Uninterruptible power supply

Abstract

This invention provides an uninterruptible power supply (UPS), comprising: an AC input terminal and an AC output terminal; a normally closed safety switch device, including a normally closed safety switch connected between the AC input terminal and the AC output terminal, a magnetic core, and a coil wound on the magnetic core, the first end of the coil being connected to a DC power supply; a first electronically controllable switch connected between the second end of the coil and ground; an inverter for converting DC power into AC power and transmitting it to the AC output terminal; and a control device for controlling the switching state of the first electronically controllable switch according to the voltage of the AC power at the AC input terminal, and for controlling the operating state of the inverter according to the voltage at the second end of the coil. The UPS of this invention has low cost, low losses, and improved safety.

Description

Technical Field

[0001] This invention relates to the field of electronic circuits, and more specifically to an uninterruptible power supply. Background Technology

[0002] An uninterruptible power supply (UPS) can continuously supply power to a load. When the mains voltage is normal, the mains power supplies the load; when the mains voltage is abnormal or there is a power outage, the inverter is activated to convert the DC power supplied by the rechargeable battery into AC power to supply the load. Currently, UPSs are widely used in various fields.

[0003] Figure 1 This is a circuit diagram of an existing uninterruptible power supply. For example... Figure 1 As shown, the uninterruptible power supply 1 includes an AC input terminal 10 for receiving AC power (e.g., mains power) and an AC output terminal 10' for outputting AC power, a normally open (or "normally open") safety switch device 11 and an output switch 12 connected in sequence between the AC input terminal 10 and the AC output terminal 10'; a rechargeable battery 13, a charger 14, an inverter 15, and a processor 110 for controlling the operation of the inverter 15.

[0004] The charger 14 is electrically connected to the AC input terminal 10 via a normally open safety switch 11, and is configured to charge the rechargeable battery 13 using the AC power from the AC input terminal 10. The inverter 15 controllably converts the DC power from the rechargeable battery 13 into AC power. The output switch 12 includes a common terminal connected to the AC output terminal 10', a first switching terminal 121, and a second switching terminal 122. The first switching terminal 121 is electrically connected to the normally open safety switch 11, and the second switching terminal 122 is electrically connected to the output terminal of the inverter 15. The output switch 12 is operatively or controllably such that one of the normally open safety switch 11 and the output terminal of the inverter 15 is connected to the AC output terminal 10'.

[0005] The normally open safety switch device 11 is preferably a normally open AC relay, which includes a normally open safety switch 114 connected between the AC input terminal 10 and the first switching terminal 121 of the output switch 12, a magnetic core 111, a coil 112 wound on the magnetic core 111, and a rectifier 113, wherein the input terminal of the rectifier 113 is connected to the AC input terminal 10, and its output terminal is connected to both ends of the coil 112. When the coil 112 is not energized, the normally open safety switch 114 is open; when the coil 112 is energized, the normally open safety switch 114 is closed.

[0006] The uninterruptible power supply 1 has the following two operating modes.

[0007] When the mains voltage is within a predetermined threshold voltage range (e.g., 160 volts to 290 volts), coil 112 is energized to turn on normally open safety switch 114. The mains power from AC input terminal 10 is transmitted to the input terminal of charger 14 via the turned-on normally open safety switch 114, and charger 14 begins to operate to provide auxiliary power, enabling battery-free startup of uninterruptible power supply 1. The coil of output switch 12 (… Figure 1 (Not shown) When powered by an auxiliary power supply, the common terminal of the output switch 12 and the first switching terminal 121 are electrically connected, so that the AC mains power of the AC input terminal 10 is transmitted to the AC output terminal 10' through the normally open safety switch 114 and the output switch 12. On the other hand, if the user connects a rechargeable battery 13 to the output terminal of the charger 14, the charger 14 simultaneously charges the rechargeable battery 13 using the AC mains power of the AC input terminal 10.

[0008] When the mains voltage is abnormal or there is a power outage, the normally open safety switch 114 is in the open state, and the output switch 12 is controlled to connect the output terminal of the inverter 15 to the AC output terminal 10'. The processor 110 controls the inverter 15 to operate to convert the DC power in the rechargeable battery 13 into AC power, and transmit it to the AC output terminal 10' through the output switch 12.

