A dc-dc converter for a dc microgrid

Abstract

The application relates to the technical field of voltage conversion, and discloses a DC converter for a DC microgrid, which comprises a coupling inductor, a switch tube S1, a capacitor C1, a capacitor C2, a capacitor C3, a first unidirectional conductive unit, a second unidirectional conductive unit, an output capacitor branch and a diode branch; the coupling inductor comprises a primary winding L1 and a secondary winding L2; in actual use, the coupling inductor, the capacitor C1 to the capacitor C3, the output capacitor branch, the diode branch, the first and second unidirectional conductive units of the application realize high voltage gain, the capacitor C3 further forms a passive clamping circuit together with an output capacitor in the output capacitor branch and a diode in the diode branch, on the one hand, an additional active clamping circuit is not needed, on the other hand, device reuse is realized, and the circuit structure is simplified; the circuit of the application eliminates the influence of all parasitic parameters of components and elements except diode internal resistance and diode voltage drop on voltage balance.

Description

Technical Field

[0001] This invention relates to the field of voltage conversion technology, and more specifically to a DC converter for DC microgrids. Background Technology

[0002] In recent years, with the surge in global energy demand and the increasing depletion of traditional fossil fuels, energy supply security has faced severe challenges. At the same time, environmental problems such as the greenhouse effect and air pollution caused by the use of traditional energy sources have become increasingly prominent. Against this backdrop, clean and renewable energy sources such as hydrogen energy and biomass energy have become the focus of research in the energy field due to their sustainability and environmental friendliness. Among them, hydrogen energy has attracted much attention due to its advantages such as high energy density and zero emissions.

[0003] Because fuel cell output voltages are generally low, they cannot directly meet the needs of DC microgrid systems and long-distance transmission. Therefore, DC-DC converters are necessary for voltage boosting and energy adaptation. Existing DC-DC converters often employ external clamping circuits to clamp the voltage and avoid high-voltage loss components. This leads to complex circuit structures and high costs. Furthermore, since DC-DC converters rely on the charging and discharging of energy storage components such as capacitors during operation, the parasitic parameters of the capacitors and coil windings in the circuit can affect the balance of the output voltage. Summary of the Invention

[0004] In view of the shortcomings of the prior art, the present invention provides a DC converter for DC microgrids. The technical problem to be solved is that existing DC converters require an external clamping circuit when working, which is complex in structure, and the parasitic parameters of the capacitors and windings in the circuit will affect the balance of the output voltage.

[0005] To solve the above technical problems, the present invention provides the following technical solution: a DC-DC converter for DC microgrids, comprising a coupling inductor, a switching transistor S1, capacitors C1, C2, and C3, a first unidirectional conductive unit, a second conductive unit, an output capacitor branch, and a diode branch; the coupling inductor comprises a primary winding L1 and a secondary winding L2; One end of the primary winding L1 is electrically connected to one end of capacitor C3, the output end of switch S1, and one end of secondary winding L2. The input end of switch S1 and the other end of primary winding L1 are used to connect to external power supply Vin. The other end of secondary winding L2 is electrically connected to one end of capacitor C1 and one end of capacitor C2. The other end of the capacitor C1 is sequentially connected to the first unidirectional conductive unit, the output capacitor branch, the diode branch, and the other end of the primary winding L1. The conductive direction of the first unidirectional conductive unit is from the capacitor C1 to the output capacitor branch. The middle node of the output capacitor branch is electrically connected to the other end of the primary winding L1. The other end of capacitor C2 is electrically connected to the first intermediate terminal of the diode branch, and the other end of capacitor C3 is electrically connected to the second intermediate terminal of the diode branch. The voltage at the first intermediate terminal is higher than the voltage at the second intermediate terminal. The other end of the primary winding L1 is electrically connected to the other end of the capacitor C1 through the second unidirectional conductive unit, and the conductive direction of the second unidirectional conductive unit is from the other end of the primary winding L1 to the other end of the capacitor C1.

[0006] In one embodiment, the first unidirectional conductive unit includes a diode D1, the anode of which is electrically connected to a capacitor C1, and the cathode of which is electrically connected to the output capacitor branch.

