A bipolar high-gain cuk dc-dc converter for dc microgrid

Abstract

The application discloses a bipolar high-gain Cuk DC-DC converter for a direct-current microgrid, and relates to the field of voltage converters.The bipolar high-gain Cuk DC-DC converter comprises a coupled input unit, a bipolar voltage boosting unit and an output unit which are adaptively connected.The coupled input unit comprises a switching tube S and a coupled inductor.The same name end of the primary winding L1 of the coupled inductor is connected with the first electrode of the switching tube S, the third electrode of the switching tube S forms the positive input end of the coupled input unit, and the non-same name end of the primary winding L1 of the coupled inductor forms the negative input end of the coupled input unit.The first electrode of the switching tube S is connected with the neutral point of the output unit through the bipolar voltage boosting unit, the negative input end of the coupled input unit is connected with the negative output end of the output unit through the bipolar voltage boosting unit, and the output voltage amplitude of the positive output end and the negative output end of the output unit relative to the neutral point is equal.The converter has the advantages of high gain, self-voltage equalization, no need of an additional clamping circuit, high efficiency and strong reliability.

Description

Technical Field

[0001] This invention relates to the field of voltage converters, and in particular to a bipolar high-gain Cuk DC-DC converter for DC microgrids. Background Technology

[0002] A fuel cell is a power generation device that directly converts the chemical energy of fuels such as hydrogen into electrical energy through an electrochemical reaction. It boasts advantages such as high conversion efficiency, clean and pollution-free operation, low noise, high power density, and continuous power supply, making it a promising candidate for applications in fuel cell vehicles, distributed power generation, backup power, and mobile power sources. However, fuel cell output typically exhibits low-voltage, high-current characteristics, and the output voltage fluctuates significantly with load variations, making it difficult to directly meet the power supply requirements of the high-voltage DC bus or the inverter's pre-amplifier stage. Therefore, fuel cell power supply systems usually require a DC-DC converter to boost the low-voltage DC output from the fuel cell to the required bus voltage and maintain output stability over a wide input range. Related research indicates that DC-DC converters for fuel cells should possess high boost gain, low input current ripple, and fast dynamic response capabilities. Specifically, the fuel cell output current ripple typically needs to be kept low to avoid affecting the normal operation of the fuel cell.

[0003] Existing DC-DC converters for fuel cells mainly fall into two categories: isolated and non-isolated. Isolated converters achieve electrical isolation and voltage boosting through high-frequency transformers, but suffer from drawbacks such as a large number of power devices, large magnetic components, and high losses and costs. Non-isolated converters have a simple structure and high efficiency, but traditional boost converters require a large duty cycle in high boost ratio applications, which can easily lead to high device voltage stress, severe diode reverse recovery, and efficiency degradation. To improve these issues, existing technologies typically employ methods such as interleaved parallel boost converters, switched capacitors, coupled inductors, and diode-capacitor voltage multiplier units to increase voltage gain and reduce input current ripple.

[0004] Currently, high boost ratio non-isolated DC-DC converters employing an interleaved parallel structure combined with coupled inductors and voltage multiplier units are common solutions. This type of solution is based on interleaved parallel boost converters, adding a voltage multiplier unit composed of diodes and capacitors to the parallel branches, and replacing ordinary inductors with coupled inductors, so that the secondary winding of the coupled inductor, together with the diodes and capacitors, forms a secondary boost structure. The interleaved parallel structure can increase the input current ripple frequency and reduce the peak-to-peak ripple; the voltage multiplier unit and the secondary boost structure jointly enhance the DC voltage gain, enabling the converter to achieve a high boost ratio at a relatively small duty cycle, suitable for applications with low input voltage and a wide voltage variation range in fuel cells. While the above-mentioned technical solutions can achieve high gain characteristics to a certain extent, they still have the following shortcomings: 1. Existing bipolar output converters typically use multi-winding coupled inductors or high-frequency transformers to construct dual outputs. The large number of windings, complex winding, and difficulty in maintaining consistent parasitic parameters result in different effects of different windings on each output, leading to output voltage deviations. In addition, the potential relationship between the input, output, and neutral points in existing technical solutions is complex, which easily generates common-mode interference and is not conducive to reducing EMI and EMC issues.

[0005] 2. Existing bipolar output schemes typically require adjusting the duty cycle or additional control circuits to maintain stable output voltage when the two-phase power is unbalanced. This complex control strategy is detrimental to the reliable operation of dual DC bus power supply systems.

