Flying capacitor control circuit and control method

Abstract

The invention relates to a flying capacitor control circuit, and the circuit comprises a basic circuit which comprises a first capacitor, a second capacitor, and a third capacitor, and the first capacitor and the second capacitor are connected in series; the control circuit comprises a first switch unit, a second switch unit, a third switch unit and a fourth switch unit; one end of the first switch unit is connected to the anode of the first capacitor, and the other end is connected to the anode of the third capacitor through the first resistor; one end of the second switch unit is connected between the first capacitor and the second capacitor, and the other end is connected to the anode of the third capacitor through the second resistor; one end of the third switch unit is connected between the first capacitor and the second capacitor, and the other end is connected to the cathode of the third capacitor through the third resistor; one end of the fourth switch unit is connected to the cathode of the second capacitor, and the other end is connected to the cathode of the third capacitor through the fourth resistor. By accurately controlling the capacitor voltage, the circuit stability is improved, the energy waste is reduced, and efficient voltage regulation is realized.

Description

Technical Field

[0001] The present application relates to the field of new energy, and in particular to a flying capacitor control circuit and a control method. Background Art

[0002] In recent years, with the rapid development of new energy fields such as electric vehicles and energy storage, DCDC power conversion equipment has gradually upgraded from two-level topology to three-level topology, among which the flying capacitor three-level topology has been widely used due to its advantages such as low cost and simple control. However, this three-level topology has some problems in actual operation, especially the flying capacitor voltage fluctuation is difficult to control. When running at high current, the voltage fluctuation range of the flying capacitor can be controlled by algorithm, but the energy flowing through the flying capacitor is small under low current, and it is difficult to control its voltage fluctuation only by algorithm, and the equipment is difficult to operate normally under low current state.

[0003] In addition, when the current is 0A, the voltage of the flying capacitor drops rapidly to close to 0V due to self-discharge. At this time, if the device runs a non-zero current again, the voltage difference between the bus capacitor and the flying capacitor is large, which can easily cause the power tube to short-circuit or damage. Therefore, how to stably control the flying capacitor voltage under low current and 0A operation conditions has become a key technical issue in the application of flying capacitor topology. Summary of the invention

[0004] To solve the above technical problems, the inventors have tried many solutions, such as: The first solution adopts the DC output channel pair operation mode, that is, the method of achieving the predetermined output through two currents. Specifically, this solution adopts two output channels, one of which outputs a large current to the outside, and the other channel inputs a large current to the inside, and the composite value of the two currents finally reaches the target value. When the device needs to output a certain current, one channel will output current to the external load, and the other channel will feed back the same current to the inside of the device. The two currents are combined to achieve the predetermined output current target. Although this design can solve the problem of controlling the flying capacitor voltage under low current or 0A operation, since a large current is always running inside the device, the device will lose more energy under low current or 0A current, resulting in additional heat loss. And because the current is not directly generated by the control circuit of the device, but through the synthesis of two current channels, the output current fluctuates greatly, making the output current of the power supply unstable and poor in accuracy. In addition, this method may also lead to a large leakage current, that is, the device may have unnecessary current leaking into the environment when it is not fully loaded, which affects the current control accuracy of some precision equipment. Especially in the field where the current ripple, accuracy and leakage current requirements are high, this solution cannot meet the performance requirements.

[0005] The second solution is to add a high-frequency isolation transformer phase-shifted full-bridge circuit between the bus capacitor and the flying capacitor to control the flying capacitor voltage under low current or 0A operation. In this solution, the voltage of the bus capacitor is twice the voltage of the flying capacitor. The voltage of the bus capacitor is stably converted to the voltage required by the flying capacitor through a high-frequency isolation transformer, thereby achieving stable control of the flying capacitor voltage. Although this solution can solve the problem of unstable flying capacitor voltage, the cost of high-frequency transformers is usually high, especially when higher power is required, the manufacturing and procurement costs of the transformer will increase further. In addition, although high-frequency isolation transformers can work effectively in lower power applications, their application in high-power applications is greatly limited due to power density limitations. The power capacity of high-frequency transformers is relatively low and cannot withstand higher power requirements, so this solution is not suitable for the design of high-power equipment. The design and manufacture of high-frequency transformers and phase-shifted full-bridge circuits require a high level of technology, involving difficulties in high-frequency electromagnetic compatibility, power conversion control, and thermal management, making the design and implementation of the overall system more complicated, especially for high-power systems. Therefore, this solution also has obvious defects.

