Lithium battery energy storage bidirectional Buck-Boost converter control method and system

Abstract

The embodiment of the invention provides a lithium battery energy storage bidirectional Buck-Boost converter control method and system, and relates to the technical field of lithium battery energy storage. The control method comprises the following steps: acquiring a bidirectional Buck-Boost converter main circuit model; constructing a bidirectional Buck-Boost converter constraint model according to the main circuit model; acquiring a charging current and a charging voltage on the lithium battery at the output end in the main circuit model, and presetting a constant-current charging current value and a charging voltage threshold value; predicting a charging current predicted value and a charging voltage predicted value of the next switching period according to the charging current and the charging voltage through the constraint model; and according to the charging cost function, the optimal charging duty ratio of the PWM wave is obtained, and stable charging of the lithium battery is realized. According to the invention, the lithium battery energy storage bidirectional Buck-Boost converter can realize stable and efficient charging and discharging processes of the lithium battery, the current of the lithium battery can be rapidly constant to a set value in the charging and discharging processes, no current overshoot and fluctuation are generated, and the safe and efficient charging and discharging control performance of the lithium battery can be realized.

Description

Technical Field

[0001] This invention relates to the field of lithium battery energy storage technology, and more specifically to a control method and system for a bidirectional Buck-Boost converter for lithium battery energy storage. Background Technology

[0002] Lithium-ion battery energy storage technology is widely used in electric vehicles and DC microgrids, where lithium-ion batteries are responsible for both energy storage and release, making them the primary components of the energy storage system. Energy storage and release in lithium-ion batteries are achieved through bidirectional converter circuits. The non-isolated H-bridge bidirectional Buck-Boost converter, with its advantages of low electrical stress on power devices and high cost-effectiveness, is widely used in lithium-ion battery energy storage systems. When the lithium-ion battery needs to store energy, the H-bridge bidirectional Buck-Boost converter operates in the forward direction, charging the battery from the DC bus. When the lithium-ion battery needs to release energy, the H-bridge bidirectional Buck-Boost converter operates in the reverse direction, charging the battery from the DC bus. The bidirectional Buck-Boost converter operates in both forward buck and reverse boost modes. Since the lithium battery is in different operating states, there are different control requirements for the lithium battery side. However, the important control objectives are to ensure that the working life of the lithium battery is not impaired and to ensure the stability of the target voltage and current during charging and discharging.

[0003] When the bidirectional Buck-Boost converter operates in forward buck mode, the lithium battery is charged and stored via the DC bus. At the beginning of charging, the Buck-Boost converter rapidly charges the lithium battery in a constant current mode. Once the lithium battery terminal voltage reaches a threshold, the Buck-Boost converter charges it in a constant voltage mode. The lithium battery charging process involves constant current charging and constant voltage charging stages. The constant current stage ensures rapid energy storage, while the constant voltage stage reduces the charging current to prevent overcharging and extend battery life. During the constant current charging stage, the charging current must quickly reach a constant reference current value to ensure energy storage efficiency. A smooth transition from constant current to constant voltage mode is crucial to avoid excessive current overcharging that could cause severe short-term overheating of the lithium battery. During the constant voltage charging stage, the charging voltage must remain stable near the reference voltage value to minimize voltage fluctuations. When the bidirectional Buck-Boost converter operates in reverse boost mode, the lithium battery releases electrical energy to the DC bus. Throughout the discharge phase, the lithium battery discharges through the Buck-Boost converter with a constant current. When the lithium battery terminal voltage drops to a protection value, the Buck-Boost converter stops operating to prevent over-discharge of the lithium battery. During the constant current discharge phase, it is necessary to ensure that the lithium battery discharge current is stable near the discharge reference current value and has high stability with minimal fluctuations. This prevents fluctuating discharge currents from causing the lithium battery to overheat due to short-term, intense discharge, or even shorten its lifespan.

[0004] Model predictive control (MDC) is an optimal control method characterized by fast dynamic response and ease of implementation, widely used in the control of lithium-ion battery energy storage converters. A paper published in the December 2018 issue of the *Journal of Electrical Engineering*, titled "Research on Constrained Model Predictive Control of Bidirectional DC-DC Converters for Electric Vehicles," proposed a model predictive control method for bidirectional Buck-Boost converters based on particle swarm optimization parameters. This method constrains the operating current of the bidirectional Buck-Boost converter through model optimization, achieving stable charging and discharging control for energy storage components such as lithium-ion batteries and supercapacitors. A paper published in the November 2021 issue of the *Journal of Energy Storage Science and Technology*, titled "Improved Model Predictive Control of Bidirectional DC-DC Converters for Hydrogen Fuel Cell Vehicles," proposed a duty cycle-constrained model predictive control method for bidirectional Buck-Boost converters. This method constrains the current of the bidirectional Buck-Boost converter, solving problems such as slow current build-up response, low current tracking stability, and large charging and discharging current ripple in energy storage components like lithium-ion batteries during charging and discharging.

