A three-phase inverter circuit overcurrent protection system

Abstract

The invention discloses a three-phase inverter circuit overcurrent protection system, and belongs to the technical field of AC-DC-AC frequency conversion circuit overcurrent protection. The existing inverter circuit overcurrent protection method includes overcurrent protection, undervoltage protection and output short circuit protection, and there are problems of slow response speed and low safety factor. The invention provides a three-phase inverter circuit overcurrent protection system, including a power supply, an STM32 microcontroller, a current sampling circuit, a current detection circuit and an overcurrent protection circuit, the current detection circuit includes a total current detection circuit, a phase current detection circuit, and the overcurrent protection circuit includes an eight-input NAND gate circuit, a signal latch circuit and a tri-state buffer gate circuit. The whole system can display the instantaneous current size under normal working state, and can respond very quickly to complete the overcurrent protection of the whole three-phase inverter circuit system when an overcurrent situation occurs, with fast response speed and high safety factor.

Description

Technical Field

[0001] The invention belongs to the technical field of overcurrent protection of AC-DC-AC frequency conversion circuits, and in particular relates to an overcurrent protection system for a three-phase inverter circuit. Background Art

[0002] At present, the frequency conversion technology adopts the AC-DC-AC frequency conversion method, which changes the circuit frequency by rectifying, filtering and then inverting, and changing the output of the inverter circuit. This design theory has been developed very maturely and has been widely used in motor AC speed regulation systems. Among them, the use of microcontrollers to output pulse width modulation (PWM) signals and then output controllable AC voltage with adjustable voltage and frequency has become the current mainstream control scheme. However, the impedance characteristics of the motor often lead to the phenomenon that large currents are easily generated during the inverter speed regulation process, causing the entire motor to burn out. In the past, individual designs would choose software systems to implement current and voltage sampling protection. However, the disadvantage of this design is that the read and write speed requirements of the microcontroller are too high, and the software system is prone to errors, which also brings inconvenience to later maintenance and program modifications. Therefore, there are few such designs at present.

[0003] The inverter protection methods that have been developed and matured are generally divided into overcurrent protection, undervoltage protection, and output short-circuit protection. Undervoltage protection mainly determines whether to perform protection action based on the comparison result between the voltage and the threshold value in a unit time. The short-circuit protection method mainly determines whether to trigger the short-circuit protection action based on whether the voltage is lower than the set threshold value in a unit time and whether the current is higher than the set value. However, a problem with the current design of the scheme is that both the undervoltage protection and the output short-circuit protection methods have a certain comparison time and slow response speed. In the process of using high-frequency PWM debugging, an instant often causes damage to the entire IGBT module, resulting in a reduced safety factor. Summary of the invention

[0004] The purpose of the present invention is to solve the problems in the prior art and provide a three-phase inverter circuit overcurrent protection system.

[0005] In order to achieve the above object, the present invention adopts the following technical solutions:

[0006] A three-phase inverter circuit overcurrent protection system includes a power supply, an STM32 microcontroller, a current sampling circuit, a current detection circuit and an overcurrent protection circuit.

[0007] The power supply includes ±15V power supply, +5V power supply, and -15V power supply ground;

[0008] The current sampling circuit is used to collect the current of the total inverter circuit, U phase and V phase, and convert the current signal into a Hall voltage signal;

[0009] The current detection circuit includes a total current detection circuit 4 and a phase current detection circuit. The phase current detection circuit includes a U-phase current detection circuit 5 and a V-phase current detection circuit 6.

[0010] The overcurrent protection circuit comprises an eight-input NAND gate circuit 7, a signal latch circuit 8 and a three-state buffer gate circuit 9, wherein the eight-input NAND gate circuit 7, the signal latch circuit 8 and the three-state buffer gate circuit 9 are connected in sequence.

[0011] The current sampling circuit, the current detection circuit and the overcurrent protection circuit are connected in sequence, and the STM32 microcontroller is connected to the signal latch circuit 8 and the three-state buffer gate circuit 9.

[0012] In the above scheme, the current sampling circuit includes a first Hall current sensor 1, a second Hall current sensor 2 and a third Hall current sensor 3. The first Hall current sensor 1 is connected to the input end of the inverter circuit, and the second Hall current sensor 2 and the third Hall current sensor 3 are respectively connected to the output ends of the U phase and the V phase of the inverter circuit.