[0006] Although the various solutions attempted by the inventors above solve the problem that the flying capacitor voltage cannot be controlled under low current or 0A current conditions, they also cause more new technical problems, so a third solution is proposed. Figure 1 As shown, the third scheme adds resistors R5, R6 and R7 to the traditional flying capacitor circuit, wherein one end of resistor R5 is connected between capacitor C1 and switch tube T5, and the other end is connected to the positive electrode of capacitor C3. One end of resistor R6 is connected to the positive electrode of capacitor C3, and the other end is connected to the negative electrode of capacitor C3. One end of resistor R7 is connected to the negative electrode of capacitor C3, and the other end is connected between capacitor C2 and switch tube C8. Since the voltage of capacitors C1 and C2 is very high, the resistance values ​​of resistors R5, R6 and R7 also need to be selected with higher resistance values. When switch tubes T5-T8 are not working, that is, 0A current, the self-discharge of capacitor C3 and the charging of capacitor C3 by resistors R5, R6 and R7 are almost equal, thereby stabilizing the voltage of capacitor C3 at half the sum of capacitors C1 and C2. When the small current is running, because the resistance value is too large, the energy provided can only meet the self-discharge of capacitor C3, and there is no excess energy to stabilize the circuit voltage, so it is impossible to achieve the voltage of the stable capacitor C3 at half the sum of the capacitor C1 and the capacitor C2. Therefore, the third scheme can only solve the problem of stabilizing the voltage when the current is 0A, but cannot solve the problem of small current operation. However, since the circuit design of the third scheme is simple, the inventor has conducted multiple research iterations on the third scheme, and finally obtained a solution that can not only solve the problem of maintaining the circuit voltage stable in two situations, but also has low cost and simple design, which is the technical solution of this application.

[0007] In a first aspect, the present application provides a flying capacitor control circuit, comprising: A basic circuit includes a first capacitor, a second capacitor and a third capacitor, wherein the first capacitor is connected in series with the second capacitor; A control circuit comprises a first switch unit, a second switch unit, a third switch unit and a fourth switch unit; one end of the first switch unit is connected to the positive electrode of the first capacitor, and the other end is connected to the positive electrode of the third capacitor through a first resistor; one end of the second switch unit is connected between the first capacitor and the second capacitor, and the other end is connected to the positive electrode of the third capacitor through a second resistor; one end of the third switch unit is connected between the first capacitor and the second capacitor, and the other end is connected to the negative electrode of the third capacitor through a third resistor; one end of the fourth switch unit is connected to the negative electrode of the second capacitor, and the other end is connected to the negative electrode of the third capacitor through a fourth resistor.

[0008] Optionally, the basic circuit further includes a fifth switch unit, a sixth switch unit, a seventh switch unit and an eighth switch unit; One end of the fifth switch unit is connected to the positive electrode of the first capacitor, and the other end is connected to the sixth switch unit; one end of the sixth switch unit is connected to the fifth switch unit, and the other end is connected to the seventh switch unit; one end of the seventh switch unit is connected to the sixth switch unit, and the other end is connected to the eighth switch unit; one end of the eighth switch unit is connected to the seventh switch unit, and the other end is connected to the negative electrode of the second capacitor.

[0009] Optionally, the first switch unit is also connected between the fifth switch unit and the sixth switch unit through a first resistor; the second switch unit is also connected between the fifth switch unit and the sixth switch unit through a second resistor; the third switch unit is also connected between the seventh switch unit and the eighth switch unit through a third resistor; the fourth switch unit is also connected between the seventh switch unit and the eighth switch unit through a fourth resistor.

[0010] Optionally, when the fifth switch unit is turned on, the second switch unit and the fourth switch unit are not turned on; when the eighth switch unit is turned on, the first switch unit and the third switch unit are not turned on.

[0011] Optionally, when the first switch unit and the third switch unit are turned on and the voltage of the third capacitor is greater than the voltage of the first capacitor, the positive electrode of the third capacitor is connected to the positive electrode of the first capacitor through the first resistor and the first switch unit connected in sequence, and the negative electrode of the third capacitor is connected to the negative electrode of the first capacitor through the third resistor and the third switch unit connected in sequence, so as to form a loop to charge the first capacitor; When the second switch unit and the fourth switch unit are turned on and the voltage of the third capacitor is greater than the voltage of the second capacitor, the positive electrode of the third capacitor is connected to the positive electrode of the second capacitor through the second resistor and the second switch unit connected in sequence, and the negative electrode of the third capacitor is connected to the negative electrode of the second capacitor through the fourth resistor and the fourth switch unit connected in sequence, thereby forming a loop to charge the second capacitor.

[0012] Optionally, when the first switch unit and the third switch unit are turned on and the voltage of the third capacitor is less than the voltage of the first capacitor, the positive electrode of the first capacitor is connected to the positive electrode of the third capacitor through the first switch unit and the first resistor connected in sequence, and the negative electrode of the first capacitor is connected to the negative electrode of the third capacitor through the third switch unit and the third resistor connected in sequence, thereby forming a loop to charge the third capacitor; When the second switch unit and the fourth switch unit are turned on and the voltage of the third capacitor is less than the voltage of the second capacitor, the positive electrode of the second capacitor is connected to the positive electrode of the third capacitor through the second switch unit and the second resistor connected in sequence, and the negative electrode of the second capacitor is connected to the negative electrode of the third capacitor through the fourth switch unit and the fourth resistor connected in sequence, thereby forming a loop to charge the third capacitor.

[0013] Optionally, the first switch unit includes a first switch tube and a first diode connected in parallel, the collector of the first switch tube is connected to the positive electrode of the first capacitor, and the emitter of the first switch tube is connected to the first resistor; the second switch unit includes a second switch tube and a second diode connected in parallel, the emitter of the second switch tube is connected between the first capacitor and the second capacitor, and the collector of the second switch tube is connected to the second resistor; the third switch unit includes a third switch tube and a third diode connected in parallel, the collector of the third switch tube is connected between the first capacitor and the second capacitor, and the emitter of the third switch tube is connected to the third resistor; the fourth switch unit includes a fourth switch tube and a fourth diode connected in parallel, the emitter of the fourth switch tube is connected to the negative electrode of the second capacitor, and the collector of the fourth switch tube is connected to the fourth resistor; The fifth switch unit includes a fifth switch tube and a fifth diode connected in parallel; the sixth switch unit includes a sixth switch tube and a sixth diode connected in parallel; the seventh switch unit includes a seventh switch tube and a seventh diode connected in parallel; the eighth switch unit includes an eighth switch tube and an eighth diode connected in parallel.