[0005] The aforementioned paper proposes a novel model predictive control method with constraints for bidirectional Buck-Boost converters in energy storage systems such as lithium batteries. This method adds constraint terms to constrain the current, ensuring precise control of the target current and further improving the dynamic response speed of the control current establishment and the fluctuation of the charging and discharging current, thus guaranteeing the safe and stable operation of the lithium battery charging and discharging process. However, the established constraint model control cost function requires complex parameter optimization using algorithms such as particle swarm optimization, or directly assigning constraint parameters based on estimation experience. This is not conducive to the fast and simple execution of the model predictive control algorithm, and may even fail to obtain the optimal solution within the working cycle of the bidirectional Buck-Boost converter. Consequently, it cannot achieve optimal control of the lithium battery charging and discharging process, leading to overheating or reduced battery life during charging and discharging. Summary of the Invention

[0006] The purpose of this invention is to provide a control method and system for a bidirectional Buck-Boost converter for lithium battery energy storage. This invention enables the bidirectional Buck-Boost converter control of lithium battery energy storage to achieve a stable and efficient lithium battery charging and discharging process. During charging and discharging, the lithium battery current can quickly stabilize at a set value without current overshoot or fluctuations, thus achieving safe and efficient charging and discharging control of the lithium battery.

[0007] To achieve the above objectives, embodiments of the present invention provide a control method for a bidirectional Buck-Boost converter for lithium battery energy storage, comprising: Obtain the main circuit model of the bidirectional Buck-Boost converter; Construct a bidirectional Buck-Boost converter constraint model based on the main circuit model; Obtain the charging current and charging voltage on the output lithium battery in the main circuit model, and preset the constant current charging current value and charging voltage threshold. The constraint model is used to predict the charging current and charging voltage for the next switching cycle based on the charging current and charging voltage. Adjust the charging constraint parameters based on the charging current, charging voltage, constant current charging current value, and charging voltage threshold. Based on the charging constraint parameters, obtain the charging cost function; Based on the charging cost function, the optimal charging duty cycle of the PWM wave is obtained to achieve stable charging of the lithium battery. Obtain the discharge current and discharge voltage of the lithium battery at the input terminal in the main circuit model, and preset the constant current discharge current value and discharge protection voltage value; The constraint model is used to predict the discharge current for the next switching cycle based on the discharge current and discharge voltage. Adjust the discharge constraint parameters based on the discharge current, discharge voltage, and constant current discharge current value; Based on the discharge constraint parameters, obtain the discharge cost function; Based on the discharge cost function, the optimal discharge duty cycle of the PWM wave is obtained, and the discharge protection state is entered when the discharge voltage is lower than the discharge protection voltage value, so as to realize the stable discharge of the lithium battery.

[0008] Optionally, the constraint model predicts the charging current and charging voltage for the next switching cycle based on the charging current and charging voltage, including: The predicted charging current for the next switching cycle is obtained according to formula (1). (1) in, For the next Predicted charging current of lithium battery during switching cycle. , The inductance value for connecting to the lithium battery terminal. For the switching cycle, The duty cycle during which the inductor discharges energy is the entire switching cycle. For the present DC bus voltage during the switching cycle For the present Charging voltage during the switching cycle, For the present The charging current during the switching cycle; The predicted charging voltage for the next switching cycle is obtained according to formula (2). (2) in, For the next Predicted charging voltage of lithium battery during switching cycle. The equivalent capacitance value during the charging process of a lithium battery.

[0009] Optionally, the charging constraint parameters are adjusted based on the charging current, charging voltage, constant current charging current value, and charging voltage threshold, including: The charging constraint parameters are obtained according to formula (3). (3) in, For charging constraint parameters, This represents the error value between the charging voltage and the charging voltage threshold. Error value The lower limit, Error value The upper limit.

[0010] Optionally, the charging cost function is obtained based on the charging constraint parameters, including: The charging cost function is obtained according to formula (4). (4) in, Let the charging cost function be... This is the constant current charging current value. This is the charging voltage threshold.

[0011] Optionally, based on the charging cost function, the optimal charging duty cycle of the PWM wave is obtained to achieve stable charging of the lithium battery, including: The optimal charging duty cycle of the PWM wave is obtained according to formula (5). (5) in, The optimal charging duty cycle for the PWM wave.

[0012] Optionally, predicting the discharge current for the next switching cycle based on the discharge current and discharge voltage using the constraint model includes: The predicted discharge current for the next switching cycle is obtained according to formula (6). (6) in, For the next Predicted discharge current of lithium battery during switching cycle. For the present Discharge voltage during the switching cycle, For the present DC bus voltage during the switching cycle For the present Discharge current during the switching cycle.

