Control method of three-level cascaded buck-boost converter and energy storage system

Abstract

The application provides a control method based on a three-level cascade Buck-Boost converter and an energy storage system. Through a mode switching point threshold calculation method based on flying capacitor voltage and inductance current dynamic characteristics, when switching between different working modes of the Buck-Boost converter, real-time data such as input and output voltages, inductance equivalent parameters and control periods are combined to dynamically determine the inductance current switching point, smooth transition between different modes is realized, the inductance current mutation caused by mode switching is effectively inhibited, the impact on the direct current bus voltage is reduced, and the stability and dynamic response speed of the voltage stabilizing control are improved.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of power electronics, and particularly relates to a control method based on a three-level cascaded Buck-Boost converter and an energy storage system. BACKGROUND

[0002] The three-level cascaded Buck-Boost converter has a wide application prospect in the fields of energy storage systems, new energy power generation and direct-current microgrids. The converter usually needs to realize the stable control of the direct-current bus voltage and the active balancing of the flying capacitor voltage, and the performance of the control strategy directly affects the reliability, dynamic response capability and overall efficiency of the system. In the traditional control architecture, the mode switching method based on a fixed threshold is usually combined with a voltage and current double-loop proportional integral (PI) controller to realize direct-current voltage stabilization. The mode switching threshold is usually calculated and set offline according to the nominal circuit parameters, and cannot be adjusted in real time according to the load power change, device parameter drift or external disturbance in actual operation. In addition, the balancing control of the flying capacitor voltage is generally realized by introducing an additional voltage balancing loop. The parameters of the control loop are usually fixed values, and the influence of the load power on the balancing dynamic process is not considered, which leads to insufficient response under high power conditions and over-regulation or oscillation under low power conditions.

[0003] The existing control method still has the following defects: the fixed switching threshold easily causes the inductor current to change suddenly, and then causes the direct-current bus voltage to drop or overshoot; the non-adaptive capacitor voltage balancing strategy cannot balance the dynamic response and steady-state stability in the whole power range, and may cause the capacitor voltage to be unbalanced for a long time; and the predictive control method based on a static model causes model mismatch when the parameters change, and the system robustness is insufficient. SUMMARY

[0004] Therefore, the embodiments of the present application provide a control method based on a three-level cascaded Buck-Boost converter and an energy storage system, aiming at solving the technical problem that the existing converter uses a fixed switching threshold to easily cause the inductor current to change suddenly.

[0005] A first aspect of the embodiments of the present application provides a control method based on a three-level cascaded Buck-Boost converter, the converter comprising an input side and an output side, an inductor being located between the input side and the output side, the inductor being used as a multiplexing inductor to store or release energy in different working states of the converter;

[0006] The control method comprises:

[0007] The current of the inductor, the voltage of the flying capacitor on the input side and the flying capacitor on the output side are collected in real time. Combined with the input voltage, output voltage, control cycle and parameters of the converter and the inductor, the threshold of the inductor current mode switching point is calculated.

[0008] Based on the real-time voltage deviation of the flying capacitor on the input side and the flying capacitor on the output side, the adaptive P controller calculates the capacitor voltage adjustment signals on the input side and the output side respectively, which are used to dynamically correct the inductor current reference signal.

[0009] A predictive control model incorporating load parameters is constructed. This predictive control model is used to estimate the changes in the equivalent parameters of the inductor in real time, and the prediction weighting coefficients of the inductor current and capacitor voltage in the predictive control model are dynamically adjusted based on the estimation results.

[0010] Construct a prediction cost function that includes the prediction weight coefficients, determine the target mode based on the prediction cost function, and calculate the target duty cycle of the converter's switching transistors based on the switching transistor action logic of the target mode and the load parameters.

[0011] The target duty cycle is input to the carrier stacking and carrier phase shift modulation unit to generate control signals for each switch, and these control signals are then input to the converter. In one embodiment, the input side includes a flying capacitor. and Switching transistor , , and The input-side bridge arm consists of switching transistors. and Main control switch transistor, switch transistor and Auxiliary switching transistor; flying capacitor and The midpoint of the series connection is taken as the midpoint potential of the input side;

[0012] The output side includes a flying capacitor. and Switching transistor , , and The output side bridge arm consists of switching transistors. and Main control switch transistor, switch transistor and Auxiliary switching transistor; flying capacitor and The midpoint of the series connection is taken as the midpoint potential of the output side;

[0013] Inductor L1 is connected between the input side and the output side.

[0014] In one embodiment, the threshold for calculating the inductor current mode switching point includes:

[0015] The mode type of the converter is determined based on the voltage gain formula; the mode type includes Buck1, Buck2, Boost1, Boost2, Buck-Boost1, and Buck-Boost2.

[0016] If the current mode is Buck1, Buck2, Boost1 or Boost2, the threshold of the switching point is determined by the integral calculation formula;

[0017] If the current mode is Buck-Boost1 or Buck-Boost2, the threshold of the switching point is determined by a piecewise linear interpolation formula.

