Full-soft switching charge-discharge control method and device for intelligent lithium battery

Abstract

The application discloses a full-soft-switching charge-discharge control method and device for an intelligent lithium battery. According to the first bridge arm side voltage, the second bridge arm side voltage and the circuit parameters of a bidirectional four-switch converter, the soft-switching current threshold corresponding to the bridge arm to be commutated under the current operating condition is determined, and the energy transmission time determined by the feedback regulation loop is combined to determine the conduction timing of each switch tube, so that the inductance current can reach the corresponding soft-switching current threshold before the bridge arm commutation, the parasitic capacitance of the switch tube in the bridge arm is charged and discharged by the inductance current, and the switch tube to be turned on is turned on when the soft turn-on condition is met. Based on this, the current condition and the conduction timing adopted by the soft-switching control adapt to the current voltage condition and the energy transmission demand of the converter, the reliability of the soft turn-on under different conditions is improved, the turn-on loss is reduced, and the inductance circulating current and the conduction loss caused by the excessive commutation margin are reduced.

Description

Technical Field

[0001] This invention relates to the field of power electronics technology, and in particular to a fully soft-switching charging and discharging control method and device for a smart lithium battery. Background Technology

[0002] Lithium-ion battery charging and discharging systems typically use bidirectional DC-DC converters to control the bidirectional power transfer between the lithium-ion battery and the DC bus, thereby enabling the charging and discharging of the lithium-ion battery. As the charging and discharging power and switching frequency of the lithium-ion battery increase, the switching losses, device temperature rise, and electromagnetic interference generated by the switching transistors in the converter under hard-switching conditions gradually increase.

[0003] The bidirectional four-switch converter enables bidirectional power transfer between the two DC sides. It typically consists of two bridge arms and an inductor connected between the midpoints of the two bridge arms. Each bridge arm is composed of two switches connected in series. By controlling the switches to turn on or off according to a specific timing sequence, the voltage across the inductor can be changed, thereby controlling the inductor current and the power transfer between the two DC sides.

[0004] In the operation of a bidirectional four-switch converter, the turn-on loss of the switching transistors is a crucial factor affecting the converter's efficiency and performance. To reduce turn-on losses, the inductor current can be used to charge or discharge the parasitic capacitance of the switching transistors during bridge arm commutation, causing the transistor to turn on after the voltage across its terminals decreases. However, the voltages across the converter and the load conditions may change during operation, and the commutation conditions required for soft turn-on vary under different operating conditions. If a fixed switching sequence or commutation is performed according to a pre-set fixed current condition, in some operating conditions, the transistor may turn on before the voltage across its terminals has sufficiently decreased, making it difficult to reliably achieve soft turn-on over a wide operating range. Conversely, if an excessively large commutation margin is reserved to ensure soft turn-on, it may generate a large circulating current in the inductor, increasing conduction losses.

[0005] Therefore, how to balance the reliability of soft turn-on of the switching transistors with the operating losses of the converter under different operating conditions has become a technical problem that needs to be solved in this field. Summary of the Invention

[0006] The purpose of this invention is to provide a fully soft-switching charging and discharging control method and device for intelligent lithium batteries, so that the current conditions and conduction timing adopted by the soft-switching control can adapt to the current voltage conditions and power transmission requirements of the converter. While ensuring normal power transmission, it improves the reliability of soft switching under different operating conditions, reduces switching losses, and reduces inductor circulating current and conduction losses caused by excessive commutation margin.

[0007] To address the aforementioned technical problems, this invention provides a fully soft-switching charge and discharge control method for a smart lithium battery, applied to a smart lithium battery charge and discharge system. The smart lithium battery charge and discharge system includes a lithium battery and a bidirectional four-switch converter connected to the lithium battery. The bidirectional four-switch converter includes two bridge arms and an inductor connected between the midpoints of the two bridge arms. Each bridge arm includes two switching transistors connected in series. The method includes: Obtain the first bridge arm side voltage and the second bridge arm side voltage of the bidirectional four-switch converter; Based on the voltage of the first bridge arm, the voltage of the second bridge arm, and the circuit parameters of the bidirectional four-switch converter, determine the soft-switching current threshold corresponding to the bridge arm to be commutated. Based on the second arm side voltage of the bidirectional four-switch converter, the energy transfer time within a switching cycle is determined through a feedback adjustment loop. Based on the soft-switching current threshold, the voltage on the first bridge arm side, the voltage on the second bridge arm side, the inductance value of the inductor, and the energy transfer time, the conduction sequence of each switch in the two bridge arms during the switching cycle is determined. According to the conduction timing, drive signals are generated for each of the switching transistors so that the current of the inductor reaches the soft-switching current threshold corresponding to the bridge arm to be switched before the bridge arm to be switched is switched, and the switching transistor to be turned on in the bridge arm to be switched is soft-turned on.

[0008] Preferably, the circuit parameters of the bidirectional four-switch converter include the parasitic capacitance values ​​of each of the switching transistors; Based on the voltage on the first bridge arm, the voltage on the second bridge arm, and the circuit parameters of the bidirectional four-switch converter, determine the soft-switching current threshold corresponding to the bridge arm to be commutated, including: Based on the voltage on the first bridge arm, the voltage on the second bridge arm, the inductance value of the inductor, and the parasitic capacitance value of each switch, a soft-switching current threshold is determined to ensure that the switch to be turned on in the bridge arm to be commutated meets the zero-voltage turn-on condition.

[0009] Preferably, the two bridge arms include a first bridge arm and a second bridge arm, and the soft-switching current threshold includes a first soft-switching current threshold and a second soft-switching current threshold. The first soft-switching current threshold is a current threshold that has a current direction from the first bridge arm to the second bridge arm and enables the corresponding switch to be turned on to meet the zero-voltage turn-on condition. The second soft-switching current threshold is a current threshold that has a current direction from the second bridge arm to the first bridge arm and enables the corresponding switch to be turned on to meet the zero-voltage turn-on condition.

[0010] Preferably, it further includes: According to the sampling parameters of the inductor current sampling circuit 4, the first soft-switching current threshold and the second soft-switching current threshold are converted into a first comparison reference value and a second comparison reference value, respectively; the inductor current sampling circuit 4 is used to sample the current of the inductor; The current sampling value of the inductor current sampling circuit 4 is acquired in real time, and the current sampling value is compared with the comparison reference value corresponding to the current bridge arm commutation in the first comparison reference value or the second comparison reference value. If the current sampling value reaches the comparison reference value corresponding to this bridge arm commutation earlier than the planned turn-off time determined according to the conduction sequence, then the current conducting switch in the bridge arm to be commutated is turned off in advance, and after a preset dead time, the switch to be turned on in the bridge arm to be commutated is turned on. If the current sampling value does not reach the comparison reference value corresponding to this bridge arm commutation before the planned turn-off time, then each of the switching transistors is controlled according to the conduction timing sequence.

[0011] Preferably, the switching cycle includes a first time period, a second time period, a third time period, and a fourth time period set sequentially; The first time period is used to control the current of the inductor to change to a soft-switching current threshold with a first current direction. The duration of the second time period is the energy transmission time and is used to transmit electrical energy through the inductor. The third time period is used to control the current of the inductor to change to a soft-switching current threshold with a second current direction, which is opposite to the first current direction. The fourth time period is the remaining time period within the switching cycle excluding the first time period, the second time period, and the third time period.

[0012] Preferably, it further includes: Obtain the output current of the bidirectional four-switch converter under the current power transmission direction; The time compensation parameters are determined based on the first bridge arm side voltage, the second bridge arm side voltage, the output side current, and the energy transfer time. The first time period or the third time period is compensated according to the time compensation parameters.