[0013] Optionally, the discharge constraint parameters can be adjusted based on the discharge current, discharge voltage, and constant current discharge current value, including: The discharge constraint parameters are obtained according to formula (7). (7) in, These are parameters for the discharge constraint term. This represents the error value between the discharge current and the constant current discharge current. For the next Predicted discharge current of lithium battery during switching cycle and current The difference in discharge current during the switching cycle.

[0014] Optionally, the discharge cost function is obtained based on the discharge constraint term parameters, including: The discharge cost function is obtained according to formula (8). (8) in, Let the discharge cost function be... This is the constant current discharge current value.

[0015] Optionally, based on the discharge cost function, the optimal discharge duty cycle of the PWM wave is obtained, and the battery enters a discharge protection state when the discharge voltage is lower than the discharge protection voltage value, thereby achieving stable discharge of the lithium battery, including: The optimal discharge duty cycle of the PWM wave is obtained according to formula (9). (9) in, To achieve the optimal discharge duty cycle for the PWM wave, , The inductance value for connecting to the lithium battery terminal. The switching cycle.

[0016] On the other hand, the present invention also provides a control system for a bidirectional Buck-Boost converter for lithium battery energy storage, the control system including a processor for executing the control method as described in any of the above.

[0017] Through the above technical solution, this invention provides a control method and system for a bidirectional Buck-Boost converter for lithium battery energy storage. By obtaining the main circuit model of the bidirectional Buck-Boost converter, a constraint model of the bidirectional Buck-Boost converter is constructed based on the main circuit model. The charging current and charging voltage prediction values ​​for the next switching cycle, or the discharging current prediction value for the next switching cycle, are predicted based on the constraint model to adjust the charging constraint parameters or discharging constraint parameters. A cost function is obtained based on the constraint parameters, and the optimal charging duty cycle or optimal discharging duty cycle of the PWM wave is obtained based on the cost function, achieving stable discharge or charging of the lithium battery. This invention enables the bidirectional Buck-Boost converter control of lithium battery energy storage to achieve a stable and efficient lithium battery charging and discharging process. During charging and discharging, the lithium battery current can quickly stabilize to a set value without current overshoot or fluctuations, achieving safe and efficient charging and discharging control performance for the lithium battery.

[0018] Other features and advantages of the embodiments of the present invention will be described in detail in the following detailed description section. Attached Figure Description

[0019] The accompanying drawings are provided to further illustrate embodiments of the present invention and form part of the specification. They are used together with the following detailed description to explain the embodiments of the present invention, but do not constitute a limitation thereof. In the drawings: Figure 1 This is a flowchart of a bidirectional Buck-Boost converter control method for lithium battery energy storage according to one embodiment of the present invention; Figure 2 This is a bidirectional Buck-Boost converter main circuit model according to one embodiment of the present invention; Figure 3 This is a flowchart illustrating the predicted charging current and charging voltage values ​​for the next switching cycle according to one embodiment of the present invention. Figure 4 This is a schematic diagram of the voltage and current response waveforms during the charging and discharging process of a lithium battery according to one embodiment of the present invention. Detailed Implementation The specific embodiments of the present invention will be described in detail below with reference to the accompanying drawings. It should be understood that the specific embodiments described herein are for illustration and explanation only and are not intended to limit the scope of the present invention.

[0020] In the embodiments of this application, certain software, components, models and other existing solutions in the industry may be mentioned. These should be regarded as exemplary and are only intended to illustrate the feasibility of implementing the technical solution of this application. However, they do not mean that the applicant has used or necessarily used the solution.

[0021] like Figure 1 The diagram shown is a flowchart of a bidirectional Buck-Boost converter control method for lithium battery energy storage according to one embodiment of the present invention. Figure 2 The figure shown is a main circuit model of a bidirectional Buck-Boost converter according to one embodiment of the present invention. Figure 1 In this context, the control method may include: In step S1, the main circuit model of the bidirectional Buck-Boost converter is obtained; In step S2, a bidirectional Buck-Boost converter constraint model is constructed based on the main circuit model; In step S3, the charging current and charging voltage of the lithium battery at the output terminal in the main circuit model are obtained, and the constant current charging current value and charging voltage threshold are preset. In step S4, the charging current and charging voltage prediction values ​​for the next switching cycle are predicted using a constraint model based on the charging current and charging voltage. In step S5, the charging constraint parameters are adjusted based on the charging current, charging voltage, constant current charging current value, and charging voltage threshold. In step S6, the charging cost function is obtained based on the charging constraint parameters; In step S7, the optimal charging duty cycle of the PWM wave is obtained according to the charging cost function to achieve stable charging of the lithium battery; In step S8, the discharge current and discharge voltage of the lithium battery at the input terminal in the main circuit model are obtained, and the constant current discharge current value and discharge protection voltage value are preset. In step S9, the discharge current prediction value for the next switching cycle is predicted based on the discharge current and discharge voltage using a constraint model. In step S10, the discharge constraint parameters are adjusted according to the discharge current, discharge voltage, and constant current discharge current value. In step S11, the discharge cost function is obtained based on the discharge constraint term parameters; In step S12, the optimal discharge duty cycle of the PWM wave is obtained according to the discharge cost function, and the discharge protection state is entered when the discharge voltage is lower than the discharge protection voltage value, so as to realize the stable discharge of the lithium battery.