[0018] In one embodiment, the integral calculation formula is as follows:

[0019] ;in This represents the instantaneous value of the voltage across inductor L1 at time t within the current mode; This represents the inductor current threshold at the j-th mode switching point in the current period k. This represents the inductor current threshold at the previous mode switching point j-1 in the current cycle k. This represents the real-time equivalent inductance value of inductor L1 at time t;

[0020] The piecewise linear interpolation formula is as follows:

[0021] .

[0022] In one embodiment, the step of calculating the capacitor voltage regulation signals on the input side and the output side respectively by the adaptive P controller includes:

[0023] Based on the power demand of the converter at the current moment, the proportional coefficient of the adaptive P controller is dynamically adjusted to dynamically adjust the capacitor voltage regulation signals on the input side and the output side.

[0024] The input-side capacitor voltage adjustment signal is calculated using the following formula:

[0025] ;in , The proportional gain of the input-side P controller. This represents the reference command value for the inductor current in the current period k;

[0026] The capacitor voltage adjustment signal on the output side is calculated using the following formula:

[0027] ;

[0028] in , The proportional gain of the output-side P controller. This represents a reference value for the converter's output voltage. The calculation is for the voltage regulation deviation of the DC bus output of the converter.

[0029] In one embodiment, the step of dynamically adjusting the prediction weight coefficients of inductor current and capacitor voltage in the predictive control model based on the estimation results includes: calculating the equivalent inductance value of the inductor and the external disturbance; calculating the load resistance; and dynamically adjusting the prediction weight coefficients based on the equivalent inductance value, the external disturbance, and the load resistance.

[0030] In one embodiment, constructing the prediction cost function including the prediction weight coefficients includes:

[0031] Inductor current deviation under the target mode The voltage deviation of the flying capacitor on the input side The voltage deviation of the flying capacitor on the output side Perform a weighted summation;

[0032] The formula for calculating the prediction cost function is as follows:

[0033] ;

[0034] in, , , The prediction weight coefficient is denoted as .

[0035] In one embodiment, after determining the target mode based on the prediction cost function, the method further includes: if the target mode is Buck-Boost1 or Buck-Boost2, then further determining the symmetry deviation of the flying capacitor voltage on the input side and the output side; if the symmetry deviation exceeds a preset threshold, then introducing symmetry compensation to calculate the target duty cycle.

[0036] In one embodiment, the target duty cycle is calculated using the following formula:

[0037] ;

[0038] in, This represents the duty cycle without the introduction of symmetry compensation. , This is the capacitor voltage symmetry compensation coefficient. , The symmetry deviation of the flying capacitor voltage on the input side and the output side.

[0039] A second aspect of this application provides an energy storage system including a three-level cascaded Buck-Boost converter and a control unit, the control unit being used to implement any of the control methods mentioned in the above embodiments.

[0040] The beneficial effects of the embodiments of this application are as follows:

[0041] In determining the inductor current switching point, this technical solution breaks through the existing practice of using a fixed threshold or setting the switching point offline based on a simplified circuit model. Instead, it proposes a dynamic calculation method based on real-time parameters and mode determination, thereby maintaining the continuity and smoothness of the inductor current during mode switching.

[0042] By introducing a power demand-driven adaptive adjustment strategy, the problem of fixed proportional controller parameters and difficulty in balancing voltage balance speed and current loop stability under high and low power conditions in existing technologies is effectively solved.

[0043] A combined approach of extended state observer and online parameter identification was introduced to achieve real-time estimation of load parameters and dynamic adjustment of prediction weights. The real-time estimated parameters are incorporated into the MPC model, and the weighting coefficients of the inductor current deviation term and capacitor voltage deviation term are dynamically adjusted based on the deviation of the inductance value or load resistance value from the nominal value. This ensures that the MPC maintains high prediction accuracy and optimal control performance even under conditions of device parameter drift, load changes, or external disturbances.

[0044] When the target mode is Buck-Boost mode, a capacitor voltage symmetry judgment and compensation mechanism is introduced to ensure the voltage symmetry of the flying capacitor, avoid the adverse effects of midpoint voltage deviation on DC bus voltage and output waveform quality, thereby further improving the system's voltage regulation accuracy and output quality. Attached Figure Description

[0045] To more clearly illustrate the technical solutions in the embodiments of this application, 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.

[0046] Figure 1 A schematic diagram of a three-level cascaded Buck-Boost converter provided in an embodiment of this application;

[0047] Figure 2 This is a flowchart illustrating a control method provided in an embodiment of this application. Detailed Implementation

[0048] To make the objectives, technical solutions, and advantages of this application clearer, the following detailed description is provided in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the scope of this application.

[0049] It should be noted that when a component is referred to as being "fixed to" or "set on" another component, it can be directly on or indirectly on that other component. When a component is referred to as being "connected to" another component, it can be directly connected to or indirectly connected to that other component.

