suppression factor and the thermal balance factor into independent control coefficients of each sub-module. The application solves the problem of inconsistent loss calculation benchmarks in the distributed architecture, reduces the configuration complexity, and improves the overall operation efficiency of the MMSST.

Description

Technical Field

[0001] This invention belongs to the field of efficiency optimization technology for solid-state transformers, and specifically relates to an efficiency optimization system and method based on modular multilevel solid-state transformers. Background Technology

[0002] In distributed energy grid-connected systems, modular multilevel solid-state transformers (MMSSTs) are gradually replacing traditional power frequency transformers due to their multiple functions, including voltage level transformation, electrical isolation, bidirectional power flow, and power quality regulation. An MMSST consists of dozens to hundreds of cascaded power submodules. Each submodule includes power semiconductor switching devices (such as IGBTs or SiC MOSFETs), a drive circuit, a DC capacitor, and a bypass switch. In actual operation, the total loss of an MMSST mainly consists of the switching and conduction losses of each submodule, and load changes, environmental conditions (temperature, humidity, harmonic content), and cooling conditions all significantly affect the loss distribution and conversion efficiency.

[0003] In existing technologies, efficiency optimization of MMSST typically employs a distributed control architecture. Each power submodule is equipped with an independent local controller, which independently performs loss calculations and parameter tuning (such as adjusting switching frequency, dead time, or carrier phase shift angle) based on locally sampled voltage, current, and temperature. However, this distributed architecture has the following problems: First, the local controllers of each submodule use loss parameter models from different sources or with different versions, leading to inconsistent loss calculation benchmarks among different submodules within the same MMSST. This results in optimization decision bias, causing increased circulating current between submodules and a decrease in overall efficiency. Second, each submodule requires independent optimization controller hardware, increasing system cost and communication bus load. Furthermore, the lack of coordination between controllers prevents the achievement of global thermal balancing. Third, when load changes or environmental conditions change, operators need to configure parameters for each submodule individually, a cumbersome, time-consuming, and error-prone process. Fourth, existing systems lack the ability to monitor and predict the long-term accumulation of submodule losses, failing to anticipate and dynamically reconfigure submodules before their lifespan is nearing its end, leading to sudden failures and shutdowns. Fifth, on-site operating condition information (such as power grid harmonic content, ambient humidity, and coolant flow rate) is not included in the correction mechanism of the loss model, causing the benchmark loss model to become disconnected from the actual operating environment and limiting the optimization effect. Summary of the Invention

[0004] The purpose of this invention is to overcome the defects in the prior art and provide an efficiency optimization system and method based on a modular multilevel solid-state transformer.

[0005] This invention provides an efficiency optimization system based on a modular multilevel solid-state transformer (MMSST). The system is configured to dynamically regulate the efficiency of the MMSST in a distributed energy grid-connected system. The system includes an MMSST system-level controller, comprising a main control processor and a single energy efficiency optimization unit operably coupled to the main control processor. The energy efficiency optimization unit includes a main loss analysis control module operably coupled to at least one sub-module loss control module, and the main loss analysis control module is configured to configure the operating parameters of at least one sub-module loss control module. By replacing multiple distributed power module controllers with this single energy efficiency optimization unit, the main loss analysis control module centrally manages the switching and conduction losses of all sub-modules.

[0006] Furthermore, the main loss analysis control module stores the set of main loss model parameters used for personalized MMSST dynamic efficiency optimization strategies in at least one of the sub-module loss control modules; wherein, the set of main loss model parameters includes the switching frequency-loss curve coefficients, junction temperature-on resistance mapping table, and capacitor voltage ripple weighting factor of each sub-module; the main loss analysis control module is configured to actively write the set of main loss model parameters into the dedicated storage area of ​​each sub-module loss control module when MMSST starts or when there is a sudden load change, so that each sub-module independently performs local efficiency optimization based on a unified loss calculation benchmark.

[0007] Furthermore, at least one of the sub-module loss control modules includes multiple distributed sub-module loss control modules, the number of which is the same as and corresponds one-to-one with the number of power sub-modules in the MMSST; each distributed sub-module loss control module is embedded in the local driver module of the corresponding power sub-module and establishes a securely isolated bidirectional communication channel with the main loss analysis control module; the main loss analysis control module collects the real-time loss samples reported by each distributed sub-module loss control module through polling or interruption, and uses the aggregated global loss distribution map to adjust subsequent configuration commands.

[0008] Furthermore, the plurality of distributed submodule loss control modules include one or more of the following: a high-voltage side submodule switching loss optimization module, which is arranged to dynamically adjust the turn-off delay time of the insulated gate bipolar transistor to reduce turn-off loss; a medium-voltage side submodule conduction loss balancing module, which is arranged to redistribute the carrier phase based on the temperature coefficient of the on-resistance of the silicon carbide metal oxide semiconductor field-effect transistor; a low-voltage side submodule ripple loss suppression module, which is arranged to reduce heat loss on the equivalent series resistance of the capacitor by adjusting the duty cycle increment of the pulse width modulation wave; and a DC bus coupling submodule circulating current loss elimination module, which is arranged to inject a compensation voltage opposite in phase to the circulating current component to offset the reactive circulating current loss between submodules.

[0009] Furthermore, the main loss analysis control module is configured to receive a single configuration command to set an optimization strategy set for multiple sub-module loss control modules of the MMSST, wherein the multiple sub-module loss control modules provide at least one of the following: a real-time loss monitoring service running within the MMSST, a carrier phase shift angle optimization service running within the MMSST, a dead time adaptive adjustment service running within the MMSST, and a virtual impedance injection service running within the MMSST; wherein the single configuration command contains a unified optimization target vector, which includes an efficiency priority factor, a ripple suppression factor, and a thermal equalization factor, and the main loss analysis control module decouples the optimization target vector into independent control coefficients for each sub-module loss control module.

[0010] Furthermore, the main loss analysis control module is partially pre-assigned with general MMSST structure information, which includes the number of cascaded submodules, the topology type of each submodule, and a reference loss distribution table under rated power. The general MMSST information is supplemented by the field condition information provided in the single configuration instruction, which includes the current effective value of the load current, the percentage of DC bus voltage deviation, and the radiator inlet air temperature.

[0011] Furthermore, the individual energy efficiency optimization unit is arranged to provide a centralized loss sensing and dynamic reconfiguration system for multiple power regulation services and thermal management operating within the MMSST; wherein the centralized loss sensing and dynamic reconfiguration system includes: a global loss database for storing the loss trajectory of each submodule within a continuous time window; a fault predictor for predicting the remaining service life of the submodule based on the slope of the loss trajectory; and a dynamic reconfigurator for issuing an instruction to bypass the submodule and activate redundant submodules when the predicted loss accumulation of a submodule exceeds a threshold.

[0012] Furthermore, the main loss analysis control module is configured to establish a secure communication link with at least one of the sub-module loss control modules based on a lightweight encryption protocol before securely transmitting the optimization coefficient matrix from the main loss analysis control module to at least one of the sub-module loss control modules; wherein, the establishment of the secure communication link includes bidirectional certificate exchange and session key negotiation, and after the secure communication link is established, the main loss analysis control module uses a rolling code mechanism to send updated switching loss compensation coefficients sequentially.

[0013] This invention also provides an efficiency optimization method for modular multilevel solid-state transformers (MMSSTs) in distributed energy grid-connected systems, used for dynamic efficiency control of MMSSTs. The method includes: connecting a main control processor within the MMSST system-level controller to a single energy efficiency optimization unit within the MMSST system-level controller; connecting a main loss analysis control module within the single energy efficiency optimization unit to at least one sub-module loss control module within the single energy efficiency optimization unit; and configuring operating parameters of at least one sub-module loss control module by the main loss analysis control module, wherein the configuration includes writing updated switching loss compensation coefficients or carrier phase shift angles to the sub-module loss control module.

