Output protection circuit of an inverter circuit

Abstract

The present invention discloses an output protection circuit of an inverter circuit, comprising an inverter circuit, an output current and output voltage sampling circuit, a working current sampling circuit, a first and a second short-circuit current judgment circuit, a short-circuit voltage judgment circuit, a delay circuit and a reference voltage control circuit. The output current and output voltage sampling circuits are used to respectively sample the output current and the output voltage and transmit them to the first short-circuit current judgment circuit and the short-circuit voltage judgment circuit for output short-circuit judgment, and jointly control the reference voltage control circuit to lower the reference voltage of the second short-circuit current judgment circuit when the output is short-circuited. The working current sampling circuit is used to sample the working current of the switch tube and transmit it to the second short-circuit current judgment circuit for short-circuit judgment, and output the short-circuit signal to the drive circuit of the inverter circuit for short-circuit protection. The delay circuit is used to delay the reference voltage of the second short-circuit current judgment circuit to recover to an initial voltage value.

Description

Technical Field

[0001] The invention belongs to the technical field of inverter circuits, and in particular relates to an output protection circuit of an inverter circuit. Background Art

[0002] The inverter circuit corresponds to the rectifier circuit and is a conversion circuit used to convert direct current into alternating current. The inverter circuit can be used to form various AC power supplies and is widely used in industry.

[0003] The inverter bridge circuit is a key circuit of the inverter circuit, with high cost, and it works in a high voltage, high current, and high stress state; if there is no short-circuit protection circuit for short-circuit protection, when the external load is short-circuited, the continuous large current impact is very likely to cause damage and direct damage to the switch tube (MOS / IGBT tube) of the inverter bridge circuit. Although there are some output short-circuit protection circuits for inverter circuits, the existing output short-circuit protection circuit has two large short-circuit impact currents in each cycle of the AC power after the load end of the inverter circuit is short-circuited, which will still cause damage and direct damage to the switch tube (MOS / IGBT tube) of the inverter bridge circuit, and has low safety and reliability. Summary of the invention

[0004] The object of the present invention is to provide an output protection circuit of an inverter circuit to solve the above-mentioned technical problems.

[0005] To achieve the above-mentioned purpose, the technical scheme adopted by the present invention is: an output protection circuit of an inverter circuit, comprising an inverter circuit, an output current sampling circuit, an output voltage sampling circuit, a working current sampling circuit, a first short-circuit current judgment circuit, a second short-circuit current judgment circuit, a short-circuit voltage judgment circuit, a delay circuit and a reference voltage control circuit, wherein the output current sampling circuit and the output voltage sampling circuit are used to respectively sample the current and voltage of the AC output of the inverter circuit and transmit them to the first short-circuit current judgment circuit and the short-circuit voltage judgment circuit respectively, the output ends of the first short-circuit current judgment circuit and the short-circuit voltage judgment circuit jointly control the reference voltage control circuit, which is used to control the reference voltage control circuit to lower the reference voltage of the second short-circuit current judgment circuit when a short circuit occurs in the AC output of the inverter circuit, the working current sampling circuit is used to sample the working current of the switch tube of the inverter circuit and transmit it to the second short-circuit current judgment circuit, the output end of the second short-circuit current judgment circuit is used to output a short-circuit signal to the drive circuit of the inverter circuit for short-circuit protection, and the delay circuit is used to delay the reference voltage of the second short-circuit current judgment circuit to recover to the initial voltage value when the reference voltage control circuit stops working.

[0006] Furthermore, the first short-circuit current judgment circuit is implemented by a first comparator circuit, the output end of the output current sampling circuit is connected to the non-inverting input end of the first comparator circuit, the short-circuit voltage judgment circuit is implemented by a second comparator circuit, the output end of the output voltage sampling circuit is connected to the inverting input end of the second comparator circuit, and the output ends of the first comparator circuit and the second comparator circuit are simultaneously connected to the control input end of the reference voltage control circuit.

