Regenerative passive soft switching-Boost type PFC circuit

Abstract

The invention relates to the technical field of power electronics, and discloses a regenerative passive soft switching-Boost type PFC (Power Factor Correction) circuit, which comprises a main power transmission loop and a passive regenerative buffer loop. The main power transmission loop constructs an electric energy transmission path. In the passive regeneration buffer loop, a buffer inductor is connected in series with a main switch tube branch, a buffer capacitor is connected in parallel with two ends of a main switch tube, and an auxiliary winding and a main inductor share a magnetic core and are connected to the circuit. According to the circuit, a buffer inductor is used for hindering current abrupt change so as to limit the switch-on current rise rate, a buffer capacitor is used for hindering voltage abrupt change so as to limit the switch-off voltage rise rate, zero-current switch-on and zero-voltage switch-off of a main switch tube are achieved, and meanwhile an auxiliary winding transfers energy captured by a buffer loop in a lossless mode through magnetic coupling and feeds the energy back to a load side. Switching loss is eliminated, electromagnetic interference is suppressed, active control is not needed, and circuit efficiency and reliability are improved.

Description

Technical Field

[0001] This invention relates to the field of power electronics technology, specifically to a regenerative passive soft-switching-Boost type PFC circuit. Background Technology

[0002] Boost-type power factor correction circuits are widely used in power electronic converters. Because power switches are non-ideal devices, their turn-on and turn-off processes involve transit time. At the moment of turn-on, there is a time difference between the voltage drop and current rise, resulting in an overlap between the voltage and current waveforms; similarly, there is also an overlap between the voltage rise and current drop at the moment of turn-off. This waveform overlap generates switching losses, which are proportional to the switching frequency. While higher frequencies help reduce the size of passive components and achieve miniaturization and weight reduction of devices, under hard-switching conditions, the increased switching losses reduce converter efficiency and limit the improvement of the switching frequency.

[0003] Furthermore, power switches operating in hard-switching mode generate high voltage and current change rates. Especially at the moment of switch turn-on, large spike currents are generated in the circuit due to the reverse recovery characteristics of the boost diode. These high-frequency transients increase the electrothermal stress on the devices, posing a risk of damage due to the devices exceeding their safe operating range. They also induce electromagnetic interference, increasing the requirements for filtering circuits.

[0004] To address the aforementioned issues, existing technologies typically employ buffer circuits or soft-switching techniques to limit transient overvoltages, overcurrents, and rates of change. However, traditional energy-consuming buffer circuits (such as resistor-capacitor-diode buffer circuits) dissipate the absorbed parasitic energy in the resistive element, converting it into heat, resulting in additional energy loss. While soft-switching technology, which introduces active auxiliary switches, can reduce losses, it increases the complexity of the control circuit and system cost, and reduces system reliability. Therefore, how to achieve lossless recovery of buffered energy while realizing soft switching and reducing electromagnetic interference is a technical problem that needs to be solved in this field. Summary of the Invention

[0005] To address the problems of high switching losses and severe electromagnetic interference in existing Boost-type power factor correction circuits under hard-switching mode, as well as low energy utilization and reduced system efficiency due to resistor heating in traditional RCD snubber circuits, this invention provides a regenerative passive soft-switching Boost-type PFC circuit, which achieves soft switching of the main switch and feedback of snubber energy through a passive network.

[0006] To achieve the above objectives, the present invention provides the following technical solution:

[0007] A regenerative passive soft-switching Boost-type PFC circuit mainly includes a main power transmission circuit and a passive regenerative buffer circuit. The main power transmission circuit connects the positive terminal of the input voltage source to the same-name terminal of the main inductor, and the opposite-name terminal of the main inductor to a first circuit node, so that the anode of the main diode is connected to the first circuit node. The cathode of the main diode is connected to one end of the output capacitor and the load, and both the cathode of the main diode and the source of the main switching transistor are connected to a common ground, thereby constructing a power transmission path.

[0008] The passive regenerative buffer circuit utilizes the buffer inductor connected between the first circuit node and the second circuit node to access the main power transmission circuit. The anode of the first buffer diode and the cathode of the second buffer diode are connected to the second circuit node together, so that the cathode of the first buffer diode is connected to the common ground via the buffer capacitor, and the anode of the second buffer diode is connected to the drain of the main switch. The auxiliary winding that shares the same magnetic core as the main inductor is used to connect the positive terminal of the input voltage source to the drain of the main switch for energy feedback.

[0009] Furthermore, the auxiliary winding is wound on the same magnetic core as the main inductor to establish a magnetic coupling channel. The opposite-named terminal of the auxiliary winding is connected to the drain of the main switch. During the conduction of the main switch, an energy feedback channel is established through magnetic coupling, feeding back the energy stored in the passive regenerative buffer circuit to the load side, so that the auxiliary winding can be connected to the switching circuit network to participate in energy exchange.

[0010] Furthermore, the inductance value of the main inductor in the main power transmission circuit is greater than that of the buffer inductor in the passive regenerative buffer circuit. Utilizing the large inductance of the main inductor suppresses current ripple, ensuring a constant input current during the switching cycle, thereby establishing a steady-state energy transmission path that supports continuous conduction mode operation.

[0011] Furthermore, the buffer inductor is connected in series in the current path of the main switch, and its inductance is a non-zero finite value. At the instant the main switch is turned on, the buffer inductor's characteristic of impeding transient current changes limits the rate of rise of the current flowing through the main switch. At this time, the buffer inductor shunts the current originally flowing through the main diode in the main power transmission circuit, causing the current flowing through the buffer inductor to increase linearly, while the current flowing through the main diode decreases linearly. During this process, the rate of change of the current flowing through the main switch is constrained by the voltage relationship of the buffer inductor circuit, thereby eliminating the overlap of voltage and current at the instant of turn-on and reducing turn-on losses.

