CN-122001187-A - Pre-charge control method and circuit of fly capacitor three-level totem pole PFC

CN122001187ACN 122001187 ACN122001187 ACN 122001187ACN-122001187-A

Abstract

The invention discloses a pre-charge control method and a pre-charge control circuit for a flying capacitor three-level totem pole PFC, wherein the method comprises the following steps of 1, charging a direct current bus by power grid alternating current, 2, entering a step 3 when the voltage of the power grid alternating current is larger than the lower limit of a device protection value, 3, controlling a power tube to be conducted through a proportional controller if the voltage of the flying capacitor is lower than a given value, charging the flying capacitor by the power grid alternating current, switching off the power tube when the voltage of the flying capacitor is higher than the given value, discharging the flying capacitor through a discharge resistor, and 4, ending the pre-charge stage when the voltage of the flying capacitor and the given value are kept within a preset range, exiting the pre-charge circuit after the voltage of the direct current bus is increased, and enabling the device to enter a normal working mode. Under the condition that an external circuit is not added, the pre-charge of the flying capacitor three-level totem pole PFC is realized by utilizing a proportional controller algorithm which is easy to realize.

Inventors

Request for anonymity
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Assignees

艾乐德电子（南京）有限公司

Dates

Publication Date: 20260508
Application Date: 20260409

Claims (8)