[0022] In Figure 1 In the method shown, step S1 can be used to obtain the main circuit model of the bidirectional Buck-Boost converter. This bidirectional Buck-Boost converter main circuit model can be as follows: Figure 2 As shown. In this Figure 2 In the model, the main circuit of the bidirectional Buck-Boost converter consists of capacitors. Switching transistor and its body diode ,inductance and Composition, capacitor The voltage across the two ends is Connected to the DC bus, switching transistor and its body diode composition Bridge structure connected to capacitor Both ends, The two middle arms of the bridge are respectively connected to the inductor. and One end, inductor and The other end is connected to both ends of the lithium battery. Step S2 can be used to construct a bidirectional Buck-Boost converter constraint model based on the main circuit model. Step S3 can be used to obtain the charging current and charging voltage on the output lithium battery in the main circuit model, and preset the constant current charging current value and charging voltage threshold. During the charging process, the constraint model in step S2 is a lithium battery forward charging constraint model. Through this forward charging constraint model, in step S4, the predicted charging current and charging voltage values ​​for the next switching cycle are predicted based on the charging current and charging voltage, so that the predicted charging current value tracks the given constant current charging current value in advance, further improving the lithium battery constant current charging current establishment rate and ensuring the efficiency of the charging process. The specific method for predicting the predicted charging current and charging voltage values ​​for the next switching cycle can be of various forms known to those skilled in the art. In one example of the present invention, the specific method for predicting the predicted charging current and charging voltage values ​​for the next switching cycle can include, for example, Figure 3 The steps are shown. Specifically: In step S21, the predicted charging current value for the next switching cycle is obtained according to formula (1). (1) in, For the next Predicted charging current of lithium battery during switching cycle. , The inductance value for connecting to the lithium battery terminal. For the switching cycle, The duty cycle during which the inductor discharges energy is the entire switching cycle. For the present DC bus voltage during the switching cycle For the present Charging voltage during the switching cycle, For the present The charging current during the switching cycle; In step S22, the predicted charging voltage for the next switching cycle is obtained according to formula (2). (2) in, For the next Predicted charging voltage of lithium battery during switching cycle. The equivalent capacitance value during the charging process of a lithium battery.

[0023] In Figure 3 In the method shown, step S21 can be used to obtain the predicted charging current value for the next switching cycle according to formula (1). Define the switching transistor. A drive signal of 1 indicates conduction, and a drive signal of 0 indicates cutoff. During lithium battery charging, there are three operating states, including inductive energy storage (…). =1、 =0、 =0、 When =1), the constraint equations for the lithium battery terminal voltage and charging current can be expressed by formula (10). (10) in, , The inductance value for connecting to the lithium battery terminal. This is the time derivative of the lithium battery current. This is the DC bus terminal voltage. This is the charging voltage; In the inductor energy release ( =1、 =0、 =1、 =0), ( =0、 =1、 =0、 When =1), the constraint equations for the lithium battery terminal voltage and charging current can be expressed by formula (11). (11) The duty cycle of the inductor's energy release time during the entire switching cycle is defined as follows: Then, by combining formulas (10) and (11) over the entire switching cycle, we can obtain formula (12). (12) Discretizing formula (12) yields formula (1), which is the predicted charging current value for the next switching cycle obtained in step S21. (1) in, For the next Predicted charging current of lithium battery during switching cycle. For the switching cycle, The duty cycle during which the inductor discharges energy is the entire switching cycle. For the present DC bus voltage during the switching cycle For the present Charging voltage during the switching cycle, For the present The charging current during the switching cycle.

[0024] Throughout the entire lithium battery charging process, the current of the lithium battery is equal to the inductor current, thus formula (13) exists. (13) in, The equivalent capacitance value during the charging process of a lithium battery; Discretizing formula (13) yields formula (2), which is the predicted charging voltage for the next switching cycle obtained in step S22. (2) in, For the next Predicted charging voltage of lithium battery during switching cycle.

[0025] To ensure a smooth transition between the constant current charging and constant voltage charging processes of the lithium battery, an adaptive adjustment mechanism for the weight parameters of the constant current and constant voltage charging constraint terms is designed. This allows the charging constraint parameters to be adaptively adjusted according to the real-time charging status of the lithium battery, avoiding large overcharging currents during the transition from constant current charging to constant voltage charging. Furthermore, step S5 can be used to adjust the charging constraint parameters based on the charging current, charging voltage, constant current charging current value, and charging voltage threshold.