[0007] In one embodiment, the second unidirectional conductive unit includes a diode D2, the anode of which is electrically connected to the other end of the primary winding L1, and the cathode of which is electrically connected to the capacitor C1.

[0008] In one embodiment, the switching transistor S1 further includes a control terminal, which turns on when a high-level control signal is input to the control terminal and turns off when a low-level control signal is input to the switching transistor S1.

[0009] In one embodiment, the switching transistor S1 is an NMOS transistor.

[0010] In one embodiment, the output capacitor branch includes an output capacitor CO1 and an output capacitor CO2. One end of the output capacitor CO1 is electrically connected to the first unidirectional conductive unit, and the other end of the output capacitor CO1 is electrically connected to one end of the output capacitor CO2 and the other end of the primary winding L1, respectively. The other end of the output capacitor CO2 is electrically connected to the diode branch.

[0011] In one embodiment, the diode branch includes diodes D5, D3, and D4 connected in series. The anode of diode D5 is electrically connected to the output capacitor branch, the cathode of diode D5 is electrically connected to the other end of capacitor C3, the cathode of diode D3 is electrically connected to the other end of capacitor C2, and the cathode of diode D4 is electrically connected to the other end of the primary winding L1.

[0012] In one implementation, within one operating cycle T of the DC-DC converter, the switching transistor S1 is first turned on for a first time t1, and then turned off for a second time t2, and t1+t2=T.

[0013] In one implementation, the DC-DC converter has five modes sequentially within one duty cycle T, as follows: Mode 1: Switch S1 is turned on, diodes D1, D2, D4, and D5 are reverse biased and cut off, diode D3 is forward biased and turned on, secondary winding L2 is in freewheeling state and is connected in series with capacitor C2 to charge capacitor C3, output capacitors CO1 and CO2 supply power to the load, when the freewheeling of secondary winding L2 is completed, mode 1 ends and mode 2 begins; Mode 2: Switch S1 is continuously on, the current in the secondary winding L2 increases, diodes D2, D3 and D5 are reverse biased and cut off, diode D1 is forward biased and conducts, external power supply Vin charges the leakage inductance and magnetizing inductance of the primary winding L1, capacitor C1 charges the output capacitor CO1 through switch S1 and diode D1, and output capacitor CO2 discharges at this time. When switch S1 changes from on to off, mode 2 ends and mode 3 begins. Mode 3: Switch S1 is off, diodes D2 and D3 are reverse biased and cut off, diodes D1, D4 and D5 are positive biased and conduct, secondary winding L2 is in the freewheeling decreasing stage, primary winding L1 freewheels through the passive clamping circuit composed of output capacitor CO2, diode D5 and capacitor C3, secondary winding L2 and capacitor C1 are connected in series to charge output capacitors CO1 and CO2, when the current of secondary winding L2 drops to zero, mode 3 ends and mode 4 begins; Mode 4: Switch S1 is turned off, diodes D1, D3, and D4 are reverse biased and cut off, diodes D2 and D5 are forward biased and conduct, capacitor C1 is charged through the series primary winding L1, secondary winding L2, and diode D2, primary winding L1 continues to freewheel through the passive clamping circuit composed of output capacitor CO2, diode D5, and capacitor C3, output capacitor CO1 and output capacitor are charged and discharged alternately, when diode D5 changes from forward biased conduction to reverse bias cut off, mode 4 ends and mode 5 begins; Mode 5: Switch S1 remains off, diodes D1, D5, and D4 are reverse biased and cut off, diodes D2 and D5 are forward biased and conduct, capacitor C2 and the series-connected secondary winding L2 charge capacitor C3. When switch S1 changes from off to on, mode 5 ends and mode 1 begins.

[0014] In one embodiment, both the output capacitor CO1 and the output capacitor CO2 are CBB capacitors.