[0009] Normally open safety switch 11 directly uses the mains power with a large voltage to power its coil 112, resulting in a large number of turns, large size, and high cost for the coil 112. Moreover, the mains voltage at the AC input terminal 10 is within the normal range for most of the time (e.g., more than 99%), and the coil 112 of the normally open safety switch 11 is energized for most of the time, leading to significant losses in the normally open safety switch 11. Summary of the Invention

[0010] To address the aforementioned technical problems in the existing technology, the present invention provides an uninterruptible power supply, comprising:

[0011] AC input and AC output terminals;

[0012] A normally closed safety switch device includes a normally closed safety switch connected between the AC input terminal and the AC output terminal, a magnetic core, and a coil wound on the magnetic core, the first end of the coil being connected to a DC power supply;

[0013] A first electronically controllable switch is connected between the second end of the coil and ground;

[0014] An inverter for converting direct current (DC) into alternating current (AC) and transmitting it to the AC output terminal; and

[0015] A control device is used to control the switching state of the first electronically controllable switch according to the voltage of the AC power at the AC input terminal, and to control the operating state of the inverter according to the voltage at the second end of the coil.

[0016] Preferably, the control device includes a processor, the processor being configured to:

[0017] When the voltage of the alternating current is within a predetermined threshold voltage range, it outputs a drive signal of a first logic level to the control terminal of the first electronically controllable switch to control the first electronically controllable switch to turn off, and the normally closed safety switch to close; and

[0018] When the voltage of the AC power is not within the predetermined threshold voltage range, it outputs a second logic level drive signal to the control terminal of the first electronically controllable switch to control the first electronically controllable switch to turn on, and the normally closed safety switch to turn off.

[0019] Preferably, the first logic level is a low level and the second logic level is a high level.

[0020] Preferably, the first electronically controllable switch is a first transistor, the collector of the first transistor is connected to the second end of the coil, and the emitter is grounded. The uninterruptible power supply also includes a first resistor connected between the base of the first transistor and the processor.

[0021] Preferably, when the voltage at the second end of the coil is high, the processor controls the inverter to not operate; and when the voltage at the second end of the coil is low, the processor controls the inverter to operate.

[0022] Preferably, the processor has a first pulse width modulation signal output terminal for outputting a first pulse width modulation signal and a second pulse width modulation signal output terminal for outputting a second pulse width modulation signal; the control device includes a safety control circuit connected to the second end of the coil and the first and second pulse width modulation signal output terminals. The safety control circuit is configured to clamp the first and second pulse width modulation signals to a low level when the voltage at the second end of the coil is high, and to disconnect the conduction path between the first and second pulse width modulation signals and ground when the voltage at the second end of the coil is low.

[0023] Preferably, the safety control circuit includes: a second electronically controllable switch, which is connected between the first pulse width modulation signal output terminal and ground, and its control terminal is electrically connected to the second terminal of the coil; and a third electronically controllable switch, which is connected between the second pulse width modulation signal output terminal and ground, and its control terminal is electrically connected to the second terminal of the coil.

[0024] Preferably, the second electronically controllable switch is a second transistor, the collector of which is connected to the first pulse width modulation signal output terminal and its emitter is grounded; the third electronically controllable switch is a third transistor, the collector of which is connected to the second pulse width modulation signal output terminal and its emitter is grounded; the safety control circuit includes a second resistor connected between the base of the second transistor and the second end of the coil, and a third resistor connected between the base of the third transistor and the second end of the coil.

[0025] Preferably, the uninterruptible power supply includes an output switch that controllably connects one of the normally closed safety switch and the output terminal of the inverter to the AC output terminal.

[0026] Preferably, the uninterruptible power supply includes: a rechargeable battery connected to the input of the inverter; and a charger configured to charge the rechargeable battery using AC power from the AC input.

[0027] The uninterruptible power supply of the present invention can achieve battery-free start-up, with low cost and low loss, effectively avoiding the risk of electric shock in battery mode and improving safety. Attached Figure Description

[0028] The embodiments of the present invention will be further described below with reference to the accompanying drawings, wherein:

[0029] Figure 1 This is a circuit diagram of an existing uninterruptible power supply.

[0030] Figure 2 This is a circuit diagram of an uninterruptible power supply according to the first embodiment of the present invention.

