Uninterruptible power supply and soft start method, device and controller thereof

Abstract

The invention provides an uninterruptible power supply and a soft start method and device thereof, and a controller, in the uninterruptible power supply, an inverter circuit is provided with a three-phase output end, and two output ends of a pre-charging circuit are correspondingly and electrically connected with any two-phase output ends of the inverter circuit instead of being directly and electrically connected with a direct-current bus; when the uninterruptible power supply charges the bus capacitor through the pre-charging circuit, the bus capacitor can be charged through energy storage operation and follow current operation of the inverter circuit, so that the voltage of the bus capacitor is larger than the peak value of the mains supply, and when the mains supply relay is powered on, the voltage value of one end, electrically connected with the mains supply, of the mains supply relay is lower than the voltage of the bus capacitor. Due to the limitation of the conduction direction of the rectifying device in the rectifying circuit, impact current does not occur any more, the arc discharge phenomenon of a relay contact caused by the impact current is reduced, and the stability of the uninterruptible power supply in the power-on process is improved.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of uninterruptible power supply, and in particular to an uninterruptible power supply and a soft starting method, device and controller thereof. BACKGROUND

[0002] An uninterruptible power supply (UPS) is a device for providing stable power to downstream devices in a data center. The UPS includes a mains relay, a pre-charge circuit, a rectifier circuit, a bus capacitor and an inverter circuit. The pre-charge circuit is electrically connected between the mains and the bus capacitor, and includes an uncontrolled three-phase bridge circuit, a pre-charge relay, a current-limiting resistor and a filter capacitor.

[0003] After the UPS is started, the bus capacitor is pre-charged by uncontrolled rectification of the pre-charge circuit. When the voltage difference between the bus capacitor voltage and the mains voltage is within a preset voltage difference range, the mains relay is controlled to be turned on, so that the rectifier circuit charges the bus capacitor. Due to the voltage division of the current-limiting resistor in the pre-charge circuit, the first voltage difference between the mains peak voltage and the neutral line voltage has an absolute value greater than the second voltage difference between the bus voltage and the neutral line voltage, thereby causing a large impact current when the mains relay is closed, causing the relay contact to arc, increasing the failure rate of the mains relay, and further affecting the reliability of the uninterruptible power supply.

[0004] Therefore, how to improve the stability of the power-on process of the uninterruptible power supply has become a research focus. SUMMARY

[0005] The present application provides an uninterruptible power supply and a soft starting method, device and controller thereof to solve the above technical problems.

[0006] In a first aspect, the present application provides an uninterruptible power supply, comprising: a rectifier circuit, a pre-charge circuit, an inverter circuit, a first bus capacitor, a second bus capacitor, a mains relay;

[0007] The three-phase mains input end of the rectifier circuit is correspondingly electrically connected to the three input ends of the pre-charge circuit through the mains relay, and the positive output end of the rectifier circuit is electrically connected to the positive input end of the inverter circuit through a positive DC bus, and the negative output end of the rectifier circuit is electrically connected to the negative input end of the inverter circuit through a negative DC bus, the first bus capacitor and the second bus capacitor are electrically connected in series between the positive DC bus and the negative DC bus, and the connection point of the first bus capacitor and the second bus capacitor is electrically connected to a neutral line.

[0008] The inverter circuit is provided with three-phase output ends, and the positive output end and the negative output end of the pre-charge circuit are correspondingly electrically connected to any two-phase output ends of the inverter circuit.

[0009] In the above technical solution, in the uninterruptible power supply, the two output ends of the pre-charge circuit and the output ends of any two phases of the inverter circuit are correspondingly electrically connected, instead of being directly electrically connected to the DC bus. When the uninterruptible power supply charges the bus capacitor by using the pre-charge circuit, the bus capacitor can be charged by the energy storage operation and the freewheeling operation of the inverter circuit, so that the voltage of the bus capacitor is greater than the peak value of the commercial power. When the commercial power relay is powered on, the voltage of the end electrically connected to the commercial power is lower than the voltage of the bus capacitor. Due to the limitation of the conduction direction of the rectifier device in the rectifier circuit, the inrush current will not appear again, the relay contact arc phenomenon caused by the inrush current is reduced, and the stability during the power-on process of the uninterruptible power supply is improved.

[0010] Optionally, the inverter circuit comprises at least one inverter unit, each inverter unit comprises a three-phase three-level inverter circuit, the three-phase three-level inverter circuit comprises three single-phase three-level inverter circuits, and each single-phase three-level inverter circuit comprises a first switch module, a second switch module, a midpoint freewheeling module and an energy storage module.

[0011] In the single-phase three-level inverter circuit, a first end of the first switch module is electrically connected to a positive input end of the inverter circuit, a second end of the second switch module is electrically connected to a negative input end of the inverter circuit, a second end of the first switch module, a first end of the second switch module and the midpoint freewheeling module are electrically connected, a first end of the midpoint freewheeling module is electrically connected to a corresponding phase output end of the inverter unit through the energy storage module, and a second end of the midpoint freewheeling module is electrically connected to the neutral line.

[0012] Optionally, the three-level inverter circuit is a T-type three-level inverter circuit, and the second end of the first switch module, the first end of the second switch module and the first end of the midpoint freewheeling module are electrically connected.

[0013] When the inverter circuit is energized, a first conduction current path of the midpoint freewheeling module coupled to the positive output end of the pre-charge circuit is a path from the first end to the second end thereof, and a first conduction current path of the midpoint freewheeling module coupled to the negative output end of the pre-charge circuit is a path from the second end to the first end thereof.

[0014] When the inverter circuit freewheels, each midpoint freewheeling module is turned off.

[0015] Optionally, the midpoint freewheeling module comprises a first controllable switching device and a second controllable switching device.

[0016] A first end of the first controllable switching device serves as a first end of the midpoint freewheeling module.

[0017] a second end of the first controllable switching device and a second end of the second controllable switching device are electrically connected;

[0018] a first end of the second controllable switching device is electrically connected to a second end of the midpoint freewheeling module.

[0019] Optionally, the three-level inverter circuit is an I-type three-level inverter circuit, a second end of the first switching module and a third end of the midpoint freewheeling module are electrically connected, and a first end of the second switching module and a fourth end of the midpoint freewheeling module are electrically connected.

[0020] When the inverter circuit is storing energy, a first conduction current path of the midpoint freewheeling module coupled to the positive output end of the pre-charge circuit is a path from a first end of the midpoint freewheeling module to a second end of the midpoint freewheeling module through a fourth end of the midpoint freewheeling module, and a first conduction current path of the midpoint freewheeling module coupled to the negative output end of the pre-charge circuit is a path from the second end of the midpoint freewheeling module to the first end of the midpoint freewheeling module through a third end of the midpoint freewheeling module.

[0021] When the inverter circuit is freewheeling, a second conduction current path of the midpoint freewheeling module coupled to the positive output end of the pre-charge circuit is a path from the first end of the midpoint freewheeling module to the third end of the midpoint freewheeling module, and a second conduction current path of the midpoint freewheeling module coupled to the negative output end of the pre-charge circuit is a path from the fourth end of the midpoint freewheeling module to the first end of the midpoint freewheeling module.

[0022] Optionally, the midpoint freewheeling module comprises a first controllable switching device, a second controllable switching device, a first energy storage diode, and a second energy storage diode.

[0023] a first end of the first controllable switching device and a second end of the second controllable switching device are electrically connected, as a first end of the midpoint freewheeling module;

[0024] a second end of the first controllable switching device and a first end of the first energy storage diode are electrically connected, as a fourth end of the midpoint freewheeling module;

[0025] a second end of the first energy storage diode and a first end of the second energy storage diode are electrically connected, as a second end of the midpoint freewheeling module;

[0026] a first end of the second controllable switching device and a second end of the second energy storage diode are electrically connected, as a third end of the midpoint freewheeling module.