[0015] The beneficial effects of this invention compared with the prior art are as follows: the coupling inductor, capacitors C1-C3, output capacitor branch, diode branch, and first and second unidirectional conductive units of this invention achieve high voltage gain, while capacitor C3, together with the output capacitor in the output capacitor branch and the diode in the diode branch, form a passive clamping circuit. On the one hand, there is no need to set up an additional active clamping circuit, and on the other hand, device reuse is realized, simplifying the circuit structure. In addition, the circuit of this invention eliminates the influence of all parasitic parameters of components other than diode internal resistance and diode voltage drop on voltage balance, as detailed in the specific embodiments. Attached Figure Description

[0016] Figure 1 This is a circuit diagram of the present invention in an embodiment; Figure 2 for Figure 1 A schematic diagram of the current flow when the circuit is operating in mode one; Figure 3 for Figure 1 A schematic diagram of the current flow direction when the circuit is operating in mode two; Figure 4 for Figure 1 A schematic diagram of the current flow direction when the circuit is operating in mode three; Figure 5 for Figure 1 A schematic diagram of the current flow when the circuit is operating in mode four; Figure 6 for Figure 1 A schematic diagram of the current flow when the circuit is operating in mode five; Figure 7 for Figure 1 The diagram shows the voltage across output capacitors CO1 and CO2 during circuit simulation. Figure 8 for Figure 1 The diagram shows the output voltage during circuit simulation. Detailed Implementation

[0017] The present invention will now be described in further detail with reference to the accompanying drawings. These drawings are simplified schematic diagrams, illustrating only the basic structure of the invention, and therefore only show the components relevant to the invention.

[0018] To eliminate the need for additional active clamping circuitry in the DC-DC converter and to eliminate the influence of parasitic parameters of components other than diodes on the output voltage balance, such as... Figure 1As shown, this embodiment provides a DC-DC converter for a DC microgrid, including a coupling inductor, a switching transistor S1, capacitors C1, C2, and C3, a first unidirectional conductive unit 3, a second conductive unit 4, an output capacitor branch 1, and a diode branch 2; the coupling inductor includes a primary winding L1 and a secondary winding L2.

[0019] In this embodiment, the connection relationships of the DC-DC converter devices are as follows: One end of the primary winding L1 is electrically connected to one end of capacitor C3, the output end of switch S1, and one end of secondary winding L2. The input end of switch S1 and the other end of primary winding L1 are used to connect to external power supply Vin. The other end of secondary winding L2 is electrically connected to one end of capacitor C1 and one end of capacitor C2. The other end of capacitor C1 is connected in sequence to the first unidirectional conductive unit 3, the output capacitor branch 1, the diode branch 2 and the other end of the primary winding L1. The conductive direction of the first unidirectional conductive unit 3 is from capacitor C1 to the output capacitor branch 1. The middle node of the output capacitor branch 1 is connected to the other end of the primary winding L1. The other end of capacitor C2 is electrically connected to the first intermediate terminal of diode branch 2, and the other end of capacitor C3 is electrically connected to the second intermediate terminal of diode branch 2. The voltage at the first intermediate terminal is higher than the voltage at the second intermediate terminal. The other end of the primary winding L1 is electrically connected to the other end of the capacitor C1 through the second unidirectional conductive unit 4. The conductive direction of the second unidirectional conductive unit 4 is from the other end of the primary winding L1 to the other end of the capacitor C1.

[0020] In practical use, the coupling inductor, capacitors C1-C3, output capacitor branch 1, diode branch 2, first unidirectional conductive unit 3 and second unidirectional conductive unit 4 of the present invention achieve high voltage gain. At the same time, capacitor C3, together with the output capacitor in output capacitor branch 1 and the diode in diode branch 2, forms a passive clamping circuit. On the one hand, there is no need to set up an additional active clamping circuit, and on the other hand, device reuse is realized, simplifying the circuit structure.

[0021] Specifically, in this embodiment, in Figure 1, the first unidirectional conductive unit 3 includes a diode D1, the anode of the diode D1 is electrically connected to the capacitor C1, and the cathode of the diode D1 is electrically connected to the output capacitor branch 1.

[0022] Specifically, in this embodiment, in Figure 1, the second unidirectional conductive unit 4 includes a diode D2, the anode of the diode D2 is electrically connected to the other end of the primary winding L1, and the cathode of the diode D2 is electrically connected to the capacitor C1.

[0023] Specifically, in this embodiment, as shown in Figure 1, the switch S1 also includes a control terminal. When a high-level control signal is input to the control terminal, the switch S1 is turned on, and when a low-level control signal is input to the switch S1, it is turned off. In this circuit, the switch S1 can be an NMOS transistor, with the drain of the NMOS transistor being the input terminal of the switch S1, the source of the NMOS transistor being the output terminal of the switch S1, and the gate of the NMOS transistor being the control terminal of the switch S1.

