TW201535953A - Bridge circuit with short circuit protection and method thereof - Google Patents

Abstract

A bridge circuit with short circuit protection comprises an input power source, a conversion unit, a first capacitor, a second capacitor, a detection unit and a bridge inverter unit. The input power source has a first electrode and a second electrode. The conversion unit is coupled to the input power source. The first capacitor has a first end and a second end, the first end of the first capacitor is coupled to the conversion unit, and the second end of the first capacitor is coupled to the second electrode. The second capacitor has a first end and a second end, the first end of the second capacitor is coupled to the first end of the first capacitor. The detection unit is coupled to the second end of the second capacitor. The bridge inverter unit has a plurality of switches and is coupled to the conversion unit, the first capacitor, the second capacitor, the detection unit and the second electrode. When the detection unit detects a current change flowing through the second capacitor, the detection unit outputs a short-circuit signal to a control unit.

Description

Bridge circuit with short circuit protection and method thereof

The invention relates to a bridge circuit with short circuit protection and a method thereof, in particular to a bridge circuit with short circuit protection and a method thereof.

Please refer to the converter shown in FIG. 1A. In a converter with a bridge inverter unit, the short circuit protection of the switch K1~K12 on the same bridge arm is the core of protection. Therefore, the prior art has a current sensor on each of the bridge arms. However, for a converter with multiple bridge arms, the converter shown in FIG. 1A requires six current sensors T1~T6 to sense the switch K1~K12 on each bridge arm. Current. As a result, manufacturing costs will increase, the size of the circuit will increase, or the complexity of the circuit design will increase.

Another simplified method is to string a current transformer on the DC bus to detect the total current of the back-coupled bridge circuit, such as the full-bridge inverter in Figure 1B. In this method, if the current transformer adopts a transformer type transformer, the high frequency fluctuation of the voltage across the bridge arm is increased due to the increase of the line inductance, and the transformer type transformer has an unresolved reset problem. If the current transformer uses a Hall sensor, the cost is too high.

The embodiment provides a bridge circuit with short circuit protection and a method thereof. The present embodiment detects the bridge inverter unit in a short circuit state by detecting a current change of a small capacity high frequency capacitor, thereby reducing the circuit. The volume and cost, and improve the short circuit protection of the bridge circuit.

In this embodiment, a bridge circuit with short circuit protection is provided, including an input power source, a conversion unit, a first capacitor, a second capacitor, a detecting unit, and a bridge inverter unit. The input power source has a first pole and a second pole. The conversion unit is coupled to the input power source. The first capacitor has a first end and a second end. The first end of the first capacitor is coupled to the conversion unit, and the second end of the first capacitor is coupled to the second end. The second capacitor has a first end and a second end, and the first end of the second capacitor is coupled to the first end of the first capacitor. The detecting unit is coupled to the second end of the second capacitor. The bridge type inverter unit has a plurality of switch switches, and is coupled to the conversion unit, the first capacitor, the second capacitor, the detecting unit, and the second pole. When the detecting unit detects a current change flowing through the second capacitor, the detecting unit outputs a short circuit signal to a control unit.

This embodiment provides a short circuit protection method for a bridge circuit, which is applicable to a bridge circuit. The bridge circuit includes an input power source, a conversion unit, a first capacitor, a second capacitor, a detecting unit, and a bridge inverter. unit. The short circuit protection method includes: the detecting unit determines whether a current change flowing through the second capacitor is detected; if the determination result is yes, the detecting unit outputs a short circuit signal to a control unit.

In summary, the short circuit protection bridge circuit of the present embodiment detects the bridge inverter unit in a short circuit state by detecting a current change of the small capacity second capacitor, wherein the current flowing through the second capacitor It occupies a small part of the current on the DC bus. Therefore, the small current change of the second capacitor can be further analyzed and distinguished. For example, when the optocoupler receives the preset current and is turned on, the detecting unit outputs a short circuit signal to the control unit. In this way, the short circuit protection of the bridge arm circuit is achieved, the volume of the circuit is reduced, and the short circuit protection of the bridge circuit is improved. In this way, the embodiment can indeed improve the usability of the bridge circuit with short circuit protection.

