Protection circuit and control method for output current during parallel operation of bidirectional inverters

Abstract

The invention discloses a protection circuit and a control method for output current during parallel operation of bidirectional inverters, and belongs to the technical field of power electronics. The circuit is applied to the bidirectional inverter, an inversion full-bridge circuit is arranged in the bidirectional inverter, and the protection circuit comprises an inversion current sampling circuit, a double-limit comparator circuit, a DSP control unit and an inversion output module. The inverter full-bridge circuit is respectively connected with the inverter output module and the inverter current sampling circuit, and the inverter current sampling circuit is respectively connected with the double-limit comparator circuit and the DSP control unit. And the inversion output module, the double-limit comparator circuit and the inversion current sampling circuit are respectively connected with the DSP control unit. The circuit can realize protection of output current when a load is disconnected under the condition of parallel operation of inverters.

Description

Technical Field

[0001] This application belongs to the field of power electronics technology, and particularly relates to a protection circuit and control method for the output current when bidirectional inverters are paralleled. Background Art

[0002] Existing inverter overcurrent protection generally achieves the effect of output overcurrent protection through inverter current protection, bus current protection, etc. Traditional inverter current overcurrent protection usually uses inverter current sampling to judge that when the current reaches the current limit value, the software closes the inverter drive, thereby turning off the inverter drive to achieve the effect of software protection. However, the above methods have disadvantages such as slow action time and poor accuracy.

[0003] When two or more inverters are paralleled, when the hot machine is turned on and off or the mode is switched, due to the presence of components such as relays at the output end, the relays between the inverters cannot achieve ideal simultaneous disconnection and closure, which may cause the risk that one of the inverters bears the large current impact when the load is disconnected in the case of inverter parallel connection and is damaged. Summary of the Invention

[0004] This application aims to solve at least one of the technical problems existing in the prior art. For this purpose, this application proposes a protection circuit and control method for the output current when bidirectional inverters are paralleled, which can achieve the protection of the output current when the load is disconnected in the case of inverter parallel connection.

[0005] In a first aspect, this application provides a protection circuit for the output current when bidirectional inverters are paralleled, which is applied to a bidirectional inverter. An inverter full-bridge circuit is provided in the bidirectional inverter. The protection circuit includes an inverter current sampling circuit, a dual-limit comparator circuit, a DSP control unit, and an inverter output module;

[0006] The inverter full-bridge circuit is respectively connected to the inverter output module and the inverter current sampling circuit. The inverter current sampling circuit is respectively connected to the dual-limit comparator circuit and the DSP control unit. The inverter output module, the dual-limit comparator circuit, and the inverter current sampling circuit are respectively connected to the DSP control unit;

[0007] The inverter full-bridge circuit is used to convert the DC BUS voltage into a first AC voltage;

[0008] The inverter current sampling circuit is used to sample the inverter current corresponding to the first AC voltage, generate a sampling signal and a current detection signal corresponding to the sampling signal;

[0009] The dual-limit comparator circuit is used to compare the sampling signal with a set value and generate a comparison signal;

[0010] The DSP control unit is configured to output a first control signal and a second control signal to the inverter output module according to the current detection signal and the comparison signal.

[0011] The inverter output module is configured to perform current limiting control on the first AC voltage according to the first control signal, and control the switches of the inverter drive of the full-bridge inverter circuit according to the second control signal.

[0012] According to an embodiment of the present application, the inverter current sampling circuit includes a first-stage sampling circuit and a second-stage sampling circuit connected in sequence.

[0013] The first-stage sampling circuit is configured to amplify or attenuate the inverter current to obtain a current signal corresponding to the sampling range voltage of the DSP control unit.

[0014] The second-stage sampling circuit is configured to sample the current signal and output a sampling signal and a current detection signal.

[0015] According to an embodiment of the present application, the first-stage sampling circuit includes a first operational amplifier module, a first voltage-dividing resistor, a second voltage-dividing resistor, a third voltage-dividing resistor, a fourth voltage-dividing resistor, a filter capacitor, a first RC filter module, a first double diode, and a second double diode.

[0016] The inverter current is input to the inverting input terminal of the first operational amplifier module through the first voltage-dividing resistor.

[0017] The signal output terminal of the first operational amplifier module outputs the positive voltage of the current signal through the second voltage-dividing resistor.

[0018] The non-inverting input terminal of the first operational amplifier module is grounded through the third voltage-dividing resistor.

[0019] The signal output terminal of the first operational amplifier module outputs the negative voltage of the current signal through the fourth voltage-dividing resistor and the filter capacitor.

[0020] The inverting input terminal of the first operational amplifier module is connected to the signal output terminal of the first operational amplifier module through the first RC filter module.

[0021] The inverting input terminal of the first operational amplifier module is connected to the common connection of the first double diode D2, and the non-inverting input terminal of the first operational amplifier module is connected to the common connection terminal of the second double diode D3.

[0022] According to an embodiment of the present application, the second-stage sampling circuit includes a second operational amplifier module, a fifth voltage-dividing resistor, a sixth voltage-dividing resistor, a second RC filter module, a third RC filter module, a fourth RC filter module, and a third double diode.

[0023] The positive voltage of the current signal is input to the positive input terminal of the second operational amplifier module through the fifth voltage-dividing resistor;

[0024] The negative voltage of the current signal is input to the negative input terminal of the second operational amplifier module through the sixth voltage-dividing resistor;

[0025] The positive input terminal of the second operational amplifier module is connected to the +1.65V voltage through the second RC filtering module;

[0026] The negative input terminal of the second operational amplifier module is connected to the signal output terminal of the second operational amplifier module through the third RC filtering module;

[0027] The signal output terminal of the second operational amplifier module is connected to one end of the fourth RC filtering module, and the other end of the fourth RC filtering module outputs a current detection signal;

[0028] The other end of the fourth RC filtering module is connected to the common connection terminal of the third double diode.

[0029] According to an embodiment of the present application, in the dual-limit comparator circuit, the sampling signal is input to the negative output terminal of the first comparator through the resistor R20, and the negative output terminal of the first comparator is grounded through the capacitor C9;

[0030] The signal output terminal of the first comparator is connected to one end of the resistor R19, and the other end of the resistor R19 outputs a comparison signal;

[0031] The sampling signal is input to the positive output terminal of the second comparator through the resistor R36, the positive output terminal of the second comparator is grounded through the capacitor C11, the positive output terminal of the second comparator is connected to the other end of the resistor R19 through the resistor R25, and the other end of the resistor R19 is connected to the positive input terminal of the first comparator through the capacitor R22;

[0032] The positive input terminal of the first comparator is grounded through the parallel-connected R24 and capacitor C10, and the positive input terminal of the first comparator is also connected to the +12V voltage through the resistors R21 and R23;

[0033] The positive power supply terminal of the second comparator is connected to the +12V voltage and grounded through the capacitor C15;

[0034] The negative power supply terminal of the second comparator is connected to the -12V voltage and grounded through the capacitor C12;

[0035] The +3.3VA voltage is connected to the signal output terminal of the first comparator, the signal output terminal of the second comparator, and the capacitor C13 is grounded through the resistor R18;

[0036] The inverting input terminal of the second comparator is grounded through a parallel combination of a capacitor C14 and a resistor R27;

[0037] The other end of the resistor R19 is grounded through a parallel combination of a capacitor C8 and an anti-connected diode D4.