[0006] 3. Existing high-gain converters typically require coupling inductors, voltage multiplier units, or clamping capacitors to achieve voltage boost, resulting in complex circuit structures and a large number of components, which increases cost, size, and design difficulty. At the same time, some solutions require additional clamping circuits to absorb leakage inductance energy or suppress voltage spikes, but clamping capacitors introduce additional voltage balancing and energy cycling issues, affecting system efficiency and reliability.

[0007] 4. In the existing solutions, some converters still operate in hard switching mode, resulting in large switching losses and diode reverse recovery losses. Alternatively, additional circuitry may be required to achieve soft switching of the switching transistors, which can reduce converter efficiency, especially in low-voltage, high-current input scenarios for fuel cells. Summary of the Invention

[0008] To address the aforementioned problems and technical requirements, this invention proposes a bipolar high-gain CukDC-DC converter for DC microgrids. The technical solution of this invention is as follows: A bipolar high-gain Cuk DC-DC converter for DC microgrids includes a coupled input unit, a bipolar boost unit, and an output unit with adaptive connections. The coupling input unit includes a switching transistor S and a coupling inductor. The same-name terminal of the primary winding L1 of the coupling inductor is connected to the first electrode of the switching transistor S. The third electrode of the switching transistor S forms the positive input terminal of the coupling input unit. The non-same-name terminal of the primary winding L1 of the coupling inductor forms the negative input terminal of the coupling input unit. The first electrode of the switching transistor S is connected to the neutral point of the output unit through a bipolar boost unit, and the negative input terminal of the coupling input unit is connected to the negative output terminal of the output unit through a bipolar boost unit. The output voltage amplitudes of the positive and negative output terminals of the output unit relative to the neutral point are equal.

[0009] A further technical solution is that the output unit includes an output capacitor C. o1 and output capacitor Co2 Wherein, the output capacitor C o2 The first end forms the positive output terminal of the output unit, and the output capacitor C o2 The second terminal is connected to the output capacitor C o1 The first terminal is connected to form the neutral point of the output unit, and the output capacitor C o1 The second end forms the negative output terminal of the output unit.

[0010] A further technical solution is that the bipolar boost unit includes diode D1, capacitor C1, diode D2, diode D3, diode D4, diode D5, capacitor C2, and capacitor C3, wherein... One end of the capacitor C1 is connected to the first electrode of the switching transistor S and the same-name terminal of the primary winding L1 of the coupling inductor. The other end of the capacitor C1 is connected to the cathode of diode D1, the anode of diode D2 and one end of the capacitor C2. The anode of diode D1 is connected to the non-same-name terminal of the primary winding L1 of the coupling inductor and the cathode of diode D5. The other end of capacitor C2 is connected to one end of capacitor C3 and the same-name end of the secondary winding L2 of the coupling inductor. The non-same-name end of the secondary winding L2 of the coupling inductor is connected to the cathode of diode D2, the neutral point of the output unit, and the anode of diode D3. The other end of capacitor C3 is connected to the cathode of diode D3 and the anode of diode D4. The cathode of diode D4 is connected to the positive output terminal of the output unit, and the anode of diode D5 is connected to the negative output terminal of the output unit.

[0011] A further technical solution is that the positive input terminal and the negative input terminal of the coupling input unit are connected to the positive and negative terminals of the input power supply, respectively. The output unit is connected to a load, which includes resistors R1 and R2. Resistor R2 is connected to the output capacitor C. o1 The resistor R1 and the output capacitor C are connected in parallel. o2 in parallel.

[0012] A further technical solution is that, within one operating cycle of the bipolar high-gain Cuk DC-DC converter for DC microgrids, including t 0 o'clock~ t At time 4, among which, t 0 o'clock to t During the instant of 1, the switch S is in the on state; t 1 hour to t During time 4, the switch S is in the off state; tFrom time 4 until the end of the current working cycle, the switch S is in the on state.