[0014] Furthermore, the main loss analysis control module stores a set of main loss model parameters for personalized MMSST dynamic efficiency optimization strategies, and the configuration step further includes: when the main loss analysis control module detects that the load power change rate of the MMSST exceeds a preset threshold, it automatically writes a set of sub-parameters from the main loss model parameter set that matches the current load range into at least one of the sub-module loss control modules; wherein, the main loss model parameter set is divided into a light load parameter area, a medium load parameter area, and a heavy load parameter area, and each parameter area contains an upper limit of the switching frequency and a lower limit of the modulation ratio optimized for that load range.

[0015] Furthermore, at least one of the submodule loss control modules includes multiple distributed submodule loss control modules, which include: a high-voltage side submodule switching loss optimization module, a medium-voltage side submodule conduction loss balancing module, a low-voltage side submodule ripple loss suppression module, and a DC bus coupling submodule circulating current loss elimination module; and the configuration step further includes: the main loss analysis control module, based on the real-time collected temperature distribution map of each submodule, first sends an instruction to reduce the switching frequency to the submodule loss control module corresponding to the submodule with the highest temperature, and simultaneously sends an instruction to increase the switching frequency to the submodule loss control module corresponding to the submodule with the lowest temperature.

[0016] Furthermore, the main loss analysis control module receives a single user-level configuration operation to set the optimization strategy set of multiple sub-module loss control modules of the MMSST, wherein the multiple sub-module loss control modules provide loss monitoring services and carrier angle optimization services running within the MMSST; and after receiving the single user-level configuration operation, the main loss analysis control module automatically generates an independent configuration file corresponding to each sub-module loss control module, and sends it to each sub-module loss control module respectively through the secure communication link.

[0017] Furthermore, the main loss analysis control module is partially pre-assigned with general MMSST structure information, which includes submodule topology type and reference loss model. The method further includes: in the main loss analysis control module, supplementing the general MMSST structure information with field operating condition information provided in the single user-level configuration operation to generate a complete personalized loss parameter matrix; wherein, the field operating condition information includes power grid harmonic content, ambient humidity, and cooling system coolant flow rate, and the main loss analysis control module corrects the additional loss factor in the reference loss model based on the field operating condition information.

[0018] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0019] The main loss analysis control module centrally stores and maintains the parameter sets for switching and conduction losses of all sub-modules, including a unified switching frequency-loss curve coefficient, junction temperature-on-resistance mapping table, and capacitor voltage ripple weighting factor. During MMSST startup or load surges, the main loss analysis control module actively writes this unified parameter set into the dedicated storage area of ​​each sub-module's loss control module. Since all sub-module loss control modules receive and store the exact same loss calculation benchmark, each sub-module, when independently performing local efficiency optimization, uses the same set of calibration data for the switching frequency-loss relationship, temperature dependence of on-resistance, and ripple loss weighting. This fundamentally solves the problem of inconsistent loss estimation caused by different manufacturing batches, software versions, or empirical formulas used by sub-module controllers in existing technologies. When all sub-modules make local decisions based on the same physical model, the coordination of switching actions between sub-modules is improved, circulating current components are suppressed, and the overall MMSST conversion efficiency remains stable and predictable across different load ranges.

[0020] The main loss analysis control module is configured to receive a single configuration command containing a unified optimization objective vector (including an efficiency priority factor, a ripple suppression factor, and a thermal equalization factor). The main loss analysis control module automatically decouples this vector into independent control coefficients for each sub-module's loss control module and generates an independent configuration file for each sub-module. These configuration files are then sent to each sub-module's loss control module via a secure communication link.

[0021] The main loss analysis control module periodically collects the real-time temperature of each submodule's heat sink or power semiconductor substrate, generating a temperature distribution map. It then identifies the submodules with the highest and lowest temperatures and sends differentiated instructions to their respective loss control modules: a command to reduce the switching frequency to the high-temperature submodule and a command to increase the switching frequency to the low-temperature submodule. Since switching frequency is positively correlated with switching losses, reducing the switching frequency of the high-temperature submodule reduces its heat generation, while increasing the switching frequency of the low-temperature submodule causes it to bear more losses and thus heat up. After several iterative adjustments of the thermal time constant, the temperature deviation between the submodules gradually decreases to within a preset threshold. This mechanism fully utilizes the degree of freedom of the switching frequency as a controllable variable, making the heat distribution inside the MMSST tend to be uniform without increasing additional hardware costs. Attached Figure Description

[0022] The following figures are for illustrative purposes only and are not intended to limit the scope of the invention, wherein:

[0023] Figure 1 : A flowchart of the system in this invention;

[0024] Figure 2 : A flowchart illustrating the main loss analysis control module in this invention;

[0025] Figure 3 : A flowchart illustrating the method in this invention. Detailed Implementation

[0026] To make the objectives, technical solutions, design methods, and advantages of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings and specific embodiments. It should be understood that the specific embodiments described herein are for illustrative purposes only and are not intended to limit the invention.

[0027] like Figure 1As shown, this invention provides an efficiency optimization system based on a modular multilevel solid-state transformer (MMSST). The efficiency optimization system is configured to dynamically regulate the efficiency of a MMSST in a distributed energy grid-connected system. The efficiency optimization system includes an MMSST system-level controller, which includes a main control processor and a single energy efficiency optimization unit operably coupled to the main control processor. The energy efficiency optimization unit includes a main loss analysis control module operably coupled to at least one sub-module loss control module, and the main loss analysis control module is configured to configure the operating parameters of at least one of the sub-module loss control modules. By replacing multiple distributed power module controllers with the single energy efficiency optimization unit, the main loss analysis control module centrally manages the switching and conduction losses of all sub-modules.

[0028] In the above embodiments, the Modular Multilevel Solid State Transformer (MMSST) includes multiple voltage levels: a high-voltage side, a medium-voltage side, and a low-voltage side, each consisting of multiple cascaded power submodules. The efficiency optimization system includes an MMSST system-level controller, which is physically independent of the local drive circuits of each power submodule but connected to all power submodules via a communication bus. The system-level controller contains a main control processor, which can be any of an ARM-based microcontroller, a digital signal processor (DSP), or a field-programmable gate array (FPGA). The main control processor runs a real-time operating system and is responsible for communicating with the upper-level energy management system and issuing overall control targets. A single energy efficiency optimization unit is integrated within the system-level controller, and its operable coupling with the main control processor is achieved through an internal parallel data bus or a high-speed serial peripheral interface, enabling the main control processor to transmit global parameters such as load current sampling values ​​and DC bus voltage setpoints to the energy efficiency optimization unit in real time. The energy efficiency optimization unit can physically be an independent microcontroller or a security chip, internally storing specially designed firmware. The energy efficiency optimization unit includes a main loss analysis control module, which exists as a software module or firmware library and has access to the non-volatile memory and random access memory within the energy efficiency optimization unit. The main loss analysis control module is operatively coupled to at least one sub-module loss control module, where each sub-module loss control module corresponds to a power sub-module in the MMSST. This operative coupling refers to a bidirectional data link established through a communication network (e.g., Controller Area Network (CAN), Controller Area Network Flexible Data Rate (CAN-FD), or Ethernet) between the system-level controller and each power sub-module. The main loss analysis control module is configured to configure the operating parameters of at least one of the sub-module loss control modules.