[0031] Figure 3 yes Figure 2 The diagram shown is an equivalent circuit diagram of an uninterruptible power supply when the mains voltage is within a predetermined threshold voltage range.

[0032] Figure 4 yes Figure 2 The diagram shows the equivalent circuit of the uninterruptible power supply in battery mode.

[0033] Figure 5This is a circuit diagram of an uninterruptible power supply according to a second embodiment of the present invention.

[0034] Figure 6 yes Figure 5 The diagram shown is an equivalent circuit diagram of an uninterruptible power supply when the mains voltage is within a predetermined threshold voltage range.

[0035] Figure 7 yes Figure 5 The diagram shows the equivalent circuit of the uninterruptible power supply in battery mode. Detailed Implementation

[0036] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings and specific embodiments.

[0037] exist Figure 1 In a conventional uninterruptible power supply 1, in order to reduce the switching time of the output switch 12, the gap between the first switching terminal 121 and the second switching terminal 122 of the output switch 12 is small (e.g., 0.3 mm). However, in battery mode, the AC power output by the inverter 15 is transmitted to the AC output terminal 10' through the second switching terminal 122 of the output switch 12, and the AC power output by the inverter 15 may creep to the first switching terminal 121 and be transmitted to the normally open safety switch 114.

[0038] To prevent operators or users from being electrocuted by touching the AC input terminal 10 in battery mode, the normally open safety switch 11 in the existing uninterruptible power supply 1 must be a normally open switch to remain open in battery mode. If a normally closed (or "normally closed") relay is used, in battery mode, the coil 112 of the normally closed relay is energized, causing the normally open safety switch 114 to open. If the rectifier 113 of the normally closed relay malfunctions, resulting in no current in the coil 112, the normally closed relay will close. In this case, an operator or user accidentally touching the AC input terminal 10 may pose a risk of electric shock. Based on safety regulations, the prior art prohibits those skilled in the art from... Figure 1 The normally open safety switch device 11 in the middle is replaced with a normally closed safety switch device.

[0039] For ease of description, the terms "high level" and "low level" used below are relative. "High level" can be a voltage higher than 2 volts, such as 3.3 volts, 5 volts, or 12 volts; "low level" can be a voltage lower than 0.3 volts or lower than 0.7 volts. These values ​​can vary depending on the electronic components and DC power supply voltage, and this invention does not intend to limit their specific values. In the field of electronic circuits, the terms "high level" and "low level" used in this invention are well known to those skilled in the art.

[0040] Figure 2 This is a circuit diagram of an uninterruptible power supply according to the first embodiment of the present invention. Figure 2 As shown, it is similar to Figure 1 They are basically the same, except that the uninterruptible power supply 2 includes a normally closed safety switch device 21, a transistor Q21 and a resistor R21, as well as a control device consisting of a processor 210 in the multiplexed uninterruptible power supply 2.

[0041] The normally closed safety switch device 21 is preferably a normally closed DC relay, which includes a normally closed safety switch 214 connected between the AC input terminal 20 and the first switching terminal 221 of the output switch 22, a magnetic core, and a coil 212 wound on the magnetic core. The first end of the coil 212 is connected to the DC power supply Vcc, and the second end is connected to the collector of the transistor Q21. The emitter of the transistor Q21 is grounded, and the base is connected to the drive signal output terminal of the processor 210 through a resistor R21. The processor 210 controls the inverter 25 to operate or not operate by monitoring the voltage of the collector of the transistor Q21; and outputs a high-level or low-level drive signal Vd to the base of the transistor Q21 by monitoring the mains voltage of the AC input terminal 20.

[0042] The following will use the equivalent circuit diagram of the uninterruptible power supply 2 to illustrate its working mode.

