Low current ripple bipolar converter based on three-winding coupled inductors

Abstract

The present application relates to a kind of low current ripple bipolar converter based on three-winding coupled inductor.It includes: three-winding coupled inductor, including primary winding and two secondary windings, wherein the corresponding turn ratio of two secondary windings and primary winding is the same;Bipolar output capacitor unit, at least including two output capacitors;The main switch branch in the low current ripple unit is connected with auxiliary switch branch, to utilize auxiliary switch branch to carry out active clamping and soft switch regulation to the main switch branch;Based on the switching state of main switch branch and auxiliary switch branch, three-winding coupled inductor, low current ripple unit and bipolar output capacitor unit are sequentially configured in corresponding working mode, and the stable target conversion voltage is output through bipolar output capacitor unit.The present application can obtain higher output voltage under lower duty cycle condition, while reducing input ripple and device stress, improving voltage variation efficiency and stability.

Description

Technical Field

[0001] This invention relates to a bipolar converter, and more particularly to a low-current ripple bipolar converter based on a three-winding coupled inductor. Background Technology

[0002] With the development of photovoltaic power generation, energy storage systems, electric vehicles, and high-voltage direct current (HVDC) transmission technology, the demand for low-voltage DC energy to supply power to high-voltage DC buses is increasing. Photovoltaic modules, fuel cells, and low-voltage energy storage batteries typically output low-voltage DC power ranging from tens to hundreds of volts. However, downstream inverters, high-voltage DC buses, and industrial drive systems often require DC voltages of hundreds or even thousands of volts during operation. Therefore, high-gain DC-DC boost converters are needed for voltage conversion.

[0003] Traditional boost converters have a simple structure, but their voltage gain is limited by the duty cycle. Specifically, when the duty cycle is close to 1, the voltage and current stress of the switching transistors and diodes in the boost converter increases significantly, which leads to a sharp increase in conduction losses and switching losses, resulting in a significant decrease in efficiency and making it difficult to meet the requirements of high-gain scenarios.

[0004] To improve boost capability, existing technologies have proposed various high-gain topologies, such as interleaved boost converters, coupled inductor boost converters, switched capacitor voltage doubler boost structures, and high-gain converters combining coupled inductors and voltage doublers. Among these, adjusting the inductor value can reduce input current ripple and improve input current continuity; coupled inductors can utilize turns ratio to increase voltage gain; and voltage doublers can achieve high output voltage under low duty cycle conditions. However, existing high-gain boost structures generally require high duty cycles, resulting in greater stress on the devices and affecting the efficiency and reliability of voltage conversion. Summary of the Invention

[0005] The purpose of this invention is to overcome the shortcomings of the prior art and provide a low-current ripple bipolar converter based on a three-winding coupled inductor, which can obtain a higher output voltage under a lower duty cycle condition, while reducing input ripple and device stress, and improving the efficiency and stability of voltage changes.

[0006] According to the technical solution provided by this invention, a low-current ripple bipolar converter based on a three-winding coupled inductor is provided, the bipolar converter comprising: A three-winding coupled inductor includes a primary winding and two secondary windings that can cooperate with the primary winding to form a transformer working capability. The two secondary windings have the same turns ratio as the primary winding and the same parasitic parameters. The bipolar output capacitor unit includes at least two output capacitors. The bipolar neutral point formed by the two output capacitors is connected to the input power supply. The other end of the bipolar neutral point formed by the corresponding connection of each output capacitor is connected to a non-same-name terminal of a corresponding secondary winding via a voltage multiplier component. During the voltage conversion process, each secondary winding can increase the capacitor voltage of the corresponding output capacitor through the connected voltage multiplier component, and the two output capacitors are in an alternating parallel charging and discharging state. The low-current ripple unit is adapted to connect with the input power supply and primary winding. The main switch branch in the low current ripple unit is adapted to and connected to an auxiliary switch branch so that the auxiliary switch branch can be used to perform active clamping and soft switching control on the main switch branch. Based on the switching operation states of the main switch branch and the auxiliary switch branch, the three-winding coupled inductor, the low-current ripple unit, and the bipolar output capacitor unit are configured to be in their respective operating modes in sequence, and the stable target conversion voltage is output through the bipolar output capacitor unit.

[0007] When the two output capacitors in the bipolar output capacitor unit are respectively output capacitor C o1 With output capacitor C o2 When, the output capacitor C o1 The negative terminal and the output capacitor C o2 The positive poles connect with each other to form a bipolar neutral point. When the two secondary windings are the secondary winding L2 and the tertiary winding L3 respectively, then: The voltage multiplier assembly adapted to the secondary winding L2 includes diode D1, capacitor C1, and diode D2. The voltage multiplier assembly adapted to the tertiary winding L3 includes diode D3, capacitor C2, and diode D4. The anode of diode D1 is connected to the same-name terminal of the secondary winding L2 and the same-name terminal of the tertiary winding L3. The cathode of diode D1 is connected to the positive terminal of capacitor C1 and the anode of diode D2. The cathode of capacitor C1 is connected to the non-same-name terminal of the secondary winding L2. The cathode of diode D2 is connected to the output capacitor C. o1 Positive extreme connection; The non-identical terminal of the tertiary winding L3 is connected to the positive terminal of capacitor C2. The negative terminal of capacitor C2 is connected to the anode of diode D4 and the cathode of diode D3. The anode of diode D3 is connected to the output capacitor C. o2 Negative extreme connections; The cathode of diode D1 is connected to the bipolar neutral point.

[0008] The main switch branch includes a main switch transistor S1, and the auxiliary switch branch includes an auxiliary switch transistor S2 and an auxiliary capacitor C. b ,in, The source terminal of the main switch S1, capacitor C b The negative terminal of the main switch S1 is connected to the bipolar neutral point, and the drain terminal of the main switch S1 is adapted to the non-same-name terminal of the primary winding and connected to the corresponding same-name terminals of the secondary winding L2 and the tertiary winding L3. Capacitor C b The positive terminal of the main switch S1 is connected to the drain terminal of the auxiliary switch S2, and the source terminal of the auxiliary switch S2 is connected to the drain terminal of the main switch S1. The main switch S1 and the auxiliary switch S2 are in a complementary conduction state.

[0009] The low-current ripple unit also includes an inductor L0, a diode D5, a diode D6, and a capacitor C. in ,in, The first terminal of the input power supply is connected to the bipolar neutral point, the second terminal of the input power supply is connected to one end of the inductor L0, the other end of the inductor L0 is connected to the anode of diode D5 and the anode of diode D6, and the cathode of diode D6 is connected to the non-same-name terminal of the primary winding. The cathode of diode D5 is connected to the corresponding terminal of the primary winding, and the corresponding terminal of the primary winding is also connected to capacitor C. in One end is connected to capacitor C in The other end is connected to the bipolar neutral point and the source terminal of the main switch S1.

[0010] After entering the steady-state operating phase, in each switching cycle, the main switch S1 and the auxiliary switch S2 are turned on sequentially once, and the main switch S1 and the auxiliary switch S2 are not in the on state at the same time, so as to configure the main switch S1 and the auxiliary switch S2 to be in the corresponding switching operating state respectively. After the previous switching cycle ends, the auxiliary switch S2 switches from the on state to the off state while the main switch S1 remains in the off state. Then the three-winding coupled inductor, the low current ripple unit, and the bipolar output capacitor unit enter the first mode. After entering the current switching cycle, the main switch S1 switches from the off state to the on state. During the period when the main switch S1 is in the on state, the three-winding coupled inductor, the low current ripple unit and the bipolar output capacitor unit enter the second mode, the third mode and the fourth mode in sequence. During the current switching cycle, when the main switch S1 switches from the on state to the off state again and the auxiliary switch S2 also remains off, the three-winding coupled inductor, the low current ripple unit, and the bipolar output capacitor unit enter the fifth mode. During the current switching cycle, when the auxiliary switch S2 switches from the off state to the on state, the three-winding coupled inductor, the low-current ripple unit, and the bipolar output capacitor unit sequentially enter the sixth mode, the seventh mode, the eighth mode, the ninth mode, and the tenth mode.

[0011] Upon entering the first mode, we have: Diodes D1, D3, and D5 are turned off, while diodes D2, D4, and D6 are forward biased. The primary winding, secondary winding L2, and tertiary winding L3 are all in the freewheeling phase. The parasitic capacitance of the auxiliary switch S2 is charged, while the parasitic capacitance of the main switch S1 is discharged. When the voltage at the source-drain terminal of the main switch S1 drops rapidly to zero, the parasitic body diode ZCS of the main switch S1 is turned on. When the main switch S1 is turned on, the first mode ends.

[0012] When the main switch S1 is driven from the off state to the on state, it enters the second mode, wherein... When entering the second mode, the main switch S1 achieves ZVS turn-on, the auxiliary switch S2 is turned off, and the primary winding, secondary winding L2, and tertiary winding L3 are all in the freewheeling stage; at the same time, the input power supply and inductor L0 and secondary winding L2 are connected in series to the output capacitor C. o1 During charging, the second mode ends when the current of the main switch S1 increases to zero. After the second mode ends, the third mode immediately begins, in which... When entering the third mode, the primary winding, secondary winding L2, and tertiary winding L3 are all in the freewheeling stage; the current direction of the main switch S1 is reversed, and the capacitor C... in When the current in the primary winding continues to rise to a value greater than zero, then changes direction and continues to increase, and the currents in the secondary winding L2 and the tertiary winding L3 reverse, the third mode ends, and at the same time, diodes D2 and D4 turn off naturally. After the third mode ends, the fourth mode immediately begins, in which... Upon entering the fourth mode, the current flowing through the secondary winding L2 and the tertiary winding L3 continuously increases, and diodes D1 and D3 achieve ZCS turn-on; the tertiary winding L3 and capacitor C2 are connected in series to the load capacitor C. o2 Power is supplied, and at the same time, the secondary winding L2 charges the capacitor C1 through the diode D1. When the main switch S1 is turned off, the fourth mode ends.

