Converter soft start device, control method and computer readable storage medium

Abstract

The invention provides a converter soft start device, a control method and a computer readable storage medium. The soft start device further comprises a pre-charging loop, a first contactor, an MOSFET power tube and a soft start control unit. The pre-charging loop is connected in series to the positive direct current bus; the first contactor, the MOSFET power tube and the pre-charging loop are connected in parallel; the soft start control unit is connected with the control end of the first contactor through a first output end and connected with the control end of the MOSFET power tube through a second output end, and the soft start control unit is used for outputting a driving voltage with a gradually increasing amplitude to the MOSFET power tube after the pre-charging of the pre-charging loop is completed, and outputting the driving voltage to the MOSFET power tube. The MOSFET power tube is enabled to gradually enter an amplification region from a cut-off region, and after the MOSFET power tube enters a saturated conduction state, a signal enabling the first contactor to be conducted is output. According to the invention, no secondary impact current occurs in the closing process of the main contactor, and the safety of the system is improved.

Description

Technical Field

[0001] The present invention relates to the field of power electronic equipment, and more specifically, to a converter soft starting device and a control method. Background Art

[0002] A converter is a power electronic device that converts one voltage / current into another voltage / current. It includes three types: rectifier, inverter and DC-DC converter. It is currently widely used in high-frequency switching power supplies, uninterruptible power supplies, wind power converters and energy storage converters.

[0003] The converters in the above devices usually adopt the BOOST boost circuit topology based on IGBT or MOSFET, and the DC output needs to be filtered by a large-capacity DC capacitor (i.e., DC bus capacitor). Before the converter is powered on, there is no voltage on the DC bus capacitor; after the AC input is powered on, the AC power is first rectified by the anti-parallel diode of the IGBT or MOSFET of the converter and then directly reaches the DC bus capacitor. At this time, the DC bus is equivalent to a short circuit, which will cause a huge impact current on the AC input side, often causing damage to the power devices of the converter and tripping of the front-end AC power distribution switch. At present, in order to solve the above problems, Figure 1 As shown, a soft start circuit 10 is usually designed on the AC input side of the converter. The soft start circuit 10 uses a contactor in series with a current limiting resistor to suppress the inrush current when the AC input is powered on, and accurately limits the input inrush current by adjusting the resistance value of the soft start.

[0004] However, since there are usually certain loads on the DC bus of the converter, such as the voltage-equalizing resistor of the DC bus capacitor, the DC bus discharge resistor, and the circuit board that draws power from the DC bus, even after the soft start circuit reaches the soft start steady state, there is still a certain steady-state current to provide energy for the auxiliary load on the DC bus, so there is a certain voltage drop in the current limiting resistor in the soft start circuit. In this case, when the main contactor is closed to end the soft start process, a large secondary impact current will be generated when the main contactor is closed due to the voltage difference, which may cause damage to the IGBT / MOSFET power devices of the converter in severe cases. Summary of the invention

[0005] The technical problem to be solved by the present invention is that, in view of the problem that the soft start circuit connected to the AC side of the converter still generates secondary shock due to the existence of the DC bus load when the main contactor is closed, a converter soft start device, a control method and a computer-readable storage medium are provided.

[0006] The technical solution of the present invention to solve the above technical problems is to provide a converter soft-start device, wherein the converter includes a positive DC bus, a negative DC bus, a DC bus capacitor and a DC load powered by the DC bus, and the soft-start device also includes a pre-charge circuit, a first contactor, a MOSFET power tube and a soft-start control unit; the pre-charge circuit is connected in series to the positive DC bus, and the pre-charge circuit is located in the front stage of the DC bus capacitor; the first contactor, the MOSFET power tube and the pre-charge circuit are connected in parallel;

[0007] The soft start control unit includes a first output end and a second output end, and is connected to the control end of the first contactor through the first output end and to the control end of the MOSFET power tube through the second output end. The soft start control unit is used to output a driving voltage with a gradually increasing amplitude to the MOSFET power tube through the second output end after the pre-charging of the pre-charging loop is completed, so that the MOSFET power tube gradually enters the amplification area from the cut-off area, and after the MOSFET power tube enters the saturated conduction state, output a signal to turn on the first contactor through the first output end.

