A multi-port cascaded h-bridge energy storage system energy balance control method and related products

Abstract

This application discloses an energy balance control method and related products for a multi-port cascaded H-bridge energy storage system, relating to the field of power electronics technology. The control method provided in this application integrates the fundamental frequency and third harmonic circulating currents, eliminating the filter stage required in traditional frequency division control. This fundamentally avoids amplitude attenuation and phase lag during signal extraction, ensuring that the circulating current signal received by the controller accurately reflects the actual system state. Simultaneously, since the fundamental frequency and third harmonic circulating currents are no longer separated into independent control loops but are treated as a unified total circulating current for overall regulation, the improved repetitive controller can directly and periodically compensate for the total circulating current deviation during system operation. Its internal periodic delay stage works in conjunction with the compensator to quickly eliminate steady-state errors and accurately track the periodic circulating current signal, thereby improving control accuracy.

Description

Technical Field

[0001] This application relates to the field of power electronics technology, and in particular to an energy balance control method and related products for a multi-port cascaded H-bridge energy storage system. Background Technology

[0002] With the popularization of new power systems, the large-scale integration of distributed photovoltaic (PV) power and electric vehicle (EV) charging piles is changing the operation of traditional distribution networks. However, the inherent randomness and volatility of distributed PV power output can easily lead to problems such as grid voltage exceeding limits and power flow reversal under high penetration conditions. Simultaneously, the high concentration of charging pile loads in time and space often results in local feeders and distribution transformers operating under heavy or even overload conditions for extended periods, significantly exacerbating the operational pressure on the distribution network. Traditional radial distribution networks, limited by their inherent flexible regulation capabilities, struggle to effectively support the large-scale integration of such new sources of load with strong uncertainties. To address these challenges, large-capacity battery energy storage power conversion systems based on cascaded H-bridge topologies are considered a key approach to solving the renewable energy consumption problem due to their modular design, scalability, and high efficiency. A compact, transformerless multiport delta cascaded H-bridge energy storage system (MD-CHB-ESS) has been proposed in the existing technology. This topology allows multiple distribution feeders to be connected to the same energy storage unit simultaneously, which not only enables power sharing and energy storage resource sharing between AC power grids in different regions, effectively improving the utilization rate of energy storage equipment, but also significantly reduces the overall construction cost and land requirements of the system.

[0003] In the actual operation of MD-CHB-ESS, in order to ensure the internal power balance of the system and the safe and efficient operation of the battery pack, two different frequencies of circulating current need to be injected into the device at the same time: the base frequency circulating current, which is mainly used to realize the phase-to-phase state of charge (SoC) equalization control of the battery pack; and the third harmonic frequency circulating current, which is mainly used to realize the energy balance control of the DC bus.

[0004] To address the control requirements of this complex circulating current, current technologies generally employ a frequency-division control strategy. Specifically, this involves first extracting the fundamental frequency component and the third harmonic component from the total circulating current using filters, and then feeding these two extracted components into two independent control loops for individual tracking and adjustment. However, in practical applications, the introduction of filters in this frequency-division control method introduces amplitude attenuation and phase lag, causing the extracted signals to fail to accurately reflect the actual circulating current state. This results in a persistent static error in the closed-loop control. Furthermore, after the fundamental and third harmonics are forcibly divided, although the two inner loops are formally independent, the final output modulation waves must be superimposed on the same controlled object. This generates mutual constraints and coupling effects during adjustment, ultimately leading to a significant reduction in the reliability of the energy balance control in the MD-CHB-ESS system, making it difficult to meet high-precision operation requirements. Summary of the Invention

[0005] This application provides an energy balance control method and related products for a multi-port cascaded H-bridge energy storage system, which aims to improve the accuracy of circulating current control and enhance the stability and reliability of the system.

[0006] To achieve the above-mentioned objectives, the first aspect of this application provides an energy balance control method for a multi-port cascaded H-bridge energy storage system, comprising: Collect the total circulating current value of a multi-port cascaded H-bridge energy storage system; Obtain the system parameters of the multi-port cascaded H-bridge energy storage system, and then calculate the total circulating current reference value of the multi-port cascaded H-bridge energy storage system based on the system parameters; The total circulating current value and the total circulating current reference value are substituted into the control function of the preset improved repetitive controller, so that the improved repetitive controller performs closed-loop tracking of the circulating current based on the deviation between the total circulating current value and the total circulating current reference value.

[0007] Preferably, the control function of the improved repetitive controller is as follows:

[0008] In the formula, This is the output reference value for CHB. For compensators used to compensate for amplitude and phase, The compensation coefficient is used to compensate for the amplitude. This represents the actual total circulation value. This is the reference value for the total circulation. The third-harmonic voltage output by the PBCM device. This represents the periodic delay stage, where n is the number of sampling points per period.

[0009] Preferably, the control function of the improved repetitive controller is as follows:

[0010] In the formula, This is the output reference value for CHB. For compensators used to compensate for amplitude and phase, The compensation coefficient is used to compensate for the amplitude. This represents the actual total circulation value. This is the reference value for the total circulation. The third-harmonic voltage output by the PBCM device. This represents the periodic delay stage, where n is the number of sampling points per period. The proportional gain of the PI element in the improved repetitive controller. Let be the integral coefficient of the PI element in the improved repetitive controller, and s be the Laplace operator.

[0011] Preferably, calculating the total circulating current reference value of the multi-port cascaded H-bridge energy storage system based on the system parameters includes: Based on the system parameters, calculate the base frequency circulating current reference value and the third harmonic circulating current reference value of the multi-port cascaded H-bridge energy storage system; The total circulating current reference value is obtained by summing the fundamental frequency circulating current reference value and the third harmonic circulating current reference value.

[0012] Preferably, the system parameters include: three-phase DC bus capacitor voltage value, DC bus voltage reference value, grid AB phase line voltage phase, and SoC data of the three-phase battery pack.

[0013] Preferably, calculating the base frequency circulating current reference value and the third harmonic circulating current reference value of the multi-port cascaded H-bridge energy storage system based on the system parameters includes: The three-phase DC bus capacitor voltage value, DC bus voltage reference value, and grid AB phase line voltage phase are substituted into the voltage outer loop control formula constructed based on PI control logic, so that the voltage outer loop control formula calculates the third harmonic circulating current reference value based on the deviation between the DC bus voltage reference value and the average value of the three-phase DC bus capacitor voltage value. Calculate the three-phase SoC imbalance of the three-phase battery pack based on the SoC data of the three-phase battery pack; Performing a Clark transform on the three-phase SoC imbalance, we obtain the three-phase SoC imbalance at... shaft and The imbalance component on the axis is then used to calculate the interphase SoC imbalance and the phase angle of the three-phase SoC based on the imbalance component. Based on the phase imbalance of the interphase SoC and the phase angle of the three-phase SoC, the effective value of the baseband circulating current and the phase angle of the baseband circulating current are calculated. Then, based on the effective value of the baseband circulating current and the phase angle of the baseband circulating current, the preset baseband circulating current expression is substituted to calculate the reference value of the baseband circulating current.

[0014] A second aspect of this application provides an energy balance control device for a multi-port cascaded H-bridge energy storage system, comprising: The circulating current data acquisition unit is used to collect the total circulating current value of the multi-port cascaded H-bridge energy storage system; The total circulating current reference value calculation unit is used to obtain the system parameters of the multi-port cascaded H-bridge energy storage system, and then calculate the total circulating current reference value of the multi-port cascaded H-bridge energy storage system based on the system parameters. A circulation tracking control unit is used to substitute the total circulation value and the total circulation reference value into a preset control function of an improved repetitive controller, so that the improved repetitive controller performs closed-loop tracking of the circulation based on the deviation between the total circulation value and the total circulation reference value.

[0015] A third aspect of this application provides an energy balance control terminal for a multi-port cascaded H-bridge energy storage system, comprising: a memory and a processor; The memory is used to store program code, which corresponds to an energy balance control method for a multi-port cascaded H-bridge energy storage system as provided in the first aspect of this application. The processor is used to read and execute the program code to implement the energy balance control method of the multi-port cascaded H-bridge energy storage system.

[0016] The fourth aspect of this application provides a computer-readable storage medium storing program code, the program code being related to the energy balance control method for a multi-port cascaded H-bridge energy storage system provided in the first aspect of this application.

[0017] The fifth aspect of this application provides a computer program product consisting of program code, which corresponds to the energy balance control method for a multi-port cascaded H-bridge energy storage system provided in the first aspect of this application. The program code is used to be read and executed by a processor to implement the energy balance control method for the multi-port cascaded H-bridge energy storage system.