[0007] Furthermore, the reference voltage control circuit is implemented by transistor Q5, which is connected between the reference voltage input terminal of the second short-circuit current judgment circuit and ground, and the base of transistor Q5 is simultaneously connected to the output terminals of the first comparator circuit and the second comparator.

[0008] Furthermore, the delay circuit includes a charging capacitor C23, and the charging capacitor C23 is connected between the reference voltage input terminal of the second short-circuit current judgment circuit and the ground.

[0009] Furthermore, the second short-circuit current judgment circuit is implemented by a third comparator circuit, and the output end of the working current sampling circuit is connected to the non-phase input end of the third comparator circuit.

[0010] Furthermore, it also includes an overload judgment circuit, the input end of the overload judgment circuit is connected to the output end of the output current sampling circuit, and the output end of the overload judgment circuit is used to output an overload signal to the drive circuit of the inverter circuit for overload protection.

[0011] Furthermore, the overload judgment circuit is implemented by a fourth comparator circuit, and the output end of the output current sampling circuit is connected to the non-phase input end of the fourth comparator circuit.

[0012] Furthermore, the output current sampling circuit is implemented by using a current sensor.

[0013] Furthermore, the output voltage sampling circuit is implemented by using an optical coupler.

[0014] Furthermore, the output voltage sampling circuit is implemented by using a voltage sensor.

[0015] Beneficial technical effects of the present invention:

[0016] The present invention effectively controls and limits the impact current when the AC output is short-circuited. Even if the load end is short-circuited for a long time, it can ensure that the switch tube of the inverter bridge is not impacted by a large current. In the entire short-circuit process, there is only an instantaneous large current impact during the initial short-circuit. In the entire subsequent short-circuit process, an extremely small short-circuit current always exists until the short circuit is released. The impact and damage of the switch tube of the inverter bridge caused by the load short-circuit of the inverter circuit is solved, so that the switch tube of the inverter bridge can work more safely and reliably, and there is no need to consider the selection of a switch tube with a larger current and a higher quality, thereby making selection more convenient and reducing costs. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] In order to more clearly illustrate the technical solutions in the embodiments of the present invention, the drawings required for use in the description of the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0018] Figure 1 is a circuit diagram of a driving circuit of an inverter circuit according to a first embodiment of the present invention;

[0019] Figure 2 A circuit diagram of an inverter bridge, a working current sampling circuit, an output current sampling circuit and an output voltage sampling circuit according to a first embodiment of the present invention;

[0020] Figure 3 A circuit diagram of an overload judgment circuit, a first short-circuit current judgment circuit, a second short-circuit current judgment circuit, a short-circuit voltage judgment circuit, a delay circuit, and a reference voltage control circuit according to a first embodiment of the present invention;

[0021] Figure 4 4 is a circuit diagram of an output voltage sampling circuit according to a second embodiment of the present invention. DETAILED DESCRIPTION

[0022] To further illustrate the various embodiments, the present invention provides drawings. These drawings are part of the disclosure of the present invention, which are mainly used to illustrate the embodiments and can be used in conjunction with the relevant descriptions in the specification to explain the operating principles of the embodiments. With reference to these contents, a person of ordinary skill in the art should be able to understand other possible implementations and advantages of the present invention. The components in the figures are not drawn to scale, and similar component symbols are generally used to represent similar components.

[0023] The present invention will now be further described with reference to the accompanying drawings and specific implementation methods.