[0008] As a further improvement of the present invention, the pre-charging circuit includes a pre-charging current limiting resistor and a second contactor connected in series, and the MOSFET power tube is connected in parallel with the pre-charging current limiting resistor, and the first contactor is connected in parallel with the series-connected pre-charging current limiting resistor and the second contactor;

[0009] The soft start control unit includes a third output terminal, and is connected to the control terminal of the second contactor via the third output terminal.

[0010] As a further improvement of the present invention, the soft start control unit includes a voltage detection terminal electrically connected to the positive DC bus, and the connection point between the voltage detection terminal and the positive DC bus is located at the rear stage of the DC bus capacitor;

[0011] The soft start control unit controls the driving voltage output by the second output terminal to make the slope of the voltage rise at the voltage detection terminal smaller than a preset slope before the MOSFET power tube reaches a saturated conduction state.

[0012] As a further improvement of the present invention, the soft start control unit outputs a signal through the second output terminal to turn on the second contactor, so that the pre-charging circuit enters a pre-charging state.

[0013] As a further improvement of the present invention, the soft start control unit confirms that the pre-charging of the pre-charging loop is completed when the voltage at the voltage detection end reaches a first preset voltage.

[0014] As a further improvement of the present invention, the soft start control unit confirms that the MOSFET power tube enters a saturated conduction state when the voltage at the voltage detection end reaches a second preset voltage.

[0015] As a further improvement of the present invention, after the soft start control unit outputs a signal to turn on the first contactor through the first output terminal, it outputs a driving voltage to turn off the MOSFET power tube through the second output terminal, and outputs a voltage to turn off the second contactor through the third output terminal.

[0016] As a further improvement of the present invention, the DC load is one or more of the following: a control power supply, a fan, a voltage-equalizing resistor on a DC bus, and a bleeder resistor.

[0017] The present invention also provides a control method for the converter soft start device as described above, the method comprising:

[0018] After the pre-charging of the pre-charging loop is completed, a driving voltage with a gradually increasing amplitude is output to the MOSFET power tube, so that the MOSFET power tube gradually enters the amplification region from the cut-off region;

[0019] After the MOSFET power tube enters a saturated conduction state, a signal is outputted to turn on the first contactor.

[0020] The present invention also provides a computer-readable storage medium, on which a computer program is stored. When the computer program is executed by a processor, the steps of the control method described above are implemented.

[0021] The present invention has the following beneficial effects: by controlling the driving voltage of the MOSFET power tube connected in parallel with the pre-charging circuit, no secondary impact current will occur during the closing process of the main contactor, thereby improving the safety of the system. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 It is a schematic diagram of an existing soft start circuit applied to a converter.

[0023] Figure 2 Schematic diagram of a converter soft start device provided by an embodiment of the present invention applied to a converter.

[0024] Figure 3 It is a flow chart of a control method of a converter soft start device provided in an embodiment of the present invention. DETAILED DESCRIPTION

[0025] In order to make the purpose, technical solution and advantages of the present invention more clearly understood, the present invention is further described in detail below in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not intended to limit the present invention.

[0026] like Figure 2 As shown, it is a schematic diagram of the converter soft start device provided by an embodiment of the present invention applied to a converter, the converter may be an inverter or a similar device, and the converter includes a positive DC bus DC+, a negative DC bus DC-, DC bus capacitors C3, C4 (the DC bus capacitors C3, C4 are connected in series between the positive DC bus DC+ and the negative DC bus DC-, and in practical applications a single capacitor or more capacitors connected in series may be used) and a DC load powered by the DC bus, wherein the DC load may specifically be a control power supply (for example, an auxiliary power supply circuit board), a fan, a voltage equalizing resistor connected between the positive DC bus DC+ and the negative DC bus DC-, a discharge resistor, etc.