[0050] It should be understood that the terms "length", "width", "upper", "lower", "front", "rear", "left", "right", "vertical", "horizontal", "top", "bottom", "inner", "outer", etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are only for the convenience of describing this application and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on this application.

[0051] Furthermore, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of technical features indicated. Thus, a feature defined as "first" or "second" may explicitly or implicitly include one or more of that feature. In the description of this application, "multiple" means two or more, unless otherwise explicitly specified.

[0052] Please see Figure 1 This application provides a control method based on a three-level cascaded Buck-Boost converter. The converter includes an input side and an output side. An inductor L1 is located between the input side and the output side. The inductor L1 serves as a multiplexed inductor for storing or releasing energy in different operating states of the converter.

[0053] The input side includes a DC input power supply. Flying capacitor and Switching transistor , , and The input-side bridge arm consists of switching transistors. and Main control switch transistor, switch transistor and Auxiliary switching transistor; flying capacitor and The midpoint of the series connection serves as the midpoint potential of the input side and is connected to the main switch bridge arm on the input side. Buck or Boost energy conversion on the input side is achieved through the conduction of different switch combinations. The energy transfer element of the circuit is a reusable inductor L1, located between the input and output sides, used for energy storage and release under different operating modes. Between the input and output bridge arms, inductor L1 can function as an output filter element in Buck mode and as an energy storage element in Boost mode, supporting bidirectional power flow.

[0054] The output side structure is similar to the input side, and the output side includes a flying capacitor. and Switching transistor , , and The output side bridge arm consists of switching transistors. and Main control switch transistor, switch transistor and A flying capacitor is used to assist the switching transistor. and The midpoint of the series connection serves as the midpoint potential of the output side. Different switching combinations of the switching transistors enable boost, buck, or Buck-Boost hybrid operation modes on the output side. The output side is connected to a load or energy storage unit for bidirectional energy exchange.

[0055] Please see Figure 2 The control method based on a three-level cascaded Buck-Boost converter provided in this application includes the following steps:

[0056] S100: Real-time acquisition of inductor current, voltage of flying capacitor on the input side and flying capacitor on the output side; combined with the input voltage, output voltage, control cycle and inductor parameters of the converter, to calculate the threshold of the inductor current mode switching point.

[0057] In this embodiment, the inductance of the three-level cascaded Buck-Boost converter is collected in real time. Real-time current Input-side flying capacitor and voltage , Flying capacitor on the output side and voltage , And based on the inductor current at the current moment The input and output flying capacitor voltage values, combined with the converter's input voltage. Output voltage Control cycle and inductance Based on the parameter characteristics, calculate the threshold of the inductor current mode switching point. .

[0058] S200: Based on the real-time voltage deviation of the flying capacitor on the input side and the flying capacitor on the output side, an adaptive P controller calculates capacitor voltage adjustment signals for the input and output sides respectively, which are used to dynamically correct the inductor current reference signal. In this embodiment, the real-time deviation of the flying capacitor voltages on the input and output sides is input to the adaptive P controllers on the input and output sides respectively to generate the input capacitor voltage adjustment signal. and output capacitor voltage regulation signal Used for dynamically correcting the inductor current reference signal .

[0059] S300. Construct a predictive control model that includes load parameters. The predictive control model is used to estimate the changes in the equivalent parameters of the inductor in real time, and dynamically adjusts the prediction weight coefficients of the inductor current and capacitor voltage in the predictive control model based on the estimation results.

[0060] In this embodiment, the inductor current collected in step S100 is used as the basis for the measurement. The adjustment signal generated in step S200 , and the flying capacitor voltage on the input and output sides , , , A predictive control model (MPC) including a load parameter estimation module is constructed. The load parameter estimation module estimates the inductance in real time through an extended state observer. The equivalent parameter changes are calculated, and the prediction weight coefficients of inductor current and capacitor voltage in the MPC model are dynamically adjusted based on the estimation results.

[0061] S400. Construct a prediction cost function containing prediction weight coefficients, determine the target mode based on the prediction cost function, and calculate the target duty cycle of the converter's switching transistors based on the switching transistor action logic and load parameters of the target mode.

[0062] In this embodiment, by constructing a prediction cost function that includes prediction weight coefficients, the control effect of each preset mode under the current operating condition is quantitatively evaluated, providing a quantitative basis for the selection of the optimal target mode. This enables the prediction cost function to accurately reflect the control priority of the system under different operating conditions, thereby selecting the optimal target mode that can minimize the deviation of state variables and adapt to changes in load parameters. This provides a reliable target mode benchmark for subsequent duty cycle calculation, ensuring that the control strategy can still achieve stable control of the DC bus voltage under parameter fluctuations or disturbances.

[0063] S500: Input the target duty cycle to the carrier stacking and carrier phase shift modulation unit to generate control signals for each switch transistor, and input the control signals to the converter.

