Pre-charging device and cascaded frequency converter

Abstract

The utility model provides a pre-charging device and a cascaded frequency converter. The pre-charging device is used for the cascaded frequency converter. The cascaded frequency converter comprises a plurality of power unit groups, each power unit group comprises a plurality of cascaded power units, each power unit comprises a capacitor, and the capacitor is connected with a direct current bus of the power unit. The pre-charging device comprises a boosting transformer, the boosting transformer comprises a first output end, a second output end, a first input end and a second input end, and the first output end can be connected with a neutral point of the output end of the cascaded frequency converter; the second output end can be connected with one phase output end of the cascaded frequency converter; the first input end and the second input end can be connected with a power supply so as to pre-charge the capacitor. The pre-charging device can pre-charge the capacitor of the power unit, reduce surge current at the moment of high voltage on the cascaded frequency converter, reduce thermal stress and mechanical stress generated by electrodynamic force, improve safety and reliability of the cascaded frequency converter, optimize device type selection and reduce cost.

Description

Technical Field

[0001] This utility model generally relates to the field of pre-charging technology, and in particular to a pre-charging device and a cascaded frequency converter. Background Technology

[0002] A variable-frequency drive (VFD) is a power control device that controls a motor by changing the frequency and amplitude of its output voltage. VFDs are widely used in applications such as fans, pumps, belt conveyors, and laboratory power supplies. Some existing cascaded VFDs cannot pre-charge their power units, which can easily lead to excessive inrush current and damage upon power-up. While some cascaded VFDs can pre-charge their power units, this is costly. Therefore, there is an urgent need for a device that can pre-charge cascaded VFDs, improving their safety and reliability while reducing costs.

[0003] The content of the background section is merely the technology known to the inventor and does not necessarily represent the prior art in this field. Utility Model Content

[0004] To address one or more of the problems existing in the prior art, this utility model provides a pre-charging device for a cascaded frequency converter. The cascaded frequency converter includes multiple power unit groups, each power unit group including multiple cascaded power units, and each power unit including a capacitor connected to the DC bus of the power unit. The pre-charging device includes a step-up transformer, which includes a first output terminal, a second output terminal, a first input terminal, and a second input terminal. The first output terminal can be connected to the neutral point of the output terminal of the cascaded frequency converter; the second output terminal can be connected to one phase output terminal of the cascaded frequency converter; the first input terminal and the second input terminal can be connected to a power supply to pre-charge the capacitor.

[0005] Optionally, the pre-charging device further includes: a first switch connected to the first input terminal and the power supply, and a second switch connected to the second input terminal and the power supply, wherein the first switch and the second switch are turned on, and the power supply pre-charges the capacitor.

[0006] Optionally, the pre-charging device further includes a control module, which is connected to the first switch and the second switch and controls the on / off state of the first switch and the second switch.

[0007] Optionally, the power unit includes a control unit connected to the capacitor and the control module, which can monitor the charging time and / or voltage of the capacitor and communicate the charging time and / or voltage to the control module; the control module controls the on / off state of the first switch and the second switch based on the charging time and / or voltage.

[0008] Optionally, the pre-charging device further includes: a control module, a third switch, and a fourth switch. The third switch is connected to the first output terminal of the step-up transformer and the neutral point. The fourth switch is connected to the second output terminal of the step-up transformer and one of the phase output terminals. The third switch and the fourth switch are also connected to the control module, which can control the on / off state of the third switch and the fourth switch.

[0009] Optionally, the pre-charging device further includes: a first current limiting module and / or a second current limiting module, wherein the first current limiting module is connected to the first input terminal and the second input terminal of the step-up transformer and the power supply; the second current limiting module is connected to the first output terminal and the second output terminal of the step-up transformer, the neutral point and one of the phase output terminals.

[0010] Optionally, the pre-charging device further includes a voltage acquisition module and a control module. The voltage acquisition module is connected to the first and second input terminals of the step-up transformer and the control module. The control module can detect the input voltage of the step-up transformer and / or the output voltage of the cascaded frequency converter based on the first voltage acquired by the voltage acquisition module.

[0011] Optionally, the voltage acquisition module is also connected to the control power supply of the cascaded frequency converter. The control power supply is connected to the main control module of the cascaded frequency converter and the power supply. The control module can detect whether the control power supply is normal based on the second voltage acquired by the voltage acquisition module.

