CN106487239A - A kind of auxiliary power circuit of high voltage converter - Google Patents

Abstract

The invention provides an auxiliary power supply circuit of a high-voltage frequency converter, which includes two AC input power supplies, two rectification circuits, filter energy storage elements, and two power conversion circuits, wherein: each AC input power supply is connected to the rectification circuit, and the AC input power supply The output alternating current is rectified into direct current by the rectifier circuit and output; the output terminals of the two rectifier circuits are connected in parallel, and the output terminal is connected with the filter energy storage element to form a first loop, and the output terminal is output by the filter energy storage element The direct current is used for energy storage and filtering; the filter energy storage element is respectively connected to the two power conversion circuits to form a loop, and the power conversion circuit is used to respectively convert the direct current at both ends of the filter energy storage element into an AC voltage; the two The output terminals of the power conversion circuit are respectively connected to the loads and supply power to the loads at the same time. On the basis of reducing the power supply cost, the present invention can ensure that no power failure occurs during power switching and realize seamless switching.

Description

An Auxiliary Power Supply Circuit of a High Voltage Frequency Converter

technical field

The invention relates to the technical field of power supply design, in particular to an auxiliary power supply circuit of a high-voltage frequency converter.

Background technique

The auxiliary power circuit of the high-voltage inverter is mainly to supply power to the main control system of the high-voltage inverter. In order to ensure the reliability of the power supply of the main control system in the existing high-voltage inverter system, two power supplies are required to supply power to the auxiliary power supply circuit, so there are 380V mains power and 6kV/10kV high voltage through the auxiliary winding to provide 380V power for mutual switching. The auxiliary power supply circuit jointly supplies power to the main control system. At present, there are mainly the following plans:

A primary power supply is used. The primary power supply refers to converting 380V into a nominal value of 48V DC. The incoming line of the primary power supply adopts a high and low voltage cold standby method. This solution requires high and low voltage switching contactors, detection circuits, capacitor batteries and other related signals and Device, 380V mains and 6kV/10kV high voltage are connected to the primary power supply through the high and low voltage switching contactor through the 380V power supply provided by the auxiliary winding. The detection circuit is used to detect the two power supplies, and the main control is notified when a certain power supply is detected to be faulty. system, the main control system sends a control signal to control the high and low voltage switching contactor, and switches to another power supply to supply power to the primary power supply.

In this scheme, the detection circuit is specifically to connect the detection relay in parallel in the 380V mains circuit, and judge whether the 380V mains circuit is live through the detection relay, so as to choose whether to switch the power supply, which has a process from detection to execution to switching Time, because this time is long, in order to ensure that the main control system does not lose power, it is necessary to use batteries or capacitors for support, occupying multiple electrical components, making switching unstable and costly.

Contents of the invention

The invention provides an auxiliary power supply circuit of a high-voltage frequency converter. On the basis of reducing the power supply cost, it can ensure that no power failure occurs during power supply switching and realize seamless switching.

An auxiliary power supply circuit for a high-voltage frequency converter, comprising a first AC input power supply, a second AC input power supply, a first rectification circuit, a second rectification circuit, a filter energy storage element, a first power conversion circuit and a second power conversion circuit, in:

The first AC input power supply is connected to the first rectifier circuit, and the first AC input power supply outputs AC power, which is rectified into DC power by the first rectifier circuit and output;

The second AC input power supply is connected to the second rectifier circuit, and the second AC input power supply outputs AC power, which is rectified into DC power by the second rectifier circuit and output;

The output terminal of the first rectification circuit is connected in parallel with the output terminal of the second rectification circuit, and the output terminal is connected with the filter energy storage element to form a first loop, and the output terminal is output by the filter energy storage element direct current for energy storage and filtering;

The filter energy storage element is respectively connected with the first power conversion circuit to form a second loop, and connected with the second power conversion circuit to form a third loop, and the first power conversion circuit and the second power conversion circuit are used for Respectively convert the direct current at both ends of the filter energy storage element into alternating voltage;

The output terminals of the first power conversion circuit and the second power conversion circuit are respectively connected to the load, and supply power to the load at the same time.

Preferably, the voltage of the first AC input power supply is 220V, the voltage of the second AC input power supply is 220V, the second AC input power supply is provided by the auxiliary winding of a high-voltage transformer, and the first AC input power supply and the second AC input power supply The voltage phase of the AC input power supply is the same;

The first AC input power supply is a 380V power supply provided by the mains, and the voltage of the second AC input power supply is a 380V power supply provided by a high voltage frequency converter through an auxiliary winding.