[0014] In a second aspect, the present application provides a control method for the flying capacitor control circuit as described above, the method comprising: Detecting the voltages of the first capacitor, the second capacitor, and the third capacitor, and comparing the voltage of the third capacitor with half of the sum of the first capacitor and the second capacitor to obtain a voltage difference; When the voltage difference is greater than a first threshold, the flying capacitor control circuit enters a working state; The conduction time of the first switch unit, the third switch unit or the second switch unit, the fourth switch unit is adjusted, and the voltage of the third capacitor is stabilized by the first capacitor and the second capacitor.

[0015] Optionally, the step of adjusting the duty cycle of the first switch unit, the third switch unit or the second switch unit, the fourth switch unit, and stabilizing the voltage of the third capacitor through the first capacitor and the second capacitor specifically includes: Compare the set value of the flying capacitor voltage with the actual sampled value to obtain a voltage error value; Perform proportional and integral calculations according to the voltage error value to obtain a control signal; The control signal is converted into a PWM waveform signal to adjust the conduction time of the first switch unit, the second switch unit, the third switch unit and the fourth switch unit.

[0016] Optionally, the method further comprises: When the voltage difference is less than the second threshold, the flying capacitor control circuit enters a waiting state, and the first switch unit, the second switch unit, the third switch unit and the fourth switch unit are all in an off state.

[0017] This application adopts the design of connecting the power switch unit and the non-inductive small resistance resistor in series, and the flying capacitor control circuit and the basic circuit are semi-decoupled, avoiding the problems of large current ripple and poor current accuracy when the DC output channel is towed in the traditional circuit, ensuring the high performance and high reliability of the system. In addition, when the high current is running, the flying capacitor control circuit does not need to run, and only works when the current is small or 0A, thereby avoiding unnecessary energy loss and improving the overall energy efficiency. Due to the simple circuit structure and easy implementation of the control method, this application can not only effectively reduce the production cost, but also simplify the maintenance and debugging process of the equipment. On the whole, the circuit scheme of this application significantly reduces the complexity and cost of the system while ensuring high efficiency, making it suitable for the field of high-power equipment and meeting the market demand for low-cost, high-performance solutions.

[0018] Furthermore, by adding specific switch units and resistor designs, the circuit can accurately control the voltage changes between the first capacitor, the second capacitor and the third capacitor under different working conditions, ensuring the smooth exchange of energy and the balanced charging and discharging of the capacitor. These optimizations not only effectively prevent the phenomenon of voltage imbalance, but also greatly improve the reliability of the equipment, avoiding the failure problem caused by capacitor imbalance in traditional circuits. The technical solution of the present application enables the equipment to achieve efficient and stable operation in high-power applications, with higher performance and lower cost, meeting the current market demand for high-efficiency and high-power equipment. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Figure 1 A circuit diagram of a flying capacitor control circuit of a preliminary solution of the inventor of the present application is shown; Figure 2 A circuit diagram of a flying capacitor control circuit according to an embodiment of the present application is shown; Figure 3 A schematic diagram showing the current flow when a flying capacitor control circuit works according to an embodiment of the present application is shown; Figure 4 A schematic diagram showing the current flow of a flying capacitor control circuit when it is working according to another embodiment of the present application is shown; Figure 5 A schematic flow chart of a flying capacitor control method according to an embodiment of the present application is shown. DETAILED DESCRIPTION

[0020] In order to make the above-mentioned purposes, features and advantages of the present application more obvious and easy to understand, the specific implementation methods of the present application are described in detail below in conjunction with the accompanying drawings. It is to be understood that the specific embodiments described herein are only used to explain the present application, rather than to limit the present application. It should also be noted that, for ease of description, only some structures related to the present application are shown in the accompanying drawings, rather than all structures. Based on the embodiments in the present application, all other embodiments obtained by ordinary technicians in this field without making creative work are within the scope of protection of this application.

[0021] The terms "including" and "having" and any variations thereof in this application are intended to cover non-exclusive inclusions. For example, a process, method, system, product or device comprising a series of steps or units is not limited to the listed steps or units, but may optionally include steps or units not listed, or may optionally include other steps or units inherent to these processes, methods, products or devices.

[0022] Reference to "embodiments" herein means that a particular feature, structure, or characteristic described in conjunction with the embodiments may be included in at least one embodiment of the present application. The appearance of the phrase in various locations in the specification does not necessarily refer to the same embodiment, nor is it an independent or alternative embodiment that is mutually exclusive with other embodiments. It is explicitly and implicitly understood by those skilled in the art that the embodiments described herein may be combined with other embodiments.