[0027] The converter soft-start device of this embodiment also includes a pre-charging circuit 21, a first contactor KM1, a MOSFET power tube Q1 and a soft-start control unit 22, wherein the pre-charging circuit 21 is connected in series to the positive DC bus DC+, and the pre-charging circuit 21 is located in the front stage of the DC bus capacitor, that is, the current from the current source (such as a rectifier, a DC power supply) first flows through the pre-charging circuit 21 and then flows into the DC bus capacitors C3 and C4; the first contactor KM1 and the MOSFET power tube Q1 are both connected in parallel to the pre-charging circuit 21. The above-mentioned pre-charging circuit 21, the first contactor KM1, the MOSFET power tube Q1, etc. can all adopt conventional devices in the field, which will not be repeated here.

[0028] The soft start control unit 22 can adopt a control chip, or can be composed of a control chip and a peripheral circuit. The soft start control unit 22 includes a first output end and a second output end, and is connected to the control end of the first contactor KM1 (i.e., the control loop for controlling the conduction and disconnection of the coil) through the first output end, and is connected to the control end of the MOSFET power tube Q1 (i.e., the gate) through the second output end, that is, the soft start control unit 22 can output different signals to the first contactor KM1 through the first output end to turn the first contactor KM1 on or off, and can output different control signals to the MOSFET power tube Q1 through the second output end to make the MOSFET power tube Q1 in the cut-off area, the amplification area, the saturation conduction area, etc.

[0029] The soft start control unit 22 is used to output a driving voltage Vgs with a gradually increasing amplitude to the MOSFET power tube Q1 through the second output terminal after the pre-charging of the pre-charging loop 22 is completed, so that the MOSFET power tube Q1 gradually enters the amplification zone from the cut-off zone. Since the gate driving voltage Vgs of the MOSFET power tube is proportional to the equivalent resistance Rds of the MOSFET power tube in the amplification zone, the equivalent resistance of the MOSFET power tube is controlled by controlling the driving voltage Vgs, and the MOSFET power tube enters the amplification zone from the cut-off zone by increasing the driving voltage Vgs. The equivalent resistance Rds continues to decrease, thereby gradually reducing the voltage at both ends of the MOSFET power tube Q1 by reducing the equivalent resistance of the MOSFET power tube Rds. Since the MOSFET power tube Q1 is connected in parallel with the pre-charging loop, the voltage drop at both ends of the pre-charging loop is also gradually reduced until the MOSFET power tube Q1 enters the saturated conduction zone. After the MOSFET power tube Q1 enters the conduction saturation zone, the soft start control unit 22 outputs a signal to turn on the first contactor KM1 through the first output terminal, thereby completing the start-up of the converter.

[0030] The converter soft start device controls the driving voltage of the MOSFET power tube Q1 connected in parallel with the pre-charging circuit 21 so that no secondary impact current occurs during the closing process of the main contactor (ie, the first contactor KM1), thereby improving the safety of the system.

[0031] In one embodiment of the present invention, the above-mentioned pre-charging circuit 21 includes a pre-charging current limiting resistor Rs and a second contactor KM2, which are connected in series on the positive DC bus DC+ and are located in the front stage of the DC bus capacitor. The MOSFET power tube Q1 is connected in parallel with the pre-charging current limiting resistor Rs, and the first contactor KM1 is connected in parallel with the series-connected pre-charging current limiting resistor Rs and the second contactor KM2. Correspondingly, the soft start control unit 22 includes a third output terminal, and is connected to the control terminal of the second contactor KM2 (i.e., the control circuit for controlling the conduction and disconnection of the coil) through the third output terminal, that is, the soft start control unit 22 can output different signals to the second contactor KM2 through the second output terminal to turn on or off the second contactor KM2.

[0032] Specifically, when the converter starts, the soft start control unit 22 outputs a signal through the second output terminal to turn on the second contactor KM2, so that the pre-charging circuit 21 enters the pre-charging state; and when the converter soft start is completed, the soft start control unit 22 outputs a signal through the second output terminal to turn off the second contactor KM2. The second contactor KM2 and the pre-charging current limiting resistor Rs can suppress the impact current when the AC input is powered on.

[0033] In one embodiment of the present invention, the soft start control unit 22 includes a voltage detection terminal electrically connected to the positive DC bus, and a connection point between the voltage detection terminal and the positive DC bus DC+ is located at a subsequent stage of the DC bus capacitor.