[0043] Figure 3 yes Figure 2 The diagram shows the equivalent circuit of the uninterruptible power supply (UPS) when the mains voltage is within a predetermined threshold voltage range. When the processor 210 detects that the mains voltage is within the predetermined threshold voltage range, the processor 210 outputs a low-level drive signal Vd, which is output to the base (i.e., the control terminal) of transistor Q21 through resistor R21. At this time, the emitter of transistor Q21 is reverse biased, transistor Q21 is cut off, coil 212 is not energized, and therefore normally closed safety switch 214 is turned on. The mains power from AC input terminal 20 is transmitted to the input terminal of charger 24 through the turned-on normally closed safety switch 214. Charger 24 starts working to provide auxiliary power, enabling battery-free startup of the UPS 2. In another embodiment, a rechargeable battery can also be connected as an auxiliary power source for startup. With the auxiliary power supply, the common terminal of the output switch 22 and the first switching terminal 221 are electrically connected, so that the AC mains power of the AC input terminal 20 is transmitted to the AC output terminal 20' through the normally closed safety switch 214 and the output switch 22. On the other hand, if the user connects the rechargeable battery 23 to the output terminal of the charger 24, the charger 24 will simultaneously use the AC mains power of the AC input terminal 20 to charge the rechargeable battery 23.

[0044] Figure 4 yes Figure 2The diagram shows the equivalent circuit of the uninterruptible power supply in battery mode. When the processor 210 detects that the mains voltage is outside the predetermined threshold voltage range, i.e., an abnormality or power outage, the processor 210 outputs a high-level drive signal Vd to the base of transistor Q21. The emitter of transistor Q21 is forward biased, transistor Q21 conducts, coil 212 is energized and has a current I, and normally closed safety switch 214 is opened. At the same time, output switch 22 is controlled to connect the output of inverter 25 to AC output terminal 20'. When the processor 210 detects that the collector voltage Uc of transistor Q21 is low, it controls inverter 25 to operate to convert the DC power in rechargeable battery 23 into AC power, and transmits it to AC output terminal 20' through output switch 22.

[0045] If a short circuit occurs between the collector and emitter of transistor Q21 in battery mode, current I still flows in coil 212, and the normally closed safety switch 214 opens, thus preventing electric shock. Simultaneously, the collector voltage Uc of transistor Q21 is low. When processor 210 detects that the collector voltage Uc of transistor Q21 remains low, it controls inverter 25 to operate and convert the DC power from rechargeable battery 23 into AC power.

[0046] If, in battery mode, the collector and emitter of transistor Q21 are disconnected, the current in coil 212 will drop to zero, and the normally closed safety switch 214 will turn on. At this time, the voltage Uc at the collector of transistor Q21 changes, from a low level to a high level (approximately less than the DC power supply Vcc). When processor 210 detects that the voltage Uc at the collector of transistor Q21 is high, processor 210 will output a control signal (e.g., a low-level control signal) to inverter 25 to stop it from operating.

[0047] In this embodiment, the processor 210 monitors the collector voltage Uc of transistor Q21. When the collector voltage Uc of transistor Q21 is high, it controls the inverter 25 to not operate; and when the collector voltage Uc of transistor Q21 is low, it controls the inverter 25 to operate. In summary, when transistor Q21 fails in battery mode, its collector voltage Uc switches from low to high, the normally closed safety switch 214 is turned on, and the processor 210 simultaneously stops the inverter 25 from operating, effectively avoiding the risk of electric shock and improving safety.

[0048] In this embodiment, the DC power supply Vcc can be provided by an auxiliary power supply or a rechargeable battery 23, without increasing the cost of the uninterruptible power supply 2.

[0049] Figure 5 This is a circuit diagram of an uninterruptible power supply according to a second embodiment of the present invention. Figure 5 As shown, it is similar to Figure 1 They are basically the same, except that the uninterruptible power supply 3 includes a normally closed safety switch device 31, a first transistor Q31, a first resistor R31, and a control device consisting of a processor 310 and a safety control circuit 36.

[0050] The normally closed safety switch device 31 also includes a normally closed safety switch 314, a magnetic core, and a coil 312 wound on the magnetic core. The normally closed safety switch device 31, the first resistor R31, and the first transistor Q31 and their connection structure are similar to... Figure 2 The normally closed safety switch device 21, resistor R21 and transistor Q21 shown are the same, and will not be described again here.

[0051] The safety control circuit 36 ​​includes a second resistor R32, a second transistor Q32, a third resistor R33, and a third transistor Q33. The base of the second transistor Q32 is connected to the collector of the first transistor Q31 via the second resistor R32, and its collector is connected to the first pulse width modulation signal output terminal of the processor 310. Its emitter is grounded. The base of the third transistor Q33 is connected to the collector of the first transistor Q31 via the third resistor R33, and its collector is connected to the second pulse width modulation signal output terminal of the processor 310. Its emitter is grounded.