[0013] In the above scheme, the total current detection circuit 4 includes a voltage follower circuit and a single hysteresis comparison circuit, and the U-phase current detection circuit 5 includes a voltage follower circuit and a double hysteresis comparison circuit;

[0014] The single hysteresis comparison circuit includes an LM393 voltage comparator, a switching diode D3, a resistor R16, a resistor R19 and a potentiometer R17, one end of the potentiometer R17 is connected to a +15V power supply, and the other end is divided into two paths, one of which is connected in series with the resistor R16 and the switching diode D6 to the first end of the LM393 voltage comparator, and the other is connected in series with the resistor R19 to the second end of the LM393 voltage comparator. The switching diode D6 is used to convert the hysteresis comparator into a single hysteresis comparator, and the potentiometer R17 is connected in series with the resistor R19 to divide the voltage, which is used to adjust the reference current of the LM393 voltage comparator;

[0015] The dual hysteresis comparison circuit includes two LM339 voltage comparators.

[0016] The V-phase current detection circuit 5 is the same as the U-phase current detection circuit 6.

[0017] In the above scheme, the signal latch circuit 8 includes an RS latch, a hardware reset button and a software reset unit. The hardware reset button and the software reset unit are connected to the 7th end of the RS latch. The hardware reset button and the software reset unit are used for the next signal latch protection after the overcurrent protection occurs and is resolved.

[0018] In the above scheme, the output port of the tri-state buffer gate is connected to a row of about 3K pull-up resistors, which are used to prevent interference between latches. The tri-state buffer gate circuit can be used to realize the shutdown of the IGBT inverter circuit.

[0019] In the above solution, the -15V power ground is used to separate the power supply of the device part from the power supply of the main system to achieve electrical isolation.

[0020] Compared with the prior art, the present invention has the following beneficial effects:

[0021] The invention provides an inverter overcurrent protection system, which utilizes a Hall current sensor to convert the current of each part in the inverter circuit into a Hall voltage signal, and utilizes the rapidity of a hysteresis comparison circuit and the parasitic coupling-free characteristics of a voltage comparator, and realizes the switching of a microcontroller on a drive signal of the inverter circuit through a latching circuit to realize the protection of the entire inverter circuit system. The entire system adopts the control method of an STM32 microcontroller, so that during the current sampling process, the input current signal size can be displayed on a display through the operation of a processor, and the instantaneous current size can be displayed under normal working conditions. At the same time, when an overcurrent situation occurs, it can respond very quickly to complete the overcurrent protection of the entire three-phase inverter circuit system, and has a fast response speed and a high safety factor. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 is a system structure diagram of the present invention;

[0023] Figure 2 It is a schematic diagram of the structure of the Hall current sensor circuit of the present invention;

[0024] Figure 3 It is a schematic diagram of the structure of the inverter total current detection circuit of the present invention;

[0025] Figure 4 It is a schematic diagram of the structure of the U-phase current detection circuit of the present invention;

[0026] Figure 5 It is a schematic diagram of the structure of an eight-input NAND gate circuit of the present invention;

[0027] Figure 6 It is a schematic diagram of the structure of the signal latch circuit of the present invention;

[0028] Figure 7 It is a schematic diagram of the structure of the tri-state buffer gate circuit of the present invention.

[0029] Among them: 1-first Hall current sensor; 2-second Hall current sensor; 3-third Hall current sensor; 4-total current detection circuit; 5-U phase current detection circuit; 6-V phase current detection circuit; 7-eight-input NAND gate circuit; 8-signal latch circuit; 9-three-state buffer gate circuit. DETAILED DESCRIPTION

[0030] The present invention is further described in detail below in conjunction with the accompanying drawings:

[0031] See also Figure 1 The present invention includes a power supply, an STM32 microcontroller, a current sampling circuit, a current detection circuit and an overcurrent protection circuit.

[0032] The power supply includes ±15V power, +5V power, and -15V power ground; the -15V power ground is used to separate the power supply of the device part from the power supply of the main system to achieve electrical isolation;

[0033] The sampling circuit is used to collect the current of the total inverter circuit, the U phase, and the V phase, and convert the current signal into a Hall voltage signal;

[0034] The current detection circuit includes a total current detection circuit 4 and a phase current detection circuit. The phase current detection circuit includes a U-phase current detection circuit 5 and a V-phase current detection circuit 6.

[0035] The overcurrent protection circuit comprises an eight-input NAND gate circuit 7, a signal latch circuit 8 and a three-state buffer gate circuit 9, wherein the eight-input NAND gate circuit 7, the signal latch circuit and the three-state buffer gate circuit 9 are connected in sequence.

[0036] The current sampling circuit, the current detection circuit and the overcurrent protection circuit are connected in sequence, and the STM32 microcontroller is connected to the signal latch circuit 8 and the three-state buffer gate circuit 9.