[0034] Before the MOSFET power tube Q1 enters the saturated conduction region, the soft start control unit 22 controls the driving voltage output by the second output terminal so that the slope of the voltage rise at the voltage detection terminal is less than the preset slope. The preset slope K1 can be set according to the use scenario of the converter soft start device. For example, the smaller the starting impact current requirement of the converter startup input and the slower the current rise, the smaller the preset slope K1 can be set. For example, for medical power supply equipment, the preset slope K1 is relatively small.

[0035] During the period when the soft start control unit 22 adjusts the driving voltage Vgs of the MOSFET power tube Q1 connected in parallel with the pre-charge current limiting resistor Rs, the soft start control unit 22 continuously detects the rising slope Kbus of the DC bus voltage through the voltage detection terminal, and adjusts the rising slope Kbus of the DC bus voltage to be less than the preset slope K1 by controlling the rising slope of the driving voltage Vgs of the MOSFET power tube Q1, thereby limiting the excessive impact current during the second stage soft start. As the driving voltage Vgs rises to a certain value, the MOSFET power tube Q1 enters a saturated conduction state, and the equivalent resistance Rds is almost zero. At this time, the equivalent resistance R of the MOSFET power tube Q1 is After ds is connected in parallel with the pre-charge current limiting resistor Rs, its resistance is almost zero. Even if the DC load on the DC bus of the converter draws a certain current from the input end and flows through the parallel MOSFET power tube Q1 and the pre-charge current limiting resistor Rs, the MOSFET power tube Q1 has entered the saturated conduction state at this time, so the voltage drop of the pre-charge current limiting resistor Rs is also approximately 0. At this time, the soft start control unit 22 determines that the soft start process is over. When the first contactor KM1 is closed again, since the voltage drop of the circuit in parallel with the first contactor KM1 is approximately zero, the closing of the first contactor KM1 will not cause secondary impact current, which solves the problem of the traditional soft start circuit.

[0036] In one embodiment of the present invention, the soft start control unit 22 confirms whether the pre-charging circuit is pre-charged through the voltage of the voltage detection terminal. For example, the soft start control unit 22 can confirm that the pre-charging circuit 21 is pre-charged and enters a steady state when the voltage of the voltage detection terminal reaches a first preset voltage (at this time, the voltage drop △U across the first contactor KM1 is less than a preset threshold value Us1). Specifically, the above-mentioned first preset voltage can be set according to the use occasion of the converter.

[0037] Similarly, the soft start control unit 22 can also confirm whether the MOSFET power tube Q1 enters the saturated conduction region through the voltage at the voltage detection terminal. For example, the soft drive control unit 22 can confirm that the MOSFET power tube Q1 enters the saturated conduction state when the voltage at the voltage detection terminal reaches the second preset voltage (at this time, the voltage drop △U across the first contactor KM1 is less than the preset threshold value Us2). Specifically, the second preset voltage can be set according to the use occasion of the converter, and the value of the second preset voltage is greater than the value of the first preset voltage.

[0038] like Figure 3 As shown, the present invention also provides a control method for the converter soft start device as described above, the control method can be executed by the soft start control unit as described above, and the method includes:

[0039] Step S31: after the pre-charging of the pre-charging loop is completed, a driving voltage with a gradually increasing amplitude is output to the MOSFET power tube, so that the MOSFET power tube gradually enters the amplification region from the cut-off region;

[0040] Step S32: after the MOSFET power tube enters the saturated conduction state, output a signal to turn on the first contactor.

[0041] The control method of the converter soft start device in this embodiment is similar to the above Figure 2 The converter soft start device in the corresponding embodiment belongs to the same concept, and its specific implementation process is detailed in the corresponding device embodiment, and the technical features in the device embodiment are applicable to the method embodiment, which will not be repeated here.