[0038] According to an embodiment of the present application, the inverter output module includes an inverter output circuit and an SCR unit circuit, and the DSP control unit is connected to the SCR unit circuit;

[0039] The inverter output circuit is used to correct and compensate the first AC voltage and output a second AC voltage;

[0040] The SCR unit circuit is used to perform current limiting control on the second AC voltage according to the control signal.

[0041] According to an embodiment of the present application, the inverter output circuit includes a relay RY1, a relay RY2, a triode Q4, a triode Q5, and a current transformer CT;

[0042] The triode Q5 is connected to the coil of the relay RY1, the triode Q4 is connected to the coil of the relay RY2, and the common terminals of the relay RY1 and the relay RY2 are respectively connected to the input end and the output of the primary winding of the current transformer CT;

[0043] The common terminals of the relay RY1 and the relay RY2 are used to receive the first AC voltage, and the secondary winding output terminal of the current transformer CT.

[0044] According to an embodiment of the present application, the SCR unit circuit 242 includes a thyristor Q1, a thyristor Q2, a switching tube Q3, and a transformer TX1;

[0045] The pin 1 of the transformer TX1 receives the input signal HFPW+ through a resistor R11, the gate of the switching tube Q3 is used to receive the control signal, the drain of the switching tube Q3 is connected to the pin 4 of the transformer TX1, and the source of the switching tube Q3 is grounded and connected to the gate of the switching tube Q3 through a resistor R13;

[0046] The pin 5 of the transformer TX1 is connected to the control electrode of the thyristor through a diode D3 and a parallel combination of a resistor R10 and a resistor R12;

[0047] The cathode of the diode D3 is connected to the pin 6 of the transformer TX1 through a capacitor C8;

[0048] The pin 6 of the transformer TX1 is connected to the anode of the thyristor Q1 and the cathode of the thyristor Q2, and is used to output the line voltage of the second AC voltage;

[0049] The 6th pin of the transformer TX1 is connected to the control electrode of the thyristor Q1 through the diode D3 and the parallel-connected resistors R10 and R12;

[0050] The 6th pin of the transformer TX1 is connected to the gate of the thyristor Q2 through the parallel-connected capacitor C9 and resistor R9;

[0051] The 6th pin of the transformer TX1 is connected to the 7th pin of the transformer TX1 through the resistor R8 and the capacitor C7;

[0052] The 7th pin of the transformer TX1 is connected to the cathode of the thyristor Q1 and the anode of the thyristor Q2, and is used to receive the signal O / P.L_SCR;

[0053] The 8th pin of the transformer TX1 is connected to the control electrode of the thyristor Q1 through the diode D1 and the parallel-connected resistors R5 and R6;

[0054] The cathode of the diode D1 is connected to the 7th pin of the transformer TX1 through the capacitor C5, and the 7th pin of the transformer TX1 is connected to the control electrode of the thyristor Q1 through the parallel-connected capacitor C6 and resistor R7.

[0055] In a first aspect, the present application provides a control method for a protection circuit of an output current during parallel operation of bidirectional inverters, which is applied to a protection circuit of an output current during parallel operation of bidirectional inverters as in the first aspect. The method includes:

[0056] Converting the DC BUS voltage into a first AC voltage through an inverter full-bridge circuit;

[0057] Sampling the inverter current corresponding to the first AC voltage through an inverter current sampling circuit to generate a sampling signal and a current detection signal corresponding to the sampling signal;

[0058] Comparing the sampling signal with a set value through a dual-limit comparator circuit to generate a comparison signal;

[0059] Outputting a first control signal and a second control signal to the inverter output module by a DSP control unit according to the current detection signal and the comparison signal;

[0060] An inverter output module is used to perform current limiting control on the first AC voltage according to the first control signal, and control the switches of the inverter drive of the inverter full-bridge circuit according to the second control signal.

[0061] According to an embodiment of the present application, sampling the inverter current corresponding to the first AC voltage by the inverter current sampling circuit to generate a sampling signal and a current detection signal corresponding to the sampling signal includes:

[0062] Gain or attenuate the inverter current through a first-stage sampling circuit to obtain a current signal corresponding to the sampling range voltage of the DSP control unit;

[0063] Sample the current signal through a second-stage sampling circuit and output a sampling signal and a current detection signal.

[0064] Additional aspects and advantages of the present application will be given in part in the following description, become apparent in part from the following description, or be learned through the practice of the present application.

[0065] A protection circuit and control method for the output current during parallel operation of bidirectional inverters provided by the present application have the following beneficial effects compared with the prior art:

[0066] (1) Based on the overcurrent protection at the software level of the inverter current sampling circuit, a dual-limit comparator circuit is added after the inverter current sampling circuit for hardware current limiting, achieving dual protection of software and hardware. The dual-limit comparator circuit compares the level of the sampling signal with a set value. Once the comparison value is reached, the TZ signal immediately flips to implement overcurrent protection. The inverter drive is forcibly turned off inside the DSP control unit. Through the collaborative design of hardware and software, the protection circuit can effectively avoid misoperation, improve the reliability and stability of the system, and can solve the problem that the electronic components of the inverter may be damaged due to the slow response of the traditional protection circuit during parallel operation of the inverter. It can protect the output current when the load is disconnected during parallel operation of the inverter and can maintain stable operation in a complex power grid environment.

[0067] (2) A thyristor control module circuit, i.e., an SCR unit circuit, is added to the output end of the inverter. By judging the output of the inverter and utilizing the characteristics of fast switching speed, high current and voltage withstand capacity of the thyristor, the thyristor is turned on before the output relay is turned on to withstand the impact of the instantaneous large current when the relay receives it, further improving the overcurrent protection system of the inverter. It better prevents more losses caused by output overcurrent of the inverter from the source. Compared with the traditional overcurrent protection circuit, the combination of the SCR unit circuit and the dual-limit comparator circuit can more comprehensively and accurately complete the inverter overcurrent protection quickly. The SCR unit circuit provides overcurrent protection for the devices at the output end of the inverter according to the actual application situation of inverter parallel operation. Moreover, the SCR has a low cost, is suitable for large-scale applications, the control circuit is simple, can be controlled by a simple trigger signal, and has good stability and reliability within a wide temperature range. Brief Description of the Drawings

[0068] The above and / or additional aspects and advantages of the present application will become apparent and be readily understood from the following description of embodiments in conjunction with the accompanying drawings, where:

[0069] Figure 1 is a schematic structural diagram of a protection circuit for the output current during parallel operation of bidirectional inverters provided by an embodiment of the present application;

[0070] Figure 2 is a schematic structural diagram of a full-bridge inverter circuit provided by an embodiment of the present application;

[0071] Figure 3 is a schematic structural diagram of a DSP control unit provided by an embodiment of the present application;

[0072] Figure 4 is a schematic structural diagram of a first-stage sampling circuit provided by an embodiment of the present application;

[0073] Figure 5 is a schematic structural diagram of a second-stage sampling circuit provided by an embodiment of the present application;

[0074] Figure 6 is a schematic structural diagram of a dual-limit comparator circuit provided by an embodiment of the present application;

[0075] Figure 7 is a schematic structural diagram of an inverter output module provided by an embodiment of the present application;

[0076] Figure 8 is a schematic structural diagram of an SCR unit circuit provided by an embodiment of the present application;

[0077] Figure 9 is a schematic flowchart of a control method for a protection circuit for the output current during parallel operation of bidirectional inverters provided by an embodiment of the present application.