Preferably, the first rectification circuit and/or the second rectification circuit is a rectification bridge; or

The first rectification circuit and/or the second rectification circuit is a rectification circuit composed of four diodes.

Preferably, the filtering energy storage element is a capacitive element, or two capacitive elements connected in series.

Preferably, when the filtering energy storage element is two capacitive elements connected in series, the circuit further includes:

A voltage equalizing resistor connected in parallel across each capacitive element.

Preferably, the first power conversion circuit or the second power conversion circuit includes a PWM control chip, a first switch tube, a second switch tube and a transformer, wherein:

The transformer includes a primary side and at least one secondary side, the first input end of the primary side is connected to one end of the filter energy storage element through the first switch tube, and the second input end of the primary side is connected to the filter energy storage element through the second switch tube The other end of the component is connected;

The first switching tube is respectively connected to both ends of the PWM control chip and the filter energy storage element;

The second switching tube is respectively connected to both ends of the PWM control chip and the filtering energy storage element;

The PWM chip controls the first switch tube K1 to be turned on or off by sending out a PWM pulse signal, and controls the second switch tube K2 to be turned off or turned on;

The transformer is used to transfer the voltage input from the primary side to each secondary side and output it.

Preferably, the transformer includes multiple secondary sides, and the multiple secondary sides are mutually isolated or non-isolated multi-tap.

Preferably, the output terminals of the first power conversion circuit and the second power conversion circuit are respectively connected to the load through a diode connected in series with the load.

Preferably, the output terminals of the first power conversion circuit and the second power conversion circuit are both connected to a capacitive element connected in parallel with the load.

Preferably, it also includes a first lightning protection circuit and a first EMC filter circuit, a second lightning protection circuit and a second EMC filter circuit, wherein:

After the first lightning protection circuit and the first EMC filter circuit are connected in series, they are connected between the first AC input power supply and the first rectification circuit;

After the second lightning protection circuit and the second EMC filter circuit are connected in series, they are connected between the second AC input power supply and the second rectification circuit.

Utilize the auxiliary power supply circuit of the high-voltage frequency converter provided by the present invention, specifically the following technical effects:

1) Compared with the original power supply system, the structure of the power supply circuit is greatly simplified, and the contactor for high and low voltage switching, the battery or capacitor used to maintain the switching time is removed, which saves the time required for power switching. element;

2) Due to the adoption of the rectifier circuit rear bus parallel current source mode, the reliability of the system power supply is greatly improved;

3) Due to the redundant design of hot backup, the system can supply power to the load at the same time by two power supplies in parallel. When any one power supply fails or the power supply is lost, it can ensure that no power failure occurs when the power supply is switched. Slit switching improves the reliability of power supply.

Description of drawings

FIG. 1 is a circuit diagram of an auxiliary power supply circuit of a high-voltage frequency converter provided in Embodiment 1 of the present invention;

FIG. 2 is a circuit diagram of an auxiliary power supply circuit of a high-voltage frequency converter provided in Embodiment 2 of the present invention;

Fig. 3 is a circuit diagram of the auxiliary power supply circuit of the high-voltage frequency converter provided by Embodiment 3 of the present invention.

detailed description

The auxiliary power supply circuit of the high-voltage frequency converter provided by the present invention will be described in detail below in conjunction with the drawings and embodiments.

The invention provides an auxiliary power supply circuit of a high-voltage frequency converter, which includes a first AC input power supply, a second AC input power supply, a first rectification circuit, a second rectification circuit, a filter energy storage element, a first power conversion circuit and a second power supply conversion circuit, where:

The first AC input power supply is connected to the first rectifier circuit, and the first AC input power supply outputs AC power, which is rectified into DC power by the first rectifier circuit and output;

The second AC input power supply is connected to the second rectifier circuit, and the second AC input power supply outputs AC power, which is rectified into DC power by the second rectifier circuit and output;

The output terminal of the first rectification circuit is connected in parallel with the output terminal of the second rectification circuit, and the output terminal is connected with the filter energy storage element to form a first loop, and the output terminal is output by the filter energy storage element direct current for energy storage and filtering;

The filter energy storage element is respectively connected with the first power conversion circuit to form a second loop, and connected with the second power conversion circuit to form a third loop, and the first power conversion circuit and the second power conversion circuit are used for Respectively convert the direct current at both ends of the filter energy storage element into alternating voltage;

The output terminals of the first power conversion circuit and the second power conversion circuit are respectively connected to the load, and supply power to the load at the same time.

