Soft start circuit for ups power system

Abstract

The utility model discloses a kind of soft-starting circuit of UPS power system, for the pre-charging of DC bus capacitor in the drive circuit of UPS power system, comprising: pre-charging circuit, its input end is connected with UPS battery, output end is connected with DC bus capacitor, first resistance and first switch tube are arranged in series;Start timing circuit, its input end is connected with UPS battery, output end is connected with the control end of first switch tube, and control switch is internally provided;Control circuit, its input end is connected with UPS battery, output end is connected with auxiliary power supply circuit, and starting switch and switch control unit are connected in series in this control circuit, starting switch control circuit on-off, and switch control unit controls control switch on duration.The UPS power system is started in battery mode, by the soft-starting circuit of this system, avoid the large impact current caused by directly applying battery voltage to rear end, prolong the service life of equipment.Simultaneously, avoid occupying main controller IO port resource, applicable to IO port resource nervous scene.

Description

Technical Field

[0001] This utility model relates to the field of UPS power supply system technology, and in particular to a soft start circuit for a UPS power supply system. Background Technology

[0002] Uninterruptible power supply (UPS) systems are widely used in scenarios requiring continuous power supply to ensure stable power support for load devices even when AC mains power is interrupted. In a UPS system, both the AC input and battery input must charge the DC bus capacitor to a target voltage level (e.g., 360Vdc) to supply the subsequent inverter circuitry for AC output.

[0003] However, when the UPS is powered on in battery mode (i.e., without AC mains power and directly powered by the battery), if the control switch of the power drive circuit is activated directly, the battery voltage will be applied directly to the DC bus capacitor through the inductor, resulting in a huge inrush current. This inrush current may not only cause overvoltage or overheating damage to the DC bus capacitor, but may also cause the power transistor to fail due to overcurrent, seriously affecting the reliability and lifespan of the UPS system.

[0004] To solve the above problems, it is usually necessary to precharge the DC bus capacitor when powering on in battery mode (i.e., soft start). This means that the voltage across the DC bus capacitor is precharged to a level close to the battery voltage, and then gradually boosted to the target voltage (such as 360Vdc) through a boost circuit, thereby effectively avoiding the generation of inrush current.

[0005] Currently, commonly used soft-start circuits employ a "current-limiting resistor + relay" scheme. This scheme achieves rapid startup by connecting a current-limiting resistor in series in the pre-charge circuit and bypassing the resistor through the relay at the appropriate time. Its advantages lie in its simple circuit structure and the ability to simultaneously achieve current limiting and rapid startup through multi-stage parallel design. However, this scheme also has significant drawbacks: driving the relay requires the input / output (I / O) ports of the digital signal processor (DSP), limiting its applicability in applications where DSP resources are limited. Furthermore, the mechanical structure of the relay may lead to slower response speed, limited lifespan, and lower reliability. Utility Model Content

[0006] The purpose of this invention is to provide a soft-start circuit for a UPS power supply system that pre-charges the DC bus capacitor while reducing the demand on I / O port resources.

[0007] To achieve the above objectives, this utility model provides a soft-start circuit for a UPS power system, used to pre-charge the DC bus capacitor in the drive circuit of the UPS power system. The soft-start circuit includes: The pre-charge circuit has its input terminal electrically connected to the UPS battery and its output terminal electrically connected to the DC bus capacitor. A first resistor and a first switching transistor are connected in series in the pre-charge circuit. A start-up timing circuit is provided, the input terminal of which is electrically connected to the UPS battery, and the output terminal of which is electrically connected to the control terminal of the first switching transistor to control the conduction duration of the first switching transistor. The start-up timing circuit is also provided with a control switch for controlling the output state. The control loop has its input terminal electrically connected to the UPS battery and its output terminal electrically connected to the auxiliary power supply circuit. The auxiliary power supply circuit provides the necessary auxiliary power to the main controller of the UPS power system during the startup phase. The control loop also includes a start switch and a switch control unit connected in series. The start switch controls the on / off state of the control loop, and the switch control unit is electrically connected to the control switch and controls the on-time of the control switch.