[0013] A further technical solution is that, within one duty cycle of the bipolar high-gain Cuk DC-DC converter for DC microgrids, the operating process includes five modes performed sequentially, wherein... First mode: by t Starting at time 0, the switching transistor S is turned on, and diodes D2 and D4 are also turned on. The input power supply charges the primary winding L1 of the coupled inductor through the switching transistor S; the secondary winding L2 of the coupled inductor and capacitor C3 charge the output capacitor C through diode D4. o2 In addition, resistor R1 provides power; the secondary winding L2 of the coupled inductor also charges capacitor C2 through diode D2. t The first mode ends when the switch S is turned off at time 1. Second mode: Switch S is off, diodes D1 and D4 are on, and the primary winding L1 of the coupled inductor charges capacitor C1 through diode D1; meanwhile, the secondary winding L2 of the coupled inductor and capacitor C3 continue to charge the output capacitor C through diode D4. o2 And resistor R1 provides power, diode D4 is in t The second mode ends when zero current is turned off at time 2. Third mode: Switch S remains off, diodes D1, D3, and D5 are on, and the primary winding L1 of the coupled inductor charges capacitor C1 through diode D1; the secondary winding L2 of the coupled inductor and capacitor C2 charge the output capacitor C through diodes D5 and D1. o1 In addition, resistor R2 supplies power; the secondary winding L2 of the coupled inductor also charges capacitor C3 through diode D3. t The third mode ends when the current flowing through the primary winding L1 of the coupled inductor is zero at time 3. Fourth mode: Switch S remains off, diode D3 remains on, and the secondary winding L2 of the coupled inductor continues to charge capacitor C3 through diode D3. t When switch S is turned on at time 4, the fourth mode ends; Fifth mode: Switch S is in the on state, diode D3 remains on, and the input power supply charges the primary winding L1 of the coupled inductor through switch S; the secondary winding L2 of the coupled inductor continues to charge capacitor C3 through diode D3. t The fifth mode ends when diode D3 is turned off at time 5; where t 5. Time and the next work cycle t Corresponding to time 0.

[0014] A further technical solution is that the switching transistor S is a MOSFET or IGBT device, and a diode is connected in antiparallel between the first electrode and the third electrode of the switching transistor S.

[0015] A further technical solution is that the output capacitor C o1 and output capacitor C o2 The voltages at both ends are equal and are V Co , V Co It can be represented as: in, N This represents the turns ratio of the primary winding L1 to the secondary winding L2 of the coupled inductor. D For switching transistors S duty cycle, V in The output voltage is the input power supply.

[0016] A further technical solution is that the capacitance value of capacitor C1 is... C 1. The soft-switching condition is satisfied so that the switching transistor S can achieve soft switching. The soft-switching condition is: in, D For switching transistors S duty cycle, T s The switching cycle of the switching transistor S. L 1 represents the inductance value of the primary winding L1 of the coupled inductor.

[0017] A further technical solution is that, in the second and third modes, the voltage stress of the switching transistor S is clamped by the capacitor C1 and the diode D1.

[0018] The beneficial technical effects of this invention are: 1. Low Parasitic Parameters and High Gain: This invention achieves high gain and dual output voltage using a two-winding coupled inductor, avoiding the problems of numerous windings, complex winding, and inconsistent parasitic parameters associated with traditional multi-winding coupled inductors or high-frequency transformers. Since the two outputs share the secondary winding L2 of the coupled inductor, the parasitic parameters of L2 have a relatively consistent impact on the two outputs during energy transfer, thus offsetting the influence of L2's parasitic parameters on the two outputs. This eliminates the problem of different output capacitor voltages caused by different winding parasitic parameters, and the output voltage deviation caused by differences in parasitic parameters (different number of turns in different windings), making the design of the converter's magnetic components simpler and more reliable. Simultaneously, this invention achieves high-gain output through the combination of the coupled inductor and the diode-capacitor boost network, enabling higher output voltage with a smaller duty cycle and fewer components, making it suitable for applications such as fuel cells where low-voltage DC power supplies are connected to high-voltage DC buses.

[0019] 2. Output voltage self-equalization: The amplitude of the two-phase output voltage is equal and is only related to the input voltage, turns ratio, and duty cycle, and is independent of the load current. Even under the condition of unbalanced two-phase power, voltage stability can be achieved without the need for additional control circuits, adjustment of duty cycle or control method to achieve voltage stability under unbalanced two-phase power, which can help support the stable operation of the dual DC bus power supply system.

[0020] 3. Discontinuous Input Current and High Efficiency: In this invention, the primary winding current of the coupled inductor can operate in a discontinuous state, enabling the switching transistor S to achieve zero-current switching in the corresponding mode, reducing current surges and switching losses. Simultaneously, most diodes can also turn off after the current naturally drops to zero, thereby reducing reverse recovery losses. This characteristic is particularly suitable for low-voltage, high-current input scenarios in fuel cells, helping to reduce device heating and improve converter efficiency and power density.

[0021] 4. Input and Neutral Point Not Shared Ground: In the converter provided by this invention, the input and output terminals share a common ground, but the input-output common ground is not directly shared with the neutral point of the bipolar output. This weakens the interference path caused by neutral point potential fluctuations, parasitic capacitance, and common-mode voltage, thereby helping to reduce system EMI and EMC problems. Simultaneously, in dual DC bus power supply scenarios, this structure also helps improve system safety and engineering applicability.