[0023] Figure 2 FIG. 2 shows a circuit diagram of a flying capacitor control circuit according to an embodiment of the present application. Figure 2 As shown, the flying capacitor control circuit includes: The basic circuit includes a first capacitor, a second capacitor and a third capacitor, wherein the first capacitor and the second capacitor are connected in series.

[0024] The first capacitor and the second capacitor are bus capacitors, the sum of the voltages of the first capacitor and the second capacitor is the bus capacitor voltage Upn, and the voltage of the first capacitor is equal to the voltage of the second capacitor, both of which are 0.5Upn. The third capacitor is a flying capacitor, and the voltage of the third capacitor is the flying capacitor voltage. By connecting the first capacitor and the second capacitor in series, the voltage distribution can be adjusted according to the demand of the load, thereby effectively controlling the voltage of the third capacitor.

[0025] A control circuit includes a first switch unit, a second switch unit, a third switch unit and a fourth switch unit. One end of the first switch unit is connected to the positive electrode of the first capacitor, and the other end is connected to the positive electrode of the third capacitor through a first resistor. One end of the second switch unit is connected between the first capacitor and the second capacitor, and the other end is connected to the positive electrode of the third capacitor through a second resistor. One end of the third switch unit is connected between the first capacitor and the second capacitor, and the other end is connected to the negative electrode of the third capacitor through a third resistor. One end of the fourth switch unit is connected to the negative electrode of the second capacitor, and the other end is connected to the negative electrode of the third capacitor through a fourth resistor.

[0026] The first resistor, the second resistor, the third resistor, and the fourth resistor are all non-inductive small-resistance resistors. The combination of each switch unit and the non-inductive small-resistance resistor enables each group of capacitors and current paths to be precisely adjusted under different switching states. The configuration of the first switch unit, the second switch unit, the third switch unit, and the fourth switch unit allows the system to dynamically adjust the current flow direction by controlling the on and off of the switch according to actual needs, thereby ensuring precise control of the flying capacitor voltage. At the same time, the design of the switch unit in the control circuit enables the system to respond quickly to voltage changes. When the capacitor voltage is unstable, the state of the switch unit can be quickly adjusted to adjust the current path and try to ensure that the voltage of the flying capacitor is within a stable operating range. This flexible control mechanism improves the response speed of the system and helps to meet application scenarios with high voltage accuracy requirements.

[0027] Figure 3 FIG. 2 shows a schematic diagram of the current flow when the flying capacitor control circuit according to an embodiment of the present application is working. Figure 3 As shown, when the first switch unit and the third switch unit are turned on and the voltage of the third capacitor is greater than the voltage of the first capacitor, the positive electrode of the third capacitor is connected to the positive electrode of the first capacitor through the first resistor and the first switch unit connected in sequence, and the negative electrode of the third capacitor is connected to the negative electrode of the first capacitor through the third resistor and the third switch unit connected in sequence, thereby forming a loop to charge the first capacitor.

[0028] At this time, the current flows through the positive electrode of the third capacitor, through the first resistor, the first switch unit, the first capacitor, the third switch unit and the third resistor, and returns to the negative electrode of the third capacitor, forming a first working loop, so that the third capacitor charges the first capacitor to stabilize the voltage.

[0029] When the second switch unit and the fourth switch unit are turned on and the voltage of the third capacitor is greater than the voltage of the second capacitor, the positive electrode of the third capacitor is connected to the positive electrode of the second capacitor through the second resistor and the second switch unit connected in sequence, and the negative electrode of the third capacitor is connected to the negative electrode of the second capacitor through the fourth resistor and the fourth switch unit connected in sequence, thereby forming a loop to charge the second capacitor.

[0030] At this time, the current flows through the positive electrode of the third capacitor, through the second resistor, the second switch unit, the second capacitor, the fourth switch unit and the fourth resistor, and returns to the negative electrode of the third capacitor, forming a second working loop, so that the third capacitor charges the second capacitor to stabilize the voltage.

[0031] Through such a circuit design, the voltage can be effectively stabilized, the current flow can be adjusted, and the energy utilization efficiency of the circuit can be improved. These two charging circuits can achieve stable voltage regulation of the first capacitor and the second capacitor. The first circuit charges the first capacitor through the third capacitor. When the voltage of the third capacitor is higher than that of the first capacitor, the current flows through a specific path, effectively providing charging for the first capacitor and stabilizing its voltage. Similarly, the second circuit charges the second capacitor through the third capacitor to ensure that the voltage of the second capacitor remains within a reasonable range. Through the synergy of these two circuits, the voltage can be accurately regulated and stabilized, voltage fluctuations can be avoided, and the overall stability and performance of the system can be improved. At the same time, the design effectively reduces the mutual interference between capacitors, improves the energy utilization efficiency and response speed of the circuit, and helps to improve the reliability and operation efficiency of the equipment.

[0032] Figure 4 FIG. 2 shows a schematic diagram of the current flow when the flying capacitor control circuit according to another embodiment of the present application is working. Figure 4As shown, when the first switch unit and the third switch unit are turned on and the voltage of the third capacitor is less than the voltage of the first capacitor, the positive electrode of the first capacitor is connected to the positive electrode of the third capacitor through the first switch unit and the first resistor connected in sequence, and the negative electrode of the first capacitor is connected to the negative electrode of the third capacitor through the third switch unit and the third resistor connected in sequence, thereby forming a loop to charge the third capacitor.

