An overcurrent and short-circuit protection method for an inverter

Abstract

The invention discloses an overcurrent and short-circuit protection method for an inverter, and relates to the technical field of inverters. The method comprises the following steps: S1, the inverter direct current inputs DC_+ and DC-, the bus filter capacitor C80 is connected across, the shunt meter RD6 is connected to the DC_+ and IGBT DC+ input terminals, and the voltage signals DC_+ and DC_1+ converted after the shunt meter is sampled are sent to the current mirror circuit; S2, the DC_+ and DC_1+ sampled in the inverter main circuit are sent to the current mirror overcurrent detection and signal drive circuit; S3, Rd6 selects a suitable shunt meter according to the working current and power. The overcurrent and short-circuit protection values ​​of the present invention can be calculated and set. When the short-circuit point current is larger, the primary side drive current of the optocoupler is larger, and the protection delay is shorter. The scheme has good adaptability to overcurrent and short-circuit protection, and can be applied to the short-circuit of the port with small overcurrent and short-circuit impedance, and can also use the short-circuit impedance to be larger. One circuit can protect the entire inverter, and the circuit is simple and low-cost components can be implemented, and the economy is good.

Description

Technical Field

[0001] The present invention relates to the technical field of inverters, and in particular to an overcurrent and short-circuit protection method for an inverter. Background Art

[0002] IGBT is a commonly used device in high-power inverter switching devices. For the output overcurrent and short-circuit protection of IGBT inverters, the Vcesat detection technology of IGBT is usually used. The desaturation characteristics of the inverter device IGBT when a short-circuit overcurrent occurs, that is, the IGBT gradually enters the amplification area from the low Vce voltage drop of saturated conduction, resulting in an increase in Vce voltage, are detected by detecting that the IGBT Vce voltage reaches a certain threshold, triggering the Vcesat protection integrated in the IGBT drive circuit, and turning off the IGBT wave to achieve the purpose of protecting the IGBT.

[0003] In the prior art, Vcesat detection protection requires the IGBT to continuously withstand a large impact current, causing the Vce voltage of the IGBT to rise rapidly before the protection can be quickly triggered. This has certain limitations. Vcesat detection protection requires the use of a dedicated driver optocoupler with Vcesat protection or other dedicated chips. Each IGBT or each bridge arm requires one circuit, which has a high cost. Summary of the invention

[0004] In view of the deficiencies in the prior art, the present invention provides an overcurrent and short-circuit protection method for an inverter to solve the problems raised in the above background technology.

[0005] To achieve the above object, the present invention provides the following technical solution: an overcurrent and short-circuit protection method for an inverter, comprising the following steps:

[0006] S1, inverter and shunt meter connection: inverter DC input DC_+ and DC-, cross-connect bus filter capacitor C80, shunt meter RD6 connected to DC_+ and IGBT DC+ input terminal, shunt meter sampling converted voltage signals DC_+ and DC_1+ sent to the current mirror circuit, DC_+ connected to Zener diode D29, D29 connected to R116 to DC-, D29 parallel filter capacitors C95 and C89, together forming an auxiliary source;

[0007] S2, the sampling information is sent to the current mirror and signal driving circuit: the DC_+ and DC_1+ sampled in the inverter main circuit are sent to the current mirror overcurrent detection and signal driving circuit. The current mirror circuit is composed of a dual triode Q2 and connected E-pole resistors R1, RD6 and C-pole resistors R2 and R3;

[0008] S3, calculate and select the appropriate shunt meter: RD6 selects the appropriate shunt meter according to the operating current and power, and calculates and selects R1 and R2;

[0009] S4. The overcurrent signal is isolated into Vce through an optocoupler: When the inverter output is short-circuited due to overcurrent, the overcurrent signal is isolated into Vce through an optocoupler.

[0010] To further optimize the technical solution, in step S1, the inverter is a three-phase full-bridge inverter, the BC phases of the bridge arm outputs are each connected to an inverter output sampling resistor to generate an auxiliary source, and C95 and C89 are voltage stabilization filter and decoupling capacitors, respectively.