[0022] 5. No additional clamping circuit required: In this invention, capacitor C1 and diode D1 perform the function of boosting energy transfer while also acting as clamping circuits. There is no need to set up an additional independent clamping circuit to limit the drain-source voltage of the switching transistor S, which reduces circuit complexity, cost and loss, and improves the efficiency and reliability of the converter. Attached Figure Description

[0023] Figure 1 This is a circuit schematic diagram of one embodiment of the bipolar high-gain Cuk DC-DC converter for DC microgrids provided by the present invention.

[0024] Figure 2 This is a schematic diagram of the current flow of the bipolar high-gain Cuk DC-DC converter for DC microgrids provided by the present invention in the first mode.

[0025] Figure 3 This is a schematic diagram of the current flow in the second mode of the bipolar high-gain Cuk DC-DC converter for DC microgrids provided by the present invention.

[0026] Figure 4 This is a schematic diagram of the current flow in the third mode of the bipolar high-gain Cuk DC-DC converter for DC microgrids provided by the present invention.

[0027] Figure 5 This is a schematic diagram of the current flow in the fourth mode of the bipolar high-gain Cuk DC-DC converter for DC microgrids provided by the present invention.

[0028] Figure 6 This is a schematic diagram of the current flow in the fifth mode of the bipolar high-gain Cuk DC-DC converter for DC microgrids provided by the present invention. Detailed Implementation

[0029] The specific embodiments of the present invention will be further described below with reference to the accompanying drawings. It should be understood that the specific embodiments described herein are for illustrative purposes only and are not intended to limit the scope of this disclosure.

[0030] To address the problems of existing solutions, such as complex multi-winding coupled inductor structures leading to output voltage deviations due to inconsistent parasitic parameters, the need for additional control strategies when two-phase power is unbalanced, the large number of circuit components requiring independent clamping circuits, and high switching losses, this invention provides a bipolar high-gain Cuk DC-DC converter for DC microgrids, comprising a coupled input unit, a bipolar boost unit, and an output unit with adaptive connections. The coupling input unit includes a switching transistor S and a coupling inductor. The same-name terminal of the primary winding L1 of the coupling inductor is connected to the first electrode of the switching transistor S. The third electrode of the switching transistor S forms the positive input terminal of the coupling input unit. The non-same-name terminal of the primary winding L1 of the coupling inductor forms the negative input terminal of the coupling input unit. The first electrode of the switching transistor S is connected to the neutral point of the output unit through a bipolar boost unit, and the negative input terminal of the coupled input unit is connected to the negative output terminal of the output unit through a bipolar boost unit; the output voltage amplitudes of the positive and negative output terminals of the output unit relative to the neutral point are equal.

[0031] Specifically, Figure 1 A circuit schematic of one embodiment of a bipolar high-gain Cuk DC-DC converter for DC microgrids is shown, as follows: Figure 1 As shown, in this embodiment, the output unit includes an output capacitor C. o1 and output capacitor C o2 Wherein, the output capacitor C o2 The first end forms the positive output terminal of the output unit, and the output capacitor C o2 The second terminal is connected to the output capacitor C o1 The first terminal is connected to form the neutral point of the output unit, and the output capacitor C o1 The second terminal forms the negative output terminal of the output unit. It should be noted that... Figure 1 The inductor L is connected in parallel with the primary winding L1 of the coupling inductor. m This is the equivalent magnetizing inductance of the coupling inductor. The positive and negative input terminals of the coupling input unit are connected to the positive and negative terminals of the input power supply, respectively; the resistor R2 and the output capacitor C... o1 The resistor R1 and the output capacitor C are connected in parallel. o2 in parallel.

[0032] In the DC-DC converter provided by this invention, the negative input terminal is connected to the negative output terminal through a bipolar boost unit, meaning the input and output terminals share a common ground. However, the common ground of the input and output is not directly shared with the neutral point of the bipolar output, thereby reducing interference caused by neutral point potential fluctuations, parasitic capacitance, and common-mode voltage. Simultaneously, the DC-DC converter provided by this invention has self-equalizing voltage capability, meaning the voltage amplitudes output from the positive and negative output terminals are the same, and the voltages output from the positive and negative output terminals are only related to the output voltage of the input power supply. V in Duty cycle of switching transistor S D and the turns ratio of the primary winding L1 to the secondary winding L2 of the coupled inductor N It is related to the load current and does not require adjusting the duty cycle or other means to achieve voltage stability when the two-phase power is unbalanced. The specific structure of the bipolar boost unit and the specific working principle of the converter can be found in the following description.