[0013] Preferably, the time compensation parameter is determined by a pre-established correspondence, which is established by adjusting the first time period or the third time period under different first bridge arm side voltages, second bridge arm side voltages, output side currents and energy transmission times, and determining the corresponding time compensation parameter based on the current of the inductor.

[0014] Preferably, compensating the first time period or the third time period according to the time compensation parameter includes: Determine the direction of power transmission of the bidirectional four-switch converter during the current switching cycle; When electrical energy is transmitted from the side where the first bridge arm is located to the side where the second bridge arm is located, the first time period is compensated according to the time compensation parameter; When electrical energy is transmitted from the side of the second bridge arm to the side of the first bridge arm, the third time period is compensated according to the time compensation parameter.

[0015] Preferably, compensation for the first time period or the third time period includes: Adjust the first time period or the third time period before compensation according to the time compensation parameters to obtain the first time period or the third time period after compensation. Based on the compensated first or third time period, the conduction sequence of each switch transistor within the switching cycle is re-determined.

[0016] To address the aforementioned technical problems, this invention provides a fully soft-switching charge and discharge control device for a smart lithium battery, comprising: Memory, used to store computer programs; A processor is used to implement the steps of the fully soft-switching charge and discharge control method for a smart lithium battery as described above when executing a computer program.

[0017] This application provides a fully soft-switching charge and discharge control method and apparatus for a smart lithium battery. Based on the first arm voltage, the second arm voltage, and circuit parameters of a bidirectional four-switch converter, the soft-switching current threshold corresponding to the arm to be commutated under the current operating conditions is determined. Combined with the energy transfer time determined by the feedback adjustment loop, the conduction sequence of each switch is determined, ensuring that the inductor current reaches the corresponding soft-switching current threshold before the arm commutation. This allows the inductor current to charge and discharge the parasitic capacitance of the switches in the arm, enabling the switch to be turned on when the soft-turn-on conditions are met. Based on this, the current conditions and conduction sequence used in the soft-switching control adapt to the current voltage conditions and energy transfer requirements of the converter. While ensuring normal energy transfer, this improves the reliability of soft-turn-on under different operating conditions, reduces turn-on losses, and lowers the inductor circulating current and conduction losses caused by excessive commutation margin. Attached Figure Description

[0018] To more clearly illustrate the embodiments of the present invention, the accompanying drawings used in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0019] Figure 1 A flowchart illustrating a fully soft-switching charge and discharge control method for a smart lithium battery provided in this application; Figure 2 A schematic diagram of a bidirectional four-switch converter provided in this application; Figure 3 A schematic diagram of the conduction timing of a switching transistor provided in this application; Figure 4 This is a schematic diagram of the structure of a fully soft-switching charge and discharge control device for a smart lithium battery provided in this application. Detailed Implementation

[0020] The core of this invention is to provide a fully soft-switching charging and discharging control method and device for intelligent lithium batteries, which enables the current conditions and conduction timing adopted by the soft-switching control to adapt to the current voltage conditions and power transmission requirements of the converter. While ensuring normal power transmission, it improves the reliability of soft switching under different operating conditions, reduces switching losses, and reduces inductor circulating current and conduction losses caused by excessive commutation margin.

[0021] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0022] Please refer to Figure 1 , Figure 1 This application provides a flowchart illustrating a fully soft-switching charge / discharge control method for a smart lithium battery, applicable to a smart lithium battery charge / discharge system. The system includes a lithium battery and a bidirectional four-switch converter connected to the battery. The bidirectional four-switch converter includes two bridge arms and an inductor L1 connected between the midpoints of the two bridge arms. Each bridge arm includes two switching transistors connected in series. Please refer to... Figure 2 , Figure 2This is a schematic diagram of a bidirectional four-switch converter provided in this application. In the diagram, 1 represents the bus voltage, 2 represents the bidirectional four-switch converter topology, 3 represents the smart lithium battery, 4 represents the inductor current sampling circuit, and 5 represents the processor and surrounding circuitry. For ease of explanation, the two bridge arms are referred to as the first bridge arm and the second bridge arm, respectively. The first bridge arm includes a first switch Q1 and a second switch Q2 connected in series, with the connection point between the first switch Q1 and the second switch Q2 being the midpoint of the first bridge arm. The second bridge arm includes a third switch Q3 and a fourth switch Q4 connected in series, with the connection point between the third switch Q3 and the fourth switch Q4 being the midpoint of the second bridge arm. An inductor L1 is connected between the midpoint of the first bridge arm and the midpoint of the second bridge arm.

[0023] The intelligent lithium battery in this embodiment may include a lithium battery and a processor for detecting and controlling the charging and discharging process of the lithium battery. The lithium battery is connected to the DC bus through a bidirectional four-switch converter. The processor can acquire the lithium battery voltage, bus voltage, inductor current, charging and discharging control commands, and target voltage, and determine the soft-switching current threshold, energy transfer time, and conduction sequence of each switch according to the acquired parameters to control the charging or discharging of the lithium battery. "Intelligent" means that the processor can dynamically determine the control parameters according to the current charging and discharging conditions of the lithium battery and the operating parameters of the bidirectional four-switch converter, and is not intended to limit the specific packaging form or communication method of the lithium battery. Full soft switching means that when the first switch Q1 to the fourth switch Q4 in the bidirectional four-switch converter are used as switches to be turned on for commutation in the two energy transfer directions corresponding to the charging and discharging of the lithium battery, the current of the inductor L1 reaches the corresponding soft-switching current threshold, and the parasitic capacitance of the switch to be turned on is discharged by the current of the inductor L1, so that the voltage across the switch to be turned on is reduced to meet the soft-turn-on condition before it is turned on. Therefore, the term "full soft switching" indicates that each switch in a bidirectional four-switch converter can achieve soft turn-on during its corresponding commutation process. It does not mean that each switch can achieve soft turn-on unconditionally under any load, any voltage, or any abnormal operating condition, nor does it mean that each switch can simultaneously achieve zero-voltage turn-on and zero-current turn-off.

[0024] The first and second bridge arms are each connected to a DC side. For example, the first bridge arm side can be connected to a DC bus, and the second bridge arm side can be connected to a battery; in other embodiments, the first and second bridge arms can also be connected to different energy storage units, DC loads, DC power supplies, or DC distribution buses. Since the bidirectional four-switch converter can transmit power in both directions, the first bridge arm side is not always the input side, and the second bridge arm side is not always the output side. Therefore, in this embodiment, the voltage on the first bridge arm side is referred to as the first bridge arm side voltage, and the voltage on the second bridge arm side is referred to as the second bridge arm side voltage.

[0025] The soft-switching control method provided in this embodiment can be executed by a digital signal processor, microcontroller, programmable logic controller, or other processor with arithmetic and pulse width modulation functions. The processor is connected to the voltage sampling circuits on both bridge arms and to the drive circuits of each switching transistor. The processor may also have an enhanced pulse width modulation module, which generates the corresponding drive signal for each switching transistor based on the calculated conduction timing.

[0026] The methods include: S11: Obtain the first and second bridge arm voltages of the bidirectional four-switch converter; The voltage on the first bridge arm side can be obtained through a first voltage sampling circuit connected to the side where the first bridge arm is located, and the voltage on the second bridge arm side can be obtained through a second voltage sampling circuit connected to the side where the second bridge arm is located. The first and second voltage sampling circuits can each include one or more of the following: a voltage divider resistor, a filter circuit, an isolation sampling circuit, and an analog-to-digital converter circuit. The processor can periodically read the sampling results from the first and second voltage sampling circuits, or it can read the corresponding sampling results before the start of each switching cycle.