[0012] Furthermore, the buffer capacitor is connected in parallel across the main switch transistor, and its capacitance is a non-zero finite value. At the instant the main switch transistor turns off, the drain-source voltage of the main switch transistor is clamped by utilizing the characteristic that the voltage across the buffer capacitor cannot change abruptly. After turn-off, the buffer capacitor is charged using the input current, maintaining it in a constant-current charging state driven by the input current. During this process, the rise of the drain-source voltage of the main switch transistor is constrained by the constant-current charging relationship of the capacitor, causing the voltage to rise slowly and staggering the current fall time, thereby eliminating turn-off losses.

[0013] Furthermore, during the energy regeneration stage, a resonant discharge circuit comprising a buffer capacitor and an auxiliary winding is constructed. This resonant discharge circuit generates a transient voltage in the buffer capacitor that decays according to a cosine function, with the transient voltage change conforming to the resonant discharge law. Through this mechanism, the energy captured and stored by the passive regeneration buffer circuit during the switching cycle is transferred losslessly to the main power transmission circuit using the principle of electromagnetic induction, and ultimately fed back to the load.

[0014] Furthermore, during the commutation process, when the main diode is turned on, the input current is distributed between the branch containing the buffer inductor and the branch containing the main diode. This distribution process follows Kirchhoff's current law, constraining the sum of the distributed current flowing through the buffer inductor and the current flowing through the main diode to equal the input current.

[0015] This invention provides a regenerative passive soft-switching Boost-type PFC circuit. It has the following advantages: 1. This invention reduces the switching losses and electromagnetic interference of the main switch by combining a series buffer inductor and a parallel buffer capacitor. By utilizing the characteristics of inductors to impede sudden current changes and capacitors to impede sudden voltage changes, it achieves zero-current turn-on and zero-voltage turn-off of the main switch, eliminating the overlap of voltage and current waveforms at the moment of turn-on and turn-off, and suppressing high-frequency noise caused by high-gradient voltage or current changes.

[0016] 2. This invention utilizes the magnetic coupling effect of the auxiliary winding to achieve energy feedback, solving the problem of high energy loss in traditional buffer circuits. Through the coupling between the auxiliary winding and the main inductor, the energy absorbed by the buffer capacitor during the turn-off period of the switching transistor is transferred and delivered to the load side, avoiding energy dissipation in the form of heat on the resistive element and improving the overall efficiency of the converter.

[0017] 3. This invention uses all passive components to construct the auxiliary circuit, which improves the reliability and cost advantage of the system. The realization of soft switching and energy feedback functions does not rely on additional active power devices or complex drive control logic, which reduces the number of components and control difficulty, and reduces the system failure rate and hardware cost. Attached Figure Description

[0018] Figure 1This is a circuit schematic diagram of a regenerative passive soft-switching-Boost type PFC circuit according to an embodiment of the present invention. Figure 2 This is a flowchart of a control method for a regenerative passive soft-switching-Boost type PFC circuit according to an embodiment of the present invention; Figure 3 This is a schematic diagram of the equivalent circuit and current path for the buffer energy regeneration and potential bootstrap feedback stage in an embodiment of the present invention. Figure 4 This is a schematic diagram of the equivalent circuit and current path during the main switch turn-off and buffer capacitor charging clamping stages in an embodiment of the present invention. Detailed Implementation

[0019] The technical solutions in 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, and 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.

[0020] Reference Appendix Figure 1 This invention provides a regenerative passive soft-switching-Boost type PFC circuit, which mainly includes a main power transmission circuit and a passive regenerative buffer circuit.

[0021] The main power transmission circuit includes an input voltage source Ui, a main inductor Lp, a main diode VD, an output capacitor Co, a load Ro, and a main switch S. The positive terminal of the input voltage source Ui is connected to the same-name terminal of the main inductor Lp, and the opposite-name terminal of the main inductor Lp is connected to the first circuit node. The anode of the main diode VD is connected to the first circuit node, and the cathode of the main diode VD is connected to one end of the output capacitor Co and one end of the load Ro. The other end of the output capacitor Co and the other end of the load Ro are connected to the negative terminal (common ground) of the input voltage source Ui. The main switch S controls the switching on and off of the main power transmission circuit, and its source is connected to the common ground.

[0022] A passive regenerative snubber circuit is used to achieve soft switching and energy regeneration of the main switching transistor S. It includes an auxiliary winding La, a snubber inductor Ls, a first snubber diode VD1, a second snubber diode VD2, and a snubber capacitor Cs. The auxiliary winding La and the main inductor Lp are wound on the same magnetic core, forming a coupled inductor structure. The terminal of the auxiliary winding La is connected to the positive terminal of the input voltage source Ui. One end of the snubber inductor Ls is connected to the first circuit node, and the other end is connected to the second circuit node.

[0023] The anode of the second buffer diode VD2 is connected to the second circuit node, and its cathode is connected to the drain of the main switch S. The opposite terminal of the auxiliary winding La is connected to the drain of the main switch S, and the auxiliary winding La is configured, through magnetic coupling and circuit network connection, to provide an energy feedback path to the load side during the conduction of the main switch S, thereby enabling the auxiliary winding La to participate in energy exchange in the switching circuit network.

[0024] In the overall circuit architecture, the main inductor Lp serves as the primary energy storage component, with its inductance value designed to be significantly larger than that of the buffer inductor Ls, ensuring that the input current Is remains constant within one switching cycle. The output capacitor Co has a sufficiently large capacitance to maintain a constant output voltage Uo. The circuit is configured to operate in continuous conduction mode, and through the cooperation of various components, it sequentially completes the zero-current turn-on of the switching transistor, the regenerative feedback of the buffer energy, the energy storage in the main circuit, the zero-voltage turn-off of the switching transistor, and the inductor freewheeling reset process within one switching cycle.