[0012] Optionally, the pre-charging device further includes: a fifth switch disposed between the first input terminal and the second input terminal of the step-up transformer and the voltage acquisition module, and a sixth switch disposed between the control power supply and the voltage acquisition module. The control module is connected to the fifth switch and the sixth switch and can control the on / off state of the fifth switch and / or the sixth switch to control the voltage acquisition module to acquire the first voltage and / or the second voltage.

[0013] Optionally, the control module controls the fifth switch to be turned on and the sixth switch to be turned off, so that the step-up transformer supplies power to the cascaded frequency converter.

[0014] Optionally, the power source includes 220V AC mains power.

[0015] This utility model also provides a cascaded frequency converter, comprising: multiple power unit groups, each power unit group including multiple cascaded power units, each power unit including a capacitor connected to the DC bus of the power unit; and a pre-charging device as described above, the pre-charging device being connected to the neutral point of the output terminal of the cascaded frequency converter, one phase output terminal of the cascaded frequency converter, and a power supply, and capable of pre-charging the capacitor.

[0016] This invention's pre-charging device connects the first output terminal of a step-up transformer to the neutral point of the output terminal of a cascaded frequency converter, connects the second output terminal to one phase output terminal of the cascaded frequency converter, and connects the first and second input terminals to a power supply. Before the cascaded high-voltage frequency converter is connected to the high-voltage transformer (e.g., 10kV / 50Hz), the capacitors of the power unit can be pre-charged. This reduces the surge current of high-voltage electricity in the internal circuitry of the cascaded frequency converter, reduces thermal stress and mechanical stress generated by electrodynamics, and improves the safety and reliability of the cascaded frequency converter. Simultaneously, it optimizes the selection of components such as the rectifier bridge, fuses, and power unit bus capacitors, reducing costs. Attached Figure Description

[0017] The accompanying drawings are provided to further illustrate the present invention and form part of the specification. They are used together with the embodiments of the present invention to explain the present invention, but do not constitute a limitation thereof. In the drawings:

[0018] Figure 1 A schematic diagram of a pre-charging device according to some embodiments of the present invention is shown.

[0019] Figure 2 A schematic diagram of a power unit without bypass function according to some embodiments of the present invention is shown.

[0020] Figure 3 A schematic diagram of a power unit with bypass function according to some embodiments of the present invention is shown.

[0021] Figure 4 A schematic diagram of a pre-charging device according to some embodiments of the present invention is shown.

[0022] Figure 5 A schematic diagram of a pre-charging device according to some embodiments of the present invention is shown.

[0023] Figure 6 A schematic diagram of a pre-charging device according to some embodiments of the present invention is shown.

[0024] Figure 7 A schematic diagram of a pre-charging device according to some embodiments of the present invention is shown.

[0025] Figure 8 A schematic diagram of a cascaded frequency converter according to some embodiments of the present invention is shown. Detailed Implementation

[0026] In the following description, only certain exemplary embodiments are briefly described. As those skilled in the art will recognize, the described embodiments can be modified in various ways without departing from the spirit or scope of this invention. Therefore, the drawings and description are considered exemplary in nature and not restrictive.

[0027] In the description of this utility model, it should be understood that the terms "center," "longitudinal," "lateral," "length," "width," "thickness," "upper," "lower," "front," "rear," "left," "right," "vertical," "horizontal," "top," "bottom," "inner," "outer," "clockwise," and "counterclockwise," etc., indicating the orientation or positional relationship, are based on the orientation or positional relationship shown in the accompanying drawings and are only for the convenience of describing this utility model and simplifying the description. They do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation, and therefore should not be construed as a limitation of this utility model. Furthermore, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of technical features indicated. Thus, a feature defined with "first" or "second" may explicitly or implicitly include one or more of the stated features. In the description of this utility model, "multiple" means two or more, unless otherwise explicitly specified.

[0028] In the description of this utility model, it should be noted that, unless otherwise explicitly specified and limited, the terms "installation," "connection," "linking," and "coupling" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral connection; they can refer to a mechanical connection, an electrical connection, or a connection that allows for mutual communication; they can refer to a direct connection or an indirect connection through an intermediate medium; they can refer to the internal communication of two components or the interaction between two components. Those skilled in the art can understand the specific meaning of the above terms in this utility model according to the specific circumstances.