[0052] The following will use the equivalent circuit diagram of the uninterruptible power supply 3 to illustrate its working mode.

[0053] Figure 6 yes Figure 5 The diagram shows the equivalent circuit of the uninterruptible power supply (UPS) when the mains voltage is within a predetermined threshold voltage range. When the processor 310 detects that the mains voltage is within the predetermined threshold voltage range, the processor 310 outputs a low-level drive signal Vd to the first resistor R31. The emitter of the first transistor Q31 is reverse-biased, the first transistor Q31 is cut off, the coil 312 is not energized, and therefore the normally closed safety switch 314 is turned on. The mains power from the AC input terminal 30 is transmitted to the input terminal of the charger 34 through the turned-on normally closed safety switch 314. The charger 34 starts working to provide auxiliary power, realizing the battery-free startup of the UPS 3. Under the power supply of the auxiliary power, the common terminal of the output switch 32 and the first switching terminal 321 are electrically connected so that the mains power from the AC input terminal 30 is transmitted to the AC output terminal 30' through the turned-on normally closed safety switch 314 and the output switch 32. On the other hand, if the user connects a rechargeable battery 33 to the output of the charger 34, the charger 34 will simultaneously charge the rechargeable battery 33 using the AC mains power from the AC input terminal 30.

[0054] exist Figure 6In the equivalent circuit diagram shown, the collector voltage Uc of the first transistor Q31 is high (approximately less than the DC power supply Vcc), the emitters of the second transistor Q32 and the third transistor Q33 are forward biased, and both transistors Q32 and Q33 have base currents. To ensure that the normally closed safety switch 314 is turned on, the second resistor R32 and the third resistor R33 are selected with relatively large resistance values ​​(e.g., 100 kΩ) so that the sum of the base currents of the second transistor Q32 and the third transistor Q33 is in the microampere range. This prevents excessive current in the coil 312 from causing the normally closed safety switch 314 to switch from the on state to the off state.

[0055] Figure 7 yes Figure 5 The diagram shows the equivalent circuit of the uninterruptible power supply in battery mode. When the processor 310 detects that the mains voltage is not within the predetermined threshold voltage range, i.e., an abnormality or power outage, the processor 310 outputs a high-level drive signal Vd to the base of the first transistor Q31. The emitter of the first transistor Q31 is forward biased, the first transistor Q31 is turned on, the coil 312 is energized and has a current I, thereby causing the normally closed safety switch 314 to open. At the same time, the output switch 32 is controlled to connect the output terminal of the inverter 35 to the AC output terminal 30'.

[0056] In battery mode, the high-level drive signal Vd output by processor 310 turns on the first transistor Q31, and the collector voltage Uc of the first transistor Q31 is low. The emitters of the second transistor Q32 and the third transistor Q33 are reverse-biased, therefore both transistors are in the off state. Thus, the first pulse width modulation signal PWM1 output from the first pulse width modulation signal output terminal and the second pulse width modulation signal PWM2 output from the second pulse width modulation signal output terminal of processor 310 are not clamped to a low level. The first pulse width modulation signal PWM1 and the second pulse width modulation signal PWM2 output by processor 310 are respectively provided to the upper arm drive circuit and the lower arm drive circuit of inverter 35. Figure 7 In (not shown), the inverter 35 is controlled to operate to convert the DC power in the rechargeable battery 33 into AC power, and transmit it to the AC output terminal 30' through the output switch 32.

[0057] In battery mode, if the collector and emitter of the first transistor Q31 are short-circuited, current I still flows in coil 312, and the normally closed safety switch 314 is open, thus preventing electric shock. Simultaneously, the collector voltage Uc of the first transistor Q31 is low, therefore the second transistor Q32 and the third transistor Q33 are in the off state. The first pulse width modulation signal PWM1 and the second pulse width modulation signal PWM2 output by the processor 310 are provided to the upper and lower bridge arm drive circuits of the inverter 35, controlling the inverter 35 to convert the DC power from the rechargeable battery 33 into AC power.