The above summary and the following embodiments are provided to further illustrate the technical means and the efficiencies of the embodiments, and the embodiments and the drawings are provided for reference only, and are not intended to limit the embodiments.

1, 1a‧‧‧Short-circuit protected bridge circuit

9‧‧‧load

10, 10a‧‧‧ input power

12, 12a‧‧‧ conversion unit

14, 14a‧‧‧Detection unit

16, 16a‧‧‧ Bridge Inverter Unit

160, K1~K12‧‧‧Toggle switch

18‧‧‧Control unit

C1‧‧‧first capacitor

C2‧‧‧second capacitor

C101‧‧‧First end of the first capacitor

C201‧‧‧ the first end of the second capacitor

C102‧‧‧The second end of the first capacitor

C202‧‧‧ second end of the second capacitor

D1‧‧‧First Diode

U1‧‧‧Optocoupler

U11‧‧‧first sensing element

U12‧‧‧Second sensing element

R‧‧‧resistance

VCC‧‧‧ working voltage source

L1‧‧‧Inductance components

D2‧‧‧ diode components

IGBT‧‧‧ switching components

L2‧‧‧Inverter inductance

C3‧‧‧Filter Capacitor

Vsc‧‧‧Short-circuit signal

V _bus ‧‧‧DC bus voltage waveform

Current waveform of Isc‧‧‧ bridge arm short circuit

K1PWM‧‧‧Control signal waveform

Iop‧‧‧ threshold current

T, T1~T6‧‧‧ current sensor

C‧‧‧ capacitor

+‧‧‧first pole

-‧‧‧Second pole

Ic1, ic2, id1, id2‧‧‧ current

S501~S507‧‧‧Process steps

FIG. 1A is a schematic diagram of a bridge circuit with short circuit protection according to an embodiment of the prior art.

FIG. 1B is a schematic diagram of a bridge circuit with short circuit protection according to an embodiment of the prior art.

2 is a functional block diagram of a bridge circuit with short circuit protection according to an embodiment of the present invention.

3 is a circuit diagram of a bridge circuit with short circuit protection according to another embodiment of the present invention.

4A is a voltage waveform diagram of a bridge circuit with short circuit protection according to another embodiment of the present invention.

4B is a partial enlarged view of a voltage waveform of a bridge circuit with short circuit protection according to another embodiment of the present invention of FIG. 4A.

FIG. 5 is a flowchart of a method for protecting a bridge arm short circuit according to another embodiment of the present invention.

2 is a functional block diagram of a bridge circuit with short circuit protection according to an embodiment of the present invention. Please refer to Figure 2. A bridge circuit 1 with short circuit protection includes an input power source 10, a conversion unit 12, a first capacitor C1, a second capacitor C2, a detecting unit 14, and a bridge inverter unit 16. In practice, the conversion unit 12 is coupled to the input power source 10, the first capacitor C1, the second capacitor C2, the detecting unit 14, and a bridge inverter unit 16. The first capacitor C1 is connected in parallel with the conversion unit 12, the second capacitor C2 is connected in parallel with the first capacitor C1, and the second capacitor C2 is connected in series with the detecting unit 14. The bridge inverter unit 16 is coupled to the conversion unit 12, the first capacitor C1, the second capacitor C2, the detecting unit 14, and the load 9. The control unit 18 is coupled to the switch 160 of the bridge inverter unit 16.