[0029] In this invention, unless otherwise explicitly specified and limited, "above" or "below" the second feature can include direct contact between the first and second features, or contact between the first and second features through another feature between them. Furthermore, "above," "over," and "on top" of the second feature includes the first feature directly above or diagonally above the second feature, or simply indicates that the first feature is at a higher horizontal level than the second feature. "Below," "below," and "under" the second feature includes the first feature directly below or diagonally below the second feature, or simply indicates that the first feature is at a lower horizontal level than the second feature.

[0030] The following provides many different embodiments or examples for implementing various structures of this invention. To simplify the invention, specific examples of components and arrangements are described below. Of course, these are merely examples and are not intended to limit the invention. Furthermore, reference numerals and / or letters may be repeated in different examples; such repetition is for simplification and clarity and does not in itself indicate a relationship between the various embodiments and / or arrangements discussed. In addition, examples of various specific processes and materials are provided in this invention, but those skilled in the art will recognize the application of other processes and / or the use of other materials.

[0031] The preferred embodiments of the present invention will be described below with reference to the accompanying drawings. It should be understood that the preferred embodiments described herein are for illustration and explanation only and are not intended to limit the present invention.

[0032] This invention provides a pre-charging device for a cascaded frequency converter. The cascaded frequency converter can be a cascaded high-voltage frequency converter. The cascaded frequency converter includes multiple power unit groups, each power unit group including multiple cascaded power units, and each power unit including a capacitor connected to the DC bus of the power unit. The pre-charging device includes a step-up transformer, which includes a first output terminal, a second output terminal, a first input terminal, and a second input terminal. The first output terminal can be connected to the neutral point of the output terminal of the cascaded frequency converter. The second output terminal can be connected to one phase output terminal of the cascaded frequency converter. The first and second input terminals can be connected to a power supply to pre-charge the capacitor.

[0033] Some traditional cascaded frequency converters lack any pre-charge circuit. Upon power-up, the fuses, rectifier bridge, bus capacitors, and secondary side of the phase-shifting transformer in the power unit all experience high surge currents. Thermal stress and mechanical stress generated by electrodynamics threaten the reliability of the cascaded frequency converter. Simultaneously, due to the transformer leakage inductance, the power unit bus voltage is prone to overcharging, even exceeding the power unit's tolerance, easily leading to power unit damage. Some traditional cascaded frequency converters employ high-voltage pre-charge, such as connecting a resistor in series between the three-phase input and the grid, and adding a resistor bypass switch; however, this method is costly. Other traditional cascaded frequency converters use low-voltage pre-charge, such as pre-charging through the low-voltage coil of the phase-shifting transformer itself. For example, a resistor can be connected in series between the three-phase input of the transformer's low-voltage coil and the low-voltage grid, and a resistor bypass switch can be added. However, this requires strengthening the insulation between the low-voltage and high-voltage coils, resulting in high transformer cost, size, and weight.

[0034] Unlike traditional methods, this invention's pre-charging device connects the first output terminal of a step-up transformer to the neutral point of the cascaded frequency converter's output terminal, connects the second output terminal to one phase output terminal of the cascaded frequency converter, and connects the first and second input terminals to a power supply. Before the cascaded high-voltage frequency converter is connected to the user's power grid (e.g., 10kV / 50Hz), the power supply is stepped up by the transformer and then charged by a rectifier bridge composed of an insulated-gate bipolar transistor (IGBT) and a freewheeling diode in the power unit. This pre-charges the power unit's capacitors, reducing the surge current caused by high voltage in the cascaded frequency converter's internal circuitry, reducing thermal stress and mechanical stress generated by electrodynamics, and improving the safety and reliability of the cascaded frequency converter. It also optimizes the selection of components such as the rectifier bridge, fuses, and power unit bus capacitors, reducing costs. A detailed description follows.