[0008] Preferably, the start-up timing circuit includes a first regulated power supply circuit and a delay circuit. The input terminal of the first regulated power supply circuit is electrically connected to the UPS battery, and the output terminal of the first regulated power supply circuit is electrically connected to the delay circuit through the control switch. The delay circuit is electrically connected to the control terminal of the first switching transistor. The first regulated power supply circuit is used to provide start-up power to the delay circuit, and the delay circuit controls the conduction time of the first switching transistor based on the consumption time of the start-up power provided by the first regulated power supply circuit.

[0009] Preferably, the delay circuit includes a second resistor and a first capacitor constituting an RC charging loop.

[0010] Preferably, the second resistor is connected in series with the first capacitor, one end of the second resistor is electrically connected to one of the conducting terminals of the control switch, one end of the first capacitor is electrically connected to the positive terminal of the DC bus capacitor, and the connection node between the second resistor and the first capacitor is electrically connected to the control terminal of the first switch.

[0011] Preferably, a third resistor is connected in parallel across the two ends of the first capacitor.

[0012] Preferably, the first regulated power supply circuit includes a fourth resistor and a second capacitor connected in series, and a first Zener diode connected in parallel with the second capacitor. One end of the fourth resistor is electrically connected to the positive terminal of the UPS battery, and the other end of the second capacitor is electrically connected to the positive terminal of the DC bus capacitor. The connection node between the fourth resistor and the second capacitor is electrically connected to one of the conducting terminals of the control switch.

[0013] Preferably, the input terminal of the control loop is electrically connected to the UPS battery through a second voltage regulator circuit, the second voltage regulator circuit including a second Zener diode and a third capacitor connected in parallel across the UPS battery.

[0014] Preferably, the switch control unit includes a fifth resistor, a fourth capacitor, and a switch controller connected in series in the control circuit. The second regulated power supply charges the fourth capacitor through the fifth resistor. The fourth capacitor provides the switch controller with the duration of operation based on the charging time. The switch controller is electrically connected to the control switch. When the switch controller is in operation, the control switch is in the ON state.

[0015] Preferably, the output terminal of the control loop is electrically connected to the auxiliary power supply circuit via a switching circuit; the switching circuit includes a second switching transistor and a third switching transistor, the control terminal of the second switching transistor is electrically connected to one of the conducting terminals of the third switching transistor, the two conducting terminals of the second switching transistor are respectively electrically connected to the positive terminal of the third capacitor and the positive terminal of the auxiliary power supply circuit, the control terminal of the third switching transistor is electrically connected to the positive terminal of the fourth capacitor, and the other conducting terminal of the third switching transistor is electrically connected to the positive terminal of the auxiliary power supply circuit.

[0016] Preferably, a temperature-sensitive resistor is also connected in series in the pre-charge circuit, and the resistance of the temperature-sensitive resistor is negatively correlated with temperature.

[0017] Compared with existing technologies, the soft-start circuit for a UPS power system provided by this invention firstly pre-charges the DC bus capacitor through the first resistor and the first switching transistor in the pre-charge circuit when the UPS power system is powered on in battery mode. This gradually increases the voltage across the DC bus capacitor to a level close to the battery voltage, avoiding the large inrush current caused by directly applying the battery voltage. This effectively reduces the overcurrent and overvoltage risks to the DC bus capacitor and power transistor, protecting the reliability of key components in the UPS system and extending the equipment's lifespan. Furthermore, this solution uses the first switching transistor as the control element of the pre-charge circuit, precisely controlling the conduction time of the first switching transistor through a start-up timing circuit, eliminating the need for mechanical switching actions of relays. This control method avoids occupying the I / O port resources of the main controller, making it particularly suitable for applications with limited I / O port resources, improving the system's design flexibility and resource utilization efficiency. Attached Figure Description

[0018] Figure 1 This is a circuit diagram of the UPS power supply system in an embodiment of this utility model.