[0078] Reference numerals:

[0079] Bidirectional inverter 100; full-bridge inverter circuit 110; protection circuit 200; inverter current sampling circuit 210; dual-limit comparator circuit 220; DSP control unit 230; inverter output module 240; inverter output circuit 241; SCR unit circuit 242. Detailed implementation manners

[0080] Next, the technical solutions in the embodiments of the present application will be clearly described in conjunction with the accompanying drawings in the embodiments of the present application. Obviously, the described embodiments are some, but not all, of the embodiments of the present application. All other embodiments obtained by those of ordinary skill in the art based on the embodiments in the present application belong to the scope of protection of the present application.

[0081] The terms "first", "second", etc. in the description and claims of this application are used to distinguish similar objects, rather than to describe a specific order or sequence. It should be understood that the data used in this way can be interchanged under appropriate circumstances, so that the embodiments of this application can be implemented in an order other than those illustrated or described herein, and the objects distinguished by "first", "second", etc. are usually of the same type, and the number of objects is not limited. For example, the first object can be one or more. In addition, "and / or" in the description and claims means at least one of the connected objects, and the character " / " generally indicates an "or" relationship between the associated objects before and after.

[0082] The following will combine the accompanying drawings and, through specific embodiments and their application scenarios, elaborate in detail on the protection circuit for the output current during parallel operation of bidirectional inverters and the control method for the protection circuit for the output current during parallel operation of bidirectional inverters provided by the embodiments of this application.

[0083] As Figure 1 shown, the protection circuit for the output current during parallel operation of bidirectional inverters is applied to the bidirectional inverter 100. An inverter full-bridge circuit 110 is provided in the bidirectional inverter 100. The protection circuit 200 includes an inverter current sampling circuit 210, a dual-limit comparator circuit 220, a DSP control unit 230, and an inverter output module 240;

[0084] The inverter full-bridge circuit 110 is respectively connected to the inverter output module 240 and the inverter current sampling circuit 210. The inverter current sampling circuit 210 is respectively connected to the dual-limit comparator circuit 220 and the DSP control unit 230. The inverter output module 240, the dual-limit comparator circuit 220, and the inverter current sampling circuit 210 are respectively connected to the DSP control unit 230;

[0085] The inverter full-bridge circuit 110 is used to convert the DC BUS voltage into a first AC voltage;

[0086] The inverter current sampling circuit 210 is used to sample the inverter current corresponding to the first AC voltage to generate a sampling signal and a current detection signal corresponding to the sampling signal;

[0087] The dual-limit comparator circuit 220 is used to compare the sampling signal with a set value to generate a comparison signal;

[0088] The DSP control unit 230 is used to output a control signal to the inverter output module according to the current detection signal and the comparison signal;

[0089] The inverter output module 240 is used to perform current limiting control on the first AC voltage according to the control signal, and to control the switches of the inverter drive of the full-bridge inverter circuit.

[0090] As Figure 2 shown, the inverter drive of the full-bridge inverter circuit 110 includes switching transistors QNU1, QLU1, QND1, and QLD1. The conduction and cutoff of the switching transistors are controlled by control signals S1, S2, S3, and S4 applied to the gates. The emitter (E) of switching transistor QLU1 and the collector (C) of QLD1 are connected to the interface for receiving signal INV-LMID, and are connected to the interface for receiving the line voltage (signal INV.L) of the first AC voltage through inductor L1. The E of switching transistor QNU1 and the C of switching transistor QND1 are connected to the interface for outputting the neutral line voltage (signal INV-N) of the first AC voltage.

[0091] As Figure 3 shown, the chip model of the DSP chip in the DSP control unit 230 is TMS320F 28062. The 19th pin of the DSP chip is used to receive the current detection signal (signal INVL.I), and the 87th pin of the DSP chip outputs control signal S1, the 86th pin outputs control signal S3, the 84th pin outputs control signal S1, and the 83rd pin outputs control signal S2.

[0092] Among them, the bidirectional inverter 100 can convert direct current and alternating current mutually, and is used in scenarios such as energy storage systems and uninterruptible power supplies (UPS), supporting bidirectional energy flow.

[0093] The full-bridge inverter circuit 110 of the bidirectional inverter 100 is a bidirectional inverter topology structure. A bridge circuit is formed by switching transistors QNU1, QLU1, QND1, and QLD1 to convert direct current into alternating current.

[0094] The inverter current sampling circuit 210 monitors the inverter output current in real time through a current transformer or a sampling resistor, and can provide accurate current signals for control and protection.

[0095] The dual-limit comparator circuit 220 is used to compare the sampling signal (signal INV.I.AO) with the set values of the upper and lower limits, and generate a comparison signal corresponding to the comparison result to trigger a protection action.

[0096] The DSP control unit 230 is built-in with a digital signal processor (DSP), which is used to process the current detection signal (signal INVL.I) in real time, generate control signals, trigger a protection mechanism in case of an abnormality, and adjust the output of the inverter.

[0097] The inverter output module 240 performs current limiting control and drive control on the output of the full-bridge inverter circuit 110, judges overcurrent and implements protection at the software level to ensure that the output current is within a safe range.

[0098] Among them, the sampling signal (signal INV.I.AO) is applicable to occasions that require fast response and precise control, such as real-time current monitoring and fast protection mechanisms; the current detection signal (signal INVL.I) is applicable to occasions that require stable signals, such as per-wave current limiting and overcurrent protection mechanisms, to ensure that the current can operate stably under various working conditions.

[0099] In actual execution, the full-bridge inverter circuit 110 converts the DC BUS voltage into an AC voltage by controlling the switching transistors QNU1, QLU1, QND1, and QLD1 through pulse width modulation (PWM). Its working principle is the on-off of the switching devices, thereby realizing the conversion from DC to AC, with high efficiency and stability.

[0100] The inverter current sampling circuit 210 uses a current transformer or a sampling resistor to sample the inverter output current in real time. The current transformer can effectively isolate the high-voltage and low-voltage parts, and at the same time provide an accurate current detection signal (signal INVL.I) and sampling signal (signal INV.I.AO) of the inverter current, which are transmitted to the dual-limit comparator circuit 220 and the DSP control unit 230.

[0101] The dual-limit comparator circuit 220 is used for hardware current limiting of the inverter current, realizes monitoring and implementation of protection against overcurrent at the hardware level. By setting a comparison value, the sampling signal (signal INV.I.AO) is compared with the set upper and lower limit values. When the current exceeds the set value and reaches the overcurrent point, the dual-limit voltage comparator circuit 220 outputs an overcurrent signal TZ that flips to a low level and is transmitted to the DSP control unit 230 through the IO port. The generated comparison signal is used to trigger the current limiting or turn-off action of the inverter output module 240. The dual-limit comparator circuit 220 can effectively avoid misoperation and protect the equipment under large current impact, ensuring the accuracy and reliability of the protection mechanism.

[0102] The DSP control unit 230 processes the current detection signal (signal INVL.I) in real time, and the software in the DSP judges whether the current limiting point is reached. If it is reached, the inverter drive is turned off for software current limiting, completing the first loop of overcurrent protection and generating a PWM control signal to adjust the output current of the inverter. In case of abnormal conditions such as overcurrent or short circuit, the DSP triggers the protection mechanism according to the signal of the dual-limit comparator to ensure system safety.