[0029] The configuration operations include, but are not limited to: writing the upper limit of the switching frequency, the dead time compensation amount, the initial value of the carrier phase shift angle, and the duty cycle fine-tuning coefficient of the modulation wave to the submodule loss control module. The single energy efficiency optimization unit replaces the distributed architecture of configuring an independent optimization controller for each power submodule in the traditional scheme. Previously, each power submodule's local controller needed to independently perform loss calculations and parameter tuning; now, the main loss analysis control module uniformly performs loss modeling and parameter generation for all submodules. The main loss analysis control module centrally manages the switching and conduction loss modules of all submodules, specifically including: maintaining a global submodule loss database, indexed by submodule number, storing the switching device model, junction temperature history, current switching frequency, and current RMS value of the conduction current for each submodule; based on the stored information, the main loss analysis control module calculates the estimated switching and conduction losses for each submodule in real time.

[0030] Furthermore, the main loss analysis control module stores the set of main loss model parameters used for personalized MMSST dynamic efficiency optimization strategies in at least one of the sub-module loss control modules; wherein, the set of main loss model parameters includes the switching frequency-loss curve coefficients, junction temperature-on resistance mapping table, and capacitor voltage ripple weighting factor of each sub-module; the main loss analysis control module is configured to actively write the set of main loss model parameters into the dedicated storage area of ​​each sub-module loss control module when MMSST starts or when there is a sudden load change, so that each sub-module independently performs local efficiency optimization based on a unified loss calculation benchmark.

[0031] In the above embodiments, the main loss analysis control module internally maintains a set of main loss model parameters. This set of parameters serves as a unified loss calculation benchmark for all power submodules in the current MMSST. This set of main loss model parameters is not statically stored within the main loss analysis control module; instead, it is designed as a data packet that can be distributed. The main loss analysis control module stores the set of main loss model parameters in at least one submodule loss control module. Specifically, the storage location is a dedicated storage area within each submodule loss control module. This dedicated storage area can be a write-protected region within an electrically erasable programmable read-only memory or flash memory.

[0032] The main loss model parameter set specifically includes three subsets: the first is the switching frequency-loss curve coefficient of each submodule, which adopts a quadratic polynomial form (a×f). 2The equation (+b×f+c) describes the quantitative relationship between the switching frequency f and the switching power loss, where the coefficients a, b, and c are obtained by fitting the double-pulse test results at the time of device delivery; the second term is the junction temperature-on-resistance mapping table, which records the on-resistance value corresponding to each temperature point in the range of -40°C to 175°C with degrees Celsius as the temperature interval, and is used to correct the on-loss calculation results based on the real-time junction temperature; the third term is the capacitor voltage ripple weighting factor, which is a dimensionless coefficient between 0 and 1, used to characterize the contribution ratio of capacitor ripple current in the total loss. The main loss analysis control module is configured to actively perform parameter writing operations under two specific trigger conditions: the first trigger condition is the MMSST startup process, i.e., after the system powers on but before the main power circuit is turned on, the main loss analysis control module sequentially writes the aforementioned parameter set to the dedicated storage area of ​​each sub-module loss control module via the communication bus; the second trigger condition is a load mutation event, i.e., when the main control processor detects that the effective value of the load current changes by more than 20% of the rated value within 10 milliseconds, it sends an interrupt signal to the main loss analysis control module, which then rereads the updated parameter set (e.g., selects the corresponding curve coefficient according to the new load range) and rewrites it to each sub-module loss control module. Through the above writing operations, each sub-module loss control module obtains the same loss calculation benchmark as other sub-modules, i.e., a unified switching frequency-loss curve coefficient, a unified junction temperature-on resistance mapping table, and a unified capacitor voltage ripple weighting factor. Based on this, each submodule loss control module can independently calculate the local loss estimate based on its own real-time sampled switching frequency, junction temperature, and capacitor voltage ripple value, and execute local efficiency optimization decisions (such as fine-tuning the switching frequency or modulation ratio), thereby achieving a balance between distributed local optimization and global benchmark consistency.

[0033] Furthermore, at least one of the sub-module loss control modules includes multiple distributed sub-module loss control modules, the number of which is the same as and corresponds one-to-one with the number of power sub-modules in the MMSST; each distributed sub-module loss control module is embedded in the local driver module of the corresponding power sub-module and establishes a securely isolated bidirectional communication channel with the main loss analysis control module; the main loss analysis control module collects the real-time loss samples reported by each distributed sub-module loss control module through polling or interruption, and uses the aggregated global loss distribution map to adjust subsequent configuration commands.

[0034] In the above embodiments, at least one of the sub-module loss control modules specifically refers to multiple distributed sub-module loss control modules existing in the entire system. The number of these modules is exactly the same as the number of power sub-modules in the MMSST, and a one-to-one mapping relationship is established between them. For example, if the MMSST contains N power sub-modules (N is usually a multiple of 6, such as 36, 72, or 108), then there are N distributed sub-module loss control modules, each belonging exclusively to a single power sub-module. Each distributed sub-module loss control module is not independent of the power sub-module's hardware but is embedded in the corresponding power sub-module's local driver module. The local driver module includes: a sub-module controller, a gate drive circuit, a voltage and current sampling circuit, and a communication interface circuit. The distributed sub-module loss control modules are burned into the program memory of the sub-module controller in the form of software code, sharing the same processor core with the gate drive logic, but functional isolation is achieved through memory partitioning and task priority allocation. A securely isolated bidirectional communication channel is established between each distributed sub-module loss control module and the main loss analysis control module. The security isolation is achieved through the following methods: the physical layer uses differential twisted-pair cabling or optical fiber, the link layer uses encryption protocols, and the network layer uses Virtual Local Area Network (VLAN) partitioning to separate loss control communication traffic from ordinary control signaling traffic. The bidirectional communication channel supports sending configuration commands (downlink) from the main loss analysis control module to the sub-module loss control module, and also supports reporting data (uplink) from the sub-module loss control module to the main loss analysis control module. The main loss analysis control module collects real-time loss samples reported by each distributed sub-module loss control module through polling or interruption. Polling means that the main loss analysis control module sends request frames to each sub-module loss control module at fixed time intervals, and the sub-module loss control module replies with a data frame containing local loss samples upon receiving the request. Interruption means that when a sub-module loss control module detects a change in loss value exceeding a preset dead zone (e.g., a change rate greater than 5%), it actively sends an asynchronous interrupt message to the main loss analysis control module, which responds to the interrupt and reads the loss samples. The main loss analysis control module aggregates the real-time loss samples collected from all submodules to form a global loss distribution map. This distribution map is an N-dimensional vector, where each component corresponds to the estimated total loss power of a submodule at the current moment. The main loss analysis control module stores the global loss distribution map in its local RAM and uses it to adjust the configuration commands subsequently sent to the loss control modules of each submodule. For example, when the loss value of a certain submodule is significantly higher than that of its neighboring submodules in the distribution map, the main loss analysis control module sends a command to the loss control module of that submodule to reduce the switching frequency.

[0035] Furthermore, the plurality of distributed submodule loss control modules include one or more of the following: a high-voltage side submodule switching loss optimization module, which is arranged to dynamically adjust the turn-off delay time of the insulated gate bipolar transistor to reduce turn-off loss; a medium-voltage side submodule conduction loss balancing module, which is arranged to redistribute the carrier phase based on the temperature coefficient of the on-resistance of the silicon carbide metal oxide semiconductor field-effect transistor; a low-voltage side submodule ripple loss suppression module, which is arranged to reduce heat loss on the equivalent series resistance of the capacitor by adjusting the duty cycle increment of the pulse width modulation wave; and a DC bus coupling submodule circulating current loss elimination module, which is arranged to inject a compensation voltage opposite in phase to the circulating current component to offset the reactive circulating current loss between submodules.