[0058] In battery mode, if the collector and emitter of the first transistor Q31 are disconnected, the current I in coil 312 will drop to zero, and the normally closed safety switch 314 will be turned on. At this time, the voltage Uc at the collector of the first transistor Q31 changes from a low level to a high level (approximately less than the DC power supply Vcc). The emitters of the second transistor Q32 and the third transistor Q33 are forward biased, and the second transistor Q32 and the third transistor Q33 are turned on, causing the first pulse width modulation signal PWM1 and the second pulse width modulation signal PWM2 output by the processor 310 to be clamped to a low level, and the inverter 35 is controlled to stop working.

[0059] In this embodiment, the safety control circuit 36 ​​receives the collector voltage Uc of the first transistor Q31. When the collector voltage Uc of the first transistor Q31 is high, the safety control circuit 36 ​​clamps the first pulse width modulation signal PWM1 and the second pulse width modulation signal PWM2 output by the processor 310 to a low level, so that the inverter 35 does not work; and when the collector voltage Uc of the first transistor Q31 is low, the safety control circuit 36 ​​does not affect the first pulse width modulation signal PWM1 and the second pulse width modulation signal PWM2 output by the processor 310, so that the inverter 35 works. In summary, when the first transistor Q31 fails in battery mode, its collector voltage Uc switches from low to high, the normally closed safety switch 314 is turned on, and at the same time, the safety control circuit 36 ​​causes the inverter 35 to stop working, effectively avoiding the risk of electric shock and improving safety.

[0060] The transistors and other electronically controllable switches and resistors in the uninterruptible power supply of this invention are extremely inexpensive, and the price of the DC relay is far lower than that of the AC relay in existing uninterruptible power supplies, thus reducing the cost of the uninterruptible power supply of this invention. The coil of the normally closed safety switch is supplied with a low-voltage DC power supply Vcc, and its coil loss is small. In addition, the uninterruptible power supply is in normal power supply mode most of the time, and the coil of the normally closed safety switch is not conducting and has no loss most of the time, thus greatly reducing losses.

[0061] By overcoming the technical biases in the prior art, the applicant of this invention selected a normally closed safety switch, which effectively avoids the risk of electric shock in battery mode, while reducing costs and losses.

[0062] In other embodiments of the present invention, various electronic controllable switches, such as metal-oxide-semiconductor field-effect transistors, insulated-gate bipolar transistors, or turn-off thyristors, can be used to replace the transistors Q21 and Q31 in the above embodiments. At the same time, the first electronic controllable switch connected between the second terminal of the coil and ground is preferably controlled to be cut off under a first logic level (e.g., low level) drive signal and controlled to be turned on under a second logic level (e.g., high level) drive signal. Thus, the processor outputs a low-level drive signal for most of the time to control the first electronic controllable switch to be in the cut-off state for most of the time, thereby reducing the power consumption of the processor.

[0063] In other embodiments of the present invention, the first electronically controllable switch can be controlled to be turned on under a first logic level drive signal and controlled to be turned off under a second logic level drive signal.

[0064] In other embodiments of the present invention, voltage-controlled power switches such as metal-oxide-semiconductor (MOSFET) or insulated-gate bipolar transistor (IGBT) are used to replace the second transistor Q32 and the third transistor Q33 in the safety control circuit 36. The gate of the MOSFET or the gate of the IGBT (i.e., its control terminal) is electrically connected to the collector of the first transistor Q31, and the first pulse width modulation signal output terminal and the second pulse width modulation signal output terminal of the processor 310 are respectively grounded through the MOSFET or IGBT.

[0065] In other embodiments of the present invention, the safety control circuit 36 ​​in the above embodiments is replaced by another safety control circuit. This safety control circuit is electrically connected to the collector of the first transistor Q31 and the pulse width modulation signal output terminal of the processor 310. When the voltage Uc of the collector of the first transistor Q31 is high, the safety control circuit is configured to ground or clamp the first pulse width modulation signal PWM1 and the second pulse width modulation signal PWM2 output by the processor 310 to a low level, so that the inverter stops working; and when the voltage Uc of the collector of the first transistor Q31 is low, the safety control circuit is configured to disconnect the conduction path between the first pulse width modulation signal PWM1 and the second pulse width modulation signal PWM2 output by the processor 310 and ground.

