Isolated three-level DCDC step-down conversion circuit

Abstract

The utility model relates to the technical field of voltage conversion circuits, in particular to an isolation type three-level DCDC voltage reduction conversion circuit which comprises a capacitor C1 and a capacitor C2 which are connected in series at a high-voltage input end, a switch tube Q1, a switch tube Q2, a switch tube Q3 and a switch tube Q4 which are connected in series with the capacitor C1 and the capacitor C2, and a diode D1 and a diode D2 which are connected in series with the switch tube Q2 and the switch tube Q3. The switch tube Q2 and the switch tube Q3 are connected with a capacitor C3, an inductor L1 and an isolation transformer T1 which are connected in series, the isolation transformer is connected with a diode D3, a diode D4, a diode D5 and a diode D6 which are connected in series, and the diode D4 is connected with an inductor L2, a capacitor C4 and a low-voltage output end which are connected in series. And the electrical safety characteristic is improved.

Description

Technical Field

[0001] The utility model relates to the technical field of voltage conversion circuits, in particular to an isolated three-level DCDC step-down conversion circuit. Background Art

[0002] DCDC converter (Direct Current-Direct Current Converter), that is, DC to DC can realize the conversion between different DC power supply values. Any component that meets this definition is called a DCDC converter. The DCDC circuit realizes the change between high and low voltage DC power and can adapt to a wider range of input and output voltages.

[0003] At present, in the new energy industry, solar photovoltaic modules and energy storage battery modules have been connected in series to a voltage level of 1500V. In the field of rail transportation, 1500V DC power supply is often used to power the contact network, and 1500V DC is used to power equipment for long-distance transmission on smart highway sections. However, the 1500V DC power supply cannot directly power the equipment, and one or more levels of DCDC conversion are required to convert a wide range of input voltage DC into a voltage suitable for normal operation of the equipment.

[0004] The input DC voltage of the DCDC converter in the existing technology is as high as 1500V. Due to the limited voltage resistance of semiconductor devices such as MOS tubes and IGBTs, the original two-level DCDC converter topology is difficult to meet high voltage applications above 1000V. In addition, the existing DCDC converters with high voltage input often do not have electrical isolation capabilities and have low safety. Utility Model Content

[0005] The utility model provides an isolated three-level DCDC buck conversion circuit to solve the problems that the existing DCDC converter topology is difficult to meet the high voltage application of more than 1000V and has no electrical isolation capability and low safety.

[0006] The utility model is realized by the following technical solutions:

[0007] An isolated three-level DCDC step-down conversion circuit comprises a capacitor C1 and a capacitor C2 connected in series at a high voltage input end, the capacitors C1 and C2 are connected to switch tubes Q1, Q2, Q3 and Q4 connected in series, the switch tubes Q2 and Q3 are connected to diodes D1 and D2 connected in series, the switch tubes Q2 and Q3 are connected to capacitor C3, inductor L1 and an isolation transformer T1 connected in series, the isolation transformer is connected to diodes D3, D4, D5 and D6 connected in series, and the diode D4 is connected to the inductor L2, capacitor C4 and a low voltage output end connected in series.

[0008] Furthermore, the high voltage input end is provided with input voltage acquisition Vin and input current acquisition Iin, the input side of the isolation transformer T1 is provided with neutral current acquisition IL, and the low voltage output end is provided with output voltage acquisition Vo and output current acquisition Iout.

[0009] Furthermore, the switch tube Q1, the switch tube Q2, the switch tube Q3, and the switch tube Q4 are insulated gate bipolar transistors, field effect transistors, or silicon carbide field effect transistors.

[0010] Furthermore, the capacitor C1 and the capacitor C2 are DC filter support capacitors, the capacitor C3 is a resonant capacitor, and the capacitor C4 is a filter capacitor.

[0011] Furthermore, the diode D1 and the diode D2 are freewheeling diodes, and the diode D3, the diode D4, the diode D5, and the diode D6 are rectifying and filtering diodes.