The power supply circuit of the embodiment of the present invention adopts the new technology of hot standby seamless switching to replace the original power supply system. Compared with the original power supply system, the power supply circuit is greatly simplified and the high and low voltage switching is removed. The contactor, the battery or capacitor used to maintain the switching time saves the electrical components required for the power switching time; since the dual power supply is used to supply power to the load at the same time, the reliability of the power supply is improved; due to the use of the rectifier bridge The bus parallel current source method greatly improves the reliability of the system power supply.

Preferably, the voltage of the first AC input power supply is 220V, the voltage of the second AC input power supply is 220V, the second AC power supply is provided by the auxiliary winding of the rectifier transformer in the high-voltage frequency converter, and the first AC input The voltage phase of the power supply and the second AC input power supply are the same. If they are not connected to the same phase, the input voltage will not be 220V but the line voltage, which will cause damage to the rear devices;

The first AC input power supply is a 380V power supply provided by the mains, and the voltage of the second AC input power supply is a 380V power supply provided by a high voltage frequency converter through an auxiliary winding. When using 380V power supply, the phases of the two power supplies can be the same or not.

Preferably, the first rectification circuit and/or the second rectification circuit is a rectification bridge; or

The first rectification circuit and/or the second rectification circuit is a rectification circuit composed of four diodes.

Of course, the rectification circuit can also be other rectification circuits with rectification function.

Preferably, the filtering energy storage element is a capacitive element, or two capacitive elements connected in series.

The output terminals of the two rectification circuits are connected in parallel, that is, the busbars of the two rectifier circuits are connected in parallel, and after the parallel connection, the filter energy storage element is used for energy storage. When the busbar voltage is low, a capacitor element can be used. When the busbar voltage is high, in order to To prevent bus capacitors from being damaged, two capacitor elements connected in series are used.

Preferably, when the filtering energy storage element is two capacitive elements connected in series, in order to prevent the uneven voltage division of the two capacitors from increasing the voltage equalizing resistance, the circuit further includes: a voltage equalizing resistor connected in parallel at both ends of each capacitive element , whose main function is to equalize the capacitor voltage.

Preferably, the first power conversion circuit or the second power conversion circuit includes a PWM control chip, a first switch tube, a second switch tube and a transformer, wherein:

The transformer includes a primary side and at least one secondary side, the first input end of the primary side is connected to one end of the filter energy storage element through the first switch tube, and the second input end of the primary side is connected to the filter energy storage element through the second switch tube The other end of the component is connected;

The first switching tube is respectively connected to both ends of the PWM control chip and the filter energy storage element;

The second switching tube is respectively connected to both ends of the PWM control chip and the filtering energy storage element;

The PWM chip controls the first switch tube K1 to be turned on or off by sending out a PWM pulse signal, and controls the second switch tube K2 to be turned off or turned on;

The transformer is used to transfer the voltage input from the primary side to each secondary side and output it.

The functions of the first power conversion circuit and the second power conversion circuit are to convert direct current into square wave alternating current, and the specific circuits are not limited to the above structures.

Preferably, the transformer includes a plurality of secondary sides, and the multiple secondary sides are mutually isolated, that is, the multiple secondary sides are mutually isolated, or are non-isolated multi-tap methods, that is, the multiple secondary sides are connected through multiple The taps are generated but not isolated from each other.

Preferably, the output terminals of the first power conversion circuit and the second power conversion circuit are respectively connected to the load through a diode connected in series with the load.

Preferably, the output terminals of the first power conversion circuit and the second power conversion circuit are respectively connected to a capacitive element connected in parallel with the load.

Preferably, in order to further increase the stability of power supply, the auxiliary power supply circuit provided by the present invention further includes a first lightning protection circuit and a first EMC filter circuit, a second lightning protection circuit and a second EMC filter circuit, wherein:

After the first lightning protection circuit and the first EMC filter circuit are connected in series, they are connected between the first AC input power supply and the first rectification circuit;

After the second lightning protection circuit and the second EMC filter circuit are connected in series, they are connected between the second AC input power supply and the second rectification circuit.