[0035] Figure 1 A schematic diagram of a pre-charging device 10 according to some embodiments of the present invention is shown. Figure 2 A schematic diagram of a power unit 21 without bypass function according to some embodiments of the present invention is shown. Figure 3 A schematic diagram of a power unit 21 with bypass function according to some embodiments of the present invention is shown. Figures 1 to 3As shown, the pre-charging device 10 is used in a cascaded frequency converter 20. The cascaded frequency converter 20 includes multiple power unit groups G. Each power unit group includes multiple cascaded power units 21 (a purple rectangle represents one power unit, one row of power units constitutes one power unit group, and three rows of power units constitute three power unit groups). Each power unit 21 includes capacitors C1 to Cn, where n is a positive integer. Capacitors C1 to Cn are connected to the DC bus (DC+, DC-) of the power unit 21. The pre-charging device 10 includes a step-up transformer 11. The step-up transformer 11 includes a first output terminal out1, a second output terminal out2, a first input terminal in1, and a second input terminal in2. The first output terminal out1 can be connected to the neutral point N of the output terminals of the cascaded frequency converter 20 formed by the multiple power unit groups G. The second output terminal out2 can be connected to one phase output terminal U / V / W of the cascaded frequency converter 20 formed by the multiple power unit groups G (exemplarily shown in the figure connected to the W phase output terminal, equivalent to the input terminal of the motor M or other load). The U / V phase output terminals can be connected to the W phase output terminals via the windings of motor M (not shown in the figure). The first input terminal in1 and the second input terminal in2 can be connected to the power supply P to simultaneously pre-charge the capacitors C1 to Cn of the three-phase power units (U, V, and W). The cascaded frequency converter 20 is powered on only after the voltage of capacitors C1 to Cn in the power unit 21 is greater than or equal to a voltage threshold and / or the charging time is greater than or equal to a time threshold, thus preventing damage to components from the instantaneous surge current of high-voltage electricity in the internal circuitry.

[0036] In some embodiments, the power supply P can be a user power supply, such as 220V AC mains power. That is, the pre-charging device 10 can pre-charge the capacitor of the power unit using 220V AC mains power.

[0037] In some embodiments, such as Figure 1 As shown, the number of step-up transformers 11 can be one, and its second output terminal out2 can be connected to one of the phase output terminals U / V / W of the cascaded frequency converter 20 (exemplarily shown in the figure as connected to the W phase output terminal). In some embodiments, although not shown in the figure, the number of step-up transformers can be multiple. For example, the number of step-up transformers is two, and the second output terminals of the two step-up transformers are respectively connected to two of the U / V / W phase output terminals of the cascaded frequency converter 20. Another example is the number of step-up transformers, which are three. The second output terminals of these three step-up transformers are respectively connected to the U, V, and W phase output terminals of the cascaded frequency converter 20. The three phase output terminals U, V, and W of the cascaded frequency converter 20 are respectively connected to the motor M. These are all within the protection scope of this utility model.

[0038] The pre-charging device 10 will now be described using a step-up transformer 11 as an example.

[0039] In some embodiments, the power unit 21 may include a control unit (not shown). The control unit is connected to capacitors C1 to Cn and can monitor the charging time and / or voltage of capacitors C1 to Cn.

[0040] In some embodiments, such as Figure 3 As shown, power unit 21 includes a bypass switch Thy1 disposed at the output terminal of power unit 21. When bypass switch Thy1 is turned on, power unit 21 is bypassed. When bypass switch Thy1 is turned off, power unit 21 is not bypassed. The control unit is connected to bypass switch Thy1 and can control the on / off state of bypass switch Thy1 based on control commands from the main control module M0.

[0041] In some embodiments, such as Figure 2 and Figure 3 As shown, power unit 21 may also include fuses Fuse1 and Fuse2, diodes D1 to D10, insulated gate bipolar transistors IGBT1 to IGBT4, and a control unit (not shown in the figure). The control unit is connected to the control terminals g1 to g4 of IGBT1 to IGBT4 and can control the on / off state of IGBT1 to IGBT4 based on the control commands of the main control module M0.

[0042] Figure 4 A schematic diagram of a pre-charging device 10 according to some embodiments of the present invention is shown. Figure 4 As shown, the pre-charging device 10 also includes a first switch K1 and a second switch K2. The first switch K1 is connected to the first input terminal in1 and the power supply P. The second switch K2 is connected to the second input terminal in2 and the power supply P. The first switch K1 and the second switch K2 can function as charging switches. When the first switch K1 and the second switch K2 are turned on, the power supply P pre-charges the capacitors C1 to Cn. When the first switch K1 and / or the second switch K2 are turned off, the power supply P does not pre-charge the capacitors C1 to Cn.

[0043] In some embodiments, the pre-charging device 10 further includes a control module. The control module is connected to the first switch K1 and the second switch K2, and controls the on / off state of the first switch K1 and the second switch K2. In some embodiments, the pre-charging device 10 can be externally mounted to the cascaded frequency converter 20. In this case, the control module can be set up separately, and the control module, the control unit of the power unit 21, and the main control module M0 can communicate with each other. Alternatively, the pre-charging device 10 can be built into the cascaded frequency converter 20. In this case, the main control module M0 of the cascaded frequency converter 20 can serve as the control module to save space and cost, and the control unit of the power unit 21 and the main control module M0 can communicate with each other.