[0018] As can be seen from the above technical solutions, this application has the following advantages: The control method provided in this application integrates the fundamental frequency and third harmonic circulating currents, eliminating the filter stage required in traditional frequency division control. This fundamentally avoids amplitude attenuation and phase lag during signal extraction, ensuring that the circulating current signal received by the controller accurately reflects the actual system state. Furthermore, since the fundamental frequency and third harmonic circulating currents are no longer separated into independent control loops but are treated as a unified total circulating current for overall regulation, the dynamic interaction effects generated when control loops of different frequencies act superimposed on the same controlled object are effectively avoided. For example, during system operation, the improved repetitive controller can directly and periodically compensate for the total circulating current deviation. Its internal periodic delay element works in conjunction with the compensator to quickly eliminate steady-state errors and accurately track the periodic circulating current signal, thereby significantly improving control accuracy. Attached Figure Description

[0019] To more clearly illustrate the technical solutions in the embodiments of this application or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of this application. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0020] Figure 1 A flowchart illustrating an embodiment of an energy balance control method for a multi-port cascaded H-bridge energy storage system provided in this application; Figure 2 A schematic diagram of the topology of a transformerless cascaded H-bridge energy storage system; Figure 3 This is a schematic diagram for calculating the total circulation. Figure 4 The control block diagram for an ideal repetitive controller; Figure 5 Control block diagram of a repetitive controller that incorporates amplitude and phase compensation; Figure 6 This is a control block diagram of the improved repetitive controller described in this application; Figure 7 The waveforms are the actual and reference values ​​of the circulating current. Figure 8 This is the waveform of the DC bus capacitor voltage; Figure 9 Waveforms of CHB-ESS absorbed power in each phase under the control strategy provided in this application; Figure 10 This is a schematic diagram of the architecture of an embodiment of an energy balance control device for a multi-port cascaded H-bridge energy storage system provided in this application. Detailed Implementation

[0021] In the operation of a multi-port energy storage system based on a cascaded H-bridge topology, the existing composite circulating current control strategy uses a frequency division method to extract the fundamental frequency and third harmonic components for independent adjustment. However, the amplitude and phase frequency characteristics of the filter inevitably introduce amplitude attenuation and phase lag, causing the extracted signal to fail to accurately reflect the actual circulating current state, resulting in a continuous static error in the closed-loop control process. Furthermore, since the fundamental frequency and third harmonic components still need to be superimposed on the same controlled object after being separated, a dynamic coupling effect occurs between the control loops, causing the adjustment process to be mutually constrained. This reduces the reliability of energy balance control and affects the system voltage stability and power balance accuracy.

[0022] For example, in urban distribution networks with high penetration of distributed photovoltaic (PV) power, when rapid cloud movement causes drastic fluctuations in PV output, and multiple electric vehicle charging stations simultaneously activate fast charging, the system needs to adjust the circulating current in real time to maintain stable feeder voltage. In this scenario, the frequency division control strategy suffers from filter response delays, resulting in the base frequency circulating current extraction value deviating from actual requirements, and the third harmonic circulating current control response lagging. This leads to an increased range of DC bus voltage fluctuations and exacerbates the imbalance in phase-to-phase charge states, thereby increasing the risk of grid voltage exceeding limits and potential overload of distribution transformers. If these problems are not effectively addressed, the system will struggle to maintain internal power balance under dynamic operating conditions, and battery packs may operate in an unbalanced state for extended periods, accelerating equipment aging. Simultaneously, the continuous deterioration of grid voltage stability may trigger abnormal operation of protection devices, interrupting power supply services. This weakens the distribution network's ability to accommodate renewable energy and affects the safe and stable operation of the new power system.

[0023] In view of this, embodiments of this application provide an energy balance control method and related products for a multi-port cascaded H-bridge energy storage system, which aims to improve the accuracy of circulating current control and enhance the stability and reliability of the system.

[0024] To make the inventive objectives, features, and advantages of this application more apparent and understandable, the technical solutions in the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the embodiments described below are only some embodiments of this application, and not all embodiments. Based on the embodiments in this application, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application.

[0025] First, this application provides a detailed description of an embodiment of an energy balance control method for a multi-port cascaded H-bridge energy storage system.

[0026] Please see Figure 1 This application provides an embodiment of an energy balance control method for a multi-port cascaded H-bridge energy storage system, the steps of which include: Step 101: Collect the total circulating current value of the multi-port cascaded H-bridge energy storage system; Step 102: Obtain the system parameters of the multi-port cascaded H-bridge energy storage system, and then calculate the total circulating current reference value of the multi-port cascaded H-bridge energy storage system based on the system parameters. Step 103: Substitute the total circulating current value and the total circulating current reference value into the preset control function of the improved repetitive controller, so that the improved repetitive controller performs closed-loop tracking of the circulating current based on the deviation between the total circulating current value and the total circulating current reference value.

[0027] For ease of understanding, the following explains some key terms in this embodiment: The Multi-Port Cascaded H-Bridge Energy Storage System (MD-CHB-ESS) is an advanced power conversion system that employs a modular cascaded H-bridge topology, allowing multiple distribution feeders to simultaneously connect to the same energy storage unit. This system aims to achieve power sharing and energy storage resource sharing between AC power grids in different regions, thereby improving the utilization rate of energy storage devices and reducing system construction costs.

[0028] The baseband circulating current value refers to the circulating current component with the same frequency as the grid baseband injected during the operation of a multi-port cascaded H-bridge energy storage system to achieve balanced control of the state of charge (SoC) between battery phases. This circulating current component adjusts the charging and discharging state of each battery pack by flowing between phases, thereby maintaining the consistency of the SoC of each phase battery.

[0029] The third-harmonic circulating current refers to the circulating current component with a frequency three times the grid fundamental frequency injected during the operation of a multi-port cascaded H-bridge energy storage system to achieve DC bus energy balance control. This circulating current component is mainly used to compensate for DC bus voltage fluctuations and ensure stable energy transmission within the system.

[0030] The total circulating current value refers to the combined value of the fundamental frequency circulating current and the third harmonic circulating current in a multi-port cascaded H-bridge energy storage system. In some control strategies, this total circulating current value can be treated as a whole to simplify the control structure and improve control performance.

[0031] The total circulating current reference value is the target total circulating current value that the system expects to achieve. This reference value is usually calculated based on factors such as the system's operating status, battery SoC balancing requirements, and DC bus energy balance requirements, and serves as the setpoint for the controller to perform closed-loop tracking.

[0032] An improved repetitive controller is a special type of controller designed for the precise tracking and suppression of periodic disturbances or reference signals. By introducing a periodic delay element and an appropriate compensation mechanism, this controller can effectively eliminate steady-state errors and achieve high-precision tracking of periodic signals.

[0033] A control function is an improved mathematical expression or algorithmic logic within a repetitive controller. It defines how the controller generates an output control quantity based on an input signal (such as the deviation between the actual value and a reference value). This function determines the controller's dynamic response and steady-state performance.

[0034] Closed-loop tracking refers to the process by which the controller continuously adjusts its output based on the deviation between the actual measured value and the reference value, so that the actual value is as close to the reference value as possible. Through the closed-loop feedback mechanism, the system can automatically correct the deviation and maintain stable operation.

[0035] More specifically, this embodiment provides an energy balance control method for a multi-port cascaded H-bridge energy storage system. The method first requires acquiring the total circulating current value of the multi-port cascaded H-bridge energy storage system. This acquisition process can be achieved by installing current sensors on critical current paths within the system. These sensors monitor the current flowing through the system in real time and convert analog signals into digital signals for subsequent control algorithm processing. For example, current transformers can be configured on the AC or DC side of each H-bridge module to obtain the current information of each module, and then synthesize the total circulating current value of the system.

[0036] Secondly, it is necessary to obtain the system parameters of the multi-port cascaded H-bridge energy storage system and calculate the total circulating current reference value based on these parameters. Obtaining the system parameters can be accomplished by deploying various sensors, such as voltage and temperature sensors, to monitor the system's operating status in real time. After obtaining these system parameters, a pre-defined mathematical model or algorithm can be used to calculate the expected total circulating current reference value. This mathematical model can determine a reasonable target circulating current value based on factors such as the system's current operating mode, load conditions, and the overall health of the battery pack, through simple linear or nonlinear mapping relationships.

[0037] Therefore, this method involves substituting the acquired total circulating current value and the calculated total circulating current reference value into the control function of a pre-defined improved repetitive controller. This allows the improved repetitive controller to perform closed-loop tracking of the circulating current based on the deviation between the total circulating current value and the total circulating current reference value. The total circulating current reference value can be obtained based on a pre-defined target for system operation. For example, a constant total circulating current reference value can be pre-set according to system design requirements or operating strategies. Alternatively, this reference value can be determined by looking up tables or simple logical judgment based on operating parameters such as the current state of charge and DC bus voltage level. The improved repetitive controller receives the deviation signal between the actual total circulating current value and the total circulating current reference value and generates a corresponding control output based on its internal control function. This control function can be a proportional-integral (PI) controller structure combined with a periodic compensation element to achieve effective tracking of the periodic circulating current. For example, the controller can include a feedforward path and a feedback path, where the feedback path is used to eliminate steady-state errors, while the feedforward path is used for rapid response to dynamic changes. In this way, the controller can continuously adjust the operating state of the system so that the actual total circulating current value can accurately track the total circulating current reference value, thereby achieving closed-loop tracking of the circulating current.

