FSBB super capacitor energy storage method based on feedforward-single loop control

Abstract

The invention discloses an FSBB super capacitor energy storage method based on feedforward-single loop control, and relates to the field of energy storage systems. According to the invention, the feed-forward channel is added in the control process, so that the dynamic response speed when the input and output voltage of the system changes in a wide voltage range is improved, the sensitivity of the system to parameters is reduced, and the harmful phenomena such as circulation and the like caused by untimely response or incapability of accurately reaching a set value are prevented; therefore, the lithium battery and the super capacitor are damaged. The voltage and current of the lithium battery and the voltage and current of the supercapacitor bank are detected through real-time sampling, the working power of the lithium battery and the working power of the supercapacitor bank are calculated, corresponding power closed-loop control is carried out, the problems of charging and discharging over-current and over-voltage of the lithium battery and the supercapacitor are effectively avoided, and the stability of the system is improved.

Description

Technical Field

[0001] The present invention relates to an energy storage system, and in particular, to an energy storage system using FSBB for energy conversion. Background Art

[0002] To implement a distributed energy system, it is necessary to focus on improving the flexibility and reliability of the energy system. Among them, high-power and high-response energy storage technologies are the key supports for ensuring the stable operation of the power system and promoting the consumption of renewable energy. Supercapacitors have irreplaceable advantages in scenarios such as electric energy storage, new energy grid connection, and rail transit braking energy recovery due to their instantaneous charge and discharge capabilities, long cycle life, and low-temperature characteristics. However, with the rapid increase in the scale and complexity of the power system, supercapacitor energy storage systems are facing severe challenges in dynamic response, efficiency optimization, and stable control. From the perspective of technical applications, the failure of supercapacitor control may cause problems such as overvoltage and overcurrent, resulting in thermal runaway and life attenuation of supercapacitor modules and lithium battery modules, and even triggering safety accidents. Moreover, the system recovery after a fault requires a large amount of resources and incurs high economic costs. Therefore, it is crucial to design a control method for supercapacitor energy storage systems that can adapt to high dynamics and wide operating conditions.

[0003] Although traditional double-loop control strategies are widely used in energy storage inverters, their cascaded structure has problems such as a large adjustment range and complex parameter tuning, making it difficult to meet the millisecond-level requirements of supercapacitor transient power modulation. The time-domain simulation method relies on an accurate model and takes a long time to calculate when the operating conditions change suddenly, and cannot be adapted in real time. Although direct current control has a simple structure, it is easily affected by input voltage disturbances and load mutations, resulting in mode switching oscillations and a sharp drop in efficiency. In contrast, the single-loop control method based on feed-forward compensation can significantly improve the response speed and robustness through disturbance prediction and dynamic correction.

[0004] Currently, there are still technical bottlenecks in supercapacitor energy storage systems based on the FSBB topology: on the one hand, traditional control strategies are difficult to balance dynamic response and steady-state accuracy, and problems such as high-frequency switching losses and electromagnetic interference are prominent; on the other hand, the existing methods have insufficient adaptability to non-linear factors such as the time-varying characteristics of supercapacitor internal resistance and temperature drift, resulting in the accumulation of model prediction errors and restricting the reliability of the system. Although algorithms such as MPC and SMC have optimization potential in theory, they rely on high-precision parameter identification and massive data training, and face challenges such as poor real-time performance and limited hardware computing power in engineering applications. Therefore, there is an urgent need for a new control architecture that takes into account rapidity, efficiency, and robustness to unleash the technical potential of supercapacitor energy storage in high-fluctuation scenarios. Summary of the Invention

[0005] The object of the present invention is to propose a control method based on feedforward-single loop for the problems existing in the traditional double-loop control. By coarsely modeling the system and combining with the current loop, constant power energy conversion control is realized, the system response is improved, the sensitivity of the system to parameters is reduced, and the possibility of system instability is reduced.