[0064] In this embodiment, the DC voltage regulation accuracy and system robustness are significantly improved, mainly due to the introduction of a mode switching point threshold calculation method based on the dynamic characteristics of the flying capacitor voltage and inductor current. When switching between different operating modes (Buck, Boost, Buck-Boost), this embodiment does not use traditional fixed thresholds or simplified circuit model calculations, but combines real-time data such as input and output voltages, inductor equivalent parameters, and control cycles to dynamically determine the inductor current switching point. This achieves a smooth transition between different modes, effectively suppresses the sudden change in inductor current caused by mode switching, thereby reducing the impact on the DC bus voltage and improving the stability and dynamic response speed of voltage regulation control.

[0065] In one embodiment, calculating the threshold for the inductor current mode switching point in step S100 specifically includes:

[0066] The mode type of the converter is determined based on the voltage gain formula; the mode type includes Buck1, Buck2, Boost1, Boost2, Buck-Boost1, and Buck-Boost2.

[0067] If the current mode is Buck1, Buck2, Boost1 or Boost2, the threshold of the switching point is determined by the integral calculation formula.

[0068] If the current mode is Buck-Boost1 or Buck-Boost2, the threshold of the switching point is determined by a piecewise linear interpolation formula.

[0069] Specifically, based on the input voltage at the current moment Output voltage ,inductance equivalent parameters and control cycle According to the voltage gain formula:

[0070] Determine the current mode type (Buck1, Buck2, Boost1, Boost2, Buck - Boost1, Buck - Boost2). If the current mode is Buck2 (0.5 < m < 1) or Boost2 (1 < m < 2), then through the integral calculation formula:

[0071] ;

[0072] Determine the switching point current, where is the instantaneous value of the voltage across inductor L1 at time t within the current mode; represents the threshold of the inductor current at the j - th mode switching point in the current cycle k, represents the threshold of the inductor current at the previous mode switching point j - 1 in the current cycle k, represents the real - time equivalent inductance value of inductor L1 at time t. If the current mode is Buck - Boost1 or Buck - Boost2 (corresponding to the dead - zone), then through the piece - wise linear interpolation formula:

[0073] ;

[0074] Determine the switching point current, where is the dead - zone transition coefficient; Through this dynamic switching point calculation method, smooth transition between different modes is achieved, avoiding the impact of the sudden change of inductor current caused by mode switching on the DC bus voltage.

[0075] In one embodiment, in step S200, the adaptive P controller calculates the capacitance voltage regulation signals on the input side and the output side respectively, including: according to the real - time deviation of the flying - capacitor voltages on the input side and the output side, input them into the adaptive P controllers on the input side and the output side respectively to generate the input - side capacitance voltage regulation signal and the output - side capacitance voltage regulation signal , which are used to dynamically correct the inductor current reference command 9>, the generation of the flying - capacitor voltage regulation signals on the input side and the output side 、 combines the load power demand. Specifically, it includes:

[0076] Input - side flying - capacitor voltage regulation signal:

[0077] ; where 、 are the proportionality coefficients of the input - side P controller, represents the reference command value of the inductor current in the current cycle k.

[0078] Output side flying capacitor voltage regulation signal:

[0079] ;in , The proportional gain of the output-side P controller. This represents a reference value for the converter's output voltage. The calculation is for the voltage regulation deviation of the DC bus output of the converter.

[0080] When the converter is in constant power charging and discharging mode (such as in bidirectional energy storage scenarios), it dynamically adjusts the power according to the current power demand. , , , The coefficient value, for example, during high-power charging and discharging, increases. and The coefficient value is prioritized to balance the flying capacitor voltage, and in low-power mode, it is reduced. and The coefficient value is adjusted to reduce the current loop regulation intensity. This power demand-driven regulation signal generation strategy achieves rapid response of the flying capacitor voltage and stability of the DC bus voltage under charging and discharging power fluctuation scenarios. The core function of the calculation formulas for the input and output flying capacitor voltage regulation signals is to dynamically maintain the stability and balance of the voltage across the flying capacitor by accurately calculating and generating corresponding regulation signals. Specifically, the input-side formula targets the flying capacitor in the circuit input stage, while the output-side formula focuses on the flying capacitor in the output stage. Together, they ensure that the flying capacitor voltage remains within the set target range under different operating conditions, thereby providing stable voltage support for the entire circuit system, ensuring power conversion efficiency, suppressing harmonic interference, and preventing device damage or circuit performance degradation due to capacitor voltage imbalance, ultimately achieving safe and efficient circuit operation.

[0081] In one embodiment, step S300, which dynamically adjusts the prediction weighting coefficients of the inductor current and capacitor voltage in the predictive control model based on the estimation results, includes:

[0082] Calculate the equivalent inductance of the inductor and the amount of external disturbance.

[0083] Calculate the load resistance.