[0037] This system can ultimately achieve the protection of inverter systems including but not limited to 3KW power, so the voltage level of the main circuit is relatively high, and the protection circuit is relatively weak current signal. In order to avoid mutual interference when detecting the main circuit, the current signal detection of the main circuit part uses Hall components with electrical isolation function, see Figure 2 The current sampling circuit uses three Hall current sensors to sample the current. The first Hall current sensor 1 is connected to the input end of the inverter circuit as the current sampling of the inverter total loop. The second Hall current sensor 2 and the third Hall current sensor 3 are respectively connected to the U phase and V phase of the inverter output loop as the output three-phase current size sampling, thereby converting the current signal into a Hall voltage signal.

[0038] See also Figure 3, the total current Hall voltage signal obtained by sampling will enter the comparison circuit for total inverter current detection. In the total inverter current detection, in order to prevent the entire circuit from fluctuating, a voltage follower circuit is added to the front end of the signal comparison circuit to increase the input impedance for isolation. The operational amplifier uses the LM358 chip, and resistors R10 and R7 are used to eliminate reflections to prevent the reflected signal from oscillating at the input point and reducing the signal quality. Capacitors C11 and C13 are used to absorb the reflected signal to prevent oscillation. At the same time, they can also filter out the harmonics of the signal to the ground to ensure the stability of the signal. Because the currents of the U and V phases are AC signals, dual power supplies of ±15V are used to meet the voltage variation range. At the same time, electrolytic capacitors C7, C18 and ceramic capacitors C5, C14 are added to each power supply end to ensure the stability of the power supply. The -15V power supply ground is used to separate the power supply of the device part from the main system power supply to achieve electrical isolation.

[0039] The single hysteresis comparator circuit adopts LM393 voltage comparator to form hysteresis comparator. Once the output state of hysteresis comparator is changed, as long as the interference near the jump voltage value does not exceed ΔU, the output voltage is stable. At the same time, positive feedback is performed through resistor R16 to increase the threshold width. This method can speed up the response speed of comparator and avoid self-excited oscillation caused by parasitic coupling of circuit, so it has the conditions for fast response. Although the increase of threshold width will enhance the anti-interference ability, too large threshold width will also affect the sensitivity. The recommended external circuit given by the device manual can be found. When R16 takes 1MΩ, the effect is best.

[0040] At the same time, a switching diode D6 is designed in the circuit to turn the hysteresis comparator into a single hysteresis comparator. When the output is at a high level, no positive feedback is performed, ensuring the sensitivity of the circuit during normal operation. When the output is at a low level, positive feedback is added, which has strong anti-interference and prevents false protection operations. The protection action response speed is fast.

[0041] The reference voltage of the single hysteresis comparator circuit is generally adjustable. The reference voltage signal enters the input of the comparator after being divided by the potentiometer R17 and the fixed current limiting resistor. After a simple calculation, it can be known that when the potentiometer is 50KΩ and the fixed resistor is 2.5KΩ, the reference voltage is adjustable from 0.7V to 15V. The upper limit of the signal to be protected calculated before is 0.8V, so the reference voltage can be adjusted to 0.8V. If it is considered for the future, when the current reaches the rated value of 10A, the converted voltage is only 4V, which fully meets the debugging standards. The design method of this potentiometer can be applied to various current ranges.

[0042] The detection method of the inverter U and V phase currents is the same. Here, the U phase current detection is used to explain. Figure 4The U-phase current detection circuit also uses a first-level voltage follower design, because the biggest advantage of using voltage signals to protect current signals is that there is basically no current in the comparator, so it can reduce a lot of interference problems. However, in the output part of the inverter circuit, the current becomes a positive and negative alternating current. Therefore, while protecting the positive signal, the negative signal must also be protected. Therefore, a double-limit hysteresis comparator is used in the signal comparison part to solve it. The double-limit hysteresis comparator uses two LM339 voltage comparators. Since the output of the comparator has only two states, low level and high level, the integrated operational amplifier often works in the nonlinear region. While comparing the upper limit of the AC signal, the lower limit is also compared. Because the negative voltage is the greater the absolute value, the smaller the actual voltage, so the input interface of the upper limit and the lower limit is different. The negative comparison is the positive input terminal, and the positive comparison is the negative input terminal, to ensure that the upper and lower limits do not exceed the reference voltage.