[0024] Embodiment 1

[0025] like Figure 1-3As shown, an output protection circuit of an inverter circuit includes an inverter circuit, an output current sampling circuit, an output voltage sampling circuit, a working current sampling circuit, a first short-circuit current judgment circuit, a second short-circuit current judgment circuit, a short-circuit voltage judgment circuit, a delay circuit and a reference voltage control circuit. In this specific embodiment, the inverter circuit includes a drive circuit, an inverter bridge and an LC filter circuit. The drive circuit includes a controller 1 and two dual-channel high-voltage half-bridge drive chips U1 and U2. The inverter bridge is an inverter full bridge, which is composed of switch tubes Q1, Q2, Q3 and Q4 (MOS tubes in this embodiment, but not limited to this. In other embodiments, IGBT tubes, etc.) are formed. The controller 1 can be an MCU processor, DSP, etc. The controller 1 generates a high-frequency SPWM wave modulated by a sine wave, which is processed by the drive chips U1 and U2 and output to the switch tubes Q1, Q2, Q3 and Q4 for inversion. After inversion, it is filtered by the LC filter circuit and outputs 110V / 60Hz, 220V / 50Hz or any desired AC voltage for use in various AC electrical equipment. For specific circuits, please see Figure 1 and 2 However, the present invention is not limited thereto, and in other embodiments, the inverter circuit may also be other existing inverter circuits.

[0026] The output current sampling circuit and the output voltage sampling circuit are used to respectively sample the current and voltage of the inverter circuit's AC output and transmit them to the first short-circuit current judgment circuit and the short-circuit voltage judgment circuit respectively. In this specific embodiment, the output current sampling circuit includes a current sensor T1, a diode D5, a diode D6, a diode D9, a diode D10, a filter capacitor C18 and a sampling resistor R18. The current sensor T1 is connected in series in the inverter circuit's AC output loop to isolate and sample the AC output current. After rectification by diodes D5, D6, D9 and D10 and filtering by filter capacitor C18, a current sampling signal IAC is formed on the sampling resistor R18. The output current sampling circuit has good anti-interference performance and high reliability, but is not limited to this. In other embodiments, other existing current sampling circuits can also be used to implement it.

[0027] In this specific embodiment, the output voltage sampling circuit includes a resistor R22, a resistor R29, an optical coupler U3, an optical coupler U6 and a capacitor C21. For specific circuit connections, see Figure 2 , which will not be described in detail, the output voltage sampling circuit outputs a voltage sampling signal VAC, and the output voltage sampling circuit is small in size and has good anti-interference. Of course, in other embodiments, the output voltage sampling circuit can also be implemented by other existing voltage sampling circuits.

[0028] The working current sampling circuit is used to sample the working current of the switch tube of the inverter circuit and transmit it to the second short-circuit current judgment circuit. In this specific embodiment, the working current sampling circuit includes sampling resistors RS1 and RS2. The sampling resistors RS1 and RS2 are connected in series in the working loop of the switch tubes Q1, Q2, Q3 and Q4. The output ends of the sampling resistors RS1 and RS2 output the working current sampling signal IFB. Of course, in other embodiments, the working current sampling circuit can also be implemented by other existing current sampling circuits.

[0029] The output ends of the first short-circuit current judgment circuit and the short-circuit voltage judgment circuit jointly control the reference voltage control circuit, which is used to control the reference voltage control circuit to lower the reference voltage of the second short-circuit current judgment circuit when a short circuit occurs in the AC output of the inverter circuit. The output end of the second short-circuit current judgment circuit is used to output a short-circuit signal to the drive circuit of the inverter circuit for short-circuit protection. The delay circuit is used to delay the reference voltage of the second short-circuit current judgment circuit to recover to an initial voltage value when the reference voltage control circuit stops working.

[0030] In this specific embodiment, the first short-circuit current judgment circuit is implemented by the first comparator circuit, and the first comparator circuit is implemented by the four-way comparator U5. The 10th pin of the four-way comparator U5 is the inverting input terminal of the first comparator circuit, connected to the first reference voltage, the 11th pin of the four-way comparator U5 is the non-inverting input terminal of the first comparator circuit, connected to the current sampling signal IAC (that is, connected to the output terminal of the output current sampling circuit), and the 13th pin of the four-way comparator U5 is the output terminal of the first comparator circuit, connected to the control input terminal of the reference voltage control circuit, but it is not limited to this. In other embodiments, the first short-circuit current judgment circuit can also be implemented by other existing comparison circuits.