[0027] In a second aspect, the present application provides a soft start method of an uninterruptible power supply, the method being applied to the uninterruptible power supply of any one of the first aspect, and the method comprising:

[0028] controlling the pre-charge circuit to conduct;

[0029] The control method comprises the following steps:

[0030] obtaining a first voltage difference of a positive DC bus voltage and a neutral voltage and a second voltage difference of a negative DC bus voltage and the neutral voltage;

[0031] when the first voltage difference is greater than a first preset voltage difference and an absolute value of the second voltage difference is greater than the first preset voltage difference, controlling the AC power relay to be closed;

[0032] The first preset voltage difference is greater than or equal to an absolute value of a difference between an AC peak voltage and the neutral voltage.

[0033] Optionally, the inverter circuit comprises at least one inverter unit, and the inverter unit comprises three single-phase three-level inverter circuits, the single-phase three-level inverter circuit comprising a first switch module, a second switch module and a midpoint freewheeling module, a second end of the first switch module, a first end of the second switch module, a first end of the midpoint freewheeling module and a corresponding phase output end of the inverter unit being electrically connected, and a second end of the inverter circuit and the neutral line being electrically connected;

[0034] The midpoint freewheeling module comprises a first controllable switching device and a second controllable switching device, the first controllable switching device being in a first conduction current path of the midpoint freewheeling module coupled with the positive output end of the pre-charge circuit, and the second controllable switching device being in a first conduction current path of the midpoint freewheeling module coupled with the negative output end of the pre-charge circuit; the first conduction current path in the midpoint freewheeling module coupled with the positive output end of the pre-charge circuit is a path from the first end of the midpoint freewheeling module to the second end thereof, and the first conduction current path in the midpoint freewheeling module coupled with the negative output end of the pre-charge circuit is a path from the second end of the midpoint freewheeling module to the first end thereof;

[0035] controlling the inverter circuit to perform the energy storage operation, comprising:

[0036] controlling the first controllable switching device and the second controllable switching device to be conductive;

[0037] controlling other switching devices in the inverter circuit to be non-conductive.

[0038] Optionally, the control method further comprises:

[0039] controlling all switching devices in the inverter circuit to be non-conductive.

[0040] Optionally, after the AC power relay is controlled to be closed, the method further comprises:

[0041] controlling the pre-charge circuit to be powered off.

[0042] In a third aspect, the application provides a soft starting device of an uninterruptible power supply, comprising:

[0043] a processing module configured to control the pre-charging circuit to be turned on and control the inverter circuit to alternately perform energy storage operation and freewheeling operation;

[0044] a obtaining module configured to obtain a first voltage difference between the positive DC bus voltage and the neutral voltage and a second voltage difference between the negative DC bus voltage and the neutral voltage;

[0045] The processing module is further configured to control the mains relay to be closed when the first voltage difference is greater than a first preset voltage difference and the absolute value of the second voltage difference is greater than the first preset voltage difference.

[0046] The first preset voltage difference is greater than or equal to the absolute value of the difference between the mains peak voltage and the neutral voltage.

[0047] In a fourth aspect, the application provides a controller, comprising a processor and a memory connected with the processor in communication;

[0048] The memory stores computer execution instructions.

[0049] The processor, when executing the computer execution instructions, is configured to implement the method of any one of the second aspect.

[0050] The application provides an uninterruptible power supply and a soft starting method, device and controller thereof. In the uninterruptible power supply, the inverter circuit is provided with three-phase output ends, and two output ends of the pre-charging circuit are correspondingly connected with any two-phase output ends of the inverter circuit, instead of being directly connected with the DC bus. When the pre-charging circuit is used to charge the bus capacitor, the bus capacitor can be charged through the energy storage operation and freewheeling operation of the inverter circuit, so that the voltage of the bus capacitor is greater than the mains peak value. When the mains relay is powered on, the voltage of the end connected with the mains is lower than the voltage of the bus capacitor. Due to the limitation of the conduction direction of the rectifier device in the rectifier circuit, the impact current will not appear again, the relay contact arc phenomenon caused by the impact current is reduced, and the stability during the power-on process of the uninterruptible power supply is improved. BRIEF DESCRIPTION OF DRAWINGS

[0051] The accompanying drawings, which are incorporated into and form a part of the specification, illustrate one embodiment consistent with the application and, together with the description, serve to explain the principles of the application.

[0052] Figure 1 FIG. 1 is a structural schematic diagram of an uninterruptible power supply according to an example embodiment of the application;

[0053] Figure 2 FIG. 2 is a structural schematic diagram of an uninterruptible power supply end according to another example embodiment of the application.

[0054] Figure 3A Structure diagram of inverter unit according to an exemplary embodiment of the present application;

[0055] Figure 3B Structure diagram of inverter unit according to another exemplary embodiment of the present application;

[0056] Figure 3C Structure diagram of inverter unit according to another exemplary embodiment of the present application;

[0057] Figure 4A Energy storage diagram of T-type three-level inverter circuit according to an exemplary embodiment of the present application;

[0058] Figure 4B Freewheeling diagram of T-type three-level inverter circuit according to an exemplary embodiment of the present application;

[0059] Figure 5A Energy storage diagram of I-type three-level inverter circuit according to an exemplary embodiment of the present application;

[0060] Figure 5B Freewheeling diagram of I-type three-level inverter circuit according to an exemplary embodiment of the present application;

[0061] Figure 6 Flow diagram of soft start method of uninterruptible power supply according to an exemplary embodiment of the present application;

[0062] Figure 7 Structure diagram of soft start device of uninterruptible power supply according to an exemplary embodiment of the present application;

[0063] Figure 8 Structure diagram of controller according to an exemplary embodiment of the present application.

[0064] The specific embodiments of the present application have been shown by way of example in the above figures and will be described in more detail hereafter. These figures and the written description together serve to fully disclose the application to those skilled in the art, and not intended in any way to limit the scope of the present application as set forth in the appended claims. DETAILED DESCRIPTION

[0065] The exemplary embodiments will now be described in detail with reference to the accompanying drawings. If desired, the same numbers can be used in different drawings to identify the same elements. The following detailed description is not intended to limit the application, as claimed. Rather, the detailed description is intended to explain the exemplary embodiments of the present application for a complete understanding of the application.

[0066] A data center, commonly known as a computer room, includes computer systems, communication systems, storage systems, environmental control equipment, monitoring equipment, and various security devices. Stable power supply of the data center is a prerequisite for ensuring stable operation of the data center. Therefore, an uninterruptible power supply is generally provided in the data center, electrically connected between the commercial power and the electrical equipment in the data center, for stably and continuously supplying power to each electrical equipment.

[0067] Figure 1 The circuit structure of the uninterruptible power supply in the related art is provided for an exemplary embodiment of the present application. As shown in Figure 1 The uninterruptible power supply includes a pre-charge circuit 10, a rectifier circuit 11, an inverter circuit 12, a commercial power relay RL3, a first bus capacitor C1, and a second bus capacitor C2.

[0068] The UPS front power distribution transformer can provide three-phase power lines U, V, and W, and a neutral line N. In the uninterruptible power supply, the first port of the commercial power relay RL3 is electrically connected to the three-phase power lines, and the second port is electrically connected to the input end of the rectifier circuit 11.

[0069] The commercial power relay RL3 includes three controllable relays. The first ends of the three controllable relays form the first port of the commercial power relay RL3, and the first ends of the three controllable relays are electrically connected to the three-phase power lines in correspondence. The second ends of the three controllable relays form the second port of the commercial power relay RL3.

[0070] The rectifier circuit 11 is provided with an alternating current input end, which includes three-phase power input ends and is electrically connected to the second ends of the three controllable relays in the second port of the commercial power relay RL3.

[0071] The rectifier circuit 11 includes a rectification unit, which includes rectifier devices D7, D8, D9, D10, D11, D12, controllable switching devices Q25, Q26, Q27, Q28, Q29, Q30, and inductors L7, L8, and L9. As shown in Figure 1 In the circuit structure shown, the plurality of rectifier devices and the plurality of controllable switching devices in the rectification unit form a Vienna structure.