[0043] The overcurrent protection circuit includes an eight-input NAND gate circuit, a signal latch circuit and a three-state buffer gate circuit. In the eight-input NAND gate circuit, since all current detections adopt a positive feedback hysteresis comparator method, a low-level protection method is selected in the protection logic. According to the NAND logic, when the input terminal signal appears a low level, a high level signal will be output at the output terminal;

[0044] Since the output signal of the current comparison part is generated instantaneously, a signal latch circuit needs to be added after the output of the eight-input NAND gate circuit. Figure 5 The signal latch circuit includes an RS latch, a hardware reset button and a software reset unit. The hardware reset button and the software reset unit are connected to the 7th terminal of the RS latch. The hardware reset button and the software reset unit are used for the next signal latch protection after the overcurrent protection occurs and is resolved. The signal latch circuit defaults to a high level and is reset at a low level. When the RS latch inputs a high level, the STM32 microcontroller controls the RS latch reset through the software reset unit. If the STM32 microcontroller program fails, it can also be manually reset through the hardware reset button, which greatly improves the safety and reliability of the system.

[0045] See also Figure 7 In the tri-state buffer gate circuit, since the CMOS output port cannot be left floating, a row of 3K pull-up resistors is added to the input part to prevent interference between the latches. The tri-state buffer gate circuit can be used to turn off the IGBT inverter circuit.

[0046] When the high-level trigger signal in the RS latch is input into the three-state buffer gate, the output of the three-state buffer gate is in a high-impedance state, thereby quickly cutting off the modulation signal of the inverter circuit, shutting down the IGBT inverter circuit, and realizing overcurrent protection of the entire three-phase inverter circuit system.

[0047] The above are only preferred embodiments of the present invention and are not intended to limit the present invention. For those skilled in the art, the present invention may have various modifications and variations. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. A three-phase inverter circuit overcurrent protection system, characterized in that: It includes a power supply, an STM32 microcontroller, a current sampling circuit, a current detection circuit and an overcurrent protection circuit, wherein the power supply includes a ±15V power supply, a +5V power supply and a -15V power supply ground; The current sampling circuit is used to collect the current of the total inverter circuit, U phase and V phase, and convert the current signal into a Hall voltage signal; The current detection circuit comprises a total current detection circuit (4) and a phase current detection circuit; the phase current detection circuit comprises a U-phase current detection circuit (5) and a V-phase current detection circuit (6); the overcurrent protection circuit comprises an eight-input NAND gate circuit (7), a signal latch circuit (8) and a three-state buffer gate circuit (9); the eight-input NAND gate circuit (7), the signal latch circuit (8) and the three-state buffer gate circuit (9) are connected in sequence; the current sampling circuit, the current detection circuit and the overcurrent protection circuit are connected in sequence; and the STM32 microcontroller is connected to the signal latch circuit (8) and the three-state buffer gate circuit (9); The current sampling circuit comprises a first Hall current sensor (1), a second Hall current sensor (2) and a third Hall current sensor (3), wherein the first Hall current sensor (1) is connected to an input end of an inverter circuit, and the second Hall current sensor (2) and the third Hall current sensor (3) are respectively connected to output ends of a U phase and a V phase of the inverter circuit; The total current detection circuit (4) comprises a voltage follower circuit and a single hysteresis comparison circuit, and the U-phase current detection circuit (5) comprises a voltage follower circuit and a double hysteresis comparison circuit; The single hysteresis comparison circuit includes an LM393 voltage comparator, a switching diode D3, a resistor R16, a resistor 19 and a potentiometer R17. One end of the potentiometer R17 is connected to a +15V power supply, and the other end is divided into two paths, one of which is connected in series with the resistor R16 and the switching diode D6 to the first end of the LM393 voltage comparator, and the other is connected in series with the resistor R19 to the second end of the LM393 voltage comparator. The switching diode D6 is used to convert the hysteresis comparator into a single hysteresis comparator. The potentiometer R17 is connected in series with the resistor R19 to divide the voltage and is used to adjust the reference current of the LM393 voltage comparator. The dual hysteresis comparison circuit comprises two LM339 voltage comparators, and the V-phase current detection circuit (6) is the same as the U-phase current detection circuit (5); The signal latch circuit (8) comprises an RS latch, a hardware reset button and a software reset unit, wherein the hardware reset button and the software reset unit are connected to the seventh terminal of the RS latch, and the hardware reset button and the software reset unit are used for performing the next signal latch protection after the overcurrent protection occurs and is resolved.

2. A three-phase inverter circuit overcurrent protection system according to claim 1, characterized in that: The output port of the tri-state buffer gate is connected to a row of about 3K pull-up resistors, which are used to prevent interference between latches. The tri-state buffer gate circuit can be used to realize the shutdown of the IGBT inverter circuit.

3. A three-phase inverter circuit overcurrent protection system according to claim 1, characterized in that: The -15V power ground is used to separate the power supply of the device part from the power supply of the main system to achieve electrical isolation.

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