[0103] The inverter output module 240 performs current limiting control on the output of the full-bridge inverter circuit according to the control signal of the DSP control unit 230, and turns off the inverter drive signal when necessary to protect the circuit.

[0104] In the case of overcurrent caused by anomalies such as overload, instantaneous load connection, or short - circuit of switching tubes during the inverter's load - carrying process, the rising speed of the inverter current is extremely fast. The software needs to complete protection through actions such as sampling, counting, judgment, and executing instructions to turn off the inverter drive. There may be a situation where overcurrent protection cannot be achieved in a timely manner, resulting in corresponding power devices withstanding the overcurrent or being directly damaged.

[0105] According to the protection circuit for the output current during the parallel operation of bidirectional inverters provided by the embodiments of the present application, based on the overcurrent protection at the software level of the inverter current sampling circuit, a double - limit comparator circuit is added after the inverter current sampling circuit for hardware current limiting, achieving dual protection of software and hardware. The double - limit comparator circuit compares the level of the sampling signal with the set value. Once the comparison value is reached, the TZ signal immediately flips to implement overcurrent protection, and the DSP control unit internally forcibly turns off the inverter drive. Through the collaborative design of hardware and software, the protection circuit can effectively avoid misoperation, improve the reliability and stability of the system, solve the problem that the traditional protection circuit of the inverter in parallel operation has a slow response, resulting in damage to electronic components, realize the protection of the output current when the load is disconnected during the parallel operation of the inverter, and can maintain stable operation in a complex power grid environment.

[0106] In some embodiments, the inverter current sampling circuit 210 includes a first - stage sampling circuit and a second - stage sampling circuit connected in sequence;

[0107] The first - stage sampling circuit is used to amplify or attenuate the inverter current to obtain a current signal corresponding to the sampling - range voltage of the DSP control unit 230;

[0108] The second - stage sampling circuit is used to sample the current signal and output a sampling signal (signal INV.I.AO) and a current detection signal.

[0109] Among them, the inverter current sampling circuit 210 is a circuit for real - time monitoring of the inverter output current, composed of a sampling resistor, a current transformer, etc., and can provide accurate current signals for control and protection.

[0110] The first - stage sampling circuit amplifies or attenuates the inverter current to make the output current signal match the sampling - range voltage of the DSP control unit.

[0111] The second - stage sampling circuit samples the current signal processed by the first - stage to obtain the final sampling signal (signal INV.I.AO) and the current detection signal (signal INVL.I) corresponding to the sampling signal for subsequent control and protection.

[0112] In actual implementation, the first-stage sampling circuit processes the inverter current through components such as operational amplifiers or resistor networks. For example, a current transformer is used to convert a large current into a small current, and then the voltage amplitude is adjusted through resistor voltage division or an operational amplifier to match the sampling range of the DSP. During the sampling process, components such as current transformers or optocouplers are used to achieve electrical isolation to ensure the safety between the sampling circuit and the main circuit of the inverter.

[0113] The second-stage sampling circuit samples the current signal at a specific moment and holds the amplitude of the signal for subsequent analog-to-digital conversion and processing. For example, sampling is performed during the zero vector period of the PWM signal to avoid sampling current spikes, and the sampled analog signal is converted into a digital signal for further processing and analysis by the DSP control unit.

[0114] In this embodiment, through the processing of the two-stage sampling circuit, for different inverter application scenarios, it can be flexibly adjusted according to different inverter output current ranges and the sampling requirements of the DSP. When abnormal conditions such as overcurrent or short circuit occur in the inverter, the abnormal current can be quickly detected, and the protection mechanism can be triggered to avoid damage to the equipment, accurately measure the inverter current, and at the same time achieve electrical isolation, improve safety. Through accurate current monitoring and a fast protection mechanism, the stability and reliability of the inverter system are improved, ensuring that it can operate safely and stably under various working conditions.

[0115] In some embodiments, as Figure 4 shown, the first-stage sampling circuit includes a first operational amplifier module, first voltage-dividing resistors (R8, R9, R10), second voltage-dividing resistors (R11, R12), third voltage-dividing resistors (R13, R14, R15), fourth voltage-dividing resistors (R16, R17), a filtering capacitor (C6), a first RC filtering module, a first double diode, and a second double diode;

[0116] The inverter current is input to the inverting input terminal (IN-) of the first operational amplifier module through the first voltage-dividing resistors (R8, R9, R10);

[0117] The signal output terminal (OUT) of the first operational amplifier module outputs the positive voltage of the current signal through the second voltage-dividing resistors (R11, R12);

[0118] The non-inverting input terminal (IN+) of the first operational amplifier module is grounded through the third voltage-dividing resistors (R13, R14, R15);

[0119] The signal output terminal (OUT) of the first operational amplifier module outputs the negative voltage of the current signal through the fourth voltage-dividing resistors (R16, R17) and the filtering capacitor (C6);

[0120] The inverting input terminal (IN-) of the first operational amplifier module is connected to the signal output terminal of the first operational amplifier module through the first RC filtering module;

[0121] The inverting input terminal (IN-) of the first operational amplifier module is connected to the common connection of the first double diode D2, and the non-inverting input terminal (IN+) of the first operational amplifier module is connected to the common connection terminal of the second double diode D3.

[0122] As Figure 4 shown, the operational amplifier integrated chip U2 in the first operational amplifier module U2 is IC LIN TI / OP07CDR SOIC-8, which is used to amplify or attenuate the input inverter current signal. The first voltage dividing resistor is the series-connected resistors R8, R9, and R10. The second voltage dividing resistor is the series-connected resistors R11 and R12. The third voltage dividing resistor is the series-connected resistors R16 and R17. The fourth voltage dividing resistor is the series-connected resistors R16 and R17. The signal output terminal (OUT) of the first operational amplifier module is also grounded through the filtering capacitor C6.

[0123] The inverter current is the current value corresponding to the signal INV-N. The positive voltage of the current signal is the signal INVL.I+, and the negative voltage of the current signal is the signal INVL.I-.

[0124] The first voltage dividing resistor (R8, R9, R10), the second voltage dividing resistor (R11, R12), the third voltage dividing resistor (R13, R14, R15), and the fourth voltage dividing resistor (R16, R17) are used to divide the input and output signals and adjust the voltage amplitude of the signals to make them suitable for the processing of subsequent circuits.

[0125] The filtering capacitor C6 is used to filter out the high-frequency interference components in the signal and improve the purity and stability of the signal.

[0126] The first RC filtering module includes the parallel-connected capacitor C2 and resistor R7.

[0127] The non-inverting input terminal is also grounded through the capacitor C7. The cathodes of the first double diode D2 and the second double diode D3 are connected to the +12V_OP voltage, and the anodes of the first double diode D2 and the second double diode D3 are connected to the -12V_OP voltage.

[0128] In actual implementation, the inverter current is initially voltage-adjusted through the first voltage-dividing resistors (R8, R9) to reduce the voltage amplitude input to the operational amplifier module, preventing damage to the operational amplifier module due to excessive voltage. It is input to the inverting input terminal (IN-interface) of the first operational amplifier module. The first operational amplifier module attenuates the input current signal according to the circuit design to make it reach a voltage level matching the sampling range of the DSP control unit. The processed signal outputs the positive voltage of the current signal through the signal output terminal (OUT) of the first operational amplifier module via the second voltage-dividing resistors (R11, R12), and outputs the negative voltage of the current signal through the third voltage-dividing resistors (R16, R17) and the filter capacitor C6. The filter capacitor C6 is used to filter out high-frequency interference components in the signal and improve the stability of the signal.