[0066] This invention does not intend to limit the specific line connection relationship of the inverter; it can be a full-bridge inverter or a half-bridge inverter.

[0067] This invention does not intend to limit the specific numerical range of the predetermined threshold voltage. It can be set according to the magnitude of the mains power and the working voltage of the load. For example, for a 220-volt mains power, the predetermined threshold voltage range can be 160 to 290 volts, or it can be 180 to 240 volts, etc.

[0068] While the present invention has been described through preferred embodiments, it is not limited to the embodiments described herein, and various changes and modifications are made without departing from the scope of the invention.

Claims

1. An uninterruptible power supply, characterized in that, The uninterruptible power supply includes: AC input and AC output terminals; A normally closed safety switch device includes a normally closed safety switch connected between the AC input terminal and the AC output terminal, a magnetic core, and a coil wound on the magnetic core, the first end of the coil being connected to a DC power supply; A first electronically controllable switch is connected between the second end of the coil and ground; An inverter for converting direct current (DC) into alternating current (AC) and transmitting it to the AC output terminal; and A control device is configured to control the switching state of the first electronically controllable switch based on the voltage of the AC power at the AC input terminal, and to control whether the inverter operates based on the logic level of the voltage at the second terminal of the coil. The control device includes a processor, which is configured to: When the voltage of the alternating current is within a predetermined threshold voltage range, it outputs a drive signal of a first logic level to the control terminal of the first electronically controllable switch to control the first electronically controllable switch to turn off, and the normally closed safety switch to close; and When the voltage of the AC power is not within the predetermined threshold voltage range, it outputs a second logic level drive signal to the control terminal of the first electronically controllable switch to control the first electronically controllable switch to turn on, and the normally closed safety switch to turn off.

2. The uninterruptible power supply according to claim 1, characterized in that, The first logic level is low, and the second logic level is high.

3. The uninterruptible power supply according to claim 1, characterized in that, The first electronically controllable switch is a first transistor, the collector of the first transistor is connected to the second end of the coil, and the emitter is grounded. The uninterruptible power supply also includes a first resistor connected between the base of the first transistor and the processor.

4. The uninterruptible power supply according to any one of claims 1 to 3, characterized in that, When the voltage at the second end of the coil is high, the processor controls the inverter to not operate; and when the voltage at the second end of the coil is low, the processor controls the inverter to operate.

5. The uninterruptible power supply according to any one of claims 1 to 3, characterized in that, The processor has a first pulse width modulation signal output terminal for outputting a first pulse width modulation signal and a second pulse width modulation signal output terminal for outputting a second pulse width modulation signal; the control device includes a safety control circuit connected to a second end of the coil and the first and second pulse width modulation signal output terminals. The safety control circuit is configured to clamp the first and second pulse width modulation signals to a low level when the voltage at the second end of the coil is high, and to disconnect the conduction path between the first and second pulse width modulation signals and ground when the voltage at the second end of the coil is low.

6. The uninterruptible power supply according to claim 5, characterized in that, The safety control circuit includes: A second electronically controllable switch is connected between the first pulse width modulation signal output terminal and ground, and its control terminal is electrically connected to the second terminal of the coil; and A third electronically controllable switch is connected between the output terminal of the second pulse width modulation signal and ground, and its control terminal is electrically connected to the second terminal of the coil.

7. The uninterruptible power supply according to claim 6, characterized in that, The second electronically controllable switch is a second transistor, the collector of which is connected to the first pulse width modulation signal output terminal, and its emitter is grounded; the third electronically controllable switch is a third transistor, the collector of which is connected to the second pulse width modulation signal output terminal, and its emitter is grounded; the safety control circuit includes a second resistor connected between the base of the second transistor and the second end of the coil, and a third resistor connected between the base of the third transistor and the second end of the coil.

8. The uninterruptible power supply according to any one of claims 1 to 3, characterized in that, The uninterruptible power supply includes an output switch that controllably connects one of the normally closed safety switch and the output terminal of the inverter to the AC output terminal.

9. The uninterruptible power supply according to claim 8, characterized in that, The uninterruptible power supply includes: A rechargeable battery, the rechargeable battery being connected to the input of the inverter; and A charger configured to charge the rechargeable battery using AC power from the AC input terminal.

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