[0038] The following example will provide a more detailed explanation of the above technical solution: In a multi-port cascaded H-bridge energy storage system (MD-CHB-ESS), due to imbalances in the state of charge (SoC) of the battery packs and fluctuations in the DC bus voltage, fundamental and third-harmonic circulating currents that need to be suppressed are generated within the system. This method is applied to this MD-CHB-ESS to achieve balanced energy control of the system.

[0039] First, the system acquires the current signals flowing through each phase in real time using its internal current sensors and signal processing module. These current signals are fed into a digital signal processor, where a specific algorithm (e.g., based on Fast Fourier Transform or synchronous rotating coordinate system transformation) accurately separates and extracts the current fundamental frequency circulating current value and the third harmonic circulating current value. For example, at a certain moment, the system detects a fundamental frequency circulating current value of I_f1 and a third harmonic circulating current value of I_f3.

[0040] Subsequently, based on the acquired fundamental frequency circulating current value I_f1 and third harmonic circulating current value I_f3, the system calculates the total circulating current value. This calculation process can be simply achieved by superimposing the two circulating current values; for example, the total circulating current value I_total = I_f1 + I_f3. This direct superposition method avoids the complexity of processing the two circulating currents independently, treating them as a unified control objective.

[0041] Simultaneously, the system determines a total circulating current reference value I_ref based on the current operating conditions and energy balance requirements. For example, if the system goal is to completely eliminate circulating current, I_ref might be set to zero. If the system needs to inject specific circulating current to achieve a certain balance, I_ref will be set to a corresponding non-zero value.

[0042] Next, the calculated total circulating current value I_total and the preset total circulating current reference value I_ref are input together into an improved repetitive controller. This controller contains a carefully designed control function. This function receives the deviation signal between I_total and I_ref (I_error = I_ref - I_total) and, based on this deviation signal and its periodic compensation mechanism, generates a control output. For example, when I_total deviates from I_ref, the controller adjusts the system's modulation signal according to the magnitude and direction of the deviation to change the switching state of the H-bridge module, thereby affecting the circulating current within the system.

[0043] This improved repetitive controller enables the system to perform closed-loop tracking of the total circulating current. This means the controller continuously monitors the actual total circulating current value and compares it to a reference value. Upon detecting a deviation, the controller immediately adjusts its output to reduce it. For example, if the actual total circulating current value is higher than the reference value, the controller issues a command to generate a reverse circulating current component to offset the excess circulating current; conversely, it does the opposite. Because this controller performs overall control of the total circulating current, rather than separately controlling the fundamental and third harmonic circulating currents, it avoids the amplitude attenuation and phase lag problems caused by filters in traditional frequency division control, and also eliminates the mutual coupling effects between control loops of different frequency circulating currents. Ultimately, through this precise closed-loop tracking, the fundamental and third harmonic circulating currents within the system are effectively suppressed or precisely controlled within the target range, thereby achieving energy balance in the multi-port cascaded H-bridge energy storage system.

[0044] This method directly calculates the total circulating current value from the fundamental frequency and third harmonic circulating current values, and then performs unified closed-loop tracking on this total circulating current value. This approach avoids the amplitude attenuation and phase lag problems inherent in filters in traditional frequency division control. In traditional schemes, the presence of filters prevents the circulating current signal received by the controller from accurately reflecting the actual situation, making it difficult to eliminate static errors in closed-loop control. This method, by directly processing the total circulating current, ensures the accuracy of the control signal, thereby achieving more precise circulating current tracking and effectively reducing steady-state errors. Simultaneously, this method employs an improved repetitive controller for overall closed-loop tracking of the total circulating current. In the example above, the controller directly adjusts based on the deviation of the total circulating current, eliminating the need to process the fundamental frequency and third harmonic circulating currents separately. This integrated control strategy fundamentally eliminates the mutual coupling problem between control loops of different frequency circulating currents, simplifies the control structure, and improves the dynamic response capability and overall operational reliability of the system. Therefore, this method provides a simpler, more efficient, and higher-precision composite circulating current control scheme, effectively solving the technical problem of poor reliability in energy balance control of existing MD-CHB-ESS systems.

[0045] In some of the above embodiments, this application proposes to obtain the total circulating current reference value of a multi-port cascaded H-bridge energy storage system based on system parameters, and to perform closed-loop tracking based on this value. This application further proposes that, based on the system parameters, the calculation of the total circulating current reference value of the multi-port cascaded H-bridge energy storage system includes: calculating the base frequency circulating current reference value and the third harmonic circulating current reference value of the multi-port cascaded H-bridge energy storage system based on the system parameters; and obtaining the total circulating current reference value by summing the base frequency circulating current reference value and the third harmonic circulating current reference value.

[0046] The calculation of the fundamental frequency circulating current reference value and the third harmonic circulating current reference value of the multi-port cascaded H-bridge energy storage system aims to determine the expected values ​​of the fundamental frequency component and the third harmonic component in the circulating current. These two components are usually the main factors causing energy imbalance and voltage ripple in multi-port cascaded H-bridge energy storage systems. By calculating their reference values ​​separately, the control system can more effectively target and mitigate these specific harmonic problems. One approach is to perform frequency domain analysis on the system parameters, such as using Fourier transform or digital filter banks, to separate the fundamental frequency and third harmonic components, and calculate the reference values ​​of these two components separately based on the current operating state of the system and the energy balance target. Another approach is to construct independent control strategies or estimation models, such as based on instantaneous power theory or voltage imbalance, to derive the fundamental frequency circulating current reference value and the third harmonic circulating current reference value separately, in order to achieve precise control of the circulating current at specific frequencies. Subsequently, the total circulating current reference value is obtained by summing the fundamental frequency circulating current reference value and the third harmonic circulating current reference value. This step involves superimposing the independently calculated fundamental frequency circulating current reference value and the third harmonic circulating current reference value to form a comprehensive total circulating current reference value. This total circulating current reference value will serve as the target input for improving the repetitive controller, guiding it to perform closed-loop tracking of the actual circulating current. Specifically, the two reference values ​​can be linearly superimposed in the time domain using a simple adder or digital signal processing module. Alternatively, if the two reference values ​​are obtained in the frequency domain, they can be synthesized in the frequency domain and then the total circulating current reference value in the time domain can be obtained through inverse transformation.

[0047] In overall energy balance control methods, accurate calculation of the total circulating current reference value is crucial for guiding improvements to the repetitive controller. The system parameters of a multi-port cascaded H-bridge energy storage system reflect its operating state and inherently contain information about various frequency components of the circulating current. By decomposing the calculation of the total circulating current reference value into the calculation of the fundamental frequency circulating current reference value and the third harmonic circulating current reference value, the control system can gain a more detailed understanding of the characteristics of the circulating current. Specifically, the fundamental frequency circulating current is typically related to power imbalances between phases or modules, while the third harmonic circulating current is typically related to DC bus voltage ripple and energy fluctuations within the H-bridge modules. By determining the reference values ​​of these two main components based on the system parameters, the control system can accurately target and compensate for their contributions to the total circulating current. Subsequently, summing these independent reference values ​​yields a comprehensive total circulating current reference value that accurately represents the desired state of the fundamental and third harmonic components. This refined reference value serves as a more precise target for improving the repetitive controller, enabling it to perform more effective closed-loop tracking and thus achieve superior system energy balance. This approach makes circulating current control more precise and robust, and solves the problem of specific harmonics that may be ignored by a single, undifferentiated total reference value.

[0048] As a specific implementation method, when calculating the total circulating current reference value of a multi-port cascaded H-bridge energy storage system, the base frequency circulating current reference value and the third harmonic circulating current reference value can be estimated or calculated separately by analyzing system parameters, such as the DC bus capacitor voltage value of each phase, the DC bus voltage reference value, the phase of the AB phase line voltage of the grid, and the SoC data of the three-phase battery pack. For example, the base frequency circulating current reference value can be determined based on the SoC imbalance of each phase battery pack and the system power demand, aiming to balance the energy distribution between phases. The third harmonic circulating current reference value can be calculated based on the ripple of the DC bus voltage or its deviation from the reference value, in order to suppress DC side voltage fluctuations. Once the reference values ​​of these two components are calculated independently, the total circulating current reference value can be obtained by simple linear superposition. This synthesized reference value is then fed into the improved repetitive controller as its tracking target.

[0049] In some of the above embodiments, this application proposes an energy balance control method that obtains system parameters and calculates the total circulating current reference value based on these parameters, and then uses an improved repetitive controller to perform closed-loop tracking of the circulating current. Based on this, this application further proposes that the system parameters include: three-phase DC bus capacitor voltage value, DC bus voltage reference value, grid AB phase line voltage phase and three-phase battery pack SoC data.