[0129] In this embodiment, through the cooperation of the first operational amplifier module and the voltage-dividing resistors, the inverter current signal can be accurately amplified or attenuated to match the input requirements of the subsequent circuit, improving the accuracy and reliability of signal processing. The electrical isolation function of the voltage-dividing resistors in the circuit can reduce the interference of the inverter current to the subsequent circuit, and at the same time protect the operational amplifier module and other circuit components from excessive voltage impact. The use of the filter capacitor effectively filters out high-frequency interference components in the signal, improving the purity and stability of the signal, enabling the subsequent circuit to sample and process the signal more accurately. The first-stage sampling circuit can adapt to different ranges of inverter current input. By reasonably selecting the parameters of the voltage-dividing resistors and the operational amplifier module, the gain and input / output impedance of the circuit can be flexibly adjusted to meet the requirements of different application scenarios.

[0130] In some embodiments, as Figure 5 shown, the second-stage sampling circuit includes a second operational amplifier module, a fifth voltage-dividing resistor (R2), a sixth voltage-dividing resistor (R5), a second RC filter module (C1, R1), a third RC filter module (C4, R6), a fourth RC filter module (R3, C3, R4, C5), and a third double diode (D1);

[0131] The positive voltage of the current signal is input to the non-inverting input terminal of the second operational amplifier module through the fifth voltage-dividing resistor (R2);

[0132] The negative voltage of the current signal is input to the inverting input terminal of the second operational amplifier module through the sixth voltage-dividing resistor (R5);

[0133] The non-inverting input terminal of the second operational amplifier module is connected to the +1.65V voltage through the second RC filter module (C1, R1);

[0134] The inverting input terminal of the second operational amplifier module is connected to the signal output terminal of the second operational amplifier module through the third RC filter module (C4, R6);

[0135] The signal output terminal of the second operational amplifier module is connected to one end of the fourth RC filtering module (R3, C3, R4, C5), and the other end of the fourth RC filtering module (R3, C3, R4, C5) outputs a current detection signal (signal INVL.I);

[0136] The other end of the fourth RC filtering module (R3, C3, R4, C5) is connected to the common connection terminal of the third double diode D1.

[0137] The model of the second operational amplifier module UA1 is TL074SMD, and the signal output terminal of the second operational amplifier module is used to output a sampling signal (signal INV.I.AO).

[0138] The fifth voltage-dividing resistor includes resistor R2, the sixth voltage-dividing resistor includes resistor R5, the second RC filtering module is a parallel combination of capacitor C1 and resistor R1, the third RC filtering module is a parallel combination of capacitor C6 and resistor R6, the fourth RC filtering module includes series-connected resistors R3 and R4, R4 is in parallel with series-connected capacitors C3 and C5, the connection terminal of capacitors C3 and C5 is grounded, the cathode of the third double diode D1 is connected to the +3.3VD voltage, and the anode of the third double diode D1 is grounded.

[0139] In the embodiment of the present application, for the protection circuit of the output current during the parallel operation of bidirectional inverters, the overcurrent protection of the inverter is divided into three modes: software monitoring overcurrent protection, hardware overcurrent protection, and the protection of the SCR for the instantaneous large current switching of the output terminal components. These three modes cooperate with each other to make up for the deficiencies of the other two modes in different overcurrent protection situations, forming a perfect overcurrent protection system.

[0140] In the software monitoring overcurrent protection, the software monitoring overcurrent protection includes an inverter current sampling circuit 210 and a DSP control unit 230. The inverter current sampling circuit 210 is divided into two stages, and the current is sampled by means of sampling resistors. The sampling resistors include resistors R1, R2, and R3. The first-stage sampling circuit is a differential operational amplifier composed of U2, and the power supply is +12V and -12V; the second-stage sampling circuit is a differential operational amplifier circuit with a bias formed by U1, and the power supply is +3.3V and +1.65V. The appropriate sampling multiples are set by setting the proportional resistor of the operational amplifier. The output terminal of the inverter current sampling circuit 210 outputs the sampling signal (signal INV.I.AO) The converted voltage value is 1.65V corresponding to the inverter current sampling 0 current, 0V corresponds to the maximum sampling signal in the negative direction, and +3.3V corresponds to the maximum inverter current sampling signal value in the positive direction. When the inverter encounters excessive linear or nonlinear loads or is instantly connected to the inverter system during the discharge process of daily operation, the inverter current will instantly increase or even exceed the tolerance range of the inverter switch tube. The DSP control unit 230 will set two values ​​lower than the instantaneous current value that the inverter switch tube can withstand as current limiting points in the running software. By counting the number of times the inverter current sampling value reaches the current limiting point, when the value of the current detection signal (signal INVL.I) reaches the first current limiting point a certain number of times, the inverter switch tube drive is forced to close a cycle PWM, and then the PWM is re-printed. When the value of the signal INVL.I reaches the second current limiting point a certain number of times, the inverter switch tube drive PWM is forced to close, the machine no longer outputs the inverter drive PWM and the inverter reports an error, thereby achieving the protection of the machine inverter overcurrent, that is, the purpose of protecting the machine output overcurrent.

[0141] In some embodiments, Figure 6 As shown, in the dual-limit comparator circuit 220, the sampling signal (signal INV.I.AO) is input to the inverting output terminal of the first comparator U3D through the resistor R20, and the inverting output terminal of the first comparator U3D is grounded through the capacitor C9;

[0142] The signal output terminal of the first comparator U3D is connected to one end of the resistor R19, and the other end of the resistor R19 outputs a comparison signal (signal ˜INV_I_LMT, TZ signal);

[0143] The sampling signal (signal INV.I.AO) is input to the positive output terminal of the second comparator U3A through the resistor R36, the positive output terminal of the second comparator U3A is grounded through the capacitor C11, the positive output terminal of the second comparator U3A is connected to the other end of the resistor R19 through the resistor R25, and the other end of the resistor R19 is connected to the positive input terminal of the first comparator U3D through the capacitor R22;

[0144] The non-inverting input terminal of the first comparator U3D is grounded through the parallel-connected R24 and capacitor C10, and the non-inverting input terminal of the first comparator U3D is also connected to the +12V voltage through resistor R21 and resistor R23;

[0145] The positive power supply terminal of the second comparator U3A is connected to the +12V voltage and grounded through capacitor C15;

[0146] The negative power supply terminal of the second comparator U3A is connected to the -12V voltage and grounded through capacitor C12;

[0147] The +3.3VA voltage is connected to the signal output terminal of the first comparator U3D, the signal output terminal of the second comparator U3A and capacitor C13 is grounded through resistor R18;

[0148] The inverting input terminal of the second comparator U3A is grounded through the parallel-connected capacitor C14 and resistor R27;

[0149] The other end of resistor R19 is grounded through the parallel-connected capacitor C8 and reverse-connected diode D4.

[0150] Among them, the comparison signal (signal ~ INV_I_LMT) is input to the DSP control unit 230 through pin 48 of the DSP chip.