[0042] In view of the soft-start current limiting resistor with a fixed resistance value used in the traditional soft-start circuit, the DC bus of the power electronic converter generally has power-consuming auxiliary circuits and loads (for example, the control power supply, fans and other auxiliary devices draw power from the DC bus, and the DC bus also has voltage-equalizing resistors and discharge resistors). After the first stage of precharging of the soft-start current limiting resistor reaches a steady state, these auxiliary circuits and loads will still draw a certain current from the input end, resulting in a voltage drop on the soft-start current limiting resistor, and usually there will be a voltage drop of tens of volts. At this time, closing the main contactor will cause the input power amplitude to still be tens of volts higher than the DC bus voltage, resulting in a secondary impact current, which seriously threatens the safety of the anti-parallel diodes of power devices such as the converter IGBT and MOSFET, and easily causes the problem of device damage. The above converter soft-start device and control method use MOSFET to The equivalent resistance Rds of the ET power tube is controlled by the amplitude of the driving voltage Vgs. By connecting the MOSFET power tube in parallel at both ends of the pre-charging current limiting resistor, after the first stage of soft start ends (that is, the pre-charging of the pre-charging loop reaches a steady state), the soft start control unit slowly adjusts the voltage value of the MOSFET power tube driving voltage Vgs, and continuously reduces the equivalent resistance Rds of the power MOSFET power tube, so that the resistance of the total current limiting resistor of the soft start loop slowly decreases from a fixed value Rs to 0, thereby achieving zero voltage drop in the soft start loop. In this process, the slope of the DC bus voltage rise is detected and compared with the preset slope. By adjusting the rising slope of the driving Vgs driving voltage, the DC bus voltage rising slope Kbus is always controlled within the preset slope range, thereby avoiding the occurrence of impact current during the second stage of soft start.

[0043] The present invention also provides a computer-readable storage medium, on which a computer program is stored. When the computer program is executed by a processor, the steps of the control method of the converter soft start device as described above are implemented.

[0044] The computer-readable storage medium in this embodiment is the same as the above Figure 2 The converter soft start device in the corresponding embodiment belongs to the same concept, and its specific implementation process is detailed in the corresponding device embodiment, and the technical features in the device embodiment are applicable in this storage medium embodiment, which will not be repeated here.

[0045] It should be understood that the size of the serial numbers of the steps in the above embodiments does not mean the order of execution. The execution order of each process should be determined by its function and internal logic, and should not constitute any limitation on the implementation process of the embodiments of the present application.

[0046] Those skilled in the art can clearly understand that, for the convenience and simplicity of description, only the division of the above-mentioned functional units and modules is used as an example for illustration. In actual applications, the above-mentioned functions can be assigned to different functional units and modules as needed. The functional units and modules in the embodiments can be integrated into a processor, or each unit can exist physically separately, or two or more units can be integrated into one unit. The above-mentioned integrated units can be implemented in the form of hardware or in the form of software functional units. In addition, the specific names of the functional units and modules are only for the convenience of distinguishing each other, and are not used to limit the scope of protection of this application. The specific working process of the units and modules in the above-mentioned system can refer to the corresponding process in the aforementioned method embodiment, which will not be repeated here.

[0047] In the above embodiments, the description of each embodiment has its own emphasis. For parts that are not described or recorded in detail in a certain embodiment, reference can be made to the relevant descriptions of other embodiments.

[0048] Those of ordinary skill in the art will appreciate that the units and algorithm steps of each example described in conjunction with the embodiments disclosed herein can be implemented in electronic hardware, or a combination of computer software and electronic hardware. Whether these functions are performed in hardware or software depends on the specific application and design constraints of the technical solution. Professional and technical personnel can use different methods to implement the described functions for each specific application, but such implementation should not be considered to be beyond the scope of this application.

[0049] In the embodiments provided in the present application, it should be understood that the disclosed converter soft start device and control method can be implemented in other ways. For example, the control method embodiment of the converter soft start device described above is only illustrative.

[0050] In addition, each functional unit in each embodiment of the present application may be integrated into one processor, or each unit may exist physically separately, or two or more units may be integrated into one unit. The above integrated unit may be implemented in the form of hardware or in the form of software functional units.

[0051] If the integrated module / unit is implemented in the form of a software functional unit and sold or used as an independent product, it can be stored in a computer-readable storage medium. Based on this understanding, the present application implements all or part of the processes in the above-mentioned embodiment method, and can also be completed by instructing the relevant hardware through a computer program. The computer program can be stored in a computer-readable storage medium, and the computer program can implement the steps of the above-mentioned various method embodiments when executed by the processor. Among them, the computer program includes computer program code, and the computer program code can be in source code form, object code form, executable file or some intermediate form. The computer-readable medium may include: any entity or interface switching device that can carry the computer program code, recording medium, U disk, mobile hard disk, disk, optical disk, computer memory, read-only memory (ROM), random access memory (RAM), electrical carrier signal, telecommunication signal and software distribution medium, etc.