[0033] The second electrode of the switching transistor S receives the PWM drive signal, and the duty cycle DThis refers to the duty cycle of the PWM drive signal received by the switch S. The switch S is either a MOSFET or an IGBT, and a diode is connected in anti-parallel between the first and third electrodes of the switch S. Specifically, for a MOSFET, the first electrode is the source, the second electrode is the gate, and the third electrode is the drain; for an IGBT, the first electrode is the emitter, the second electrode is the base, and the third electrode is the collector. Furthermore, for a MOSFET, the diode connected in anti-parallel with the switch S is a parasitic diode of the switch S; for an IGBT, an anti-parallel diode is typically integrated or externally connected. In this embodiment, the switch S is a MOSFET. In specific implementations, the device type of the switch S can be set according to actual conditions.

[0034] Furthermore, the bipolar boost unit includes diode D1, capacitor C1, diode D2, diode D3, diode D4, diode D5, capacitor C2, and capacitor C3, wherein... One end of the capacitor C1 is connected to the first electrode of the switching transistor S and the same-name terminal of the primary winding L1 of the coupling inductor. The other end of the capacitor C1 is connected to the cathode of diode D1, the anode of diode D2 and one end of the capacitor C2. The anode of diode D1 is connected to the non-same-name terminal of the primary winding L1 of the coupling inductor and the cathode of diode D5. The other end of capacitor C2 is connected to one end of capacitor C3 and the same-name end of the secondary winding L2 of the coupling inductor. The non-same-name end of the secondary winding L2 of the coupling inductor is connected to the cathode of diode D2, the neutral point of the output unit, and the anode of diode D3. The other end of capacitor C3 is connected to the cathode of diode D3 and the anode of diode D4. The cathode of diode D4 is connected to the positive output terminal of the output unit, and the anode of diode D5 is connected to the negative output terminal of the output unit.

[0035] The coupling input unit is used to store and transfer electrical energy from the input power supply. The bipolar boost unit is used to boost the voltage using the capacitor charge pump principle, raising the output voltage of the input power supply and outputting it bipolarly through the output unit, thereby converting the low-voltage DC voltage of the input power supply into a dual-path symmetrical high-voltage DC voltage output. In this embodiment, within one operating cycle of the bipolar high-gain Cuk DC-DC converter for DC microgrids, including... t 0 o'clock~ t At time 4, among which, t 0 o'clock to t During the instant of 1, the switch S is in the on state; t 1 hour to tDuring time 4, the switch S is in the off state; t From time 4 until the end of the current working cycle, the switch S is in the on state.

[0036] It is understandable that, due to the different operating states of the switching transistor S at different times within a working cycle, the converter will exhibit different operating modes within a working cycle. In one embodiment of the present invention, the operation of the bipolar high-gain Cuk DC-DC converter includes five modes performed sequentially within one working cycle, which are described below in conjunction with... Figures 2-6 The corresponding working modes are described in detail.

[0037] First mode: Please refer to Figure 2 ,Depend on t Starting at time 0, the switch S is turned on, diodes D2 and D4 are turned on, and diodes D1, D3 and D5 are reverse biased. The input power supply and the primary winding L1 of the coupling inductor form a charging circuit to charge the primary winding L1 of the coupling inductor, and the current on the primary winding L1 gradually increases. The secondary winding L2 of the coupled inductor is connected in series with capacitor C3, and together they form the output capacitor C through diode D4. o2 The power supply is provided by resistor R1, meaning the voltages across the secondary winding L2 of the coupled inductor and capacitor C3 are connected in series and superimposed to form a boost voltage higher than the secondary winding voltage. This boost voltage is output to the output capacitor C through diode D4. o2 and the parallel load resistor R1, for the output capacitor C o2 It charges and supplies power to the load resistor R1, establishing a positive output voltage +Vo between the positive output terminal and the neutral point; simultaneously, the secondary winding L2 of the coupled inductor also charges the capacitor C2 through diode D2. t The first mode ends when the switch S is turned off at time 1.

[0038] Second mode: Please refer to Figure 3 When switch S is off, diode D4 remains on, diode D1 is on, diode D2 is off, and diodes D3 and D5 remain off. The primary winding L1 of the coupled inductor, through diode D1 and capacitor C1, forms a charging circuit to charge capacitor C1, and the primary winding L1 of the coupled inductor resonates with capacitor C1. Based on the continuity of inductor current, the secondary winding L2 of the coupled inductor and capacitor C3 continue to charge the output capacitor C through diode D4. o2 And power supply via resistor R1, in t The second mode ends when diode D4 turns off with zero current at time 2.