Briefly, when the switch 160 of the bridge inverter unit 16 is in a normal operating state, the sum of the current ic1 flowing through the first capacitor C1 and the current ic2 flowing through the second capacitor C2 is flowing through the DC bus. The difference between current id2 and id1 (ic1+ic2=id2-id1). Under normal steady state, that is, the input voltage, load and control are stable, the losses of the first capacitor C1 and the second capacitor C2 are ignored, and the DC bus voltage is stable, and the average current of the current ic1 and the current ic2 is zero. However, there are charging and discharging ripple currents at the switching frequency on the currents ic1 and ic2, and the current still depends on Ic1+ic2=id2-id1, this value is small, and the capacitance value of the second capacitor C2 is much smaller than the capacitance value of the first capacitor C1, so the ripple current of the current ic2 is almost negligible and the current ic2 is zero. In addition, the switching switch 160 of the bridge type inverter unit 16 is in an abnormal operating state, for example, the current id2 rapidly increases in the short-circuit state, and the instantaneous current id1 does not change. Therefore, the currents ic1, ic2 flowing through the first and second capacitors C1, C2 increase as the id2 increases rapidly. In practical applications, the first capacitor C1 is a large-capacity electrolytic capacitor. The second capacitor C2 selects the capacitance value of the second capacitor C2 according to the maximum current (im) allowed by the switch 160, the threshold current (iop) of the photocoupler, and the first capacitor C1 (C2=iop*C1/( Im-id1-iop)). The capacitance value of the second capacitor C2 is much smaller than the capacitance value of the first capacitor C1. Therefore, the current ic2 flowing through the second capacitor C2 is much smaller than the current ic1 flowing through the first capacitor C1. Therefore, in this embodiment, the detecting unit 14 detects a small current ic2 flowing through the second capacitor C2 to detect the short circuit signal.

The input power source 10 has a first pole and a second pole. In practice, the input power source 10 is, for example, an input DC power source, wherein the input DC power source is converted, for example, via an AC power source. The first pole is for example the anode + and the second pole is for example the cathode. In other embodiments, the first pole is, for example, a cathode, and the second pole is, for example, an anode. This embodiment does not limit the input power source 10, the first pole and the second pole. The input power source 10 is, for example, transmitted through a filter circuit or/and a rectifier circuit to output a DC power source. For example, the waveform of the AC power source is filtered or/and the input DC power source used for the conversion unit 12 after rectification, and the input power source 10 is a full-wave pulsed DC.

The conversion unit 12 is coupled to the input power source 10. In practice, the conversion unit 12 is, for example, a booster circuit. For convenience of explanation, the conversion unit 12 of the present embodiment is illustrated by a booster circuit. In other embodiments, the conversion unit 12 is, for example, a step-down circuit or a step-up and step-down circuit. This embodiment does not limit the aspect of the conversion unit 12. Those skilled in the art should know the operation of the booster circuit, the step-down circuit or the buck-boost circuit, and will not be described here.

The first capacitor C1 has a first end C101 and a second end C102. The first end C101 of the first capacitor C1 is coupled to the conversion unit 12, and the second end C102 of the first capacitor C1 is coupled. The second pole of the input power source 10 is connected. In practice, the first end C101 of the first capacitor C1 is coupled to the anode of the DC bus, and the second end C102 of the first capacitor C1 is coupled to the cathode of the DC bus. The first capacitor C1 is a large-capacity electrolytic capacitor. Therefore, the capacitance of the first capacitor C1 can be regarded as equivalent to the input power source 10, and the embodiment does not limit the aspect of the first capacitor C1.

The second capacitor C2 has a first end C201 and a second end C202. The first end C201 of the second capacitor C2 is coupled to the first end C101 of the first capacitor C1. In practice, the capacitance of the first capacitor C1 is much larger than the capacitance of the second capacitor C2. The second capacitor C2 is a small-capacity high-frequency capacitor. This embodiment does not limit the aspect of the second capacitor C2.

The detecting unit 14 is coupled to the second end C202 of the second capacitor C2. In practice, the detecting unit 14 is implemented by, for example, a circuit composed of a diode, an optocoupler, an operating voltage source, and a resistor. This embodiment does not limit the aspect of the detecting unit 14. The detecting unit 14 is configured to detect a current change of the second capacitor C2, and the detecting unit 14 outputs a normal signal or a short circuit signal to the control unit 18 according to the current change.

The bridge type inverter unit 16 has a plurality of switch switches 160 and is coupled to the conversion unit 12, the first capacitor C1, the second capacitor C2, the detecting unit 14, and the second pole. In practice, the bridge inverter unit 16 is a single-phase bridge inverter or a three-phase bridge inverter. The bridge inverter unit 16 can be realized by a half bridge inverter or a full bridge inverter. The bridge type inverter unit 16 is configured to convert the input power source 10 into an alternating current to output an alternating voltage to a load 9. This embodiment does not limit the aspect of the detecting unit 14. The other switch 160 is, for example, a gold oxide half field effect transistor (MOSFET) or a power transistor. This embodiment does not limit the aspect of the switch 160.