[0072] Among them, the second ends of the rectifier devices D7, D8, and D9 are electrically connected to the positive direct current bus Bus+, serving as the positive output end of the rectifier circuit 11; the first ends of the rectifier devices D10, D11, and D12 are electrically connected to the negative direct current bus Bus-, serving as the negative output end of the rectifier circuit 11. The positive output end of the rectifier circuit 11 is electrically connected to the first end of the first bus capacitor C1, the negative output end of the rectifier circuit 11 is electrically connected to the second end of the second bus capacitor C2, and the second end of the first bus capacitor C1 is electrically connected to the first end of the second bus capacitor C2, and is then electrically connected to the neutral line N.

[0073] The second end of the rectifier D10 and the first end of D7, the second end of the inductor L7 are electrically connected, the second end of the rectifier D11 and the first end of D8, the second end of the inductor L8 are electrically connected, the second end of the rectifier D12 and the first end of D9, the second end of the inductor L9 are electrically connected. The first end of the three inductors is coupled to the second end of the three controllable relays of the power relay RL3.

[0074] In Figure 1 In the circuit structure shown, the rectifier can be a diode, and the rectifier can also be a switch tube, such as MOSFET, IGBT, etc.

[0075] The pre-charge circuit 10 includes an uncontrollable three-phase bridge circuit, pre-charge relays RL1, RL2, current limiting resistors R1, R2. The uncontrollable three-phase bridge circuit includes diodes D1, D2, D3, D4, D5, D6.

[0076] The cathodes of diodes D1, D2 and D3 are electrically connected, and then connected to the first end of the filter capacitor C1 through the current limiting resistor R1 and the pre-charge relay RL1, serving as the positive output end of the pre-charge circuit 10; the anodes of diodes D4, D5 and D6 are electrically connected, and then connected to the second end of the filter capacitor C2 through the current limiting resistor R2 and the pre-charge relay RL2, serving as the negative output end of the pre-charge circuit 10.

[0077] In some embodiments, the pre-charge circuit 10 further includes a filter capacitor C3, the positive output end of the pre-charge circuit 10 and the first end of the filter capacitor C3 are electrically connected, and the negative output end of the pre-charge circuit 10 and the second end of the filter capacitor C3 are electrically connected.

[0078] The anode of diode D1 and the cathode of D4 are electrically connected and connected to the power line U, the anode of diode D2 and the cathode of D5 are electrically connected and connected to the power line V, and the anode of diode D3 and the cathode of D6 are electrically connected and connected to the power line W.

[0079] In Figure 1 In the circuit structure shown, the positive output end of the pre-charge circuit 10 is electrically connected to the positive DC bus Bus+, and the negative output end is electrically connected to the negative DC bus Bus-.

[0080] After the UPS is started, the mains relay RL3 is in an open state, the pre-charge relays RL1 and RL2 in the pre-charge circuit 10 are closed, and then the uncontrolled three-phase bridge circuit generates a rectified electrical signal based on the three-phase mains power, and the rectified electrical signal is provided to the first end of the first bus capacitor C1 through the current-limiting resistor R1, the pre-charge relay RL1, and the positive DC bus Bus+, and the rectified electrical signal is provided to the second end of the second bus capacitor C2 through the current-limiting resistor R2, the pre-charge relay RL2, and the negative DC bus Bus-.

[0081] With the pre-charge circuit 10 continuously charging the bus capacitor, the difference between the voltage at the first end of the first bus capacitor C1 and the voltage of the neutral line N continuously increases, and the absolute value of the difference between the voltage at the second end of the first bus capacitor C1 and the voltage of the neutral line N continuously increases.

[0082] Correspondingly, the difference between the positive peak voltage of the mains power and the voltage of the positive DC bus Bus+ decreases, and the absolute value of the difference between the negative peak voltage of the mains power and the voltage of the negative DC bus Bus- decreases.

[0083] When the absolute values of the above differences are within the corresponding preset difference ranges, for example, when the difference between the positive peak voltage of the mains power and the voltage of the positive DC bus Bus+ is less than a preset voltage difference threshold, and the absolute value of the difference between the negative peak voltage of the mains power and the voltage of the negative DC bus Bus- is less than the preset voltage difference threshold, the mains relay RL3 is closed to control the rectifier circuit 11 to perform a rectification operation and jointly charge the bus capacitor with the pre-charge circuit 10.

[0084] Due to the voltage division of the current-limiting resistors R1 and R2 in the pre-charge circuit 10, the absolute value of the mains peak voltage is always greater than the absolute value of the bus voltage. In addition, the voltage at the first end of the controllable relay in the mains relay RL3 is associated with the mains voltage, and the voltage at the second end of the controllable relay is associated with the bus voltage (without considering the voltage drops generated by the paths and devices, the voltage at the first end of the controllable relay is approximately equal to the mains voltage, and the voltage at the second end of the controllable relay is approximately equal to the bus voltage), so there is a large voltage difference between the voltages at the first end and the second end of the controllable relay.

[0085] In addition, due to the existence of a forward current path between the mains power supply end and the bus in the rectifier circuit (for example, there is a diode D7 between the U-phase mains power supply and the first end of the first bus capacitor C1, and the current conduction sequence defined by the diode D7 is from the U-phase power supply end to the bus end), when the controllable relay is controlled to be closed, a large impact current will be generated, which will cause the relay contact to arc, increase the failure rate of the mains relay, and further affect the reliability of the uninterruptible power supply.

[0086] Therefore, how to improve the stability of the power-on process of the uninterruptible power supply has become a research focus.

[0087] To solve the above problems, the application provides an uninterrupted power supply and a soft starting method, device and controller thereof. In the uninterrupted power supply, the inverter circuit is provided with three-phase output terminals, and two output terminals of the pre-charging circuit are correspondingly electrically connected with any two-phase output terminals of the inverter circuit instead of being directly electrically connected with the DC bus. When the uninterrupted power supply charges the bus capacitor by using the pre-charging circuit, the bus capacitor can be charged by energy storage operation and freewheeling operation of the inverter circuit, so that the voltage of the bus capacitor is greater than the peak value of the commercial power. When the commercial power relay is powered on, the voltage value of one end of the commercial power relay electrically connected with the commercial power is lower than the voltage of the bus capacitor. Due to the limitation of the conduction direction of the rectifier device in the rectifier circuit, the impact current will not appear again, the relay contact arc phenomenon caused by the impact current is reduced, and the stability of the uninterrupted power supply during the power-on process is improved.

[0088] The technical solutions of the application will be described in detail below with specific examples. The following specific examples can be combined with each other, and the same or similar concepts or processes can not be described in some examples.

[0089] First, the circuit structure of the uninterrupted power supply provided by the application is explained.

[0090] Figure 2 As shown in FIG. 1, the uninterrupted power supply provided by the application according to an exemplary embodiment includes a pre-charging circuit 10, a rectifier circuit 11, an inverter circuit 12, a commercial power relay RL3, a first bus capacitor C1 and a second bus capacitor C2. Figure 2

[0091] The front stage of the uninterrupted power supply is provided with a UPS front-stage power distribution transformer, and the UPS front-stage power distribution transformer is electrically connected with the AC input terminal of the rectifier circuit 11 through the commercial power relay RL3.

[0092] In some embodiments, three commercial power fuses are further connected in series between the UPS front-stage power distribution transformer and the commercial power relay RL3, and the use process of each-phase power is protected.

[0093] In some embodiments, the circuit structure of the rectification unit in the rectifier circuit 11 is as shown in FIG. 2. Figure 2 ​The rectifier unit includes six rectifier modules, three energy storage modules and three midpoint freewheeling modules. The first ends of the first rectifier module, the second rectifier module and the third rectifier module are electrically connected, serving as the positive output end of the rectifier unit. The second ends of the fourth rectifier module, the fifth rectifier module and the sixth rectifier module are electrically connected, serving as the negative output end of the rectifier unit. The second end of the first rectifier module and the first end of the fourth rectifier module are electrically connected, and the second end of the first energy storage module and the first end of the first midpoint freewheeling module are electrically connected. The second end of the second rectifier module and the first end of the fifth rectifier module are electrically connected, and the second end of the second energy storage module and the first end of the second midpoint freewheeling module are electrically connected. The second end of the third rectifier module and the first end of the sixth rectifier module are electrically connected, and the second end of the third energy storage module and the first end of the third midpoint freewheeling module are electrically connected. The first ends of the three energy storage modules are electrically connected to the second ends of the three controllable relays in the power relay RL3, and the second ends of the three midpoint freewheeling modules are electrically connected to the neutral line.