[0019] Figure 2 This is a circuit diagram of the pre-charge circuit of the soft-start circuit in this embodiment of the present invention.

[0020] Figure 3 This is a circuit diagram of the control loop of the soft-start circuit in an embodiment of this utility model. Detailed Implementation

[0021] To explain in detail the technical content, structural features, objectives and effects of this utility model, the following description is provided in conjunction with the embodiments and accompanying drawings.

[0022] This embodiment discloses a soft-start circuit for a UPS power system, used to implement a soft start of the UPS power system's drive circuit from the off state to the on state when the UPS power system is powered on in battery mode, that is, when the AC power supply is disconnected and only when the UPS battery is supplied.

[0023] To facilitate understanding of the working principle of this soft-start circuit, the drive circuit of the UPS power supply system will be explained first.

[0024] like Figure 1 The drive circuit includes a power control circuit, a rectifier circuit, and an output circuit.

[0025] The power control circuit includes power transistors Q11 and Q12. The input of the power control circuit is electrically connected to the rectifier circuit and selectively electrically connected to the UPS battery BAT. Specifically, selector switches S3 and S4 are provided between the UPS battery BAT and the power control circuit. When AC power is supplied, selector switches S3 and S4 (such as SCRs) are in the open state; when AC power is disconnected, selector switches S3 and S4 are in the closed state to supply power through the UPS battery BAT.

[0026] The rectifier circuit is used for electrical connection with the AC power supply and includes rectifier switches S1 and S2. The output circuit includes two DC bus capacitors C0, which receive electrical energy from the power control circuit and supply it to the subsequent inverter circuit.

[0027] If the selector switches S3 and S4 are turned on directly during the battery mode startup of the UPS power system, the UPS battery BAT will be directly connected to the two ends of the DC bus capacitor C0 through the inductors L1 and L2, which will generate a large inrush current and cause the DC bus capacitor C0 to be damaged by overcurrent.

[0028] Therefore, when powering on in battery mode, the voltage across the DC bus capacitor C0 needs to be pre-charged to the battery voltage via a soft-start circuit before being boosted to 360Vdc.

[0029] like Figure 2 and Figure 3 The soft-start circuit includes a pre-charge circuit 10, a start timing circuit 11, and a control circuit 20.

[0030] like Figure 2 The input terminal of the precharge circuit 10 is electrically connected to the UPS battery BAT, and the output terminal of the precharge circuit 10 is electrically connected to the DC bus capacitor C0. A first resistor R1 and a first switching transistor Q1 are connected in series on the precharge circuit 10.

[0031] The input terminal of the start-up timing circuit 11 is electrically connected to the UPS battery BAT, and the output terminal of the start-up timing circuit 11 is electrically connected to the control terminal of the first switching transistor Q1 to control the conduction duration of the first switching transistor Q1. The start-up timing circuit 11 is also equipped with a control switch K for controlling the output state.

[0032] like Figure 3 The input terminal of control loop 20 is electrically connected to the UPS battery BAT, and the output terminal of control loop 20 is electrically connected to the auxiliary power circuit Aux. The auxiliary power circuit Aux is used to provide the required auxiliary power to the main controller of the UPS power system during the startup phase. A start switch S0 and a switch control unit 21 are also connected in series in control loop 20. The start switch S0 is used to control the on / off state of control loop 20. The switch control unit 21 is electrically connected to the control switch K and is used to control the on-time of control switch K.

[0033] This embodiment achieves soft start of DC bus capacitor C0 by setting up a pre-charge circuit 10, a start timing circuit 11, and a control circuit 20.