[0027] In some embodiments, the voltage sampling results obtained at multiple consecutive sampling times can be averaged or digitally filtered, and the processed voltage values ​​can be determined as the first bridge arm voltage and the second bridge arm voltage, respectively. A switching cycle is typically much shorter than the time required for significant changes in the two bridge arm voltages. Therefore, when determining the conduction timing within the current switching cycle, the first and second bridge arm voltages can be considered to remain constant or approximately constant within the current switching cycle. This reduces the impact of single-sample noise on subsequent timing calculations while reflecting the current operating conditions.

[0028] S12: Determine the soft-switching current threshold corresponding to the bridge arm to be commutated based on the voltage of the first bridge arm, the voltage of the second bridge arm, and the circuit parameters of the bidirectional four-switch converter. The circuit parameters of a bidirectional four-switch converter refer to parameters that affect the commutation process of the bridge arm, the rate of change of inductor current, or the voltage change process across the switching transistor. These circuit parameters can be written into the memory before the product leaves the factory, or they can be determined by the processor based on the device model, temperature, or operating status. The soft-switching current threshold represents the current condition that the inductor L1 needs to reach before commutation in order for the switching transistor in the bridge arm to be commutated to meet the soft-turn-on conditions.

[0029] The bridge arm to be commutated can be either the first bridge arm or the second bridge arm. The currently conducting switch in the bridge arm to be commutated refers to the switch that is in the conducting state before commutation begins and will be turned off during the commutation process; the switch to be turned on refers to another switch located in the same bridge arm as the currently conducting switch and will be turned on after the dead zone ends. For example, when the first bridge arm switches from the conducting state of the first switch Q1 to the conducting state of the second switch Q2, the first bridge arm is the bridge arm to be commutated, the first switch Q1 is the currently conducting switch, and the second switch Q2 is the switch to be turned on.

[0030] In some embodiments, the soft-switching current threshold can be determined based on a pre-established correspondence between voltage conditions and current thresholds. The processor uses the current first-arm and second-arm voltages as lookup parameters to read the corresponding soft-switching current threshold from a lookup table. In other embodiments, the processor can calculate the soft-switching current threshold in real time based on the first-arm voltage, the second-arm voltage, and circuit parameters. Using a lookup table reduces the amount of computation the processor performs in each switching cycle, while real-time calculation allows the soft-switching current threshold to be determined based on sampled voltage changes.

[0031] S13: Based on the voltage on the second arm side of the bidirectional four-switch converter, the energy transfer time within one switching cycle is determined through a feedback adjustment loop. The feedback regulation loop receives the feedback value of the second-arm side voltage and the corresponding voltage reference value, and outputs the energy transfer time based on the deviation between the feedback value and the voltage reference value. Specifically, after the processor acquires the second-arm side voltage, it compares the second-arm side voltage with a preset target voltage to obtain the voltage deviation, and inputs the voltage deviation into the feedback regulation loop. The feedback regulation loop then determines the energy transfer time within one switching cycle. The output of the feedback regulation loop characterizes the required energy transfer level for the current switching cycle and can be converted into a second time period. The duration of the second time period. When the voltage on the second bridge arm side is lower than the preset target voltage and it is necessary to increase the electrical energy transmitted to the side where the second bridge arm is located, the feedback regulation loop can correspondingly increase the second time period. When the voltage on the second bridge arm side approaches the preset target voltage, the second time period can be reduced accordingly. Therefore, the second time period It is not determined solely by the magnitude relationship between the voltages on both sides, but rather dynamically determined by the feedback regulation loop based on the deviation between the current output voltage and the target voltage.

[0032] The preset target voltage can be determined based on the battery's target charging voltage, the rated operating voltage of the DC load, or a voltage command issued by the upper-level controller. During discharge, the voltage on the second arm side, serving as feedback, can also be adjusted to the controlled DC side voltage according to the direction of energy transfer. In other words, determining the energy transfer time based on the second arm side voltage can be understood as at least forming a feedback deviation based on the second arm side voltage and calculating the energy transfer time using the feedback adjustment loop.

[0033] The feedback control loop can be a proportional-integral-derivative (PID) control loop or a two-pole-two-zero control loop, i.e., a 2P2Z control loop. The 2P2Z control loop calculates the current control quantity based on the voltage deviation of the current sampling period, the voltage deviation of the previous sampling period, and the previously output control quantity, and converts this control quantity into energy transfer time. In other embodiments, the feedback control loop can also determine the energy transfer time based on the voltage and current on the second bridge arm side, to achieve constant voltage control, constant current control, or constant power control.

[0034] It should be noted that the energy transfer time of the feedback regulation loop output reflects the current power transfer demand, rather than directly representing the length of the entire switching cycle. By separately determining the energy transfer demand and the soft-switching current conditions required for bridge arm commutation, it is possible to reserve the corresponding inductor current change process for bridge arm commutation while meeting the output regulation requirements.

[0035] S14: Determine the conduction sequence of each switch in the two arms during the switching cycle based on the soft-switching current threshold, the voltage on the first arm side, the voltage on the second arm side, the inductance value of inductor L1, and the energy transfer time. The turn-on timing of each switch can include the turn-on time, turn-off time, conduction duration, and dead time between two switches in the same bridge arm. Based on the voltages of the first and second bridge arms and the inductance value, the processor can determine the voltage across inductor L1 when different switch combinations are turned on, and determine the time required for the current in inductor L1 to change from its current value to the soft-switching current threshold based on the relationship between the inductor current change rate, the voltage across inductor L1, and the inductance value.

[0036] Specifically, the change in current of inductor L1 can be determined by dividing the product of the voltage across inductor L1 and the corresponding time by the inductance value. Given the voltages on the first and second bridge arms and the inductance value, the corresponding inductor current settling time can be deduced from the target soft-switching current threshold. The processor then converts the inductor current settling time, the energy transfer time determined by the feedback regulation loop, and the preset dead time into the turn-on and turn-off times of each switching transistor.

[0037] In some embodiments, the processor can pre-store the correspondence between the conduction states of each switch and the voltage across inductor L1, and select the corresponding switch state sequence according to the direction of power transmission. For example, the processor can sequentially control the first switch Q1 and the fourth switch Q4 to conduct together, the first switch Q1 and the third switch Q3 to conduct together, the second switch Q2 and the third switch Q3 to conduct together, and the second switch Q2 and the fourth switch Q4 to conduct together. A corresponding dead time is set between each conduction state to prevent two switches in the same bridge arm from conducting simultaneously.

[0038] In other embodiments, multiple first-arm side voltages, second-arm side voltages, and energy transfer times can be pre-calculated offline to generate a timing parameter table. During operation, the processor reads adjacent timing parameters based on the current operating conditions and calculates the conduction timing corresponding to the current switching cycle through interpolation. This method also allows the conduction timing to change with the current voltage conditions and power transfer requirements.

[0039] S15: Generate the drive signal corresponding to each switch according to the conduction timing, so that the current of inductor L1 reaches the soft switching current threshold corresponding to the bridge arm to be commutated before the bridge arm to be commutated, and enable the switch to be turned on in the bridge arm to be commutated to achieve soft turn-on.

[0040] The processor can write the timing parameters corresponding to each switching transistor into the compare register and period register of the enhanced pulse width modulation module. The enhanced pulse width modulation module outputs four drive control signals according to the parameters in the corresponding registers. The drive circuit then performs level conversion or power amplification on the drive control signals to obtain the drive signals used to control each switching transistor.

[0041] Before the commutation of the bridge arm to be commutated, the turn-on timing ensures that the current in inductor L1 reaches the corresponding soft-switching current threshold. After the currently conducting switch is turned off, the current in inductor L1 continues to flow during the dead time, charging and discharging the parasitic capacitances of the two switches in the bridge arm to be commutated, causing the voltage across the switch to be turned on to drop. After the dead time, the processor controls the switch to be turned on, so that the switch is turned on when the voltage across it has dropped to the corresponding range.