[0011] To further optimize the technical solution, in step S2, Q2 is a dual triode, and the characteristics of the two triodes are exactly the same. DC_+ and DC_1+ are sent to the e-stage of the Q2B triode, and the g-stage and c-stage of Q2B are connected together, and the g-stage is also connected to the g-stage of Q2A. R3 is the C-stage connection resistor, C2 is its filter capacitor, R1 is the Q2A e-stage connection resistor, R2 is the Q2A c-stage connection resistor, C1 is its filter capacitor, and the c-stage of Q2A is simultaneously connected to the g-stage of the triode Q3, the e-stage of Q3 is connected to D1 as a voltage-stabilizing diode, and the c-stage of Q3 is connected to the resistor R4, which is connected in series with the primary side of the optocoupler U1, and then connected to the voltage positive pole DC_+ of the auxiliary source, and R5 and C3 are a voltage divider circuit.

[0012] To further optimize the technical solution, the g and c levels of Q2B are short-circuited, and its Vge is a diode voltage drop of 0.7V. The voltage drop of the bus current on the shunt meter is equal to the voltage drop on the load resistor, and a suitable resistor is selected.

[0013] To further optimize the technical solution, D29 is an 18V voltage regulator tube, and R3 is 47k.

[0014] To further optimize the technical solution, in step S3, the circuit can set the current protection point of the IGBT, and select 2-3 times of the IGBT protection current Ic.

[0015] To further optimize the technical solution, the Vce signal in step S4 is synthesized with other protection function circuits, such as the inverter current comparison protection signal designed to detect the inverter output current sampling, and is shaped to form a DSP_OC signal, which is sent to the interrupt protection signal of the DSP or MCU unit. R11 and C11 filter the OC signal, which is then compared with the reference value, output in the same direction through the operational amplifier U2, and then ORed with Vce, filtered by R16 and C14, and sent to the interrupt receiving port of the DSP or MCU.

[0016] To further optimize the technical solution, in step S4 corresponding to the three-phase inverter, since the detection point is at the DC input end of the three-phase bridge arm, any two phases of the output of the three-phase inverter are short-circuited, and the three phases are short-circuited. Beneficial Effects

[0017] Compared with the prior art, the present invention provides an overcurrent and short-circuit protection method for an inverter, which has the following beneficial effects:

[0018] 1. The overcurrent and short-circuit protection method of the inverter uses a shunt meter to sample the inverter DC bus current, combines a current mirror circuit, amplifies it through a transistor, drives an optocoupler, triggers a protection signal, and the auxiliary source is realized by a resistor regulator voltage division, which is simple and practical.

[0019] 2. The overcurrent and short-circuit protection method of the inverter can be calculated and set through the inverter overcurrent and short-circuit protection values. The larger the short-circuit point current, the larger the primary drive current of the optocoupler and the longer the protection time.

[0020] 3. The overcurrent and short-circuit protection method of the inverter can protect the six IGBTs of the entire inverter through one circuit. The circuit is simple and can be realized with low-cost components. It is economical and can be combined with the output circuit detection limit overcurrent protection of other inverters and the CBC current limiting protection circuit to form a comprehensive inverter protection circuit. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 A schematic diagram of a flow chart of an inverter overcurrent and short-circuit protection method proposed by the present invention;

[0022] Figure 2 The main circuit diagram of the inverter of the overcurrent and short-circuit protection method of the inverter proposed by the present invention;

[0023] Figure 3 A current mirror circuit diagram of an inverter overcurrent and short-circuit protection method proposed by the present invention;

[0024] Figure 4 This is a circuit diagram of the Vce signal and other protection functions of an inverter overcurrent and short-circuit protection method proposed by the present invention. DETAILED DESCRIPTION

[0025] The following will be combined with the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0026] Please refer to Figure 1-Figure 3 The present invention discloses an overcurrent and short circuit protection method for an inverter, comprising the following steps:

[0027] S1, inverter connected with shunt meter: inverter DC input DC_+ and DC-, cross-connect bus filter capacitor C80, shunt meter RD6 connected to DC_+ and IGBT DC+ input, shunt meter sampling converted voltage signals DC_+ and DC_1+ sent to the current mirror circuit, the inverter is a three-phase full-bridge inverter, bridge arm output BC phase each connected to the inverter output sampling resistor, D29 is an 18V voltage regulator, R116 is a high resistance resistor, after the two voltage division, generate 18V auxiliary source, C95 and C89 are voltage regulator filter and decoupling capacitors respectively;