[0036] In the above embodiments, a traditional MMSST typically includes a high-voltage DC side, a medium-voltage AC side, a low-voltage DC side, and a DC bus coupling section. The power submodules at different locations use different types of power semiconductor devices, operate at different frequencies, and have different loss mechanisms. Therefore, the multiple distributed submodule loss control modules are divided into four dedicated module types. The first type is the high-voltage side submodule switching loss optimization module. This type of module is arranged in the power submodules corresponding to the high-voltage DC bus side of the MMSST. These submodules typically use insulated-gate bipolar transistors (IGBTs) as switching devices, and their losses are mainly switching losses. The high-voltage side submodule switching loss optimization module is configured to dynamically adjust the IGBT turn-off delay time, which refers to the time interval from issuing the turn-off command to the collector current dropping to 10%. This module monitors the collector voltage change rate dv / dt, calculates the optimal turn-off gate resistance value in real time, and changes the turn-off delay time through a programmable gate drive circuit. Each adjustment step is 10 nanoseconds, and the adjustment range is from 200 nanoseconds to 800 nanoseconds.

[0037] The second type is the medium-voltage side submodule conduction loss balancing module. This type of module is arranged on the medium-voltage AC side of the MMSST, which typically uses silicon carbide metal-oxide-semiconductor field-effect transistors (SiCMOSFETs). Its on-resistance has a positive temperature coefficient (i.e., the on-resistance increases with temperature). The medium-voltage side submodule conduction loss balancing module is arranged to redistribute the carrier phase based on this positive temperature coefficient. Specifically, this module collects the heatsink temperature of each medium-voltage side submodule, shifts the carrier phase of the submodule with the highest temperature forward by an angle (e.g., π / N), causing the switching action of this submodule to be staggered from the peak current moment, thereby reducing its effective conduction current value; simultaneously, it shifts the carrier phase of the submodule with the lowest temperature backward by the same angle, allowing it to handle more conduction current.

[0038] The third type is the low-voltage side submodule ripple loss suppression module. This type of module is located on the low-voltage DC side. An electrolytic capacitor is connected in parallel at the output of this submodule, and the equivalent series resistance (ESR) of the capacitor will generate ripple loss. The low-voltage side submodule ripple loss suppression module is arranged to reduce the heat loss on the capacitor ESR by adjusting the duty cycle increment of the pulse width modulation wave. Specifically, a small signal fine-tuning amount Δd, which is out of phase with the output voltage ripple, is superimposed on the original duty cycle D. The value of Δd ranges from -0.02 to +0.02.

[0039] The fourth type is the DC bus coupling submodule circulating current loss elimination module. This type of module is arranged in the coupling submodule connecting the DC bus and the AC bus to suppress the circulating current component caused by the asynchronous switching of the submodules. The DC bus coupling submodule circulating current loss elimination module is arranged to inject a compensation voltage with the opposite phase to the circulating current component. This module first extracts the fundamental component of the circulating current (the frequency is usually an integer multiple of the switching frequency) through a fast Fourier transform, and then generates a compensation voltage with the same amplitude but 180 degrees out of phase through the inverter. This compensation voltage is superimposed on the output of the submodule, thereby electrically canceling the reactive circulating current and eliminating the additional copper and iron losses caused by it.

[0040] Furthermore, the main loss analysis control module is configured to receive a single configuration command to set an optimization strategy set for multiple sub-module loss control modules of the MMSST, wherein the multiple sub-module loss control modules provide at least one of the following: a real-time loss monitoring service running within the MMSST, a carrier phase shift angle optimization service running within the MMSST, a dead time adaptive adjustment service running within the MMSST, and a virtual impedance injection service running within the MMSST; wherein the single configuration command contains a unified optimization target vector, which includes an efficiency priority factor, a ripple suppression factor, and a thermal equalization factor, and the main loss analysis control module decouples the optimization target vector into independent control coefficients for each sub-module loss control module.

[0041] In the above embodiments, the main loss analysis control module is configured to receive a single configuration command, which can originate from the upper-level energy management system, the vehicle-mounted human-machine interface, or a cloud server. The single configuration command refers to a data frame containing a command header and a command body. The command header identifies the command as a global optimization strategy setting command, and the command body contains a unified optimization target vector. Unlike existing technologies that require sending configuration commands separately to each submodule, this system can simultaneously set the optimization strategy set of all submodule loss control modules in the MMSST using a single command. The optimization strategy set refers to a combination of services provided by multiple submodule loss control modules. These services include: real-time loss monitoring service (i.e., the submodule loss control module periodically reports loss samples to the main loss analysis control module), carrier phase shift angle optimization service (i.e., the submodule loss control module adjusts the local carrier phase according to the global command), dead time adaptive adjustment service (i.e., the submodule loss control module automatically fine-tunes the dead time of the upper and lower bridge arm drive signals according to the real-time load current direction), and virtual impedance injection service (i.e., the submodule loss control module simulates a virtual resistor in the voltage control loop to suppress oscillation). The unified optimization objective vector contained in a single configuration instruction is a three-dimensional vector [α, β, γ], where α is the efficiency priority factor, ranging from 0 to 1; β is the ripple suppression factor, ranging from 0 to 1; and γ is the thermal equilibrium factor, ranging from 0 to 1. The three factors satisfy α + β + γ = 1. The main loss analysis control module is arranged to decouple the optimization objective vector into independent control coefficients for each sub-module loss control module. The decoupling process includes: first, determining the sensitivity coefficient vector [k1, k2, k3] of each submodule to three factors based on its voltage level (high voltage side, medium voltage side, low voltage side, or coupling side); then, calculating the independent control coefficient vector [α', β', γ'] of the submodule, where α' = α*k1 / (k1+k2+k3), β' = β*k2 / (k1+k2+k3), and γ' = γ*k3 / (k1+k2+k3); finally, packaging the independent control coefficient vector of each submodule into downlink data frames and sending them to the corresponding submodule loss control module via the communication bus. Upon receiving the independent control coefficients, each submodule loss control module uses them as weights in its local optimization algorithm to adjust the priority of its local control behavior.

[0042] Furthermore, the main loss analysis control module is partially pre-assigned with general MMSST structure information, which includes the number of cascaded submodules, the topology type of each submodule, and a reference loss distribution table under rated power. The general MMSST information is supplemented by the field condition information provided in the single configuration instruction, which includes the current effective value of the load current, the percentage of DC bus voltage deviation, and the radiator inlet air temperature.

[0043] In the above embodiments, the non-volatile memory inside the main loss analysis control module pre-stores general MMSST structure information. This information is written by the manufacturer at the time of system shipment or initial installation and is independent of the specific installation site conditions. The general MMSST structure information specifically includes three items: the first item is the number of cascaded submodules, that is, the number of power submodules connected in series on each phase arm of the MMSST, for example, 8 submodules per phase arm on the high-voltage side, 6 submodules per phase arm on the medium-voltage side, and 4 submodules per phase arm on the low-voltage side; the second item is the topology type of each submodule, which can be any of half-bridge, full-bridge, or clamped dual-level submodules. The topology type of each submodule is stored in an encoded form (for example, 00 represents half-bridge, 01 represents full-bridge, and 10 represents clamped dual-level); the third item is a reference loss distribution table under rated power. This table is the reference loss value of each submodule obtained through simulation or actual measurement under rated load conditions (e.g., rated voltage, rated current, and rated switching frequency), in watts per submodule. The general MMSST structural information is static and does not change with operating conditions. However, actual field conditions change dynamically. Therefore, the main loss analysis control module is configured to supplement the general information with the field condition information provided in the single configuration command. In addition to the optimization target vector, the single configuration command also includes a field condition information field, which specifically includes: the current effective value of the load current (in amperes, measured in real time by the current transformer installed on the output side of the MMSST and forwarded to the energy efficiency optimization unit by the main control processor), the DC bus voltage deviation percentage (i.e., the difference between the current DC bus voltage and the rated voltage divided by the rated voltage, expressed as a percentage, such as +5% or -3%), and the radiator inlet air temperature (in degrees Celsius, measured by the temperature sensor installed at the inlet of the MMSST cooling duct). After receiving the field operating condition information, the main loss analysis control module performs supplementary operations: First, it calculates the corrected loss baseline under the current load from the baseline loss distribution table using linear interpolation based on the effective value of the load current; then, it adjusts the constant term in the switching loss curve coefficient according to the DC bus voltage deviation percentage, as the voltage deviation affects overvoltage energy during the switching process; finally, it corrects the temperature offset in the junction temperature-on-resistance mapping table based on the radiator inlet air temperature. Through these supplements, the general MMSST structure information is converted into a personalized set of loss parameters adapted to the current field operating conditions.