[0033] At this time, the current flows through the positive electrode of the first capacitor, the first switch unit, the first resistor, the third capacitor, the third resistor and the third switch unit back to the negative electrode of the first capacitor, forming a third working loop, so that the first capacitor charges the third capacitor to stabilize the voltage.

[0034] When the second switch unit and the fourth switch unit are turned on and the voltage of the third capacitor is less than the voltage of the second capacitor, the positive electrode of the second capacitor is connected to the positive electrode of the third capacitor through the second switch unit and the second resistor connected in sequence, and the negative electrode of the second capacitor is connected to the negative electrode of the third capacitor through the fourth switch unit and the fourth resistor connected in sequence, thereby forming a loop to charge the third capacitor.

[0035] At this time, the current flows through the positive electrode of the second capacitor, the second switch unit, the second resistor, the third capacitor, the fourth resistor and the fourth switch unit back to the negative electrode of the second capacitor, forming a fourth working loop, so that the second capacitor charges the third capacitor to stabilize the voltage.

[0036] By controlling the flow of current between different capacitors, accurate voltage regulation and stabilization can be achieved. Each working loop is charged and discharged according to the voltage difference between the capacitors, thereby effectively balancing and adjusting the voltage of each capacitor and avoiding the instability caused by voltage fluctuations. Specifically, when the voltage of the third capacitor is less than or greater than the first or second capacitor, the system can automatically transfer electrical energy from the capacitor with higher voltage to the capacitor with lower voltage through the corresponding loop, thereby ensuring that the voltage of the system remains within a predetermined range and improving overall stability and reliability. In addition, through this design, the system can dynamically control charging according to the voltage difference of the capacitor to improve the efficiency of energy transmission. The design of this charging loop keeps the voltage of each capacitor at an appropriate level, while reducing the mutual interference between the capacitors in the system, ensuring that each capacitor operates in a suitable working state. In addition, the use of multiple independent working loops can effectively share the load, reduce the pressure of a single loop, and improve the reliability and durability of the circuit, especially under high-power operating conditions.

[0037] In some embodiments, the basic circuit further includes a fifth switch unit, a sixth switch unit, a seventh switch unit and an eighth switch unit. One end of the fifth switch unit is connected to the positive electrode of the first capacitor, and the other end is connected to the sixth switch unit. One end of the sixth switch unit is connected to the fifth switch unit, and the other end is connected to the seventh switch unit. One end of the seventh switch unit is connected to the sixth switch unit, and the other end is connected to the eighth switch unit. One end of the eighth switch unit is connected to the seventh switch unit, and the other end is connected to the negative electrode of the second capacitor.

[0038] The fifth switch unit, the sixth switch unit, the seventh switch unit and the eighth switch unit are connected in series, and one end of the fifth switch unit is connected to the positive electrode of the first capacitor, and one end of the eighth switch unit is connected to the negative electrode of the second capacitor. The design of the series connection ensures the effective control of the current path. Under this configuration, the fifth to eighth switch units form an adjustable switch array, which can accurately control the charging and discharging process of the capacitor. The series design of the fifth to eighth switch units can also realize the multi-stage adjustment function, accurately control the opening and closing of each switch unit, further improve the accuracy of capacitor control, and avoid the phenomenon of voltage imbalance. Through this series structure, the circuit can more flexibly cope with different current loads, ensure the reliability and stability of the system, especially when operating at high power, avoiding the failure problem caused by voltage imbalance.

[0039] In some embodiments, the first switch unit is further connected to the fifth switch unit and the sixth switch unit through a first resistor. The second switch unit is further connected to the fifth switch unit and the sixth switch unit through a second resistor. The third switch unit is further connected to the seventh switch unit and the eighth switch unit through a third resistor. The fourth switch unit is further connected to the seventh switch unit and the eighth switch unit through a fourth resistor.

[0040] In some embodiments, the first switch unit, the second switch unit, the third switch unit and the fourth switch unit are small current switch units, and the fifth switch unit, the sixth switch unit, the seventh switch unit and the eighth switch unit are large current switch units. The small current switch unit and the large current switch unit bear different current loads respectively, and the small current switch unit is responsible for the fine control under the condition of lower current, while the large current switch unit is responsible for the switching of high current transmission and high power. Through this division of labor, the circuit can be efficiently switched under different working conditions, and the small current switch unit can be prevented from being damaged or overheated due to excessive current, and the large current switch unit will not increase unnecessary burden due to the control demand of small current. The resistor is connected in series between the small current switch unit and the large current switch unit, which helps to control the distribution of current and voltage through these switch units. The small current switch unit limits the amplitude of the current through the resistor, so that the large current switch unit can focus on the transmission of high current without being affected by the low current switching process. The presence of the resistor ensures that the working state of each switch unit is more stable, avoids excessive current fluctuations, and reduces the interference that may occur in the circuit.

[0041] In some embodiments, when the fifth switch unit is turned on, the second switch unit and the fourth switch unit are not turned on; when the eighth switch unit is turned on, the first switch unit and the third switch unit are not turned on.