[0094] In some embodiments, the rectifier module includes a diode, the anode of the diode serving as the second end of the rectifier module, and the cathode of the diode serving as the first end of the rectifier module. The structure of the corresponding rectifier module constructed by using diodes D7, D8, D9, D10, D11 and D12 is shown in Figure 2

[0095] In some embodiments, the rectifier module includes a controllable switching device, which can be a controllable transistor such as a field effect transistor or a triode, or a controllable device such as a relay or a contactor. Taking a rectifier module including an N-type field effect transistor as an example, the source of the CMOS serves as the first end of the rectifier module, and the drain of the CMOS serves as the second end of the rectifier module.

[0096] In some embodiments, the rectifier module can include a controllable switching device and a parallelly connected related device, which can be a diode. When the parallelly connected related device is a diode, the diode and the controllable switching device are anti-parallelly connected, i.e., the conduction direction of the controllable switching device is from the second end to the first end of the rectifier module, and the conduction direction of the diode is from the first end to the second end of the rectifier module.

[0097] In some embodiments, the energy storage module includes an inductor, the first end of the inductor serving as the first end of the energy storage module, and the second end of the inductor serving as the second end of the energy storage module. The structure of the energy storage module constructed by using inductors L7, L8 and L9 is shown in Figure 2

[0098] ​​In some embodiments, the midpoint freewheeling module is a controllable bidirectional conduction module, including at least two controllable switching devices: a first controllable switching device and a second controllable switching device, a first end of the first controllable switching device and a first end of the midpoint freewheeling module are electrically connected or coupled, a second end of the first controllable switching device and a second end of the midpoint freewheeling module are electrically connected or coupled; a first end of the second controllable switching device and the second end of the midpoint freewheeling module are electrically connected or coupled, a second end of the second controllable switching device and the first end of the midpoint freewheeling module are electrically connected or coupled. When the midpoint freewheeling module conducts from its first end to its second end, the first controllable switching device conducts in the conduction direction; when the midpoint freewheeling module conducts from its second end to its first end, the second controllable switching device conducts in the conduction direction.

[0099] In Figure 2 In the embodiment shown, the first midpoint freewheeling module includes controllable switching devices Q25 and Q26, the second midpoint freewheeling module includes controllable switching devices Q27 and Q28, and the third midpoint freewheeling module includes controllable switching devices Q29 and Q30. Within each midpoint freewheeling module, the two controllable switching devices are connected in reverse series. Taking controllable switching devices Q25 and Q26 as an example, a first end of controllable switching device Q25 is electrically connected to a second end of corresponding inductor L7, a second end of controllable switching device Q25 is electrically connected to a second end of controllable switching device Q26, a first end of controllable switching device Q26 is electrically connected to neutral line N, and the two controllable switching devices in the midpoint freewheeling module are used to maintain a bidirectional conduction path between the input end of the rectifier circuit and neutral line N.

[0100] The controllable switching device includes a CMOS and a diode connected in anti-parallel with the CMOS. Taking an N-type CMOS as an example, a drain of the CMOS is electrically connected to a cathode of the anti-parallel diode, and a source of the CMOS is electrically connected to an anode of the anti-parallel diode. Taking controllable switching device Q25 as an example, a first end of controllable switching device Q25 is electrically connected to a second end of corresponding inductor L7, a second end of controllable switching device Q25 is electrically connected to a second end of controllable switching device Q26, a first end of controllable switching device Q26 is electrically connected to neutral line N, and the two controllable switching devices in the midpoint freewheeling module are used to maintain a bidirectional conduction path between the input end of the rectifier circuit and neutral line N. Figure 2 Taking the first midpoint freewheeling module as an example, the CMOS in controllable switching devices Q25 and Q26 is connected in common source. When the midpoint freewheeling module conducts from its second end to its first end, the CMOS in controllable switching device Q26 conducts, and the anti-parallel diode in controllable switching device Q25 conducts; when the midpoint freewheeling module conducts from its first end to its second end, the CMOS in controllable switching device Q25 conducts, and the anti-parallel diode in controllable switching device Q26 conducts.

[0101] The midpoint freewheeling module has other internal structures, which will be explained in the circuit structure of the subsequent inverter circuit.

[0102] In other embodiments, the circuit structure in the rectifier module can also be replaced by a double boost circuit.

[0103] The inverter circuit 12 comprises at least one inverter unit 121, each inverter unit 121 comprising a three-phase three-level inverter circuit, the three-phase three-level inverter circuit comprising three single-phase three-level inverter circuits, each single-phase three-level inverter circuit comprising a first switch module, a second switch module, a midpoint freewheeling module and an energy storage module;

[0104] In the single-phase three-level inverter circuit, the first end of the first switch module is electrically connected to the positive input end of the inverter circuit, the second end of the second switch module is electrically connected to the negative input end of the inverter circuit, the second end of the first switch module, the first end of the second switch module and the midpoint freewheeling module are electrically connected, the first end of the midpoint freewheeling module is electrically connected through the energy storage module and the corresponding phase output end of the inverter unit, and the second end of the midpoint freewheeling module is electrically connected to the neutral line.

[0105] In some embodiments, the three-level inverter circuit is a T-type three-level inverter circuit, and the second end of the first switch module, the first end of the second switch module and the first end of the midpoint freewheeling module are electrically connected;

[0106] When the inverter circuit is energized, the first conduction current path of the midpoint freewheeling module coupled to the positive output end of the pre-charging circuit is from the first end to the second end thereof, and the first conduction current path of the midpoint freewheeling module coupled to the negative output end of the pre-charging circuit is from the second end to the first end thereof;

[0107] When the inverter circuit is freewheeling, each midpoint freewheeling module is turned off, and there is no conduction current path.

[0108] The midpoint freewheeling module comprises a first controllable switching device and a second controllable switching device, the first end of the first controllable switching device serving as the first end of the midpoint freewheeling module, the second end of the first controllable switching device and the second end of the second controllable switching device being electrically connected, and the first end of the second controllable switching device serving as the second end of the midpoint freewheeling module.

[0109] One circuit structure of the inverter circuit 12 based on the T-type three-level inverter circuit can be as shown in Figure 2 The first inverter unit comprises switching devices Q1, Q2, Q3, Q10, Q11 and Q12, controllable switching devices Q4, Q5, Q6, Q7, Q8 and Q9, and freewheeling inductors L1, L2 and L3. The second inverter unit comprises switching devices Q13, Q14, Q15, Q22, Q23 and Q24, controllable switching devices Q16, Q17, Q18, Q19, Q20 and Q21, and freewheeling inductors L4, L5 and L6.

[0110] Taking the first inverter unit 121, i.e. Figure 2 The midpoint of the upper inverter unit 121 is taken as an example to explain the circuit structure of the T-type three-level inverter circuit.

[0111] The first inverter unit 121 includes a U-phase three-level inverter circuit, a V-phase three-level inverter circuit and a W-phase three-level inverter circuit. In the U-phase three-level inverter circuit, the first switch module includes a switch device Q1, the second switch module includes a switch device Q10, the energy storage module includes a freewheeling inductor L1, and the midpoint freewheeling module includes controllable switch devices Q7 and Q4.

[0112] Each of the switch devices and the controllable switch devices includes a CMOS. Taking an N-type CMOS as an example, the U-phase three-level inverter circuit is explained. The switch device Q1 includes an N-type CMOS, the drain of the CMOS is electrically connected to the positive input end of the inverter circuit as the first end of the first switch module, and the source of the CMOS is electrically connected to the first end of the freewheeling inductor L1 as the second end of the first switch module, and the second end of the freewheeling inductor L1 is electrically connected to the U-phase output end of the inverter circuit.

[0113] The switch device Q10 includes an N-type CMOS, the drain of the CMOS is electrically connected to the source of the CMOS in the switch device Q1 as the first end of the second switch module, and the source of the CMOS is electrically connected to the negative input end of the inverter circuit as the second end of the second switch module.