[0084] The prediction weighting coefficients are dynamically adjusted based on the equivalent inductance, external disturbance, and load resistance. In this embodiment, the inductor current collected in step S100 is used as the basis for the prediction. The adjustment signal generated in step S200 , and the flying capacitor voltage on the input and output sides , , , A predictive control model including a load parameter estimation module is constructed. The specific implementation of the load parameter estimation module includes:

[0085] Inductors via Extended State Observer (ESO) equivalent parameters Real-time estimation is performed using inductor current. Input voltage Output voltage As the input quantity, the equivalent inductance of inductor L1 and the external disturbance quantity are calculated using the state equation. Simultaneously, through the crossing capacitor voltage deviation and inductor current Based on the real-time relationship, combined with the least squares method or Kalman filtering algorithm, the load resistance is estimated. estimated , and Used to dynamically adjust the weighting coefficients of the inductor current deviation term and the capacitor voltage deviation term in the MPC model. , The formula for adjusting the weighting coefficients is as follows:

[0086] ;in , This is the nominal value. , By using a preset adjustment coefficient and adjusting the dynamic weight, the prediction deviation problem caused by changes in load parameters in the traditional MPC model is solved, thereby improving the adaptability of voltage regulation control.

[0087] After completing step S200, which involves generating the input and output side flying capacitor voltage adjustment signals and dynamically correcting the inductor current reference command, step S300 constructs an MPC model including a load parameter estimation module based on the corrected inductor current reference signal. At this point, the adjustment signal generated in step S200 not only serves as the basis for correcting the current command, but its contained flying capacitor voltage deviation information and current deviation characteristics also serve as auxiliary inputs to the load parameter estimation module. This provides richer dynamic characteristic references for the extended state observer, making the estimation of inductor equivalent parameters and load resistance values ​​more closely match actual operating conditions. This ensures that the MPC model can reliably predict the future state of the system based on real-time corrected reference commands and accurately estimated load parameters. In one embodiment, step S400 constructs a prediction cost function including prediction weight coefficients. The calculation of the prediction cost function specifically includes: calculating the inductor current deviation under the target mode... Input side flying capacitor voltage deviation Output side flying capacitor voltage deviation Perform a weighted summation to form the total cost function: ;

[0088] Input-side flying capacitor voltage deviation: ;

[0089] Output side flying capacitor voltage deviation: ;in, , , The predicted weighting coefficients are based on the load parameters estimated in step S300. , and external disturbances Make adjustments in real time.

[0090] For example, when the inductor Compared to nominal value When it is too high, Increase to preferentially suppress current deviation; when the load resistance value When there are large fluctuations, or Increase the priority to stabilize capacitor voltage; through this multi-dimensional dynamic cost function design, the MPC model can still prioritize the response to key state variables when parameters change, reducing the sensitivity of voltage regulation control.

[0091] By constructing a predictive cost function with multi-dimensional dynamic weights, the control effect of each preset mode under the current operating condition is quantitatively evaluated, providing a quantitative basis for the selection of the optimal mode. By dynamically adjusting the weight coefficients, the cost function can accurately reflect the control priority of the system under different operating conditions, thereby selecting the optimal mode that can minimize the deviation of state variables and adapt to changes in load parameters. This provides a reliable target mode benchmark for subsequent duty cycle calculation, ensuring that the control strategy can still achieve stable control of the DC bus voltage under parameter fluctuations or disturbances.

[0092] In one embodiment, after determining the target mode based on the prediction cost function, the method further includes:

[0093] If the target mode is Buck-Boost1 or Buck-Boost2, then the symmetry deviation of the flying capacitor voltage on the input and output sides is further determined.

[0094] If the symmetry deviation exceeds a preset threshold, symmetry compensation is introduced to calculate the target duty cycle. In this embodiment, the target duty cycle... The calculation incorporates flying capacitor voltage balance constraints, specifically including:

[0095] After selecting the target mode with the lowest cost at the current moment, if the target mode is Buck-Boost1 or Buck-Boost2, then the symmetry deviation of the cross-capacitor voltage on the input and output sides is further determined. The symmetry deviation of the cross-capacitor voltage on the input side is as follows: ;

[0096] Symmetry deviation of the output-side trans-capacitor voltage: Determine whether the symmetry deviation exceeds a preset threshold. If the value exceeds the limit, the duty cycle calculation formula for the target mode is adjusted, and a capacitor voltage symmetry compensation term is introduced: ;

[0097] in This is the calculated duty cycle value before compensation. , If the capacitor voltage symmetry compensation coefficient is not exceeded, the output will be directly applied. .

[0098] By applying the above constraints, the midpoint voltage shift caused by capacitor voltage asymmetry is avoided, thereby indirectly increasing the DC bus voltage. To ensure the stability and output waveform quality of the converter, the optimal switching mode is dynamically determined and the target duty cycle of the main control switch is accurately calculated, balancing the high efficiency and stability of the converter. On the one hand, by selecting the mode with the lowest cost, the switching action logic is ensured to meet the optimization target under the current operating conditions, providing a foundation for efficient energy conversion. On the other hand, when calculating the duty cycle, a flying capacitor voltage balance constraint is introduced. By judging the voltage symmetry deviation and dynamically adjusting the calculation formula, the midpoint voltage offset caused by capacitor voltage asymmetry is effectively avoided, thereby indirectly ensuring the stability of the DC bus voltage and the output waveform quality, ultimately achieving stable and reliable operation of the converter on the basis of high efficiency.