[0042] If the fifth switch unit and the second switch unit or the fourth switch unit are turned on at the same time, or the eighth switch unit and the first switch unit or the third switch unit are turned on at the same time, a short circuit path will be formed in the circuit, resulting in a large current impact, which may damage the device. By designing interlocking logic, the second switch unit and the fourth switch unit are not turned on when the fifth switch unit is turned on, and the first switch unit and the third switch unit are not turned on when the eighth switch unit is turned on, this short circuit can be avoided and the safety of the circuit can be improved.

[0043] The voltage Uf of the flying capacitor needs to be maintained at a certain level during operation to achieve the balance and voltage division of the bus capacitor voltage Upn in the circuit. The fifth switch unit and the eighth switch unit respectively control different paths of the current. When the fifth switch unit is turned on, the current flows between C1 and C3, and the charging and discharging of C3 is achieved through the control of the first switch unit and the third switch unit; when the eighth switch unit is turned on, the current flows between C2 and C3, and the charging and discharging of C3 is achieved through the control of the second switch unit and the fourth switch unit. Therefore, by alternately controlling the conduction state of the fifth switch unit and the eighth switch unit, combined with the conduction and shutdown of the first switch unit to the fourth switch unit, the dynamic charging and discharging of the flying capacitor can be achieved, and the required flying capacitor voltage Uf can be maintained.

[0044] In some embodiments, the first switch unit includes a first switch tube and a first diode connected in parallel, the collector of the first switch tube is connected to the positive electrode of the first capacitor, and the emitter of the first switch tube is connected to the first resistor; the second switch unit includes a second switch tube and a second diode connected in parallel, the emitter of the second switch tube is connected between the first capacitor and the second capacitor, and the collector of the second switch tube is connected to the second resistor; the third switch unit includes a third switch tube and a third diode connected in parallel, the collector of the third switch tube is connected between the first capacitor and the second capacitor, and the emitter of the third switch tube is connected to the third resistor; the fourth switch unit includes a fourth switch tube and a fourth diode connected in parallel, the emitter of the fourth switch tube is connected to the negative electrode of the second capacitor, and the collector of the fourth switch tube is connected to the fourth resistor; the fifth switch unit includes a fifth switch tube and a fifth diode connected in parallel; the sixth switch unit includes a sixth switch tube and a sixth diode connected in parallel; the seventh switch unit includes a seventh switch tube and a seventh diode connected in parallel; the eighth switch unit includes an eighth switch tube and an eighth diode connected in parallel.

[0045] By connecting the switch tube in parallel with the diode, each switch unit can effectively protect the switch tube from reverse current and voltage spikes during operation, extending the device life and improving the stability of the circuit. At the same time, the diode ensures the smooth flow of current, reduces energy loss, and improves work efficiency. In addition, this design reduces the complexity of the circuit, enhances the flexibility and adaptability of the circuit, and can operate stably under a variety of current and voltage conditions, providing high reliability and reducing costs.

[0046] The first switch tube, the second switch tube, the third switch tube and the fourth switch tube are all small current IGBT or MOS power tubes, and the first diode, the second diode, the third diode and the fourth diode are parallel diodes of the corresponding switch tubes. The fifth switch tube, the sixth switch tube, the seventh switch tube and the eighth switch tube are all large current IGBT or MOS power tubes, and the fifth diode, the sixth diode, the seventh diode and the eighth diode are parallel diodes of the corresponding switch tubes.

[0047] According to the above embodiments, the present application adds a specific switch unit and a resistor design, and the circuit can accurately control the voltage change between the first capacitor, the second capacitor, and the third capacitor under different working conditions, ensuring the smooth exchange of energy and the balanced charge and discharge of the capacitor. These optimizations not only effectively prevent the phenomenon of voltage imbalance, but also greatly improve the reliability of the equipment, avoiding the failure problem caused by capacitor imbalance in traditional circuits. The technical solution of the present application enables the equipment to achieve efficient and stable operation in high-power applications, with higher performance and lower cost, meeting the current market demand for high-efficiency and high-power equipment.

[0048] Figure 5 FIG. 2 shows a schematic flow diagram of a flying capacitor control method according to an embodiment of the present application. Figure 5 As shown, the present application also provides a control method for the above-mentioned flying capacitor control circuit, the method comprising the following steps: Step S100, detecting the voltages of the first capacitor, the second capacitor, and the third capacitor, and comparing the voltage of the third capacitor with half of the sum of the first capacitor and the second capacitor to obtain a voltage difference.

[0049] The flying capacitor control circuit detects the voltages of the first capacitor, the second capacitor, and the third capacitor, and compares the voltage of the third capacitor with half of the sum of the voltages of the first capacitor and the second capacitor to obtain the voltage difference. This process ensures that the circuit can monitor the voltage changes of the capacitors in real time and reflect the relationship between the voltages. By detecting the voltage difference, the circuit can accurately evaluate the voltage difference between the capacitors, provide a basis for subsequent control decisions, help to promptly identify the voltage imbalance between the capacitors, and ensure that the circuit can maintain a stable voltage environment during operation, thereby avoiding unnecessary damage caused by excessive voltage differences.

[0050] Step S200: When the voltage difference is greater than a first threshold, the flying capacitor control circuit enters a working state.

[0051] Setting the threshold can effectively avoid the circuit's misoperation when the voltage fluctuates too much, ensuring that the circuit only enters the working state when needed, avoiding unnecessary energy consumption. At the same time, when the voltage difference reaches the predetermined threshold, the circuit automatically enters the working state, effectively improving the sensitivity and response speed of the control.