[0025] See attached document Figure 3 , Figure 3 This is a flowchart illustrating the operation of a regenerative passive soft-switching-Boost type PFC circuit according to an embodiment of the present invention. The present invention provides a control method for a regenerative passive soft-switching-Boost type PFC circuit, comprising the following steps: S1, when the main switch S receives the turn-on signal, the buffer inductor Ls connected in series in the current path of the main switch S limits the rate of change of current, so that the current flowing through the main switch S increases linearly, and zero-current turn-on is completed. S2, after completing zero-current turn-on and turning off the main diode VD, uses the magnetic coupling between the main inductor Lp and the auxiliary winding La to generate an induced electromotive force, causing the circuit potential to bootstrap, and feeding the energy stored in the buffer capacitor Cs back to the load end through the auxiliary winding La, entering the energy regeneration state. S3, after the energy regeneration state ends and the buffer capacitor Cs is discharged, the main switch S is kept on, so that the input voltage Ui is applied across the main inductor Lp, the main inductor Lp performs linear energy storage, and the main on-state energy storage is maintained until the off signal is received. S4. When the main switch S ends and the main switch S receives the turn-off signal, the input current is used to charge the buffer capacitor Cs. The voltage clamping effect of the buffer capacitor Cs limits the voltage rise rate across the main switch S, thus completing the zero-voltage turn-off. S5, when the zero-voltage turn-off is completed and the voltage of the buffer capacitor Cs rises to the output voltage Uo, turns on the main diode VD, releases the remaining energy in the buffer inductor Ls and transfers the current, so that the main inductor Lp releases energy to the load through the main diode VD, maintaining the main freewheeling state until the start of the next switching cycle.

[0026] The physical processes and electrical characteristics of each of the above working steps will be explained in detail below, in conjunction with circuit modal analysis.

[0027] In this embodiment, the circuit is in a critical transition period from the main freewheeling state to the main switch conduction state. During this stage, the passive regenerative buffer circuit intervenes in the main power transmission circuit's operation through its internal inductive element characteristics, forcing the main switch S to complete its turn-on operation under zero-current conditions. The specific implementation steps and physical process are as follows: S101, at the start of the switching cycle at time t1, the drive control circuit applies a high-level turn-on signal to the gate of the main switch S. At this instant, although the conductive channel inside the main switch S is physically established, the current does not immediately flow through the main switch S due to the inductive constraint of the external circuit. At this time, the main diode VD is still in the conducting state and carries all the load current. As the main switch S turns on, the positive terminal of the input voltage source Ui is connected to the drain of the main switch S through the main winding Lp of the coupling inductor, the buffer inductor Ls in the passive regenerative buffer circuit, and the second buffer diode VD2, thus constructing a parallel current shunt branch outside the original freewheeling circuit of the main diode VD.

[0028] S102 utilizes the physical characteristic of an inductor to impede transient changes in current. A buffer inductor Ls, connected in series in the drain current path of the main switch S, provides hardware-level limitation on the rise rate of the branch current. According to Kirchhoff's voltage law, under ideal conditions where parasitic line resistance and diode forward voltage drop are ignored, the voltage across the output capacitor Co is sufficiently large, making it a constant source. This clamps the voltage across the buffer inductor Ls to the output voltage Uo. To quantify this current-limiting effect and ensure the smoothness of the current rise, preventing electromagnetic shocks caused by sudden current changes, in this embodiment, the inductance of the buffer inductor Ls is set to a non-zero finite value, ensuring that the rate of rise of the current flowing through the main switch S follows the following buffer inductor loop voltage formula: ; in, This indicates the inductance value of the buffer inductor; This represents the derivative of the current flowing through the buffer inductor with respect to time (i.e., the rate of change of current). This represents the current flowing through the buffer inductor; Indicates the current time; This represents the output voltage. The formula reveals the physical law that the rate of change of current is directly proportional to the output voltage and inversely proportional to the value of the buffer inductance, establishing that by adjusting... The technical approach of using parameters to control the activation speed.

[0029] S103 performs linear commutation operation of the main power circuit under the condition of limited current change rate. This is because the inductance of the main inductor Lp is much larger than that of the buffer inductor. The preset conditions can be approximated by assuming that the input current Is from the input terminal remains constant within an extremely short commutation time window. According to Kirchhoff's current law constraining the current at the first circuit node, as the current flowing through the buffer inductor... The current flowing through the main diode VD increases linearly. A complementary linear decrease must occur. At this point, the instantaneous evolution of the current in each branch of the circuit satisfies the following formulas for the linear increase of the buffer inductor current and the linear decrease of the main diode current: ; ; in, This represents the current flowing through the buffer inductor; Indicates the output voltage; This indicates the inductance value of the buffer inductor; Indicates the current time; Indicates the start time of activation; This indicates the current flowing through the main diode; This represents the input current. This linear relationship indicates that the transfer of current from the main diode VD to the main switch S is a controlled, gradual process, rather than a step abrupt change.

[0030] S104, based on the aforementioned current evolution law, achieves zero-current turn-on of the main switch S and suppresses the diode reverse recovery effect. By... Substituting into the above formula, we can see that the current flowing through the main switch S at the initial moment is zero. This physically ensures that there is no overlap between voltage and current in the main switch S at the instant of turn-on, thus achieving zero-current turn-on and effectively eliminating turn-on losses. More importantly, the current drop rate reflected in the formula ( The value of the buffer inductor is entirely determined by the circuit parameters. This can be achieved by selecting a larger inductance value. This reduces the rate of current drop before the main diode VD is turned off, thereby significantly reducing the reverse recovery charge and peak reverse recovery current of its internal PN junction during the turn-off process, thus suppressing the generation of high-frequency electromagnetic interference at its source. The specific microscopic physical mechanism of charge storage in the diode PN junction is well-known in the field and will not be elaborated upon here.