[0114] In some embodiments, each of the switch devices includes a CMOS and a diode anti-parallel to the CMOS.

[0115] In the U-phase three-level inverter circuit, the midpoint freewheeling module includes a first controllable switch device Q4 and a second controllable switch device Q7, and each of the controllable switch devices includes a CMOS and a diode anti-parallel to the CMOS.

[0116] When the CMOS is an N-type CMOS, the drain of the CMOS in the first controllable switch device Q4 is electrically connected to the source of the CMOS in the second controllable switch device Q7 as the first end of the midpoint freewheeling module, the source of the CMOS in the first controllable switch device Q4 and the source of the CMOS in the second controllable switch device Q7 are electrically connected, and the drain of the CMOS in the second controllable switch device Q7 is electrically connected to the N line as the second end of the midpoint freewheeling module.

[0117] When the current conduction direction of the midpoint freewheeling module is from the first end to the second end, the CMOS in the first controllable switch device Q4 is turned on, and the diode in the second controllable switch device Q7 is turned on; when the current conduction direction of the midpoint freewheeling module is from the second end to the first end, the diode in the first controllable switch device Q4 is turned on, and the CMOS in the second controllable switch device Q7 is turned on.

[0118] In some embodiments, Figure 2 In the circuit structure shown, the conduction current path generated in the energy storage process of the inverter unit is as shown in Figure 4AAs shown, the positive output end of the pre-charge circuit is electrically connected to the Uo end of the inverter circuit to obtain a forward signal, which sequentially passes through the freewheeling inductor L1, the CMOS in the controllable switching device Q4, the diode in the controllable switching device Q7, the N line, the CMOS in the controllable switching device Q9, the diode in the controllable switching device Q6, the freewheeling inductor L3, the Wo end of the inverter circuit, and the negative output end of the pre-charge circuit.

[0119] The conduction current path generated in the freewheeling process of the inverter unit is as shown in Figure 4B As shown, the Uo end of the inverter circuit, the freewheeling inductor L1, the diode in the switching device Q1, the first bus capacitor C1, the second bus capacitor C2, the diode in the switching device Q12, the freewheeling inductor L3, and the Wo end of the inverter circuit are sequentially connected.

[0120] In other embodiments, the CMOS in the midpoint freewheeling module can also be connected in common-drain mode. As shown in Figure 2 The first controllable switching device Q4 and the second controllable switching device Q7 are replaced, or the CMOS in the controllable switching device is replaced by a P-type CMOS.

[0121] In other embodiments, the first controllable switching device Q4 and the second controllable switching device Q7 in the midpoint freewheeling module can be electrically connected in parallel. In some cases, in order to limit the current conduction direction of the circuit branch in which the controllable switching device is located, a diode is connected in series with each controllable switching device, and the conduction direction of the diode is consistent with the conduction direction of the CMOS in the controllable switching device. The circuit connection relationship is as shown in Figure 3A In other cases, only the CMOS is included in the controllable switching device, and the CMOS in the two controllable switching devices are connected in anti-parallel, that is, the source of the CMOS in the controllable switching device Q4 and the drain of the CMOS in the controllable switching device Q7 are electrically connected, and the drain of the CMOS in the controllable switching device Q4 and the source of the CMOS in the controllable switching device Q7 are electrically connected. The circuit connection relationship is as shown in Figure 3B .

[0122] In other embodiments, the three-level inverter circuit is an I-type three-level inverter circuit. A circuit structure of an inverter unit 121 based on the I-type three-level inverter circuit can be as shown in Figure 3C As shown, the I-type three-level inverter circuit includes a U-phase three-level inverter circuit, a V-phase three-level inverter circuit, and a W-phase three-level inverter circuit. In the U-phase three-level inverter circuit, the first switching module includes the switching device Q1, the second switching module includes the switching device Q10, the energy storage module includes the freewheeling inductor L1, and the midpoint freewheeling module includes the controllable switching devices Q7 and Q4, the first energy storage diode D13, and the second energy storage diode D14. The devices included in the three-level inverter circuits of other phases are similar, and are not listed one by one.

[0123] The following takes the U-phase inverter circuit shown in Figure 3C The circuit structure is explained taking the U-phase inverter circuit shown in FIG. 1 as an example.

[0124] The second end of the first switch module and the third end of the midpoint freewheeling module are electrically connected to point A, and the first end of the second switch module and the fourth end of the midpoint freewheeling module are electrically connected to point B; the first end of the midpoint freewheeling module and the first end of the freewheeling inductor L1 are electrically connected to point D, and the second end of the midpoint freewheeling module and the N line are electrically connected to point C.

[0125] When the inverter circuit stores energy, the first conduction current path of the midpoint freewheeling module coupled with the positive output end of the pre-charge circuit is a path from the first end of the midpoint freewheeling module, through the fourth end, to the second end; and the first conduction current path of the midpoint freewheeling module coupled with the negative output end of the pre-charge circuit is a path from the second end of the midpoint freewheeling module, through the third end, to the first end.

[0126] When the inverter circuit freewheels, the second conduction current path of the midpoint freewheeling module coupled with the negative output end of the pre-charge circuit is a path from the second end of the midpoint freewheeling module, through the third end, to the first end.

[0127] The midpoint freewheeling module includes a first controllable switching device, a second controllable switching device, a first energy storage diode, and a second energy storage diode. The first end of the first controllable switching device serves as the first end (point D) of the midpoint freewheeling module. The second end of the first controllable switching device and the first end of the first energy storage diode are electrically connected, serving as the fourth end (point B) of the midpoint freewheeling module. The second end of the first energy storage diode and the first end of the second energy storage diode are electrically connected, serving as the second end (point C) of the midpoint freewheeling module. The first end of the second controllable switching device and the second end of the second energy storage diode are electrically connected, serving as the third end (point A) of the midpoint freewheeling module. The second end of the second controllable switching device and the first end of the first controllable switching device are electrically connected. The circuit structures of the first switch module and the second switch module are the same as those of Figure 2 The structures of the switch modules in the corresponding embodiments are the same, and will not be described again here.

[0128] In the midpoint freewheeling module, each controllable switching device includes a CMOS and a diode connected in antiparallel with the CMOS. When the CMOS is an N-type CMOS, the drain of the CMOS in the controllable switching device Q4 is electrically connected to the first end of the midpoint freewheeling module and the first end of the freewheeling inductor L1, the source of the CMOS in the controllable switching device Q4 is electrically connected to the anode of the first energy storage diode D13, which is the fourth end of the midpoint freewheeling module, the anodes of the first energy storage diode D13 and the second energy storage diode D14 are electrically connected, which are the second end of the midpoint freewheeling module, the cathode of the second energy storage diode D14 is electrically connected to the drain of the CMOS in the controllable switching device Q7, which is the third end of the midpoint freewheeling module, and the source of the CMOS in the controllable switching device Q7 is electrically connected to the drain of the CMOS in the controllable switching device Q4.

[0129] The connection relationship of the three-level inverter circuit of the other phase is similar to that of the U-phase three-level inverter circuit, and will not be described here.

[0130] In the above circuit structure, the controllable switching device can be a controllable transistor such as a field effect transistor or a triode, and can also be a controllable device such as a relay or a contactor.

[0131] When the pre-charging circuit 10 and the inverter circuit 12 are connected, the two output ends of the pre-charging circuit 10 are electrically connected to any two output ends of the inverter circuit 12. Figure 2 In the circuit connection relationship shown, the positive output end of the pre-charging circuit 10 is electrically connected to the U-phase output end of the inverter circuit 12, and the negative output end of the pre-charging circuit 10 is electrically connected to the W-phase output end of the inverter circuit 12.

[0132] The conduction current path generated by the energy storage process of the inverter circuit is shown in Figure 5A , and is in turn: the inverter circuit Uo end, the freewheeling inductor L1, the CMOS in the controllable switching device Q4, the first energy storage diode D13, the second energy storage diode D18, the CMOS in the controllable switching device Q9, the freewheeling inductor L3, and the inverter circuit Wo end.