[0044] Furthermore, the individual energy efficiency optimization unit is arranged to provide a centralized loss sensing and dynamic reconfiguration system for multiple power regulation services and thermal management operating within the MMSST; wherein the centralized loss sensing and dynamic reconfiguration system includes: a global loss database for storing the loss trajectory of each submodule within a continuous time window; a fault predictor for predicting the remaining service life of the submodule based on the slope of the loss trajectory; and a dynamic reconfigurator for issuing an instruction to bypass the submodule and activate redundant submodules when the predicted loss accumulation of a submodule exceeds a threshold.

[0045] In the above embodiments, the individual energy efficiency optimization unit is not limited to performing real-time efficiency regulation, but is also arranged to provide a centralized loss sensing and dynamic reconfiguration system for multiple power regulation services and thermal management operating within the MMSST. This system includes three core components: a global loss database, a fault predictor, and a dynamic reconfigurator. The global loss database is a circular buffer that stores the loss trajectory of each submodule within a continuous time window. The length of the continuous time window is configurable, defaulting to the past 10 minutes. For each submodule, the global loss database records a data point at a fixed sampling interval (e.g., every 100 milliseconds), which includes a timestamp and an estimate of the total loss power of that submodule at the current moment. The loss trajectories of all submodules are stored in regions according to submodule number, enabling retrieval of the loss change sequence of any submodule over the past 10 minutes. The fault predictor is an algorithm module running in the main loss analysis control module, arranged to predict the remaining lifetime of the submodule based on the slope of the loss trajectory. Specifically, the fault predictor performs linear regression on the loss trajectory sequence of each submodule to calculate the rate of change of loss power relative to time (i.e., the slope, in watts per second). Based on a pre-calibrated loss-life curve (i.e., the relationship between accumulated energy loss and device failure time), the fault predictor extrapolates the current slope to the time required for accumulated loss to reach the end-of-life threshold; this time is the predicted remaining lifespan. The fault predictor generates a predicted remaining lifespan for each submodule, in hours. The dynamic reconfigurator is a decision module configured to issue a command to bypass the submodule and activate redundant submodules when the predicted accumulated loss of a submodule exceeds a threshold. The threshold can be set to a remaining lifespan of less than 100 hours, or current power loss exceeding 150% of rated loss. When the dynamic reconfigurator determines that a submodule meets the bypass condition, it first sends a bypass command to the submodule's local drive module via the main control processor. This command closes the bypass switch (usually a mechanical contactor or thyristor) in the submodule, disconnecting it from the main power circuit. Simultaneously, the dynamic reconfigurator sends activation commands to pre-configured redundant submodules in the MMSST (usually one to two more than the theoretically required number), putting the redundant submodules into operation to replace the function of the bypassed submodule. After performing bypass and activation operations, the dynamic reconfigurator updates the global submodule mapping table and broadcasts the new topology to all submodule loss control modules, ensuring that subsequent efficiency optimization calculations are based on the correct submodule number.

[0046] Furthermore, the main loss analysis control module is configured to establish a secure communication link with at least one of the sub-module loss control modules based on a lightweight encryption protocol before securely transmitting the optimization coefficient matrix from the main loss analysis control module to at least one of the sub-module loss control modules; wherein, the establishment of the secure communication link includes bidirectional certificate exchange and session key negotiation, and after the secure communication link is established, the main loss analysis control module uses a rolling code mechanism to send updated switching loss compensation coefficients sequentially.

[0047] In the above embodiments, since the loss optimization coefficient matrix is ​​a core parameter affecting the operating efficiency of MMSST, and the communication bus may be exposed to external interfaces, a secure communication link needs to be established. The main loss analysis control module is configured to establish a secure communication link with the loss control module based on a lightweight encryption protocol before securely transmitting the optimization coefficient matrix from itself to at least one sub-module loss control module. The lightweight encryption protocol refers to an encryption protocol with low computational resource consumption suitable for embedded microcontrollers. The establishment of the secure communication link includes two steps: bidirectional certificate exchange and session key negotiation. Bidirectional certificate exchange refers to the main loss analysis control module and the sub-module loss control module each sending a digital certificate issued by the system-level root certificate to the other. Each certificate contains a unique identifier for the module (such as a MAC address or serial number) and a public key. The receiver uses the public key of the root certificate to verify the signature of the other party's certificate; after successful verification, the other party's identity is confirmed. Session key negotiation refers to the two parties using the Diffie-Hellman key exchange algorithm to generate a temporary session key after successful bidirectional authentication. This key is only used in the current communication session and expires after the session ends. During session key negotiation, both parties generate random numbers, encrypt them using the public key in their certificates, and exchange them to calculate a shared symmetric key. After the secure communication link is established, the main loss analysis control module uses a rolling code mechanism to send updated switching loss compensation coefficients sequentially. The rolling code mechanism means that each transmitted data frame contains an incrementing sequence number, and the entire data frame is encrypted using the session key. The receiver (the loss control module in the submodule) maintains a receiving window, accepting only data frames with a sequence number strictly greater than the previously received sequence number, discarding duplicate, out-of-order, or excessively large sequence number jumps. Simultaneously, each data frame also includes a Message Authentication Code (MAC), calculated by the sender using the session key and sequence number. The receiver recalculates the MAC using the same algorithm and compares it; only data frames with matching MACs are accepted as valid. This rolling code mechanism prevents replay attacks and tampering attacks. The switching loss compensation coefficients sent sequentially by the main loss analysis control module through this secure link are K-dimensional vectors, where K is the number of adjustable parameters in the submodule, and the coefficient value sent each time is calculated based on the latest global loss distribution map.

[0048] This invention also provides an efficiency optimization method for modular multilevel solid-state transformers (MMSSTs) in distributed energy grid-connected systems, used for dynamic efficiency control of MMSSTs. The method includes: connecting a main control processor within the MMSST system-level controller to a single energy efficiency optimization unit within the MMSST system-level controller; connecting a main loss analysis control module within the single energy efficiency optimization unit to at least one sub-module loss control module within the single energy efficiency optimization unit; and configuring operating parameters of at least one sub-module loss control module by the main loss analysis control module, wherein the configuration includes writing updated switching loss compensation coefficients or carrier phase shift angles to the sub-module loss control module.