[0042] This embodiment does not employ a fixed commutation current or a fixed turn-on sequence under all operating conditions. Instead, it determines the soft-switching current threshold based on the current voltages and circuit parameters of both bridge arms, and uses this threshold in conjunction with the current power transfer requirements to determine the turn-on sequence. Therefore, when the voltages of the first and second bridge arms, or the load, change, the current conditions and turn-on sequence used for bridge arm commutation can be adjusted accordingly. This ensures reliable soft-start of the switching transistors while maintaining power transfer through inductor L1, and reduces the inductor circulating current caused by excessive fixed commutation margin. Based on this, it can adapt to changes in the power transfer direction and voltages on both sides during lithium battery charging and discharging, enabling each switch in the bidirectional four-switch converter to achieve soft-start during the corresponding commutation process, reducing switching losses during lithium battery charging and discharging.

[0043] Based on the above embodiments: As a preferred embodiment, the circuit parameters of the bidirectional four-switch converter include the parasitic capacitance values ​​of each switch. Based on the voltages of the first and second bridge arms and the circuit parameters of the bidirectional four-switch converter, determine the soft-switching current threshold corresponding to the bridge arm to be commutated, including: Based on the voltage on the first bridge arm, the voltage on the second bridge arm, the inductance value of the inductor, and the parasitic capacitance value of each switch, determine the soft-switching current threshold that enables the switch to be turned on in the bridge arm to be commutated to meet the zero-voltage turn-on condition.

[0044] In this embodiment, the circuit parameters of the bidirectional four-switch converter include the parasitic capacitance values ​​of each switch. These parasitic capacitance values ​​can be the output capacitance values ​​of the switches. The output capacitance values ​​of the switches can be determined from the switch's datasheet or from the output capacitance curves of the switches under different drain-source voltages. For switches whose output capacitance values ​​change significantly with drain-source voltage, the equivalent output capacitance value within the corresponding operating voltage range can be determined based on the current voltage on the first or second bridge arm.

[0045] Based on the voltages of the first and second bridge arms, the inductance value, and the parasitic capacitance value of each switching transistor, a soft-switching current threshold is determined to ensure that the switching transistor in the bridge arm to be commutated meets the zero-voltage turn-on condition. The zero-voltage turn-on condition can be either that the voltage between the drain and source of the switching transistor drops to zero before turn-on, or that it drops to a value no greater than a preset voltage. The preset voltage value can be determined based on the allowable turn-on loss of the switching transistor, the response error of the drive circuit, and the voltage detection accuracy.

[0046] Specifically, after the currently conducting switch in the bridge arm turns off, the current in inductor L1 needs to charge and discharge the output capacitors of the two switches in the same bridge arm during the dead time. To ensure that the drain-source voltage of the switch to be turned on drops to meet the zero-voltage turn-on condition before the dead time ends, the current in inductor L1 should be able to provide the corresponding charge. The current threshold can be determined based on the relationship between the amount of charge to be transferred from the output capacitor and the dead time.

[0047] As a specific implementation method, the soft-switching current threshold can be determined according to the following formula: .

[0048] in, Indicates the soft-switching current threshold. This indicates the output capacitance value of the switching transistor. Indicates the voltage on the first bridge arm side. Indicates the voltage on the second bridge arm side. The first term in the formula represents the current component required for the output capacitor of the switching transistor to complete charge transfer within the preset dead time, and the second term represents the change in inductor current caused by the voltage across inductor L1 within the preset dead time.

[0049] Since the dead time is relatively short compared to the switching cycle, the change in inductor current during the dead time can be considered a linear change. The larger of the voltages on the first and second bridge arms is used to reflect the larger voltage conditions that need to be handled during the current commutation process. Determining the soft-switching current threshold based on the larger voltage conditions ensures that the corresponding inductor current has sufficient charge transfer capability.

[0050] In a preferred embodiment, the two bridge arms include a first bridge arm and a second bridge arm, and the soft-switching current threshold includes a first soft-switching current threshold and a second soft-switching current threshold. The first soft-switching current threshold is a current threshold that has a current direction from the first bridge arm to the second bridge arm and enables the corresponding switch to be turned on to meet the zero-voltage turn-on condition. The second soft-switching current threshold is a current threshold that has a current direction from the second bridge arm to the first bridge arm and enables the corresponding switch to be turned on to meet the zero-voltage turn-on condition.

[0051] In this embodiment, the two bridge arms include a first bridge arm and a second bridge arm, and the soft-switching current threshold includes a first soft-switching current threshold and a second soft-switching current threshold. To distinguish the current direction of inductor L1, the direction from the first bridge arm to the second bridge arm can be defined as the first current direction, and the direction from the second bridge arm to the first bridge arm can be defined as the second current direction.

[0052] The first soft-switching current threshold has a current direction from the first bridge arm to the second bridge arm, and its current magnitude is sufficient to enable the corresponding switch to be turned on to meet the zero-voltage turn-on condition. The second soft-switching current threshold has a current direction from the second bridge arm to the first bridge arm, and its current magnitude is sufficient to enable the corresponding switch to be turned on to meet the zero-voltage turn-on condition. If the first current direction is defined as positive, then the first soft-switching current threshold can be expressed as positive. The second soft-switching current threshold can be expressed as a negative value. .

[0053] The absolute values ​​of the first soft-switching current threshold and the second soft-switching current threshold can be the same or different. When the first and second bridge arms use the same type of switching transistor, and the voltage on both sides has a basically symmetrical effect on the commutation process, the first and second soft-switching current thresholds can have the same absolute value. When the switching transistor types, parasitic capacitance values, or voltages during commutation of the first and second bridge arms are different, the first and second soft-switching current thresholds can be calculated separately.

[0054] For example, when the current in inductor L1 reaches the first soft-switching current threshold along the first current direction, the inductor current in that direction can discharge the output capacitor of the switch to be turned on in the corresponding bridge arm and charge the output capacitor of the other switch. When the current in inductor L1 reaches the second soft-switching current threshold along the second current direction, the charging and discharging directions of the output capacitor are reversed, thereby providing a zero-voltage turn-on condition for the switch to be turned on in the other commutation state.

[0055] The first and second soft-switching current thresholds include not only the current magnitude but also the current direction. When determining the soft-switching current threshold corresponding to the current bridge arm commutation, the processor needs to simultaneously determine the current direction required for this commutation. This avoids mistaking an inductor current in the opposite direction for the commutation requirement based solely on the absolute value of the current.

[0056] As a preferred embodiment, it also includes: Based on the sampling parameters of the inductor current sampling circuit 4, the first soft-switching current threshold and the second soft-switching current threshold are converted into a first comparison reference value and a second comparison reference value, respectively; the inductor current sampling circuit 4 is used to sample the current of inductor L1; The current sampling value of the inductor current sampling circuit 4 is acquired in real time, and the current sampling value is compared with the comparison reference value corresponding to the current bridge arm commutation in the first comparison reference value or the second comparison reference value. If the current sampling value reaches the comparison reference value corresponding to this bridge arm commutation earlier than the planned turn-off time determined according to the conduction sequence, the current conducting switch in the bridge arm to be commutated is turned off in advance, and the switch to be turned on in the bridge arm to be commutated is turned on after a preset dead time. If the current sampling value does not reach the comparison reference value corresponding to this bridge arm commutation before the planned turn-off time, then each switch is controlled according to the conduction sequence.

[0057] In this embodiment, the bidirectional four-switch converter further includes an inductor current sampling circuit 4. The inductor current sampling circuit 4 is used to sample the current of inductor L1 and convert the current of inductor L1 into a current sampling value that can be input to the comparator inside the processor. The current sampling value can be an analog voltage value proportional to the inductor current.