[0024] In this embodiment, the on / off control process of the switching transistor S1 is as follows: Within one operating cycle T of the DC-DC converter, the switching transistor S1 is first turned on for a first time t1, and then turned off for a second time t2, and t1+t2=T.

[0025] Specifically, in this embodiment, in Figure 1, the output capacitor branch 1 includes an output capacitor CO1 and an output capacitor CO2. One end of the output capacitor CO1 is electrically connected to the first unidirectional conductive unit 3, and the other end of the output capacitor CO1 is electrically connected to one end of the output capacitor CO2 and the other end of the primary winding L1, respectively. The other end of the output capacitor CO2 is electrically connected to the diode branch 2.

[0026] For output capacitor branch 1, output capacitors CO1 and CO2 are used to output DC voltage, which can power two loads; in addition, output capacitors CO1 and CO2 can be CBB capacitors.

[0027] Specifically, in this embodiment, in Figure 1, diode branch 2 includes diodes D5, D3 and D4 connected in series. The anode of diode D5 is electrically connected to the output capacitor branch 1, the cathode of diode D5 is electrically connected to the other end of capacitor C3, the cathode of diode D3 is electrically connected to the other end of capacitor C2, and the cathode of diode D4 is electrically connected to the other end of primary winding L1.

[0028] for Figure 1 The circuit shown has five modes sequentially within one operating cycle T, as detailed below: Mode 1: Switch S1 is turned on, diodes D1, D2, D4, and D5 are reverse biased and cut off, diode D3 is forward biased and turned on, the secondary winding L2 is in freewheeling mode, and it is connected in series with capacitor C2 to charge capacitor C3. Output capacitors CO1 and CO2 supply power to the load. When the freewheeling of the secondary winding L2 is complete, Mode 1 ends and Mode 2 begins; at this time, the process of Mode 1... Figure 1 The direction of current flow in the circuit is as follows Figure 2 As shown; Mode 2: Switch S1 remains on, increasing the current in the secondary winding L2. Diodes D2, D3, and D5 are reverse-biased and cut off, while diode D1 is forward-biased and conducts. External power supply Vin charges the leakage inductance and magnetizing inductance of the primary winding L1. Capacitor C1 charges the output capacitor CO1 through switch S1 and diode D1. At this time, output capacitor CO2 discharges. When switch S1 changes from on to off, Mode 2 ends, and Mode 3 begins. The process in Mode 1 continues... Figure 1 The direction of current flow in the circuit is as follows Figure 3 As shown; Mode 3: Switch S1 is off, diodes D2 and D3 are reverse biased and cut off, diodes D1, D4, and D5 are positive biased and conduct, and the secondary winding L2 is in the freewheeling decreasing phase. The primary winding L1 freewheels through the passive clamping circuit composed of output capacitor CO2, diode D5, and capacitor C3. The secondary winding L2 and capacitor C1 are connected in series to charge output capacitors CO1 and CO2. When the current in the secondary winding L2 drops to zero, Mode 3 ends, and Mode 4 begins; at this time, the process of Mode 1... Figure 1 The direction of current flow in the circuit is as follows Figure 4 As shown; Mode 4: Switch S1 is off, diodes D1, D3, and D4 are reverse biased and cut off, while diodes D2 and D5 are forward biased and conduct. Capacitor C1 is charged through the series connection of the primary winding L1, secondary winding L2, and diode D2. The primary winding L1 continues to freewheel through the passive clamping circuit composed of output capacitor CO2, diode D5, and capacitor C3. Output capacitor CO1 and the output capacitor alternately charge and discharge. When diode D5 changes from forward biased conduction to reverse bias cutoff, Mode 4 ends, and Mode 5 begins; at this time, the process of Mode 1... Figure 1 The direction of current flow in the circuit is as follows Figure 5 As shown; Mode 5: Switch S1 remains off, diodes D1, D5, and D4 are reverse-biased and off, while diodes D2 and D5 are forward-biased and on. Capacitor C2 and the series-connected secondary winding L2 charge capacitor C3. When switch S1 changes from off to on, Mode 5 ends, and Mode 1 begins. At this point, the process in Mode 1... Figure 1 The direction of current flow in the circuit is as follows Figure 6 As shown.