A preferred embodiment of the auxiliary power supply circuit of the high-voltage frequency converter provided by the present invention is given below.

Example 1

As shown in Figure 1, the first AC input power supply is a 380V power supply provided by the mains, and the voltage of the second AC input power supply is a 380V power supply provided by a high-voltage inverter through an auxiliary winding. The two 380V power supplies can be three-phase Four-wire system.

For each power supply, it is input to the EMC filter circuit for filtering through the lightning protection circuit first, and then input to the rectifier circuit for rectification after filtering to output AC power.

The rectification circuit is specifically a rectification circuit composed of four diodes. Diodes D1, D2, D3 and D4 in FIG. 1 constitute the first rectification circuit, and diodes D5, D6, D7 and D8 in FIG. 1 constitute the second rectification circuit. The function of the first rectification circuit/second rectification circuit is to convert the alternating current into direct current, and for a 380V power supply, the rectified output is 583V direct current.

The busbars of the two rectification circuits are directly connected in parallel, that is, the output terminals of the first rectification circuit and the second rectification circuit are connected in parallel, and then the filter capacitor element is connected to form a loop.

In this embodiment, because the bus voltage is relatively high, the first capacitor C1 and the second capacitor C2 are connected in series, and the first voltage equalizing resistor L1 and the second voltage equalizing resistor L2 are added in order to prevent uneven voltage division of the two capacitors. The equalizing resistor L1 is connected in parallel with the first capacitor C1, and the second equalizing resistor L2 is connected in parallel with the second capacitor C2.

In this embodiment, the two ends of the filter energy storage element are respectively connected to the first power conversion circuit and the second power conversion circuit, and the DC voltage is converted into an AC voltage in the form of a square wave. As shown in Figure 1, the first power conversion circuit includes a PWM The control chip, the switch tube K1, the switch tube K2 and the transformer, the second power conversion circuit PWM control chip, the switch tube K3, the switch tube K4 and the transformer, and the switch tube K1 are respectively connected with the PWM control chip and the filter storage in the first power conversion circuit The two ends of the energy element are connected, the switch tube K2 is respectively connected with the PWM control chip in the first power conversion circuit and the two ends of the filter energy storage element; the switch tube K3 is respectively connected with the PWM control chip and the filter energy storage element in the second power conversion circuit The two ends of the energy storage element are connected, and the switch tube K4 is respectively connected with the PWM control chip in the first power conversion circuit and the two ends of the filter energy storage element.

The switch tube may be, but not limited to, a MOS tube.

The transformer in the first power conversion circuit in this embodiment includes a primary side and a secondary side, the first input terminal of the primary side is connected to one end of the filter energy storage element through the switch tube K1, and the second input terminal of the primary side is connected to one end of the filter energy storage element through the switch The tube K2 is connected with the other end of the filter energy storage element.

The transformer in the second power conversion circuit in this embodiment includes a primary side and a secondary side, the first input terminal of the primary side is connected to one end of the filter energy storage element through the switch tube K3, and the second input terminal of the primary side is connected to one end of the filter energy storage element through the switch The tube K4 is connected with the other end of the filter energy storage element.

The PWM chip in the first power conversion circuit controls the switching tube K1 to be turned on or off by sending out a PWM pulse signal, and controls the switching tube K2 to be turned off or on, so as to control the transformer to transfer the voltage input from the primary side to the secondary side and output it.

The PWM chip in the second power conversion circuit controls the switch tube K3 to be turned on or off by sending out a PWM pulse signal, and controls the switch tube K4 to be turned off or on, so as to control the transformer to transfer the voltage input from the primary side to the secondary side and output it.

As shown in Figure 1, in the first power conversion circuit, the end of the switch tube K1 connected to the primary side can also be connected to one end of the filter energy storage element through the diode d1, and the end of the switch tube K2 connected to the primary side can also be It is connected to one end of the filter energy storage element through a diode d2. In the second power conversion circuit, the end of the switch tube K1 connected to the primary side can also be connected to one end of the filter energy storage element through the diode d4, and the end of the switch tube K4 connected to the primary side can also be connected to the filter storage element through the diode d5. One end of the energy element is connected. Diodes d1 and d2 are clamping diodes, which work when the reverse voltage is high, and limit the reverse voltage of the switch tubes K1 and K2 to the bus voltage to prevent damage to the MOS tubes, that is, loss of the switch tubes K1 and K2. Diodes d4 and d5 are clamping diodes, which work when the reverse voltage is high, and limit the reverse voltage of the switch tubes K3 and K4 to the bus voltage to prevent damage to the MOS tubes, that is, mode loss switch tubes K3 and K4.