[0050] The system parameters refer to various physical quantities or data used to describe the operating state and characteristics of the multi-port cascaded H-bridge energy storage system. These parameters provide the necessary input for the energy balance control algorithm to accurately assess the system state and calculate control commands. They can be obtained through direct measurement by sensors, for example, by using high-precision sensors to collect data in real time; or through estimation by a state estimator, for example, by using an observer algorithm to extrapolate parameters that are difficult to measure directly; or by reading preset values ​​from the system configuration database, for example, some fixed parameters can be pre-stored in the system. The three-phase DC bus capacitor voltage values ​​refer to the voltage measurement values ​​across the DC-side capacitors of each H-bridge unit in the multi-port cascaded H-bridge energy storage system. These voltage values ​​directly reflect the energy state of each H-bridge unit and are important feedback signals for voltage balance control. They can be obtained by directly measuring the DC bus voltage of each H-bridge unit using high-precision voltage sensors and converting the analog signal into a digital signal for the controller; or by periodically sampling the DC bus voltage of each phase using a voltage sampling circuit and performing filtering. The DC bus voltage reference value refers to the target value of the DC bus voltage that the system expects to maintain. This reference value serves as the setpoint for the outer voltage loop control, used to compare with the average DC bus voltage to generate a voltage deviation signal. Its setting method can be a fixed value preset according to system design requirements, for example, loaded during system initialization; or dynamically adjusted according to the grid operating status or the energy storage system's charging and discharging needs, for example, modified via host computer commands. The grid AB phase line voltage phase refers to the instantaneous phase information of the AB phase line voltage connected to the grid. This phase information provides an accurate synchronization reference for circulating current control, ensuring that the injected or absorbed circulating current is synchronized with the grid voltage, avoiding unnecessary reactive power or harmonics. It can be obtained by extracting phase information from the grid voltage signal using a phase-locked loop (PLL) algorithm, for example, using a PLL in a synchronous rotating coordinate system; or by determining the phase through zero-crossing detection combined with a counter, for example, by detecting the zero-crossing points of the voltage waveform and calculating the time interval. The SoC data of the three-phase battery pack refers to the state of charge (SOC) data of each phase battery pack in the multi-port cascaded H-bridge energy storage system. System-on-Chip (SoC) data reflects the remaining energy of the battery pack and is the core basis for battery pack energy balance control, used to assess the degree of energy imbalance among different phases of the battery pack. It can be obtained by estimating using a combination of coulomb counting (current integration method) and open-circuit voltage method, for example, integrating the charge / discharge current and combining it with the correspondence between the battery open-circuit voltage and SoC; or by using advanced algorithms such as Kalman filtering and neural networks for precise estimation, for example, using battery models and real-time data for state prediction.

[0051] The aforementioned method, by explicitly specifying "system parameters" as three-phase DC bus capacitor voltage values, DC bus voltage reference values, grid AB phase line voltage phases, and SoC data of the three-phase battery packs, provides comprehensive and crucial input information for the energy balance control of multi-port cascaded H-bridge energy storage systems. Specifically, these parameters work synergistically, enabling the system to accurately calculate the baseband circulating current reference value and the third harmonic circulating current reference value. The three-phase DC bus capacitor voltage values ​​and DC bus voltage reference values ​​form the basis of voltage outer-loop control, used to assess the DC-side voltage balance of each H-bridge unit and indirectly affect the generation of the third harmonic circulating current to suppress DC bus voltage fluctuations. The grid AB phase line voltage phase provides a precise synchronization reference for circulating current injection, ensuring the correct phase relationship between the circulating current and the grid voltage, and avoiding unnecessary reactive power or harmonics. Most importantly, the SoC data of the three-phase battery packs directly reflects the degree of energy imbalance among the battery packs. By acquiring this SoC data, the system can quantify the energy differences between the battery packs, thus serving as the core basis for calculating the baseband circulating current reference value. The introduction of the baseband circulating current is precisely for energy transfer between different phases to balance the system-on-chip (SoC) of each battery pack. Obtaining these specific parameters allows the system to accurately calculate the required baseband and third harmonic circulating current reference values ​​from both voltage balance and battery energy balance perspectives. This provides an accurate tracking target for subsequent improvements to the repetitive controller, effectively solving the problem of inaccurate circulating current reference value calculation caused by unclear system parameters, and significantly improving the accuracy and robustness of energy balance control in multi-port cascaded H-bridge energy storage systems.

[0052] Based on this embodiment, this application further proposes that, according to the system parameters, the calculation of the fundamental frequency circulating current reference value and the third harmonic circulating current reference value of the multi-port cascaded H-bridge energy storage system includes: The three-phase DC bus capacitor voltage value, DC bus voltage reference value, and grid AB phase line voltage phase are substituted into the voltage outer loop control formula constructed based on PI control logic, so that the voltage outer loop control formula calculates the third harmonic circulating current reference value based on the deviation between the DC bus voltage reference value and the average value of the three-phase DC bus capacitor voltage value. Based on the SoC data of the three-phase battery pack, the three-phase SoC imbalance is calculated; the three-phase SoC imbalance is subjected to Clark transformation to obtain the imbalance components on the x-axis and y-axis; then, based on the imbalance components, the phase imbalance between phases and the phase angle of the three-phase SoC are calculated; based on the phase imbalance between phases and the phase angle of the three-phase SoC, the effective value of the baseband circulating current and the phase angle of the baseband circulating current are calculated; then, based on the effective value of the baseband circulating current and the phase angle of the baseband circulating current, the preset baseband circulating current expression is substituted to calculate the baseband circulating current reference value.

[0053] The three-phase DC bus capacitor voltage value refers to the voltage measurement value on the DC side capacitor of each H-bridge unit in the multi-port cascaded H-bridge energy storage system. It reflects the energy state of each H-bridge unit and serves as feedback for the voltage outer loop control. This voltage value can be directly measured using a high-precision voltage sensor or sampled through a voltage divider resistor network. The DC bus voltage reference value is the target DC bus voltage value that the system aims to maintain. It serves as the setpoint for the voltage outer loop control and can be preset according to system design or dynamically adjusted according to operational requirements. The grid AB phase line voltage phase is the instantaneous phase information of the grid-side AB phase line voltage, providing a synchronization reference for the voltage outer loop control and ensuring that the third harmonic circulating current reference value is synchronized with the grid voltage phase. This phase information can be obtained through phase-locked loop (PLL) technology or zero-crossing detection. The voltage outer loop control formula based on PI control logic is a control loop designed using a proportional-integral (PI) control algorithm. It outputs a control quantity based on the deviation of the DC bus voltage to calculate the third harmonic circulating current reference value, effectively eliminating steady-state errors. This control formula can be implemented in a digital controller through software programming or using analog circuits. The voltage outer loop control calculates the third harmonic circulating current reference value based on the deviation between the DC bus voltage reference value and the average value of the three-phase DC bus capacitor voltage. This process compares the expected value with the actual average value, generates an error signal by the PI controller, and calculates the third harmonic circulating current reference value for balancing the DC bus voltage to suppress DC bus voltage pulsation.

[0054] The SoC data of the three-phase battery pack refers to the state of charge information of each battery pack in the three-phase battery pack connected to the multi-port cascaded H-bridge energy storage system. It reflects the remaining capacity of the battery pack and serves as the basis for evaluating the energy balance of the battery pack. This data can be estimated in real time by the battery management system (BMS) or obtained through methods such as open-circuit voltage and current integration. The three-phase SoC imbalance is the degree of difference in SoC between the three-phase battery packs. It quantifies the energy imbalance between battery packs and can calculate the deviation between the SoC of each phase and the average value. The Clark transformation is a coordinate transformation that transforms the quantities in the three-phase stationary coordinate system to the two-phase stationary coordinate system (αβ coordinate system), decoupling the three-phase SoC imbalance into two orthogonal components for easier analysis and control. This transformation can be achieved through preset matrix operations or by calling a transformation function. The imbalance components on the α and β axes are the projection components of the three-phase SoC imbalance on the α and β axes after the Clark transformation, serving as intermediate variables for subsequent calculations. The interphase SoC imbalance refers to the degree of SoC imbalance among the three-phase battery packs, usually expressed as an amplitude, reflecting the severity of the overall imbalance. It can be calculated by taking the square root of the sum of the squares of the α-axis and β-axis imbalance components. The phase angle of the three-phase SoC is the phase information of the three-phase battery pack SoC imbalance, reflecting the directionality of the imbalance and guiding the injection direction of the baseband circulating current. It can be calculated using the arctangent function. The effective value of the baseband circulating current is the effective value of the baseband circulating current used to balance the SoC imbalance of the three-phase battery pack, determining the intensity of the baseband circulating current. It can be obtained by mapping the interphase SoC imbalance through a proportional gain or PI controller. The phase angle of the baseband circulating current is the phase angle of the baseband circulating current used to balance the SoC imbalance of the three-phase battery pack, determining the injection direction of the baseband circulating current to effectively transfer energy. It can be directly used as the phase angle of the three-phase SoC or phase compensation can be performed. The preset fundamental frequency circulation expression is a mathematical formula used to generate an instantaneous fundamental frequency circulation reference value based on the effective value and phase angle of the fundamental frequency circulation, and to convert the amplitude and phase information into a time-domain waveform, such as a sine function expression.