[0026] During the lithium battery charging process, the initial stage involves constant current charging, resulting in a constant charging current for the lithium battery. Quickly reach the given constant current charging current value As the charging process progresses, the charging voltage at the lithium battery terminal... Rising to near the charging voltage threshold After that, it will switch to constant voltage charging mode to adjust the charging voltage. Stabilized at the charging voltage threshold Nearby, in the voltage and current constraints of the charging cost function, the parameters of the charging constraint terms adaptively adjust with the charging state. This allows for a smooth transition from constant current charging to constant voltage charging, where the charging constraint parameters can be obtained from formula (3). (3) in, For charging constraint parameters, This represents the error value between the charging voltage and the charging voltage threshold. Error value The lower limit, Error value The upper limit. The charging constraint parameters shown in formula (3) It has the characteristic of being differentiable and smoothly reachable between the values ​​0 and 1, which ensures the adaptive and smooth change of the parameters of the constant current charging constraint term and the constant voltage charging constraint term.

[0027] To ensure that the lithium battery charging process can automatically and smoothly transition from constant current charging to constant voltage charging, thereby improving the efficiency and safety of the lithium battery charging process, step S6 can be used to obtain the charging cost function based on the charging constraint parameters. By establishing a charging cost function with charging constraint parameters based on the lithium battery charging characteristics, and by adaptively adjusting the weights of the current constraint and voltage constraint terms of the charging cost function according to the lithium battery charging state, the problem of battery overheating due to overcharging during the charging process is avoided. Specifically, the charging cost function can be obtained according to formula (4). (4) in, Let the charging cost function be... This is the constant current charging current value. The charging voltage threshold. The charging cost function with charging constraint parameters during the charging process. There are voltage and current constraints in the process, especially during the initial charging phase. The value is set to 0. The charging cost function mainly realizes the tracking of the constant current charging current value of the lithium battery charging current. This is to achieve constant current charging; as the charging process progresses, the charging voltage at the lithium battery terminal increases and approaches the charging voltage threshold. back, As the value increases, the voltage and current constraint terms work together, with the voltage constraint becoming stronger and the current constraint becoming weaker. The lithium battery charging process begins to smoothly transition towards the constant voltage charging stage. When the lithium battery terminal voltage reaches the charging voltage threshold... back, The value is 1, and the charging cost function mainly aims to stabilize the lithium battery terminal voltage at the charging voltage threshold. The charging current decreases slowly in the vicinity to achieve constant voltage charging.

[0028] Step S7 can be used to obtain the optimal charging duty cycle of the PWM wave according to the charging cost function, so as to realize stable charging of lithium battery. According to formula (4), the charging cost function has formula (14). (14) The optimal charging duty cycle of the PWM wave during lithium battery charging can be obtained according to formula (14), specifically expressed by formula (5). (5) in, The optimal charging duty cycle for the PWM wave.

[0029] Based on the obtained optimal charging duty cycle of the PWM wave The system automatically updates based on the real-time charging status of the lithium battery. Initially, the constant current charging component is primarily active. As the constant voltage charging threshold approaches, both the constant current and constant voltage components work together, with the constant voltage charging component taking over. The duty cycle is [missing information]. The PWM wave acts on the four switches of the bidirectional Buck-Boost converter. Above, control The switching on and off of the circuitry is used to achieve stable charging of the lithium battery.

[0030] During the discharge process, the main circuit model of the bidirectional Buck-Boost converter is consistent with the circuit in step S1. The discharge process will transfer energy from the lithium battery terminal to the DC bus terminal. At this time, the constraint model in step S2 is the lithium battery reverse discharge constraint model. Step S8 can be used to obtain the discharge current and discharge voltage on the lithium battery at the input terminal in the main circuit model, and preset the constant current discharge current value and discharge protection voltage value. In step S9, the lithium battery reverse discharge constraint model predicts the discharge current prediction value for the next switching cycle based on the discharge current and discharge voltage. This allows the discharge current prediction value to track the given constant current discharge current value in advance, improving the lithium battery constant current discharge current establishment rate and ensuring rapid discharge of the lithium battery. The specific method for predicting the discharge current prediction value for the next switching cycle can be of various forms known to those skilled in the art. In one example of the present invention, there are also 3 working states during the lithium battery discharge process, including inductor energy storage ( =1、 =0、 =1、 =0) and ( =0、 =1、 =0、 When =1), the constraint equations for the lithium battery terminal voltage and current can be expressed by formula (15). (15) Among them, the energy released by the inductor ( =1、 =0、 =0、 When =1), the constraint equations for the lithium battery terminal voltage and current can be expressed by formula (16). (16) Combining formulas (15) and (16) yields formula (17). (17) Discretizing formula (17) yields formula (6), which provides the predicted discharge current value for the next switching cycle. (6) in, For the next Predicted discharge current of lithium battery during switching cycle. For the present Discharge voltage during the switching cycle, For the present DC bus voltage during the switching cycle For the present Discharge current during the switching cycle.