[0151] In the hardware overcurrent protection, the input terminal of the dual-limit comparator is the output terminal of the inverter current sampling circuit. The power supply of the dual-limit comparator circuit is +12V, -12V, +3.3V. The comparison values of 0V and 3.3V are set through the external resistors R21 and R23. Once the value of the current detection signal (signal INVL.I) reaches one of the two values, the TZ signal at the output terminal of the comparator flips to a low level, triggering the DSP to block the PWM of the inverter drive to achieve the current limiting effect. If the current drops to the overcurrent point limited by the software, the TZ signal is cleared and the inverter drive PWM is restored. If the current never reaches below the overcurrent point, the DSP will continuously block the inverter drive PWM to achieve overcurrent protection.

[0152] The comparison signal output by the dual-limit comparator circuit 220 triggers the blocking of the inverter drive PWM, making up for the slow speed of software current limiting, and completing the dual protection of software and hardware. The thyristor control circuit at the output terminal of the inverter needs to cooperate with the output control circuit of the bidirectional inverter. By detecting the inverter startup signal through the DSP, the thyristor is controlled to turn on before the relay closes or opens, completing the overcurrent protection of the components at the output terminal during the large current switching of the machine.

[0153] In some embodiments, the inverter output module 240 includes an inverter output circuit 241 and an SCR unit circuit 242, and the DSP control unit is connected to the SCR unit circuit 242;

[0154] The inverter output circuit 241 is used to correct and compensate the first AC voltage (signal INV.L) and output a second AC voltage.

[0155] The SCR unit circuit 242 is used to limit the current of the second AC voltage according to the control signal.

[0156] The inverter output circuit 241 is used to convert direct current into alternating current, and correct and compensate the output alternating current to improve the stability and accuracy of the output voltage, adapt to different load and grid conditions, and ensure that the output alternating current meets the requirements.

[0157] The SCR unit circuit 242 is a thyristor (SCR)-based circuit, which is used to limit the current of the output current according to the control signal of the DSP control unit 230, control and protect the output current of the inverter, and prevent overcurrent or short circuit.

[0158] In some embodiments, as Figure 7 shown, the inverter output circuit 241 includes a relay RY1, a relay RY2, a triode Q4, a triode Q5, and a current transformer CT.

[0159] The triode Q5 is connected to the coil (pin 2) of the relay RY1, the triode Q4 is connected to the coil (pins 1 and 2) of the relay RY2. The common terminal (pin 4) of the relay RY1 and the common terminal (pin 4) of the relay RY2 are respectively connected to the primary winding input terminal (pin 1) and the primary winding output (pin 3) of the current transformer CT.

[0160] The common terminals of the relay RY1 and the relay RY2 are used to receive the first AC voltage, and the secondary winding output terminal (pin 4) of the current transformer CT.

[0161] The coil current of the relay is controlled by the triode to realize the on-off control of the inverter output, ensuring that the inverter output can respond and adjust quickly as needed.

[0162] The current transformer CT monitors the inverter output current in real time, provides a signal for overcurrent protection, and ensures that the inverter can take protection measures in time in case of abnormality to avoid equipment damage. When the current transformer CT detects that the output current exceeds the set value, it will trigger a protection mechanism to cut off the inverter output and protect the inverter and other equipment from overcurrent or short circuit damage.

[0163] The control signal (signal O / P_SCR) output by the inverter output circuit 241.

[0164] GRID.N is the negative pole of the power grid, and GRID.L is the positive pole of the power grid, which is used to monitor and control the connection between the inverter and the power grid, ensure the stability and safety of the power grid, and is used in the power grid connection and protection mechanism to ensure the stability and safety of the power grid.

[0165] O / P.N and O / P.L are the output terminals of the inverter, which are used to monitor and control the output of the inverter, and are used in the inverter output control and protection mechanism to ensure that the inverter output is within a safe range.

[0166] The 17th pin of the DSP chip outputs O / P.I+.

[0167] In some embodiments, as Figure 8 shown, the SCR unit circuit 242 includes thyristor Q1, thyristor Q2, switch Q3, and transformer TX1;

[0168] The 1st pin of the transformer TX1 receives the input signal HFPW+ through the resistor R11. The gate (G pole) of the switch Q3 is used to receive the control signal (signal O / P_SCR). The drain (D pole) of the switch Q3 is connected to the 4th pin of the transformer TX1. The source (S pole) of the switch Q3 is grounded and connected to the gate (G pole) of the switch Q3 through the resistor R13;

[0169] The 5th pin of the transformer TX1 is connected to the control pole (G pole) of the thyristor through the diode D3 and the parallel resistors R10 and R12;

[0170] The cathode of the diode D3 is connected to the 6th pin of the transformer TX1 through the capacitor C8;

[0171] The 6th pin of the transformer TX1 is connected to the anode (A pole) of the thyristor Q1 and the cathode (K pole) of the thyristor Q2, and is used to output the line voltage (signal O / P.L) of the second AC voltage;

[0172] The 6th pin of the transformer TX1 is connected to the control pole (G pole) of the thyristor Q1 through the diode D3, the parallel resistors R10 and R12;

[0173] The 6th pin of the transformer TX1 is connected to the gate (G pole) of the thyristor Q2 through the parallel capacitor C9 and resistor R9;

[0174] The 6th pin of the transformer TX1 is connected to the 7th pin of the transformer TX1 through the resistor R8 and the capacitor C7;

[0175] Pin 7 of the transformer TX1 is connected to the cathode (K pole) of the thyristor Q1 and the anode (A pole) of the thyristor Q2, and is used to receive the signal O / P.L_SCR;

[0176] Pin 8 of the transformer TX1 is connected to the control electrode (G electrode) of the thyristor Q1 through a diode D1, a resistor R5 and a resistor R6 connected in parallel;

[0177] The cathode of the diode D1 is connected to the pin No. 7 of the transformer TX1 through the capacitor C5, and the pin No. 7 of the transformer TX1 is connected to the control electrode (G electrode) of the thyristor Q1 through the capacitor C6 and the resistor R7 connected in parallel.

[0178] Among them, the signal HFPW+ is used to control the output frequency and pulse width of the inverter to achieve precise output control, and the signal O / P.L_SCR is used to control the current output from the inverter to the load to prevent overcurrent or short circuit.

[0179] In actual implementation, the SCR unit circuit 242 protects the output end components from instantaneous high current switching, wherein the power supply of the control signal (signal O / P_SCR) is a high-frequency signal with an amplitude of plus or minus 20V. The level of the I / O port of the DSP chip controls the conduction of the switch tube Q3, so that the secondary side of the transformer TX1 is coupled to generate a current that can turn on the thyristor, and the two ends of the thyristor are connected in parallel to the two ends of the output relay RY2. When the inverter is turned on and off in parallel or the parallel working mode is switched at the customer application end, such as from the AC mode to the battery mode, the instantaneous high current is too late for the software and hardware overcurrent protection to react, and the high current far exceeding the output relay RY2 will directly act on the relay RY2, causing damage to the output relay RY2. In this regard, the DSP chip detects the inverter startup signal, shutdown signal and mode switching signal. When any of the above three signals is activated, the DSP control unit 230 controls the signal of O / P_SCR to become high level synchronously, and the OP.SCR unit circuit starts working. Since relay RY2 is a mechanical switch, the switching speed and current resistance are far inferior to those of the electronic switch thyristor. The synchronous opening of the three signals and the thyristor signal can ensure that the thyristor withstands the large current impact before relay RY2 is closed, thereby achieving the effect of protecting the output relay RY2.