[0049] In the above embodiments, the method includes three main steps. Step 1: Connecting the main control processor within the MMSST system-level controller to a single energy efficiency optimization unit within the MMSST system-level controller. This connection operation is implemented during the system hardware design phase through printed circuit boards, specifically including: connecting the pins of the main control processor's general-purpose input / output ports or dedicated communication interfaces (e.g., SPI or I2C interfaces) to the corresponding input pins of the single energy efficiency optimization unit via traces. At the software level, this connection operation also includes initializing the communication protocol stack and configuring the data exchange format between the main control processor and the energy efficiency optimization unit, such as defining shared memory address mapping or configuring DMA channels. After the connection is completed, the main control processor can write global operating parameters to the input registers of the energy efficiency optimization unit in real time. Step 2: Connecting the main loss analysis control module within the single energy efficiency optimization unit to at least one sub-module loss control module within the single energy efficiency optimization unit. This connection operation is completed at the software architecture level of the energy efficiency optimization unit, specifically including: assigning a task ID to the main loss analysis control module in the operating system of the energy efficiency optimization unit, and assigning a corresponding communication port number or handle to each sub-module loss control module. The main loss analysis control module establishes a logical connection with the sub-module loss control module by calling the inter-process communication API provided by the operating system. At the hardware level, the energy efficiency optimization unit is connected to the external communication bus through its communication controller, and the sub-module loss control module acts as a node on this bus, with each node having a unique address. The main loss analysis control module maintains an address mapping table, mapping the logical name of each sub-module loss control module to a physical address on the bus. The third step involves the main loss analysis control module configuring the operating parameters of at least one of the sub-module loss control modules. The specific configuration operation includes writing updated switching loss compensation coefficients or carrier phase shift angles to the sub-module loss control module. The switching loss compensation coefficient is a dimensionless multiplier factor, ranging from 0.5 to 2.0, used to correct the switching loss reference value in the local loss calculation model. The carrier phase shift angle is an angle value in degrees, ranging from 0° to 360°, used to adjust the phase difference of the sub-module's carrier signal relative to the system reference carrier. Before sending configuration data, the main loss analysis control module first calculates the coefficients or angle values ​​required for each submodule from the global loss distribution map. Then, according to the secure communication link (if established) or ordinary communication link as described in claim 8, it encapsulates the configuration data into frames and sends them sequentially to the loss control modules of each submodule. After receiving the configuration data, the submodule loss control module stores it in its local configuration register and applies it to the pulse width modulation waveform generation logic at the beginning of the next switching cycle.

[0050] Furthermore, the main loss analysis control module stores a set of main loss model parameters for personalized MMSST dynamic efficiency optimization strategies, and the configuration step further includes: when the main loss analysis control module detects that the load power change rate of the MMSST exceeds a preset threshold, it automatically writes a set of sub-parameters from the main loss model parameter set that matches the current load range into at least one of the sub-module loss control modules; wherein, the main loss model parameter set is divided into a light load parameter area, a medium load parameter area, and a heavy load parameter area, and each parameter area contains an upper limit of the switching frequency and a lower limit of the modulation ratio optimized for that load range.

[0051] In the above embodiment, the main loss analysis control module continuously monitors the load power of the MMSST and calculates the load power change rate. The load power is obtained by multiplying the sampled values ​​from the voltage transformer and current transformer by the main control processor. The change rate is the difference between the power value at the current sampling moment and the power value at the previous sampling moment, divided by the sampling interval. When the load power change rate is detected to exceed a preset threshold, the main loss analysis control module automatically performs a parameter switching operation. The preset threshold can be set to 10% of the rated power per millisecond, that is, if the load power increases or decreases by more than 10% of the rated power within 1 millisecond, a switching is triggered. After triggering, the main loss analysis control module determines the current load range based on the absolute value of the current load power, extracts a set of sub-parameters matching the load range from the main loss model parameter set, and then writes the set of sub-parameters into at least one sub-module loss control module (usually all sub-module loss control modules). The main loss model parameter set is pre-divided into three parameter areas: light load parameter area, medium load parameter area, and heavy load parameter area. The light load parameter zone corresponds to load power less than 20% of the rated power. This zone includes upper limits for the switching frequency and lower limits for the modulation ratio optimized for light loads. Under light loads, switching losses dominate; therefore, the upper limit for the switching frequency in this zone is set to a lower value (e.g., 50% of the rated frequency) to reduce switching losses, while the lower limit for the modulation ratio is set to a higher value (e.g., 0.8) to maintain high voltage utilization. The medium load parameter zone corresponds to load power between 20% and 70% of the rated power. In this zone, the upper limit for the switching frequency is set to 80% of the rated frequency, and the lower limit for the modulation ratio is set to 0.6 to balance switching and conduction losses. The heavy load parameter zone corresponds to load power greater than 70% of the rated power. In this zone, the upper limit for the switching frequency is set to 100% of the rated frequency, and the lower limit for the modulation ratio is set to 0.4. At this point, conduction losses dominate, requiring a lower modulation ratio to reduce the effective current value, while allowing a higher switching frequency to improve output waveform quality. When writing parameters, the main loss analysis control module packages the upper limit of the switching frequency and the lower limit of the modulation ratio of the selected parameter area into a configuration frame and sends it to each sub-module loss control module. After receiving the frame, the sub-module loss control module clamps the locally running switching frequency to within the upper limit and limits the modulation amplitude to within the lower limit.

[0052] Furthermore, at least one of the submodule loss control modules includes multiple distributed submodule loss control modules, which include: a high-voltage side submodule switching loss optimization module, a medium-voltage side submodule conduction loss balancing module, a low-voltage side submodule ripple loss suppression module, and a DC bus coupling submodule circulating current loss elimination module; and the configuration step further includes: the main loss analysis control module, based on the real-time collected temperature distribution map of each submodule, first sends an instruction to reduce the switching frequency to the submodule loss control module corresponding to the submodule with the highest temperature, and simultaneously sends an instruction to increase the switching frequency to the submodule loss control module corresponding to the submodule with the lowest temperature.

[0053] In the above embodiment, the main loss analysis control module periodically collects the real-time temperature of each submodule through the uplink communication link of each submodule's loss control module. The temperature data comes from negative temperature coefficient thermistors or thermocouples embedded in the heat sink or power semiconductor device substrate of each power submodule. The main loss analysis control module summarizes all collected temperature values ​​to form a temperature distribution map, which is a histogram with the submodule number as the horizontal axis and temperature as the vertical axis. The main loss analysis control module identifies the submodule with the highest temperature and the submodule with the lowest temperature from the temperature distribution map. The submodule with the highest temperature may face the risk of overheating, while the submodule with the lowest temperature may not be fully utilized. To address this, the main loss analysis control module executes differentiated instruction sending: it prioritizes sending an instruction to reduce the switching frequency to the loss control module corresponding to the submodule with the highest temperature, while simultaneously sending an instruction to increase the switching frequency to the loss control module corresponding to the submodule with the lowest temperature. The instruction to reduce the switching frequency carries a negative step value, such as reducing the current switching frequency by 5%; the instruction to increase the switching frequency carries a positive step value, such as increasing the current switching frequency by 5%. The adjustment range of the switching frequency is limited to the upper limit of the switching frequency as described in claim 10. By reducing the switching frequency of the high-temperature submodule, its switching losses can be reduced, thereby lowering its junction temperature; by increasing the switching frequency of the low-temperature submodule, it can bear more switching losses, thereby increasing its junction temperature. This differentiated adjustment makes the temperature between the submodules tend to be more balanced. After each instruction is sent, the main loss analysis control module waits for a thermal time constant (e.g., 5 seconds) and then re-acquires the temperature distribution map to determine whether the temperature difference has decreased. If the temperature difference has not decreased, further adjustment instructions are sent until the temperature deviation of all submodules is less than a preset temperature difference threshold (e.g., 5°C). This method utilizes the positive correlation between switching frequency and loss to achieve passive thermal balance, avoiding the need for overall derating due to local overheating.