[0012] Furthermore, the inductor L1 is a resonant inductor, and the inductor L2 is a filter inductor.

[0013] Furthermore, the gate of the switch tube Q1 is connected to the driving signal PWM-T1, the gate of the switch tube Q2 is connected to the driving signal PWM-T2, the gate of the switch tube Q3 is connected to the driving signal PWM-T3, and the gate of the switch tube Q4 is connected to the driving signal PWM-T4.

[0014] Beneficial effects of the utility model:

[0015] (1) The utility model proposes an isolated three-level DCDC step-down conversion circuit, which can achieve efficient energy conversion, reduce energy loss and improve overall efficiency by adopting advanced power semiconductor devices such as insulated gate bipolar transistors, field effect transistors or silicon carbide field effect transistors.

[0016] (2) The utility model proposes an isolated three-level DCDC step-down converter circuit, in which capacitors C1 and C2 are connected in series at the high voltage input end, which can provide voltage balance and voltage division, and help protect subsequent circuit components from possible damage caused by the high voltage input end.

[0017] (3) The utility model proposes an isolated three-level DCDC step-down conversion circuit, which can effectively filter out the pulsation and noise at the output end and provide a stable output voltage by using the filter capacitor C4 and the filter inductor L2.

[0018] (4) The utility model proposes an isolated three-level DCDC step-down conversion circuit, which forms a resonant circuit through capacitor C3 and inductor L1, which helps to reduce switching losses during the conversion process and improve conversion efficiency.

[0019] (5) The utility model proposes an isolated three-level DCDC step-down converter circuit, which can accurately control the on and off time of the switch tubes Q1, Q2, Q3 and Q4 by using driving signals such as PWM-T1, PWM-T2, PWM-T3 and PWM-T4, thereby adjusting the output voltage and current of the conversion circuit.

[0020] (6) The utility model proposes an isolated three-level DCDC step-down conversion circuit, which can monitor the voltage, current and power of the input and output ends in real time by collecting signals such as Vin, Iin, IL, Vo and Iout, so as to achieve effective management and control of circuit performance.

[0021] (7) The utility model proposes an isolated three-level DCDC step-down conversion circuit, which solves the problem of higher DC voltage access conversion under the existing IGBT and MOSFET withstand voltage level, while increasing electrical isolation and improving electrical safety characteristics. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] In order to more clearly illustrate the technical solutions in the embodiments of the present invention, the drawings required for use in the description of the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without creative work.

[0023] Figure 1 This is a circuit topology diagram of an isolated three-level DCDC buck conversion circuit proposed by the utility model;

[0024] Figure 2 The circuit topology working state of an isolated three-level DCDC buck conversion circuit proposed by the utility model is Figure 1 ;

[0025] Figure 3 The circuit topology working state of an isolated three-level DCDC buck conversion circuit proposed by the utility model is Figure 2 ;

[0026] Figure 4 The circuit topology working state of an isolated three-level DCDC buck conversion circuit proposed by the utility model is Figure 3 ;

[0027] Figure 5 The circuit topology working state of an isolated three-level DCDC buck conversion circuit proposed by the utility model is Figure 4 . DETAILED DESCRIPTION

[0028] In order to make the purpose, technical solutions and advantages of the utility model more clearly understood, the utility model is further described in detail below in conjunction with embodiments and drawings. The schematic implementation manner of the utility model and its description are only used to explain the utility model and are not intended to limit the utility model.