[0034] The first resistor R1 is used to limit the charging current during the charging of the DC bus capacitor C0 to prevent excessive inrush current. The first switch Q1 serves as the on / off control element of the pre-charge circuit 10, and its on / off state directly affects the pre-charge process. The start-up timing circuit 11 determines the pre-charge time of the DC bus capacitor C0 by precisely controlling the on-time of the first switch Q1 to ensure a smooth charging process. In this embodiment, the first switch Q1 is preferably a MOSFET. A unidirectional diode D1 is also provided in the pre-charge circuit 10, which is connected in series with the DC bus capacitor C0. In addition, a seventh resistor R7 is connected in parallel across the DC bus capacitor C0 as the discharge resistor for the DC bus capacitor C0.

[0035] The start switch S0 in the control loop 20 is used to manually or automatically control the on / off state of the control loop 20, thereby initiating the entire soft-start process according to the user's intention.

[0036] During the entire soft start process, when the start switch S0 is closed, the control loop 20 starts working and outputs a power signal to the auxiliary power circuit Aux, thereby enabling the main controller (such as the main control chip) of the UPS power system to start. The main controller controls the power control circuit in the drive circuit to cooperate with the start-up process.

[0037] Simultaneously, the switch control unit 21 drives the control switch K to conduct within a predetermined time period, thereby activating the start-up timing circuit 11 and controlling the first switch transistor Q1 to conduct, pre-charging the DC bus capacitor C0. During the pre-charging period, the output of the control loop 20 continuously outputs a power signal to the auxiliary power supply circuit Aux.

[0038] After the start switch S0 is closed for a predetermined time (e.g., 3 seconds), the DC bus capacitor C0 is pre-charged. Then the start switch S0 is opened, the control circuit 20 stops outputting power signals to the auxiliary power supply circuit Aux, and at the same time, the control switch K in the start timing circuit 11 is opened.

[0039] Therefore, this embodiment achieves effective soft-start of the DC bus capacitor C0 in the UPS power system by configuring the start-up timing circuit 11 and the control loop 20. First, when the UPS system is powered on in battery mode, the DC bus capacitor C0 is pre-charged through the first resistor R1 and the first switching transistor Q1 in the pre-charge loop 10, gradually increasing the voltage across the DC bus capacitor C0 to a level close to the battery voltage. This avoids the large inrush current caused by directly applying the battery voltage, thereby effectively reducing the overcurrent and overvoltage risks of the DC bus capacitor C0 and the power transistor, protecting the reliability of key components in the UPS power system, and extending the service life of the equipment.

[0040] Furthermore, in this embodiment, the soft-start circuit uses the first switching transistor Q1 as the control element of the pre-charge circuit 10. The on-time of the first switching transistor Q1 is precisely controlled by the start-up timing circuit 11, eliminating the need for mechanical switching actions of relays. This control method avoids occupying the I / O port resources of the main controller, making it particularly suitable for application scenarios with limited I / O port resources, thus improving the system's design flexibility and resource utilization efficiency.

[0041] On the other hand, such as Figure 2The start-up timing circuit 11 includes a first regulated power supply circuit 110 and a delay circuit 111. The input terminal of the first regulated power supply circuit 110 is electrically connected to the UPS battery BAT, and the output terminal of the first regulated power supply circuit 110 is electrically connected to the delay circuit 111 through a control switch K. The delay circuit 111 is electrically connected to the control terminal of the first switching transistor Q1. The first regulated power supply circuit 110 is used to provide start-up power to the delay circuit 111, and the delay circuit 111 controls the conduction time of the first switching transistor Q1 based on the consumption time of the start-up power provided by the first regulated power supply circuit 110.

[0042] In this embodiment, the start-up timing circuit 11 mainly consists of a first regulated power supply circuit 110 and a delay circuit 111. The input terminal of the first regulated power supply circuit 110 is electrically connected to the UPS battery BAT, providing the delay circuit 111 with stable start-up power unaffected by voltage fluctuations in the UPS battery BAT, ensuring a constant timing reference voltage for the delay circuit 111, thereby guaranteeing the accuracy of the pre-charge duration. The output terminal of the first regulated power supply circuit 110 is electrically connected to the delay circuit 111 via a control switch K.