[0031] S105, determines the termination condition of mode 1 based on the completion of current transfer. When the current flowing through the buffer inductor... Rise to equal the input current At that time, according to the complementary relationship, the current flowing through the main diode... When the circuit naturally crosses zero, the main diode VD experiences reverse voltage and is naturally blocked, marking the end of the commutation process and the circuit about to enter the energy regeneration state. The duration of this commutation process is determined by the following formula: ; in, This represents the duration of mode 1; This indicates the inductance value of the buffer inductor; Indicates the input current; This represents the output voltage. In this embodiment, the duration of this duration must be designed to be much shorter than the switching cycle to ensure efficient circuit operation and that the duty cycle of the main power transmission is not significantly affected.

[0032] In this embodiment, as the main switch S completes zero-current turn-on and the main diode VD is completely turned off due to zero current, the circuit's operating state naturally switches to the buffer energy regeneration and potential bootstrap feedback stage. During this stage, the passive regenerative buffer circuit, through the electromagnetic coupling mechanism of the magnetic components, transfers the voltage spike energy captured and stored by the buffer capacitor Cs during the turn-off process of the previous switching cycle to the load side in a lossless resonant manner, thereby achieving efficient energy recovery and utilization. (Refer to Appendix) Figure 3 The current path is marked by a red dashed line. The specific implementation steps and physical mechanism of this process are as follows: In S201, the moment the main diode VD is turned off, an induced electromotive force is established using the polarity coupling characteristic of the transformer's same-name terminals to achieve a potential bootstrapping effect. At this time, the main switch S is in a low-impedance conducting state, and the input voltage source Ui is applied across the main inductor Lp, causing the current flowing through the main inductor Lp to increase linearly. Based on Faraday's law of electromagnetic induction, this changing magnetic flux induces a voltage across the auxiliary winding La, which shares the same magnetic core. The auxiliary winding La is configured to be connected in series in the passive regenerative buffer circuit, so that the polarity of the induced electromotive force generated by the auxiliary winding La is superimposed with the polarity of the voltage on the buffer capacitor Cs. This potential superposition effect raises the potential of the regenerative branch, making it higher than the output voltage Uo, thus opening the energy feedback channel and establishing a voltage potential energy basis for the release of capacitor energy.

[0033] S202, driven by this bootstrap voltage, constructs a closed resonant circuit that releases energy from the buffer capacitor Cs to the load Ro. Under the influence of the induced electromotive force, the charge stored in the buffer capacitor Cs begins to be released. (See attached diagram.) Figure 3The current flow shown is as follows: the current flows out from the buffer capacitor Cs, is boosted by the induced voltage provided by the auxiliary winding La, and is injected into the load Ro (or the parallel output capacitor Co) on the output side through the regenerative diode branch. Finally, it returns through the common ground loop. This process changes the traditional RCD buffer circuit's heat dissipation mode of consuming energy on the resistor, and instead uses passive components to build a low-impedance energy feedback loop, improving the overall conversion efficiency of the circuit.

[0034] S203, perform energy release operation based on LC resonance characteristics. Since the above discharge circuit includes inductive elements (auxiliary winding La and line distributed inductance) and capacitive elements (buffer capacitor Cs), the transient changes in discharge current and voltage are not a simple linear relationship, but rather exhibit quasi-resonant characteristics. The voltage across the buffer capacitor Cs decays with time according to a cosine function, following a resonance law. In this embodiment, the formula for the buffer capacitor resonant discharge voltage used to describe this transient voltage change law is: ; in, This represents the instantaneous voltage across the buffer capacitor. This represents the initial discharge voltage of the buffer capacitor (i.e., the voltage amplitude stored in the buffer capacitor at the beginning of discharge, which is usually approximately equal to the output voltage). This represents the operations of cosine and trigonometric functions; This represents the resonant angular frequency (its value is determined by the capacitance of the buffer capacitor and the equivalent inductance of the circuit). Indicates the current time; This indicates the start time of the energy regeneration state. The formula reveals the waveform characteristics of energy release, demonstrating that by properly matching the inductor and capacitor parameters, the discharge duration can be precisely controlled, ensuring energy transfer is completed before the main switch S is turned off.

[0035] S204 sets the preset conditions for lossless energy transfer and zero-voltage turn-off. As the resonant discharge process progresses, the instantaneous voltage of the buffer capacitor... When the voltage drops to zero or near zero volts, the unidirectional conductive devices in the circuit naturally block due to the loss of forward voltage drop support, preventing reverse current oscillation and marking the termination of the energy regeneration process. At this time, the buffer capacitor Cs is in a voltage reset state (i.e., the stored charge is cleared). This reset state has a dual technical effect: on the one hand, it confirms that the previously absorbed turn-off loss energy has been fully recovered; on the other hand, the discharged buffer capacitor Cs provides a low-impedance voltage clamping branch for the turn-off of the main switch S in the next stage, which is a necessary physical prerequisite for achieving zero-voltage turn-off.

[0036] In this embodiment, as the buffer energy regeneration process naturally terminates, the circuit's operating mode smoothly and automatically switches to the main circuit PWM conduction and main inductor energy storage stage. During this stage, the previously active passive regeneration buffer circuit completes its energy recovery mission and temporarily ceases operation. The circuit topology is electrically equivalent to the conduction state of a conventional PWM converter. At this time, the main switch S maintains a low-impedance conduction state, working with the main inductor Lp to obtain and store energy from the input voltage source Ui, accumulating potential energy for subsequent power transmission. The specific implementation steps and steady-state electrical characteristics of this process are as follows: S301, based on the physical fact that the voltage across the buffer capacitor Cs has dropped to zero volts and remains in a reset state, establishes the exclusive operating mode of the main power transmission circuit. At this time, the single-phase conductive devices in the passive regenerative buffer circuit connected to it (including the first buffer diode VD1 and the second buffer diode VD2) are all in the off state due to reverse bias voltage or zero bias. This off state makes the passive buffer branch electrically exhibit high impedance open circuit characteristics, thereby forcing the input current Is to no longer be shunt, but to flow entirely through the loop formed by the main inductor Lp and the main switch S. The establishment of this state establishes the physical boundary conditions for the circuit to perform simple magnetic energy storage, ensuring the singularity of the energy conversion process during this period.