For example, in the bridge inverter unit 16 having the bridge arm circuit, the bridge inverter unit 16 is connected in parallel with a small capacity second capacitor C2, and a detecting unit 14 detects the second capacitor C2. Discharge current. When the discharge current on the second capacitor C2 reaches a current value. The current value indicates that the bridge inverter unit 16 generates a short circuit current. Therefore, when the detecting unit 14 detects the current change, the detecting unit 14 outputs a short circuit signal to the control unit 18.

Further, when the bridge inverter unit 16 is short-circuited, the current id2 flowing through the DC bus will increase rapidly, and the current id1 flowing through the DC bus will not change instantaneously. The sum of the currents ic1, ic2 flowing through the first and second capacitors C1, C2 is equal to the difference of the current id2-id1 on the DC bus. Therefore, according to the following formula: ic1+ic2=id2-id1 and ic2=(id2-id1)*C2/(C1+C2), the current ic2 flowing through the second capacitor C2 accounts for the DC bus current id2- during the short circuit phenomenon. A small part of id1. Therefore, this embodiment employs a circuit design that detects a small current change of the second capacitor. As a result, the capacity of the current device to be detected is much smaller than the current sensor capacity required on the DC bus.

Only if this embodiment is designed with a reasonable second capacitor C2. Even if only one chip resistor is connected in series at the second end C202 of the second capacitor C2, and the voltage change of the chip resistor is detected, the current change when the bridge arm is short-circuited can be detected. The detecting unit 14 outputs a short circuit signal to a control unit 18 when the detecting unit 14 detects a current change flowing through the second capacitor C2. In this way, the embodiment can reduce the size of the circuit and accurately detect the short circuit signal.

Next, the detailed circuit and operation of the bridge circuit 1 with short circuit protection will be further described.

3 is a circuit diagram of a bridge circuit with short circuit protection according to another embodiment of the present invention. Please refer to Figure 3. In detail, the detecting unit 14a includes a first diode D1, an opto-coupler U1, a resistor R, and an operating voltage source VCC. The anode of the first diode D1 is coupled to the second end C202 of the second capacitor C2, and the cathode of the first diode D1 is coupled to the second pole. The photocoupler U1 is coupled to the first diode D1, a ground terminal, and a resistor R. The resistor R is coupled to the operating voltage source VCC. The current change is that the optocoupler U1 receives a preset current, and the optocoupler U1 is turned on according to the preset current, so that the node between the resistor R and the photocoupler U1 generates a low logic potential.

Further, the model of the optical coupler U1 is, for example, HCPL 2602, and the embodiment does not limit the aspect of the optical coupler U1. The optical coupler U1 includes a first sensing element U11 and a second sensing element U12, wherein the second sensing element U12 is coupled by light. The first sensing element U11 is coupled to the first diode D1, and the first sensing element U11 is, for example, an optical coupling inner LED. The threshold current of the other photocoupler U1 is, for example, a threshold current iop flowing through the first inductive element U11. This threshold current iop is small, for example several milliamperes (mA), and this embodiment does not limit the magnitude of the threshold current iop.

The anode of the light-emitting diode is coupled to the cathode of the first diode D1, and the cathode of the light-emitting diode is coupled to the anode of the first diode D1. The second inductive component U12 is coupled to the resistor R and the ground. The first inductive component U11 is, for example, a light emitter, and the second inductive component U12 is, for example, a photodetector. The preset current flows through the first inductive element U11 to cause the first inductive element U11 to generate an optocoupler signal to the second inductive element U12. The second sensing element U12 is turned on according to the photocoupler signal, so that the ground terminal is electrically connected to the resistor R.

When the photocoupler U1 is turned off, the first inductive element U11 and the second inductive element U12 are both in an off state. Therefore, the working voltage source VCC cannot be coupled to the ground. Therefore, the node between the optocoupler U1 and the resistor R will generate a high logic potential which is the potential of the operating voltage source VCC and the resistor R. Therefore, the signal of the high logic potential to be outputted from the node or the signal of the high logic potential detectable by the node is a signal indicating that the bridge inverter unit 16a is in a normal state.