[0043] The delay circuit 111 generates a time delay signal based on the duration of consumption of the stable power supplied by the first regulated power supply circuit 110. When the delay circuit 111 starts to consume power, its internal voltage changes over time. When it drops below a preset threshold voltage, the first switch Q1 changes from the on state to the off state, thereby completing the pre-charging process.

[0044] Specifically, the delay circuit 111 includes a second resistor R2 and a first capacitor C1 that form an RC charging loop.

[0045] On the other hand, the second resistor R2 is connected in series with the first capacitor C1. One end of the second resistor R2 is electrically connected to one of the conducting terminals (CN1) of the control switch K. One end of the first capacitor C1 is electrically connected to the positive terminal of the DC bus capacitor C0. The connection node J1 between the second resistor R2 and the first capacitor C1 is electrically connected to the control terminal of the first switch Q1.

[0046] When the control switch K is closed (conducted), the stable voltage from the first regulated power supply circuit 110 will start charging the first capacitor C1 through the control switch K and the second resistor R2. The other end of the first capacitor C1 (i.e., the other end connected in series with the second resistor R2) is electrically connected to the positive terminal of the DC bus capacitor C0. This connection method ensures that the first capacitor C1 can utilize the reference potential of the DC bus capacitor C0 when charging.

[0047] The connection node J1 between the second resistor R2 and the first capacitor C1, i.e., the midpoint of the RC series circuit, is electrically connected to the control terminal of the first switching transistor Q1. During charging, the voltage at this connection node J1 gradually increases as the first capacitor C1 charges. When the voltage at this connection node J1 reaches the trigger voltage of the first switching transistor Q1 (such as the gate threshold voltage of a MOSFET), the first switching transistor Q1 will switch from the off state to the on state, thereby connecting the charging circuit of the DC bus capacitor C0.

[0048] Furthermore, a third resistor R3 is connected in parallel across the two ends of the first capacitor C1.

[0049] When the control time of the delay circuit 111 ends, or the control switch K is opened, the power supply of the RC circuit is cut off, and the charge of the first capacitor C1 needs to be released. The third resistor R3 provides a discharge path, causing the voltage of the first capacitor C1 (i.e., the gate voltage of the first switch Q1) to drop rapidly, causing the first switch Q1 to turn off and the precharge circuit 10 to stop working.

[0050] Therefore, the third resistor R3 is a discharge resistor, whose main functions are: to provide a charge release path for the gate of the first switch Q1, ensuring that the first switch Q1 can be turned off quickly when needed; and to prevent the gate voltage of the first switch Q1 from drifting due to residual charge, thus ensuring the stability of circuit control. Therefore, by selecting a reasonable value for this third resistor R3, the turn-off speed of the first switch Q1 can be adjusted, balancing circuit performance and electromagnetic interference.

[0051] On the other hand, such as Figure 2 The first regulated power supply circuit 110 includes a fourth resistor R4 and a second capacitor C2 connected in series, and a first Zener diode ZD1 connected in parallel with the second capacitor C2. One end of the fourth resistor R4 is electrically connected to the positive terminal of the UPS battery BAT, and the other end of the second capacitor C2 is electrically connected to the positive terminal of the DC bus capacitor C0. The connection node J2 between the fourth resistor R4 and the second capacitor C2 is electrically connected to one of the conducting terminals (CN2) of the control switch K.

[0052] The first Zener diode ZD1 (usually a Zener diode) is connected in parallel across the second capacitor C2. When the voltage across the second capacitor C2 reaches the breakdown voltage of the Zener diode, the Zener diode turns on, limiting the voltage to the set value, thereby providing a stable voltage input for the subsequent circuit (delay circuit 111).

[0053] The fourth resistor R4 is connected in series in the circuit to limit the current and prevent the UPS battery BAT from directly causing excessive current surges to the second capacitor C2 or the Zener diode. At the same time, it works with the second capacitor C2 and the Zener diode to complete the voltage division function.