[0133] The conduction current path generated by the freewheeling process of the inverter circuit is shown in Figure 5B , and is in turn: the inverter circuit Uo end, the freewheeling inductor L1, the diode in the controllable switching device Q7, the diode in the switching device Q1, the first bus capacitor C1, the second bus capacitor C2, the diode in the switching device Q12, the diode in the controllable switching device Q6, the freewheeling inductor L3, and the inverter circuit Wo end.

[0134] The operation process of the uninterruptible power supply will be explained below in connection with the circuit structure shown in Figure 2 . Figure 6 The soft start method of the uninterruptible power supply provided by the present application according to an exemplary embodiment is shown in Figure 6As shown, the method comprises:

[0135] S101, control the pre-charge circuit to be turned on.

[0136] After the uninterrupted power supply is started, the pre-charge relays RL1 and RL2 of the pre-charge circuit 10 are closed, and one phase of the three-phase power supply in the positive half cycle is transmitted to the U-phase output end of the inverter circuit 12 through the positive bridge arm circuit of the uncontrollable three-phase bridge circuit, and one phase of the three-phase power supply in the negative half cycle is transmitted to the W-phase output end of the inverter circuit 12 through the negative bridge arm circuit of the uncontrollable three-phase bridge circuit.

[0137] S102, control the inverter circuit to alternately perform energy storage operation and freewheeling operation.

[0138] When the inverter circuit is controlled to perform energy storage operation, the midpoint freewheeling module coupled to the positive output end of the pre-charge circuit 10 is controlled to be turned on in a first direction, and the first direction is the direction of current flowing from the positive output end of the pre-charge circuit 10 to the neutral line.

[0139] The controllable switch unit coupled to the negative output end of the pre-charge circuit 10 is controlled to be turned on in a second direction, and the second direction is the direction of current flowing from the neutral line to the negative output end of the pre-charge circuit 10.

[0140] Control the other switching devices to be turned off.

[0141] Then, for Figure 2 As shown in the T-type three-level circuit structure, for the first inverter unit, the controllable switching devices Q4 and Q7 coupled to the U-phase output end Uo are turned on, and the controllable switching devices Q9 and Q6 coupled to the W-phase output end Wo are turned on, thereby forming the following loop: the power supply, the positive bridge arm circuit of the uncontrollable three-phase bridge circuit of the pre-charge circuit 10, the current limiting resistor R1, the pre-charge relay RL1, the freewheeling inductor L1, the CMOS in the controllable switching device Q4, the diode in the controllable switching device Q7, the neutral line N, the CMOS in the controllable switching device Q9, the diode in the controllable switching device Q6, the freewheeling inductor L3, the pre-charge relay RL2, the current limiting resistor R2, the negative bridge arm circuit of the uncontrollable three-phase bridge circuit of the pre-charge circuit 10, and the power supply.

[0142] For Figure 3AIn the shown T-type three-level circuit structure, the controllable switching device Q4 coupled to the U-phase output terminal Uo is turned on, and the controllable switching device Q9 coupled to the W-phase output terminal Wo is turned on, thereby forming a loop as follows: the power supply, the positive bridge arm circuit of the non-controllable three-phase bridge circuit in the pre-charge circuit 10, the current-limiting resistor R1, the pre-charge relay RL1, the freewheeling inductor L1, the CMOS in the controllable switching device Q4, the neutral line N, the CMOS in the controllable switching device Q9, the freewheeling inductor L3, the pre-charge relay RL2, the current-limiting resistor R2, the negative bridge arm circuit of the non-controllable three-phase bridge circuit in the pre-charge circuit 10, and the power supply.

[0143] For Figure 3B In the shown T-type three-level circuit structure, the controllable switching device Q4 coupled to the U-phase output terminal Uo is turned on, and the controllable switching device Q9 coupled to the W-phase output terminal Wo is turned on, thereby forming a loop as follows: the power supply, the positive bridge arm circuit of the non-controllable three-phase bridge circuit in the pre-charge circuit 10, the current-limiting resistor R1, the pre-charge relay RL1, the freewheeling inductor L1, the CMOS in the controllable switching device Q4, the neutral line N, the CMOS in the controllable switching device Q9, the freewheeling inductor L3, the pre-charge relay RL2, the current-limiting resistor R2, the negative bridge arm circuit of the non-controllable three-phase bridge circuit in the pre-charge circuit 10, and the power supply.

[0144] For Figure 3C In the shown I-type three-level circuit structure, the controllable switching device Q4 coupled to the U-phase output terminal Uo is turned on, and the controllable switching device Q9 coupled to the W-phase output terminal Wo is turned on, thereby forming a loop as follows: the power supply, the positive bridge arm circuit of the non-controllable three-phase bridge circuit in the pre-charge circuit 10, the current-limiting resistor R1, the pre-charge relay RL1, the freewheeling inductor L1, the CMOS in the controllable switching device Q4, the first energy storage diode D13, the neutral line N, the second energy storage diode D18, the CMOS in the controllable switching device Q9, the freewheeling inductor L3, the pre-charge relay RL2, the current-limiting resistor R2, the negative bridge arm circuit of the non-controllable three-phase bridge circuit in the pre-charge circuit 10, and the power supply.

[0145] The switching devices at corresponding positions in other inverter circuits are also turned on to generate similar energy storage loops, which are not described herein again.

[0146] When the inverter circuit is controlled to perform freewheeling operation, all the switching devices in the inverter circuit are turned off.

[0147] Then, referring to the T-type three-level circuit structure shown in Figure 2 , Figure 3A , Figure 3B The freewheeling loop formed for the first inverter unit includes:

[0148] AC power supply, positive bridge arm circuit of the uncontrolled three-phase bridge circuit in the pre-charge circuit 10, current-limiting resistor R1, pre-charge relay RL1, freewheeling inductor L1, diode in switch Q1, first bus capacitor C1, second bus capacitor C2, diode in switch Q12, freewheeling inductor L3, pre-charge relay RL2, current-limiting resistor R2, negative bridge arm circuit of the uncontrolled three-phase bridge circuit in the pre-charge circuit 10, AC power supply.

[0149] Reference Figure 3C The I-type three-level circuit structure shown in the figure, the freewheeling circuit comprises:

[0150] AC power supply, positive bridge arm circuit of the uncontrolled three-phase bridge circuit in the pre-charge circuit 10, current-limiting resistor R1, pre-charge relay RL1, freewheeling inductor L1, diode in switch Q7, diode in switch Q1, first bus capacitor C1, second bus capacitor C2, diode in switch Q12, diode in switch Q6, freewheeling inductor L3, pre-charge relay RL2, current-limiting resistor R2, negative bridge arm circuit of the uncontrolled three-phase bridge circuit in the pre-charge circuit 10, AC power supply.

[0151] Since the freewheeling current generated by the freewheeling inductor L1 is from the U-phase output end Uo to the neutral line N, and the freewheeling current generated by the freewheeling inductor L3 is from the neutral line N to the W-phase output end Wo during the energy storage operation, the voltage value at the first end of the first bus capacitor C1 is increased based on the energy storage of the freewheeling inductor L1 and the positive forward signal of the AC power supply, and the voltage value at the second end of the second bus capacitor C2 is decreased based on the energy storage of the freewheeling inductor L3 and the reverse signal of the AC power supply.

[0152] After the energy storage operation and the freewheeling operation are repeated for a plurality of times, the absolute value of the difference between the bus voltage and the neutral line voltage is greater than the absolute value of the difference between the AC voltage peak value and the neutral line voltage.

[0153] S103, obtain a first voltage difference between the positive direct current bus voltage and the neutral line voltage, and a second voltage difference between the negative direct current bus voltage and the neutral line voltage.

[0154] In the process of charging the bus capacitor, the voltage value of the positive direct current bus Bus+ and the first voltage difference between the voltage of the neutral line N, and the voltage value of the negative direct current bus Bus- and the second voltage difference between the voltage of the neutral line N are sampled based on a preset time interval.

[0155] S104, when the first voltage difference is greater than a first preset voltage difference, and the absolute value of the second voltage difference is greater than the first preset voltage difference, control the AC relay to be closed.