[0029] Example 1

[0030] refer to Figure 1 The present embodiment proposes an isolated three-level DCDC step-down converter circuit, which mainly utilizes the chopping control principle of the switch tube to convert a DC power supply with a wide range and high voltage input into a DC power supply that meets the power supply voltage range of the electrical equipment, and at the same time utilizes the magnetic induction principle of the transformer to achieve electrical safety isolation. An isolated three-level DC-DC step-down conversion circuit comprises a DC bus filter support capacitor C1 and C2 connected in series, a switch tube Q1, a switch tube Q2, a switch tube Q3, and a switch tube Q4 connected in series, a freewheeling diode D1 and a diode D2 connected in series, a resonant capacitor C3 connected in series, a resonant inductor L1 connected in series, an isolation transformer T1, a rectifier filter diode D3, a rectifier filter diode D4, a rectifier filter diode D5, and a rectifier filter diode D6 connected in series, a filter inductor L2 and a filter capacitor C4 connected in series, a drive signal PWM-T1 of the switch tube Q1, a drive signal PWM-T2 of the switch tube Q2, a drive signal PWM-T3 of the switch tube Q3, and a drive signal PWM-T4 of the switch tube Q4, an input voltage acquisition Vin, an input current acquisition Iin, a DC neutral line current acquisition IL, an output voltage acquisition Vo, and an output current acquisition Iout.

[0031] The bus filter support capacitors C1 and C2 are high-frequency aluminum electrolytic capacitors in this embodiment, and can also be polyester film capacitors or polypropylene capacitors (CBB). They are connected to the DC input in series to achieve DC input filtering, provide instantaneous peak power during switch control, and absorb current harmonics and voltage spikes during switch switching of the switch tube.

[0032] The switch tubes Q1, Q2, Q3, and Q4 are insulated gate bipolar transistors (IGBTs), field effect transistors (MOSFETs), or silicon carbide (SiC) field effect transistors in this embodiment, and are mainly used for high-frequency switching.

[0033] The series resonant capacitor C3 and the inductor L1 are used for resonant filtering. The resonant capacitor is a polyethylene film capacitor, a polypropylene capacitor (CBB), and the inductor is a customized magnetic inductive device.

[0034] The isolation transformer T1 is mainly a magnetic component made of a magnetic core of iron powder core and enameled wire, and is used for voltage conversion and electrical safety isolation.

[0035] The rectifier and filter diodes D3, D4, D5, and D6 may be Schottky diodes, which mainly play a rectifying role and are used to adjust the pulse signal output from the secondary side of the transformer into a pulsating DC power supply with a positive cycle.

[0036] The filter inductor L2 and the filter capacitor C4, the inductor L2 is a customized magnetic inductive device, the capacitor C4 is a high-frequency aluminum electrolytic capacitor, and can also be a polyethylene film capacitor, a polypropylene capacitor (CBB), mainly for filtering the voltage waveform output after diode rectification to obtain a stable DC voltage and reduce the output switching ripple.

[0037] Example 2

[0038] This embodiment proposes a connection relationship of an isolated three-level DCDC buck conversion circuit based on the first embodiment.

[0039] An isolated three-level DCDC step-down conversion circuit has an input positive electrode connected to the positive electrode of a bus filter support capacitor C1, an input negative electrode of the circuit connected to the negative electrode of a bus filter support capacitor C2, and a negative electrode of the bus filter support capacitor C1 and a positive electrode of the bus filter support capacitor C2 connected in series.

[0040] The positive electrode of the bus filter support capacitor C1 is connected to the collector or drain of the switch tube Q1, the emitter or source of the switch tube Q1 is connected to the collector or drain of the switch tube Q2, the emitter or source of the switch tube Q2 is connected to the collector or drain of the switch tube Q3, the emitter or source of the switch tube Q3 is connected to the collector or drain of the switch tube Q4, and the emitter or source of the switch tube Q4 is connected to the negative electrode of the bus filter support capacitor C2, thereby completing the series connection of the switch tubes and improving the input voltage level.

[0041] The anode of the freewheeling diode D1 is connected to the negative electrode of the bus filter support capacitor C1, the cathode of the freewheeling diode D1 is connected to the emitter or source of the switch tube Q1, the cathode of the freewheeling diode D2 is connected to the negative electrode of the bus filter support capacitor C1, and the anode of the freewheeling diode D2 is connected to the emitter or source of the switch tube Q3.