[0031] To ensure that the discharge current quickly reaches the given discharge current value during the constant current discharge process of the lithium battery, and to prevent large fluctuations in the current during stable discharge, an adaptive adjustment part of the weight parameters of the constant current discharge constraint term is designed. This allows the discharge constraint term parameters to be adaptively adjusted according to the real-time discharge state of the lithium battery, avoiding the problem of severe battery overheating caused by current fluctuations during the lithium battery discharge process. Furthermore, step S10 can be used to adjust the discharge constraint term parameters based on the discharge current, discharge voltage, and constant current discharge current value.

[0032] The discharge current and discharge current fluctuation value are adaptively adjusted to adjust the discharge constraint parameters. The value refers to the constant current discharge during the lithium battery discharge process; the lithium battery discharge current is... Quickly reach the given constant current discharge current value Furthermore, to ensure a stable discharge current, it is necessary to maintain the discharge current. Stabilized at constant current discharge current value Nearby, the discharge cost function constrains the stationary tracking of the discharge current and the rate of change of the discharge current, with discharge constraint term parameters... With the adaptive adjustment of the discharge state, the discharge constraint parameters can be obtained according to formula (7). (7) in, These are parameters for the discharge constraint term. This represents the error value between the discharge current and the constant current discharge current. For the next Predicted discharge current of lithium battery during switching cycle and current The difference in discharge current during the switching cycle. The discharge constraint parameters shown in formula (7) The value expression can adaptively adjust according to the lithium battery's discharge state, when the discharge current... With constant current discharge current value When the error is large, the discharge constraint parameters A smaller value results in a larger weight for the current stationary tracking term in the discharge cost function, leading to a larger discharge current. Rapidly track the constant current discharge current value Achieve rapid constant current discharge; when the discharge current... Achieving constant current discharge current value Then, the discharge constraint term parameters A larger value increases the weight of the discharge current change rate term in the discharge cost function, thus constraining the discharge current from fluctuating significantly.

[0033] To ensure that the lithium battery discharge current can quickly reach a constant current discharge value, and to avoid fluctuations in the lithium battery discharge current after the discharge reaches a stable state, thereby improving the safety of the lithium battery discharge process and preventing overheating during discharge that could damage the battery's lifespan, step S11 can be used to obtain the discharge cost function based on the discharge constraint parameters. Specifically, the discharge cost function can be obtained according to formula (8). (8) in, Let the discharge cost function be... This represents the constant current discharge current value. The discharge cost function includes discharge constraint terms for the discharge process. There are constraints on the stable tracking of the discharge current and the rate of change of the discharge current in lithium batteries. During the initial charging phase, the discharge constraint parameters... With a relatively small value, the discharge cost function mainly enables the lithium battery discharge current to quickly track the constant current discharge current value. To achieve rapid constant current discharge; when the lithium battery discharge current approaches the constant current discharge current value Then, the discharge constraint parameters As the value increases, the discharge cost function mainly constrains the fluctuation of the discharge current at the lithium battery terminal, ensuring that the discharge current of the lithium battery will not fluctuate significantly, thus achieving the goal of stable current discharge.

[0034] Step S12 can be used to obtain the optimal discharge duty cycle of the PWM wave based on the discharge cost function, and enter the discharge protection state when the discharge voltage is lower than the discharge protection voltage value, thereby achieving stable discharge of the lithium battery. According to formula (8), the discharge cost function has formula (18). (18) The optimal discharge duty cycle of the PWM wave during lithium battery discharge can be obtained according to formula (18), specifically expressed by formula (9). (9) in, To achieve the optimal discharge duty cycle for the PWM wave, , The inductance value for connecting to the lithium battery terminal. The switching period is used to determine the optimal duty cycle of the PWM waveform. Automatically updated based on the real-time discharge status of the lithium battery; when the discharge voltage during the lithium battery discharge process falls below the discharge protection voltage value. At that time, the optimal discharge duty cycle of the PWM wave It will become 0 and thus Turn off; the duty cycle is obtained as The PWM wave acts on the four switches of the bidirectional Buck-Boost converter. Above, control The switching on and off of the circuitry is used to achieve stable discharge of the lithium battery.

[0035] In one example of this invention, a simulation analysis of a bidirectional Buck-Boost converter control method for lithium battery energy storage is performed. The simulation parameters are: DC bus voltage of 1100V, and four switching transistors with freewheeling diodes. The bridge circuit is used, with the lithium battery constant current charging current set to 100A, the constant voltage charging threshold set to 480V, the constant current discharging current set to 100A, and the inductance value set to 5mH. This control method is used to achieve energy storage control of a lithium battery based on a bidirectional Buck-Boost converter. The simulation waveform is shown below. Figure 4 As shown in the simulation waveforms, during the charging process, the lithium battery charging current can quickly reach a constant charging current value of 100A. During constant current charging, the lithium battery terminal voltage gradually increases, entering constant voltage charging state when it reaches the constant voltage charging threshold of 480V. The lithium battery charging current gradually decreases without current overshoot, and the transition from constant current charging overshoot to constant voltage charging is very smooth. During the discharging process, the lithium battery discharging current can quickly reach a constant discharging current value of 100A. The current during discharging is almost stable at the set discharging current value of 100A, resulting in a smooth and efficient discharging process. The simulation waveforms demonstrate that this invention enables the bidirectional Buck-Boost converter control of lithium battery energy storage to achieve a smooth and efficient lithium battery charging and discharging process. During charging and discharging, the lithium battery current can quickly stabilize at the set value without current overshoot or fluctuation, achieving safe and efficient charging and discharging control performance for lithium batteries.