[0099] In one embodiment, in step S500, the target duty cycle is input to the carrier stacking and carrier phase shift modulation unit to generate control signals for each switch, and the control signals are input to the converter, specifically including:

[0100] Calculate the target duty cycle The input is fed to the carrier stacking and carrier phase-shift modulation unit to generate control signals for each switch. These control signals are then output to the main control switches on the input and output sides of the three-level cascaded Buck-Boost converter via a fixed switching frequency modulation strategy (such as SVPWM). This achieves coordinated control of the inductor current and the flying capacitor voltage. Simultaneously, dynamically adjusted prediction weighting coefficients compensate for model deviations caused by load parameter changes or component aging, thereby improving the DC bus voltage. The voltage regulation accuracy and system robustness.

[0101] Furthermore, the specific implementation of the carrier stacking and carrier phase-shifting modulation unit includes:

[0102] Dynamically calculated target duty cycle Decomposed into the input-side Buck converter main control switch ( and Duty cycle and the main control transistor of the output-side Boost converter ( and Duty cycle ,in, ;

[0103] The input-side Buck converter and the output-side Boost converter are cascaded, with a target duty cycle. During decomposition, the input-side Buck stage can be activated first to stabilize the voltage at an intermediate value. Then, the output-side Boost stage adjusts this intermediate value to the final target voltage. A fixed input-side Buck duty cycle can be preset, for example... Then, based on the target duty cycle Calculate based on the above formula (1) Similarly, a fixed output-side Boost duty cycle can be preset first, and then adjusted according to the target duty cycle. Calculate based on the above formula (2) .

[0104] By using a stacked modulation strategy, and The signals are mapped onto the input and output carrier signals respectively to generate the corresponding turn-on signals for the switching transistors. Simultaneously, a phase-shift modulation strategy is used to adjust the phase difference between the input and output carrier signals. To suppress inductor current ripple caused by dynamic changes in duty cycle, phase difference The adjustment formula is:

[0105] ;

[0106] in Ripple suppression coefficient, This represents the inductor current deviation at the current moment. This modulation strategy achieves low-loss control at a fixed switching frequency while reducing the impact of inductor current ripple on DC bus voltage regulation.

[0107] The working principle of this scheme is to stabilize the DC bus voltage of the energy storage inverter through a multi-stage collaborative closed-loop control logic: First, core state variables such as inductor current and input / output side flying capacitor voltage are collected in real time, and dynamic mode switching thresholds are calculated to avoid current surges caused by mode switching; then, based on the flying capacitor voltage deviation and power demand, an adaptive P controller generates an adjustment signal to correct the inductor current reference command and balance the capacitor voltage; next, an MPC model with a load parameter estimation module is constructed to estimate inductor, load parameters and disturbances in real time and dynamically adjust the prediction weights to improve the model's adaptability to parameter changes; then, the prediction cost function of each preset mode is calculated, the optimal mode is selected, and the target duty cycle is dynamically calculated by combining hardware constraints and capacitor voltage balance constraints; finally, a switching signal is generated through carrier stacking and phase-shift modulation to achieve coordinated control of inductor current and flying capacitor voltage, compensate for parameter deviations, and ultimately ensure the stability of the DC bus voltage and the quality of the output waveform under scenarios such as charging and discharging power fluctuations and parameter changes. This application provides an energy storage system, including a three-level cascaded Buck-Boost converter and a control unit for implementing the control method provided in this application. In one specific embodiment, a bidirectional energy storage inverter in the energy storage system is used to achieve bidirectional energy conversion and voltage regulation control between the battery and the DC bus.

[0108] The specific requirements are as follows:

[0109] Input: Battery pack (voltage range 400~600VDC); Output: DC bus (target voltage 500VDC, allowable ripple ≤±10V); Load power: 0~5kW (supports charging and discharging mode switching, power fluctuation rate ≤2kW / 10ms); Environment: Operating temperature -20℃~60℃, must be able to withstand device parameter drift (such as inductor aging causing value changes of ±10%).

[0110] Based on the control method provided in this application, a verification test was conducted, and the process is as follows: First, the dynamic mode switching point was calculated, and state variables were acquired (at time k, i.e., the kth control cycle). The acquired values ​​were: input voltage... Output voltage Inductor current .

[0111] Input capacitor voltage , Output capacitor voltage , .

[0112] Perform mode determination: voltage gain It is determined to be in Buck-Boost mode (corresponding to a dead zone m≈1).

[0113] Switching point threshold calculation:

[0114] Estimating the equivalent value of the inductor using an extended state observer. Dead zone transition coefficient .