[0044] In some embodiments, the power unit 21 includes a control unit (not shown), which is connected to capacitors C1-Cn and a control module, and the two can communicate with each other. The control unit can monitor the charging time and / or voltage of the capacitors and communicate the charging time and / or voltage to the control module. The control module can control the on / off state of the first switch K1 and the second switch K2 based on the charging time and / or voltage. For example, when the charging time of the capacitor is greater than or equal to a time threshold and / or the voltage is greater than or equal to a voltage threshold, the control module can control the first switch K1 and the second switch K2 to be off. As another example, when the charging time of the capacitor is less than the time threshold and the voltage is less than the voltage threshold, the control module can control the first switch K1 and the second switch K2 to be on.

[0045] In some embodiments, the pre-charging device 10 may include a display module, which may be connected to the control module. The display module may display the charging time and / or voltage of the capacitor. This invention does not limit the implementation of the display module; the display module may include one or more of a display screen, an indicator light, and a voice broadcast module. The display screen may include an LCD (liquid-crystal display), an LED (light emitting diode), an OLED (organic light emitting diode), etc. The indicator light may display different colors according to the charging time and / or voltage. For example, if the charging time of the capacitor is less than a time threshold, the indicator light displays red; if the charging time of the capacitor is greater than or equal to the time threshold, the indicator light displays green. As another example, if the voltage of the capacitor is less than a voltage threshold, the indicator light displays red; if the voltage of the capacitor is greater than or equal to the voltage threshold, the indicator light displays green. The voice broadcast module may include a speaker.

[0046] In some embodiments, the pre-charging device 10 may include a wireless communication module (not shown). The wireless communication module may include one or more of a Bluetooth module, a WiFi module, a ZigBee module, a 4G module, or a 5G module. In some embodiments, the pre-charging device 10 can communicate with a user's mobile terminal via the wireless communication module, allowing the user to view the charging time and / or voltage of the capacitor in the power unit in real time. The mobile terminal includes, but is not limited to, mobile phones, tablets, laptops, wearable devices, etc.

[0047] In some embodiments, the pre-charging device 10 can communicate with one or more of the following via a wireless communication module: the main control module MO of the cascaded inverter 20, the human machine interface (HMI), the drive advisor (DA), the programmable logic controller (PLC), and the control unit of the power unit 21, to share data information.

[0048] In some embodiments, such as Figure 4 As shown, the pre-charging device 10 may further include a third switch K3 and a fourth switch K4. The third switch K3 connects the first output terminal out1 of the step-up transformer 11 to the neutral point N. The fourth switch K4 connects the second output terminal out2 of the step-up transformer 11 to one phase output terminal U / V / W of the cascaded frequency converter 20 (exemplarily shown in the figure connected to the W phase output terminal). The third switch K3 and the fourth switch K4 are also connected to a control module. The control module can control the on / off state of the third switch K3 and the fourth switch K4. It should be noted that the third switch K3 and the fourth switch K4 are optional and not mandatory. If the isolation performance between the high-voltage side and the low-voltage side of the step-up transformer 11 can meet the system insulation requirements (higher insulation requirements also mean higher costs), the third switch K3 and the fourth switch K4 may not be necessary for cost control. If the isolation performance between the high-voltage side and the low-voltage side of the step-up transformer 11 is not particularly ideal, the third switch K3 and the fourth switch K4 may be provided. Once the power unit's capacitor is fully charged, switches K3 and K4 are disconnected to prevent the step-up transformer 11 from experiencing excessive insulation stress. It is important to note that switches K3 and K4 must meet insulation performance requirements for system safety. In practical applications, these switches can be configured according to specific needs.

[0049] In some embodiments, the pre-charging device 10 further includes a first current limiting module 12-1 and / or a second current limiting module 12-2, which can prevent the pre-charging device 10 from being damaged due to excessive current in the circuit when the power supply P is turned on.

[0050] Figure 5 A schematic diagram of a pre-charging device 10 according to some embodiments of the present invention is shown. Figure 5 As shown, in this embodiment, the pre-charging device 10 may only include the first current limiting module 12-1. The first current limiting module 12-1 is connected to the first input terminal in1 and the second input terminal in2 of the step-up transformer 11 and the power supply P.