[0156] The first preset voltage difference is greater than or equal to an absolute value of a difference between the peak mains voltage and the neutral voltage.

[0157] In some embodiments, when the first preset voltage difference is equal to the absolute value of the difference between the peak mains voltage and the neutral voltage, the uninterruptible power supply can control the mains relay to close after the absolute value of the bus capacitor voltage exceeds the absolute value of the peak mains voltage.

[0158] In other embodiments, when the first preset voltage difference is greater than the absolute value of the difference between the peak mains voltage and the neutral voltage, the uninterruptible power supply can control the mains relay to close when the absolute value of the bus capacitor voltage exceeds the absolute value of the peak mains voltage by a preset voltage value, where the preset voltage value is a difference between the first preset voltage difference and a voltage difference between the peak mains voltage and the neutral voltage.

[0159] After the mains relay is closed, the uninterruptible power supply can charge the bus capacitor through a rectified current.

[0160] When the mains relay RL3 is closed, during a positive half cycle of any phase mains signal, the midpoint freewheeling module corresponding to the phase in the rectifier circuit 11 is turned on from its first end to its second end, storing energy in the energy storage inductor corresponding to the phase, and then the midpoint freewheeling module is turned off, so that the phase mains and the energy stored in the energy storage inductor charge the first bus capacitor C1; during a negative half cycle of the phase mains signal, the midpoint freewheeling module corresponding to the phase is turned on from its second end to its first end, storing energy in the energy storage inductor corresponding to the phase, and then the midpoint freewheeling module is turned off, so that the phase mains and the energy stored in the energy storage inductor discharge the second bus capacitor C2.

[0161] For example, when the U-phase mains positive half cycle is running, the controllable switching device Q25 is turned on, and then a conduction loop is formed between the U-phase power supply, the mains relay RL3, the energy storage inductor L7, the CMOS in the controllable switching device Q25, the diode in the controllable switching device Q26, and the neutral line N, charging the energy storage inductor L7, and the energy storage current direction of the energy storage inductor L7 is from left to right. After the energy storage is completed, the CMOS in the controllable switching device Q25 is turned off, a conduction loop is formed between the U-phase power supply, the mains relay RL3, the energy storage inductor L7, the diode D7, the first bus capacitor C1, and the neutral line N, the U-phase power supply and the energy storage inductor L7 charge the first end of the first bus capacitor C1, and the voltage value of the first end of the first bus capacitor C1 increases.

[0162] When the U-phase half cycle of the mains power is in operation, the controllable switch Q26 is turned on, and a conduction loop is formed by the neutral line N, the CMOS in the controllable switch Q26, the diode in the controllable switch Q25, the energy storage inductor L7, the mains relay RL3 and the U-phase power supply, so as to charge the energy storage inductor L7, and the energy storage current of the energy storage inductor L7 flows from right to left. After the energy storage is completed, the CMOS in the controllable switch Q26 is turned off, and a conduction loop is formed by the neutral line N, the diode D10, the energy storage inductor L7, the mains relay RL3 and the U-phase power supply, so as to continuously discharge the second bus capacitor C2, and the voltage value of the second end of the second bus capacitor C2 is reduced.

[0163] The operation processes of other phases are similar, and will not be described here.

[0164] After the mains relay is closed, the pre-charge circuit is turned off.

[0165] In the above technical solution, the two output ends of the pre-charge circuit and the output ends of any two phases of the inverter circuit are correspondingly connected, instead of being directly connected to the DC bus, and when the pre-charge circuit charges the bus capacitor, the bus capacitor can be charged by the energy storage operation and the freewheeling operation of the inverter circuit, so that the voltage of the bus capacitor is greater than the peak value of the mains power, and when the mains relay is powered on, the voltage of the end connected to the mains power is lower than the voltage of the bus capacitor. Due to the limitation of the conduction direction of the rectifier device in the rectifier circuit, the inrush current will not appear again, the phenomenon of relay contact arc caused by the inrush current is reduced, and the stability of the power-on process of the uninterruptible power supply is improved. In addition, due to the energy storage operation of the inverter circuit, the charging time of the bus capacitor can be shortened, so that the bus voltage in the uninterruptible power supply reaches the target threshold as soon as possible.

[0166] Figure 7 A structure diagram of a soft start device of an uninterruptible power supply according to an embodiment of the present application is provided, and the soft start device 400 of the uninterruptible power supply includes an acquisition module 401 and a processing module 402, wherein,

[0167] The processing module 402 is configured to control the pre-charge circuit to be turned on and control the inverter circuit to alternately perform the energy storage operation and the freewheeling operation.

[0168] The acquisition module 401 is configured to acquire a first voltage difference between the positive DC bus voltage and the neutral line voltage and a second voltage difference between the negative DC bus voltage and the neutral line voltage.

[0169] The processing module 402 is further configured to control the mains relay to be closed when the first voltage difference is greater than a first preset voltage difference and the absolute value of the second voltage difference is greater than the first preset voltage difference.

[0170] The first preset voltage difference is greater than or equal to the absolute value of the difference between the peak value of the mains power and the neutral line voltage.

[0171] In some possible embodiments, the processing module 402 is specifically configured to:

[0172] control the first controllable switching device and the second controllable switching device to be turned on;

[0173] control other switching devices in the inverter circuit to be turned off;

[0174] The inverter circuit includes at least one inverter unit, and the inverter unit includes three single-phase three-level inverter circuits, each single-phase three-level inverter circuit including a first switching module, a second switching module and a midpoint freewheeling module, the second end of the first switching module, the first end of the second switching module, the first end of the midpoint freewheeling module and the corresponding phase output end of the inverter unit being electrically connected, and the second end of the inverter circuit and the neutral line being electrically connected.

[0175] The midpoint freewheeling module includes the first controllable switching device and the second controllable switching device, the first controllable switching device being located on a first conduction current path of the midpoint freewheeling module coupled with the positive output end of the pre-charge circuit, and the second controllable switching device being located on a first conduction current path of the midpoint freewheeling module coupled with the negative output end of the pre-charge circuit; the first conduction current path in the midpoint freewheeling module coupled with the positive output end of the pre-charge circuit is a path from the first end of the midpoint freewheeling module to the second end thereof, and the first conduction current path in the midpoint freewheeling module coupled with the negative output end of the pre-charge circuit is a path from the second end of the midpoint freewheeling module to the first end thereof.

[0176] In some possible embodiments, the processing module 402 is specifically configured to:

[0177] control all switching devices in the inverter circuit to be turned off.

[0178] In some possible embodiments, the processing module 402 is further configured to:

[0179] control the pre-charge circuit to be turned off.

[0180] Figure 8 A structural schematic diagram of a controller provided by the present application according to an embodiment is shown. The controller 500 includes a memory 501 and a processor 502, and the memory 501 is configured to store computer instructions executable by the processor. The memory 501 can include a random access memory (RAM) and can also include a non-volatile memory (NVM), such as at least one disk memory, and can also be a U disk, a mobile hard disk, a read-only memory, a magnetic disk or an optical disk, etc.

[0181] The processor 502 implements each step in the soft start method of the uninterruptible power supply with the controller as the execution subject in the above embodiments when executing computer instructions. Details can be referred to the related description in the foregoing method embodiments. The processor 502 can be a central processing unit (CPU), and can also be other general-purpose processors, digital signal processors (DSP), application specific integrated circuits (ASIC), etc. The general-purpose processor can be a microprocessor, or the processor can also be any conventional processor, etc. The steps of the method disclosed in the application can be directly embodied as hardware processor execution, or executed by a combination of hardware and software modules in the processor.

[0182] Optionally, the memory 501 can be independent or integrated with the processor 502. When the memory 501 is independently arranged, the controller 500 further includes a bus for connecting the memory 501 and the processor 502. The bus can be an industry standard architecture (ISA) bus, a peripheral component interconnect (PCI) bus, an extended industry standard architecture (EISA) bus, etc. The bus can be divided into an address bus, a data bus, a control bus, etc. For the convenience of representation, the bus in the drawings of the present application does not limit to only one bus or one type of bus.