[0055] This application's solution achieves precise energy balance within a multi-port cascaded H-bridge energy storage system by meticulously calculating the fundamental frequency circulating current reference value and the third harmonic circulating current reference value. Specifically, to suppress DC bus voltage pulsations and maintain the overall DC link stability of the H-bridge module, the system continuously monitors the three-phase DC bus capacitor voltage values ​​and compares their average value with the DC bus voltage reference value. The voltage outer loop control, based on PI control logic, utilizes this deviation, combined with the grid AB phase line voltage phase information, to accurately calculate the third harmonic circulating current reference value. This third harmonic component effectively offsets DC bus voltage fluctuations. Simultaneously, to address the state of charge (SoC) imbalance problem among the three-phase battery packs, the system acquires the SoC data of the three-phase battery packs and calculates the three-phase SoC imbalance degree. Subsequently, a Clark transformation is performed on this imbalance degree, decomposing it into imbalance degree components on the α and β axes, thereby calculating the inter-phase SoC imbalance degree (amplitude) and the phase angle (direction) of the three-phase SoC. Using this information, the system can accurately calculate the effective value and phase angle of the baseband circulating current, and substitute them into a preset baseband circulating current expression to generate a baseband circulating current reference value. This baseband component is specifically used for energy transfer between battery packs at different SoC levels, thereby actively balancing their state of charge. In this way, the solution of this application not only stabilizes the DC bus voltage, but also ensures the energy balance and efficient operation of the entire energy storage system under complex operating conditions by actively adjusting the battery pack SoC. These accurately calculated baseband and third harmonic circulating current reference values, as components of the total circulating current reference value, provide accurate instructions for subsequent improvements to the closed-loop tracking of the repetitive controller, thereby significantly improving the accuracy and response speed of energy balance control.

[0056] Based on the above implementation methods, more specifically, the calculation expression for the total circulation reference value proposed in this application can be:

[0057] In the formula, This is the reference value for the total circulation. This is the reference value for the third harmonic circulating current. This is the reference value for the fundamental frequency circulating current. This is the proportional gain for the PI stage. Let be the integral coefficient of the PI element, and s be the Laplace operator. Let be the DC bus capacitor voltage value of phase i. This is the reference value for the DC bus voltage. The phase of the AB phase line voltage in the power grid is represented by t, which represents a time quantity. This is the effective value of the fundamental frequency circulating current. The phase angle is the fundamental frequency circulating current.

[0058] The formula for calculating the total circulating current reference value serves to provide an accurate and dynamically adjustable reference target for closed-loop tracking of the circulating current in a multi-port cascaded H-bridge energy storage system. This formula comprehensively considers various internal system factors to ensure that the generated reference value accurately reflects the system's energy balance requirements. This formula can be implemented through programming by a digital signal processor (DSP) or microcontroller (MCU) in the system controller, or through hardware acceleration via application-specific integrated circuits (ASICs) or field-programmable gate arrays (FPGAs). This is the total circulating current reference value, representing the target total circulating current value that the system expects to achieve. This reference value is the basis for improving the closed-loop tracking of the repetitive controller, and its accuracy directly affects the performance of the circulating current control. This reference value can be a fixed value or a variable that is dynamically adjusted according to the system's operating state. This is a reference value for the third harmonic circulating current, used to set the desired third harmonic circulating current component of the system. In multi-port cascaded H-bridge energy storage systems, the third harmonic circulating current is commonly used to suppress DC-side voltage fluctuations or achieve specific energy balance strategies. This reference value can be preset according to system design requirements or adaptively adjusted based on real-time operating data. This is the baseband circulating current reference value, used to set the desired baseband circulating current component of the system. The baseband circulating current is typically closely related to the system's external power exchange and interphase energy balance. This reference value can be dynamically calculated or adjusted based on factors such as system load and the state of charge (SoC) of the energy storage units. This is the proportional gain for the PI stage. The integral coefficients of the PI controller and the integral coefficients together constitute the parameters of the proportional-integral (PI) controller. Here, the PI controller generates a compensation component based on the deviation of the DC bus voltage to maintain its stability. These coefficients can be optimized using classical PID controller tuning methods (such as the Ziegler-Nichols method) or modern control theory methods (such as model predictive control) to achieve the desired control response speed and stability. s is the Laplace operator, used in control theory to represent differential operations, enabling the control function to be analyzed and designed in the frequency domain. Let be the DC bus capacitor voltage value of phase i, which is the voltage across the DC bus capacitor of phase i actually measured by the system. This voltage value is usually sampled in real time by a high-precision voltage sensor and then input to the controller after analog-to-digital conversion (ADC). This is the DC bus voltage reference value, which is the target DC bus voltage value that the system expects to maintain. This reference value is usually set by the system designer based on the characteristics of the energy storage unit and the system operating requirements. The phase of the AB phase line voltage in the power grid represents the phase information of the grid voltage. This phase information can be extracted from the grid voltage using phase-locked loop (PLL) technology for synchronization control with the grid. t represents a time quantity, a continuous time variable used to describe the dynamic behavior of the system. This is the effective value of the fundamental frequency circulating current, representing its amplitude. This effective value can be calculated based on factors such as the system's phase-to-phase charge imbalance, phase-to-phase balance coefficient, and the three-phase voltage of the CHB (Central Helical Block). This is the phase angle of the fundamental frequency circulating current, which represents the phase information of the fundamental frequency circulating current. This phase angle can be calculated based on factors such as the phase angles of the three-phase state of charge and the phase angle of the CHB.

[0059] It should be noted that the calculation process of the total circulation reference value proposed in this embodiment can be referred to in the following example: First, there is a calculation example of the third harmonic circulation current, such as... Figure 2 Taking the compact transformerless multi-port cascaded H-bridge energy storage system topology shown as an example, a loop exists within its triangular circuit. The power balance control module (PBCM) of the device generates a third-harmonic voltage. And the triple frequency circulation injected inside the triangle Interactive operation achieves DC bus energy balance, stabilizing the voltage of each DC bus capacitor at the reference value. Inside the triangle, Kirchhoff's voltage law states: (1) in, The voltage is the third harmonic voltage output by the PBCM device; The third harmonic voltage output by CHB; It is a third harmonic circulating current; and These are the bridge arm inductance and bridge arm resistance, respectively. Taking the Laplace transform of the above equation, we get: (2) From the complex frequency domain model, it can be seen that the CHB regulates the third harmonic voltage of the output. This enables control of the internal circulating current of the CHB-ESS. Therefore, a PI controller is used to construct the voltage outer loop, and its expression is as follows: (3) in, This is a reference value for the third harmonic circulating current; and These are the proportional and integral coefficients for PI control, respectively. This is the reference value for the DC bus voltage; The voltage value of the DC bus capacitor for phase i (i=a, b, c); This represents the phase voltage of phases AB in the power grid. The reference value for the third harmonic circulating current, necessary to achieve energy balance at the DC bus, can be obtained using the outer voltage loop.

[0060] The following is a calculation example of the fundamental frequency circulation current: It should be noted that the triangular CHB-ESS submodules are connected to battery packs in a distributed manner. Inconsistent SoCs among the battery packs can lead to overcharging or over-discharging, affecting battery life; a "bottleneck effect" can occur when the SoC of some battery packs is too low. Inter-phase SoC balancing control employs the method of injecting zero-sequence baseband circulating current to adjust the power absorbed or released by the three-phase battery packs, achieving inter-phase SoC balancing. Let the required injected zero-sequence baseband circulating current be... for: (4) in, This is the effective value of the fundamental frequency circulating current. The phase angle is the fundamental frequency circulating current. ( =ab,bc,ca) average SoC of phase cells, average SoC of three-phase cells and The phase cell imbalance is shown in equations (5), (6), and (7), respectively: (5) (6) (7) in, for Average SoC of the phase cell; This represents the average SoC of a three-phase battery. for The imbalance of the phase cells; This represents the number of cascaded submodules for each phase. It also represents the SoC imbalance of the three-phase battery. Perform Clark transformation: (8) In the formula, , Indicates the imbalance of the three-phase SoC. and Components on the axis, defined The expression for phase-to-phase SoC imbalance is as follows: (9) Phase angle of a three-phase SoC Indicates that it is in Distribution in coordinate system: (10) Let the CHB-ESS three-phase voltage The additional power generated by the interaction with the baseband circulating current is proportional to the imbalance of each phase SoC, which can be obtained as follows: (11) From the above formula, we can see that: (12) Therefore, injecting baseband circulating current can redistribute the three-phase active power of MCP-DC-CHB-ESS without affecting the system output power, thereby achieving phase-to-phase SoC balance of the three-phase battery cells.

[0061] Combining equation (11), the effective value of the injected baseband circulating current required for phase-to-phase SoC equalization control can be obtained. and phase angle As shown in equation (13).

[0062] (13)

[0063] In the formula The phase-to-phase equalization coefficient is proportional to the zero-sequence voltage and the additional power generated. Under the constraint of no modulation in the submodule, increasing it... It can accelerate the SoC equalization speed between phases.

[0064] Combining equations (3) and (13), the reference values ​​for the third harmonic circulating current to achieve DC bus energy balance can be obtained respectively. and the baseband circulating current reference value for achieving phase-to-phase SoC equalization Adding the two together gives the reference value for the total circulation. The calculation is illustrated as follows: Figure 3 As shown.