[0051] Figure 6 A schematic diagram of a pre-charging device 10 according to some embodiments of the present invention is shown. Figure 6As shown, in this embodiment, the pre-charging device 10 may only include the second current limiting module 12-2. The second current limiting module 12-2 is connected to the first output terminal out1 and the second output terminal out2 of the step-up transformer 11, as well as the neutral point N and one of the phase output terminals U / V / W (the figure exemplarily shows the connection to the W phase output terminal).

[0052] Figure 7 A schematic diagram of a pre-charging device 10 according to some embodiments of the present invention is shown. Figure 7 As shown, in this embodiment, the pre-charging device 10 may simultaneously include a first current limiting module 12-1 and a second current limiting module 12-2.

[0053] In some embodiments, the first current limiting module 12-1 and / or the second current limiting module 12-2 may include one or more of a current limiting resistor R, an inductor, a thyristor, an IGBT, a soft starter, or a frequency converter, or other similar devices. The current limiting resistor R may be an adjustable resistor. The inductor may be an adjustable inductor. For example, a control module may be connected to the first current limiting module 12-1 and / or the second current limiting module 12-2, and the conduction angle of the thyristor may be adjusted to regulate the current. For example, the control module may adjust the duty cycle of the IGBT to regulate the current. This invention does not limit the implementation of the first current limiting module 12-1 and / or the second current limiting module 12-2. In practical applications, the implementation can be customized based on cost, installation controls, insulation requirements, safety considerations, etc.

[0054] In some embodiments, such as Figure 7 As shown, the pre-charging device 10 may further include a voltage acquisition module 13. When the pre-charging device 10 is externally located in the cascaded frequency converter 20, the voltage acquisition module 13 can be independently located inside the pre-charging device 10. When the pre-charging device 10 is built into the cascaded frequency converter 20, the pre-charging device 10 and the cascaded frequency converter 20 can share the voltage acquisition module 13 (see [reference]). Figure 7 The voltage acquisition module 13 may include a voltage sampling circuit or a voltage sampling sensor. The voltage acquisition module 13 is connected to the first input terminal in1 and the second input terminal in2 of the step-up transformer 11, and a control module (e.g., a main control module M0 or a separately configured control module). Based on the first voltage acquired by the voltage acquisition module 13, the control module can detect the input voltage of the step-up transformer 11 and / or the output voltage of the cascaded frequency converter 20 (e.g., whether it is normal, etc.). The output voltage of the cascaded frequency converter 20 can be calculated based on the input voltage of the step-up transformer 11. The first voltage is the input side voltage of the step-up transformer 11.

[0055] In some embodiments, the step-up transformer 11 can be used as a voltage transformer. For example... Figure 7As shown, after pre-charging is complete, the first switch K1 and the second switch K2 are disconnected. At this time, the step-up transformer 11 can be used as a voltage transformer to sense the output voltage of the cascaded frequency converter 20, reduce the high voltage output of the cascaded frequency converter 20 to a low voltage signal acceptable to the voltage acquisition circuit, and transmit it to the voltage acquisition module 13. In this way, it is not necessary to set up an additional high voltage acquisition module at the output of the cascaded frequency converter 20, which can save costs and space.

[0056] In some embodiments, such as Figure 7 As shown, the cascaded frequency converter 20 includes a main control module M0 and a control power supply 22 connected to the main control module M0. A voltage acquisition module 13 is connected to the control power supply 22. The control power supply 22 is connected to the main control module M0 and the power supply P. The control module can detect whether the control power supply 22 is normal based on the second voltage acquired by the voltage acquisition module 13, so as to detect whether the power supply path formed by the power supply P, the control power supply 22, and the main control module M0 is normal. The second voltage can be the voltage across the control power supply 22. It should be noted that this utility model does not limit the magnitude relationship between the first voltage and the second voltage.

[0057] In some embodiments, such as Figure 7 As shown, the step-up transformer 11 can be used as a step-down frequency converter. After pre-charging is complete, the first switch K1 and the second switch K2 are disconnected. When the cascaded frequency converter 20 is operating and has output, the step-up transformer 11 can be used as a step-down frequency converter to reduce the higher voltage output by the cascaded frequency converter 20 to a lower voltage and pass the lower voltage to the control power supply 22 of the cascaded frequency converter 20. In this way, the step-up transformer 11 can serve as a redundant backup power supply for the control power supply 22 of the cascaded frequency converter 20. When the control power supply 22 is de-energized, the step-up transformer 11 (backup power supply) can continue to supply power to the main control module M0 of the cascaded frequency converter 20, improving power supply reliability.