[0058] like Figure 2 As shown, the inductor current sampling circuit 4 may include a sampling resistor R1, a differential amplifier circuit OPA1, and a bias circuit. The sampling resistor R1 can be placed in the current path between the first and second bridge arms. For example, the sampling resistor R1 can be placed between the source of the second switch Q2 and the source of the fourth switch Q4 to collect the instantaneous current flowing through the bidirectional four-switch converter. The resistance value of the sampling resistor R1 can be determined based on the maximum inductor current, the allowable sampling loss, and the input range of the differential amplifier circuit OPA1.

[0059] The differential amplifier circuit OPA1 differentially amplifies the voltage across the sampling resistor R1, and the bias circuit superimposes a DC bias voltage onto the differentially amplified voltage. The DC bias voltage can be the voltage corresponding to the midpoint of the current sampling signal range; for example, when the comparator input range is 0V to 3.3V, the DC bias voltage can be 1.65V. When the inductor current is zero, the current sampling value equals the DC bias voltage; when the inductor current flows in the first current direction, the current sampling value changes relative to the DC bias voltage in the first direction; when the inductor current flows in the second current direction, the current sampling value changes relative to the DC bias voltage in the opposite direction.

[0060] If the current-voltage conversion relationship of the inductor current sampling circuit 4 is as follows: , in, This is the current sample value. This is the bias voltage when the inductor current is zero. The conversion coefficient of inductor current sampling circuit 4 is... Let L be the current in inductor L1. Then the first comparison reference value and the second comparison reference value can be expressed as follows: ; .

[0061] The first soft-switching current threshold. The second soft-switching current threshold is set when the resistance of sampling resistor R1 is [value missing]. When the gain of the differential amplifier circuit OPA1 is G, According to The product of G and G is used to determine the current threshold. The first comparison reference value and the second comparison reference value mentioned above correspond to the first soft-switching current threshold and the second soft-switching current threshold, respectively.

[0062] The above sampling parameters may include one or more of the following: the resistance value of the sampling resistor R1, the gain of the differential amplifier circuit OPA1, the DC bias voltage, and the analog-to-digital conversion ratio.

[0063] The processor acquires current sample values ​​in real time and compares them with the corresponding reference value for this bridge arm change. The processor can internally configure two comparators, such as... Figure 2 As shown, the first comparator COMP1 is used to detect whether the current sample value reaches the first comparison reference value, and the second comparator COMP2 is used to detect whether the current sample value reaches the second comparison reference value. The comparators can directly receive analog current sample values; when using digital comparison, the analog-to-digital converter module can convert the current sample value into a digital value, and then the digital comparison unit in the processor can compare this digital value with the digital comparison reference value. The processor can calculate the first soft-switching current threshold and the second soft-switching current threshold in real time based on the current voltage on the first bridge arm, the voltage on the second bridge arm, and the circuit parameters of the bidirectional four-switch converter. Based on the conversion relationship of the inductor current sampling circuit 4, the two soft-switching current thresholds are converted into the first comparison reference value and the second comparison reference value, respectively. The first comparison reference value and the second comparison reference value can be written into the reference value registers of the two comparators inside the controller, respectively.

[0064] When one of the comparators detects that the current sample value has reached the corresponding comparison reference value, the comparator generates an edge-triggered event. This edge-triggered event can be directly transmitted to the enhanced pulse width modulation (PWM) module through the event selection module inside the controller. The PWM module then forces the currently conducting switch to turn off and, after a preset dead time, controls the switch to be turned on in the same bridge arm. Because the comparator event can directly affect the PWM module through the hardware signal path, the impact of software interrupt response and program execution time on the commutation timing can be reduced.

[0065] If the current sample value reaches the comparison reference value corresponding to this bridge arm commutation earlier than the planned turn-off time determined according to the conduction timing, it indicates that the current of inductor L1 has reached the soft-switching current threshold required for this commutation ahead of schedule. At this time, the processor controls the currently conducting switch in the bridge arm to be commutated to turn off in advance, and controls the switch to be turned on after a preset dead time. Early turn-off can be directly triggered by the comparator output event to trigger the forced turn-off input of the enhanced pulse width modulation module, thereby reducing the delay caused by software interrupts and program execution time.

[0066] If the current sample value does not reach the comparison reference value corresponding to this bridge arm commutation before the planned turn-off time, the processor controls each switch according to the original turn-on sequence. In other words, the planned turn-off time constitutes the latest turn-off time of the currently conducting switch, and the comparator trigger event constitutes the condition that can turn off the currently conducting switch earlier. Even if the comparison reference value is not reached earlier due to sampling noise, transient disturbances, or inductor L1 parameter deviation, the conduction time of the currently conducting switch will not be extended indefinitely.

[0067] In some embodiments, a blanking time can be set at the comparator input. Within a preset time after the current bridge arm completes commutation, the processor temporarily refrains from responding to the comparator output event to eliminate sampling spikes caused by switching transients. In other embodiments, it can be required that the current sample value continuously reaches the corresponding comparison reference value and remains at that value for a preset number of samplings before confirming that the current of inductor L1 has reached the soft-switching current threshold.

[0068] In a preferred embodiment, the switching cycle includes a first time period, a second time period, a third time period, and a fourth time period set sequentially; The first time period is used to control the current change of inductor L1 to a soft-switching current threshold with a first current direction. The duration of the second time period is the energy transfer time and is used to transfer electrical energy through inductor L1. The third time period is used to control the current change of inductor L1 to a soft-switching current threshold with a second current direction, which is opposite to the first current direction. The fourth time period is the remaining time period within the switching cycle excluding the first, second, and third time periods.

[0069] Please refer to Figure 3 , Figure 3 The present application provides a schematic diagram of the conduction timing of a switching transistor, wherein one switching cycle includes a first time period set sequentially. Second time period The third time period and the fourth time period 6 shows the PWM drive waveforms for Q1~Q4; 7 shows the current waveform of inductor L1 when V1 is the input and V2 is the output; 8 shows the current waveform of inductor L1 when V2 is the input and V1 is the output. The first, second, third, and fourth time periods together constitute a complete switching cycle. ,Right now: .

[0070] The first time period is used to control the current change of inductor L1 to a soft-switching current threshold with a first current direction. The first time period may include the dead time between two switches in the same bridge arm and the time during which the corresponding switch combinations are simultaneously turned on. For example, the first time period may include the dead time between the first switch Q1 and the second switch Q2, and the time during which the first switch Q1 and the fourth switch Q4 are simultaneously turned on. When the first switch Q1 and the fourth switch Q4 are simultaneously turned on, a voltage is formed across inductor L1 that causes the inductor current to change along the first current direction, thus the current of inductor L1 gradually reaches the first soft-switching current threshold.

[0071] The end time of the first time period can be determined based on the pre-calculated conduction sequence or the time when the inductor current sampling value reaches the first comparison reference value. When the inductor current sampling value reaches the first comparison reference value ahead of schedule, the first time period can be shortened accordingly to ensure that subsequent bridge arm commutation occurs in a timely manner.

[0072] The second time period is the energy transfer time and is used to transfer electrical energy through inductor L1. The second time period may include the time during which the first switch Q1 and the third switch Q3 are both on, as well as the adjacent dead time. During the second time period, the current in inductor L1 changes according to the relationship between the voltages on the first and second bridge arms, while simultaneously transferring electrical energy between the two bridge arm sides.

[0073] When the voltage on the first bridge arm is equal to or the voltage on the second bridge arm is within a small range, the inductor current slope during the second time period can be zero or close to zero. When the voltages on the two bridge arms are not equal, the inductor current during the second time period changes according to the corresponding slope. When the voltage on the first bridge arm is close to the voltage on the second bridge arm, the inductor current slope changes continuously, thus enabling the bidirectional four-switch converter to smoothly transition between different voltage conversion states.