[0028] S2, the sampling information is sent to the current mirror and signal driving circuit: the DC_+ and DC_1+ sampled in the inverter main circuit are sent to the current mirror overcurrent detection and signal driving circuit, Q2 is a dual triode, the characteristics of the two triodes are exactly the same, DC_+ and DC_1+ are sent to the e-stage of the Q2B triode, the g-stage and c-stage of Q2B are connected together, and the g-stage is also connected to the g-stage of Q2A, R3 is the C-stage connection resistor, C2 is its filter capacitor, R1 is the Q2A e-stage connection resistor, and R2 is the Q2A The c-level is connected to the resistor, C1 is its filter capacitor, the c-level of Q2A is also connected to the g-level of the transistor Q3, the e-level of Q3 is connected to D1 as a voltage-stabilizing diode, the c-level of Q3 is connected to the resistor R4, and is connected in series with the primary side of the optocoupler U1, and then connected to the positive voltage DC_+ of the auxiliary source, R5 and C3 are protection circuits to prevent the optocoupler from bearing a large reverse voltage when it is reversed, the secondary side signal Vce of U1 is the protection signal, the g-level and c-level of Q2B are short-circuited, and its Vge is a diode voltage drop of 0.7V. The voltage drop of the bus current on the shunt meter is equal to the voltage drop on the load resistor. Select a suitable resistor,

[0029] Vdc=RD6*Idc,Ic1=Vrc1 / Rc1

[0030] Ic1 is approximately equal to Ie1, Re=Ie1*Re

[0031] When Vr2 is greater than 5.1+0.7=5.8V, the ge level of transistor Q3 is forward biased.

[0032] At this time, Ve1=5.8V, the forward bias critical point of the ge level can be calculated:

[0033] Ie1=5.8 / R2, 5.8 / R2*Rl=RD6*Idc, it can be concluded that:

[0034] R1 / R2=RD6*Idc / 5.8

[0035] D29 is an 18V voltage regulator, R3 is 47k, then Ie2=(18-0.7) / 47=0.38mA, R1= RD6*Idc / 0.38, calculate R2 in the same way;

[0036] S3, calculate and select the appropriate shunt meter: RD6 selects the appropriate shunt meter according to the working current and power. In this example, 2m ohms is selected. According to the short-time current that the IGBT bears and the actual inverter output short-circuit current, the appropriate protection value is selected, and R1 and R2 can be calculated and selected. This circuit can set the current protection point of the IGBT by itself, and select 2-3 times of the IGBT protection current Ic. Compared with the Vcesat protection of the IGBT, the IGBT current needs to be at least 4 times Ic before the IGBT enters the desaturation state;

[0037] S4, overcurrent signal is isolated into Vce through optocoupler: When the inverter output overcurrent short circuit occurs, Idc current rises rapidly, Vr2 voltage rises, and when it exceeds 5.8V, Q3's ge level is forward biased, Q is turned on, and the optocoupler U1 is driven. The overcurrent signal is isolated into Vce through optocoupler. The Vce signal is integrated with other protection function circuits, such as the inverter current comparison protection signal designed for detecting the inverter output current sampling, etc., and after shaping processing, it forms DSP_OC signal, which is sent to the interrupt protection signal of the control DSP or MCU unit. , for rapid shutdown protection, R11 and C11 are for OC signal filtering, and then compared with the reference value, through the operational amplifier U2, the same direction output, and then with Vce phase OR, after R16 and C14 filtering, sent to the DSP or MCU interrupt receiving port, so as to quickly perform protection, corresponding to the three-phase inverter, since the detection point is at the three-phase bridge arm DC input end, the output of the three-phase inverter is short-circuited between any two phases, the three-phase short-circuited, or the short-circuited of other bridge arms to the bus, as long as there is a large current flowing through the DC bridge arm input end, it can be well detected and protected.

[0038] The beneficial effects of the present invention are as follows: the inverter direct current inputs DC_+ and DC-, the bus filter capacitor C80 is connected across, the shunt meter RD6 is connected to the DC_+ and IGBT DC+ input terminals, the voltage signals DC_+ and DC_1+ converted after the shunt meter samples are sent to the current mirror circuit, the inverter is a three-phase full-bridge inverter, the bridge arm outputs BC phases are respectively connected to the inverter output sampling resistor, D29 is an 18V voltage regulator tube, R116 is a high resistance resistor, and after the two are divided, an 18V auxiliary source is generated, C95 and C89 are voltage regulator filter and decoupling capacitors respectively, the DC_+ and DC_1+ sampled in the inverter main circuit are sent to the current mirror overcurrent detection and signal drive circuit, DC_+ and DC_1+ are sent to the e-level of the Q2B transistor, the g-level and c-level of Q2B are short-circuited, and its Vge is a diode voltage drop of 0.7V, the bus The voltage drop of line current on the shunt meter is equal to the voltage drop on the load resistor. Select the appropriate resistor, RD6, according to the working current and power, select the appropriate shunt meter, according to the short-time current borne by the IGBT and the actual inverter output short-circuit current, select the appropriate protection value, the overcurrent and short-circuit protection values ​​can be calculated and set. The larger the short-circuit point current, the larger the primary drive current of the optocoupler and the shorter the protection delay. This solution has good adaptability to overcurrent and short-circuit protection, and can be used for short-circuiting ports with small overcurrent and short-circuit impedance, or for short-circuiting ports with large short-circuit impedance. One circuit can protect the entire inverter. The circuit is simple and can be implemented with low-cost components, which is economical.