[0065] The proposed solution combines a third-harmonic circulating current reference value, a fundamental frequency circulating current reference value, and a compensation component generated by adjusting the DC bus voltage deviation through a PI controller to form a comprehensive total circulating current reference value. Specifically, the system first obtains the deviation between the DC bus capacitor voltage value of the i-th phase and the DC bus voltage reference value, and inputs this deviation into the PI controller. The proportional and integral coefficients of the PI controller determine its output compensation effect. Simultaneously, based on preset or dynamically calculated third-harmonic and fundamental frequency circulating current reference values ​​(their effective values ​​and phase angles can be determined according to system conditions such as state-of-charge imbalance and grid phase), the system superimposes these components with the output of the PI controller to obtain the final total circulating current reference value. This calculation process ensures that the total circulating current reference value not only includes the fundamental and third-harmonic circulating current components required by the system but also allows for real-time adjustment based on actual fluctuations in the DC bus voltage. This enables more accurate guidance of the circulating current during closed-loop tracking by the improved repeating controller, effectively suppressing DC bus voltage fluctuations and promoting energy balance within the multi-port cascaded H-bridge energy storage system. In this way, the calculation formula provides a dynamic, accurate and adaptive reference target for the closed-loop tracking of the aforementioned circulation, significantly improving the performance and robustness of the entire energy balance control method.

[0066] By using the aforementioned formula for calculating the total circulating current reference value, this application provides an accurate and dynamically adjustable reference target for closed-loop tracking of the circulating current in a multi-port cascaded H-bridge energy storage system. This formula comprehensively considers the fundamental frequency circulating current, the third harmonic circulating current, and the deviation of the DC bus voltage, ensuring that the generated total circulating current reference value accurately reflects the actual energy balance requirements of the system. This effectively solves the problem of insufficient control accuracy and decreased system stability that may result from the lack of an accurate and dynamically adaptable total circulating current reference value when relying solely on the improved repetitive controller for circulating current tracking. By providing a reference value closely related to the system state, the improved repetitive controller can more effectively suppress circulating current and smooth DC bus voltage fluctuations, thereby significantly improving the energy balance control performance and operational reliability of the multi-port cascaded H-bridge energy storage system.

[0067] In some of the above embodiments, this application proposes an energy balance control method for a multi-port cascaded H-bridge energy storage system. This method improves the repetitive controller for closed-loop tracking of the circulating current. Furthermore, this application proposes the following control function for the improved repetitive controller:

[0068] In the formula, This is the output reference value for CHB. For compensators used to compensate for amplitude and phase, The compensation coefficient is used to compensate for the amplitude. This represents the actual total circulation value. This is the reference value for the total circulation. The third-harmonic voltage output by the PBCM device. This represents the periodic delay stage, where n is the number of sampling points per period.

[0069] in, The CHB output reference value represents the compensation amount that the cascaded H-bridge converter needs to output when controlling circulating current. It is a control command calculated by the controller to adjust the system's operating state to eliminate circulating current. This output reference value directly affects the cascaded H-bridge converter's ability to suppress circulating current and is a key control variable for achieving energy balance. This refers to a compensator used to compensate for amplitude and phase, which corrects for potential amplitude attenuation and phase lag in the control loop to ensure the controller can accurately track periodic signals. This compensator can be implemented in various forms; for example, it can be a lead-lag compensator that provides the desired phase lead or lag by adjusting its zeros and poles, and adjusts the gain to compensate for amplitude. The compensation coefficient, used to compensate for amplitude, primarily functions to finely adjust the controller gain to compensate for energy losses or gain mismatches in the circulating path, ensuring that the actual output compensation precisely corresponds to the expected value. This compensation coefficient can be a fixed value, pre-calibrated based on system characteristics; or it can be an adaptive value, dynamically adjusted based on the system's operating state through online identification or optimization algorithms to adapt to different operating conditions. This is the actual total circulating current value, which is the total circulating current signal measured or estimated in real time in a multi-port cascaded H-bridge energy storage system, reflecting the current energy imbalance state of the system. This value serves as the feedback input to the controller and is the basis for closed-loop control. The total circulating current reference value represents the ideal total circulating current level that the system is expected to achieve. It is typically set to zero or a minimum value to achieve energy balance. The deviation between this reference value and the actual total circulating current value is the basis for the controller to generate control actions. The third harmonic voltage output by the PBCM device is a voltage component injected by the Power Balance Control Module (PBCM) to suppress specific harmonics (such as third harmonics). In multi-port cascaded H-bridge systems, third harmonic circulating current is a common harmonic component, and the introduction of this voltage helps to directly cancel or suppress it, thereby improving system stability. The periodic delay stage plays a crucial role in repetitive controllers. It delays the error information from the previous cycle by one cycle before feeding it back to the current control cycle, thus enabling precise tracking and suppression of periodic disturbances. This stage is typically implemented using the memory in a digital signal processor (DSP), storing the current sampled value and retrieving it after one cycle. 'n' represents the number of sampling points per cycle, determining the storage depth of the periodic delay stage and the controller's resolution. The selection of 'n' is closely related to the system's fundamental frequency and sampling frequency, and is usually equal to the sampling frequency divided by the fundamental frequency, ensuring a sufficient number of sampling points within one cycle to accurately reconstruct the periodic signal.

[0070] It should be noted that repetitive control is based on the internal model principle, constructing a dynamic model of the external signal and forming a high-precision positive feedback controller through a delay element. Due to the effects of delay and positive feedback, the repetitive controller can continuously accumulate the error. Once the error is sufficiently amplified, it can effectively suppress the current error. The control block diagram of an ideal repetitive controller in the discrete domain is as follows: Figure 4 As shown, its transfer function is as follows: (14) In the formula, This is the output reference value for CHB; This represents the number of sampling points per cycle; This represents the actual circulation value inside the triangle.

[0071] The system's transfer function struggles to achieve stability with its eigenvalues ​​located within the unit circle across the entire frequency domain. Therefore, amplitude and phase compensation are introduced, and the control block diagram is shown below. Figure 5 As shown, its expression is as follows: (15) In the formula, It is a compensator used to compensate for amplitude and phase; This is the compensation coefficient, which is also used to compensate for the amplitude.

[0072] This application's solution achieves precise closed-loop tracking of the circulating current in a multi-port cascaded H-bridge energy storage system by introducing a control function of an improved repetitive controller, as described above. This control function takes the deviation between the actual total circulating current value and the total circulating current reference value as input, and uses a periodic delay stage to memorize and compensate for the error of the previous cycle, thereby effectively suppressing the periodic circulating current. Specifically, the compensator used to compensate for amplitude and phase corrects for amplitude attenuation and phase lag in the control loop, ensuring the controller's tracking accuracy under different frequencies and dynamic conditions. Simultaneously, the compensation coefficient used to compensate for amplitude further finely adjusts the controller's gain, enabling the output CHB reference value to accurately offset the actual circulating current. Furthermore, the introduction of the third harmonic voltage output from the PBCM device directly suppresses the common third harmonic circulating current within the system, combining with the periodic compensation mechanism of the repetitive controller to enhance the comprehensiveness and effectiveness of circulating current suppression. In this way, the control function overcomes the shortcomings of traditional repetitive controllers in amplitude and phase compensation, significantly improving the dynamic performance and steady-state accuracy of circulating current tracking, thus more effectively achieving energy balance in the multi-port cascaded H-bridge energy storage system.

[0073] Through the above technical solution, the control function of the improved repetitive controller is clearly defined, and compensators for amplitude and phase compensation, as well as compensation coefficients for amplitude compensation, are introduced. This enables the controller to more accurately compensate for amplitude attenuation and phase lag within the system, significantly improving the tracking accuracy and suppression effect of circulating current in multi-port cascaded H-bridge energy storage systems. In particular, combined with the third harmonic voltage output by the PBCM device, this scheme can effectively suppress periodic disturbances such as fundamental frequency circulating current and third harmonic circulating current, thereby achieving faster and more stable energy balance control under both dynamic and steady-state conditions. This avoids energy imbalance problems caused by imperfect control functions, improving the system's operating efficiency and reliability.

[0074] Based on the above embodiments, this application further proposes another expression for the control function of the improved repetitive controller, specifically: (16) In the formula, and These are the proportional and integral coefficients of the PI element in the improved repetitive controller. The CHB-ESS circulating current reference value is then used. Compared with actual value By comparison, the deviation value is processed by an improved repeating controller to achieve closed-loop tracking of the circulating flow.

[0075] Considering the poor dynamic performance of the single repetitive controller mentioned above, this embodiment further utilizes a PI controller connected in parallel with the repetitive controller based on the control function of the improved repetitive controller described above, thereby forming another improved repetitive controller as shown in Formula 16. Its control block diagram can be found in [reference needed]. Figure 6 .