[0042] One end of the resonant capacitor C3 is connected to the emitter or source of the switch tube Q2, and the other end of the resonant capacitor C3 is connected in series to one end of the resonant inductor L1. The other end of the resonant inductor L1 is connected to the same-name end of the transformer T1, and the other end of the same-name end of the transformer T1 is connected to the negative electrode of the bus filter support capacitor C1.

[0043] The opposite-name end of transformer T1 is connected to the anode of rectifier diode D4 and the cathode of rectifier diode D6, the cathode of rectifier diode D4 and the cathode of rectifier diode D3 are connected to filter inductor L2, and the other opposite-name end of transformer T1 is connected to the cathode of rectifier diode D5 and the anode of rectifier diode D3. The anode of rectifier diode D5 and the anode of rectifier diode D6 are connected to the output negative pole.

[0044] The filter inductor L2 is connected to the positive electrode of the filter capacitor C4 and the positive electrode of the DC converter output, and the negative electrode of the filter capacitor C4 is connected to the negative electrode of the DC converter output.

[0045] In traditional DCDC conversion circuits, the supported input voltage amplitude is limited by the insulation withstand voltage level of the switch tube. A 1200V switch tube can accept a maximum voltage input of 1000V.

[0046] The three-level structure in the isolated three-level DCDC step-down conversion circuit proposed in this embodiment doubles the acceptable input voltage amplitude under the same single switch tube insulation withstand voltage level, expanding the applicable scenarios and scope. Using a single-tube switch tube with an insulation withstand voltage of 1200V, the input voltage amplitude can reach 2000V. The circuit designed in this embodiment adopts the principle of electromagnetic induction energy transmission of the transformer. In the event of a power failure, the voltage on the high-voltage side of the input cannot reach the low-voltage power supply side, avoiding the risk of low-voltage electrical equipment being broken down by the input high voltage, and improving the power supply safety.

[0047] Example 3

[0048] This embodiment proposes a specific implementation of an isolated three-level DCDC buck converter circuit based on the embodiment 1.

[0049] refer to Figure 2 In this working state, the circuit input side is powered on, and the DC bus filter support capacitors C1 and C2 begin to charge. Under PWM control, when the switch tubes Q1 and Q2 are turned on at the same time and the switch tubes Q3 and Q4 are turned off at the same time, the bus filter support capacitor C1 begins to discharge. The current of the resonant capacitor C3 and the resonant inductor L1 increases, and they begin to charge and store energy. The input DC power supply is controlled by the switch tube PWM to generate a pulsating chopped DC power supply with a fixed switching frequency, which passes through the primary side of the transformer T1 and returns to the bus filter support capacitor C1. The secondary side of the transformer T1 forms an induced voltage with a corresponding turns ratio, generating a pulsating chopped DC power supply with the same frequency but different amplitude as the primary side. The DC power supply on the secondary side of the transformer T1 rectifies the pulsating chopped DC power supply into a DC waveform of the positive half axis through the rectifier diodes D4 and D5. The rectified output power supply is smoothed and filtered through the filter inductor L2 and the filter capacitor C4 to obtain a constant DC output voltage. The output voltage amplitude is adjusted according to the duty cycle values ​​of the drive signals PWM-T1 and PWM-T2 of the switch tubes Q1 and Q2.

[0050] refer to Figure 3 In this working state, PWM control is used, and the switch tube Q2 is turned off from on, and the current of the resonant capacitor C3 and the resonant inductor L1 decreases and disappears, generating a reaction induced electromotive force, forming a reverse voltage acting on the switch tube Q2. To avoid excessive reverse voltage from breaking down the switch tube Q2, the induced electromotive force is consumed through the absorption loop formed by the diode D1 and the busbar support capacitor C1 connection line.