[0039] Although embodiments of the present invention have been shown and described, it will be appreciated by those skilled in the art that various changes, modifications, substitutions and variations may be made to the embodiments without departing from the principles and spirit of the present invention, and that the scope of the present invention is defined by the appended claims and their equivalents.

Claims

1. An overcurrent and short-circuit protection method for an inverter, characterized in that: The following steps are involved: S1, the inverter is connected with the shunt meter: the inverter DC input DC_+ and DC-, the bus filter capacitor C80 is connected across, the shunt meter RD6 is connected to the DC_+ and IGBT DC+ input terminals, the voltage signals DC_+ and DC_1+ converted after the shunt meter is sampled are sent to the current mirror circuit, DC_+ is connected to the voltage stabilizing diode D29, D29 is connected to R116 to DC-, D29 is connected in parallel with the filter capacitors C95 and C89, together forming an auxiliary source, in the step S1, the inverter is a three-phase full-bridge inverter, the bridge arm output BC phases are each connected to the inverter output sampling resistor to generate an auxiliary source, C95 and C89 are the voltage stabilizing filter and decoupling capacitors respectively; S2, the sampling information is sent to the current mirror and signal driving circuit: the DC_+ and DC_1+ sampled in the inverter main circuit are sent to the current mirror overcurrent detection and signal driving circuit, the current mirror circuit is composed of a dual triode Q2 and connected E-pole resistors R1, RD6 and C-pole resistors R2 and R3. In the step S2, Q2 is a dual triode, and the characteristics of the two triodes are exactly the same. DC_+ and DC_1+ are sent to the e-stage of the Q2B triode, and the g-stage and c-stage of Q2B are connected together. At the same time, the g-stage is also connected to the g-stage of Q2A. R3 is the C-stage connection resistor, C2 is its filter capacitor, R1 is the Q2A e-stage connection resistor, and R2 is the Q2A filter capacitor. The c-stage is connected to the resistor, C1 is its filter capacitor, the c-stage of Q2A is also connected to the g-stage of the transistor Q3, the e-stage of Q3 is connected to D1 as a voltage-stabilizing diode, the c-stage of Q3 is connected to the resistor R4, and is connected in series with the primary side of the optocoupler U1, and then connected to the positive voltage DC_+ of the auxiliary source, R5 and C3 are a voltage divider circuit; S3, calculate and select a suitable shunt meter: RD6 selects a suitable shunt meter according to the operating current and power, calculates and selects R1 and R2. In step S3, the circuit sets the current protection point of the IGBT and selects 2-3 times of the IGBT protection current Ic; S4, the overcurrent signal is isolated into Vce through an optocoupler: When the inverter outputs an overcurrent short circuit, the overcurrent signal is isolated into Vce through an optocoupler. In step S4, the Vce signal is synthesized with the protection signals of other protection function circuits and shaped to form a DSP_OC signal, which is sent to the interrupt protection signal of the DSP or MCU unit. R11 and C11 filter the OC signal, which is then compared with the reference value and output in the same direction through the operational amplifier U2, and then ORed with Vce, filtered by R16 and C14, and sent to the interrupt receiving port of the DSP or MCU.

2. The overcurrent and short-circuit protection method for an inverter according to claim 1, characterized in that: The g and c stages of Q2B are short-circuited, and its Vge is a diode voltage drop of 0.7V. The voltage drop of the bus current on the shunt meter is equal to the voltage drop on the load resistor, so a suitable resistor is selected.

3. The overcurrent and short-circuit protection method for an inverter according to claim 1, characterized in that: The D29 is an 18V voltage regulator tube, and R3 is 47k.

4. The overcurrent and short-circuit protection method for an inverter according to claim 1, characterized in that: In step S4, for the three-phase inverter, since the detection point is at the DC input end of the three-phase bridge arm, any two phases of the output of the three-phase inverter are short-circuited, and the three phases are short-circuited.

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