[0076] The control function of the improved repetitive controller in this embodiment is also the core algorithm expression used to generate the control output. It takes the deviation between the actual total circulating current value and the total circulating current reference value as input, and outputs the reference value of CHB through internal control logic and parameter adjustment to achieve accurate tracking of the circulating current. The design of this function aims to combine the advantages of different control strategies to improve the overall performance of the control system. The proportional coefficient and integral coefficient of the PI element are key parameters in the proportional-integral (PI) controller, which together determine the response characteristics of the PI controller to error signals. The proportional coefficient mainly affects the system's response speed and steady-state error. A larger proportional coefficient can speed up the response but may lead to overshoot. The integral coefficient is mainly used to eliminate the system's steady-state error by gradually adjusting the output through accumulated error, but an excessively large integral coefficient may cause system oscillation. These coefficients can be tuned through offline simulation and system identification methods, such as using optimization algorithms such as the Ziegler-Nichols method or genetic algorithms, to find the optimal combination of control parameters. Alternatively, these coefficients can also be dynamically adjusted through online adaptive or self-tuning techniques, such as adaptive PI controllers based on fuzzy logic or neural networks, to adapt to changes in system parameters or external disturbances. Using a PI controller and a repetitive controller in parallel is a composite control strategy designed to combine the advantages of both. The repetitive controller excels at tracking periodic signals and eliminating periodic errors, but its dynamic response is relatively slow; the PI controller, on the other hand, possesses excellent dynamic response capabilities and the ability to suppress aperiodic disturbances. By connecting them in parallel, the PI controller can respond quickly to transient changes and aperiodic disturbances, while the repetitive controller focuses on eliminating periodic circulating errors, thereby improving the dynamic performance and steady-state accuracy of the entire control system. In software implementation, the outputs of the PI controller and the repetitive controller can be directly superimposed to form the final control signal, which is then fed into the CHB modulator. In hardware implementation, separate PI controller and repetitive controller modules can be designed, and their output signals can be combined using an adder to generate the final control command.

[0077] By employing the aforementioned technical solution, the parallel connection of a PI controller and a repetitive controller effectively compensates for the slow dynamic response speed of traditional repetitive controllers. When the multi-port cascaded H-bridge energy storage system faces dynamic conditions such as load surges or grid disturbances, the PI controller can rapidly provide correction, quickly suppressing transient errors, thereby significantly improving the dynamic response speed and stability of the circulating current control system. Simultaneously, the repetitive controller continues to leverage its advantage in eliminating periodic circulating currents, ensuring high-precision tracking performance of the system in steady state. This combination makes the system more robust in maintaining energy balance, enabling it to more effectively cope with complex and changing operating environments and ensuring the stable and reliable operation of the energy storage system.

[0078] Based on the step-by-step logic embodiment of the energy balance control method for a multi-port cascaded H-bridge energy storage system provided in the above embodiments, to further verify the feasibility and effectiveness of the proposed energy balance and equalization method, an 80V / 1.5kVA three-port MP-CHB-ESS simulation verification model was built on the MATLAB / Simulink platform. The simulation parameters are shown in Table 1, and the simulation operating conditions are shown in Table 2. The average SOC of phases ab, bc, and ca inside the device are 40%, 50%, and 60%, respectively.

[0079]

[0080] Figure 7 This indicates that the actual circulating value can accurately track the circulating reference value, resulting in precise control and good dynamic response. Figure 8 and Figure 9 This indicates that during the power flow regulation and energy storage charging and discharging process of MP-CHB-ESS, the DC bus capacitor voltage remains constant. At the same time, the additional power absorbed by each phase arm CHB-ESS is proportional to the phase SOC imbalance, verifying the correctness and effectiveness of the proposed control strategy.

[0081] Simulation results show that the proposed energy balance and equalization control strategy for a multi-port cascaded H-bridge energy storage system based on repetitive control can achieve DC bus energy balance and inter-phase SoC equalization, and has the feasibility of application in multi-port cascaded H-bridge energy storage system scenarios.

[0082] The above is a detailed description of an embodiment of an energy balance control method for a multi-port cascaded H-bridge energy storage system provided in this application. The following is a detailed description of an embodiment of an energy balance control device for a multi-port cascaded H-bridge energy storage system provided in this application.

[0083] Please see Figure 10 This application provides an energy balance control device for a multi-port cascaded H-bridge energy storage system, comprising: The circulating current data acquisition unit 201 is used to collect the total circulating current value of the multi-port cascaded H-bridge energy storage system. The total circulating current reference value calculation unit 202 is used to obtain the system parameters of the multi-port cascaded H-bridge energy storage system, and then calculate the total circulating current reference value of the multi-port cascaded H-bridge energy storage system based on the system parameters. The circulation tracking control unit 203 is used to substitute the total circulation value and the total circulation reference value into the control function of a preset improved repetitive controller, so that the improved repetitive controller performs closed-loop tracking of the circulation based on the deviation between the total circulation value and the total circulation reference value.

[0084] This embodiment directly calculates the total circulating current value from the fundamental frequency and third harmonic circulating current values, and uses an improved repetitive controller to perform overall closed-loop tracking of this total circulating current value, avoiding the amplitude attenuation and phase lag problems caused by the introduction of filters in traditional frequency division control strategies. Since it is no longer necessary to extract the fundamental frequency and third harmonic circulating currents separately and feed them into independent control loops, this scheme fundamentally eliminates the mutual coupling between control loops of different frequency circulating currents, simplifying the control structure. The improved repetitive controller, through periodic delay elements and compensation mechanisms, can effectively eliminate steady-state errors and perform high-precision tracking of periodic signals, thereby ensuring the internal power balance of the system and the safe and efficient operation of the battery pack. Compared with existing technologies, this embodiment no longer relies on filters to separate circulating current components, but instead uses the total circulating current as a unified control target, making the closed-loop control process more direct and accurate. Through the above technical solution, this embodiment significantly improves the reliability of energy balance control of multi-port cascaded H-bridge energy storage system, effectively solves the technical problems of low control accuracy and poor reliability caused by frequency division control in existing MD-CHB-ESS systems, and provides technical guarantee for the stable operation of distribution networks in high-penetration distributed photovoltaic and electric vehicle charging pile access scenarios.

[0085] Furthermore, in some embodiments, this application also proposes an energy balance control terminal for a multi-port cascaded H-bridge energy storage system, including a memory and a processor. The memory stores program code corresponding to the aforementioned energy balance control method for the multi-port cascaded H-bridge energy storage system. The processor reads and executes the program code to implement the energy balance control method for the multi-port cascaded H-bridge energy storage system.

[0086] The core innovation of this embodiment lies in storing the energy balance control method of the multi-port cascaded H-bridge energy storage system as program code in the memory, and having the processor execute this code. This avoids the amplitude attenuation and phase lag problems introduced by filters in traditional frequency division control, eliminates the mutual coupling between the fundamental frequency and third harmonic circulating current control loops, and achieves the effect of improving the reliability of energy balance control. Specifically, during operation, the processor calls the program code in the memory to directly perform closed-loop tracking control on the total circulating current value, without the need to separate the fundamental frequency and third harmonic components through filters. Therefore, it can track the circulating current reference value more accurately and effectively reduce steady-state error. At the same time, since the fundamental frequency circulating current value and the third harmonic circulating current value are uniformly processed into the total circulating current value, the mutual restraint between control loops of different frequencies is avoided, significantly improving the dynamic response capability and operational reliability of the system. For example, when the processor executes the program code, it first obtains the base frequency circulating current value and the third harmonic circulating current value of the multi-port cascaded H-bridge energy storage system. Then, it calculates the total circulating current value and substitutes this total circulating current value along with a total circulating current reference value into the control function of the improved repetitive controller to achieve closed-loop tracking of the circulating current. Through this technical solution, the terminal effectively solves the technical problem of poor energy balance control reliability caused by frequency division control in existing MD-CHB-ESS systems, ensuring stable operation of the system under conditions of high-penetration distributed photovoltaic and electric vehicle charging pile access.

[0087] In other embodiments, this application proposes a computer-readable storage medium storing program code corresponding to the above-described energy balance control method for a multi-port cascaded H-bridge energy storage system.

[0088] The program code is configured to implement the specific steps of the aforementioned control method when executed by the processor. Specifically, by executing the program code, the processor first obtains the base frequency circulating current value and the third harmonic circulating current value of the multi-port cascaded H-bridge energy storage system; then, based on the base frequency circulating current value and the third harmonic circulating current value, it calculates the total circulating current value; finally, it substitutes the total circulating current value and the obtained total circulating current reference value into the preset control function of the improved repetitive controller, so that the improved repetitive controller performs closed-loop tracking of the circulating current based on the deviation between the total circulating current value and the total circulating current reference value.

[0089] Through the execution of this program code, the system achieves unified closed-loop tracking control of the total circulating current. Since there is no need to separate the fundamental frequency and third harmonic components using filters, signal amplitude attenuation and phase lag problems are avoided. Simultaneously, the fundamental frequency and third harmonic circulating currents are processed as a whole, eliminating the mutual coupling between control loops, thereby significantly improving control accuracy and system reliability. Therefore, this technical solution effectively solves the technical problem of poor energy balance control reliability in existing MD-CHB-ESS systems, providing a reliable guarantee for the stable operation of distribution networks with high penetration of distributed power sources.