[0058] In some embodiments, such as Figure 7 As shown, the pre-charging device 10 may further include a fifth switch K5 and a sixth switch K6. The fifth switch K5 is located between the first input terminal in1 and the second input terminal in2 of the step-up transformer 11 and the voltage acquisition module 13. The sixth switch K6 is located between the control power supply 22 and the voltage acquisition module 13. The control module is connected to the fifth switch K5 and the sixth switch K6, and can control the on / off state of the fifth switch K5 and / or the sixth switch K6 to control the voltage acquisition module 13 to acquire a first voltage and / or a second voltage. Specifically, by controlling the fifth switch K5 to be on and the sixth switch K6 to be off, the control module can control the voltage acquisition module 13 to acquire the first voltage. By controlling the fifth switch K5 to be off and the sixth switch K6 to be on, the control module can control the voltage acquisition module 13 to acquire the second voltage.

[0059] In some embodiments, the step-up transformer 11 can serve as a backup power source for the cascaded frequency converter 20. For example... Figure 7 As shown, when the control power supply 22 of the cascaded frequency converter 20 is abnormal, the control module can control the fifth switch K5 to conduct and the sixth switch K6 to open, so that the step-up transformer 11 supplies power to the cascaded frequency converter 20 (main control module M0, etc.), thereby improving the reliability of the cascaded frequency converter operation. Alternatively, when the power supply P is abnormal, the control module can control the fifth switch K5 and the sixth switch K6 to conduct, so that the electrical energy output by the cascaded frequency converter 20 can supply power to the step-up transformer 11, so that the step-up transformer 11 supplies power to the control power supply 22, thereby supplying power to the main control module M0, improving the reliability of the cascaded frequency converter 20 operation. It should be noted that the fifth switch K5 and the sixth switch K6 are optional and not mandatory; in practical applications, they can be determined according to requirements.

[0060] In some embodiments, the first switch K1 / second switch K2 / third switch K3 / fourth switch K4 / fifth switch K5 / sixth switch K6 / bypass switch Thy1 may include any switching device that can perform an equivalent or similar function, such as a field-effect transistor (FET), a bipolar junction transistor (BJT), a relay, a silicon controlled rectifier (SCR), a contactor, a circuit breaker, a potentiometer, or a mechanical switch. The FET may be a metal-oxide-semiconductor field-effect transistor (MOSFET). The MOSFET may be a P-channel metal-oxide-semiconductor field-effect transistor (PMOS). Alternatively, the FET may be an N-channel metal-oxide-semiconductor field-effect transistor (NMOS). MOSFETs can be power devices such as silicon carbide (SiC) MOSFETs and gallium nitride (GaN) MOSFETs, offering lower losses, higher efficiency, and superior performance. The choice depends on the specific application requirements. All of these fall within the scope of this invention.

[0061] In some embodiments, the control module / main control module / control unit may include control circuits, central processing unit (CPU), micro control unit (MCU), digital signal processor (DSP), other general-purpose processors, application-specific integrated circuit (ASIC), field-programmable gate array (FPGA), complex programmable logic device (CPLD) or other programmable logic device, discrete gate or transistor logic device, discrete hardware components, and other components and circuits.

[0062] This utility model also provides a cascaded frequency converter. Figure 8 A schematic diagram of a cascaded frequency converter 20 according to some embodiments of the present invention is shown. Figure 8 As shown, the cascaded frequency converter 20 includes multiple power unit groups and a pre-charging device 10 as described above. Each power unit group includes multiple cascaded power units, and each power unit includes a capacitor connected to the DC bus of the power unit. The pre-charging device 10 is connected to the neutral point of the output terminal of the cascaded frequency converter, one phase output terminal of the cascaded frequency converter, and the power supply, and can pre-charge the capacitor.

[0063] The cascaded frequency converter of this utility model, by setting the pre-charging device as described above, can pre-charge the capacitor of the power unit, which can improve the safety and reliability of the cascaded frequency converter. At the same time, it can optimize the selection of components such as rectifier bridge, fuse, and power unit bus capacitor, and reduce costs.

[0064] It should be noted that although several modules of the pre-charging device / cascaded inverter have been mentioned in the detailed description above, this division is not mandatory. In fact, according to embodiments of this utility model, the features and functions of two or more modules described above can be implemented in one module. Conversely, the features and functions of one module described above can be further divided and specified by multiple modules.