[0037] S302, based on the circuit condition that the main switch S is in the on state, applies a constant excitation voltage to the main inductor Lp. According to Kirchhoff's Voltage Law (KVL) and Faraday's law of electromagnetic induction, the input voltage source Ui is directly applied across the main inductor Lp (ignoring the slight influence of the switch's on-state voltage drop and the line's parasitic resistance). The main inductor Lp, as the core energy storage element, has a current change rate proportional to the voltage applied across it. To quantify this electromagnetic induction process and ensure the validity of the mathematical model (i.e., the denominator...), a specific calculation is needed. (where the value is non-zero and finite), the formula describing the differential relationship between the main inductor voltage and current in this stage is the following main inductor energy storage voltage equation: ; in, This indicates the inductance value of the main inductor; This represents the derivative of the current flowing through the main inductor with respect to time (i.e., the rate of change of current). This represents the input voltage. From a physical perspective, the equation shows that, under the premise of a constant input voltage, the main inductor current will rise with a fixed positive slope. At this time, electrical energy is continuously converted into magnetic field energy and stored in the air gap of the magnetic core of the main inductor Lp.

[0038] S303 performs linear integration of the current and accumulation of magnetic energy. Based on the above differential relationship, the current flowing through the main inductor Lp increases linearly with time. Within the time interval of mode 3, the instantaneous value of the main inductor current follows the following linear growth formula: ; in, This represents the current flowing through the main inductor; This represents the initial current of the main inductor (i.e., at the beginning of the main inductor's energy storage state). (The current value already present in the main inductor); Indicates the input voltage; This indicates the inductance value of the main inductor; Indicates the current time; This indicates the start time of the dominant on-state energy storage. This formula accurately describes the energy accumulation process of the system during steady-state conduction, laying the necessary current foundation for energy transfer to the load during subsequent off-state periods.

[0039] S304 maintains the energy decoupling and load power supply state on the output side. During the conduction of the main switch S, the potential of the first circuit node (i.e., the anode of the main diode VD) is pulled down to near ground potential, while the output capacitor Co maintains a higher output voltage Uo, causing the main diode VD to withstand reverse voltage and turn off. At this time, the input power supply is disconnected from the load, and the energy required by the load Ro is entirely provided by the charge stored in the output capacitor Co. The output capacitor Co is in a discharging state, and its voltage will experience a slight ripple over time. The magnitude of this ripple is determined by the capacitance value and the load current, which is a capacitor filtering characteristic known in the art.

[0040] S305 determines the mode termination condition and maintains the optimal state before shutdown. This dominant on-state energy storage will continue until the PWM control signal changes. When the control circuit issues a shutdown command (t=t4), the main switch S prepares to turn off. As a preferred approach, the circuit parameters are designed to ensure that the voltage across the buffer capacitor Cs remains zero at the instant the mode ends. This initial zero-voltage state is crucial for achieving zero-voltage turn-off in the next stage because it ensures that the drain-source voltage rises slowly from zero at the moment the switch begins to turn off, rather than jumping, thus eliminating turn-off losses.

[0041] In this embodiment, when the control circuit removes the gate drive signal, causing the main switch S to switch from the on state to the off state, the circuit operation mode automatically enters the critical main switch turn-off and buffer capacitor charging clamping stage. During this stage, the passive regenerative buffer circuit utilizes the physical characteristic that the voltage across the capacitor cannot change abruptly to hard clamp the rate of voltage rise (du / dt) across the main switch, thereby forcibly achieving zero-voltage turn-off (ZVS). (See attached figure...) Figure 4 The current path is marked in the image. The specific implementation steps and physical mechanism of this process are as follows: In S401, at the turn-off initiation time t4, the drive circuit pulls down the gate voltage of the main switch S, causing its internal conductive channel to disappear rapidly. Due to the large inductance characteristic of the main inductor Lp in maintaining a constant current (which can be considered a constant current source on this microsecond timescale), the input current Is flowing through the main inductor Lp cannot instantaneously change to zero. Constrained by Kirchhoff's current law, this current is forced to shift from the high-impedance branch of the main switch S, seeking a new low-impedance path. (See Appendix) Figure 4 As shown, the current path is reconstructed as follows: the positive terminal of the input voltage source Ui passes through the main inductor Lp, the first circuit node, the buffer inductor Ls, the second circuit node, and the first buffer diode VD1, finally injecting into the buffer capacitor Cs. During this process, the first buffer diode VD1 quickly conducts under the drive of the forward current, seamlessly connecting the buffer capacitor Cs into the main current loop, thus taking over the current that originally flowed through the switching transistor.

[0042] S402, a buffer capacitor charging operation based on the constant current source characteristics is performed. Since the input current Is remains constant during the extremely short turn-off transition period and is entirely injected into the buffer capacitor Cs (ignoring line leakage current and parasitic parameter effects), the buffer capacitor Cs exhibits a constant current charging state. Its voltage rises linearly from an initial zero volt (determined by the reset state at the end of mode 3). As a preferred approach, the capacitance value of the buffer capacitor Cs is selected as a non-zero finite value that meets design requirements to ensure that the voltage rise rate is within a controllable range. In this embodiment, the buffer capacitor constant current charging equation describing the relationship between the voltage change rate and current during this charging process is: ; in, This indicates the capacitance value of the buffer capacitor; This represents the derivative of the instantaneous voltage across the buffer capacitor with respect to time (i.e., the rate of voltage rise). This represents the input current. The equation physically reveals that the voltage rise slope depends entirely on the ratio of the capacitor's capacitance to the load current, establishing that by appropriately increasing... This is a technical approach to slow down the rate of voltage rise, thereby suppressing turn-off voltage spikes.