In the first power conversion circuit, the secondary side of the transformer can be connected to a diode d3 connected in series with the load, and then connected to a capacitive element connected in parallel with the load. In the second power conversion circuit, the secondary side of the transformer can be connected to A diode d6 connected in series with the load, and a capacitive element connected in parallel with the load.

Preferably, the output terminal of the first power conversion circuit is connected to the load through a diode d7 connected in series with the load, and the output terminal of the second power conversion circuit is connected to the load through a diode d8 connected in series with the load.

Before the output terminals of the first power conversion circuit and the second power conversion circuit are connected to the load, they are both connected to a capacitive element C3 connected in parallel with the load.

The output terminal, that is, the voltage output at both ends of C3 can be any voltage value, and there is no given value at present, and the function of C3 is filtering and energy storage.

In the embodiment of the present invention, the mains power supply 380Vac and the secondary winding 380Vac are two mutually independent power sources, respectively passing through two rectification circuits, the rectified busbars are directly connected in parallel, and the two independent power supplies are connected in parallel to the rectified busbars. The output of the switching power supply uses diodes as backup for each other, and the dual power supplies supply power to the load at the same time. When a power supply fails, it can realize non-disruptive switching to ensure the stability of the control power supply.

Example 2

The difference between the embodiment of the present invention and embodiment 1 is that the number of secondary sides in the transformer is 2, as shown in Figure 2, wherein K1 is the primary side of the transformer, K2 is the secondary side circuit of the transformer, and K3 is the diode thermal redundancy output circuit . That is, when the transformer has multiple secondary sides, one secondary side in the first power conversion circuit and one secondary side in the second power conversion circuit are simultaneously connected to the load via diodes. For a power conversion circuit with multiple secondary sides, multiple loads can be powered.

The number of circuits of K2 can be 1, 2, 3 and so on.

The K2 circuits can be in a non-isolated multi-tap mode, or in a mutual isolation mode, and this embodiment adopts a mutual isolation mode.

The number of bus capacitors connected in series is determined according to the bus voltage behind the rectifier bridge. In this embodiment, two capacitors are connected in series.

The working process of this embodiment is basically the same as that of Embodiment 1, except that the number of outputs can be two, and the specific power supply process will not be described in detail here.

Example 3

As shown in Figure 3, the difference between this embodiment and Embodiment 2 is that the first AC input power supply is a 220V power supply provided by the mains, and the voltage of the second AC input power supply is provided by the high voltage generated by the high voltage inverter through the auxiliary winding. 220V power supply, two 220V power supplies must be the same phase power supply. The filtering energy storage element is a capacitive element, and there is no need to connect resistors in parallel at both ends of the capacitor.

After the two-way power supply passes through the lightning protection circuit and rectifier circuit, the busbars are directly connected in parallel. The voltage on the busbar is 450V. Since the busbar voltage is low, a common capacitor below 450V can be used. The output of the high-frequency transformer directly connected in parallel to the current source busbar passes through two The diodes are connected in parallel and output to the load.

Among them, K1 is the primary side of the high-frequency transformer, K2 is the secondary side circuit of the high-frequency transformer, and K3 is the diode thermal redundancy output circuit.

The number of circuits of K2 can be 1, 2, 3..., and the number of K2 in this embodiment is 2.

Preferably, an analog detection circuit can be connected in parallel between the output terminals of the two power supplies to detect the state of the switching power supply in real time, and the fault status of the output of the two switching power supplies is provided to the main control of the high-voltage frequency converter after passing through the AND gate. If a certain output of a switch fails, the detection circuit will send a fault signal to the main control to provide an alarm or protection.

The embodiment provided by the present invention greatly simplifies the system configuration. The contactor for high and low voltage switching, the battery or capacitor used to maintain the switching time is removed, and the electrical components required for the power switching time are saved. Due to the adoption of the busbar parallel current source mode behind the rectifier bridge, the reliability of the system power supply is greatly improved. Due to the redundant design of hot backup, the system can use two power supplies in parallel to supply power to the load at the same time. When any one power supply fails or the power supply is lost, it can ensure that there is no power failure during power switchover and realize seamless switchover. . The adoption of this system improves the reliability of the system on the basis of reducing the system cost.