[0039] Third mode: Please refer to Figure 4With switch S remaining off, diodes D1, D3, and D5 are conducting, while diodes D2 and D4 are off. The primary winding L1 of the coupled inductor continues to charge capacitor C1 through diode D1, creating resonance between the primary winding L1 and capacitor C1. The secondary winding L2 of the coupled inductor is connected in series with capacitor C2, and together they charge the output capacitor C through diodes D5 and D1. o1 The power supply is provided by resistor R2, meaning the voltages across the secondary winding L2 of the coupled inductor and capacitor C2 are connected in series and superimposed to form a boost voltage higher than the voltage across the secondary winding. This boost voltage is output to the output capacitor C through diodes D1 and D5. o1 and the parallel load resistor R2, for the output capacitor C o1 Charging is performed and power is supplied to the load resistor R2, establishing a negative output voltage -Vo between the negative output terminal and the neutral point; simultaneously, the secondary winding L2 of the coupled inductor also charges the capacitor C3 through diode D3, and the current flowing through the primary winding L1 of the coupled inductor continuously decreases. t The third mode ends when the current flowing through the primary winding L1 of the coupled inductor decays to zero at time 3. In the second and third modes, diode D1 and capacitor C1 clamp the voltage between the first and third electrodes of the switching transistor S through the input power supply to prevent voltage spikes from damaging the device.

[0040] Fourth mode: Please refer to Figure 5 With switch S remaining off, diode D3 remaining on, and diodes D1, D2, D4, and D5 reverse-biased, the secondary winding L2 of the coupled inductor continues to charge capacitor C3 through diode D3. t When switch S is turned on at time 4, the fourth mode ends; Fifth mode: Please refer to Figure 6 With switch S turned on, diode D3 remains on, and diodes D1, D2, D4, and D5 remain reverse biased. The current flowing through the primary winding L1 of the coupled inductor decays to zero in the third mode and remains on in the fourth mode. Switch S achieves zero-current conduction. The input power supply forms a charging circuit with the primary winding L1 of the coupled inductor through switch S, recharging the primary winding L1. The current in the primary winding L1 increases linearly from zero. The secondary winding L2 of the coupled inductor continues to charge capacitor C3 through diode D3. Once capacitor C3 is fully charged, t The fifth mode ends when diode D3 turns off with zero current at time 5; where t 5. Time and the next work cycle t At time 0, the converter enters the next working cycle.

[0041] Regarding the above Figures 2-6The diagram shows a bipolar high-gain Cuk DC-DC converter. Arrows indicate current flow. Switches, diodes, inductors, and capacitors in non-operating states are represented by gray lines, while those in operating states are represented by black lines. It should be noted that during converter operation, the output capacitor C... o1 Output capacitor C o2 Always supply power to load resistor R2 and resistor R1 to maintain the output voltage.

[0042] As can be seen from the above description, in this invention, the primary winding current can operate in an intermittent state, and the switching transistor S can achieve zero-current conduction in the fifth mode, thereby realizing soft switching of the switching transistor S to effectively reduce switching losses. However, the following conditions must be met to achieve soft switching: in, The resonant period of the primary winding L1 of the coupled inductor and the capacitor C1. C 1 represents the capacitance value of capacitor C1. L 1 represents the inductance value of the primary winding L1 of the coupled inductor. T s Given the switching cycle of the switching transistor S, the capacitance value of capacitor C1 can be further obtained. C 1. Soft-switching conditions must be met for the switching transistor S to achieve soft switching. The soft-switching conditions are: The voltage gain of the above converter can be obtained by applying the inductor volt-second balance principle. Specifically, the output capacitor C o2 The voltage across the two ends is V Co2 The voltage across capacitor C3 is V C3 Let the voltage across the primary winding L1 of the coupling inductor be when the switching transistor S is turned on. The on-time of switch S within one working cycle is When the switching transistor S is turned off, the voltage on the primary winding L1 of the coupling inductor is The turn-off time of switch S within one working cycle is Then we have: The voltage across capacitor C3 can be obtained from the above formula. V C3 It can be represented as: The voltage across capacitor C2 can be obtained based on the first mode. V C2 = NV in ; Furthermore, the output capacitance C can be obtained based on the first and third modes. o1 Output capacitor C o2 voltage at both ends V Co1 , V Co2 It can be represented as: From the above formula, it can be seen that the output capacitor C o1 With output capacitor C o2 The voltages at both ends are equal, that is V Co1 = V Co2 = V Co This DC-DC converter has a self-equalizing voltage function, independent of load conditions. The gain of the DC-DC converter can be calculated by solving the above equations. M The expression is: As can be seen from the above formula, this DC-DC converter can be adjusted by changing the duty cycle of the switching transistor S and the primary winding of the coupling inductor. L 1 and secondary winding L A turns ratio of 2 is used to obtain a larger gain.