[0013] After the fourth mode ends, the fifth mode immediately begins, in which... After entering the fifth mode, both the main switch S1 and the auxiliary switch S2 are in the off state, diodes D1, D3, and D5 are forward biased, and diodes D2, D4, and D6 are turned off. The parasitic capacitance of the main switch S1 is charged, and the parasitic capacitance of the auxiliary switch S2 is discharged. Then, the parasitic diode ZCS of the auxiliary switch S2 is turned on. When the auxiliary switch S2 is driven to conduct, the fifth mode ends.

[0014] Upon entering the sixth mode, auxiliary switch S2 achieves ZVS turn-on, and main switch S1 is controlled by capacitor C. b The clamping phase occurs when the secondary winding and the tertiary winding L3 are in the freewheeling phase. When the current in the tertiary winding L3 increases to zero, the sixth mode ends and the diode D3 turns off naturally. After the sixth mode ends, the seventh mode immediately begins, in which... After entering the seventh mode, the current flowing through the tertiary winding L3 remains zero, and the secondary winding L2 is still in the freewheeling stage. When the current in the secondary winding L2 increases to zero, the seventh mode ends, and the diode D1 turns off naturally. After the seventh mode ends, the eighth mode immediately begins, in which... When entering the eighth mode, the corresponding currents flowing through the secondary winding L2 and the tertiary winding L3 reverse and continue to rise, while the primary winding is still in the freewheeling stage, and diodes D2 and D4 achieve ZCS turn-on. After entering the eighth mode, the input power supply, inductor L0, primary winding, secondary winding L2, and capacitor C1 are connected in series to the output capacitor C. o1 Power supply: When the current of auxiliary switch S2 increases to zero, the eighth mode ends. After the eighth mode ends, the ninth mode begins immediately, in which... At the moment of entering the ninth mode, the current flowing through the auxiliary switch S2 reverses and continues to rise; and when the current in the primary winding L1 decreases to zero, the ninth mode ends. After the ninth mode ends, the tenth mode begins immediately, in which... At the moment of entering the tenth mode, the current in the primary winding continues to decrease after crossing zero; the secondary winding L2, capacitor C1, and capacitor C... b The output capacitor C is connected in series. o1 When the auxiliary switch S2 is turned off, the tenth mode ends and the current switching cycle ends.

[0015] The two secondary windings have the same number of turns and winding method; When the input power source is a photovoltaic panel, the ground of the photovoltaic panel is connected to the bipolar neutral point.

[0016] Advantages of this invention: By utilizing the turns ratio boosting characteristics of a three-winding coupled inductor, the secondary and tertiary windings are connected to corresponding voltage multiplier components to achieve voltage superposition and charge different output capacitors, effectively improving voltage gain. A high boost ratio can be obtained under conditions of low duty cycle and small coupled inductor turns ratio, avoiding problems such as increased leakage inductance, high core loss, and excessive device stress caused by the reliance on extremely high duty cycle or ultra-large turns ratio in traditional topologies. It significantly improves the boosting capability under a wide input voltage range and is suitable for scenarios where low-voltage new energy sources such as photovoltaics and energy storage supply power to high-voltage DC buses.

[0017] The three-winding coupled inductor uses a parallel winding method for the secondary and tertiary windings to reduce the voltage imbalance caused by the difference in parasitic parameters between the two windings, effectively reducing the complexity of winding the three-winding coupled inductor.

[0018] Based on the connection of the secondary and tertiary windings of the three-winding coupled inductor to the bipolar output capacitor unit via a voltage multiplier component, the turns ratio limitation between the two secondary windings and the primary winding can be eliminated, so that the number of turns of the two secondary windings is the same and can be arbitrarily selected as needed, which can reduce the impact of inconsistent winding parameters on the output voltage balance. When implementing soft switching, the two secondary windings form current supply paths, so that the current of the main switch is determined by the primary winding and the two secondary windings. This makes it easier to achieve soft switching of the main switch when transitioning from the first mode to the second mode. Even if the current in the primary winding is in the positive direction, the main switch can still achieve soft switching through the current in the secondary and tertiary windings, thereby improving the reliability and feasibility of soft switching.

[0019] Based on the connection and coordination of the bipolar output capacitor unit and the two secondary windings, the influence of all diodes and input power supply parasitic parameters can be eliminated. It is only affected by the on-resistance of the switching transistor and the corresponding copper resistance of the two secondary windings. The influence of the copper resistance of the two secondary windings can be eliminated as much as possible by selecting the same turns ratio for parallel winding, thereby improving the stability and reliability of the output target voltage conversion.

[0020] By employing a low-current ripple unit and ensuring that the main switch branch and the auxiliary switch branch are in a complementary conduction state, the need for a 180° phase shift between the two phases to reduce input current ripple can be eliminated.

[0021] The bipolar output capacitor unit uses two output capacitors to alternately charge and discharge, which can further effectively reduce the fluctuation of the output voltage. During the steady-state operation, there will be no voltage inequality due to power inequality. It can operate normally when the power is unbalanced and will not produce voltage drop. It is not affected by the load, and the bipolar voltage will not cause power imbalance.

[0022] The input power supply ground is shared with the bipolar neutral point, which can suppress the leakage current of the photovoltaic panel when the input power supply is a photovoltaic panel. Attached Figure Description

[0023] Figure 1 This is an equivalent circuit schematic diagram of one embodiment of the bipolar converter of the present invention.

[0024] Figure 2 This is a timing diagram of an embodiment of the bipolar converter after it enters the steady-state operating stage of the present invention.

[0025] Figure 3 This is a schematic diagram of the circuit operation of the present invention in the first mode.

[0026] Figure 4 This is a schematic diagram of the circuit operation of the present invention in the second mode.

[0027] Figure 5 This is a schematic diagram of the circuit operation of the present invention in the third mode.

[0028] Figure 6 This is a schematic diagram of the circuit operation of the present invention in the fourth mode.

[0029] Figure 7 This is a schematic diagram of the circuit operation of the present invention in the fifth mode.

[0030] Figure 8 This is a schematic diagram of the circuit operation of the present invention in the sixth mode.

[0031] Figure 9 This is a schematic diagram of the circuit operation of the present invention in the seventh mode.

[0032] Figure 10 This is a schematic diagram of the circuit operation of the present invention in the eighth mode.

[0033] Figure 11 This is a schematic diagram of the circuit operation of the present invention in the ninth mode.

[0034] Figure 12 This is a schematic diagram of the circuit operation of the present invention in the tenth mode.

[0035] Figure 13 This is an equivalent circuit diagram of the parasitic parameters of the bipolar converter of the present invention. Detailed Implementation

[0036] The present invention will be further described below with reference to specific accompanying drawings and embodiments.

[0037] To achieve a high output voltage under low duty cycle conditions while reducing input ripple and device stress, this invention provides a low-current ripple bipolar converter based on a three-winding coupled inductor. Specifically, the bipolar converter includes: A three-winding coupled inductor includes a primary winding and two secondary windings that can cooperate with the primary winding to form a transformer working capability. The two secondary windings have the same turns ratio as the primary winding and the same parasitic parameters. The bipolar output capacitor unit includes at least two output capacitors. The bipolar neutral point formed by the two output capacitors is connected to the input power supply. The other end of the bipolar neutral point formed by the corresponding connection of each output capacitor is connected to a non-same-name terminal of a corresponding secondary winding via a voltage multiplier component. During the voltage conversion process, each secondary winding can increase the capacitor voltage of the corresponding output capacitor through the connected voltage multiplier component, and the two output capacitors are in an alternating parallel charging and discharging state. The low-current ripple unit is adapted to connect with the input power supply and primary winding. The main switch branch in the low current ripple unit is adapted to and connected to an auxiliary switch branch so that the auxiliary switch branch can be used to perform active clamping and soft switching control on the main switch branch. Based on the switching operation states of the main switch branch and the auxiliary switch branch, the three-winding coupled inductor, the low-current ripple unit, and the bipolar output capacitor unit are configured to be in their respective operating modes in sequence, and the stable target conversion voltage is output through the bipolar output capacitor unit.

[0038] Similar to existing bipolar converters, the bipolar converter of this invention can transform the input voltage provided by the input power supply to obtain a target transformed voltage with bipolar capability. To achieve a higher output voltage, i.e., a higher target transformed voltage, even with a relatively low duty cycle, the bipolar converter of this invention should include a three-winding coupled inductor. This three-winding coupled inductor includes one primary winding and two secondary windings. Each secondary winding can cooperate with the primary winding to form a transformer operation. Specifically, the primary winding and two secondary windings can be wound on the same magnetic core. The method by which the secondary windings cooperate with the primary winding to form a transformer operation is consistent with existing technology and will not be elaborated here.

[0039] In order to achieve the target bipolar voltage conversion output, the bipolar converter of the present invention should also include a bipolar output capacitor unit. The bipolar output capacitor unit should include at least two output capacitors. It should be understood that the number of output capacitors in the bipolar output capacitor unit can be selected as needed to meet the requirements of bipolar output. For example, when there are multiple sub-capacitors, the multiple sub-capacitors can be equivalent to two output capacitors.

[0040] In practical implementation, the two output capacitors within the bipolar output capacitor unit can be connected to form a bipolar neutral point. After forming the bipolar neutral point, it is adapted and connected to the input power supply, thus solving the problem in existing bipolar converters where the input power supply ground cannot share a common ground with the bipolar neutral point. When the input power supply is a photovoltaic panel module, the ground of the photovoltaic panel module shares a common ground with the bipolar neutral point, effectively suppressing leakage current from the photovoltaic panel module. When the input power supply is of other types, the adapted connection between the input power supply and the bipolar neutral point provides stability and reliability of the target conversion voltage output by the bipolar output capacitor unit.

[0041] To achieve the required boost voltage and output the target converted voltage, each output capacitor should be adapted and connected to a corresponding secondary winding via a voltage multiplier component. That is, when two output capacitors exist / are formed, the output capacitors, secondary windings, and corresponding voltage multiplier components are connected in a one-to-one correspondence. Specifically, during the adaptation connection, the other end of the output capacitor corresponding to the bipolar neutral point should be connected to the non-same-name terminal of the corresponding secondary winding via the voltage multiplier component. When each output capacitor is equivalently formed by multiple capacitors, please refer to this section for details on the connection method with the corresponding secondary winding.