[0054] Furthermore, the main loss analysis control module receives a single user-level configuration operation to set the optimization strategy set of multiple sub-module loss control modules of the MMSST, wherein the multiple sub-module loss control modules provide loss monitoring services and carrier angle optimization services running within the MMSST; and after receiving the single user-level configuration operation, the main loss analysis control module automatically generates an independent configuration file corresponding to each sub-module loss control module, and sends it to each sub-module loss control module respectively through the secure communication link.

[0055] In the above embodiments, the set of optimization strategies specifically includes two services in this claim: a loss monitoring service and a carrier angle optimization service running within the MMSST. The loss monitoring service defines the period for loss reporting, the granularity of the reported data, and the alarm threshold. The carrier angle optimization service defines the distribution pattern of carrier phase shift and the frequency of angle updates. After receiving the single user-level configuration operation, the main loss analysis control module automatically executes the generation and transmission steps. First, it generates an independent configuration file corresponding to each sub-module loss control module. The main loss analysis control module generates N configuration files cyclically based on the total number N of sub-modules. The sub-module number field in each configuration file is filled with the corresponding number (from 1 to N). For the initial value of the carrier angle, the main loss analysis control module automatically calculates it according to the distribution pattern selected by the user: if the user selects an arithmetic distribution, the initial angle of the i-th sub-module is (i-1)×360° / N; if the user selects a random distribution, a random number between 0° and 360° is generated for each sub-module. After generating all independent configuration files, the main loss analysis control module sends them to each sub-module loss control module via a secure communication link. During transmission, the main loss analysis control module encrypts the corresponding configuration file using the independent session key of each sub-module loss control module and sends it via unicast through the communication bus. Upon receiving the encrypted configuration file, each sub-module loss control module decrypts it using its own session key, verifies that the sub-module number in the file header matches its own number, loads the configuration parameters into its local runtime structure, and returns an acknowledgment frame to the main loss analysis control module. After receiving acknowledgment frames from all sub-modules, the main loss analysis control module returns a configuration success message to the user interface. If a sub-module times out without acknowledgment, the main loss analysis control module retransmits the configuration three times and then reports a configuration failure.

[0056] Furthermore, the main loss analysis control module is partially pre-assigned with general MMSST structure information, which includes submodule topology type and reference loss model. The method further includes: in the main loss analysis control module, supplementing the general MMSST structure information with field operating condition information provided in the single user-level configuration operation to generate a complete personalized loss parameter matrix; wherein, the field operating condition information includes power grid harmonic content, ambient humidity, and cooling system coolant flow rate, and the main loss analysis control module corrects the additional loss factor in the reference loss model based on the field operating condition information.

[0057] In the above embodiments, the main loss analysis control module is partially pre-assigned with general MMSST structural information, including submodule topology type and a reference loss model. The reference loss model is a pre-calibrated mathematical relationship used to calculate the total power loss of a single power submodule under standard test conditions. This reference loss model expresses the total loss as a linear combination of three main contributing terms: the first term is proportional to the square of the switching frequency, characterizing switching losses; the second term is proportional to the square of the effective value of the phase current, characterizing conduction losses; and the third term is proportional to the square of the DC bus voltage, characterizing voltage-related losses (such as capacitor ripple losses). Each term is multiplied by a reference coefficient, which is obtained by fitting experimental data under factory test conditions. The standard test conditions are defined as an ambient temperature of 25 degrees Celsius, a mains voltage without harmonic distortion, standard air cooling with rated cooling airflow.

[0058] In the main loss analysis control module, the general MMSST structural information is supplemented with the field operating condition information provided in a single user-level configuration operation to generate a complete personalized loss parameter matrix. The field operating condition information is input once by the operator through the user interface during the system installation and commissioning phase or the operation and maintenance phase, and includes three specific parameters: the first is the grid harmonic content, expressed as a percentage of total harmonic distortion, which is obtained by a power quality analyzer measured on-site, ranging from 0% to 30%; the second is the ambient humidity, expressed as a percentage of relative humidity, measured in real-time by a humidity sensor installed in the MMSST cabinet or input by the operator based on on-site climate conditions, ranging from 0% to 100%; the third is the coolant flow rate of the cooling system, measured in liters per minute by a flow meter, ranging from 0 liters per minute to 20 liters per minute.

[0059] The main loss analysis control module corrects the additional loss factor in the baseline loss model based on the above three on-site operating condition information. The correction process includes three sequentially executed sub-steps. The first sub-step: Calculate the harmonic additional loss factor based on the grid harmonic content. When the grid harmonic content is zero percent, the factor is set to one; for every 1 percent increase in grid harmonic content, the factor increases by 1 percent relative to one. This harmonic additional loss factor is applied to the term in the baseline loss model that is proportional to the square of the phase current, because harmonic components increase the effective value of the current and cause additional eddy current losses and hysteresis losses in the transformer core. The second sub-step: Calculate the humidity additional loss factor based on the ambient humidity. When the ambient humidity is not higher than 50 percent, the factor is set to one, indicating that humidity has no significant impact on losses; when the ambient humidity exceeds 50 percent, for every 1 percent increase, the factor increases by 0.5 percent relative to one. The humidity-related loss factor is applied to the constants related to insulation leakage in the baseline loss model because high humidity reduces the resistivity of the power module insulation surface, causing a small leakage current to flow through the insulation medium, thus generating additional Joule heat loss. The third sub-step involves calculating the cooling efficiency compensation factor based on the coolant flow rate. This factor is calculated with the rated flow rate as a reference. When the coolant flow rate equals the rated flow rate, the factor is one; when the coolant flow rate is lower than the rated flow rate, the factor is greater than one, indicating insufficient cooling leading to increased junction temperature, thus increasing on-resistance and switching losses; when the coolant flow rate is higher than the rated flow rate, the factor is less than one, indicating enhanced cooling can reduce junction temperature, thereby reducing temperature-related additional losses. This cooling efficiency compensation factor is applied to the sum of the entire baseline loss model, i.e., scaling all loss terms proportionally.

[0060] The main loss analysis control module combines the three correction factors mentioned above according to the multiplication rule to obtain a comprehensive correction coefficient. Specifically, the combination method is as follows: the harmonic additional loss factor, humidity additional loss factor, and cooling efficiency compensation factor are multiplied together to obtain the final comprehensive correction coefficient. Then, the main loss analysis control module multiplies each term in the benchmark loss model (i.e., the squared term of switching frequency, the squared term of phase current, and the squared term of DC bus voltage) by this comprehensive correction coefficient to generate a personalized loss parameter matrix. This matrix is ​​a two-dimensional data structure, with the submodule number as the row index and the loss type (switching loss, conduction loss, voltage-related loss) as the column index. Each element in the matrix stores the corrected loss coefficient of the corresponding submodule under the current field conditions. This personalized loss parameter matrix is ​​stored in the main loss analysis control module's internal random access memory.

[0061] The various embodiments of the present invention have been described above. These descriptions are exemplary and not exhaustive, nor are they limited to the disclosed embodiments. Many modifications and variations will be apparent to those skilled in the art without departing from the scope and spirit of the described embodiments. The terminology used herein is chosen to best explain the principles, practical application, or technical improvements to the embodiments in the market, or to enable others skilled in the art to understand the embodiments disclosed herein.

Claims

1. An efficiency optimization system based on a modular multilevel solid-state transformer, characterized in that, The efficiency optimization system is configured to dynamically regulate the efficiency of a modular multilevel solid-state transformer (MMSST) in a distributed energy grid-connected system. The efficiency optimization system includes an MMSST system-level controller, which includes a main control processor and a single energy efficiency optimization unit operably coupled to the main control processor. The energy efficiency optimization unit includes a main loss analysis control module operably coupled to at least one sub-module loss control module, and the main loss analysis control module is configured to configure the operating parameters of at least one of the sub-module loss control modules. By replacing multiple distributed power module controllers with the single energy efficiency optimization unit, the main loss analysis control module centrally manages the switching and conduction losses of all sub-modules.