[0043] The S403 achieves zero-voltage turn-off of the main switch S based on the capacitor voltage clamping effect. In the circuit topology, the drain-source (DS) terminals of the main switch S, through the conducting buffer branch, actually form a parallel potential relationship with the buffer capacitor Cs (diode voltage drop is ignored here). Therefore, the voltage across the main switch S... Following the buffer capacitor voltage It changes with the changes. Due to The voltage rises slowly and linearly from zero, which means that even when the main switch S is turned off and the current rapidly drops to zero, the voltage across it remains clamped at a low potential close to zero. The approximate formula for describing this slow voltage rise characteristic of the switch turn-off voltage rise is: ; in, This represents the drain-source voltage of the main switching transistor; Indicates the input current; This indicates the capacitance value of the buffer capacitor; Indicates the current time; Indicates the start time of shutdown; This indicates an approximate operation (ignoring the minor effects of stray line parameters and diode voltage drop). The physical significance of this formula lies in proving the effective misalignment of the voltage waveform and the current waveform on the time axis: when the current of the switching transistor has dropped to zero, the voltage across it has not yet established a significant amplitude, thus limiting the product of voltage and current (i.e., turn-off loss) to an extremely low level, effectively eliminating the turn-off loss in the traditional hard-switching mode.

[0044] S404 determines the mode termination condition and prepares for energy transfer. As the constant current charging process continues, the voltage across the buffer capacitor Cs... and the voltage across the main switch transistor The voltage rises linearly continuously. When this voltage rises to a level sufficient to overcome the sum of the output voltage Uo and the forward voltage drop of the main diode VD (i.e., ... The main diode VD is forward biased and ready to conduct. This critical state marks the end of the simple charging clamping phase, and the circuit is about to enter the main freewheeling phase, where energy is released to the load side.

[0045] In this embodiment, as the buffer capacitor charging clamping process is completed and the main switch voltage is established to the output voltage level, the circuit's operating mode naturally evolves from the transient clamping phase to the steady-state freewheeling diode conduction and circuit state reset phase. This phase, in terms of timing, encompasses the dynamic commutation process (mode 5) of current transfer from the auxiliary buffer circuit to the main freewheeling circuit, and the PWM freewheeling process (mode 6) of the main circuit independently releasing energy to the load. (Refer to Appendix) Figure 4 The specific implementation steps and electrical characteristic analysis of this process are as follows: S501 determines the critical voltage condition for the main diode to conduct. As the buffer capacitor Cs continues to charge, when the voltage across it rises slightly above the output voltage Uo (t5), the circuit node potential distribution triggers a state reversal. Specifically, the anode potential of the main diode VD (raised by the buffer capacitor voltage) exceeds its cathode potential (i.e., the output voltage Uo), causing the main diode VD to rapidly transition from the cutoff state to the forward conduction state under the influence of a forward bias voltage. Due to the low impedance of the main diode VD, the output voltage Uo is directly clamped at the first circuit node. This physical clamping effect limits the further rise of the buffer capacitor Cs voltage, keeping it near the output voltage level (ignoring the small forward conduction voltage drop of the diode).

[0046] S502, performs dynamic current commutation between the main circuit and the buffer circuit (mode 5). During the time interval t5 to t6, the input current Is no longer flows solely through the buffer branch, but instead begins to be distributed between the buffer branch (including the buffer inductor Ls) and the main freewheeling branch (including the main diode VD). Based on Kirchhoff's current law and the principle of node current conservation, the sum of the currents in the two branches is always physically constrained to be equal to the constant input current. In this embodiment, the formula describing this dynamic current distribution relationship is the Kirchhoff's current distribution formula: ; in, This represents the current flowing through the buffer inductor; This indicates the current flowing through the main diode; This represents the input current. This formula mathematically quantifies the commutation process: as the current flowing through the main diode... The current flowing through the buffer inductor gradually increases as the on-resistance decreases. The current must be reduced accordingly, thus achieving a smooth and lossless transfer of current from the auxiliary circuit to the main circuit.

[0047] S503 implements energy release and current reset of the buffer inductor Ls. During commutation, although the voltage at the first circuit node is clamped, due to the diode forward voltage drop and stray impedance in the circuit, the buffer inductor Ls actually experiences a small reverse voltage, forcing its current to decrease. To ensure the mathematical convergence and physical feasibility of the reset process, the inductance of the buffer inductor Ls is set to a non-zero finite value. The formulas describing this dynamic current distribution relationship are Kirchhoff's law formula for current distribution and the approximate formula for the rate of change of the reset current of the buffer inductor, which are as follows: ; ; in, This represents the current flowing through the buffer inductor; This indicates the current flowing through the main diode; Indicates the input current; This represents the derivative of the current flowing through the buffer inductor with respect to time (i.e., the rate of decrease of the current). This represents the sum of the conduction voltage drops in the circuit (mainly including the diode forward voltage drop and the stray resistance voltage drop of the line); This represents the inductance value of the buffer inductor. The negative sign in the formula physically reveals that the buffer inductor current exhibits a monotonically decreasing trend. When When the current naturally drops to zero (t=t6), the first buffer diode VD1 turns off naturally due to the current crossing zero, marking that the passive buffer circuit has completely stopped working and completed the state reset, thus preparing the initial state for the zero-current turn-on of the next switching cycle.