[0042] As can be seen from the above description, in the prior art, in order to obtain a higher voltage gain, a larger coupling inductor turns ratio is required, which leads to an increase in leakage inductance and core loss. In addition, some topologies use a multi-winding coupled inductor structure, which has poor winding parameter consistency and is prone to output imbalance. In one embodiment of the present invention, the turns ratios of the two secondary windings are configured to be the same as those of the primary winding, that is, the two secondary windings have the same number of turns. The secondary windings are connected to the output capacitor through a voltage multiplier component. Thus, a higher output voltage can be obtained without a large duty cycle or a large turns ratio, that is, a higher target conversion voltage can be obtained.

[0043] Furthermore, configuring the two secondary windings to have the same parasitic parameters can be achieved by winding them together using the same method. Other methods can also be used to ensure the two secondary windings have the same parasitic parameters, which will not be elaborated here. Because the two secondary windings have the same parasitic parameters, the effect of each secondary winding on its corresponding connected output capacitor is the same, and they can cancel each other out, preventing output voltage imbalance and suppressing the influence of other component parasitic parameters on the output capacitor.

[0044] To reduce input ripple, the bipolar converter of this invention should also include a low-current ripple unit. This low-current ripple unit is adapted and connected to the input power supply and the primary winding. Of course, it is also connected to the secondary winding; the specific connection details will be explained below. The low-current ripple unit can adopt a commonly used form. Since the input power supply mainly provides low-voltage DC power, to meet the voltage conversion requirements, the main switch branch and an auxiliary switch branch within the low-current ripple unit are adapted and connected to each other. The auxiliary switch branch is used to perform active clamping and soft-switching control on the main switch branch. The main switch branch can chop the low-voltage DC voltage provided by the input power supply into a sine wave. Then, the formed transformer transfers the power to the secondary winding. The auxiliary switch branch can perform active clamping and soft-switching control on the main switch branch. Soft-switching control specifically refers to enabling the main switch transistor S1 within the main switch branch to achieve soft switching, performing active clamping and soft-switching control, as explained in the corresponding description below.

[0045] During operation, the operating state of the bipolar converter of this invention can be configured by the corresponding switching states of the main switch branch and the auxiliary switch branch. This means that the operating mode can be configured within a switching cycle and during adjacent switching cycles. By changing different operating modes, the bipolar output capacitor unit can output a stable target conversion voltage. The operating modes of the bipolar converter will be described in detail below; please refer to the corresponding descriptions for details.

[0046] In one embodiment of the present invention, when the two output capacitors in the bipolar output capacitor unit are respectively output capacitor C o1 With output capacitor C o2 When, the output capacitor C o1 The negative terminal and the output capacitor C o2 The positive poles connect with each other to form a bipolar neutral point. When the two secondary windings are the secondary winding L2 and the tertiary winding L3 respectively, then: The voltage multiplier assembly adapted to the secondary winding L2 includes diode D1, capacitor C1, and diode D2. The voltage multiplier assembly adapted to the tertiary winding L3 includes diode D3, capacitor C2, and diode D4. The anode of diode D1 is connected to the same-name terminal of the secondary winding L2 and the same-name terminal of the tertiary winding L3. The cathode of diode D1 is connected to the positive terminal of capacitor C1 and the anode of diode D2. The cathode of capacitor C1 is connected to the non-same-name terminal of the secondary winding L2. The cathode of diode D2 is connected to the output capacitor C. o1 Positive extreme connection; The non-identical terminal of the tertiary winding L3 is connected to the positive terminal of capacitor C2. The negative terminal of capacitor C2 is connected to the anode of diode D4 and the cathode of diode D3. The anode of diode D3 is connected to the output capacitor C. o2 Negative extreme connections; The cathode of diode D1 is connected to the bipolar neutral point.

[0047] Figure 1 The diagram shows an equivalent circuit schematic of one embodiment of the bipolar converter of the present invention. It should be understood that the equivalence here specifically refers to the equivalence performed on the three-winding coupled inductor. Furthermore, Figure 1 The figure also shows an embodiment of a bipolar output capacitor unit, in which the output capacitor C o1 With output capacitor C o2 These are the two output capacitors within the bipolar output capacitor unit. When the output capacitor C... o1 The negative terminal and the output capacitor C o2 When the positive poles of the two poles are connected to each other, a bipolar neutral point can be formed.

[0048] Furthermore, Figure 1 The diagram also shows the equivalent case of a three-winding coupled inductor. In the figure, L1 is the equivalent primary winding, and L2 and L3 are the equivalent secondary and tertiary windings, respectively. Furthermore, Figure 1 In the middle, L m L k These are the equivalent magnetizing inductance and leakage inductance, respectively. In the equivalent circuit, the same-name terminal of the primary winding is connected to one end of the magnetizing inductance, the other end of the primary winding is connected to the other end of the magnetizing inductance and the first end of the leakage inductance, and the second end of the leakage inductance is connected to the corresponding same-name terminals of the secondary winding L2 and the tertiary winding L3.

[0049] Figure 1 The document also shows an embodiment of a voltage multiplier assembly connected to the secondary winding L2 and the tertiary winding L3. It should be noted that the positive terminal of capacitor C1 is the connection terminal formed corresponding to the positive plate of capacitor C1, and the negative terminal of capacitor C1 is the connection terminal formed corresponding to the negative plate of capacitor C1. The positive and negative terminals of other capacitors can be referred to the description here.

[0050] In one embodiment of the present invention, the main switch branch includes a main switch transistor S1, and the auxiliary switch branch includes an auxiliary switch transistor S2 and an auxiliary capacitor C. b ,in, The source terminal of the main switch S1, capacitor C b The negative terminal of the main switch S1 is connected to the bipolar neutral point, and the drain terminal of the main switch S1 is adapted to the non-same-name terminal of the primary winding and connected to the corresponding same-name terminals of the secondary winding L2 and the tertiary winding L3. Capacitor C b The positive terminal of the main switch S1 is connected to the drain terminal of the auxiliary switch S2, and the source terminal of the auxiliary switch S2 is connected to the drain terminal of the main switch S1. The main switch S1 and the auxiliary switch S2 are in a complementary conduction state.

[0051] Figure 1 The figure also illustrates an embodiment of the main switch branch and the auxiliary switch branch. In the figure, both the main switch S1 and the auxiliary switch S2 are NMOS transistors. Both the main switch S1 and the auxiliary switch S2 have corresponding parasitic capacitances and parasitic diodes. For the main switch S1, the two ends of the parasitic capacitance are connected to the source and drain terminals of the main switch S1, the anode terminal of the parasitic diode is connected to the source terminal of the main switch S1, and the cathode terminal of the parasitic diode is connected to the drain terminal of the main switch S1. The corresponding connection relationship between the parasitic capacitance, parasitic diode, and the auxiliary switch S2 can be found in the reference [reference needed]. Figure 1 The corresponding description of the main switch S1 will not be repeated here.

[0052] Furthermore, Figure 1 In the circuit, the source terminal of the main switch S1 is connected to the bipolar neutral point. The drain terminal of the main switch S1 and the source terminal of the auxiliary switch S2 are both connected to the corresponding terminals of the secondary winding L2 and the tertiary winding L3, and are also connected to the leakage inductance L. k The corresponding terminals are connected. The drain terminal of the auxiliary switch S2 is connected to capacitor C. b Connect to the bipolar neutral point.

[0053] In order to configure the operating modes of the bipolar converter, the main switch S1 and the auxiliary switch S2 are in complementary conduction states. When the main switch S1 is in the conduction state, the auxiliary switch S2 should be in the off state. Similarly, when the auxiliary switch S2 is in the conduction state, the main switch S1 should be in the off state. However, a dead time should be set within each switching cycle and between adjacent switching cycles. During this dead time, both the main switch S1 and the auxiliary switch S2 are in the off state.

[0054] In one embodiment of the present invention, the low-current ripple unit further includes an inductor L0, a diode D5, a diode D6, and a capacitor C.in ,in, The first terminal of the input power supply is connected to the bipolar neutral point, the second terminal of the input power supply is connected to one end of the inductor L0, the other end of the inductor L0 is connected to the anode of diode D5 and the anode of diode D6, and the cathode of diode D6 is connected to the non-same-name terminal of the primary winding. The cathode of diode D5 is connected to the corresponding terminal of the primary winding, and the corresponding terminal of the primary winding is also connected to capacitor C. in One end is connected to capacitor C in The other end is connected to the bipolar neutral point and the source terminal of the main switch S1.

[0055] Figure 1 An embodiment of a low-current ripple unit is also shown, controlled by the capacitor C. in In addition to connecting to the bipolar neutral point and the source terminal of the main switch S1, it should also be connected to capacitor C. b The negative extreme connection. Figure 1 In the middle, V in For the input power supply, when the input power supply is a photovoltaic panel module, the ground terminal of the photovoltaic panel module, the source terminal of the main switch S1, and the capacitor C are connected. in Capacitor C b The negative extreme connection.

[0056] In one embodiment of the present invention, after entering the steady-state operating phase, the main switch S1 and the auxiliary switch S2 are sequentially turned on once in each switching cycle, and the main switch S1 and the auxiliary switch S2 are not simultaneously in the on state, so as to configure the main switch S1 and the auxiliary switch S2 to be in the corresponding switching operating states, wherein... After the previous switching cycle ends, the auxiliary switch S2 switches from the on state to the off state while the main switch S1 remains in the off state. Then the three-winding coupled inductor, the low current ripple unit, and the bipolar output capacitor unit enter the first mode. After entering the current switching cycle, the main switch S1 switches from the off state to the on state. During the period when the main switch S1 is in the on state, the three-winding coupled inductor, the low current ripple unit and the bipolar output capacitor unit enter the second mode, the third mode and the fourth mode in sequence. During the current switching cycle, when the main switch S1 switches from the on state to the off state again and the auxiliary switch S2 also remains off, the three-winding coupled inductor, the low current ripple unit, and the bipolar output capacitor unit enter the fifth mode. During the current switching cycle, when the auxiliary switch S2 switches from the off state to the on state, the three-winding coupled inductor, the low-current ripple unit, and the bipolar output capacitor unit sequentially enter the sixth mode, the seventh mode, the eighth mode, the ninth mode, and the tenth mode.

