Power DC-DC converter

Abstract

The utility model discloses a power supply DC-DC converter comprising an input front end, an LLC half-bridge resonance circuit and an output rectification filter circuit which are connected in sequence. And the control unit is connected with the LLC half-bridge resonance circuit and the output rectification filter circuit, collects output voltage and current data, and controls the driving frequency or duty ratio of the LLC half-bridge resonance circuit according to the change of the output current, so that the converter works in the optimal state. According to the utility model, the LLC resonant circuit is combined with the digital controller, so that the digital controller changes and controls the driving frequency or the duty ratio of the switching tube of the LLC resonant circuit according to the change of the load, thereby solving the problems existing when an analog circuit controls the LLC resonant circuit.

Description

TECHNICAL FIELD

[0001] The utility model relates to a power supply DC-DC converter. BACKGROUND

[0002] With the development of electric vehicles, its battery supporting charging equipment is gradually concerned. It requires small size, light weight, high efficiency and other characteristics, so the switching power supply is the best choice for its charging equipment. Increasing switching frequency can realize high power, high power density, safety and reliability and fast response speed of circuit, but it will also cause the problem of increasing circuit and switching device loss. The effective method to reduce switching loss is to select switching device with superior frequency characteristics and shorten switching time; in the state of zero voltage or zero current, the switching device is turned on and off, that is, the switching tube works in a soft switching circuit environment.

[0003] In the soft switching circuit, the resonant soft switching is widely used, which effectively solves the problem of low efficiency under high frequency condition. It mainly includes series resonant SRC, parallel resonant PRC and series-parallel resonant converter SPRC combining the advantages of the two, which can also be called LLC resonant converter.

[0004] The half-bridge series resonant converter forms a resonant cavity through the series connection of resonant inductance Lr and resonant capacitance Cr. When the input voltage frequency is close to the resonant frequency of the series resonant cavity, the impedance of the resonant cavity will become very small (close to zero), and all the input voltage will be added to the load output. The output voltage of the series resonant converter cannot be adjusted when the load is light, and the output voltage sensitivity to frequency is reduced. At the same time, the LLC resonant converter feedback loop is difficult to be compatible with light load and heavy load, and the output capacitor ripple is large.

[0005] The parallel resonant converter resonant cavity is still a series structure, but the load and the resonant capacitor are in parallel relationship. Since a capacitor is connected in parallel with the primary side of the transformer in the topology, an output inductance must be added to the secondary side of the transformer to achieve impedance matching. When the input voltage is low, the working frequency of the parallel resonant converter is close to the resonant frequency point. When the input voltage rises, the converter frequency rises away from the resonant frequency. Unlike the series resonant converter, the DC gain of the parallel resonant converter can be greater than 1, and its working frequency range is much smaller. The switching frequency only needs to change in a very narrow range to realize the adjustment of the output voltage under light load condition. The parallel resonant converter does not have the problem of light load voltage adjustment, but a significant disadvantage of the parallel resonant converter is that a large amount of non-functional energy is still generated under light load condition.

[0006] LLC resonant converter can be regarded as a complex of series resonant cavity and parallel resonant cavity, and is the most popular resonant converter at present. It effectively solves the problems of series resonant converter, such as no-load non-adjustable, frequency regulation insensitive, etc. It also solves the problems of parallel resonant converter, such as large energy in resonant loop (especially when light load and high voltage), large reactive power, etc. LLC resonant converter can realize regulation from full load to light load in a narrow frequency range, and realizes soft switching in the whole range, effectively reduces switching loss, and improves the working efficiency of the power supply.

[0007] Although LLC resonant converter has high efficiency, it also has some shortcomings. For example, at light load, the dynamic characteristic is poor, the output capacitor ripple is large, the adjustable range of output voltage is limited, the on-state loss and switching loss are large when the input voltage is high, and the feedback loop is difficult to realize good performance in the whole range when the load changes. Practical new type content

[0008] The utility model discloses based on some field such as electric automobile battery pack to voltage wide range demand, propose a kind of power DC-DC converter, the converter can preferably realize high-efficiency output in whole power range, and output ripple is smaller.

[0009] According to an aspect of the embodiment, a power DC-DC converter is proposed, comprising: an input end, an LLC resonant circuit and a rectifier filter circuit connected in sequence, and a digital control unit connected to the input end, the LLC resonant circuit and the rectifier filter circuit, and configured to control the driving frequency or duty cycle of the LLC resonant circuit switch tube according to the change of the current input from the input end to the LLC resonant circuit, so that the output voltage of the rectifier filter circuit reaches a set value.

[0010] The power DC-DC converter includes an LLC half-bridge resonant circuit, a control unit and a sampling feedback driving peripheral circuit. When used in an electric vehicle, the power DC-DC converter takes power from a vehicle-mounted power battery and supplies power to a backup battery. Under the control of the control unit, direct current passes through the LLC half-bridge resonant unit and is converted by DC-DC to output the required direct current voltage to charge the backup battery power supply. At the same time, the control unit needs to collect the input direct current voltage and current, as well as the output voltage and current, and use PID cyclic regulation to control the driving waveform, thereby realizing stable voltage output.

[0011] When the circuit load is small, if only PFM regulation mode is adopted, the half-bridge power frequency needs to be far away from the resonant frequency, and the regulation frequency has little improvement on the ripple, the energy loss in the resonant loop is large, the parallel inductance current is large, and the dynamic loss increases, therefore, under the light load condition, PWM regulation mode is adopted, the resonant unit works at the resonant frequency, and the on-state loss is reduced, although the duty cycle is reduced when regulating in the input voltage range, the withstand voltage requirement of the rectifier diode is brought, but through the dynamic adjustment of the control signal by the DSP, the high-efficiency and reliable work can be better ensured, and the current is small under the light load, and the loss is also small.