[0006] To achieve the above object, the present invention adopts the following scheme: Step 1: Using the voltage sampling part and current sampling part in the system, sample and record the terminal voltage and output current of the four-switch BUCK-BOOST supercapacitor, the terminal voltage and output current of the four-switch BUCK-BOOST battery, and the voltage and output current of the lithium battery in the system.

[0007] Step 2: Calculate the output power of the lithium battery and the output power of the supercapacitor bank through the sampled data, and compare the obtained power with the rated power of the lithium battery.

[0008] Step 3: According to the power calculated in Step 2, compare the battery output power P bat with the battery rated power P rated If P rated is greater than P bat , then adjust the capacitor charging power to make ; if P rated is less than P bat , then adjust the capacitor discharging power to make , where P sc both refer to the charging power of the supercapacitor bank, that is, it is negative when discharging.

[0009] Step 4: According to P sc calculated in Step 3, combined with the voltage U sc of the supercapacitor bank obtained by sampling, calculate the required charging current of the supercapacitor bank.

[0010] Step 5: According to I sc calculated in Step 4, use PD control by the current loop to calculate the MOSFET duty cycle gain value, and add it to the feedforward quantity to obtain the total MOSFET duty cycle gain value.

[0011] Step 6: According to the total gain value obtained in Step 5, calculate the on-duty cycle of the four MOSFETs, where the MOSFET numbers are as Figure 2 shown.S 1 and S 2 are complementarily turned on, S 3 and S 4 are complementarily turned on.

[0012] Step 7: Enter the next control cycle, re - perform sampling, judgment, and control, and dynamically adjust the charging and discharging power of the supercapacitor bank until the working mode changes.

[0013] Furthermore, the FSBB supercapacitor energy storage system based on feed - forward - single - loop control of the present invention is characterized in that the system is composed of a lithium battery, a supercapacitor bank, a control board, and a power board, and has a topological structure as Figure 2 shown.

[0014] Furthermore, the FSBB supercapacitor energy storage system based on feed - forward - single - loop control of the present invention is characterized in that FSBB refers to four - switch BUCK - BOOST, and the topological diagram of the four - switch BUCK - BOOST is as Figure 2 shown.

[0015] Furthermore, in step 2, the calculation of the lithium - battery power and the supercapacitor charging power follows the following formula:

[0016] The rated power in step 3 P rated is determined by the lithium - battery nameplate and the calculation follows the following formula:

[0017] Furthermore, the charging current of the supercapacitor bank in step 4 I sc , and the calculation process follows the following formula:

[0018] Furthermore, the calculation of the duty - cycle gain value in step 5 follows the following formula:

[0019]

[0020] where G ff represents the gain feed - forward quantity, G pd represents the gain increment obtained by PD control, G is the total gain, and the gain is used to calculate the MOSFET duty - cycle in step 7.

[0021] Furthermore, the duty - cycle in step 7 is given by the following formula:

[0022]

[0023] Wherein, D 1 refers to S the on-duty ratio corresponding to 1, D 3 refers to S the on-duty ratio corresponding to 3.

[0024] The above technical solution of the embodiment of the present invention has the following beneficial technical effects: 1. By adding a feedforward channel to the control process, the dynamic response speed of the system input and output voltages when changing within a wide voltage range is improved, and the sensitivity of the system to parameters is reduced, preventing harmful phenomena such as circulating current due to untimely response or inability to accurately reach the set value, thereby damaging the lithium battery and supercapacitor.

[0025] 2. By detecting the voltage and current of the lithium battery and the voltage and current of the supercapacitor bank through real-time sampling, calculating their working power, and performing corresponding power closed-loop control, the problems of overcurrent and overvoltage during charging and discharging of the lithium battery and supercapacitor are effectively avoided, and the stability of the system is improved. Description of the Drawings

[0026] Figure 1 is a flowchart when the FSBB supercapacitor energy storage system based on feedforward-single loop control is operating.

[0027] Figure 2 is a schematic diagram of the PD-feedforward control process.

[0028] Figure 3 is a topology diagram of the four-switch BUCK-BOOST converter applied to the FSBB supercapacitor energy storage system based on feedforward-single loop control.