[0054] The operation of the first regulated power supply circuit 110 is as follows: When the UPS battery BAT is connected to the circuit, the current flows through the fourth resistor R4 to the second capacitor C2, and the second capacitor C2 begins to charge, and the voltage gradually rises. When the voltage across the second capacitor C2 reaches the breakdown voltage of the first Zener diode ZD1, the Zener diode turns on, limiting the voltage from rising further and ensuring that the voltage at the output node (the connection node J2 between the fourth resistor R4 and the second capacitor C2) is stable at the breakdown voltage value of the Zener diode. When the control switch K is turned on, a stable voltage is transmitted to the delay circuit 111 through the control switch K, providing the delay circuit 111 with start-up power and driving the first switch Q1 to turn on.

[0055] Therefore, the stable output voltage provided by the first regulated power supply circuit 110 ensures that the RC time constant of the delay circuit 111 is fixed, thereby ensuring that the charging time of the pre-charge circuit 10 is controllable and avoiding the pre-charge time being too short (current surge) or too long (start-up delay) due to voltage fluctuations.

[0056] On the other hand, such as Figure 3 The input terminal of the control loop 20 is electrically connected to the UPS battery BAT through the second voltage regulator circuit 22. The second voltage regulator circuit 22 includes a second voltage regulator ZD2 and a third capacitor C3 connected in parallel across the two ends of the UPS battery BAT.

[0057] In this embodiment, when the start switch S0 is closed, the UPS battery BAT charges the third capacitor C3 through the sixth resistor R6. When the voltage of the third capacitor C3 reaches the breakdown voltage of the second Zener diode ZD2, it stabilizes at this voltage level, ensuring that the control circuit 20 obtains a stable operating voltage. This completely eliminates the impact of UPS battery BAT voltage fluctuations on the operating performance of the control circuit 20, thereby significantly improving the reliability and accuracy of the soft start process.

[0058] On the other hand, the switch control unit 21 includes a fifth resistor R5, a fourth capacitor C4 and a switch controller OP1 connected in series in the control circuit 20. The second regulated power supply circuit 22 charges the fourth capacitor C4 through the fifth resistor R5. The fourth capacitor C4 provides the switch controller OP1 with the duration of operation based on the charging time. The switch controller OP1 is electrically connected to the control switch K. When the switch controller OP1 is in the operation state, the control switch K is in the on state.

[0059] Specifically, the switch controller OP1 is an optocoupler switch.

[0060] When control circuit 20 is activated by start switch S0, the stable voltage from the second regulated power supply circuit 22 begins charging the fourth capacitor C4 through the fifth resistor R5. The fifth resistor R5 here limits current and, together with the fourth capacitor C4, determines the RC charging time constant. The voltage across the fourth capacitor C4 increases exponentially over time. During the charging process of the fourth capacitor C4, the secondary windings CN1 and CN2 of the optocoupler switch are turned on, thereby turning on the control switch K, which then turns off after the fourth capacitor C4 stops charging.

[0061] On the other hand, the output of control loop 20 is electrically connected to auxiliary power supply circuit Aux through a switching circuit. The switching circuit includes a second switch Q2 and a third switch Q3. The control terminal of the second switch Q2 is electrically connected to one of the conducting terminals of the third switch Q3. The two conducting terminals of the second switch Q2 are electrically connected to the positive terminal of the third capacitor C3 and the positive terminal of the auxiliary power supply circuit Aux, respectively. The control terminal of the third switch Q3 is electrically connected to the positive terminal of the fourth capacitor C4. The other conducting terminal of the third switch Q3 is electrically connected to the positive terminal of the auxiliary power supply circuit Aux.

[0062] In this embodiment, during the charging process of the fourth capacitor C4, the second switch Q2 and the third switch Q3 will also be turned on, causing the control circuit 20 to output a power signal to the auxiliary power supply circuit Aux. Similarly, when the fourth capacitor C4 finishes charging, the second switch Q2 and the third switch Q3 will be turned off, stopping the output of a power signal to the auxiliary power supply circuit Aux.