[0057] Generally, when a bipolar converter is working, it usually goes through a non-steady-state operating stage and then enters a steady-state operating stage. For example, it will be in the non-steady-state operating stage at the beginning of operation. Therefore, the steady-state operating stage specifically refers to the stable operating stage of the bipolar converter. At this time, a stable target conversion voltage can be output through the bipolar output capacitor unit. The specific meaning of the steady-state operating stage is consistent with the existing technology and will not be described in detail here.

[0058] Similar to existing technologies, during steady-state operation, the bipolar converter operates consistently within each switching cycle. Specifically, the bipolar converter should experience the same operating mode within each switching cycle. The switching cycle here refers to the period controlling the switching states of the main switch S1 and the auxiliary switch S2. The operating time corresponding to each switching cycle should be the same, and both the main switch S1 and the auxiliary switch S2 should conduct once within each switching cycle. Generally, the duty cycle of the bipolar converter is determined based on the conduction time of the main switch S1 and the duration of the switching cycle. The specific calculation of the duty cycle will be discussed below. Figure 2 A detailed explanation will be provided.

[0059] Figure 2 The diagram illustrates a specific embodiment of switching between different switching cycles, the corresponding conduction control of the main switch S1 and auxiliary switch S2 within a single switching cycle, and the voltage and current of different devices within the entire bipolar converter. The following section combines this with... Figure 2 The working modes of the bipolar converter and the different working modes are explained in detail.

[0060] In one embodiment of the present invention, upon entering the first mode, the following occurs: Diodes D1, D3, and D5 are turned off, while diodes D2, D4, and D6 are forward biased. The primary winding, secondary winding L2, and tertiary winding L3 are all in the freewheeling phase. The parasitic capacitance of the auxiliary switch S2 is charged, while the parasitic capacitance of the main switch S1 is discharged. When the voltage at the source-drain terminal of the main switch S1 drops rapidly to zero, the parasitic body diode ZCS of the main switch S1 is turned on. When the main switch S1 is turned on, the first mode ends.

[0061] Specifically, the time interval corresponding to the first mode Figure 2 In [t0,t1], Figure 2 In the middle, V gs1The gate-source voltage of the main switch S1, V gs2 The gate-source voltage of the auxiliary switch S2 is shown in the figure. The gate-source power supply V is... gs1 The gate-source voltage V is represented by a black line. gs2 The corresponding red lines indicate this. As explained above, when both the main switch S1 and the auxiliary switch S2 are NMOS transistors, the gate-source power supply V... gs1 When the voltage is high, the main switch S1 is turned on; otherwise, the main switch S1 is turned off, and the gate-source power supply V... gs2 The conduction state of the auxiliary switch S2 can be found in the description of the main switch S1 here.

[0062] As explained above, [t0, t1] is the dead time between the end of the previous switching cycle and the start of the current switching cycle. At time t0, the gate-source voltage V... gs1 If the voltage level is low, the main switch S1 remains off, and the gate-source voltage V... gs2 When the voltage level changes from high to low, at time t0, the auxiliary switch S2 switches from the on state to the off state. At time t1, the gate-source voltage V... gs1 When the level changes from low to high, the main switch S1 switches from the off state to the on state, while the auxiliary switch S2 remains in the off state.

[0063] Figure 2 In the middle, V L1 The voltage across the primary winding L1 is, i.e. Figure 1 The voltage difference between the + terminal and the - terminal of the primary winding L1. Figure 1 In the diagram, the left end of the primary winding L1 is the positive terminal, and the right end of the primary winding is the negative terminal. L1 V represents the current flowing through the primary winding L1. L2 i represents the voltage across the secondary winding L2, that is, the voltage difference between the same-named and non-same-named terminals of the secondary winding L2. L2 V is the current flowing through the secondary winding. L3 i represents the voltage across the tertiary winding L3, which is the voltage difference between the corresponding and non-corresponding terminals of the tertiary winding L3. L3 This refers to the current flowing through the secondary winding.

[0064] V DS1 The drain-source voltage of the main switch S1, i.e., the voltage difference between the drain and source terminals of the main switch S1, is... DS1 V is the current flowing through the source and drain terminals of the main switch S1. DS2 i is the drain-source voltage of the auxiliary switch S2, that is, the voltage difference between the drain and source terminals of the auxiliary switch S2. DS2 This refers to the current flowing through the source and drain terminals of the auxiliary switch S2.

[0065] V D1 i is the voltage difference between the anode and cathode terminals of diode D1. D1 V is the current flowing through diode D1. D2 i represents the voltage difference between the anode and cathode terminals of diode D2. D2 V is the current flowing through diode D2. D3 i represents the voltage difference between the anode and cathode terminals of diode D3. D3 V is the current flowing through diode D3. D4 i represents the voltage difference between the anode and cathode terminals of diode D4. D4 This represents the current flowing through diode D4. It should be noted that... Figure 2 In the diagram, when the voltage and current of the same device are shown simultaneously, the current is represented by a red line and the voltage by a black line.

[0066] also, Figure 2 The diagram also illustrates the current directions for different devices. For the primary winding L1, secondary winding L2, and tertiary winding L3, the current direction is positive when the current flows from the same terminal to the opposite terminal; otherwise, the current direction is negative. For diodes D1 through D4, the current direction is positive when the current flows into the corresponding anode and out the corresponding cathode. For the main switch S1 and auxiliary switch S2, the current direction is positive when the current flows from the corresponding source to the corresponding drain; otherwise, the current direction is negative. Based on this explanation, the direction can be determined... Figure 2 The variation of current direction and current amplitude in the medium.

[0067] Based on the above explanation and Figure 2 It can be seen that at time t0, for the primary winding L1, the voltage V L1 The value is negative, meaning the potential at the non-corresponding terminal of the primary winding L1 is higher than the potential at the corresponding terminal of the primary winding L1, and the current i L1 It is also negative, meaning the current flows from the non-corresponding terminal of the primary winding L1 to the corresponding terminal of the primary winding L1; for the secondary winding L2, the voltage V L2 The value is positive, meaning the potential at the same-name terminal of the secondary winding L2 is higher than the potential at the non-same-name terminal of the secondary winding L2, and the current i L2 The voltage is positive, meaning the current flows from the same-name terminal of the secondary winding L2 to the non-same-name terminal of the secondary winding L2. For the tertiary winding L3, the voltage V... L3 The value is positive, meaning the potential at the same-name terminal of the tertiary winding L3 is higher than the potential at the non-same-name terminal of the tertiary winding L3, and the current i L3 It is positive, meaning that the current flows from the same-name terminal of the tertiary winding L3 to the non-same-name terminal of the tertiary winding L3.

[0068] At time t0, for the main switch S1, the voltage V DS1 The value is positive, meaning the drain potential of the main switch S1 is higher than the source potential. Since the main switch S1 is in the off state, the current i flowing through the main switch S1 is positive. DS1 The value is 0. For the auxiliary switch S2, since the etching at t0 changes it from the on state to the off state, the voltage V at this time is 0. DS2 When the current i is 0, the current i DS2 It is positive, that is, the current i DS2 The flow is from the drain terminal of the auxiliary switch S2 to the source terminal of the auxiliary switch S2.

[0069] At time t0, for diode D1, the voltage V D1 The value is positive, meaning the potential at the anode of diode D1 is higher than the potential at the cathode. Since diode D1 is in the off state, the current i... D1 The voltage is 0. For diode D2, since diode D2 is conducting, the voltage V... D2 When the current i is 0, the current i D2 The voltage is positive, meaning the current flows from the anode to the cathode of diode D2. For diode D3, the voltage V... D3 The value is positive, meaning the potential at the anode of diode D3 is higher than the potential at the cathode. Since diode D3 is off, the current i... D3 The value is 0. For diode D4, since diode D4 is conducting, the voltage V... D4 When the current i is 0, the current i D4 It is positive, meaning that the current flows from the anode of diode D4 to the cathode of diode D4.

[0070] As can be seen from the above explanation, we can obtain Figure 2 The voltage and current in this section mainly refer to ideal devices. For example, when a diode is conducting, it is considered an ideal device and there is no corresponding voltage division. For other ideal devices, please refer to the explanation here.

[0071] Furthermore, at time t1, for the primary winding L1, the voltage V L1 The value is 0, meaning the potential of the non-corresponding terminals of the primary winding L1 is equal to the potential of the corresponding terminals of the primary winding L1, and the current i L1 It is still negative, but compared to time t0, the current i L1 The amplitude decreases; for the secondary winding L2, the voltage V L2 It is positive; compared to time t0, the voltage V is positive. L2 Increase; current i L2 It remains positive; compared to time t0, the current i L2 It decreases. For the tertiary winding L3, the voltage V... L3It is positive; compared to time t0, the voltage V is positive. L32 Increase; current i L3 It remains positive; compared to time t0, the current i L3 It gets smaller.

[0072] At time t1, for the main switch S1, since the main switch S1 switches from the off state to the on state, the voltage V DS1 The current i flowing through the main switch S1 decreases to 0. DS1 It changes from 0 to negative. For the auxiliary switch S2, the voltage V DS2 If positive, the current i DS2 It is 0.

[0073] At time t1, for diode D1, the voltage V D1 It remains positive; compared to time t0, the voltage V... D1 As it increases, the current i D1 It remains 0. For diode D2, the voltage V... D2 It is still 0, current i D2 It remains positive; compared to time t0, the current i D2 It decreases. For diode D3, the voltage V... D3 It remains positive, current i D3 It remains 0. For diode D4, since diode D4 is conducting, the voltage V... D4 It remains 0, current i D4 It is positive; compared to time t0, the current i D4 To become smaller.