[0074] The third time period is used to control the current change of inductor L1 to a soft-switching current threshold with a second current direction, which is opposite to the first current direction. This third time period may include the time during which the second switch Q2 and the third switch Q3 are simultaneously turned on, along with the corresponding dead time. In this switching state, the voltage direction across inductor L1 changes, causing the current in inductor L1 to gradually change from the first current direction to the second current direction until it reaches the second soft-switching current threshold, thus creating soft-switching conditions for subsequent switches to be turned on.

[0075] The fourth time period is the remaining time within the switching cycle excluding the first, second, and third time periods. This fourth time period can include the time during which the second switch Q2 and the fourth switch Q4 are both on, along with the corresponding dead time. When both switches Q2 and Q4 are on, the voltage across inductor L1 is relatively low, and the change in inductor current can be negligible or remain within a small range. This fourth time period can be used to maintain the inductor current conditions required for subsequent commutation and to wait for the next switching cycle to begin.

[0076] In the specific conduction timing shown in this embodiment, the first time period Second time period The third time period and the fourth time period Each includes the preset dead time required for the corresponding switch state transition. Specifically, the first time period This includes the dead time required for commutation of the corresponding switching transistor in the first bridge arm and the conduction time for establishing the soft-switching current in the first current direction; the second time period Including the time when the first switch Q1 and the third switch Q3 are both turned on. And the corresponding dead time, i.e. The third time period This includes the common conduction time of the switching transistors used to change the current of inductor L1 to the second soft-switching current threshold, and the corresponding dead time; the fourth time period. This includes the time during which the second switch Q2 and the fourth switch Q4 are both turned on, as well as the corresponding dead time.

[0077] Fourth time period The dead time must not be less than the preset dead time. When according to The calculated fourth time period is less than the preset dead time. If necessary, the first, second, and third time periods or the switching cycle should be readjusted to ensure that the adjusted fourth time period is not less than the preset dead time. This allows for maintaining the minimum interval required for safe commutation between two switches in the same bridge arm, preventing simultaneous conduction of the upper and lower switches.

[0078] It should be noted that the first current direction is from the first bridge arm to the second bridge arm, and the second current direction is from the second bridge arm to the first bridge arm.

[0079] As a preferred embodiment, it also includes: Obtain the output current of the bidirectional four-switch converter under the current power transmission direction; The time compensation parameters are determined based on the voltage on the first bridge arm, the voltage on the second bridge arm, the output current, and the energy transfer time. Compensation is applied to the first or third time period based on the time compensation parameters.

[0080] In this embodiment, the output current of the bidirectional four-switch converter in the current power transmission direction is obtained. The output current can be obtained through a current sampling resistor, Hall current sensor, fluxgate current sensor, or other current sampling device installed in the corresponding output path. The current sampling value can be filtered by analog or digital filtering to obtain the average value of the output current. The output current can reflect the current required power transmission amount.

[0081] The time compensation parameters are determined based on the voltages of the first and second bridge arms, the output current, and the energy transfer time. The voltages of the first and second bridge arms reflect the current voltage conditions, the output current reflects the current load conditions, and the energy transfer time reflects the current control quantity determined by the feedback loop. The time compensation parameters can be the amount of time compensation to be added to the first or third time period, or they can be coefficients used to calculate this time compensation amount.

[0082] In some embodiments, the processor can input the first arm voltage, the second arm voltage, the output current, and the energy transfer time into a predetermined compensation function to calculate the time compensation parameters. In other embodiments, the processor can query a pre-stored compensation parameter table based on the above parameters. If the current parameter is located between multiple adjacent operating points in the compensation parameter table, linear interpolation or piecewise interpolation can be used to determine the time compensation parameters.

[0083] Compensation is applied to either the first or third time period based on time compensation parameters. Compensation can involve adding a first or third time period, or it can be a correction based on the time determined by theoretical soft-switching conditions. By compensating for the first or third time period, deviations caused by device parameter dispersion, sampling errors, drive delays, and approximations in theoretical calculations can be corrected.

[0084] The time compensation parameter is not used to arbitrarily increase the commutation time, but rather to match the first or third time period with the current operating conditions. Under the condition that the soft-start condition of the switch to be turned on is met, the duration of the fourth time period and the inductor circulating current can be limited, thereby reducing the effective value of the inductor current.

[0085] In a preferred embodiment, the time compensation parameters are determined by a pre-established correspondence. This correspondence is established by adjusting the first or third time period under different first arm side voltages, second arm side voltages, output side currents, and energy transfer times, and by determining the corresponding time compensation parameters based on the current of inductor L1.

[0086] In this embodiment, the time compensation parameters are determined through a pre-established correspondence. This correspondence can be established through offline calculation, simulation, or prototype testing before the bidirectional four-switch converter is put into operation, and stored in the processor's non-volatile memory space.

[0087] First, set multiple sets of parameters for the first arm voltage, second arm voltage, output current, soft-switching current threshold, and energy transfer time. Each set of parameters can cover the allowable voltage range, output current range, soft-switching current threshold, and energy transfer time range of the bidirectional four-switch converter. The parameter sampling interval can be determined based on control accuracy and storage capacity. For ranges where voltage changes rapidly or soft-switching conditions change significantly, a smaller sampling interval can be set.

[0088] For each group of first bridge arm side voltage, second bridge arm side voltage, output side current, soft-switching current threshold, and energy transfer time, the first or third time period is adjusted respectively. After each adjustment, a corresponding switching transistor drive signal is generated based on the adjusted time period, and the inductor current within one or more switching cycles is obtained.

[0089] The corresponding time compensation parameters are determined based on the current in inductor L1. This can include calculating the effective value of the inductor current or determining the duration of the fourth time period. When the fourth time period is shortened, the duration for which the inductor current does not undertake the current energy transfer task is correspondingly shortened, and thus the effective value of the inductor current can decrease accordingly. The time compensation parameters that bring the fourth time period to a smaller value within the allowable range and ensure that each switch to be turned on meets the soft-turn-on conditions can be determined as the time compensation parameters corresponding to this set of operating conditions.

[0090] Among them, the effective value of the inductor current and + The relationship between them is: .

[0091] One specific implementation method is to start with the initial compensation parameters and gradually increase or decrease the time compensation parameters according to a preset step size, recording the fourth time period and the effective value of the inductor current corresponding to each compensation parameter. When further adjusting the time compensation parameters no longer shortens the fourth time period, or causes the switching transistor to be turned on to fail to meet the soft-start conditions, the previous time compensation parameter is determined as the time compensation parameter corresponding to this set of operating conditions.

[0092] In other embodiments, reaching a preset duration threshold in the fourth time period can be used as a filtering condition. The preset duration threshold can be equal to a preset dead time, or it can be the sum of a preset dead time and a preset margin.

[0093] By repeating the above process for each set of operating conditions, a correspondence can be established between the voltage on the first bridge arm, the voltage on the second bridge arm, the output current, the energy transfer time, and the time compensation parameters. This correspondence can be represented using a multidimensional lookup table, a piecewise function, or a fitting function.

[0094] As an alternative method, energy transfer time can be used. As a variable, the time compensation parameter is expressed as: .

[0095] in, The fitting coefficients are defined as those corresponding to the voltages of the first and second bridge arms, the output current, the soft-switching current threshold, and the energy transfer time interval. Here, n is a preset order. Different operating conditions can correspond to different... The processor determines the corresponding [condition] based on the current voltage on the first bridge arm, the voltage on the second bridge arm, the output current, and the energy transfer time of the feedback regulation loop output. And calculate the time compensation parameters.