[0029] for Figure 1 The circuit shown has five operating states, for Figure 1 The voltage in the circuit is calculated using the following formulas: VC1=(D+N*D*K)*Vin / (1-D); VC2 = Vin + N * K * Vin; VCO1=(1+N*K)*Vin / (1-D); VCO2=(1+N*K)*Vin / (1-D); MCCM=2*(1+N*K) / (1-D); ; For the above six formulas, VC1, VC2, VCO1 and VCO2 are the terminal voltages of capacitors C1, C2, output capacitor CO1 and output capacitor CO2, respectively. MCCM is the voltage gain, D is the duty cycle of switch S1 in period T, i.e., the ratio of t1 to T, N is the turns ratio of primary winding L1 and secondary winding L2, and K is the coupling coefficient of primary winding L1 and secondary winding L2. It is the voltage difference across load resistor R1 and load resistor R2, I O1 and I O2 These are the current values ​​flowing through load resistors R1 and R2, respectively. d It is the internal resistance of the diode, V d It is the diode voltage drop. Assuming all diodes in the circuit are the same, it can be seen from the above formula that the present invention eliminates the influence of component parasitic parameters other than diode internal resistance and diode voltage drop on bipolar voltage balance.

[0030] right Figure 1 The circuit shown was simulated with the duty cycle (D) set to 0.5. The simulation results are as follows: Figure 7 and Figure 8 As shown; exist Figure 7 In the image, the upper waveform represents the voltage across output capacitor CO1, and the lower waveform represents the voltage across output capacitor CO2. Figure 7 It can be seen that the voltage fluctuation on the output capacitor CO1 is about 0.4V, and the voltage fluctuation on the output capacitor CO2 is about 0.09V. exist Figure 8 In this invention, the output voltage, which is the sum of the voltage across output capacitor CO1 and the voltage across output capacitor CO2, is stable at around 381.1V, with voltage fluctuations of around 0.3V. Combination Figure 7 and Figure 8 The simulation results show that the voltage difference between the output capacitor CO1 and the output capacitor CO2 is very small, and the connected output voltage has extremely low output voltage ripple. Based on the above description, those skilled in the art can make various changes and modifications without departing from the technical concept of this invention. The technical scope of this invention is not limited to the contents of the specification, but must be determined according to the scope of the claims.

Claims

1. A DC-DC converter for a DC microgrid, characterized in that, It includes a coupling inductor, a switching transistor S1, capacitors C1, C2, and C3, a first unidirectional conductive unit, a second unidirectional conductive unit, an output capacitor branch, and a diode branch; the coupling inductor includes a primary winding L1 and a secondary winding L2. One end of the primary winding L1 is electrically connected to one end of capacitor C3, the output end of switch S1, and one end of secondary winding L2. The input end of switch S1 and the other end of primary winding L1 are used to connect to external power supply Vin. The other end of secondary winding L2 is electrically connected to one end of capacitor C1 and one end of capacitor C2. The other end of the capacitor C1 is sequentially connected to the first unidirectional conductive unit, the output capacitor branch, the diode branch, and the other end of the primary winding L1. The conductive direction of the first unidirectional conductive unit is from the capacitor C1 to the output capacitor branch. The middle node of the output capacitor branch is electrically connected to the other end of the primary winding L1. The other end of capacitor C2 is electrically connected to the first intermediate terminal of the diode branch, and the other end of capacitor C3 is electrically connected to the second intermediate terminal of the diode branch. The voltage at the first intermediate terminal is higher than the voltage at the second intermediate terminal. The other end of the primary winding L1 is electrically connected to the other end of the capacitor C1 through the second unidirectional conductive unit, and the conductive direction of the second unidirectional conductive unit is from the other end of the primary winding L1 to the other end of the capacitor C1.

2. A DC-DC converter for a DC microgrid according to claim 1, characterized in that, The first unidirectional conductive unit includes a diode D1, the anode of which is electrically connected to a capacitor C1, and the cathode of which is electrically connected to the output capacitor branch.