On the other hand, when the photocoupler U1 is turned on, the first sensing element U11 and the second sensing element U12 are both in an on state, and the working voltage source VCC is coupled to the ground. Therefore, the node between the optocoupler U1 and the resistor R will generate a low logic potential which is the potential of the operating voltage source VCC, the resistor R and the ground terminal. Therefore, the signal of the low logic potential outputted from the node or the signal of the low logic potential detectable by the node is a short circuit signal indicating that the bridge inverter unit 16a is in an abnormal state.

It should be noted that the first capacitor C1 may be composed of a plurality of capacitor elements. For example, the capacitance value of the capacitive element is, for example, 470 UF/500 V, and is connected by 12 capacitor elements. The composition does not limit the aspect of the first capacitor C1. The model number of the second capacitor C2 is, for example, CBB21 (MPP). The capacitance value of the second capacitor C2 is, for example, 0.47 UF/630 VDC. This embodiment does not limit the aspect of the second capacitor C2. The model of the first diode D1 is, for example, 1N4148. This embodiment does not limit the aspect of the first diode D1. The impedance value of the resistor R is, for example, 1 K ohm, and this embodiment does not limit the aspect of the resistor R.

In addition, the conversion unit 12a of the present embodiment is described by a booster circuit, wherein the conversion unit 12a includes an inductance element L1, a diode element D2, and a switching element IGBT. The inductor element L1 is coupled to the first pole of the input power source 10a and the anode of the diode element D2. The cathode of the diode element D2 is coupled to the inductor element L1, the first capacitor C1, the second capacitor C2, and the bridge inverter unit 16a. .

Further, the diode element D2 is, for example, a high power rectifying diode. The model of the diode element D2 is, for example, STTH6006W, and the embodiment does not limit the aspect of the diode element D2. The switching element IGBT is, for example, a switching power tube, wherein the switching power tube is, for example, an IGBT IGW50N60H3, and the switching power tube has a collector (or C pole), an emitter (or E pole), and a base (or B pole). ). The collector (or C pole) is coupled to the inductor component L1 and the diode component D2, and the emitter (or E pole) is coupled to the second pole of the input power source 10a, the second terminal C102 of the first capacitor C1, and the detecting unit. 14. The inductance value of the inductance element L1 is, for example, 544 uH, and the embodiment does not limit the aspect of the inductance element L1.

The bridge type inverter unit 16a includes these changeover switches K1 ^to K4, the inverter inductor L2, and the filter capacitor C3. The switching switches K1 ^to K4, the inverter inductor L2, and the filter capacitor C3 are, for example, inverter output circuits. The models of the switches K1 ^to K4 are, for example, FGA25N120. This embodiment does not limit the aspects of the switches K1 ^to K4.

Further, the switch K1 ^~ K4 is, for example, a high-power switch tube, and the high-power switch tube has a source, a drain and a gate. The source of the switch K1 is coupled to the drain of the switch K3, and the source of the switch K3 is coupled to the second pole. The source of the switch K2 is coupled to the drain of the switch K4, and the source of the switch K4 is coupled to the second pole. The other end of the inverter inductor L2 is coupled to the source of the switch K2, and the other end of the inverter inductor L2 is coupled to the filter capacitor C3. The inductance value of the inverter inductor L2 is, for example, 144 uH. The filter capacitor C3 is composed of, for example, four capacitor elements having a capacitance value of 20 UF and 350 VAC. This embodiment does not limit the state of the inverter inductor L2 and the filter capacitor C3.

4A is a voltage waveform diagram of a bridge circuit with short circuit protection according to another embodiment of the present invention. 4B is a partial enlarged view of a voltage waveform of a bridge circuit with short circuit protection according to another embodiment of the present invention of FIG. 4A. Please refer to FIG. 4A and FIG. 4B. 4A shows a current waveform of a _bus bar voltage waveform V _bus (50 V/div), a short-circuit signal voltage waveform Vsc (1 V/div), and a bridge arm of a bridge inverter unit 16a, which is a current waveform Isc (50 A/div). And a control unit sends out the control signal waveform K1PWM (1V/div).