[0029] Figure 4 is a schematic diagram of the control board of the FSBB supercapacitor energy storage system based on feedforward-single loop control.

[0030] Figure 5 is a schematic diagram of the power board of the FSBB supercapacitor energy storage system based on feedforward-single loop control. Detailed Embodiment

[0031] The following further describes the present invention in detail in conjunction with the drawings and specific implementation examples.

[0032] The system should operate in a DC energy storage system with medium and low voltage and medium and high current, with the operating voltage not exceeding 48V and the operating current not exceeding 16A. It is especially suitable for small and medium-sized lithium battery-powered devices, such as robot platforms, mobile device platforms, etc.

[0033] Figure 1 The flowchart during the system operation is given. When the system starts to work, initialization is carried out first. After the initialization is completed, voltage and current sampling are performed, and the working state of the lithium battery is judged periodically. If it is detected that the lithium battery is working in an over-discharge state, the supercapacitor bank is controlled to discharge at a constant power, so as to reduce the discharge current of the lithium battery and relieve the over-discharge situation; if it is detected that the lithium battery is not working in an over-discharge state, the supercapacitor bank is controlled to charge at a constant power for energy storage for subsequent discharge. When controlling the charging or discharging of the supercapacitor bank, the working state of the lithium battery is judged again. If the lithium battery still shows an over-discharge state, the discharge power of the supercapacitor bank is increased or the charging power of the supercapacitor bank is decreased; if the lithium battery does not show an over-discharge state, the discharge power of the supercapacitor bank is decreased or the charging power of the supercapacitor bank is increased, and finally the purpose of maintaining the discharge power of the lithium battery at the rated value is achieved.

[0034] Figure 2 The specific block diagram of the system control is given. In the figure, the ratio of current to voltage is used as the input of the controller, and the voltage gain G is used as the output of the controller. First, a PD control is performed on the controlled object, e(t) is the difference between the input value and the output value. After being output by the PD controller, it is added to the gain G ff obtained by the feed-forward control to get the final output value.

[0035] Figure 3 The circuit topology diagram of the four-switch BUCK-BOOST converter is given. Among them, C in is the input filter capacitor, S1, S2, S3, S4 are switching tubes, here are MOSFETs, L is the inductor, and C out is the output filter capacitor. Here, it is stipulated that the positive direction of the current is from left to right, corresponding to U bat is the voltage of the lithium battery, and U sc is the voltage of the supercapacitor bank.

[0036] Figure 4The system control board PCB schematic diagram is given. Module 1 is an interface, including power interface CN1, U1, U2, U5, and communication interfaces U6, U7, U8, and also contains sampling resistor R1 and signal filtering capacitors C11, C12, C18, C19. Module 2 is the upper and lower board connectors H1 - H3, U4 and signal filtering capacitors C1, C2, C5, C6, C9, C10, C13, C14, pull-up and pull-down resistors R2 - R7, R11, R12. Module 3 is a 24V to 12V power module, including main chip U3 and voltage-dividing resistors R8 - R10, filtering capacitors C3, C4, C7, C8. Module 4 is a 24V to 5V power module, including main chip U9 and voltage-dividing resistors R15 - R17, filtering capacitors C15 - C17, C20 - C24, inductor U10. Module 5 is a MOSFET drive module, containing drive chips U13, U19, pull-up and pull-down resistors R19, R20, R29, R30, filtering capacitors C35, C38, C43, C53. Module 6 is a 5V to 3.3V power module, containing main chip Q1 and corresponding filtering capacitors C25, C26. Module 7 is a voltage reference module, containing main chips U11, U12 and corresponding voltage-dividing resistors R18, R21, R22, filtering capacitors C27 - C29, C31, C33, Schottky diode D1. Module 8 is a sampling module, containing voltage sampling chip U20, current sampling chips U16 - U18, voltage-dividing resistors R25 - R28, impedance matching resistors R23, R24, R32 - R34, filtering capacitors C30, C32, C34, C40 - C41, C45 - C47, filtering beads L2 - L4.