[0063] Taking a scenario where both the second switch Q2 and the third switch Q3 are transistors, the base of the second switch Q2 is electrically connected to the emitter of the third switch Q3. The emitter of the second switch Q2 is electrically connected to the positive terminal of the third capacitor C3, and the collector of the second switch Q2 is connected to the positive terminal of the auxiliary power supply circuit Aux. The base of the third switch Q3 is electrically connected to the positive terminal of the fourth capacitor C4, and the collector of the third switch Q3 is connected to the positive terminal of the auxiliary power supply circuit Aux. This connection method constitutes a Darlington transistor structure to provide higher current drive capability.

[0064] On the other hand, such as Figure 2 In addition, a temperature-sensitive resistor (NTC) is connected in series in the pre-charge circuit 10. The resistance of the NTC is negatively correlated with the temperature.

[0065] As the DC bus capacitor C0 is charged, the NTC thermistor heats up, its temperature rises, and its resistance decreases. This limits the current during the initial charging phase, thereby reducing the current rating of the first resistor R1 and the first switch Q1. Simultaneously, once the NTC's resistance decreases due to heat, the charging current of the DC bus capacitor C0 can be increased, thus rapidly charging C0 to the UPS battery's BAT voltage level.

[0066] In summary, this utility model discloses a UPS power supply system. When the UPS is powered on based on a battery, its power-on process includes the following five stages: Phase 1> The positive terminal of the UPS battery BAT is connected to the BAT+ port via the battery switch. At this time, as follows: Figure 2 The UPS battery BAT forms a circuit through the fourth resistor R4, the second capacitor C2, the first Zener diode ZD1, and the DC bus capacitor C0, charging the second capacitor C2 and ultimately stabilizing its voltage at 18V. Simultaneously, as... Figure 3 The UPS battery BAT charges the third capacitor C3 through the sixth resistor R6 and the second Zener diode ZD2, and stabilizes the voltage of the third capacitor C3 at 18V.

[0067] Phase 2> When the user powers on the UPS using battery power (BAT) by closing the start switch S0, the third capacitor C3 charges the fourth capacitor C4 through the fifth resistor R5. During the charging process of the fourth capacitor C4 (approximately 3 seconds), the secondary windings CN1 and CN2 of the optocoupler switch are turned on, i.e., the control switch K is turned on, and they are turned off after the fourth capacitor C4 stops charging. During the charging process of the fourth capacitor C4, the second switch Q2 and the third switch Q3 are also turned on, causing the auxiliary power circuit Aux of the UPS power system to start working.

[0068] After CN1 and CN2 are turned on in stage 3, the energy stored in the second capacitor C2 charges the first capacitor C1 through the second resistor R2, and turns on the first switch Q1.

[0069] Stage 4> After the first switch Q1 is turned on, the positive terminal (BAT+) of the UPS battery BAT charges the DC bus capacitor C0 through the first resistor R1, the temperature-sensitive resistor NTC, and the unidirectional diode D1.

[0070] After stage 5 > 5 seconds, the voltage of the first capacitor C1 discharges to a level lower than the conduction threshold voltage of the first switch Q1. At this time, the start switch S0 has also returned to the open state, so the first switch Q1 is turned off, and the soft start of the DC bus capacitor C0 ends.

[0071] After the soft start is completed, the UPS battery BAT outputs a power signal to the downstream inverter circuit through the DC bus capacitor C0. At the same time, the main controller is powered through the DC bus, and the UPS power system enters normal working state.

[0072] The above-disclosed embodiments are merely preferred embodiments of the present utility model and should not be construed as limiting the scope of the present utility model. Therefore, any equivalent variations made in accordance with the scope of the present utility model application shall still fall within the scope of the present utility model.