[0043] The DC-DC converter provided by this invention employs a two-winding coupled inductor structure controlled by a single switch, combined with a diode-capacitor boost network, to achieve high-gain bipolar output. Its output voltage is only related to the input voltage, turns ratio, and duty cycle, and is independent of the load current. This allows for self-stabilization of the output voltage under two-phase power imbalance without additional control circuitry, and also provides self-voltage equalization. The primary winding current operates in a discontinuous state, enabling zero-current switching of the switch. Furthermore, the capacitor and diode in the bipolar boost unit naturally clamp the voltage stress of the switch, eliminating the need for additional clamping circuitry and reducing switching losses and electromagnetic interference. In addition, the structural design where the input / output common ground and the bipolar output neutral point are not directly shared effectively weakens the common-mode interference path, improving the system's EMI and EMC characteristics. In summary, this converter boasts advantages such as high gain, fewer components, simple circuit structure, simplified magnetic component design, high efficiency, and high reliability. It is particularly suitable for DC microgrid applications where low-voltage, high-current DC power supplies, such as fuel cells, are connected to a high-voltage DC bus.

[0044] In the description of this specification, the terms "first," "second," "third," "fourth," etc., are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of technical features indicated. Therefore, a feature defined as "first" or "second" may explicitly or implicitly include at least one of that feature. In the description of this application, "multiple" means at least two, such as two, three, etc., unless otherwise explicitly specified.

[0045] The use of terms such as "one embodiment / mode," "some embodiments / modes," "example," "specific example," or "some examples," etc., refers to a specific feature, structure, material, or characteristic described in connection with that embodiment / mode or example, which is included in at least one embodiment / mode or example of this application. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment / mode or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments / modes or examples. Moreover, without contradiction, those skilled in the art can combine and integrate the different embodiments / modes or examples described in this specification, as well as the features of different embodiments / modes or examples.

[0046] Those skilled in the art should understand that the above embodiments are merely for illustrating the present disclosure and are not intended to limit the scope of the disclosure. Those skilled in the art can make other changes or modifications based on the above disclosure, and these changes or modifications still fall within the scope of the present disclosure.

[0047] The above descriptions are merely preferred embodiments of the present invention, and the present invention is not limited to the above embodiments. It is understood that other improvements and variations that can be directly derived or conceived by those skilled in the art without departing from the spirit and concept of the present invention should be considered to be included within the protection scope of the present invention.

Claims

1. A bipolar high-gain Cuk DC-DC converter for DC microgrids, characterized in that, It includes a coupled input unit with adapter connections, a bipolar boost unit, and an output unit, wherein, The coupling input unit includes a switching transistor S and a coupling inductor. The same-name terminal of the primary winding L1 of the coupling inductor is connected to the first electrode of the switching transistor S. The third electrode of the switching transistor S forms the positive input terminal of the coupling input unit. The non-same-name terminal of the primary winding L1 of the coupling inductor forms the negative input terminal of the coupling input unit. The first electrode of the switching transistor S is connected to the neutral point of the output unit through a bipolar boost unit, and the negative input terminal of the coupling input unit is connected to the negative output terminal of the output unit through a bipolar boost unit. The output voltage amplitudes of the positive and negative output terminals of the output unit relative to the neutral point are equal.

2. The bipolar high-gain Cuk DC-DC converter for DC microgrids according to claim 1, characterized in that, The output unit includes an output capacitor C. o1 and output capacitor C o2 Wherein, the output capacitor C o2 The first end forms the positive output terminal of the output unit, and the output capacitor C o2 The second terminal is connected to the output capacitor C o1 The first terminal is connected to form the neutral point of the output unit, and the output capacitor C o1 The second end forms the negative output terminal of the output unit.

3. The bipolar high-gain Cuk DC-DC converter for DC microgrids according to claim 2, characterized in that, The bipolar boost unit includes diode D1, capacitor C1, diode D2, diode D3, diode D4, diode D5, capacitor C2, and capacitor C3, wherein... One end of the capacitor C1 is connected to the first electrode of the switching transistor S and the same-name terminal of the primary winding L1 of the coupling inductor. The other end of the capacitor C1 is connected to the cathode of diode D1, the anode of diode D2 and one end of the capacitor C2. The anode of diode D1 is connected to the non-same-name terminal of the primary winding L1 of the coupling inductor and the cathode of diode D5. The other end of capacitor C2 is connected to one end of capacitor C3 and the same-name end of the secondary winding L2 of the coupling inductor. The non-same-name end of the secondary winding L2 of the coupling inductor is connected to the cathode of diode D2, the neutral point of the output unit, and the anode of diode D3. The other end of capacitor C3 is connected to the cathode of diode D3 and the anode of diode D4. The cathode of diode D4 is connected to the positive output terminal of the output unit, and the anode of diode D5 is connected to the negative output terminal of the output unit.