[0037] Figure 5 The system power board PCB schematic diagram is given, which includes filtering capacitors C1 - C32, MOS transistors S1 - S4, anti-parallel Schottky diodes D1 - D4, inductor L1, sampling resistors R1, R2, pull-up and pull-down resistors R3 - R6 and upper and lower board connection interfaces H1 - H3, CN1, CN2.

[0038] As Figure 1 shown, the FSBB supercapacitor energy storage system based on feedforward - single loop control proposed by the present invention includes the following steps: Step 1, before the system starts to run normally, first perform system initialization, including turning on peripherals such as ADC, HRTIM, DMA, CAN of the STM32F334C8T6 chip; calibrating the ADC accuracy; inputting the rated performance of the lithium battery and other steps.

[0039] Step 2: Using the operational amplifier and sampling resistors on the control board, sample and convert the terminal voltage and output current of the four-switch BUCK-BOOST supercapacitor, the terminal voltage and output current of the four-switch BUCK-BOOST battery, and the voltage and output current of the lithium battery, and convert the original sampled values into actual values in the actual physical model according to a ratio.

[0040] Step 3: Calculate the output power of the lithium battery based on the lithium battery voltage and its output current obtained in Step 2, compare it with the rated value of the lithium battery entered in Step 1, and determine whether the lithium battery has experienced over-discharge.

[0041] If it is determined that the lithium battery has experienced over-discharge, then control the supercapacitor bank to discharge, reduce the degree of over-discharge of the lithium battery, and determine again whether the lithium battery has reached the rated operating power. If the situation of exceeding the rated power occurs, then increase the discharge power of the supercapacitor bank in the next cycle for compensation; if it has been adjusted to reach or slightly less than the rated power, then maintain the current working state.

[0042] If it is determined that the lithium battery does not currently experience over-discharge, that is, there is still redundant power that can be output, then control the supercapacitor to charge, store the redundant energy into the supercapacitor bank for preparation during discharge, and then determine whether the lithium battery has reached the rated operating power. If the situation of exceeding the rated power occurs, then reduce the charging power of the supercapacitor bank in the next cycle; if it has been adjusted to reach or slightly less than the rated power, then maintain the current working state.

[0043] Step 4: In Step 3, the charging or discharging power required by the supercapacitor bank has been obtained. Use the algorithm set in the program to control the four switching tubes of the four-switch BUCK-BOOST. Specifically, from the required power P sc and the sampled supercapacitor bank voltage U sc obtain the required current I sc .

[0044] Step 5: Obtain the charging current of the supercapacitor bank in Step 4, and implement PD-feedforward control according to the control flow shown in Figure 2 where

[0045] Step 6: According to G obtained in Step 5, calculate the duty cycle of each switching tube in the four-switch BUCK-BOOST converter as shown in Figure 3 . The calculation process is according to the following formula:

[0046]

[0047] D 1 is the switch S The duty cycle corresponding to 1, D 3 is the switch S The duty cycle corresponding to 3. 0.9 is a relatively safe duty cycle threshold obtained through experiments. This value will vary for different MOSFETs and driver chips. If the value here is greater than 0.9, there may be a problem of untimely turn-off, resulting in device burnout.

[0048] According to the above steps, the efficient and safe operation of the system can be ensured during normal operation.

[0049] Finally, it should be noted that: The above is only one embodiment of the present invention and is not intended to limit the present invention. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art can still modify the foregoing specific implementation methods or perform equivalent replacements for some of the technical steps. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principle of the present invention shall be included within the protection scope of the present invention.