[0052] The embodiments described above are only used to illustrate the technical solutions of the present application, rather than to limit them. Although the present application has been described in detail with reference to the aforementioned embodiments, a person skilled in the art should understand that the technical solutions described in the aforementioned embodiments may still be modified, or some of the technical features may be replaced by equivalents. Such modifications or replacements do not deviate the essence of the corresponding technical solutions from the spirit and scope of the technical solutions of the embodiments of the present application, and should all be included in the protection scope of the present application.

Claims

1. A converter soft start device, the converter comprising a positive DC bus, a negative DC bus, a DC bus capacitor and a DC load powered by the DC bus, characterized in that: The soft start device further includes a pre-charging circuit, a first contactor, a MOSFET power tube and a soft start control unit; the pre-charging circuit is connected in series to the positive DC bus, and the pre-charging circuit is located in the front stage of the DC bus capacitor; the first contactor, the MOSFET power tube and the pre-charging circuit are connected in parallel; The soft start control unit includes a first output end and a second output end, and is connected to the control end of the first contactor through the first output end and to the control end of the MOSFET power tube through the second output end. The soft start control unit is used to output a driving voltage with a gradually increasing amplitude to the MOSFET power tube through the second output end after the pre-charging of the pre-charging loop is completed, so that the MOSFET power tube gradually enters the amplification area from the cut-off area, and after the MOSFET power tube enters the saturated conduction state, output a signal to turn on the first contactor through the first output end.

2. The converter soft start device according to claim 1, characterized in that: The pre-charging circuit comprises a pre-charging current limiting resistor and a second contactor connected in series, and the MOSFET power tube is connected in parallel with the pre-charging current limiting resistor, and the first contactor is connected in parallel with the pre-charging current limiting resistor and the second contactor connected in series; The soft start control unit includes a third output terminal, and is connected to the control terminal of the second contactor via the third output terminal.

3. The converter soft start device according to claim 2, characterized in that: The soft start control unit comprises a voltage detection terminal electrically connected to the positive DC bus, and a connection point between the voltage detection terminal and the positive DC bus is located at a rear stage of the DC bus capacitor; The soft start control unit controls the driving voltage output by the second output terminal to make the slope of the voltage rise at the voltage detection terminal smaller than a preset slope before the MOSFET power tube reaches a saturated conduction state.

4. The converter soft start device according to claim 3, characterized in that: The soft start control unit outputs a signal through the second output terminal to turn on the second contactor, so that the pre-charging circuit enters the pre-charging state.

5. The converter soft start device according to claim 3, characterized in that: The soft start control unit confirms that the pre-charging of the pre-charging loop is completed when the voltage at the voltage detection terminal reaches a first preset voltage.

6. The converter soft start device according to claim 3, characterized in that: The soft start control unit confirms that the MOSFET power tube enters a saturated conduction state when the voltage at the voltage detection terminal reaches a second preset voltage.

7. The converter soft start device according to claim 2, characterized in that: After the soft start control unit outputs a signal to turn on the first contactor through the first output terminal, it outputs a driving voltage to turn off the MOSFET power tube through the second output terminal, and outputs a voltage to turn off the second contactor through the third output terminal.

8. The converter soft start device according to claim 6, characterized in that: The DC load is one or more of the following: a control power supply, a fan, a voltage-equalizing resistor on a DC bus, and a discharge resistor.

9. A control method for a converter soft start device according to any one of claims 1 to 8, the method comprising: After the pre-charging of the pre-charging loop is completed, a driving voltage with a gradually increasing amplitude is output to the MOSFET power tube, so that the MOSFET power tube gradually enters the amplification region from the cut-off region; After the MOSFET power tube enters a saturated conduction state, a signal is outputted to turn on the first contactor.

10. A computer-readable storage medium, characterized in that: The storage medium stores a computer program, and when the computer program is executed by the processor, the steps of the control method as claimed in claim 9 are implemented.

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