[0065] It should be noted that this utility model may only include Figure 1-8 Any one or more features of any one or more embodiments. In other words, not all of the shown features need to be implemented simultaneously in the pre-charging device / cascaded inverter of this utility model.

[0066] Finally, it should be noted that the above description is merely a preferred embodiment of this utility model and is not intended to limit the utility model. Although the utility model has been described in detail with reference to the foregoing embodiments, those skilled in the art can still modify the technical solutions described in the foregoing embodiments or make equivalent substitutions for some of the technical features. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of this utility model should be included within the protection scope of this utility model.

Claims

1. A pre-charging device for a cascaded frequency converter, the cascaded frequency converter comprising multiple power unit groups, each power unit group comprising multiple cascaded power units, each power unit comprising a capacitor connected to a DC bus of the power unit, characterized in that, The pre-charging device includes: A step-up transformer includes a first output terminal, a second output terminal, a first input terminal, and a second input terminal. The first output terminal can be connected to the neutral point of the output terminal of the cascaded frequency converter. The second output terminal can be connected to one phase output terminal of the cascaded frequency converter. The first input terminal and the second input terminal can be connected to a power supply to precharge the capacitor.

2. The pre-charging device according to claim 1, characterized in that, Also includes: A first switch connects the first input terminal to the power supply, and a second switch connects the second input terminal to the power supply. When the first switch and the second switch are turned on, the power supply precharges the capacitor.

3. The pre-charging device according to claim 2, characterized in that, Also includes: A control module is provided, which is connected to the first switch and the second switch and controls the on / off state of the first switch and the second switch.

4. The pre-charging device according to claim 3, characterized in that, The power unit includes a control unit, which is connected to the capacitor and the control module. The control unit can monitor the charging time and / or voltage of the capacitor and communicate the charging time and / or voltage to the control module. The control module controls the on / off state of the first switch and the second switch based on the charging time and / or voltage.

5. The pre-charging device according to claim 1, characterized in that, Also includes: The control module, the third switch, and the fourth switch, wherein the third switch is connected to the first output terminal of the step-up transformer and the neutral point; The fourth switch is connected to the second output terminal of the step-up transformer and one of the phase output terminals. The third switch and the fourth switch are also connected to the control module, which can control the on / off state of the third switch and the fourth switch.

6. The pre-charging device according to any one of claims 1-5, characterized in that, Also includes: A first current limiting module and / or a second current limiting module, wherein the first current limiting module is connected to the first input terminal and the second input terminal of the step-up transformer and the power supply; The second current limiting module is connected to the first output terminal and the second output terminal of the step-up transformer, as well as the neutral point and one of the phase output terminals.

7. The pre-charging device according to any one of claims 1-5, characterized in that, Also includes: The voltage acquisition module is connected to the first and second input terminals of the step-up transformer and the control module. The control module can detect the input voltage of the step-up transformer and / or the output voltage of the cascaded frequency converter based on the first voltage acquired by the voltage acquisition module.

8. The pre-charging device according to claim 7, characterized in that, The voltage acquisition module is also connected to the control power supply of the cascaded frequency converter. The control power supply is connected to the main control module of the cascaded frequency converter and the power supply. The control module can detect whether the control power supply is normal based on the second voltage acquired by the voltage acquisition module.

9. The pre-charging device according to claim 8, characterized in that, Also includes: A fifth switch is disposed between the first and second input terminals of the step-up transformer and the voltage acquisition module, and a sixth switch is disposed between the control power supply and the voltage acquisition module. The control module is connected to the fifth switch and the sixth switch and can control the opening and closing of the fifth switch and / or the sixth switch to control the voltage acquisition module to acquire the first voltage and / or the second voltage.

10. The pre-charging device according to claim 9, characterized in that, The control module controls the fifth switch to be turned on and the sixth switch to be turned off, so that the step-up transformer supplies power to the cascaded frequency converter.

11. The pre-charging device according to any one of claims 1-5, characterized in that, The power supply includes 220V AC mains power.

12. A cascaded frequency converter, characterized in that, include: Multiple power unit groups, each power unit group including multiple cascaded power units, each power unit including a capacitor connected to the DC bus of the power unit; and The pre-charging device according to any one of claims 1-11, wherein the pre-charging device is connected to the neutral point of the output terminal of the cascaded frequency converter, one phase output terminal of the cascaded frequency converter, and the power supply, and can pre-charge the capacitor.

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