[0048] S504 establishes the PWM freewheeling state of the main circuit (mode 6). When the buffer circuit current drops to zero, the input current Is flows entirely through the main diode VD, and the circuit enters the simple main freewheeling stage. At this time, the main inductor Lp forms a loop with the output voltage source (output capacitor Co and load Ro) through the conducting main diode VD. As a preferred approach, the circuit parameters must be designed to ensure that the output voltage Uo is higher than the input voltage Ui (boost characteristics of the Boost converter), so that the main inductor Lp bears a defined reverse voltage. The main inductor freewheeling voltage equation describing the voltage state across the main inductor in this stage is: ; in, This represents the inductance value of the main inductor (the value must be greater than zero to avoid mathematical singularities); This represents the derivative of the current flowing through the main inductor with respect to time. Indicates the input voltage; This represents the output voltage. The equation shows that as long as the output voltage is higher than the input voltage, the rate of change of the inductor current is negative, and the main inductor begins to release the previously stored magnetic energy.

[0049] S505 executes the transfer of energy from the main inductor to the load and the linear decay of the current. Based on the voltage equation above, the main inductor current exhibits a linear decreasing trend during the freewheeling period, converting magnetic field energy into electrical energy and transferring it to the load Ro and the output capacitor Co. During the time interval t6 to t7, the instantaneous value of the main inductor current follows the following linear decay formula: ; in, This represents the current flowing through the main inductor; This represents the main inductor current at the start of mode 6 (i.e., the initial current value of mode 6); Indicates the output voltage; Indicates the input voltage; This indicates the inductance value of the main inductor; Indicates the current time; This indicates the start time of mode 6. This formula accurately describes the energy release trajectory of the system during the off period, until the start of the next switching cycle (t=t7), when the control circuit sends an on signal again, and the system returns to mode 1, repeating the cycle and achieving efficient energy conversion and transmission.

[0050] See attached document Figure 4 Based on the circuit operation mode analysis in steps S1 to S5 above, the passive soft-switching converter with magnetically coupled auxiliary winding proposed in this embodiment exhibits significant optimization in electrical performance through the coordinated operation of various passive components and physical constraints. The following details the improvements of this technical solution in terms of loss reduction, energy regeneration, and electromagnetic compatibility based on general physical principles: To address the contribution of passive soft-switching technology to switching losses and overall efficiency, this embodiment eliminates switching losses by physically separating the overlapping regions of voltage and current waveforms. In the turn-on phase of step S1, the circuit utilizes the inductive physical characteristic of the buffer inductor Ls, which prevents abrupt changes in current, to force the current flowing through the main switch S to rise linearly with a finite slope (its dynamic process follows the aforementioned formula for the linear rise of the buffer inductor current). This ensures that the drain current of the main switch S remains at an extremely low level until the drain-source voltage drops to zero, thus achieving zero-current turn-on. In the turn-off phase of step S4, the circuit utilizes the capacitive physical characteristic of the buffer capacitor Cs, which prevents abrupt changes in voltage, to take over the input current transferred from the main switch S, forcing the voltage across the main switch S to rise slowly with a finite slope (its dynamic process follows the aforementioned approximate formula for the rise of the switch turn-off voltage). This mechanism ensures that at the instant the current in the main switch S drops to zero, its drain-source voltage has not yet established a significant amplitude, thus achieving zero-voltage turn-off. This dual-edge soft-switching mechanism fundamentally eliminates the huge power loss caused by the overlap of voltage and current waveforms in the traditional hard-switching mode, so that the overall efficiency of the converter is no longer limited by the switching frequency, providing a solid physical basis for high-frequency design.

[0051] The improvement in energy recovery efficiency brought about by the regenerative topology is the main improvement of this embodiment compared to traditional RCD loss-type buffer circuits. In traditional buffer schemes, the energy stored in the buffer element is usually dissipated as heat on the resistor, limiting system efficiency. In this embodiment, based on the energy regeneration mechanism of step S2, the circuit introduces an auxiliary winding La that shares the same magnetic core as the main inductor Lp. When the circuit is in mode 2, the buffer capacitor Cs, the auxiliary winding La, and the main inductor Lp form a resonant circuit, using the principle of electromagnetic induction to transfer the energy stored in the buffer circuit to the main circuit without loss. To quantify this energy-saving effect, the single-cycle energy of the buffer circuit that is recovered in this embodiment can be calculated by the following buffer energy recovery formula: ; in, This represents the total energy recovered and fed back to the load by the buffer circuit during a single switching cycle; This indicates the inductance value of the buffer inductor; Indicates the input current; This indicates the capacitance value of the buffer capacitor; This represents the output voltage. The physical meaning of this formula is that it demonstrates that this technical solution can utilize the energy that would otherwise be dissipated by resistors in traditional circuits. The signal is fed back to the load or power supply via a magnetic coupling path, which theoretically eliminates the additional losses of the buffer circuit and improves the overall conversion efficiency of the system.

[0052] To address the electromagnetic interference suppression and power device safety protection effects of soft-switching characteristics, this embodiment improves the circuit's electromagnetic compatibility and reliability through the clamping effect of passive components. As a preferred approach, the presence of the buffer inductor Ls directly limits the rate of current change when the main switch S is turned on. This effectively suppresses voltage spikes and high-frequency radiated noise caused by lead inductance; at the same time, the presence of buffer capacitor Cs directly limits the rate of voltage change when the main switch S is turned off. This effectively suppresses common-mode interference caused by parasitic capacitance coupling. Furthermore, for the main switch S of the power device, the aforementioned soft-switching process ensures that its dynamic operating trajectory always remains within the boundary of the safe operating area, avoiding avalanche breakdown or thermal failure caused by excessive reverse recovery current or turn-off voltage overshoot. It is particularly worth mentioning that the buffer inductor Ls also plays a role in suppressing the reverse recovery current of the main diode VD. By controlling the rate of decrease of the reverse recovery current, it further extends the lifespan of the power device and improves the robustness of the system under harsh operating conditions.

[0053] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents.