[0074] Figure 3 The diagram also illustrates the operation of different devices within the entire bipolar converter in the first mode, as well as an embodiment of the current path in the first mode. It should be understood that... Figure 3 The diagram shows the operating conditions of different devices and the corresponding current paths, which should be consistent with... Figure 2 and the above-mentioned targets Figure 2 Consistent with the corresponding explanation, Figure 3 In this context, R represents the load. It should be noted that... Figure 3 Medium gray devices indicate that the corresponding devices are in a non-operating state. For example, for a diode, being in a non-operating state means that the diode is in a turned-off / non-conducting state, and for an NMOS transistor, it means that the NMOS transistor is in a turned-off state. Figure 3 In the diagram, non-gray devices indicate that the corresponding devices are in an active state. The active state specifically refers to the state opposite to the inactive state; for details on active states, please refer to the description of inactive states. Furthermore, Figures 4-12 The use of gray and black markings for devices in the text is consistent with Figure 3The functions are consistent, and please refer to this explanation for details. Furthermore, it should be noted that... Figures 3-12 In the modal diagram shown, all gray areas indicate that no current flows through the branch / component, but this does not mean that there is no voltage across the branch / component. Please refer to the corresponding explanation below for details.

[0075] Depend on Figure 3 It can be seen that since diode D6 is conducting and diode D5 is turning off, the current supplied by the input power supply flows through inductor L0 and diode D6 to the non-same-name terminal of the primary winding L1, and then through the same-name terminal of the primary winding L1 to capacitor C. in Outflow capacitor C in Part of the current flows to the input power supply, and the other part flows to the main switch S1 and the auxiliary switch S2. Since the auxiliary switch S2 is off, the current direction in the branch where the auxiliary switch S2 is located is from the drain terminal of the auxiliary switch S2 to the source terminal of the auxiliary switch S2. Therefore, the parasitic diode of the auxiliary switch S2 will be in the off state, and the current will parasitize the auxiliary switch S2, causing the voltage of the parasitic capacitor of the auxiliary switch S2 to rise rapidly.

[0076] For the branch containing the main switch S1, since the current direction is from the source terminal of the main switch S1 to the drain terminal of the main switch S1, when the parasitic capacitance of the main switch S1 discharges, the corresponding voltages at the source and drain terminals of the main switch S1 will drop rapidly to 0, and then the parasitic diode ZCS (Zero Current Switching) of the main switch S1 will turn on.

[0077] Based on the direction of the current flowing through the primary winding L1, the potentials of the corresponding non-corresponding terminals of the secondary winding L2 and the tertiary winding L3 will be higher than the potentials of their corresponding corresponding terminals. Therefore, according to the potential relationship, diodes D1 and D3 will be in the off state, while diodes D2 and D4 will be in the on state. As shown in the diagram, the current flowing through the secondary winding L2 will flow through capacitor C1 to the anode of diode D2, and the current flowing out from the cathode of diode D2 will flow to the output capacitor C1. o1 The positive terminal and the load R, the current flowing through the load R and the output capacitor C o2 The current flows to the bipolar neutral point after passing through the negative terminal. The current flowing through the tertiary winding L3 flows to the bipolar neutral point through capacitor C2 and diode D4, and of course, it also flows to the branch where the auxiliary switch S2 and the main switch S1 are located.

[0078] In one embodiment of the present invention, when the main switch S1 is driven from the off state to the on state, it enters the second mode, wherein... When entering the second mode, the main switch S1 achieves ZVS turn-on, the auxiliary switch S2 is turned off, and the primary winding, secondary winding L2, and tertiary winding L3 are all in the freewheeling stage; at the same time, the input power supply and inductor L0 and secondary winding L2 are connected in series to the output capacitor C. o1 During charging, the second mode ends when the current of the main switch S1 increases to zero. After the second mode ends, the third mode immediately begins, in which... When entering the third mode, the primary winding, secondary winding L2, and tertiary winding L3 are all in the freewheeling stage; the current direction of the main switch S1 is reversed, and the capacitor C... in When the current in the primary winding continues to rise to a value greater than zero, then changes direction and continues to increase, and the currents in the secondary winding L2 and the tertiary winding L3 reverse, the third mode ends, and at the same time, diodes D2 and D4 turn off naturally. After the third mode ends, the fourth mode immediately begins, in which... Upon entering the fourth mode, the current flowing through the secondary winding L2 and the tertiary winding L3 continuously increases, and diodes D1 and D3 achieve ZCS turn-on; the tertiary winding L3 and capacitor C2 are connected in series to the load capacitor C. o2 Power is supplied, and at the same time, the secondary winding L2 charges the capacitor C1 through the diode D1. When the main switch S1 is turned off, the fourth mode ends.

[0079] Depend on Figure 2 As explained above, time t0 is the end of the previous switching cycle, time t1 is the start of the current switching cycle, and [t0, t1] is the dead time between the previous and current switching cycles. That is, the current switching cycle begins at time t1. Since the gate-source voltage V at time t1... gs1 If the voltage level is high, the main switch S1 switches from the off state to the on state, while the auxiliary switch S2 remains off. This is because the drain-source voltage V at time t1... DS1 The voltage level is 0, therefore, the main switch S1 can achieve ZVS conduction, and the current flows from the drain terminal of the main switch S1 to the source terminal of the main switch S1. Furthermore, [t1, t2] represents the time range corresponding to the second mode.

[0080] It should be noted that in the first mode, when diode D2 is turned on, the secondary winding L2, capacitor C1, diode D2, and output capacitor C... o1 A path is formed; therefore, it can be assumed that there is a path to the output capacitor C. o1 The process of powering the load R. However, the duration of the first mode is very short, and its main function is to complete the commutation of the corresponding parasitic capacitances of the main switch S1 / auxiliary switch S2, so that the main switch S1 can achieve ZVS conduction.

[0081] Figure 4 The diagram shows the operation of different devices in the second mode of the bipolar converter of the present invention. The current and voltage conditions of different devices can be referred to the above. Figure 2 The relevant explanation regarding the first mode. (From...) Figure 4 It can be seen that diodes D1, D3, and D5 remain off, main switch S1 is on, and the branch containing auxiliary switch S2 is completely disconnected. The current flowing through the primary winding L1, secondary winding L2, and tertiary winding L3 has the same direction as the current in the first mode. The input power supply and inductor L0 and secondary winding L2 are connected in series to the output capacitor C. o1 Charging. The current in the branch containing the main switch S1 flows out through the capacitor C. in The current flowing through the main switch S1 is determined by the current flowing out of diode D4. When the current flowing through the main switch S1 increases to zero (after the main switch S1 is turned on, the polarity of the relevant winding voltage causes the current flowing through the main switch S1 to increase to zero), the current i is determined by the current flowing out of diode D4. DS1 The slope of the change is positive, therefore the current still flows in the original direction, but the absolute value of the negative value gradually decreases until it increases to zero, at which point the second mode ends. The relevant windings here specifically refer to the primary winding L1, the secondary winding L2, and the tertiary winding L3.

[0082] It should be noted that in the second mode, the auxiliary switch S2 remains off. Figure 4 Gray indicates that there is no conducting current in the branch where the auxiliary switch S2 is located. In the first mode, after the parasitic capacitance of the auxiliary switch S2 is charged, this voltage must be maintained in the second, third and fourth modes until the fifth mode commutation, when the parasitic capacitance of the auxiliary switch S2 is discharged, in preparation for the subsequent ZVS (Zero Voltage Switching) turn-on of the auxiliary switch S2.

[0083] Depend on Figure 2 It can be seen that [t2, t3] is the time range corresponding to the third mode. In the third mode, both the secondary winding L2 and the tertiary winding L3 are in the freewheeling stage. After the operation of the second mode, in the third mode, the direction of the current flowing through the main switch S1 is reversed, as shown below. Figure 5 As shown, the direction of the current flowing through the main switch S1 changes from from the source terminal to the drain terminal in the second mode to from the drain terminal to the source terminal of the main switch S1. It can be understood that this change in the direction of the current flowing through the main switch S1 will also affect the current flowing through the capacitor C. in And the direction of the current in the primary winding L1, such as causing the capacitor C to flow through it. in Furthermore, the current in the primary winding L1 will also reverse, changing from the in-phase terminal of the primary winding L1 to the non-in-phase terminal.

[0084] It should be noted that when the direction of the current flowing through the primary winding L1 reverses, the corresponding directions of the current flowing through the secondary winding L2 and the tertiary winding L3 will also change accordingly. When the corresponding directions of the current flowing through the secondary winding L2 and the tertiary winding L3 reverse, the third mode ends. From the above-mentioned relationship between the current direction flowing through the primary inductor L1 and the potentials of the corresponding terminals (same and different) of the secondary winding L2 and the tertiary winding L3, it can be seen that before the current direction of the current flowing through the secondary winding L2 and the tertiary winding L3 reverses, diodes D1 and D3 remain in the off state; however, when the current direction reverses, diodes D2 and D4 will naturally turn off. Figure 5 The diagram shows the device operation in the third mode before the current direction is reversed.

[0085] Depend on Figure 2 It can be seen that [t3, t4] is the time range corresponding to the fourth mode. From the above explanation of the third mode, it is known that as the current flowing through the secondary winding L2 and the tertiary winding L3 continues to increase (after the main switch S1 is turned on, and diodes D1 and D3 begin to conduct, the polarity of the winding voltage across the secondary winding L2 and the tertiary winding L3 is consistent with the direction of current increase; therefore, according to the inductance relationship, when the voltage polarity across the windings maintains the driving direction, the current in the secondary winding L2 and the tertiary winding L3 will continue to increase), diodes D1 and D3 can achieve ZCS conduction. Since diode D2 is turned off, at this time, the tertiary winding L3, through capacitor C2 and the conducting diode D3, can become the output capacitor C. o2 Power is supplied, and at the same time, the secondary winding can charge capacitor C1 through diode D1. The direction of the current flowing through diode D1 is from the anode to the cathode of diode D1.

[0086] Figure 6 The diagram illustrates the operation of different devices and the direction of current in the fourth mode. Figure 2 as well as Figure 6 It can be seen that the branch containing the auxiliary switch S2 remains off and no current flows through it. The current flowing through the main switch S1 is directed from the drain terminal of the main switch S1 to the source terminal of the main switch S1. The corresponding currents flowing through the tertiary winding L3 and the secondary winding L2 are directed from the non-same-name terminal to the same-name terminal. The current flowing out from the same-name terminal of the secondary winding L2 will flow to the connection node where the drain terminal of the main switch S1 is located, and the current flowing out from the source terminal of the main switch S1 will flow to the bipolar neutral point. In the following description, the connection node here will be referred to as the switching node.