[0031] The short-circuit voltage judgment circuit is implemented by the second comparator circuit, and the second comparator circuit is implemented by the four-way comparator U5. The 8th pin of the four-way comparator U5 is the inverting input terminal of the second comparator circuit, connected to the voltage sampling signal VAC (that is, connected to the output terminal of the output voltage sampling circuit), the 9th pin of the four-way comparator U5 is the non-inverting input terminal of the second comparator circuit, connected to the second reference voltage, and the 14th pin of the four-way comparator U5 is the output terminal of the second comparator circuit, connected to the control input terminal of the reference voltage control circuit, but it is not limited to this. In other embodiments, the short-circuit voltage judgment circuit can also be implemented using other existing comparison circuits.

[0032] The second short-circuit current judgment circuit is implemented by the third comparator circuit, and the third comparator circuit is implemented by the four-way comparator U5. The 4th pin of the four-way comparator U5 is the inverting input terminal of the third comparator circuit, connected to the third reference voltage, the 5th pin of the four-way comparator U5 is the non-inverting input terminal of the third comparator circuit, the series resistor R33 is connected to the working current sampling signal IFB (that is, connected to the output terminal of the working current sampling circuit), the 2nd pin of the four-way comparator U5 is the output terminal of the third comparator circuit, and the series diode D11 is connected to the enable terminal SD of the driver chip U1 and U2, but it is not limited to this. In other embodiments, the second short-circuit current judgment circuit can also be implemented by other existing comparison circuits. By configuring the third reference voltage, the maximum allowable working current of the inverter full-bridge switch tube can be limited.

[0033] In this specific embodiment, the reference voltage control circuit is implemented by using an NPN transistor Q5, which is connected between the reference voltage input terminal of the second short-circuit current judgment circuit (the 4th pin of the four-way comparator U5) and the ground, and the base series resistor R25 of the NPN transistor Q5 is simultaneously connected to the output terminals of the first comparator circuit and the second comparator circuit (the 13th and 14th pins of the four-way comparator U5). Of course, in other embodiments, the reference voltage control circuit can also be implemented by using other existing switch circuits.

[0034] In this specific embodiment, the delay circuit includes a charging capacitor C23, and the charging capacitor C23 is connected between the fourth pin of the four-way comparator U5 and the ground. However, the present invention is not limited thereto.

[0035] Furthermore, it also includes an overload judgment circuit, the input end of the overload judgment circuit is connected to the output end of the output current sampling circuit, and the output end of the overload judgment circuit is used to output an overload signal to the drive circuit of the inverter circuit for overload protection. Specifically, the overload judgment circuit is implemented by a fourth comparator circuit, and the fourth comparator circuit is implemented by a four-way comparator U5, the 6th pin of the four-way comparator U5 is the inverting input end of the fourth comparator circuit, connected to the fourth reference voltage, the 7th pin of the four-way comparator U5 is the non-inverting input end of the fourth comparator circuit, the series resistor R31 is connected to the current sampling signal IAC, and the 1st pin of the four-way comparator U5 is the output end of the fourth comparator circuit, connected to the input end of the controller 1, but it is not limited to this. In other embodiments, the overload judgment circuit can also be implemented by other existing comparison circuits.

[0036] In this specific embodiment, the first, second, third and fourth comparison circuits are implemented by four comparators U5, which have high circuit integration, simple structure and small size, but are not limited thereto.

[0037] In this specific embodiment, the first, second, third and fourth reference voltages are provided by a reference power supply, a first voltage divider circuit, a second voltage divider circuit, a third voltage divider circuit and a fourth voltage divider circuit. The reference power supply includes a resistor R20 and a voltage regulator U4. The first voltage divider circuit includes resistors R28 and R37. The second voltage divider circuit includes resistors R27 and R36. The third voltage divider circuit includes resistors R24 and R34. The fourth voltage divider circuit includes resistors R23 and R32. For specific circuit connections, please see Figure 3 , I will not go into details here, but it is not limited to this.