[0052] Step S300, adjusting the on-time of the first switch unit, the third switch unit or the second switch unit, the fourth switch unit, and stabilizing the voltage of the third capacitor through the first capacitor and the second capacitor.

[0053] By adjusting the on-time of the first switch unit, the third switch unit, or the second switch unit, the fourth switch unit, the charging and discharging of the first capacitor and the second capacitor are controlled, thereby stabilizing the voltage of the third capacitor. This operation can accurately adjust the voltage change in the circuit so that the voltage of the third capacitor is always kept within a stable range, avoiding excessive voltage fluctuations that affect the working efficiency and stability of the circuit. At the same time, this adjustment method can achieve more precise control and improve the adaptability of the circuit under complex conditions.

[0054] In one embodiment, the above step S300 of adjusting the on-time of the first switch unit, the third switch unit or the second switch unit, the fourth switch unit, and stabilizing the voltage of the third capacitor by the first capacitor and the second capacitor specifically includes the following steps: Step S310 , comparing the set value of the flying capacitor voltage with the actual sampled value to obtain a voltage error value.

[0055] By comparing the set value and the actual value, the current state of the circuit can be clearly understood and voltage deviation can be discovered in time. This feedback mechanism enables the circuit to self-regulate according to the actual working conditions, enhancing the accuracy and stability of the circuit.

[0056] Step S320, performing proportional and integral calculations according to the voltage error value to obtain a control signal.

[0057] The PI controller performs proportional and integral calculations based on the voltage error value to obtain a control signal. This control signal reflects the degree of voltage error and provides a basis for subsequent adjustments. Through proportional and integral calculations, the circuit can control the voltage more accurately and reduce the instability caused by voltage fluctuations. The proportional and integral algorithm can effectively balance the response speed and stability, improve the control accuracy of the circuit, and reduce the voltage error.

[0058] Step S330, converting the control signal into a PWM waveform signal to adjust the on-time of the first switch unit, the second switch unit, the third switch unit and the fourth switch unit.

[0059] The PI controller converts the control signal into a PWM waveform signal, and the system adjusts the on-time of the first switch unit, the second switch unit, the third switch unit, and the fourth switch unit based on the signal. This process accurately controls the switching state of the switch unit according to the frequency and duty cycle of the PWM waveform. By adjusting the on-time of each switch unit through the PWM waveform signal, accurate voltage control can be achieved to ensure that the capacitor voltage is within the set range. This adjustment method has the characteristics of high efficiency, accuracy, and fast response, and can cope with complex working environments and ensure the stable operation of the circuit.

[0060] In some embodiments, when the voltage difference is less than the second threshold, the flying capacitor control circuit enters a waiting state, and the first switch unit, the second switch unit, the third switch unit, and the fourth switch unit are all in an off state. Entering the waiting state can effectively prevent the circuit from working ineffectively when the voltage is too low, avoid unnecessary energy consumption and workload of the system, and protect the circuit from potential damage caused by too low voltage. This mechanism helps to extend the service life of the system and improve overall efficiency.

[0061] The first threshold is greater than the second threshold, and a dead zone of the flying capacitor control circuit is formed by setting a voltage difference between the first threshold and the second threshold, thereby avoiding frequent state switching of the circuit when approaching a critical point.

[0062] In the control method of the flying capacitor control circuit, the specific implementation methods in different situations refer to the relevant contents of the embodiment of the circuit, which will not be described in detail here.

[0063] The technical features of the above-described embodiments may be arbitrarily combined. To make the description concise, not all possible combinations of the technical features in the above-described embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0064] The above-mentioned embodiments only express several implementation methods of the present application, and the descriptions thereof are relatively specific and detailed, but they cannot be understood as limiting the scope of the invention patent. It should be pointed out that, for a person of ordinary skill in the art, several variations and improvements can be made without departing from the concept of the present application, and these all belong to the protection scope of the present application. Therefore, the protection scope of the patent of the present application shall be subject to the attached claims.

Claims

1. A flying capacitor control circuit, characterized in that: include: A basic circuit includes a first capacitor, a second capacitor and a third capacitor, wherein the first capacitor is connected in series with the second capacitor; A control circuit comprises a first switch unit, a second switch unit, a third switch unit and a fourth switch unit; one end of the first switch unit is connected to the positive electrode of the first capacitor, and the other end is connected to the positive electrode of the third capacitor through a first resistor; one end of the second switch unit is connected between the first capacitor and the second capacitor, and the other end is connected to the positive electrode of the third capacitor through a second resistor; one end of the third switch unit is connected between the first capacitor and the second capacitor, and the other end is connected to the negative electrode of the third capacitor through a third resistor; one end of the fourth switch unit is connected to the negative electrode of the second capacitor, and the other end is connected to the negative electrode of the third capacitor through a fourth resistor.