[0036] On the other hand, the present invention also provides a control system for a bidirectional Buck-Boost converter for lithium battery energy storage, the control system including a processor for executing the control method as described in any of the above.

[0037] Through the above technical solution, this invention provides a control method and system for a bidirectional Buck-Boost converter for lithium battery energy storage. By obtaining the main circuit model of the bidirectional Buck-Boost converter, a constraint model of the bidirectional Buck-Boost converter is constructed based on the main circuit model. The charging current and charging voltage prediction values ​​for the next switching cycle, or the discharging current prediction value for the next switching cycle, are predicted based on the constraint model to adjust the charging constraint parameters or discharging constraint parameters. A cost function is obtained based on the constraint parameters, and the optimal charging duty cycle or optimal discharging duty cycle of the PWM wave is obtained based on the cost function, achieving stable discharge or charging of the lithium battery. This invention enables the bidirectional Buck-Boost converter control of lithium battery energy storage to achieve a stable and efficient lithium battery charging and discharging process. During charging and discharging, the lithium battery current can quickly stabilize to a set value without current overshoot or fluctuations, achieving safe and efficient charging and discharging control performance for the lithium battery.

[0038] Those skilled in the art will understand that embodiments of this application can be provided as methods, systems, or computer program products. Therefore, this application can take the form of a completely hardware embodiment, a completely software embodiment, or an embodiment combining software and hardware aspects. Furthermore, this application can take the form of a computer program product embodied on one or more computer-usable storage media (including but not limited to disk storage, CD-ROM, optical storage, etc.) containing computer-usable program code.

[0039] This application is described with reference to flowchart illustrations and / or block diagrams of methods, apparatus (systems), and computer program products according to embodiments of this application. It will be understood that each block of the flowchart illustrations and / or block diagrams, and combinations of blocks in the flowchart illustrations and / or block diagrams, can be implemented by computer program instructions. These computer program instructions can be provided to a processor of a general-purpose computer, special-purpose computer, embedded processor, or other programmable data processing apparatus to produce a machine, such that the instructions, which execute via the processor of the computer or other programmable data processing apparatus, generate instructions for implementing the flowchart... Figure 1 One or more processes and / or boxes Figure 1 A device that provides the functions specified in one or more boxes.

[0040] These computer program instructions may also be stored in a computer-readable storage medium that can direct a computer or other programmable data processing device to function in a particular manner, such that the instructions stored in the computer-readable storage medium produce an article of manufacture including instruction means, which are implemented in a process Figure 1 One or more processes and / or boxes Figure 1 The function specified in one or more boxes.

[0041] These computer program instructions may also be loaded onto a computer or other programmable data processing equipment to cause a series of operational steps to be performed on the computer or other programmable equipment to produce a computer-implemented process, thereby providing instructions that execute on the computer or other programmable equipment for implementing the process. Figure 1 One or more processes and / or boxes Figure 1 The steps of the function specified in one or more boxes.

[0042] In a typical configuration, a computing device includes one or more processors (CPU), input / output interfaces, network interfaces, and memory.

[0043] Memory may include non-persistent memory in computer-readable media, such as random access memory (RAM) and / or non-volatile memory, like read-only memory (ROM) or flash RAM. Memory is an example of computer-readable media.

[0044] Computer-readable media includes both permanent and non-permanent, removable and non-removable media that can store information using any method or technology. Information can be computer-readable instructions, data structures, modules of programs, or other data. Examples of computer storage media include, but are not limited to, phase-change memory (PRAM), static random access memory (SRAM), dynamic random access memory (DRAM), other types of random access memory (RAM), read-only memory (ROM), electrically erasable programmable read-only memory (EEPROM), flash memory or other memory technologies, CD-ROM, digital versatile optical disc (DVD) or other optical storage, magnetic tape, magnetic disk storage or other magnetic storage devices, or any other non-transferable medium that can be used to store information accessible by a computing device. As defined herein, computer-readable media does not include transient computer-readable media, such as modulated data signals and carrier waves.

[0045] It should also be noted that the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such process, method, article, or apparatus. Unless otherwise specified, an element defined by the phrase "comprising one..." does not exclude the presence of other identical elements in the process, method, article, or apparatus that includes that element.