[0038] During normal operation, the current sampling signal IAC is lower than the reference value of the 6th pin of the four-way comparator U5, the 1st pin of the four-way comparator U5 outputs a low level, and the controller 1 operates normally; when the load power exceeds the set value, the current sampling signal IAC exceeds the reference value of the 6th pin of the four-way comparator U5, the 1st pin of the four-way comparator U5 outputs a high level, and after being identified and processed by the controller 1, the overload protection is started, and the outputs of SPWM1, SPWM2, SPWM3, and SPWM4 are turned off, thereby turning off the driver chips U1 and U2, that is, turning off the AC output, and performing overload protection.

[0039] During normal operation, the current sampling signal IAC is lower than the reference value of the 10th pin of the four-way comparator U5, and the 13th pin of the four-way comparator U5 outputs a low level. Regardless of the state of the 14th pin of the four-way comparator U5, the NPN transistor Q5 is turned off, and the voltage of the 4th pin of the four-way comparator U5 is the divided voltage (initial voltage value) output by the third voltage divider circuit. The working current sampling signal IFB is always lower than the reference value of the 4th pin of the four-way comparator U5, and the ground pin 2 of the four-way comparator U5 outputs a low level, and the driver chips U1 and U2 are not controlled; when starting a large inductive or capacitive load, such as when the load current instantly exceeds the set short-circuit current value, within the AC voltage cycle, the working current sampling signal IFB is instantly higher than the reference value of the 4th pin of the four-way comparator U5, and the four-way comparator U5 Pin 2 outputs a high level during the AC cycle to turn off the driver chips U1 and U2, realizing wave-by-wave current limiting of the AC output to ensure the normal startup of the load; when the load end is actually short-circuited, because the output AC voltage is close to zero, the voltage sampling signal VAC is less than the reference value of the 9th pin of the four-way comparator U5, and the short-circuit current is very large, therefore, the current sampling signal IAC exceeds the reference value of the 10th pin of the four-way comparator U5, and the 13th and 14th pins of the four-way comparator U5 are high at the same time, and the NPN transistor Q5 is turned on through the resistor R25, the charging capacitor C23 is directly discharged and the reference voltage of the 4th pin of the four-way comparator U5 is pulled down to near zero, so that the 2nd pin of the four-way comparator U5 immediately outputs a high level to turn off the driver chips U1 and U2, thereby turning off the AC output for short-circuit protection. At this time, although the load current disappears, the current sampling signal IAC is lower than the reference value of the 10th pin of the four-way comparator U5, the 14th pin of the four-way comparator U5 returns to a low level, the NPN transistor Q5 is also turned off, and the 2nd pin of the four-way comparator U5 returns to a low level to turn on the driver chips U1 and U2 again, and the AC power resumes output. However, because the reference voltage of the 4th pin of the four-way comparator U5 cannot be immediately restored to the divided voltage (it can only be gradually increased) because the charging capacitor C23 is discharged and it takes time to charge the charging capacitor C23 through the resistor R24, if the short circuit still exists, as long as there is a very small short-circuit current, the 2nd pin of the four-way comparator U5 can be triggered again to output high-level protection, until the level on the charging capacitor C23 reaches a certain value (the reference value reaches a certain value), the 13th and 14th pins of the four-way comparator U5 will be started again to output high levels to turn on the NPN transistor Q5 and discharge the charging capacitor C23 again. During the entire short-circuit process, there is only a momentary large current impact at the initial short-circuit. During the subsequent short-circuit process, there is always a very small short-circuit current until the short-circuit is released. Of course, the short-circuit signal output by the second foot of the four-way comparator U5 can also be transmitted to the controller 1 at the same time. The controller 1 calculates and configures to directly shut down the output and lock it after a certain period of short-circuit, and then shuts down and restarts to recover.