[0115] Piecewise linear interpolation formula is used: Substitute the data: .

[0116] Secondly, the flying capacitor voltage balance adjustment signal is generated. Power demand determination: current load power. (High power mode) The voltage of the flying capacitor must be balanced first.

[0117] Input-side regulation signal calculation: Input-side voltage difference .

[0118] Inductor current reference command Current deviation .

[0119] In high power mode, the proportional coefficient (Increase to quickly balance the capacitance). Reduce to lower current loop ripple: .

[0120] Output-side regulation signal calculation: Output-side voltage difference .

[0121] Output voltage deviation (Target 500V).

[0122] In high power mode, , . Corrected inductor current reference command: After correction (After unit conversion) Secondly, load parameter estimation and MPC weight adjustment.

[0123] Parameter estimation: Extended state observer input , , The estimated external disturbance amount .

[0124] Least squares method for estimating load resistance (nominal value) , ).

[0125] Weighting coefficient calculation: Inductance deviation Preset adjustment coefficient .

[0126] .

[0127] Load resistance is unbiased, preset. , Output capacitor voltage weighting (fixed).

[0128] Secondly, the cost function is calculated. For the six preset modes (Buck1 / 2, Boost1 / 2, Buck-Boost1 / 2), the cost function is calculated as follows: .

[0129] After comparison, the Buck-Boost 1 mode was selected as the target mode due to its lowest cost. In the DC voltage regulation control method for energy storage inverters based on the three-level Buck-Boost inductor reuse of flying capacitors, selecting the mode with the lowest cost as the target mode is a crucial step in achieving precise adjustment throughout the entire control logic. This process is based on real-time data collected by the system, including inductor current, input / output flying capacitor voltage, and input / output voltage. First, the potential operating mode range under the current condition is determined by dynamically calculating the mode switching point threshold. Then, combined with the flying capacitor voltage deviation and power demand, an adjustment signal is generated to correct the inductor current reference command, ensuring that the capacitor voltage balance requirement is taken into account in the control. Subsequently, with the help of an extended state observer and online parameter identification technology, key parameters such as inductance and load, as well as external disturbances, are estimated in real time. The weighting coefficients of the inductor current deviation term and capacitor voltage deviation term in the model predictive control are dynamically adjusted, enabling the cost function to accurately reflect the control priority under different operating conditions.

[0130] Finally, by calculating the prediction cost function of each preset mode (Buck1, Buck2, Boost1, Boost2, Buck-Boost1, Buck-Boost2), the mode with the lowest cost is selected as the target mode.

[0131] This technical solution significantly improves DC voltage regulation accuracy and system robustness. Instead of using traditional fixed thresholds or simplified circuit models for calculations when switching between different operating modes, it combines real-time data such as input / output voltages, inductor equivalent parameters, and control cycles, dynamically determining the inductor current switching point using integral calculations or piecewise linear interpolation. This method achieves smooth transitions between different modes, effectively suppressing sudden changes in inductor current caused by mode switching, thereby reducing the impact on the DC bus voltage and improving the stability and dynamic response speed of the voltage regulation control.

[0132] This technical solution outperforms existing technologies in terms of flying capacitor voltage balance and load fluctuation adaptability. Its key lies in its adoption of a P-controller regulation signal generation strategy based on power demand adaptive adjustment. Unlike traditional capacitor voltage balance control with a fixed proportional coefficient, this solution dynamically adjusts the proportional coefficient of the P-controller according to real-time changes in charging and discharging power. In high-power mode, it prioritizes enhancing capacitor voltage balance capabilities, while in low-power mode, it reduces the intensity of current loop regulation to minimize fluctuations. This power-driven coefficient adjustment mechanism enables the system to maintain rapid response and balance of the flying capacitor voltage even under scenarios with rapid fluctuations in charging and discharging power, while simultaneously maintaining the stability of the DC bus voltage, thus balancing steady-state performance and dynamic adaptability.

[0133] In the model predictive control (MPC) section, this scheme introduces a real-time load parameter estimation mechanism combining an extended state observer with least squares or Kalman filtering. This mechanism not only estimates the equivalent inductance and external disturbances but also acquires the load resistance in real time and dynamically adjusts the weighting coefficients of the MPC based on parameter changes. Unlike existing technologies that assume constant circuit parameters and suffer from decreased prediction accuracy due to parameter drift, this scheme maintains the accuracy of the predictive model through online adjustment of weights w1, w2, and w3, ensuring that the MPC remains accurate despite changes in inductance, load resistance, and external disturbances. This technique significantly improves the system's adaptability and control robustness under conditions such as component aging and sudden load changes, thereby achieving higher-precision DC voltage regulation control.

[0134] 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, and should all be included within the protection scope of this application.