4. The bipolar high-gain Cuk DC-DC converter for DC microgrids according to claim 3, characterized in that, The positive and negative input terminals of the coupling input unit are connected to the positive and negative terminals of the input power supply, respectively. The output unit is connected to a load, which includes resistors R1 and R2. Resistor R2 is connected to the output capacitor C. o1 The resistor R1 and the output capacitor C are connected in parallel. o2 in parallel.

5. The bipolar high-gain Cuk DC-DC converter for DC microgrids according to claim 4, characterized in that, During one duty cycle of the bipolar high-gain Cuk DC-DC converter for DC microgrids, including t 0 o'clock~ t At time 4, among which, t 0 o'clock to t During the instant of 1, the switch S is in the on state; t 1 hour to t During time 4, the switch S is in the off state; t From time 4 until the end of the current working cycle, the switch S is in the on state.

6. The bipolar high-gain Cuk DC-DC converter for DC microgrids according to claim 5, characterized in that, During one duty cycle of the bipolar high-gain Cuk DC-DC converter for DC microgrids, the operation process includes five modes performed sequentially, wherein... First mode: by t Starting at time 0, the switching transistor S is turned on, and diodes D2 and D4 are also turned on. The input power supply charges the primary winding L1 of the coupled inductor through the switching transistor S; the secondary winding L2 of the coupled inductor and capacitor C3 charge the output capacitor C through diode D4. o2 In addition, resistor R1 provides power; the secondary winding L2 of the coupled inductor also charges capacitor C2 through diode D2. t The first mode ends when the switch S is turned off at time 1. Second mode: Switch S is off, diodes D1 and D4 are on, and the primary winding L1 of the coupled inductor charges capacitor C1 through diode D1; meanwhile, the secondary winding L2 of the coupled inductor and capacitor C3 continue to charge the output capacitor C through diode D4. o2 And resistor R1 provides power, diode D4 is in t The second mode ends when zero current is turned off at time 2. Third mode: Switch S remains off, diodes D1, D3, and D5 are on, and the primary winding L1 of the coupled inductor charges capacitor C1 through diode D1; the secondary winding L2 of the coupled inductor and capacitor C2 charge the output capacitor C through diodes D5 and D1. o1 In addition, resistor R2 supplies power; the secondary winding L2 of the coupled inductor also charges capacitor C3 through diode D3. t The third mode ends when the current flowing through the primary winding L1 of the coupled inductor is zero at time 3. Fourth mode: Switch S remains off, diode D3 remains on, and the secondary winding L2 of the coupled inductor continues to charge capacitor C3 through diode D3. t When switch S is turned on at time 4, the fourth mode ends; Fifth mode: Switch S is in the on state, diode D3 remains on, and the input power supply charges the primary winding L1 of the coupled inductor through switch S; the secondary winding L2 of the coupled inductor continues to charge capacitor C3 through diode D3. t The fifth mode ends when diode D3 is turned off at time 5; where t 5. Time and the next work cycle t Corresponding to time 0.

7. The bipolar high-gain Cuk DC-DC converter for DC microgrids according to claim 1, characterized in that, The switching transistor S is a MOSFET or IGBT device, and a diode is connected in anti-parallel between the first and third electrodes of the switching transistor S.

8. The bipolar high-gain Cuk DC-DC converter for DC microgrids according to claim 2, characterized in that, The output capacitor C o1 and output capacitor C o2 The voltages at both ends are equal and are V Co , V Co It can be represented as: in, N This represents the turns ratio of the primary winding L1 to the secondary winding L2 of the coupled inductor. D For switching transistors S duty cycle, V in The output voltage is the input power supply.

9. The bipolar high-gain Cuk DC-DC converter for DC microgrids according to claim 3, characterized in that, The capacitance value of capacitor C1 C 1. The soft-switching condition is satisfied so that the switching transistor S can achieve soft switching. The soft-switching condition is: in, D For switching transistors S duty cycle, T s The switching cycle of the switching transistor S. L 1 represents the inductance value of the primary winding L1 of the coupled inductor.

10. The bipolar high-gain Cuk DC-DC converter for DC microgrids according to claim 6, characterized in that, In the second and third modes, the voltage stress of the switching transistor S is clamped by the capacitor C1 and the diode D1.

Images