Next, FIG. 4B illustrates the current bus voltage waveform _Vbus , a short circuit voltage waveform Vsc, the current waveform Isc when the bridge arm of the bridge inverter unit 16a is short-circuited, and a control unit sends the control signal waveform K1PWM. 4B is an enlarged partial enlarged view of the short circuit protection action of the short circuit protection bridge circuit of the present embodiment. The test monitors the control signal waveform of the switch K1, and the control signal is, for example, a pulse width modulation signal (PWM). As shown in FIG. 4B, when the bridge arm of the bridge inverter unit 16 is short-circuited, when the current when the bridge arm is short-circuited reaches 75 A, the short-circuit signal drops from a high logic potential of 5 V to a low logic potential. At this time, the control unit stops issuing the control signal to the switch K1. This embodiment does not limit the aspect of the voltage waveform of the bridge circuit 1 with short circuit protection.

FIG. 5 is a flowchart of a method for protecting a bridge arm short circuit according to another embodiment of the present invention. Please refer to Figure 5. A short circuit protection method is applicable to the above-mentioned short circuit protection bridge circuit, comprising the following steps: In step S501, the detecting unit determines whether a current change flowing through the second capacitor is detected. In practice, the current flowing through the first capacitor will be much larger than the current flowing through the second capacitor. When the bridge inverter unit fails, for example, when the operation of the switch that is turned on or off is abnormal, the current flowing through the first capacitor and the current flowing through the second capacitor are increased. Therefore, the current flowing through the DC bus will increase. So, detect The measuring unit can detect a small current change of the second capacitor. If the result of the determination in step S501 is no, the detecting unit continuously detects the current change flowing through the second capacitor.

If the result of the determination in step S501 is YES, then step S503 is performed. In step S503, an optical coupler of the detecting unit determines whether a preset current is received. In practice, when the current flowing through the second capacitor increases, the photocoupler of the detecting unit further determines whether a preset current is received. When the current flowing through the first inductive component of the optocoupler reaches a preset current, the first inductive component will be turned on and generate an optocoupler signal to the second inductive component, and the second inductive component receives the optocoupler signal and is turned on.

Therefore, in step S505, the photocoupler is turned on to generate a short circuit signal for the resistance of a coupling photocoupler. In practice, when the optocoupler is turned off, the working power source cannot be coupled to the ground. Therefore, the node between the optocoupler and the resistor will produce a high logic potential. This high logic potential is, for example, an operating voltage of 5 volts. Therefore, a signal such as a high logic potential will be output from the above node, or a signal such as a high logic potential can be detected at the above node. The signal of high logic potential is the normal signal of the embodiment.

Conversely, when the optocoupler is turned on, the working power source is coupled to the ground. Thus, the node between the optocoupler and the resistor will produce a low logic potential, which is, for example, 0 volts. Therefore, a signal such as a low logic potential will be output from the above node, or a signal such as a low logic potential can be detected at the above node. The low logic potential signal is the short circuit signal of the embodiment.

Then, in step S507, the detecting unit outputs a short circuit signal to a control unit. In practice, when the above node will output a signal such as a low logic potential, the signal of the low logic potential is a short circuit signal. Therefore, when the control unit receives the short circuit signal, the control unit will control the bridge type inverter unit to stop operating, thereby protecting the switch switches in the bridge type inverter unit and safely supplying power to the coupled bridge type inverter unit. Back-end electrical equipment.

In summary, the short circuit protection bridge circuit of the present invention detects the bridge inverter unit in a short circuit by detecting the current change of the small capacity second capacitor. The first sensing component generates an optocoupler signal to the second inductive component when the first inductive component of the optocoupler receives the predetermined current, so that the second inductive component conducts a path between the resistor and the ground. Therefore, the node between the second sensing element and the resistor will generate a short circuit signal with a low logic potential to the control unit, thereby achieving short circuit protection of the bridge arm circuit, reducing the volume of the circuit, and improving the short circuit protection of the bridge circuit. And other effects. In this way, the present invention can indeed improve the usability of the bridge circuit with short circuit protection.

The above description is only an embodiment of the present invention, and is not intended to limit the scope of the invention.