[0012] When the circuit load is large, if only PWM regulation mode is adopted, under the condition that the voltage range is wide, the duty cycle will deviate from 0.5 seriously, the stress of the secondary rectifier diode is increased, the load is heavy, the current is increased, and the input diode loss will be greatly increased, which will inevitably lead to the reduction of efficiency.

[0013] By combining the LLC resonant converter with the digital controller, the converter has obvious improvement effect, under different power ranges, the PWM modulation and PFM modulation switching mode can effectively solve the light load ripple problem, the DSP control circuit changes the driving frequency or the duty cycle, compared with the analog circuit, the switching control is realized, and the control circuit and the feedback loop are simple and high-efficiency and reliable, the LLC resonant half-bridge circuit is adopted, the power tube can realize ZVS, the rectifier diode can realize ZCS, and the working efficiency is greatly improved, and the highest efficiency can be above 95 %. BRIEF DESCRIPTION OF DRAWINGS

[0014] Figure 1 It is a power DC-DC converter structure block diagram according to an embodiment of the utility model.

[0015] Figure 2 It is a power DC-DC converter circuit topology diagram according to an embodiment of the utility model.

[0016] Figure 3 It is a power DC-DC converter control flow chart according to an embodiment of the utility model. DETAILED DESCRIPTION

[0017] The power DC-DC converter of the utility model can be applied to electric vehicles, electric ships and the like. Figure 1 As shown in the figure, the power DC-DC converter comprises an input end for taking power from a power battery, an LLC half-bridge resonant circuit, a rectification and filtering circuit and a control unit. The input end is used for connecting the battery and the LLC half-bridge resonant circuit. The rectification and filtering circuit rectifies and filters the current output by the LLC half-bridge resonant circuit.

[0018] The control unit can adopt a DSP controller, wherein the control unit collects input voltage and current, realizes control of a peripheral circuit, and realizes overvoltage and undervoltage protection and overcurrent protection functions.

[0019] Figure 2 The circuit topology of the converter is shown in the figure, Q1 and Q2 are switch tubes of a half-bridge circuit, the LLC resonant network is composed of a resonant inductor Lr, a resonant capacitor Cr and a leakage inductance (excitation inductance) Lp of a transformer T1, the transformer T1 adopts a full-wave rectification mode, and the AC voltage or current is converted into a smooth DC form through a filter circuit composed of rectifier diodes D1 and D2 and L1 and C1.

[0020] The LLC half-bridge resonant circuit works at a series resonant frequency fs generated by the resonant inductor and the resonant capacitor, and a series-parallel resonant frequency generated by the sum of the resonant inductor and the excitation inductor and the resonant capacitor, the primary switch tube of the transformer can realize zero-voltage switching, the rectifier diode of the secondary side of the transformer can realize zero-current output, and the efficiency is relatively high.

[0021] The converter adopts a digital controller, changes the traditional LLC drive IC control mode, and the control unit control process is as shown in the figure Figure 3 The working characteristics are that after the converter is started, the drive circuit works at the resonant frequency point fs, the duty cycle of the drive signal gradually increases, the output voltage gradually rises, the control unit monitors the input and output current and voltage in real time, when the input current is less than the set threshold value, it is regarded as a small load working mode, the control circuit adjusts the output voltage through the PWM control mode, and the voltage is maintained stable.

[0022] The contribution of the utility model lies in the circuit structure of the combination of the LLC resonant circuit and the digital controller. On this basis, the digital controller changes the drive frequency or duty cycle of the switch tube of the LLC resonant circuit according to the change of the load. The program involved in the utility model is a simple program.

Claims

1. A power supply DC-DC converter, characterized by, The application relates to a power supply device comprising an input end, an LLC resonant circuit and a rectification filter circuit connected in sequence, and a digital control unit connected with the input end, the LLC resonant circuit and the rectification filter circuit, and configured to control the driving frequency or duty cycle of the switch tube of the LLC resonant circuit according to the change of the input current of the LLC resonant circuit from the input end, so that the output voltage of the rectification filter circuit reaches a set value. The LLC resonant circuit is in a half-bridge structure.

2. The power supply DC-DC converter according to claim 1, characterized in that, When the input current is less than a set threshold value, the digital control unit controls the LLC resonant circuit through PWM to maintain the stability of the output voltage.

3. The power supply DC-DC converter according to claim 2, characterized in that, When the input current is greater than the set threshold value, the digital control unit controls the LLC resonant circuit through PFM to maintain the stability of the output voltage.

4. The power supply DC-DC converter according to claim 2, characterized in that, The digital control unit adopts a DSP.

5. The power supply DC-DC converter according to claim 3 or 4, characterized in that, The LLC resonant circuit is composed of a switch tube half-bridge circuit, a resonant inductor, a resonant capacitor and an excitation inductor.

6. The power supply DC-DC converter according to claim 4, characterized in that, The LLC half-bridge resonant circuit works at a series resonance frequency fs generated by the resonant inductor and the resonant capacitor, and a series-parallel resonance frequency generated by the sum of the resonant inductor and the excitation inductor and the resonant capacitor.

7. The power supply DC-DC converter according to claim 6, characterized in that, The primary switch tube of the LLC resonant circuit realizes zero-voltage switching, and the secondary rectification diode realizes zero-current output.

8. The power supply DC-DC converter according to claim 7, characterized in that, The digital control unit carries out overvoltage, undervoltage and overcurrent protection according to the voltage and current of the input end.

9. The power supply DC-DC converter according to claim 1, characterized in that, The input end takes power from a vehicle-mounted or ship-mounted power battery.

10. The power supply DC-DC converter according to claim 1, characterized in that, ​

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