[0183] The embodiments of the present application further provide a computer readable storage medium, and the computer readable storage medium stores computer instructions. When the processor executes the computer instructions, each step of the soft start method of the uninterruptible power supply in the above embodiments is implemented.

[0184] The embodiments of the present application further provide a computer program product, and the computer program product includes computer instructions. When the processor executes the computer instructions, each step of the soft start method of the uninterruptible power supply in the above embodiments is implemented.

[0185] Other embodiments of the application will be apparent to those skilled in the art from consideration of the specification and practice of the application disclosed herein. It is intended that the specification and examples be considered as exemplary only, with the true scope and spirit of the application being indicated by the following claims.

[0186] It is to be understood that the application is not limited to the precise construction herein disclosed and shown in the drawings, and that various modifications and changes can be made by those skilled in the art without departing from the scope of the application. The scope of the application is limited only by the claims that follow.

Claims

1. An uninterruptible power supply, characterized by The application relates to a three-phase three-level inverter circuit. The three-phase input end of the rectifier circuit is correspondingly connected with the three input ends of the power supply relay and the pre-charge circuit through the power supply relay and the pre-charge circuit, the positive output end is connected with the positive input end of the inverter circuit through a positive direct-current bus, the negative output end is connected with the negative input end of the inverter circuit through a negative direct-current bus, the first bus capacitor and the second bus capacitor are connected in series between the positive direct-current bus and the negative direct-current bus, and the connection points of the first bus capacitor and the second bus capacitor are connected with a neutral line. The inverter circuit is provided with three-phase output ends, and the positive output end and the negative output end of the pre-charge circuit are correspondingly connected with any two-phase output ends of the inverter circuit. The inverter circuit comprises at least one inverter unit, each inverter unit comprises a three-phase three-level inverter circuit, the three-phase three-level inverter circuit comprises three single-phase three-level inverter circuits, and each single-phase three-level inverter circuit comprises a first switch module, a second switch module, a midpoint freewheeling module and an energy storage module.

2. The uninterruptible power supply of claim 1, wherein, In the single-phase three-level inverter circuit, the first end of the first switch module is connected with the positive input end of the inverter circuit, the second end of the second switch module is connected with the negative input end of the inverter circuit, the second end of the first switch module, the first end of the second switch module and the midpoint freewheeling module are connected, the first end of the midpoint freewheeling module is connected with the corresponding phase output end of the inverter unit through the energy storage module, and the second end of the midpoint freewheeling module is connected with the neutral line. The three-level inverter circuit is a T-type three-level inverter circuit, the second end of the first switch module, the first end of the second switch module and the first end of the midpoint freewheeling module are connected.

3. The uninterruptible power supply of claim 2, wherein, When the inverter circuit stores energy, the first conduction current path of the midpoint freewheeling module coupled with the positive output end of the pre-charge circuit is a path from the first end to the second end, and the first conduction current path of the midpoint freewheeling module coupled with the negative output end of the pre-charge circuit is a path from the second end to the first end. When the inverter circuit freewheels, each midpoint freewheeling module is turned off. The midpoint freewheeling module comprises a first controllable switch device and a second controllable switch device.

4. The uninterruptible power supply according to claim 3, wherein: The first end of the first controllable switch device serves as the first end of the midpoint freewheeling module. The second end of the first controllable switch device and the second end of the second controllable switch device are connected. The first end of the second controllable switch device serves as the second end of the midpoint freewheeling module. The three-level inverter circuit is an I-type three-level inverter circuit, the second end of the first switch module is connected with the third end of the midpoint freewheeling module, and the first end of the second switch module is connected with the fourth end of the midpoint freewheeling module.

5. The uninterruptible power supply of claim 2, wherein, ​ In the energy storage of the inverter circuit, the first conduction current path of the midpoint freewheeling module coupled with the positive output end of the pre-charge circuit is a path from the first end to the second end through the fourth end, and the first conduction current path of the midpoint freewheeling module coupled with the negative output end of the pre-charge circuit is a path from the second end to the first end through the third end; In the freewheeling of the inverter circuit, the second conduction current path of the midpoint freewheeling module coupled with the positive output end of the pre-charge circuit is a path from the first end to the third end, and the second conduction current path of the midpoint freewheeling module coupled with the negative output end of the pre-charge circuit is a path from the fourth end to the first end.

6. The uninterruptible power supply of claim 5, wherein, The midpoint freewheeling module comprises a first controllable switching device, a second controllable switching device, a first energy storage diode and a second energy storage diode; The first end of the first controllable switching device and the second end of the second controllable switching device are electrically connected as the first end of the midpoint freewheeling module; The second end of the first controllable switching device and the first end of the first energy storage diode are electrically connected as the fourth end of the midpoint freewheeling module; The second end of the first energy storage diode and the first end of the second energy storage diode are electrically connected as the second end of the midpoint freewheeling module; The first end of the second controllable switching device and the second end of the second energy storage diode are electrically connected as the third end of the midpoint freewheeling module.

7. A soft start method of an uninterruptible power supply, characterized by, The method is applied to the uninterruptible power supply of any one of claims 1 to 6, and the method comprises: controlling the pre-charge circuit to conduct; controlling the inverter circuit to alternately perform energy storage operation and freewheeling operation; obtaining a first voltage difference between the positive DC bus voltage and the neutral line voltage and a second voltage difference between the negative DC bus voltage and the neutral line voltage; when the first voltage difference is greater than a first preset voltage difference and the absolute value of the second voltage difference is greater than the first preset voltage difference, controlling the mains relay to be closed; the first preset voltage difference is greater than or equal to the absolute value of the difference between the mains peak voltage and the neutral line voltage.

8. The method of claim 7, wherein, The inverter circuit comprises at least one inverter unit, and the inverter unit comprises three single-phase three-level inverter circuits, the single-phase three-level inverter circuit comprises a first switching module, a second switching module and a midpoint freewheeling module, the second end of the first switching module, the first end of the second switching module, the first end of the midpoint freewheeling module and the corresponding phase output end of the inverter unit are electrically connected, and the second end of the inverter circuit is electrically connected with the neutral line. The midpoint freewheeling module comprises a first controllable switching device and a second controllable switching device, the first controllable switching device is in a first conduction current path of the midpoint freewheeling module coupled with the positive output end of the pre-charge circuit, and the second controllable switching device is in the first conduction current path of the midpoint freewheeling module coupled with the negative output of the pre-charge circuit; the first conduction current path in the midpoint freewheeling module coupled with the positive output end of the pre-charge circuit is a path from the first end of the midpoint freewheeling module to the second end thereof, and the first conduction current path in the midpoint freewheeling module coupled with the negative output end of the pre-charge circuit is a path from the second end of the midpoint freewheeling module to the first end thereof; The method for controlling the inverter circuit to perform the energy storage operation comprises: Controlling the first controllable switching device and the second controllable switching device to be turned on; Controlling other switching devices in the inverter circuit to be turned off.

9. The method of claim 8, wherein, The method for controlling the inverter circuit to perform the freewheeling operation comprises: Controlling all switching devices in the inverter circuit to be turned off.

10. The method according to any one of claims 7 to 9, characterized in that, After controlling the mains relay to be closed, the method further comprises: Controlling the pre-charge circuit to be turned off.

11. A soft start apparatus for an uninterruptible power supply, comprising: Comprise: A processing module configured to control the pre-charge circuit to be turned on and control the inverter circuit to alternately perform the energy storage operation and the freewheeling operation; An acquisition module configured to acquire a first voltage difference between the positive DC bus voltage and the neutral voltage and a second voltage difference between the negative DC bus voltage and the neutral voltage; The processing module is further configured to control the mains relay to be closed when the first voltage difference is greater than a first preset voltage difference and an absolute value of the second voltage difference is greater than the first preset voltage difference; The first preset voltage difference is greater than or equal to an absolute value of a difference between the mains peak voltage and the neutral voltage.

12. A controller characterized by comprising: Comprise: A processor and a memory connected with the processor in communication; The memory stores computer execution instructions; The processor, when executing the computer execution instructions, is configured to implement the method according to any one of claims 7 to 10.

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