[0087] In one embodiment of the present invention, the fifth mode is entered immediately after the fourth mode ends, wherein, After entering the fifth mode, both the main switch S1 and the auxiliary switch S2 are in the off state, diodes D1, D3, and D5 are forward biased, and diodes D2, D4, and D6 are turned off. The parasitic capacitance of the main switch S1 is charged, and the parasitic capacitance of the auxiliary switch S2 is discharged. Then, the parasitic diode ZCS of the auxiliary switch S2 is turned on. When the auxiliary switch S2 is driven to conduct, the fifth mode ends.

[0088] Depend on Figure 2 It can be seen that [t4, t5] is the time range corresponding to the fifth mode. Since the main switch S1 is also in the off state at time t4, both the main switch S1 and the auxiliary switch S2 are in the off state in the fourth mode, which is the dead time within the current switching cycle. At time t5, V gs2 When the signal transitions to a high level, the auxiliary switch S2 can be turned on. Therefore, it can be concluded that... Figure 7 The diagram shows the operating status of each device and the corresponding current path before time t5 in the fifth mode.

[0089] Depend on Figure 7 It can be seen that after entering the fifth mode, the main switch S1 is turned off. Since the direction of the parasitic diode of the main switch S1 conflicts with the current direction, the current flowing through the main switch S1 flows out through the parasitic capacitance of the main switch S1 (that is, it charges the parasitic capacitance of the main switch S1). The outflowing current will flow to capacitor C. in And the bipolar neutral point, and at this time the direction of the current flowing through the primary winding L1 remains unchanged. Simultaneously, the current flowing from the corresponding terminal of the tertiary winding L3 and the node connected to the drain terminal of the main switch S1 both flow to the branch where the auxiliary switch S2 is located, and freewheel through the parasitic diode of the auxiliary switch S2, thereby discharging the parasitic capacitance of the auxiliary switch S2, causing its voltage to drop rapidly to zero. Afterwards, the auxiliary switch... S The parasitic diode ZCS of transistor 2 turns on. When the drive signal for auxiliary switch S2 arrives, the fifth mode ends, that is, when the gate-source voltage V... gs2 When the level is high, the fifth mode ends. Furthermore, by... Figure 7 As can be seen, in the fifth mode, the current directions of the secondary winding L2 and the tertiary winding L3 do not change. For details, please refer to the corresponding description of the fourth mode.

[0090] It should be noted that, as explained above regarding the fourth mode, when the main switch S1 is turned on, the switching node is clamped by the main switch S1, and the branch containing the auxiliary switch S2 is not forward biased. Therefore, the parasitic diode of the auxiliary switch S2 cannot freewheel. Upon entering the fifth mode, after the main switch S1 is turned off and enters the dead zone, the currents in the primary winding L1, secondary winding L2, and tertiary winding L3 cannot change abruptly. The current will transfer to the branch containing the auxiliary switch S2, causing the parasitic capacitance of the auxiliary switch S2 to discharge. When the drain-source voltage V of the auxiliary switch S2... DS2 After dropping to near zero, the parasitic diode of the auxiliary switch S2 is forward biased and freewheels, creating conditions for the ZVS turn-on of the auxiliary switch S2.

[0091] In one embodiment of the present invention, when entering the sixth mode, the auxiliary switch S2 achieves ZVS turn-on, and the main switch S1 is controlled by capacitor C. b The clamping phase occurs when the secondary winding and the tertiary winding L3 are in the freewheeling phase. When the current in the tertiary winding L3 increases to zero, the sixth mode ends and the diode D3 turns off naturally. After the sixth mode ends, the seventh mode immediately begins, in which... After entering the seventh mode, the current flowing through the tertiary winding L3 remains zero, and the secondary winding L2 is still in the freewheeling stage. When the current in the secondary winding L2 increases to zero, the seventh mode ends, and the diode D1 turns off naturally. After the seventh mode ends, the eighth mode immediately begins, in which... When entering the eighth mode, the corresponding currents flowing through the secondary winding L2 and the tertiary winding L3 reverse and continue to rise, while the primary winding is still in the freewheeling stage, and diodes D2 and D4 achieve ZCS turn-on. After entering the eighth mode, the input power supply, inductor L0, primary winding, secondary winding L2, and capacitor C1 are connected in series to the output capacitor C. o1 Power supply: When the current of auxiliary switch S2 increases to zero, the eighth mode ends. After the eighth mode ends, the ninth mode begins immediately, in which... At the moment of entering the ninth mode, the current flowing through the auxiliary switch S2 reverses and continues to rise; and when the current in the primary winding L1 decreases to zero, the ninth mode ends. After the ninth mode ends, the tenth mode begins immediately, in which... At the moment of entering the tenth mode, the current in the primary winding continues to decrease after crossing zero; the secondary winding L2, capacitor C1, and capacitor C... b The output capacitor C is connected in series. o1 When the auxiliary switch S2 is turned off, the tenth mode ends and the current switching cycle ends.

[0092] Figure 2 In the diagram, [t5, t6] represents the time of the sixth mode. At time t5, the gate-source voltage V... gs2 When the signal transitions to a high level, the auxiliary switch S2 can achieve ZVS turn-on. During the sixth mode, the auxiliary switch S2 remains in the on state, while the main switch S1 remains in the off state.

[0093] Figure 8 The diagram shows the operating states of the corresponding devices in the sixth mode and the corresponding current paths. In this mode, the main switch S1 is off, and the auxiliary switch S2 is on. Therefore, the main switch S1 is controlled by capacitor C. b Clamping, the source-drain voltage of the main switch S1 is equal to V. Cb When the current in the tertiary winding L3 increases to zero (the current flowing through the tertiary winding L3 initially flows negatively, but gradually increases to zero under the influence of the winding voltage), the sixth mode ends. Simultaneously, diode D3 naturally turns off.

[0094] Figure 8 In the circuit, because diode D5 is conducting, the direction of current flowing through the primary winding L1 is from the same-name terminal of the primary winding L1 to the non-same-name terminal of the primary winding L1. The secondary winding L2 and the tertiary winding L3 are in the freewheeling stage, and based on the voltages across the corresponding windings of the secondary winding L2 and the tertiary winding L3, the current can rise rapidly. At the same time, the current flowing out of the cathode of diode D5 will also flow to capacitor C. in The secondary winding L2 charges the capacitor C1 through the diode D1. The current flowing through the auxiliary switch S2 is determined by the current flowing out of the same-name terminal of the tertiary winding L3 and the current flowing from the non-same-name terminal of the primary winding L1. The direction of the current flowing through the auxiliary switch S2 is from the source terminal of the auxiliary switch S2 to the drain terminal of the auxiliary switch S2.

[0095] Figure 2In the diagram, [t6, t7] represents the time of the seventh mode. During the seventh mode, the main switch S1 remains off, and no current flows through the branch containing the main switch S1. The auxiliary switch S2 remains on, and the current flowing through the tertiary winding L3 remains zero (specifically, at the end of the sixth mode, the current in the tertiary winding L3 has dropped to zero, diode D3 naturally turns off, and there is temporarily no loop for the tertiary winding L3 branch to continue conducting; therefore, the current flowing through the tertiary winding L3 remains zero). The secondary winding L2 is still in the freewheeling stage (specifically, the secondary winding L2 branch still has a freewheeling path through diode D1 and capacitor C1; therefore, the current in the secondary winding L2 continues to change and remains in a freewheeling state until the current in the secondary winding L2 also increases to zero). When the current in the secondary winding L2 increases to zero, the seventh mode ends. Meanwhile, since the current flowing through the secondary winding L2 and diode D1 is 0, there is no longer a forward bias across diode D1, so diode D1 naturally turns off.

[0096] Figure 9 The diagram shows the operating states of the corresponding devices in the seventh mode and the corresponding current paths. As can be seen from the diagram, since diodes D2 and D3 are both in the off state, the output capacitor C... o1 and output capacitor C o2 When the stored electrical energy is used to supply power to the load R, the output capacitor C... o1 Output capacitor C o2 A loop is formed between the auxiliary switch S2 and the load R. The current flowing through the auxiliary switch S2 is determined by the current flowing out from the same-name terminal of the secondary winding L2 and the current flowing out from the non-same-name terminal of the primary winding L1.

[0097] Figure 2 In the diagram, [t7, t8] represents the time of the eighth mode. At time t7, the current flowing through the secondary winding L2 and the tertiary winding L3 reverses direction and continues to rise, while the primary winding L1 remains in the freewheeling phase. Diodes D2 and D4 achieve ZCS turn-on. The input power supply, inductor L0, primary winding L1, secondary winding L2, and capacitor C1 are connected in series with diode D2 to supply power to the output capacitor C. o1 Power supply for the load.

[0098] Specifically, at time t7, diodes D1 and D3 are turned off, while auxiliary switch S2 remains on. The polarity of the voltage across the coupling inductor changes, causing the current in the secondary winding L2 and the tertiary winding L3 to decrease to zero and then increase in the opposite direction. Furthermore, the output capacitor C... o1 Power supply, specifically, refers to supplying power to the output capacitor C. o1 Charging, or supplying power to a load, specifically refers to providing electrical energy to the load R. Other related explanations all have the same meaning and can be found here.

[0099] Depend on Figure 10 It can be seen that the current flowing from the non-same-name terminal of the primary winding L1, in addition to flowing into the auxiliary switch S2, also flows to the same-name terminal of the secondary winding L2 and the same-name terminal of the tertiary winding L3. When the current of the auxiliary switch S2 increases to zero, the eighth mode ends. Figure 10 It can be seen that after diode D4 is turned on, the current flowing through the tertiary winding L3 will pass through capacitor C2 and diode D4 will point to the bipolar neutral point.