3. A DC-DC converter for a DC microgrid according to claim 2, characterized in that, The second unidirectional conductive unit includes a diode D2, the anode of which is electrically connected to the other end of the primary winding L1, and the cathode of which is electrically connected to the capacitor C1.

4. A DC-DC converter for a DC microgrid according to claim 3, characterized in that, The switching transistor S1 also includes a control terminal. When a high-level control signal is input to the control terminal, the switching transistor S1 is turned on, and when a low-level control signal is input to the switching transistor S1, it is turned off.

5. A DC-DC converter for a DC microgrid according to claim 4, characterized in that, The switching transistor S1 is an NMOS transistor.

6. A DC-DC converter for a DC microgrid according to any one of claims 3-5, characterized in that, The output capacitor branch includes an output capacitor CO1 and an output capacitor CO2. One end of the output capacitor CO1 is electrically connected to the first unidirectional conductive unit, and the other end of the output capacitor CO1 is electrically connected to one end of the output capacitor CO2 and the other end of the primary winding L1, respectively. The other end of the output capacitor CO2 is electrically connected to the diode branch.

7. A DC-DC converter for a DC microgrid according to claim 6, characterized in that, The diode branch includes diodes D5, D3, and D4 connected in series. The anode of diode D5 is electrically connected to the output capacitor branch, the cathode of diode D5 is electrically connected to the other end of capacitor C3, the cathode of diode D3 is electrically connected to the other end of capacitor C2, and the cathode of diode D4 is electrically connected to the other end of the primary winding L1.

8. A DC-DC converter for a DC microgrid according to claim 7, characterized in that, Within one operating cycle T of the DC-DC converter, the switching transistor S1 is first turned on for a first time t1, and then turned off for a second time t2, and t1+t2=T.

9. A DC-DC converter for a DC microgrid according to claim 7, characterized in that, The DC-DC converter has five modes sequentially within one duty cycle T, as follows: Mode 1: Switch S1 is turned on, diodes D1, D2, D4, and D5 are reverse biased and cut off, diode D3 is forward biased and turned on, secondary winding L2 is in freewheeling state and is connected in series with capacitor C2 to charge capacitor C3, output capacitors CO1 and CO2 supply power to the load, when the freewheeling of secondary winding L2 is completed, mode 1 ends and mode 2 begins; Mode 2: Switch S1 is continuously on, the current in the secondary winding L2 increases, diodes D2, D3 and D5 are reverse biased and cut off, diode D1 is forward biased and conducts, external power supply Vin charges the leakage inductance and magnetizing inductance of the primary winding L1, capacitor C1 charges the output capacitor CO1 through switch S1 and diode D1, and output capacitor CO2 discharges at this time. When switch S1 changes from on to off, mode 2 ends and mode 3 begins. Mode 3: Switch S1 is off, diodes D2 and D3 are reverse biased and cut off, diodes D1, D4 and D5 are positive biased and conduct, secondary winding L2 is in the freewheeling decreasing stage, primary winding L1 freewheels through the passive clamping circuit composed of output capacitor CO2, diode D5 and capacitor C3, secondary winding L2 and capacitor C1 are connected in series to charge output capacitors CO1 and CO2, when the current of secondary winding L2 drops to zero, mode 3 ends and mode 4 begins; Mode 4: Switch S1 is turned off, diodes D1, D3, and D4 are reverse biased and cut off, diodes D2 and D5 are forward biased and conduct, capacitor C1 is charged through the series primary winding L1, secondary winding L2, and diode D2, primary winding L1 continues to freewheel through the passive clamping circuit composed of output capacitor CO2, diode D5, and capacitor C3, output capacitor CO1 and output capacitor are charged and discharged alternately, when diode D5 changes from forward biased conduction to reverse bias cut off, mode 4 ends and mode 5 begins; Mode 5: Switch S1 remains off, diodes D1, D5, and D4 are reverse biased and cut off, diodes D2 and D5 are forward biased and conduct, capacitor C2 and the series-connected secondary winding L2 charge capacitor C3. When switch S1 changes from off to on, mode 5 ends and mode 1 begins.

10. A DC-DC converter for a DC microgrid according to claim 6, characterized in that, Both output capacitors CO1 and CO2 are CBB capacitors.

Images