[0051] refer to Figure 4 , in this working state, PWM control is entered. When the switch tubes Q1 and Q2 are turned off at the same time and the switch tubes Q3 and Q4 are turned on at the same time, the bus filter support capacitor C2 starts to discharge and the bus filter support capacitor C1 resumes charging. The current of the resonant capacitor C3 and the resonant inductor L1 increases and starts to charge and store energy. The input DC power supply is controlled by the switch tube PWM to generate a pulsating chopped DC power supply with a fixed switching frequency, which returns to the bus filter support capacitor C2 through the primary side of the transformer T1. The secondary side of the transformer T1 forms an induced voltage corresponding to the turns ratio, generating a pulsating chopped DC power supply with the same frequency and different amplitude as the primary side. The DC power supply on the secondary side of the transformer T1 rectifies the pulsating chopped DC power supply into a DC waveform of the positive half axis through the rectifier diodes D3 and D6. The rectified output power supply is smoothed and filtered through the filter inductor L2 and the filter capacitor C4 to obtain a constant DC output voltage. The output voltage amplitude is adjusted according to the duty cycle values ​​of the drive signals PWM-T3 and PWM-T4 of the switch tubes Q3 and Q4.

[0052] refer to Figure 5 In this working state, PWM control is used, and the switch tube Q3 is turned off from on, and the current of the resonant capacitor C3 and the resonant inductor L1 decreases and disappears, generating a reaction induced electromotive force, forming a reverse voltage acting on the switch tube Q3. To avoid excessive reverse voltage from breaking through the switch tube Q3, the induced electromotive force is consumed through the absorption loop formed by the connection line of the diode D2 and the busbar support capacitor C2.

[0053] The above shows and describes the basic principle and main features of the utility model and the advantages of the utility model. Those skilled in the art should understand that the utility model is not limited by the above embodiments. The above embodiments and the description only illustrate the principle of the utility model. Without departing from the spirit and scope of the utility model, the utility model may have various changes and improvements, which fall within the scope of the utility model to be protected. The scope of protection claimed by the utility model is defined by the attached claims and their equivalents.

Claims

1. An isolated three-level DCDC step-down converter circuit, characterized in that: It includes a capacitor C1 and a capacitor C2 connected in series at the high-voltage input end. The capacitors C1 and C2 are connected to switch tubes Q1, Q2, Q3 and Q4 connected in series. The switch tubes Q2 and Q3 are connected to diodes D1 and D2 connected in series. The switch tubes Q2 and Q3 are connected to capacitor C3, inductor L1 and isolation transformer T1 connected in series. The isolation transformer is connected to diodes D3, D4, D5 and D6 connected in series. The diode D4 is connected to the inductor L2, capacitor C4 and a low-voltage output end in series.

2. The isolated three-level DCDC step-down converter circuit according to claim 1, characterized in that: The high voltage input end is provided with input voltage acquisition Vin and input current acquisition Iin, the input side of the isolation transformer T1 is provided with neutral current acquisition IL, and the low voltage output end is provided with output voltage acquisition Vo and output current acquisition Iout.

3. The isolated three-level DCDC step-down converter circuit according to claim 1, characterized in that: The switch tubes Q1, Q2, Q3 and Q4 are insulated gate bipolar transistors, field effect transistors or silicon carbide field effect transistors.

4. The isolated three-level DCDC step-down converter circuit according to claim 1, characterized in that: The capacitor C1 and the capacitor C2 are DC filter support capacitors, the capacitor C3 is a resonant capacitor, and the capacitor C4 is a filter capacitor.

5. The isolated three-level DCDC step-down converter circuit according to claim 1, characterized in that: The diode D1 and the diode D2 are freewheeling diodes, and the diode D3, the diode D4, the diode D5, and the diode D6 are rectifying and filtering diodes.

6. The isolated three-level DCDC step-down converter circuit according to claim 1, characterized in that: The inductor L1 is a resonant inductor, and the inductor L2 is a filter inductor.

7. The isolated three-level DCDC step-down converter circuit according to claim 1, characterized in that: The gate of the switch tube Q1 is connected to the driving signal PWM-T1, the gate of the switch tube Q2 is connected to the driving signal PWM-T2, the gate of the switch tube Q3 is connected to the driving signal PWM-T3, and the gate of the switch tube Q4 is connected to the driving signal PWM-T4.

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