[0090] In some other embodiments, this application proposes a computer program product consisting of program code that corresponds to the energy balance control method for a multi-port cascaded H-bridge energy storage system described above. This program code is read and executed by a processor to implement the energy balance control method for the multi-port cascaded H-bridge energy storage system.

[0091] The core innovation of this embodiment lies in calculating the total circulating current value from the fundamental frequency circulating current value and the third harmonic circulating current value, and then using an improved repetitive controller to perform closed-loop tracking of the deviation between this total circulating current value and the total circulating current reference value. This avoids the amplitude attenuation and phase lag problems introduced by filters in traditional frequency division control, and eliminates the mutual coupling between the fundamental frequency and third harmonic circulating current control loops, thereby improving the reliability of energy balance control in multi-port cascaded H-bridge energy storage systems. Specifically, when the computer program product is executed, it first obtains the fundamental frequency circulating current value and the third harmonic circulating current value of the multi-port cascaded H-bridge energy storage system; then, it calculates the total circulating current value based on the fundamental frequency circulating current value and the third harmonic circulating current value; finally, it substitutes the total circulating current value and the obtained total circulating current reference value into the preset control function of the improved repetitive controller, so that the improved repetitive controller performs closed-loop tracking of the circulating current based on the deviation between the total circulating current value and the total circulating current reference value.

[0092] Those skilled in the art will clearly understand that, for the sake of convenience and brevity, the specific working processes of the terminals, devices, and units described above can be referred to the corresponding processes in the foregoing method embodiments, and will not be repeated here.

[0093] In the several embodiments provided in this application, it should be understood that the disclosed terminals, devices, and methods can be implemented in other ways. For example, the device embodiments described above are merely illustrative; for instance, the division of units is only a logical functional division, and in actual implementation, there may be other division methods. For example, multiple units or components may be combined or integrated into another system, or some features may be ignored or not executed. Furthermore, the coupling or direct coupling or communication connection shown or discussed may be an indirect coupling or communication connection between devices or units through some interfaces, and may be electrical, mechanical, or other forms.

[0094] The terms “first,” “second,” “third,” “fourth,” etc. (if present) in the specification and accompanying drawings of this application are used to distinguish similar objects and are not necessarily used to describe a particular order or sequence. It should be understood that such data can be interchanged where appropriate so that embodiments of the application described herein can be implemented, for example, in orders other than those illustrated or described herein. Furthermore, the terms “comprising” and “having,” and any variations thereof, are intended to cover a non-exclusive inclusion; for example, a process, method, system, product, or apparatus that comprises a series of steps or units is not necessarily limited to those steps or units explicitly listed, but may include other steps or units not explicitly listed or inherent to such processes, methods, products, or apparatus.

[0095] It should be understood that in this application, "at least one (item)" means one or more, and "more than" means two or more. "And / or" is used to describe the relationship between related objects, indicating that three relationships can exist. For example, "A and / or B" can represent three cases: only A exists, only B exists, and both A and B exist simultaneously, where A and B can be singular or plural. The character " / " generally indicates that the preceding and following related objects are in an "or" relationship. "At least one (item) of the following" or similar expressions refer to any combination of these items, including any combination of single or plural items. For example, at least one (item) of a, b, or c can represent: a, b, c, "a and b", "a and c", "b and c", or "a and b and c", where a, b, and c can be single or multiple.

[0096] The units described as separate components may or may not be physically separate. The components shown as units may or may not be physical units; that is, they may be located in one place or distributed across multiple network units. Some or all of the units can be selected to achieve the purpose of this embodiment according to actual needs.

[0097] Furthermore, the functional units in the various embodiments of the present invention can be integrated into one processing unit, or each unit can exist physically separately, or two or more units can be integrated into one unit. The integrated unit can be implemented in hardware or as a software functional unit.

[0098] If the integrated unit 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, in essence, or the part that contributes to the prior art, or all or 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.

[0099] The above-described embodiments are only used to illustrate the technical solutions of this application, and are not intended to limit them. Although this application has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of this application.

Claims

1. An energy balance control method for a multi-port cascaded H-bridge energy storage system, characterized in that, include: Collect the total circulating current value of a multi-port cascaded H-bridge energy storage system; Obtain the system parameters of the multi-port cascaded H-bridge energy storage system, and then calculate the total circulating current reference value of the multi-port cascaded H-bridge energy storage system based on the system parameters; The total circulating current value and the total circulating current reference value are substituted into the control function of the preset improved repetitive controller, so that the improved repetitive controller performs closed-loop tracking of the circulating current based on the deviation between the total circulating current value and the total circulating current reference value.

2. The energy balance control method for a multi-port cascaded H-bridge energy storage system according to claim 1, characterized in that, The control function of the improved repetitive controller is specifically as follows: In the formula, This is the output reference value for CHB. For compensators used to compensate for amplitude and phase, The compensation coefficient is used to compensate for the amplitude. This represents the actual total circulation value. This is the reference value for the total circulation. The third-harmonic voltage output by the PBCM device. This represents the periodic delay stage, where n is the number of sampling points per period.

3. The energy balance control method for a multi-port cascaded H-bridge energy storage system according to claim 1, characterized in that, The control function of the improved repetitive controller is specifically as follows: In the formula, This is the output reference value for CHB. For compensators used to compensate for amplitude and phase, The compensation coefficient is used to compensate for the amplitude. This represents the actual total circulation value. This is the reference value for the total circulation. The third-harmonic voltage output by the PBCM device. This represents the periodic delay stage, where n is the number of sampling points per period. The proportional gain of the PI element in the improved repetitive controller. Let be the integral coefficient of the PI element in the improved repetitive controller, and s be the Laplace operator.

4. The energy balance control method for a multi-port cascaded H-bridge energy storage system according to claim 1, characterized in that, Based on the system parameters, the total circulating current reference value of the multi-port cascaded H-bridge energy storage system is calculated as follows: Based on the system parameters, calculate the base frequency circulating current reference value and the third harmonic circulating current reference value of the multi-port cascaded H-bridge energy storage system; The total circulating current reference value is obtained by summing the fundamental frequency circulating current reference value and the third harmonic circulating current reference value.

5. The energy balance control method for a multi-port cascaded H-bridge energy storage system according to claim 4, characterized in that, The system parameters include: three-phase DC bus capacitor voltage value, DC bus voltage reference value, grid AB phase line voltage phase, and SoC data of the three-phase battery pack.

6. The energy balance control method for a multi-port cascaded H-bridge energy storage system according to claim 5, characterized in that, The calculation of the fundamental frequency circulating current reference value and the third harmonic circulating current reference value of the multi-port cascaded H-bridge energy storage system based on the system parameters includes: The three-phase DC bus capacitor voltage value, DC bus voltage reference value, and grid AB phase line voltage phase are substituted into the voltage outer loop control formula constructed based on PI control logic, so that the voltage outer loop control formula calculates the third harmonic circulating current reference value based on the deviation between the DC bus voltage reference value and the average value of the three-phase DC bus capacitor voltage value. Calculate the three-phase SoC imbalance of the three-phase battery pack based on the SoC data of the three-phase battery pack; Performing a Clark transform on the three-phase SoC imbalance, we obtain the three-phase SoC imbalance at... shaft and The imbalance component on the axis is then used to calculate the interphase SoC imbalance and the phase angle of the three-phase SoC based on the imbalance component. Based on the phase imbalance of the interphase SoC and the phase angle of the three-phase SoC, the effective value of the baseband circulating current and the phase angle of the baseband circulating current are calculated. Then, based on the effective value of the baseband circulating current and the phase angle of the baseband circulating current, the preset baseband circulating current expression is substituted to calculate the reference value of the baseband circulating current.

7. An energy balance control device for a multi-port cascaded H-bridge energy storage system, characterized in that, include: The circulating current data acquisition unit is used to collect the total circulating current value of the multi-port cascaded H-bridge energy storage system; The total circulating current reference value calculation unit is used to obtain the system parameters of the multi-port cascaded H-bridge energy storage system, and then calculate the total circulating current reference value of the multi-port cascaded H-bridge energy storage system based on the system parameters. A circulation tracking control unit is used to substitute the total circulation value and the total circulation reference value into a preset control function of an improved repetitive controller, so that the improved repetitive controller performs closed-loop tracking of the circulation based on the deviation between the total circulation value and the total circulation reference value.

8. An energy balance control terminal for a multi-port cascaded H-bridge energy storage system, characterized in that, include: Memory and processor; The memory is used to store program code, which corresponds to the energy balance control method of a multi-port cascaded H-bridge energy storage system as described in claims 1 to 6. The processor is used to read and execute the program code to implement the energy balance control method of the multi-port cascaded H-bridge energy storage system.

9. A computer-readable storage medium, characterized in that, The computer-readable storage medium contains program code, which is related to the energy balance control method for a multi-port cascaded H-bridge energy storage system as described in any one of claims 1 to 6.

10. A computer program product, characterized in that, The computer program product consists of program code, which corresponds to the energy balance control method for the multi-port cascaded H-bridge energy storage system as described in any one of claims 1 to 6. The program code is used to be read and executed by a processor to implement the energy balance control method for the multi-port cascaded H-bridge energy storage system.

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