Obviously, those skilled in the art can make various changes and modifications to the present invention without departing from the spirit and scope of the present invention. Thus, if these modifications and variations of the present invention fall within the scope of the claims of the present invention and their equivalent technologies, the present invention also intends to include these modifications and variations.

Claims (10)

1. An auxiliary power supply circuit for a high-voltage frequency converter, characterized in that it comprises a first AC input power supply, a second AC input power supply, a first rectifier circuit, a second rectifier circuit, a filter energy storage element, a first power conversion circuit and The second power conversion circuit, wherein: The first AC input power supply is connected to the first rectifier circuit, and the first AC input power supply outputs AC power, which is rectified into DC power by the first rectifier circuit and output; The second AC input power supply is connected to the second rectifier circuit, and the second AC input power supply outputs AC power, which is rectified into DC power by the second rectifier circuit and output; The output terminal of the first rectification circuit is connected in parallel with the output terminal of the second rectification circuit, and the output terminal is connected with the filter energy storage element to form a first loop, and the output terminal is output by the filter energy storage element direct current for energy storage and filtering; The filter energy storage element is respectively connected with the first power conversion circuit to form a second loop, and connected with the second power conversion circuit to form a third loop, and the first power conversion circuit and the second power conversion circuit are used for Respectively convert the direct current at both ends of the filter energy storage element into alternating voltage; The output terminals of the first power conversion circuit and the second power conversion circuit are respectively connected to the load, and supply power to the load at the same time. 2. The circuit of claim 1, wherein The voltage of the first AC input power supply is 220V, the voltage of the second AC input power supply is 220V, the second AC input power supply is provided by the auxiliary winding of the rectifier transformer in the high-voltage frequency converter, and the first AC input power supply and The voltage phases of the second AC input power supply are the same; The first AC input power supply is a 380V power supply provided by the mains, and the voltage of the second AC input power supply is a 380V power supply provided by a high voltage frequency converter through an auxiliary winding. 3. The circuit of claim 1, wherein The first rectification circuit and/or the second rectification circuit is a rectification bridge; or The first rectification circuit and/or the second rectification circuit is a rectification circuit composed of four diodes. 4. The circuit of claim 1, wherein The filtering energy storage element is a capacitive element, or two capacitive elements connected in series. 5. The circuit according to claim 4, wherein when the filter energy storage element is two capacitor elements connected in series, the circuit further comprises: A voltage equalizing resistor connected in parallel across each capacitive element. 6. The circuit according to claim 1, wherein the first power conversion circuit or the second power conversion circuit comprises a PWM control chip, a first switch tube, a second switch tube and a transformer, wherein: The transformer includes a primary side and at least one secondary side, the first input end of the primary side is connected to one end of the filter energy storage element through the first switch tube, and the second input end of the primary side is connected to the filter energy storage element through the second switch tube The other end of the component is connected; The first switching tube is respectively connected to both ends of the PWM control chip and the filter energy storage element; The second switching tube is respectively connected to both ends of the PWM control chip and the filtering energy storage element; The PWM chip controls the first switch tube K1 to be turned on or off by sending out a PWM pulse signal, and controls the second switch tube K2 to be turned off or turned on; The transformer is used to transfer the voltage input from the primary side to each secondary side and output it. 7 . The circuit according to claim 6 , wherein the transformer comprises multiple secondary sides, and the multiple secondary sides are mutually isolated or non-isolated multi-tap. 8 . 8. The circuit according to claim 1, wherein the output ends of the first power conversion circuit and the second power conversion circuit are respectively connected to the load through a diode connected in series with the load. 9. The circuit according to claim 1, wherein the output ends of the first power conversion circuit and the second power conversion circuit are both connected to a capacitive element connected in parallel with the load. 10. The circuit according to claim 1, further comprising a first lightning protection circuit and a first EMC filter circuit, a second lightning protection circuit and a second EMC filter circuit, wherein: After the first lightning protection circuit and the first EMC filter circuit are connected in series, they are connected between the first AC input power supply and the first rectification circuit; After the second lightning protection circuit and the second EMC filter circuit are connected in series, they are connected between the second AC input power supply and the second rectification circuit.