2. The flying capacitor control circuit according to claim 1, characterized in that: When the first switch unit and the third switch unit are turned on and the voltage of the third capacitor is greater than the voltage of the first capacitor, the positive electrode of the third capacitor is connected to the positive electrode of the first capacitor through the first resistor and the first switch unit connected in sequence, and the negative electrode of the third capacitor is connected to the negative electrode of the first capacitor through the third resistor and the third switch unit connected in sequence, thereby forming a loop to charge the first capacitor; When the second switch unit and the fourth switch unit are turned on and the voltage of the third capacitor is greater than the voltage of the second capacitor, the positive electrode of the third capacitor is connected to the positive electrode of the second capacitor through the second resistor and the second switch unit connected in sequence, and the negative electrode of the third capacitor is connected to the negative electrode of the second capacitor through the fourth resistor and the fourth switch unit connected in sequence, thereby forming a loop to charge the second capacitor.

3. The flying capacitor control circuit according to claim 1, characterized in that: When the first switch unit and the third switch unit are turned on and the voltage of the third capacitor is less than the voltage of the first capacitor, the positive electrode of the first capacitor is connected to the positive electrode of the third capacitor through the first switch unit and the first resistor connected in sequence, and the negative electrode of the first capacitor is connected to the negative electrode of the third capacitor through the third switch unit and the third resistor connected in sequence, thereby forming a loop to charge the third capacitor; When the second switch unit and the fourth switch unit are turned on and the voltage of the third capacitor is less than the voltage of the second capacitor, the positive electrode of the second capacitor is connected to the positive electrode of the third capacitor through the second switch unit and the second resistor connected in sequence, and the negative electrode of the second capacitor is connected to the negative electrode of the third capacitor through the fourth switch unit and the fourth resistor connected in sequence, thereby forming a loop to charge the third capacitor.

4. The flying capacitor control circuit according to claim 1, characterized in that: The basic circuit further includes a fifth switch unit, a sixth switch unit, a seventh switch unit and an eighth switch unit; One end of the fifth switch unit is connected to the positive electrode of the first capacitor, and the other end is connected to the sixth switch unit; one end of the sixth switch unit is connected to the fifth switch unit, and the other end is connected to the seventh switch unit; one end of the seventh switch unit is connected to the sixth switch unit, and the other end is connected to the eighth switch unit; one end of the eighth switch unit is connected to the seventh switch unit, and the other end is connected to the negative electrode of the second capacitor.

5. The flying capacitor control circuit according to claim 4, characterized in that: The first switch unit is also connected between the fifth switch unit and the sixth switch unit through a first resistor; the second switch unit is also connected between the fifth switch unit and the sixth switch unit through a second resistor; the third switch unit is also connected between the seventh switch unit and the eighth switch unit through a third resistor; the fourth switch unit is also connected between the seventh switch unit and the eighth switch unit through a fourth resistor.

6. The flying capacitor control circuit according to claim 5, characterized in that: When the fifth switch unit is turned on, the second switch unit and the fourth switch unit are not turned on; when the eighth switch unit is turned on, the first switch unit and the third switch unit are not turned on.

7. The flying capacitor control circuit according to claim 6, characterized in that: The first switch unit includes a first switch tube and a first diode connected in parallel, the collector of the first switch tube is connected to the positive electrode of the first capacitor, and the emitter of the first switch tube is connected to the first resistor; the second switch unit includes a second switch tube and a second diode connected in parallel, the emitter of the second switch tube is connected between the first capacitor and the second capacitor, and the collector of the second switch tube is connected to the second resistor; the third switch unit includes a third switch tube and a third diode connected in parallel, the collector of the third switch tube is connected between the first capacitor and the second capacitor, and the emitter of the third switch tube is connected to the third resistor; the fourth switch unit includes a fourth switch tube and a fourth diode connected in parallel, the emitter of the fourth switch tube is connected to the negative electrode of the second capacitor, and the collector of the fourth switch tube is connected to the fourth resistor; The fifth switch unit includes a fifth switch tube and a fifth diode connected in parallel; the sixth switch unit includes a sixth switch tube and a sixth diode connected in parallel; the seventh switch unit includes a seventh switch tube and a seventh diode connected in parallel; the eighth switch unit includes an eighth switch tube and an eighth diode connected in parallel.

8. A control method for a flying capacitor control circuit according to any one of claims 1 to 7, characterized in that: The method comprises: Detecting the voltages of the first capacitor, the second capacitor, and the third capacitor, and comparing the voltage of the third capacitor with half of the sum of the first capacitor and the second capacitor to obtain a voltage difference; When the voltage difference is greater than a first threshold, the flying capacitor control circuit enters a working state; The conduction time of the first switch unit, the third switch unit or the second switch unit, the fourth switch unit is adjusted, and the voltage of the third capacitor is stabilized by the first capacitor and the second capacitor.

9. The flying capacitor control method according to claim 8, characterized in that: The step of adjusting the duty cycle of the first switch unit, the third switch unit or the second switch unit, the fourth switch unit, and stabilizing the voltage of the third capacitor by using the first capacitor and the second capacitor specifically includes: Compare the set value of the flying capacitor voltage with the actual sampled value to obtain a voltage error value; Perform proportional and integral calculations according to the voltage error value to obtain a control signal; The control signal is converted into a PWM waveform signal to adjust the conduction time of the first switch unit, the second switch unit, the third switch unit and the fourth switch unit.

10. The flying capacitor control method according to claim 8, characterized in that: Also includes: When the voltage difference is less than the second threshold, the flying capacitor control circuit enters a waiting state, and the first switch unit, the second switch unit, the third switch unit and the fourth switch unit are all in an off state.

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