[0096] When the query results When it is greater than zero, the processor determines according to And energy transfer time calculation time compensation parameters; when the query results When the time compensation parameter is zero, it can be set to zero, and the time period before compensation can be used directly. The order of the fitting function can be first, second, or higher, depending on the curve characteristics of the time compensation parameter changing with energy transfer time.

[0097] In some embodiments, the correspondence can also be established separately for different temperature ranges. The processor selects the corresponding parameter table based on the current switching transistor temperature or inductor temperature to reflect the changes in parasitic capacitance, inductance, and drive delay caused by temperature changes.

[0098] It should be noted that when determining the time compensation parameters for each working condition, the fourth time period can be used. Shorten to preset dead time Or close to the preset dead time As an adjustment boundary, under the premise that all switches to be turned on meet the soft-start conditions, the time compensation parameters are gradually adjusted until the fourth time period. Reaching the preset dead time Or reach the preset dead time This is the sum of the allowable timing margin. At this point, the corresponding time compensation parameters can be recorded as the time compensation parameters corresponding to the first bridge arm voltage, the second bridge arm voltage, the output current, and the energy transfer time for this group. By making the fourth time period close to its allowable lower limit, the duration of the inductor current in a state where it is not undertaking the current energy transfer task can be reduced, thereby reducing the effective value of the inductor current within one switching cycle.

[0099] As a preferred embodiment, compensation is performed on the first time period or the third time period according to the time compensation parameter, including: Determine the direction of power transfer in the current switching cycle of the bidirectional four-switch converter; When electrical energy is transmitted from the side of the first bridge arm to the side of the second bridge arm, the first time period is compensated according to the time compensation parameter. When electrical energy is transmitted from the side of the second bridge arm to the side of the first bridge arm, the third time period is compensated according to the time compensation parameter.

[0100] In this embodiment, the direction of power transmission can be determined based on charging and discharging control commands, or based on the voltage on the first bridge arm side, the voltage on the second bridge arm side, and the direction of the output current. For example, when the side where the first bridge arm is located is connected to a DC bus and the side where the second bridge arm is located is connected to a battery, the charging command can correspond to the transmission of power from the side where the first bridge arm is located to the side where the second bridge arm is located, and the discharging command can correspond to the transmission of power from the side where the second bridge arm is located to the side where the first bridge arm is located.

[0101] When electrical energy is transmitted from the side containing the first bridge arm to the side containing the second bridge arm, compensation is applied to the first time period based on the time compensation parameter. The controller can increase the time compensation parameter to the first time period initially determined based on the soft-switching current threshold, so that the inductor current within the first time period is established to the corresponding soft-switching current threshold according to the current direction of electrical energy transmission.

[0102] As a specific implementation method, under the condition that the voltage on the first bridge arm side is not lower than the voltage on the second bridge arm side, the first time period can be determined according to the following formula: .

[0103] in, This represents the base time determined based on the first soft-switching current threshold. This represents the time compensation parameter. Under this operating condition, the third time period can be determined based on the voltage on the first arm side, the voltage on the second arm side, and the compensated first and second time periods.

[0104] For example, the third time period can be determined according to the following formula: .

[0105] Furthermore, it can be confirmed that, The fourth time period ,and , The time during which the second switch Q2 and the third switch Q3 are simultaneously turned on. This is the time during which the second switch Q2 and the fourth switch Q4 are simultaneously turned on.

[0106] The above formula is used to illustrate one way to determine the third time period based on the relationship between the compensated first time period and the current voltage, and does not constitute the only limitation on the calculation method of the third time period.

[0107] When electrical energy is transmitted from the side containing the second bridge arm to the side containing the first bridge arm, compensation is applied to the third time period based on the time compensation parameters. The controller can increase the time compensation parameters to the third time period initially determined based on the second soft-switching current threshold, causing the inductor current during the third time period to change to the soft-switching current threshold in the opposite direction.

[0108] As a specific implementation method, under the condition that the voltage on the first bridge arm side is not higher than the voltage on the second bridge arm side, the third time period can be determined according to the following formula: .

[0109] in, This represents the base time determined based on the second soft-switching current threshold. The first time period can be determined based on the compensated third time period, the voltages on both bridge arms, and the second time period. For example: .

[0110] In other embodiments, the direction of power transmission may not be determined solely based on the magnitude relationship between the voltages on the two bridge arms. For example, when the bidirectional four-switch converter is in active boost or active buck mode, the direction of power transmission can be directly indicated by the upper-level charge / discharge control command. This avoids frequent switching of the compensation object when the voltages on the two bridge arms are close or affected by sampling fluctuations.

[0111] Base time This refers to the theoretical time required for the current in inductor L1 to change to the first soft-switching current threshold under the current switching state; base time. This refers to the theoretical time required for the current in inductor L1 to change to the second soft-switching current threshold. Based on the inductor current change relationship ΔI=VL×Δt / L, the base time can be calculated based on the voltage VL across inductor L1, the inductance value L, and the target current change ΔI within the corresponding time period, i.e., Δt=L×ΔI / VL.

[0112] As a preferred embodiment, compensation for the first time period or the third time period includes: Adjust the first or third time period before compensation based on the time compensation parameters to obtain the first or third time period after compensation. Based on the first or third time period after compensation, the conduction sequence of each switch transistor within the switching cycle is re-determined.

[0113] In this embodiment, the first or third time period before compensation is adjusted according to the time compensation parameter to obtain the first or third time period after compensation. The adjustment method can be to add the time compensation parameter to the time period before compensation, or to proportionally adjust the time period before compensation based on the time compensation parameter. When the time compensation parameter is zero, the time period after compensation can be equal to the time period before compensation.

[0114] After obtaining the compensated first or third time period, the conduction sequence of each switch within the switching cycle is re-determined based on the compensated first or third time period. Re-determining the conduction sequence may include re-determining the turn-off time of the currently conducting switch, the turn-on time of the switch to be turned on, the dead zone between adjacent switch states, and the duration of the fourth time period.

[0115] Maintaining the switching cycle Second time period If the time period remains unchanged, the fourth time period can be redefined according to the following formula: .

[0116] After the first time period is compensated, the third and fourth time periods can be recalculated based on the compensated first time period; similarly, after the third time period is compensated, the first and fourth time periods can be recalculated based on the compensated third time period. This ensures that the sum of the four time periods remains equal to the switching cycle, preventing overlap of adjacent switching cycles or undefined control intervals caused by local adjustments to the time periods.

[0117] The redefined turn-on timing can be converted into the counter comparison value used by the enhanced pulse width modulation module. After the controller completes the calculation within the current switching cycle, it can write the new counter comparison value into the shadow register and load it into the valid register when the counter crosses zero in the next switching cycle. This unified loading prevents transient timing errors caused by the separate updates of each drive signal within the same switching cycle.

[0118] When the two switches in the first bridge arm are driven complementaryly, the turn-off time of one switch can be determined based on the compensated first or third time period, and the turn-on time of the other switch can be determined by combining this with the preset dead time. The two switches in the second bridge arm can be determined in the same way. The dead time is kept no less than the minimum allowable dead time during the recalculation process to prevent shoot-through between the two switches in the same bridge arm.

[0119] In some embodiments, the redefined time periods can also be limited. When the compensated first or third time period is less than the corresponding minimum allowable time, it is set as the minimum allowable time; when it is greater than the maximum allowable time, it is set as the maximum allowable time. The minimum allowable time can be determined based on the soft-switching current setup requirements, and the maximum allowable time can be determined based on the maximum allowable inductor current and the switching cycle.