[0040] Embodiment 2

[0041] like Figure 4 As shown, the difference between this embodiment and the first embodiment is that the output voltage sampling circuit of this embodiment includes a voltage sensor T2, a resistor R39, a resistor R40, and diodes D12-D15. The voltage sensor T2 is connected to the AC output terminals AC_L and AC_N of the inverter circuit through resistors R39 and R40. The output of the voltage sensor T2 passes through the rectifier circuit formed by diodes D12-D15 to output a voltage sampling signal VAC.

[0042] Although the present invention has been specifically shown and described in conjunction with the preferred embodiments, it should be understood by those skilled in the art that various changes may be made to the present invention in form and details without departing from the spirit and scope of the present invention as defined by the appended claims, all of which are within the scope of protection of the present invention.

Claims

1. An output protection circuit of an inverter circuit, characterized in that: It includes an inverter circuit, an output current sampling circuit, an output voltage sampling circuit, a working current sampling circuit, a first short-circuit current judgment circuit, a second short-circuit current judgment circuit, a short-circuit voltage judgment circuit, a delay circuit and a reference voltage control circuit. The output current sampling circuit and the output voltage sampling circuit are used to respectively sample the current and voltage of the AC output of the inverter circuit and transmit them to the first short-circuit current judgment circuit and the short-circuit voltage judgment circuit respectively. The output ends of the first short-circuit current judgment circuit and the short-circuit voltage judgment circuit jointly control the reference voltage control circuit, which is used to control the reference voltage control circuit to lower the reference voltage of the second short-circuit current judgment circuit when the AC output of the inverter circuit is short-circuited. The working current sampling circuit is used to sample the working current of the switch tube of the inverter circuit and transmit it to the second short-circuit current judgment circuit. The output end of the second short-circuit current judgment circuit is used to output a short-circuit signal to the drive circuit of the inverter circuit for short-circuit protection. The delay circuit is used to delay the reference voltage of the second short-circuit current judgment circuit to recover to an initial voltage value when the reference voltage control circuit stops working; The first short-circuit current judgment circuit is implemented by a first comparator circuit, the output end of the output current sampling circuit is connected to the non-inverting input end of the first comparator circuit, the short-circuit voltage judgment circuit is implemented by a second comparator circuit, the output end of the output voltage sampling circuit is connected to the inverting input end of the second comparator circuit, and the output ends of the first comparator circuit and the second comparator are simultaneously connected to the control input end of the reference voltage control circuit; The reference voltage control circuit is implemented by a transistor Q5, which is connected between the reference voltage input terminal of the second short-circuit current judgment circuit and the ground, and the base of the transistor Q5 is connected to the output terminals of the first comparator circuit and the second comparator circuit at the same time; The delay circuit includes a charging capacitor C23, and the charging capacitor C23 is connected between the reference voltage input terminal of the second short-circuit current judgment circuit and the ground.

2. The output protection circuit of the inverter circuit according to claim 1, characterized in that: The second short-circuit current judgment circuit is implemented by a third comparator circuit, and the output end of the working current sampling circuit is connected to the non-phase input end of the third comparator circuit.

3. The output protection circuit of the inverter circuit according to claim 1, characterized in that: It also includes an overload judgment circuit, the input end of the overload judgment circuit is connected to the output end of the output current sampling circuit, and the output end of the overload judgment circuit is used to output an overload signal to the drive circuit of the inverter circuit for overload protection.

4. The output protection circuit of the inverter circuit according to claim 3, characterized in that: The overload judgment circuit is implemented by a fourth comparator circuit, and the output end of the output current sampling circuit is connected to the non-phase input end of the fourth comparator circuit.

5. The output protection circuit of the inverter circuit according to claim 1, characterized in that: The output current sampling circuit is implemented by using a current sensor.

6. The output protection circuit of the inverter circuit according to claim 1, characterized in that: The output voltage sampling circuit is implemented by using an optical coupler.

7. The output protection circuit of the inverter circuit according to claim 1, characterized in that: The output voltage sampling circuit is implemented by using a voltage sensor.

Images