Claims

1. A soft-start circuit for a UPS power system, used to pre-charge the DC bus capacitor in the drive circuit of the UPS power system, characterized in that, The soft-start circuit includes: The pre-charge circuit has its input terminal electrically connected to the UPS battery and its output terminal electrically connected to the DC bus capacitor. A first resistor and a first switching transistor are connected in series in the pre-charge circuit. A start-up timing circuit is provided, the input terminal of which is electrically connected to the UPS battery, and the output terminal of which is electrically connected to the control terminal of the first switching transistor to control the conduction duration of the first switching transistor. The start-up timing circuit is also provided with a control switch for controlling the output state. The control loop has its input terminal electrically connected to the UPS battery and its output terminal electrically connected to the auxiliary power supply circuit. The auxiliary power supply circuit provides the necessary auxiliary power to the main controller of the UPS power system during the startup phase. The control loop also includes a start switch and a switch control unit connected in series. The start switch controls the on / off state of the control loop, and the switch control unit is electrically connected to the control switch and controls the on-time of the control switch.

2. The UPS power system soft-start circuit according to claim 1, characterized in that, The startup timing circuit includes a first regulated power supply circuit and a delay circuit. The input terminal of the first regulated power supply circuit is electrically connected to the UPS battery, and the output terminal of the first regulated power supply circuit is electrically connected to the delay circuit through the control switch. The delay circuit is electrically connected to the control terminal of the first switching transistor. The first regulated power supply circuit is used to provide startup power to the delay circuit, and the delay circuit controls the conduction time of the first switching transistor based on the consumption time of the startup power provided by the first regulated power supply circuit.

3. The UPS power system soft-start circuit according to claim 2, characterized in that, The delay circuit includes a second resistor and a first capacitor that form an RC charging loop.

4. The UPS power system soft-start circuit according to claim 3, characterized in that, The second resistor is connected in series with the first capacitor. One end of the second resistor is electrically connected to one of the conducting terminals of the control switch. One end of the first capacitor is electrically connected to the positive terminal of the DC bus capacitor. The connection node between the second resistor and the first capacitor is electrically connected to the control terminal of the first switch.

5. The UPS power system soft-start circuit according to claim 4, characterized in that, A third resistor is connected in parallel across the two ends of the first capacitor.

6. The UPS power system soft-start circuit according to claim 2, characterized in that, The first regulated power supply circuit includes a fourth resistor and a second capacitor connected in series, and a first Zener diode connected in parallel with the second capacitor. One end of the fourth resistor is electrically connected to the positive terminal of the UPS battery, and the other end of the second capacitor is electrically connected to the positive terminal of the DC bus capacitor. The connection node between the fourth resistor and the second capacitor is electrically connected to one of the conducting terminals of the control switch.

7. The UPS power system soft-start circuit according to claim 1, characterized in that, The input terminal of the control loop is electrically connected to the UPS battery through a second voltage regulator circuit, which includes a second Zener diode and a third capacitor connected in parallel across the UPS battery.

8. The UPS power system soft-start circuit according to claim 7, characterized in that, The switch control unit includes a fifth resistor, a fourth capacitor, and a switch controller connected in series in the control circuit. The second regulated power supply charges the fourth capacitor through the fifth resistor. The fourth capacitor provides the switch controller with the duration of operation based on the charging time. The switch controller is electrically connected to the control switch. When the switch controller is in operation, the control switch is in the ON state.

9. The UPS power system soft-start circuit according to claim 8, characterized in that, The output terminal of the control circuit is electrically connected to the auxiliary power supply circuit through a switching circuit; the switching circuit includes a second switching transistor and a third switching transistor, the control terminal of the second switching transistor is electrically connected to one of the conducting terminals of the third switching transistor, the two conducting terminals of the second switching transistor are respectively electrically connected to the positive terminal of the third capacitor and the positive terminal of the auxiliary power supply circuit, the control terminal of the third switching transistor is electrically connected to the positive terminal of the fourth capacitor, and the other conducting terminal of the third switching transistor is electrically connected to the positive terminal of the auxiliary power supply circuit.

10. The UPS power system soft-start circuit according to claim 1, characterized in that, A thermistor is also connected in series in the pre-charge circuit, and the resistance of the thermistor is negatively correlated with temperature.

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