2. The efficiency optimization system based on a modular multilevel solid-state transformer according to claim 1, characterized in that, The main loss analysis control module stores the set of main loss model parameters used for personalized MMSST dynamic efficiency optimization strategies in at least one of the sub-module loss control modules. The set of main loss model parameters includes the switching frequency-loss curve coefficients, junction temperature-on-resistance mapping table, and capacitor voltage ripple weighting factors for each sub-module. The main loss analysis control module is configured to actively write the set of main loss model parameters into the dedicated storage area of ​​each sub-module loss control module when MMSST starts or during load abrupt changes, enabling each sub-module to independently perform local efficiency optimization based on a unified loss calculation benchmark.

3. The efficiency optimization system based on a modular multilevel solid-state transformer according to claim 1 or 2, characterized in that, At least one of the sub-module loss control modules includes multiple distributed sub-module loss control modules. The number of these distributed sub-module loss control modules is the same as the number of power sub-modules in the MMSST and corresponds one-to-one. Each distributed sub-module loss control module is embedded in the local driver module of the corresponding power sub-module and establishes a securely isolated bidirectional communication channel with the main loss analysis control module. The main loss analysis control module collects real-time loss samples reported by each distributed sub-module loss control module through polling or interruption, and uses the aggregated global loss distribution map to adjust subsequent configuration commands.

4. The efficiency optimization system based on a modular multilevel solid-state transformer according to claim 3, characterized in that, The distributed submodule loss control modules include one or more of the following: a high-voltage side submodule switching loss optimization module, which is arranged to dynamically adjust the turn-off delay time of the insulated gate bipolar transistor to reduce turn-off loss; a medium-voltage side submodule conduction loss balancing module, which is arranged to redistribute the carrier phase based on the temperature coefficient of the on-resistance of the silicon carbide metal oxide semiconductor field-effect transistor; a low-voltage side submodule ripple loss suppression module, which is arranged to reduce heat loss on the equivalent series resistance of the capacitor by adjusting the duty cycle increment of the pulse width modulation wave; and a DC bus coupling submodule circulating current loss elimination module, which is arranged to inject a compensation voltage with the opposite phase to the circulating current component to offset the reactive circulating current loss between submodules.

5. The efficiency optimization system based on a modular multilevel solid-state transformer according to claim 1, characterized in that, The main loss analysis control module is configured to receive a single configuration command to set an optimization strategy set for multiple sub-module loss control modules of the MMSST, wherein the multiple sub-module loss control modules provide at least one of the following: a real-time loss monitoring service running within the MMSST, a carrier phase shift angle optimization service running within the MMSST, a dead time adaptive adjustment service running within the MMSST, and a virtual impedance injection service running within the MMSST; wherein the single configuration command contains a unified optimization target vector, which includes an efficiency priority factor, a ripple suppression factor, and a thermal equalization factor, and the main loss analysis control module decouples the optimization target vector into independent control coefficients for each sub-module loss control module.

6. The efficiency optimization system based on a modular multilevel solid-state transformer according to claim 5, characterized in that, The main loss analysis control module is partially pre-assigned with general MMSST structure information, which includes the number of cascaded submodules, the topology type of each submodule, and a reference loss distribution table under rated power. The general MMSST information is supplemented by field condition information provided in the single configuration instruction, which includes the current effective value of the load current, the percentage of DC bus voltage deviation, and the radiator inlet air temperature.

7. The efficiency optimization system based on a modular multilevel solid-state transformer according to claim 1, characterized in that, The individual energy efficiency optimization unit is arranged to provide a centralized loss sensing and dynamic reconfiguration system for multiple power regulation services and thermal management operating within the MMSST; wherein the centralized loss sensing and dynamic reconfiguration system includes: a global loss database for storing the loss trajectory of each submodule within a continuous time window; a fault predictor for predicting the remaining service life of the submodule based on the slope of the loss trajectory; and a dynamic reconfigurator for issuing an instruction to bypass the submodule and activate redundant submodules when the predicted loss accumulation of a submodule exceeds a threshold.

8. The efficiency optimization system based on a modular multilevel solid-state transformer according to claim 1 or 6, characterized in that, The main loss analysis control module is configured to establish a secure communication link with at least one of the sub-module loss control modules based on a lightweight encryption protocol before securely transmitting the optimization coefficient matrix from the main loss analysis control module to at least one of the sub-module loss control modules; wherein, the establishment of the secure communication link includes bidirectional certificate exchange and session key negotiation, and after the secure communication link is established, the main loss analysis control module uses a rolling code mechanism to send updated switching loss compensation coefficients sequentially.

9. An efficiency optimization method for modular multilevel solid-state transformers, characterized in that, A method for dynamic efficiency control of a modular multilevel solid-state transformer (MMSST) in a distributed energy grid-connected system includes: connecting a main control processor within the MMSST system-level controller to a single energy efficiency optimization unit within the MMSST system-level controller; connecting a main loss analysis control module within the single energy efficiency optimization unit to at least one sub-module loss control module within the single energy efficiency optimization unit; and configuring operating parameters of at least one of the sub-module loss control modules by the main loss analysis control module, wherein the configuration includes writing updated switching loss compensation coefficients or carrier phase shift angles to the sub-module loss control module.

10. The method according to claim 9, characterized in that, The main loss analysis control module stores a set of main loss model parameters for personalized MMSST dynamic efficiency optimization strategies. The configuration step further includes: when the main loss analysis control module detects that the load power change rate of the MMSST exceeds a preset threshold, it automatically writes a set of sub-parameters from the main loss model parameter set that matches the current load range into at least one of the sub-module loss control modules; wherein, the main loss model parameter set is divided into a light load parameter area, a medium load parameter area, and a heavy load parameter area, and each parameter area contains an upper limit for the switching frequency and a lower limit for the modulation ratio optimized for that load range. At least one of the submodule loss control modules includes multiple distributed submodule loss control modules, which include: a high-voltage side submodule switching loss optimization module, a medium-voltage side submodule conduction loss balancing module, a low-voltage side submodule ripple loss suppression module, and a DC bus coupling submodule circulating current loss elimination module; and the configuration step further includes: the main loss analysis main control module, based on the real-time collected temperature distribution map of each submodule, first sends an instruction to reduce the switching frequency to the submodule loss control module corresponding to the submodule with the highest temperature, and at the same time sends an instruction to increase the switching frequency to the submodule loss control module corresponding to the submodule with the lowest temperature; The main loss analysis control module receives a single user-level configuration operation to set the optimization strategy set of multiple sub-module loss control modules of the MMSST, wherein the multiple sub-module loss control modules provide loss monitoring services and carrier angle optimization services running within the MMSST; and after receiving the single user-level configuration operation, the main loss analysis control module automatically generates an independent configuration file corresponding to each sub-module loss control module, and sends it to each sub-module loss control module respectively through the secure communication link; The main loss analysis control module is partially pre-assigned with general MMSST structure information, which includes submodule topology type and baseline loss model. The method further includes: in the main loss analysis control module, supplementing the general MMSST structure information with field condition information provided in the single user-level configuration operation to generate a complete personalized loss parameter matrix; wherein the field condition information includes power grid harmonic content, ambient humidity, and coolant flow rate of the cooling system, and the main loss analysis control module corrects the additional loss factor in the baseline loss model based on the field condition information.

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