[0180] The SCR unit circuit 242 implements overcurrent protection for the output relay through thyristors.

[0181] In this embodiment, a thyristor control module circuit, i.e., an SCR unit circuit, is added to the output end of the inverter. By judging the output of the inverter and taking advantage of the characteristics of the thyristor, such as fast switching speed, high current and voltage tolerance, the thyristor is turned on before the output relay is turned on to bear the impact of the instantaneous large current at the moment when the relay receives it, thus making the overcurrent protection system of the inverter more perfect. From the source, it can better prevent the inverter from suffering more losses due to output overcurrent. Compared with the traditional overcurrent protection circuit, the combination of the SCR unit circuit and the dual-limit comparator circuit can complete the inverter overcurrent protection more comprehensively and accurately and quickly. The SCR unit circuit performs overcurrent protection on the devices at the output end of the inverter according to the actual application situation of the inverter parallel operation. Moreover, the SCR has a low cost, is suitable for large-scale applications, has a simple control circuit, can be controlled by a simple trigger signal, and has good stability and reliability within a wide temperature range.

[0182] This application also provides a control method for a protection circuit of the output current when bidirectional inverters are paralleled.

[0183] In the embodiment of this application, a control method for a protection circuit of the output current when bidirectional inverters are paralleled, which is applied to the above embodiment, is as Figure 9 shown. This control method includes:

[0184] Step 910: Convert the DC BUS voltage into a first AC voltage through an inverter full-bridge circuit;

[0185] Step 920: Sample the inverter current corresponding to the first AC voltage through an inverter current sampling circuit to generate a sampling signal and a current detection signal corresponding to the sampling signal;

[0186] Step 930: Compare the sampling signal with a set value through a dual-limit comparator circuit to generate a comparison signal;

[0187] Step 940: Through a DSP control unit, according to the current detection signal and the comparison signal, output a first control signal to the inverter output module and output a second control signal to the inverter output module;

[0188] Step 950: Through an inverter output module, used to perform current limiting control on the first AC voltage according to the first control signal, and control the switches of the inverter drive of the inverter full-bridge circuit according to the second control signal.

[0189] According to the control method of the protection circuit for the output current during the parallel operation of bidirectional inverters provided by this application, based on the overcurrent protection at the software level of the inverter current sampling circuit, a dual-limit comparator circuit is added after the inverter current sampling circuit for hardware current limiting, achieving dual protection of software and hardware. The dual-limit comparator circuit compares the level of the sampling signal with the set value. Once the comparison value is reached, the TZ signal immediately flips to implement overcurrent protection. The DSP control unit internally forcibly shuts down the inverter drive. Through the collaborative design of hardware and software, the protection circuit can effectively avoid misoperation, improve the reliability and stability of the system, solve the problem that the traditional protection circuit of the inverter has a slow response during parallel operation, resulting in damage to electronic components, and achieve the protection of the output current when the load is disconnected during the parallel operation of the inverter. It can maintain stable operation in a complex power grid environment.

[0190] In some embodiments, the sampling of the inverter current corresponding to the first AC voltage by the inverter current sampling circuit to generate a sampling signal and a current detection signal corresponding to the sampling signal includes:

[0191] The inverter current is amplified or attenuated by a first-stage sampling circuit to obtain a current signal corresponding to the sampling range voltage of the DSP control unit;

[0192] The current signal is sampled by a second-stage sampling circuit to output a sampling signal and a current detection signal.

[0193] In this embodiment, through the processing of two-stage sampling circuits, it is applicable to different inverter application scenarios and can be flexibly adjusted according to different inverter output current ranges and the sampling requirements of the DSP. When abnormal situations such as overcurrent or short circuit occur in the inverter, the abnormal current can be quickly detected, and the protection mechanism can be triggered to avoid damage to the equipment, accurately measure the inverter current, and at the same time achieve electrical isolation, improve safety. Through precise current monitoring and a fast protection mechanism, the stability and reliability of the inverter system are improved, ensuring its safe and stable operation under various working conditions.

[0194] In the description of this application, "the first feature" and "the second feature" may include one or more of such features.

[0195] In the description of this application, the meaning of "a plurality" is two or more.

[0196] The embodiments of this application have been described above in conjunction with the accompanying drawings. However, this application is not limited to the above specific implementation manners. The above specific implementation manners are merely illustrative and not restrictive. Under the inspiration of this application, those of ordinary skill in the art can also make many forms without departing from the purpose of this application and the scope protected by the claims, and all of them belong to the protection scope of this application.

[0197] In the description of this specification, the description referring to terms such as "one embodiment", "some embodiments", "schematic embodiments", "examples", "specific examples", or "some examples", etc. means that the specific features, structures, materials, or characteristics described in connection with the embodiment or example are included in at least one embodiment or example of this application. In this specification, the schematic expressions of the above terms do not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials, or characteristics described can be combined in a suitable manner in any one or more embodiments or examples.

[0198] Although the embodiments of this application have been shown and described, those of ordinary skill in the art can understand that various changes, modifications, substitutions, and variations can be made to these embodiments without departing from the principles and purposes of this application, and the scope of this application is defined by the claims and their equivalents.

Claims

1. A protection circuit for the output current of a bidirectional inverter in parallel operation, characterized in that: Applied to a bidirectional inverter, the bidirectional inverter is provided with an inverter full-bridge circuit, and the protection circuit includes an inverter current sampling circuit, a dual-limit comparator circuit, a DSP control unit and an inverter output module; The inverter full-bridge circuit is respectively connected to the inverter output module and the inverter current sampling circuit, the inverter current sampling circuit is respectively connected to the dual-limit comparator circuit and the DSP control unit, and the inverter output module, the dual-limit comparator circuit and the inverter current sampling circuit are respectively connected to the DSP control unit; The inverter full-bridge circuit is used to convert the DC BUS voltage into a first AC voltage; The inverter current sampling circuit is used to sample the inverter current corresponding to the first AC voltage, and generate a sampling signal and a current detection signal corresponding to the sampling signal; The dual-limit comparator circuit is used to compare the sampled signal with a set value to generate a comparison signal; The DSP control unit is used to output a first control signal to the inverter output module and a second control signal to the inverter output module according to the current detection signal and the comparison signal; The inverter output module is used to perform current limiting control on the first AC voltage according to the first control signal, and to control the switch of the inverter drive of the inverter full-bridge circuit according to the second control signal.

2. The protection circuit for the output current of the bidirectional inverter when it is in parallel operation according to claim 1, characterized in that: The inverter current sampling circuit comprises a first-stage sampling circuit and a second-stage sampling circuit connected in sequence; The first-stage sampling circuit is used to gain or attenuate the inverter current to obtain a current signal corresponding to the sampling range voltage of the DSP control unit; The second-stage sampling circuit is used to sample the current signal and output a sampling signal and a current detection signal.