[0046] The above are merely embodiments of this application and are not intended to limit the scope of this application. Various modifications and variations can be made to this application by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of this application should be included within the scope of the claims of this application.

Claims

1. A control method of a lithium battery energy storage bidirectional Buck-Boost converter, characterized in that, The control method includes: Obtain the main circuit model of the bidirectional Buck-Boost converter; Construct a bidirectional Buck-Boost converter constraint model based on the main circuit model; Obtain the charging current and charging voltage on the output lithium battery in the main circuit model, and preset the constant current charging current value and charging voltage threshold. The constraint model is used to predict the charging current and charging voltage for the next switching cycle based on the charging current and charging voltage. Adjust the charging constraint parameters based on the charging current, charging voltage, constant current charging current value, and charging voltage threshold. Based on the charging constraint parameters, obtain the charging cost function; Based on the charging cost function, the optimal charging duty cycle of the PWM wave is obtained to achieve stable charging of the lithium battery. Obtain the discharge current and discharge voltage of the lithium battery at the input terminal in the main circuit model, and preset the constant current discharge current value and discharge protection voltage value; The constraint model is used to predict the discharge current for the next switching cycle based on the discharge current and discharge voltage. Adjust the discharge constraint parameters based on the discharge current, discharge voltage, and constant current discharge current value; Based on the discharge constraint parameters, obtain the discharge cost function; Based on the discharge cost function, the optimal discharge duty cycle of the PWM wave is obtained, and the discharge protection state is entered when the discharge voltage is lower than the discharge protection voltage value, so as to realize the stable discharge of the lithium battery.

2. The control method according to claim 1, characterized by, The constraint model predicts the charging current and charging voltage for the next switching cycle based on the charging current and charging voltage, including: The predicted charging current for the next switching cycle is obtained according to formula (1). ，（1） in, For the next Predicted charging current of lithium battery during switching cycle. , The inductance value for connecting to the lithium battery terminal. For the switching cycle, The duty cycle during which the inductor discharges energy is the entire switching cycle. For the present DC bus voltage during the switching cycle For the present Charging voltage during the switching cycle, For the present The charging current during the switching cycle; The predicted charging voltage for the next switching cycle is obtained according to formula (2). ，（2） in, For the next Predicted charging voltage of lithium battery during switching cycle. The equivalent capacitance value during the charging process of a lithium battery.

3. The control method according to claim 2, characterized in that, Adjust the charging constraint parameters based on the charging current, charging voltage, constant current charging current value, and charging voltage threshold, including: The charging constraint parameters are obtained according to formula (3). ，（3） in, For charging constraint parameters, This represents the error value between the charging voltage and the charging voltage threshold. Error value The lower limit, Error value The upper limit.

4. The control method according to claim 3, characterized by, Based on the charging constraint parameters, the charging cost function is obtained, including: The charging cost function is obtained according to formula (4). ，（4） wherein, is a charging cost function, is a constant current charging current value, is a charging voltage threshold.

5. The control method according to claim 4, characterized by, Based on the charging cost function, the optimal charging duty cycle of the PWM wave is obtained to achieve stable charging of the lithium battery, including: The optimal charging duty cycle of the PWM wave is obtained according to formula (5). ，（5） wherein, Doptis the optimal charging duty cycle for the PWM wave.

6. The control method according to claim 1, characterized by The constraint model predicts the discharge current for the next switching cycle based on the discharge current and discharge voltage, including: The predicted discharge current for the next switching cycle is obtained according to formula (6). ，（6） in, For the next Predicted discharge current of lithium battery during switching cycle. For the present Discharge voltage during the switching cycle, For the present DC bus voltage during the switching cycle For the present Discharge current during the switching cycle.

7. The control method according to claim 6, characterized by Adjust the discharge constraint parameters based on the discharge current, discharge voltage, and constant current discharge current value, including: The discharge constraint parameters are obtained according to formula (7). ，（7） in, These are parameters for the discharge constraint term. This represents the error value between the discharge current and the constant current discharge current. For the next Predicted discharge current of lithium battery during switching cycle and current The difference in discharge current during the switching cycle.

8. The control method according to claim 7, characterized in that, Based on the discharge constraint parameters, the discharge cost function is obtained, including: The discharge cost function is obtained according to formula (8). ，（8） wherein, is the discharge cost function, is the constant current discharge current value.

9. The control method according to claim 8, characterized by, Based on the discharge cost function, the optimal discharge duty cycle of the PWM wave is obtained. When the discharge voltage is lower than the discharge protection voltage value, the system enters a discharge protection state to achieve stable discharge of the lithium battery, including: The optimal discharge duty cycle of the PWM wave is obtained according to formula (9). ，（9） wherein, is the optimal discharge duty cycle of the PWM wave, , is the inductance value connected to the lithium battery terminal, is the switching period.

10. A lithium battery energy storage bidirectional Buck-Boost converter control system, characterized in that, The control system includes a processor for executing the control method as described in any one of claims 1 to 9.

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