1‧‧‧Short-circuit protected bridge circuit

10‧‧‧Input power supply

12‧‧‧Conversion unit

14‧‧‧Detection unit

16‧‧‧Bridge Inverter Unit

160‧‧‧Toggle switch

C1‧‧‧first capacitor

C2‧‧‧second capacitor

C101‧‧‧First end of the first capacitor

C201‧‧‧ the first end of the second capacitor

C102‧‧‧The second end of the first capacitor

C202‧‧‧ second end of the second capacitor

9‧‧‧load

18‧‧‧Control unit

+‧‧‧first pole

-‧‧‧Second pole

Ic1, ic2, id1, id2‧‧‧ current

Claims (11)

A bridge circuit with short circuit protection includes: an input power source having a first pole and a second pole; a conversion unit coupled to the input power source; and a first capacitor having a first end and a second end The first end of the first capacitor is coupled to the conversion unit, the second end of the first capacitor is coupled to the second pole, and the second capacitor has a first end and a second end, the first of the second capacitor The first end of the first capacitor is coupled to the first end; the detecting unit is coupled to the second end of the second capacitor; and the bridge inverting unit has a plurality of switching switches coupled to the converting unit, the first a capacitor, the second capacitor, the detecting unit and the second pole; wherein the detecting unit detects a current change flowing through the second capacitor, the detecting unit outputs a short circuit signal to a control unit. The short circuit protection bridge circuit according to claim 1, wherein the capacitance of the first capacitor is greater than the capacitance of the second capacitor, and the second capacitor is a high frequency capacitor. The short circuit-protected bridge circuit according to claim 1 or 2, wherein the detecting unit comprises a first diode, an optical coupler, a resistor and an operating voltage source, the first two The anode of the pole body is coupled to the second end of the second capacitor, the cathode of the first diode is coupled to the second pole, and the optical coupler is coupled to the first diode, a ground, and the resistor. The resistor is coupled to the working voltage source. The short circuit protection bridge circuit according to claim 3, wherein the current change is that the optical coupler receives a preset current, and the optical coupler is turned on according to the preset current, so that the resistor The node between the optocoupler produces a low logic potential. The short circuit-protected bridge circuit of claim 4, wherein the optical coupler includes a first sensing element and a second sensing element, the first sensing element is coupled to the first diode, The second sensing element is coupled to the resistor and the ground end. The short circuit protection bridge circuit according to claim 5, wherein the first sensing element is a light emitter, the second sensing component is a light detector, and the preset current flows through the first An inductive component, wherein the first inductive component generates an optocoupler signal to the second inductive component, and the second inductive component is turned on according to the optocoupler signal, so that the ground is electrically connected to the resistor, and the short circuit signal Is a low logic potential. The bridge circuit with short circuit protection as described in claim 1 or 2, wherein the conversion unit is a step-up line, a step-down line or a step-up and step line. The short circuit protection bridge circuit according to claim 1 or 2, wherein the conversion unit comprises an inductance element, a diode element and a switching element, the inductance element is coupled to the input power source a pole and an anode of the diode element, a cathode of the diode element coupled to the inductor element, the first capacitor, the second capacitor, and the bridge inverter unit. The short circuit protection bridge circuit according to claim 1 or 2, wherein the bridge inverter unit is a single phase bridge inverter or a three phase bridge inverter, wherein the bridge type The inverter unit is configured to convert the input power into an alternating current to output the alternating voltage to a load. A short circuit protection method for a bridge circuit, the bridge circuit includes an input power, a conversion unit, a first capacitor, a second capacitor, a detecting unit and a bridge inverter unit, wherein the input power is coupled to the conversion The first capacitor is coupled to the conversion unit, the second capacitor is connected to the first capacitor, and the second capacitor is connected in series with the detecting unit, and the bridge inverter unit is coupled to the second capacitor and the detector The detecting unit, the short circuit protection method includes: the detecting unit determines whether a current change through the second capacitor is detected; and if the determination result is yes, the detecting unit outputs a short circuit signal to a control unit, For the control unit to control the bridge inverter unit to stop operating. The short-circuit protection method of claim 10, wherein the step of determining whether the detecting unit detects a current flowing through the second capacitor further comprises: an optical coupling of the detecting unit The device determines whether a predetermined current is received; and if the determination result is YES, the optical coupler is turned on, so that a resistor coupled to the optical coupler generates the short circuit signal.