3. The protection circuit for the output current of the bidirectional inverter when it is connected in parallel according to claim 2, characterized in that: The first-stage sampling circuit includes a first operational amplifier module, a first voltage-dividing resistor, a second voltage-dividing resistor, a third voltage-dividing resistor, a fourth voltage-dividing resistor, a filter capacitor, a first RC filter module, a first double diode and a second double diode; The inverter current is input to the reverse input terminal of the first operational amplifier module through the first voltage-dividing resistor; The signal output terminal of the first operational amplifier module outputs a positive voltage of the current signal through the second voltage-dividing resistor; The positive input terminal of the first operational amplifier module is grounded through the third voltage-dividing resistor; The signal output end of the first operational amplifier module outputs a negative voltage of the current signal through the fourth voltage-dividing resistor and the filter capacitor; The reverse input terminal of the first operational amplifier module is connected to the signal output terminal of the first operational amplifier module through the first RC filter module; The reverse input terminal of the first operational amplifier module is connected to the common connection terminal of the first dual diode D2, and the forward input terminal of the first operational amplifier module is connected to the common connection terminal of the second dual diode D3.

4. The protection circuit for the output current of the bidirectional inverter when it is connected in parallel according to claim 2, characterized in that: The second-stage sampling circuit includes a second operational amplifier module, a fifth voltage-dividing resistor, a sixth voltage-dividing resistor, a second RC filter module, a third RC filter module, a fourth RC filter module and a third dual diode; The positive voltage of the current signal is input to the positive input terminal of the second operational amplifier module through the fifth voltage-dividing resistor; The negative voltage of the current signal is input to the reverse input terminal of the second operational amplifier module through the sixth voltage-dividing resistor; The positive input terminal of the second operational amplifier module is connected to a +1.65V voltage through the second RC filter module; The reverse input terminal of the second operational amplifier module is connected to the signal output terminal of the second operational amplifier module through the third RC filter module; The signal output end of the second operational amplifier module is connected to one end of the fourth RC filter module, and the other end of the fourth RC filter module outputs a current detection signal; The other end of the fourth RC filter module is connected to the common connection end of the third double diode.

5. The protection circuit for the output current of the bidirectional inverters in parallel operation according to any one of claims 1 to 3, characterized in that: In the dual-limit comparator circuit, the sampling signal is input to the inverting output terminal of the first comparator through the resistor R20, and the inverting output terminal of the first comparator is grounded through the capacitor C9; The signal output terminal of the first comparator is connected to one end of the resistor R19, and the other end of the resistor R19 outputs a comparison signal; The sampling signal is input to the positive output terminal of the second comparator through the resistor R36, the positive output terminal of the second comparator is grounded through the capacitor C11, the positive output terminal of the second comparator is connected to the other end of the resistor R19 through the resistor R25, and the other end of the resistor R19 is connected to the positive input terminal of the first comparator through the capacitor R22; The positive input terminal of the first comparator is grounded through R24 and capacitor C10 connected in parallel, and the positive input terminal of the first comparator is also connected to a +12V voltage through resistors R21 and R23; The positive power supply terminal of the second comparator is connected to a +12V voltage and is grounded through a capacitor C15; The negative power supply terminal of the second comparator is connected to a -12V voltage and is grounded through a capacitor C12; +3.3VA voltage is connected to the signal output terminal of the first comparator, the signal output terminal of the second comparator and the capacitor C13 through the resistor R18 and grounded; The inverting input terminal of the second comparator is grounded via a capacitor C14 and a resistor R27 connected in parallel; The other end of the resistor R19 is grounded through a parallel capacitor C8 and a reverse-connected diode D4.

6. The protection circuit for the output current of the bidirectional inverter when it is in parallel operation according to claim 1, characterized in that: The inverter output module includes an inverter output circuit and an SCR unit circuit, and the DSP control unit is connected to the SCR unit circuit; The inverter output circuit is used to correct and compensate the first AC voltage and output a second AC voltage; The SCR unit circuit is used to perform current limiting control on the second AC voltage according to the control signal.

7. The protection circuit for the output current of the bidirectional inverters in parallel as claimed in claim 6, characterized in that: The inverter output circuit includes a relay RY1, a relay RY2, a transistor Q4, a transistor Q5 and a current transformer CT; The transistor Q5 is connected to the coil of the relay RY1, the transistor Q4 is connected to the coil of the relay RY2, and the common end of the relay RY1 and the common end of the relay RY2 are respectively connected to the primary winding input end and the primary winding output end of the current transformer CT; The common end of the relay RY1 and the common end of the relay RY2 are used to receive the first AC voltage and the secondary winding output end of the current transformer CT.

8. The protection circuit for the output current of the bidirectional inverters in parallel as claimed in claim 6, characterized in that: The SCR unit circuit 242 includes a thyristor Q1, a thyristor Q2, a switch tube Q3, and a transformer TX1; Pin 1 of the transformer TX1 receives the input signal HFPW+ through the resistor R11, the gate of the switch tube Q3 is used to receive the control signal, the drain of the switch tube Q3 is connected to pin 4 of the transformer TX1, and the source of the switch tube Q3 is grounded and connected to the gate of the switch tube Q3 through the resistor R13; Pin 5 of the transformer TX1 is connected to the control electrode of the thyristor through a diode D3 and parallel resistors R10 and R12; The cathode of the diode D3 is connected to the pin 6 of the transformer TX1 through the capacitor C8; Pin 6 of the transformer TX1 is connected to the anode of the thyristor Q1 and the cathode of the thyristor Q2, and is used to output a line voltage of a second AC voltage; Pin 6 of the transformer TX1 is connected to the control electrode of the thyristor Q1 through a diode D3, a parallel resistor R10 and a resistor R12; Pin 6 of the transformer TX1 is connected to the gate of the thyristor Q2 via a capacitor C9 and a resistor R9 connected in parallel; Pin 6 of the transformer TX1 is connected to pin 7 of the transformer TX1 via a resistor R8 and a capacitor C7; Pin No. 7 of the transformer TX1 is connected to the cathode of the thyristor Q1 and the anode of the thyristor Q2, and is used to receive the signal O / P.L_SCR; Pin 8 of the transformer TX1 is connected to the control electrode of the thyristor Q1 through a diode D1, a resistor R5 and a resistor R6 connected in parallel; The cathode of the diode D1 is connected to the pin No. 7 of the transformer TX1 through the capacitor C5, and the pin No. 7 of the transformer TX1 is connected to the control electrode of the thyristor Q1 through the capacitor C6 and the resistor R7 connected in parallel.

9. A method for controlling a protection circuit for an output current of a bidirectional inverter in parallel operation, characterized in that: The method for protecting the output current of the bidirectional inverters in parallel according to any one of claims 1 to 8 comprises: Converting the DC BUS voltage into a first AC voltage through an inverter full-bridge circuit; Sampling the inverter current corresponding to the first AC voltage through an inverter current sampling circuit to generate a sampling signal and a current detection signal corresponding to the sampling signal; The sampling signal is compared with a set value by a dual-limit comparator circuit to generate a comparison signal; Outputting a first control signal to the inverter output module and outputting a second control signal to the inverter output module according to the current detection signal and the comparison signal through a DSP control unit; The inverter output module is used to perform current limiting control on the first AC voltage according to the first control signal, and to control the inverter drive switch of the inverter full-bridge circuit according to the second control signal.

10. The method for controlling the protection circuit of the output current of the bidirectional inverters in parallel as claimed in claim 9, characterized in that: The method of sampling the inverter current corresponding to the first AC voltage through the inverter current sampling circuit to generate a sampling signal and a current detection signal corresponding to the sampling signal includes: The inverter current is amplified or attenuated by a first-stage sampling circuit to obtain a current signal corresponding to a sampling range voltage of the DSP control unit; The current signal is sampled by a second-stage sampling circuit, and a sampling signal and a current detection signal are output.

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