1. The pre-charge control method of the fly capacitor three-level totem pole PFC is characterized by comprising the following steps of: the method comprises the following steps that 1, a device switch is started, power grid alternating current charges a direct current bus through a body diode of a power tube by a pre-charging circuit, an auxiliary power supply connected with the direct current bus works normally, and the auxiliary power supply supplies power to a control unit and a driving unit; Step 2, the control unit judges the running state of the equipment, and when the alternating current voltage of the power grid is greater than the lower limit of the protection value of the equipment, the step 3 is entered; The control unit collects the voltage value of the flying capacitor in real time, compares the relation between the voltage value of the flying capacitor and a given value, controls the driving unit to conduct the power tube through the proportional controller if the voltage value of the flying capacitor is lower than the given value, and enables the power grid alternating current to return to the power grid through the body diode of the power tube connected with the flying capacitor and the conducted power tube through the precharge circuit to charge the flying capacitor; and 4, when the voltage value and the given value difference value of the flying capacitor are kept within a preset range, ending the precharge phase, enabling the device to enter a direct current bus boosting phase, and controlling the precharge circuit to exit by the control unit after boosting is ended, and enabling the device to enter a normal working mode.
2. The method for controlling the precharge of the three-level totem pole PFC of the flying capacitor according to claim 1, wherein the power tube includes an upper outer tube, an upper inner tube, a lower inner tube, and a lower outer tube that form a high-frequency bridge arm, and an upper tube and a lower tube that form a low-frequency bridge arm, both ends of the high-frequency bridge arm and the low-frequency bridge arm are connected with a dc bus, one end of the precharge circuit is connected with a power grid L end, the other end of the precharge circuit is connected between the upper inner tube and the lower inner tube of the high-frequency bridge arm, and a power grid N end is connected between the upper tube and the lower tube of the low-frequency bridge arm.
3. The method of claim 1, wherein the given value of the flying capacitor is set to 1/2 dc bus voltage.
4. The method for controlling the precharge of the three-level totem pole PFC of the flying capacitor according to claim 1, wherein the control unit collects alternating current voltage and direct current bus voltage of a power grid in real time and judges the running state of equipment, and in the steps 2 to 4, if equipment fault information is identified, a power tube is turned off, the flying capacitor discharges through a discharge resistor, and when the voltage value of the flying capacitor is lower than a lower limit value, the step 3 is restarted.
5. The method of claim 2, wherein in the step 3, the driving unit is controlled to turn on the power tube by the proportional controller, the grid alternating current is returned to the grid by the precharge circuit through the body diode of the power tube connected with the flying capacitor and the turned-on power tube, and the method comprises the steps of: If the flying capacitor is charged in the positive half cycle of the power grid voltage, the lower outer tube of the high-frequency bridge arm is controlled to be conducted through the proportional controller, and power grid alternating current returns to the power grid through the precharge circuit, the body diode of the upper inner tube, the flying capacitor, the lower outer tube and the body diode of the lower tube of the low-frequency bridge arm to charge the flying capacitor; If the flying capacitor is charged in the negative half cycle of the power grid voltage, the upper inner tube of the high-frequency bridge arm is controlled to be conducted through the proportional controller, and power grid alternating current returns to the power grid through the body diode of the upper tube of the low-frequency bridge arm, the direct current bus, the body diode of the lower outer tube, the flying capacitor, the upper inner tube and the precharge circuit to charge the flying capacitor; And if the flying capacitor is charged in positive and negative half cycles of the power grid voltage, the lower outer tube of the high-frequency arm is controlled to be conducted through the proportional controller in the positive half cycle of the power grid voltage, and the upper inner tube of the high-frequency arm is controlled to be conducted through the proportional controller in the negative half cycle of the power grid voltage, so that the flying capacitor is charged.
6. The method of claim 5, wherein if the voltage value of the flying capacitor is higher than a given value in the step 3, the control unit controls the driving unit to turn off the power tube, and the flying capacitor discharges through a discharge resistor connected in parallel with the flying capacitor, and the method comprises: when the flying capacitor is charged in the positive half cycle of the power grid voltage, if the voltage value of the flying capacitor is higher than a given value or the power grid voltage is in the negative half cycle, the lower outer tube of the high-frequency bridge arm is turned off, and the flying capacitor is discharged through a discharge resistor connected in parallel with the flying capacitor; When the flying capacitor is charged in the negative half cycle of the power grid voltage, if the voltage value of the flying capacitor is higher than a given value or the power grid voltage is in the positive half cycle, the upper inner tube of the high-frequency bridge arm is turned off, and the flying capacitor is discharged through a discharge resistor connected in parallel with the flying capacitor; and when the flying capacitor is charged in positive and negative half cycles of the power grid voltage, if the voltage value of the flying capacitor is higher than a given value, the power tube is turned off, and the flying capacitor is discharged through a discharge resistor connected in parallel with the flying capacitor.
7. The method for precharge control of a flying capacitor three-level totem pole PFC of claim 1 wherein the proportional controller controls the on time of the power transistor according to the formula: , Wherein, T on represents the on time of the power tube, U dcref is the given value of the flying capacitor, U cfly is the voltage value of the flying capacitor, and k is the proportionality coefficient.
8. The control circuit based on the pre-charge control method of the flying capacitor three-level totem pole PFC of claim 1, which is characterized by comprising a power tube, a pre-charge circuit, a flying capacitor, a discharge resistor, a direct current bus, a control unit, a driving unit and an auxiliary power supply; the power tube comprises an upper outer tube, an upper inner tube, a lower inner tube and a lower outer tube which form a high-frequency bridge arm, and an upper tube and a lower tube which form a low-frequency bridge arm, wherein the two ends of the high-frequency bridge arm and the low-frequency bridge arm are connected with direct current buses, the output end of the precharge circuit is connected between the upper inner tube and the lower inner tube of the high-frequency bridge arm, and the upper tube and the lower tube of the low-frequency bridge arm are connected with the N end of a power grid; One end of the flying capacitor is connected between the upper outer tube and the upper inner tube of the high-frequency bridge arm, the other end of the flying capacitor is connected between the lower inner tube and the lower outer tube of the high-frequency bridge arm, and the flying capacitor is connected with the discharge resistor in parallel; the power grid L end is connected with the input end of the pre-charging circuit, and the power grid alternating current charges the direct current bus through the pre-charging circuit through the body diode of the power tube; The direct current bus is connected with the auxiliary power supply, and when the power grid voltage charges the direct current bus, the auxiliary power supply works as the control unit and the driving unit for supplying power; The control unit collects the alternating current voltage of the power grid, the direct current bus voltage and the voltage value of the flying capacitor in real time, judges the running state of the equipment, compares the relation between the voltage value of the flying capacitor and a given value, outputs a power tube control signal through the proportional controller, and outputs a control signal for controlling the pre-charging circuit to exit when the direct current bus voltage boosting is finished; The driving unit receives a power tube control signal of the control unit, drives the power tube to be conducted so that the power grid alternating current charges the flying capacitor through the pre-charging circuit and the power tube, and drives the power tube to be turned off so that the flying capacitor discharges through the discharge resistor.