Claims

1. A regenerative passive soft-switching-Boost type PFC circuit, characterized in that, include: The main power transmission circuit uses the positive terminal of the input voltage source to connect to the same-name terminal of the main inductor and the opposite-name terminal of the main inductor to connect to the first circuit node, so that the anode of the main diode is connected to the first circuit node, the cathode of the main diode is connected to one end of the output capacitor and the load, and the cathode of the main diode and the source of the main switch are both connected to the common ground, thereby constructing a power transmission path. The passive regenerative buffer circuit utilizes the buffer inductor connected between the first circuit node and the second circuit node to access the main power transmission circuit. The anode of the first buffer diode and the cathode of the second buffer diode are connected to the second circuit node together. The cathode of the first buffer diode is connected to the common ground via the buffer capacitor, and the anode of the second buffer diode is connected to the drain of the main switch. The auxiliary winding that shares the same magnetic core as the main inductor is used to connect the positive terminal of the input voltage source to the drain of the main switch for energy feedback.

2. The regenerative passive soft-switching-Boost type PFC circuit according to claim 1, characterized in that, The step of using an auxiliary winding sharing the same magnetic core as the main inductor to connect the positive terminal of the input voltage source to the drain of the main switching transistor for energy feedback includes: A magnetic coupling channel is established using the auxiliary winding wound on the same magnetic core as the main inductor; Connect the opposite terminal of the auxiliary winding to the drain of the main switch, so that an energy feedback channel is established through the magnetic coupling channel during the conduction of the main switch; Energy is fed back to the load side using the energy feedback channel, thereby enabling the auxiliary winding to participate in energy exchange within the switching circuit network.

3. The regenerative passive soft-switching-Boost type PFC circuit according to claim 1, characterized in that, The steps for constructing the power transmission path include: The inductance value of the main inductor in the main power transmission circuit is set to be much larger than the inductance value of the buffer inductor in the passive regenerative buffer circuit; The large inductance of the main inductor is used to suppress current ripple, so that the input current remains constant during the switching cycle. Based on the constant characteristics of the input current, a steady-state energy transmission channel supporting continuous conduction mode operation is established.

4. The regenerative passive soft-switching-Boost type PFC circuit according to claim 1, characterized in that, The step of connecting the main power transmission loop using the buffer inductor connected between the first circuit node and the second circuit node includes: The buffer inductor is connected in series in the current path of the main switch transistor, and the inductance value of the buffer inductor is set to a non-zero finite value. By utilizing the physical property of the buffer inductor to impede transient changes in current, the rate of rise of the current flowing through the main switch is limited; This ensures that the rate of change of the restricted current flowing through the main switch follows the formula for the voltage of the buffer inductor circuit.

5. A regenerative passive soft-switching-Boost type PFC circuit according to claim 1, characterized in that, The step of connecting the main power transmission loop using the buffer inductor connected between the first circuit node and the second circuit node further includes: At the instant the main switch is turned on, the buffer inductor is used to shunt the current that originally flowed through the main diode in the main power transmission circuit; This causes the current shunting process of the buffer inductor to produce a linearly increasing current flowing through the buffer inductor and a linearly decreasing current flowing through the main diode. Ensure that the instantaneous values ​​of the current flowing through the buffer inductor and the current flowing through the main diode satisfy the formulas for the linear increase of the buffer inductor current and the linear decrease of the main diode current, respectively.

6. A regenerative passive soft-switching-Boost type PFC circuit according to claim 1, characterized in that, The step of connecting the cathode of the first buffer diode to common ground via a buffer capacitor includes: The buffer capacitor is connected in parallel across the main switch transistor, and the capacitance of the buffer capacitor is set to a non-zero finite value. By utilizing the physical characteristic that the voltage across the buffer capacitor cannot change abruptly, the drain-source voltage of the main switch transistor at the moment of turn-off is clamped. This ensures that the rise of the drain-source voltage of the main switch follows the approximate formula for the rise of the switch's turn-off voltage.

7. A regenerative passive soft-switching-Boost type PFC circuit according to claim 6, characterized in that, The step of connecting the cathode of the first buffer diode to common ground via a buffer capacitor further includes: After the main switch is turned off, the input current is used to charge the buffer capacitor. The buffer capacitor is kept in a constant current charging state driven by the input current; This ensures that the relationship between the voltage change rate and current of the buffer capacitor under the constant current charging state follows the constant current charging equation for the buffer capacitor.

8. A regenerative passive soft-switching-Boost type PFC circuit according to claim 1, characterized in that, The energy feedback process includes: During the energy regeneration phase, a resonant discharge circuit comprising the buffer capacitor and the auxiliary winding is constructed. The instantaneous voltage of the buffer capacitor, which decays according to a cosine function, is generated using the resonant discharge circuit. Ensure that the transient change law of the instantaneous voltage of the buffer capacitor follows the formula of the resonant discharge voltage of the buffer capacitor.

9. A regenerative passive soft-switching-Boost type PFC circuit according to claim 5, characterized in that, The step of connecting the main power transmission loop using the buffer inductor connected between the first circuit node and the second circuit node further includes: When the main diode is turned on, the input current is distributed between the branch where the buffer inductor is located and the branch where the main diode is located; Kirchhoff's current law is used to constrain the current flowing through the buffer inductor and the current flowing through the main diode after the distribution. The relationship between the sum of the current flowing through the buffer inductor and the current flowing through the main diode and the input current follows Kirchhoff's law of current distribution.

10. A regenerative passive soft-switching-Boost type PFC circuit according to claim 1, characterized in that, The energy feedback step also includes: This allows the passive regenerative buffer circuit to capture and store energy during the switching cycle; The energy stored in the passive regenerative buffer circuit is transferred to the main power transmission circuit without loss using the principle of electromagnetic induction. This ensures that the total energy recovered and fed back to the load by the passive regenerative buffer circuit within a single switching cycle follows the buffer energy recovery formula.

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