Claims

1. A method for supercapacitor energy storage based on feedforward-single loop control, characterized in that It includes the following steps: Step 1: Use the voltage sampling part and current sampling part in the system to sample and record the terminal voltage and output current of the four-switch BUCK-BOOST supercapacitor in the system, the terminal voltage and output current of the four-switch BUCK-BOOST battery, and the voltage and output current of the lithium battery; Step 2: Calculate the output power of the lithium battery and the output power of the supercapacitor bank based on the sampled data, and compare the obtained power with the rated power of the lithium battery; Step 3: According to the power calculated in Step 2, make the battery output power P bat compared with the rated power P rated of the battery. If P rated is greater than P bat , adjust the capacitor charging power so that P bat + P sc = P rated ; if P rated is less than P bat , adjust the capacitor discharging power so that P bat + P sc = P rated . Here, P sc refers to the charging power of the supercapacitor bank, which is negative during discharging; Step 4: According to P calculated in Step 3 sc , combined with the voltage U of the supercapacitor bank obtained by sampling sc , calculate the required charging current of the supercapacitor bank; Step Five: According to I calculated in Step Four sc , the duty cycle gain value of the MOSFET is calculated by the current loop using PD control, and added to the feedforward amount to obtain the total duty cycle gain value of the MOSFET; Step 6: According to the total gain value obtained in Step 5, calculate the on-duty ratios of the four MOSFETs. S1 and S2 are turned on complementarily, and S3 and S4 are turned on complementarily; Step 7: Enter the next control cycle, re-perform sampling, judgment, and control, and dynamically adjust the charging and discharging power of the supercapacitor bank until the working mode changes.

2. The FSBB supercapacitor energy storage method based on feedforward-single loop control according to claim 1, wherein The system consists of a lithium battery, a supercapacitor bank, a control board, and a power board. Its topological structure is described as follows: The lithium battery supplies power to the control board and the power board, serves as the primary side of the FSBB, and also supplies power to the load; The supercapacitor bank is only connected to the power board and serves as the secondary side of the FSBB.

3. The FSBB supercapacitor energy storage method based on feedforward-single loop control according to claim 1, wherein, FSBB refers to four-switch BUCK-BOOST.

4. The FSBB supercapacitor energy storage method based on feedforward-single loop control according to claim 1, wherein In Step 2, the calculation of the lithium battery power and the supercapacitor charging power follows the following formula: Give the physical meaning of the letters in the formula P bat = U bat I bat , P sc = U sc I sc In the formula: P bat —— Output power of the lithium battery; U bat —— Lithium battery voltage; I bat —— Output current of the lithium battery; P sc —— Output power of the supercapacitor bank; U sc —— Voltage of the supercapacitor bank; I sc —— Output current of the supercapacitor bank, The rated power P in step three rated is determined by the lithium battery nameplate and calculated according to the following formula: P rated = U rated I rated In the formula: P rated ——Rated output power of the lithium battery; U rated —— Rated voltage of the lithium battery; I rated —— Rated output current of the lithium battery.

5. The FSBB supercapacitor energy storage method based on feedforward-single loop control according to claim 1, wherein The charging current I of the supercapacitor bank in Step 4 sc , and the calculation process follows the following formula:

6. The FSBB supercapacitor energy storage method based on feedforward-single loop control according to claim 1, wherein The calculation of the duty ratio gain value in Step 5 follows the following formula: G = G ff +G pd Among them, G ff represents the feedforward gain amount, and G pd represents the gain increment obtained by PD control. G is the total gain, and the gain is used to calculate the MOSFET duty cycle in step seven.

7. The FSBB supercapacitor energy storage method based on feedforward-single loop control according to claim 1, wherein The duty ratio in Step 6 is given by the following formula: In the formula, D1 refers to the on-duty ratio corresponding to S1, and D3 refers to the on-duty ratio corresponding to S3.

8. The FSBB supercapacitor energy storage method based on feedforward-single loop control according to claim 1, characterized in that The threshold of the switch tube duty ratio in Step 6 is set not to exceed 0.9, and when the calculated duty ratio exceeds the threshold, it is forcibly limited to the threshold to avoid hardware damage to the switch tube due to signal delay.

9. The FSBB supercapacitor energy storage system based on feedforward-single loop control according to claim 1, wherein The FSBB converter consists of two upper and lower PCB boards. The control board is a FR4 substrate, and the power board is an aluminum substrate.

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