Claims

1. A control method based on a three-level cascaded Buck-Boost converter, the converter including an input side and an output side, an inductor located between the input side and the output side, the inductor serving as a multiplexed inductor for storing or releasing energy under different operating states of the converter; Its features are, The control method includes: The current of the inductor, the voltage of the flying capacitor on the input side and the flying capacitor on the output side are collected in real time. Combined with the input voltage, output voltage, control cycle and parameters of the converter and the inductor, the threshold of the inductor current mode switching point is calculated. Based on the real-time voltage deviation of the flying capacitor on the input side and the flying capacitor on the output side, the adaptive P controller calculates the capacitor voltage adjustment signals on the input side and the output side respectively, which are used to dynamically correct the inductor current reference signal. A predictive control model incorporating load parameters is constructed. This predictive control model is used to estimate the changes in the equivalent parameters of the inductor in real time, and the prediction weighting coefficients of the inductor current and capacitor voltage in the predictive control model are dynamically adjusted based on the estimation results. Construct a prediction cost function that includes the prediction weight coefficients, determine the target mode based on the prediction cost function, and calculate the target duty cycle of the converter's switching transistors based on the switching transistor action logic of the target mode and the load parameters. The target duty cycle is input to the carrier stacking and carrier phase-shift modulation unit to generate control signals for each switch, and the control signals are input to the converter; the dynamic adjustment of the prediction weight coefficients of inductor current and capacitor voltage in the prediction control model based on the estimation results includes: Calculate the equivalent inductance value and the amount of external disturbance of the inductor; Calculate the load resistance; The prediction weighting coefficient is dynamically adjusted based on the equivalent inductance value, the external disturbance, and the load resistance value. The construction of the prediction cost function, which includes the prediction weight coefficients, includes: the inductor current deviation under the target mode. The voltage deviation of the flying capacitor on the input side The voltage deviation of the flying capacitor on the output side Perform a weighted summation; the formula for calculating the prediction cost function is: ; in, , , The prediction weight coefficient is denoted as .

2. The control method as described in claim 1, characterized in that, The input side includes a flying capacitor. and Switching transistor , , and The input-side bridge arm consists of switching transistors. and Main control switch transistor, switch transistor and Auxiliary switching transistor; flying capacitor and The midpoint of the series connection is taken as the midpoint potential of the input side; The output side includes a flying capacitor. and Switching transistor , , and The output side bridge arm consists of switching transistors. and Main control switch transistor, switch transistor and Auxiliary switching transistor; flying capacitor and The midpoint of the series connection is taken as the midpoint potential of the output side; Inductor L1 is connected between the input side and the output side.

3. The control method as described in claim 1, characterized in that, The threshold for calculating the inductor current mode switching point includes: The mode type of the converter is determined based on the voltage gain formula; the mode type includes Buck1, Buck2, Boost1, Boost2, Buck-Boost1, and Buck-Boost2. If the current mode is Buck1, Buck2, Boost1 or Boost2, the threshold of the switching point is determined by the integral calculation formula; If the current mode is Buck-Boost1 or Buck-Boost2, the threshold of the switching point is determined by a piecewise linear interpolation formula.

4. The control method as described in claim 3, characterized in that, The integral calculation formula is as follows: ;in This represents the instantaneous value of the voltage across inductor L1 at time t within the current mode; This represents the inductor current threshold at the j-th mode switching point in the current period k. This represents the inductor current threshold at the previous mode switching point j-1 in the current cycle k. This represents the real-time equivalent inductance value of inductor L1 at time t; The piecewise linear interpolation formula is as follows: 。 5. The control method as described in claim 1, characterized in that, The step of calculating the capacitor voltage adjustment signals on the input side and the output side respectively through the adaptive P controller includes: Based on the power demand of the converter at the current moment, the proportional coefficient of the adaptive P controller is dynamically adjusted to dynamically adjust the capacitor voltage regulation signals on the input side and the output side. The input-side capacitor voltage adjustment signal is calculated using the following formula: ;in , The proportional gain of the input-side P controller. This represents the reference command value for the inductor current in the current period k; The capacitor voltage adjustment signal on the output side is calculated using the following formula: ； in , The proportional gain of the output-side P controller. This represents a reference value for the converter's output voltage. The calculation is for the voltage regulation deviation of the DC bus output of the converter.

6. The control method as described in claim 1, characterized in that, After determining the target mode based on the predicted cost function, the process further includes: If the target mode is Buck-Boost1 or Buck-Boost2, then the symmetry deviation of the flying capacitor voltage on the input side and the output side is further determined. If the symmetry deviation exceeds a preset threshold, symmetry compensation is introduced to calculate the target duty cycle.

7. The control method as described in claim 6, characterized in that, The target duty cycle is calculated using the following formula: ; in, This represents the duty cycle without the introduction of symmetry compensation. , This is the capacitor voltage symmetry compensation coefficient. , The symmetry deviation of the flying capacitor voltage on the input side and the output side.

8. An energy storage system, characterized in that, It includes a three-level cascaded Buck-Boost converter and a control unit for implementing the control method according to any one of claims 1 to 7.

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