[0120] Under light load or no-load conditions, if the fourth time period is consistently shortened to the dead time, the switching frequency may increase accordingly, leading to increased drive losses. To address this, a maximum switching frequency can be set. When the switching frequency calculated based on the current timing exceeds the maximum switching frequency, the switching cycle is limited to the cycle corresponding to the maximum switching frequency; the first to third time periods are still determined according to the corresponding calculation results, and the remaining time within the switching cycle is used as the fourth time period. The minimum switching frequency can be determined based on the maximum output current, the inductor's allowable current, and the preset current margin.

[0121] By recalculating the complete conduction timing after adjusting the first or third time period, the time compensation can be kept consistent with other time periods, and the soft switching conditions, energy transfer requirements, dead time requirements, and switching cycle constraints can be implemented in the drive signals of each switching transistor.

[0122] Please refer to Figure 4 , Figure 4 This application provides a schematic diagram of a fully soft-switching charge / discharge control device for a smart lithium battery. The device controls a bidirectional four-switch converter connected between the lithium battery and the DC bus, and includes: Memory 41 is used to store computer programs; The processor 42 is used to implement the steps of the fully soft-switching charge and discharge control method for the smart lithium battery as described above when executing a computer program.

[0123] For a description of the fully soft-switching charge and discharge control device for the intelligent lithium battery provided by the present invention, please refer to the above method embodiments; the present invention will not be described again here.

[0124] It should also be noted that, in this specification, relational terms such as "first" and "second" are used only to distinguish one entity or operation from another, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Furthermore, 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 a process, method, article, or apparatus. Without further limitations, 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 said element.

[0125] The above description of the disclosed embodiments enables those skilled in the art to make or use the invention. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the invention. Therefore, the invention is not to be limited to the embodiments shown herein, but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A fully soft-switching charge and discharge control method for an intelligent lithium battery, characterized in that, An application is made in an intelligent lithium battery charging and discharging system, the intelligent lithium battery charging and discharging system including a lithium battery and a bidirectional four-switch converter connected to the lithium battery, the bidirectional four-switch converter including two bridge arms and an inductor connected between the midpoints of the two bridge arms, each bridge arm including two switching transistors connected in series, the method including: Obtain the first bridge arm side voltage and the second bridge arm side voltage of the bidirectional four-switch converter; Based on the voltage of the first bridge arm, the voltage of the second bridge arm, and the circuit parameters of the bidirectional four-switch converter, determine the soft-switching current threshold corresponding to the bridge arm to be commutated. Based on the second arm side voltage of the bidirectional four-switch converter, the energy transfer time within a switching cycle is determined through a feedback adjustment loop. Based on the soft-switching current threshold, the voltage on the first bridge arm side, the voltage on the second bridge arm side, the inductance value of the inductor, and the energy transfer time, the conduction sequence of each switch in the two bridge arms during the switching cycle is determined. According to the conduction timing, drive signals are generated for each of the switching transistors so that the current of the inductor reaches the soft-switching current threshold corresponding to the bridge arm to be switched before the bridge arm to be switched is switched, and the switching transistor to be turned on in the bridge arm to be switched is soft-turned on.

2. The fully soft-switching charge and discharge control method for intelligent lithium batteries as described in claim 1, characterized in that, The circuit parameters of the bidirectional four-switch converter include the parasitic capacitance values ​​of each of the switching transistors; Based on the voltage on the first bridge arm, the voltage on the second bridge arm, and the circuit parameters of the bidirectional four-switch converter, determine the soft-switching current threshold corresponding to the bridge arm to be commutated, including: Based on the voltage on the first bridge arm, the voltage on the second bridge arm, the inductance value of the inductor, and the parasitic capacitance value of each switch, a soft-switching current threshold is determined to ensure that the switch to be turned on in the bridge arm to be commutated meets the zero-voltage turn-on condition.

3. The fully soft-switching charge and discharge control method for intelligent lithium batteries as described in claim 2, characterized in that, The two bridge arms include a first bridge arm and a second bridge arm, and the soft-switching current threshold includes a first soft-switching current threshold and a second soft-switching current threshold. The first soft-switching current threshold is a current threshold that has a current direction from the first bridge arm to the second bridge arm and enables the corresponding switch to be turned on to meet the zero-voltage turn-on condition. The second soft-switching current threshold is a current threshold that has a current direction from the second bridge arm to the first bridge arm and enables the corresponding switch to be turned on to meet the zero-voltage turn-on condition.

4. The fully soft-switching charge and discharge control method for intelligent lithium batteries as described in claim 3, characterized in that, Also includes: Based on the sampling parameters of the inductor current sampling circuit 4, the first soft-switching current threshold and the second soft-switching current threshold are converted into a first comparison reference value and a second comparison reference value, respectively. The inductor current sampling circuit 4 is used to sample the current of the inductor; The current sampling value of the inductor current sampling circuit 4 is acquired in real time, and the current sampling value is compared with the comparison reference value corresponding to the current bridge arm commutation in the first comparison reference value or the second comparison reference value. If the current sampling value reaches the comparison reference value corresponding to this bridge arm commutation earlier than the planned turn-off time determined according to the conduction sequence, then the current conducting switch in the bridge arm to be commutated is turned off in advance, and after a preset dead time, the switch to be turned on in the bridge arm to be commutated is turned on. If the current sampling value does not reach the comparison reference value corresponding to this bridge arm commutation before the planned turn-off time, then each of the switching transistors is controlled according to the conduction timing sequence.

5. The fully soft-switching charge and discharge control method for a smart lithium battery as described in any one of claims 1 to 4, characterized in that, The switching cycle includes a first time period, a second time period, a third time period, and a fourth time period set sequentially; The first time period is used to control the current of the inductor to change to a soft-switching current threshold with a first current direction. The duration of the second time period is the energy transmission time and is used to transmit electrical energy through the inductor. The third time period is used to control the current of the inductor to change to a soft-switching current threshold with a second current direction, which is opposite to the first current direction. The fourth time period is the remaining time period within the switching cycle excluding the first time period, the second time period, and the third time period.

6. The fully soft-switching charge and discharge control method for a smart lithium battery as described in claim 5, characterized in that, Also includes: Obtain the output current of the bidirectional four-switch converter under the current power transmission direction; The time compensation parameters are determined based on the first bridge arm side voltage, the second bridge arm side voltage, the output side current, and the energy transfer time. The first time period or the third time period is compensated according to the time compensation parameters.

7. The fully soft-switching charge and discharge control method for a smart lithium battery as described in claim 6, characterized in that, The time compensation parameters are determined through a pre-established correspondence, which is established by adjusting the first time period or the third time period under different first bridge arm side voltages, second bridge arm side voltages, output side currents, and energy transmission times, and determining the corresponding time compensation parameters based on the current of the inductor.

8. The fully soft-switching charge and discharge control method for a smart lithium battery as described in claim 6, characterized in that, Compensation is applied to the first time period or the third time period according to the time compensation parameters, including: Determine the direction of power transmission of the bidirectional four-switch converter during the current switching cycle; When electrical energy is transmitted from the side where the first bridge arm is located to the side where the second bridge arm is located, the first time period is compensated according to the time compensation parameter; When electrical energy is transmitted from the side of the second bridge arm to the side of the first bridge arm, the third time period is compensated according to the time compensation parameter.

9. The fully soft-switching charge and discharge control method for a smart lithium battery as described in claim 8, characterized in that, Compensation for the first time period or the third time period includes: Adjust the first time period or the third time period before compensation according to the time compensation parameters to obtain the first time period or the third time period after compensation. Based on the compensated first or third time period, the conduction sequence of each switch transistor within the switching cycle is re-determined.

10. A fully soft-switching charge and discharge control device for an intelligent lithium battery, characterized in that, include: Memory, used to store computer programs; A processor, configured to, when executing a computer program, implement the steps of the fully soft-switching charge-discharge control method for a smart lithium battery as described in any one of claims 1 to 9.

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