[0100] Figure 2 In the diagram, [t8, t9] represents the time of the ninth mode. At time t8, as the current flowing through the primary winding L1 gradually decreases, the corresponding currents flowing through the secondary winding L2 and the tertiary winding L3 reverse and continue to increase, causing the current flowing through the auxiliary switch S2 to cross zero and reverse. Therefore, the current flowing through the auxiliary switch S2 reverses and continues to rise. Furthermore, the capacitor C... b Voltage clamping and commutation can be achieved. Within the ninth mode, the states of the remaining devices are similar to those in the eighth mode. The ninth mode ends when the current in the primary winding L1 decreases to zero. Figure 11 The diagram illustrates the operation of different devices and the corresponding current paths in the ninth mode. As shown, the current direction flowing through the primary winding L1 remains from the same-name terminal to the non-same-name terminal. Similarly, the current directions in the secondary winding L2 and tertiary winding L3 are also from the same-name terminal to the non-same-name terminal. Furthermore, Figure 11 In the middle, a portion of the current flowing out of the cathode of diode D2 flows to the output capacitor C. o1 The positive plate is used as the output capacitor C. o1 Charging, and passing through the output capacitor C o1 The negative plate returns to the bipolar neutral point; the other part flows to the load R, and then through the output capacitor C. o2 Return to the bipolar neutral point.

[0101] Figure 2 In the middle, [t9, t 10 [Temporal time] represents the time of the tenth mode. At time t9, the current in the primary winding L1 continues to decrease after crossing zero. The secondary winding L2, capacitor C1, and diode D2 are connected in series to form the output capacitor C. o1 Power is supplied to the load R. When the secondary switch S2 is turned off, the tenth mode ends, and at this time, the current switching cycle also ends.

[0102] Figure 12The figure shows the operation of different devices and the corresponding current paths in the tenth mode. As can be seen from the figure, the current flowing through the primary winding L1 is from the non-same-name terminal to the same-name terminal, while the currents corresponding to the secondary winding L2 and the tertiary winding L3 are from the same-name terminal to the non-same-name terminal. The current flowing through the auxiliary switch S2 is along the drain terminal of the auxiliary switch S2 to the source terminal of the auxiliary switch S2.

[0103] It should be noted that at the end of the tenth mode, after the auxiliary switch S2 is turned off, it enters the dead zone before the next cycle. Since the currents of inductor L0 and primary inductor L1 cannot change abruptly, the voltage at the switching node changes again, causing diode D5 to lose its forward bias, while diode D6 is forward biased. At this time, the input current is transferred to the relevant path of "inductor L0-diode D6-primary winding L1". Therefore, at the next time t0, diode D6 will be turned on.

[0104] Depend on Figure 2 It can be seen that the time from time t1 to time t5 is DTs, and the time from time t5 to time t0 of the next switching cycle is D'Ts. Specifically, for Figure 2 In the embodiment shown, the corresponding duty cycle D should be: ,in, This refers to the time corresponding to time t1 in the current switching cycle and time t1 in the next switching cycle.

[0105] As explained above, this invention can achieve voltage boost. The voltage gain of the bipolar converter of this invention will now be analyzed in detail based on its operating modes. For ease of explanation, the first to tenth modes will be represented by Mode I (first mode) to Mode X (tenth mode), respectively. Since the other modes have short durations, to simplify the steady-state analysis process, only Modes IV, VIII, IX, and X will be considered.

[0106] Specifically, based on mode IV, the following expression can be obtained: (1) in, This is the voltage of the tertiary winding in mode IV (that is, the potential difference between the corresponding same-name terminal and the non-same-name terminal of the tertiary winding L3). The voltage across capacitor C2. For the output capacitor C o2 voltage, This represents the voltage of the secondary winding in mode IV. The voltage across capacitor C1. For capacitor C in voltage, For the magnetizing inductor L m Voltage under mode IV The leakage inductance voltage in mode IV. The voltage of the input power supply. Let L0 be the voltage across inductor L0 in mode IV.

[0107] For a three-winding coupled inductor, the coupling coefficient K = Lm / (Lm + Lk), and the turns ratio is N2 = n2 / n1, N3 = n3 / n1, N2 = N3 = N, where n2 is the number of turns in the secondary winding, n1 is the number of turns in the primary winding, and n3 is the number of turns in the tertiary winding. In modes VIII, IX, and X, the following expressions are obtained: (2) in, For capacitor C b voltage, For the output capacitor C o1 voltage, for, for, for, for, for.

[0108] For input inductance L0 and magnetizing inductance L m Leakage inductance L k Using volt-second balance, we have: (3) in, This represents the voltage across inductor L0 in mode IV. For other cases, please refer to this explanation.

[0109] Substituting equations (1) and (2) into equation (3), we get: (4) in, This refers to the duty cycle of the bipolar converter in each switching cycle of the present invention. K is the coupling coefficient mentioned above. This is the voltage gain factor of the present invention.

[0110] Based on voltage gain factor It can be seen that, with a fixed coupling coefficient, the voltage gain factor... The voltage gain is related to the turns ratio N and the duty cycle D. Therefore, with a fixed turns ratio N, a higher voltage gain can be achieved with a smaller duty cycle. Conversely, with a smaller duty cycle, a higher voltage gain can be achieved without requiring a larger turns ratio.

[0111] Because the bipolar output capacitor unit consists of the output capacitor C o1 and output capacitor C o2The components, according to formula (4), their voltage difference can be calculated by formula (5): (5) According to formula (4), the larger the leakage inductance of the three-winding coupled inductor, the greater the voltage gain and the output capacitance C. o1 and output capacitor C o2 The smaller the voltage across the terminals, the lower the leakage inductance L, as can be seen from the expression for the coupling coefficient. k As the voltage increases, the coupling coefficient decreases; therefore, the voltage gain and output capacitance C... o1 Output capacitor C o2 The voltage will drop. However, since the turns ratio and parasitic parameters of the two secondary windings are the same, the output capacitance C... o1 and output capacitor C o2 If the expression remains consistent, then the leakage inductance itself will not cause an imbalance in the bipolar output voltage. Therefore, the bipolar converter of this invention has good self-balancing performance and can resist the influence of coupled inductor leakage inductance.

[0112] Regarding the voltage stress of the devices within the bipolar converter of this invention, to simplify the voltage stress analysis, the voltage ripple and leakage inductance of all capacitors are ignored, and only modes IV, VIII, IX, and X are considered. From equations (1), (2), and (4), the following expression can be obtained: (6) Based on mode VI, the average current flowing through diodes D1, D3, and D6 during the conduction period of the main switch S1 is: (7) in, The current flowing through the load R, The average current flowing through diode D1 This represents the average current flowing through diode D3. This represents the average current flowing through diode D6.

[0113] From the output voltages of diodes D1 to D6 in equation (6) above, it can be seen that the voltage stress of the diodes is relatively small, with a maximum voltage stress of Vo / 2, which is much smaller than the output voltage Vo. In specific implementation, the voltage stresses of diodes D2, D3, and D4 are the same, and the voltage stress of diode D1 is less than the corresponding voltage stresses of diodes D2, D3, and D4. Therefore, diodes of the same specification can be selected to reduce the influence of parasitic parameters on the bipolar output voltage balance.

[0114] In modes VIII, IX, and X when the main switch S1 is off, the average current flowing through diodes D2, D4, and D5 is: (8) in, This represents the average current flowing through diode D2. This represents the average current flowing through diode D4. The average current flowing through diode D5 During the period [t3, t4], the average current flowing through the secondary winding L2 and the tertiary winding L3 can be obtained by the following formula: (9) in, Let be the average current flowing through the secondary winding L2 during the period [t3, t4]. Let be the average current flowing through the third-side winding L3 during the period [t3, t4].

[0115] In [t7, t 10 During this period, the average current flowing through the secondary winding L2 and the tertiary winding L3 can be obtained by the following formula: (10) in, For [t7, t] 10 The average current flowing through the secondary winding L2 during this period, For [t7,t 10 The average current flowing through the third-side winding L3 during this period.

[0116] The average current flowing through inductor L0 during the entire switching cycle can be obtained by the following formula: (11) During the period [t3, t4], the average current flowing through the primary winding L1 can be obtained by the following formula: (12) in, Let be the average current flowing through the primary winding L1 during the period [t3, t4].

[0117] In [t7, t 10 During this period, the average current flowing through the primary winding L1 is obtained by the following formula: (13) in, For [t7, t] 10 The average current flowing through the primary winding L1 during this period.

[0118] The average current flowing through the switching transistor is obtained by the following formula: (14) (15) To facilitate the analysis of the influence of parasitic parameters, Figure 13 The equivalent circuit diagram of the parasitic parameters of the bipolar converter of the present invention is shown in the figure. Figure 13 In the middle, R in Represents the resistor of the input power supply; R represents the copper resistance of inductor L0; DS It is the on-resistance of the switching transistor; The copper resistance represents the primary winding of the coupled inductor; , L represents the copper resistance of the secondary and tertiary windings of the coupled inductor. k Leakage inductance represents the leakage inductance of a coupled inductor; V d and R d These are the forward voltage drop and on-resistance of the diode, respectively.

[0119] according to Figure 13 Based on the equivalent circuit diagram and the above explanations regarding modes IV, VIII, IX, and X, the following equation can be obtained: (16) (17) Combining equations (16) and (17) above, we get: (18) (19) (20) (twenty one) Substituting equations (18) and (19) into equations (20) and (21) respectively, we get: (twenty two) (twenty three) From equations (22) and (23), the two output capacitors C can be calculated. o1 and output capacitor C o2 The voltage difference, specifically, includes: (twenty four) From equations (22) and (23), it can be seen that the output capacitor C o1 and output capacitor C o2 The voltage across the circuit is affected by parasitic parameters of the components, such as the forward voltage drop and on-resistance of the corresponding diode, and the copper resistance and leakage inductance of the coupling inductor. Although these parasitic parameters will reduce... , However, as can be seen from equation (24), the output capacitor Co1 and output capacitor C o2 The voltage difference is determined solely by the load current, the on-resistance of the main switch S1, the duty cycle, and the copper resistances of the secondary winding L2 and the tertiary winding L3. Furthermore, since the secondary winding L2 and the tertiary winding L3 can be wound in parallel, their respective copper resistances can be made more consistent, thereby further reducing the bipolar output voltage difference. Therefore, by setting the duty cycle range and selecting appropriate components, the voltage difference between the two bipolar outputs during actual operation can be reduced, thus improving the stability of the target output voltage.