Description

Pre-charge control method and circuit of fly capacitor three-level totem pole PFC Technical Field The invention relates to the technical field of electronic circuits, in particular to a pre-charge control method and a pre-charge control circuit for a fly capacitor three-level totem pole PFC. Background With the development of new energy, the requirements of test power supplies with higher voltage and higher power density are increasingly increased, and totem pole PFC is increasingly favored by vast new energy manufacturers by virtue of the advantages of high efficiency, ‌ high power density, wide input voltage range, low harmonic distortion and the like. The three-level topology, compared with the traditional two-level design, shows a plurality of technical advantages in the power electronic conversion system, wherein the advantages are derived from the optimized control of voltage stress, harmonic distortion and switching loss by the multi-level output. At present, the pre-charging control method of the flying capacitor three-level totem pole PFC mainly adopts a pre-charging resistor and a switching device to realize pre-charging of the flying capacitor, thereby effectively controlling the voltage of a power supply when the power supply is started, avoiding damaging an MOS tube and improving the reliability of the power supply. Specifically, the method is characterized in that the front end of the flying capacitor is connected with a pre-charging resistor and a switching device, and the pre-charging is realized through the switching device connected with a circuit, so that the voltage of the flying capacitor is effectively controlled, and the voltage equalizing control is realized. This approach adds peripheral circuitry, increasing the complexity of the system and unnecessary costs. Disclosure of Invention The invention aims to provide a pre-charge control method and a pre-charge control circuit for a fly capacitor three-level totem pole PFC aiming at the defects of the prior art. The application provides a pre-charge control method of a fly capacitor three-level totem pole PFC, which comprises the following steps: the method comprises the following steps that 1, a device switch is started, power grid alternating current charges a direct current bus through a body diode of a power tube by a pre-charging circuit, an auxiliary power supply connected with the direct current bus works normally, and the auxiliary power supply supplies power to a control unit and a driving unit; Step 2, the control unit judges the running state of the equipment, and when the alternating current voltage of the power grid is greater than the lower limit of the protection value of the equipment, the step 3 is entered; The control unit collects the voltage value of the flying capacitor in real time, compares the relation between the voltage value of the flying capacitor and a given value, controls the driving unit to conduct the power tube through the proportional controller if the voltage value of the flying capacitor is lower than the given value, and enables the power grid alternating current to return to the power grid through the body diode of the power tube connected with the flying capacitor and the conducted power tube through the precharge circuit to charge the flying capacitor; and 4, when the voltage value and the given value difference value of the flying capacitor are kept within a preset range, ending the precharge phase, enabling the device to enter a direct current bus boosting phase, and controlling the precharge circuit to exit by the control unit after boosting is ended, and enabling the device to enter a normal working mode. Further, the power tube comprises an upper outer tube, an upper inner tube, a lower inner tube and a lower outer tube which form a high-frequency bridge arm, and an upper tube and a lower tube which form a low-frequency bridge arm, wherein the two ends of the high-frequency bridge arm and the low-frequency bridge arm are connected with a direct current bus, one end of the pre-charging circuit is connected with a power grid L end, the other end of the pre-charging circuit is connected between the upper inner tube and the lower inner tube of the high-frequency bridge arm, and the upper tube and the lower tube of the low-frequency bridge arm are connected with a power grid N end. Further, the given value of the flying capacitor is set to be 1/2 DC bus voltage. In the steps 2 to 4, if the equipment fault information is identified, the power tube is closed, the flying capacitor discharges through the discharge resistor, and when the voltage value of the flying capacitor is lower than the lower limit value, the step 3 is restarted. Further, in the step3, the driving unit is controlled to turn on the power tube by the proportional controller, the power grid alternating current returns to the power grid through the body diode of the power tube connected with the flying capacitor and the turned-on po