Claims

1. A low-current ripple bipolar converter based on a three-winding coupled inductor, characterized in that, The bipolar converter includes: A three-winding coupled inductor includes a primary winding and two secondary windings that can cooperate with the primary winding to form a transformer working capability. The two secondary windings have the same turns ratio as the primary winding and the same parasitic parameters. The bipolar output capacitor unit includes at least two output capacitors. The bipolar neutral point formed by the two output capacitors is connected to the input power supply. The other end of the bipolar neutral point formed by the corresponding connection of each output capacitor is connected to a non-same-name terminal of a corresponding secondary winding via a voltage multiplier component. During the voltage conversion process, each secondary winding can increase the capacitor voltage of the corresponding output capacitor through the connected voltage multiplier component, and the two output capacitors are in an alternating parallel charging and discharging state. The low-current ripple unit is adapted to connect with the input power supply and primary winding. The main switch branch in the low current ripple unit is adapted to and connected to an auxiliary switch branch so that the auxiliary switch branch can be used to perform active clamping and soft switching control on the main switch branch. Based on the switching operation states of the main switch branch and the auxiliary switch branch, the three-winding coupled inductor, the low-current ripple unit and the bipolar output capacitor unit are configured to be in the corresponding operating modes in sequence, and the stable target conversion voltage is output through the bipolar output capacitor unit. When the two output capacitors in the bipolar output capacitor unit are respectively output capacitor C o1 With output capacitor C o2 When, the output capacitor C o1 The negative terminal and the output capacitor C o2 The positive poles connect with each other to form a bipolar neutral point. When the two secondary windings are the secondary winding L2 and the tertiary winding L3 respectively, then: The voltage multiplier assembly adapted to the secondary winding L2 includes diode D1, capacitor C1, and diode D2. The voltage multiplier assembly adapted to the tertiary winding L3 includes diode D3, capacitor C2, and diode D4. The anode of diode D1 is connected to the same-name terminal of the secondary winding L2 and the same-name terminal of the tertiary winding L3. The cathode of diode D1 is connected to the positive terminal of capacitor C1 and the anode of diode D2. The cathode of capacitor C1 is connected to the non-same-name terminal of the secondary winding L2. The cathode of diode D2 is connected to the output capacitor C. o1 Positive extreme connection; The non-identical terminal of the tertiary winding L3 is connected to the positive terminal of capacitor C2. The negative terminal of capacitor C2 is connected to the anode of diode D4 and the cathode of diode D3. The anode of diode D3 is connected to the output capacitor C. o2 Negative extreme connections; The cathode of diode D1 is connected to the bipolar neutral point.

2. The low-current ripple bipolar converter based on a three-winding coupled inductor according to claim 1, characterized in that: The main switch branch includes a main switch transistor S1, and the auxiliary switch branch includes an auxiliary switch transistor S2 and an auxiliary capacitor C. b ,in, The source terminal of the main switch S1, capacitor C b The negative terminal of the main switch S1 is connected to the bipolar neutral point, and the drain terminal of the main switch S1 is adapted to the non-same-name terminal of the primary winding and connected to the corresponding same-name terminals of the secondary winding L2 and the tertiary winding L3. Capacitor C b The positive terminal of the main switch S1 is connected to the drain terminal of the auxiliary switch S2, and the source terminal of the auxiliary switch S2 is connected to the drain terminal of the main switch S1. The main switch S1 and the auxiliary switch S2 are in a complementary conduction state.

3. The low-current ripple bipolar converter based on a three-winding coupled inductor according to claim 2, characterized in that: The low-current ripple unit also includes an inductor L0, a diode D5, a diode D6, and a capacitor C. in ,in, The first terminal of the input power supply is connected to the bipolar neutral point, the second terminal of the input power supply is connected to one end of the inductor L0, the other end of the inductor L0 is connected to the anode of diode D5 and the anode of diode D6, and the cathode of diode D6 is connected to the non-same-name terminal of the primary winding. The cathode of diode D5 is connected to the corresponding terminal of the primary winding, and the corresponding terminal of the primary winding is also connected to capacitor C. in One end is connected to capacitor C in The other end is connected to the bipolar neutral point and the source terminal of the main switch S1.

4. The low-current ripple bipolar converter based on a three-winding coupled inductor according to claim 3, characterized in that: After entering the steady-state operating phase, in each switching cycle, the main switch S1 and the auxiliary switch S2 are turned on sequentially once, and the main switch S1 and the auxiliary switch S2 are not in the on state at the same time, so as to configure the main switch S1 and the auxiliary switch S2 to be in the corresponding switching operating state respectively. After the previous switching cycle ends, the auxiliary switch S2 switches from the on state to the off state while the main switch S1 remains in the off state. Then the three-winding coupled inductor, the low current ripple unit, and the bipolar output capacitor unit enter the first mode. After entering the current switching cycle, the main switch S1 switches from the off state to the on state. During the period when the main switch S1 is in the on state, the three-winding coupled inductor, the low current ripple unit and the bipolar output capacitor unit enter the second mode, the third mode and the fourth mode in sequence. During the current switching cycle, when the main switch S1 switches from the on state to the off state again and the auxiliary switch S2 also remains off, the three-winding coupled inductor, the low current ripple unit, and the bipolar output capacitor unit enter the fifth mode. During the current switching cycle, when the auxiliary switch S2 switches from the off state to the on state, the three-winding coupled inductor, the low-current ripple unit, and the bipolar output capacitor unit sequentially enter the sixth mode, the seventh mode, the eighth mode, the ninth mode, and the tenth mode.

5. The low-current ripple bipolar converter based on a three-winding coupled inductor according to claim 4, characterized in that, Upon entering the first mode, we have: Diodes D1, D3, and D5 are turned off, while diodes D2, D4, and D6 are forward biased. The primary winding, secondary winding L2, and tertiary winding L3 are all in the freewheeling phase. The parasitic capacitance of the auxiliary switch S2 is charged, while the parasitic capacitance of the main switch S1 is discharged. When the voltage at the source and drain terminals of the main switch S1 drops rapidly to zero, the parasitic body diode ZCS of the main switch S1 is turned on. When the main drive switch S1 is turned on, the first mode ends.

6. The low-current ripple bipolar converter based on a three-winding coupled inductor according to claim 4, characterized in that: When the main switch S1 is driven from the off state to the on state, it enters the second mode, wherein... When entering the second mode, the main switch S1 achieves ZVS turn-on, the auxiliary switch S2 is turned off, and the primary winding, secondary winding L2, and tertiary winding L3 are all in the freewheeling stage; at the same time, the input power supply and inductor L0 and secondary winding L2 are connected in series to the output capacitor C. o1 During charging, the second mode ends when the current of the main switch S1 increases to zero. After the second mode ends, the third mode immediately begins, in which... When entering the third mode, the primary winding, secondary winding L2, and tertiary winding L3 are all in the freewheeling stage; the current direction of the main switch S1 is reversed, and the capacitor C... in When the current in the primary winding continues to rise to a value greater than zero, then changes direction and continues to increase, and the currents in the secondary winding L2 and the tertiary winding L3 reverse, the third mode ends, and at the same time, diodes D2 and D4 turn off naturally. After the third mode ends, the fourth mode immediately begins, in which... Upon entering the fourth mode, the current flowing through the secondary winding L2 and the tertiary winding L3 continuously increases, and diodes D1 and D3 achieve ZCS turn-on; the tertiary winding L3 and capacitor C2 are connected in series to the load capacitor C. o2 Power is supplied, and at the same time, the secondary winding L2 charges the capacitor C1 through the diode D1. When the main switch S1 is turned off, the fourth mode ends.

7. The low-current ripple bipolar converter based on a three-winding coupled inductor according to claim 4, characterized in that: After the fourth mode ends, the fifth mode immediately begins, in which... After entering the fifth mode, both the main switch S1 and the auxiliary switch S2 are in the off state, diodes D1, D3, and D5 are forward biased, and diodes D2, D4, and D6 are turned off. The parasitic capacitance of the main switch S1 is charged, and the parasitic capacitance of the auxiliary switch S2 is discharged. Then, the parasitic diode ZCS of the auxiliary switch S2 is turned on. When the auxiliary switch S2 is driven to conduct, the fifth mode ends.

8. The low-current ripple bipolar converter based on a three-winding coupled inductor according to claim 4, characterized in that: When entering the sixth mode, the auxiliary switch S2 achieves ZVS turn-on, and the main switch S1 is controlled by capacitor C. b The clamping phase occurs when the secondary winding and the tertiary winding L3 are in the freewheeling phase. When the current in the tertiary winding L3 increases to zero, the sixth mode ends and the diode D3 turns off naturally. After the sixth mode ends, the seventh mode immediately begins, in which... After entering the seventh mode, the current flowing through the tertiary winding L3 remains zero, and the secondary winding L2 is still in the freewheeling stage. When the current in the secondary winding L2 increases to zero, the seventh mode ends, and the diode D1 turns off naturally. After the seventh mode ends, the eighth mode immediately begins, in which... When entering the eighth mode, the corresponding currents flowing through the secondary winding L2 and the tertiary winding L3 reverse and continue to rise, while the primary winding is still in the freewheeling stage, and diodes D2 and D4 achieve ZCS turn-on. After entering the eighth mode, the input power supply, inductor L0, primary winding, secondary winding L2, and capacitor C1 are connected in series to the output capacitor C. o1 Power supply: When the current of auxiliary switch S2 increases to zero, the eighth mode ends. After the eighth mode ends, the ninth mode begins immediately, in which... At the moment of entering the ninth mode, the current flowing through the auxiliary switch S2 reverses and continues to rise; and when the current in the primary winding L1 decreases to zero, the ninth mode ends. After the ninth mode ends, the tenth mode begins immediately, in which... At the moment of entering the tenth mode, the current in the primary winding continues to decrease after crossing zero; the secondary winding L2, capacitor C1, and capacitor C... b The output capacitor C is connected in series. o1 When the auxiliary switch S2 is turned off, the tenth mode ends and the current switching cycle ends.

9. The low-current ripple bipolar converter based on a three-winding coupled inductor according to any one of claims 1 to 8, characterized in that: The two secondary windings have the same number of turns and winding method; When the input power source is a photovoltaic panel, the ground of the photovoltaic panel is connected to the bipolar neutral point.

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