Three-phase inverter control system and method

Abstract

The invention discloses a three-phase inverter control system and method, which organically combines a main control chip circuit, a power driving chip circuit, a magnetic encoder interface circuit, a three-phase inverter two-resistance sampling circuit, an overcurrent protection circuit and a voltage sampling circuit to form a complete current detection, overcurrent protection and control feedback system. The three-phase bridge arm current of the three-phase inverter is sampled through the two resistors, the number of sampling resistors and operational amplifiers used in hardware is reduced, the PCB layout area of the three-phase inverter is reduced, and the system cost is reduced; through overcurrent protection of the three-phase inverter, a peripheral circuit is simplified, signal interference is reduced, and the sampling precision of sampling current is improved; after the circuit is simplified on the existing basis, the hardware overcurrent protection response speed is high, the sampling delay error is reduced, the damage of overcurrent to a motor and a power device can be effectively prevented, and the safe operation of a system is ensured.

Description

Technical Field

[0001] The present invention belongs to the technical field of torque motor overcurrent protection circuit and control method control, and in particular relates to a three-phase inverter control system and method. Background Art

[0002] In modern power electronics technology, three-phase inverters are widely used in industrial automation, motor control and new energy fields such as photovoltaic power generation and electric vehicles. As the core of the motor drive system, the inverter needs to accurately control the output current. Especially during the operation of the motor, real-time current detection and overcurrent protection are important links to ensure the stability and safety of the system. Most of the current sampling schemes for three-phase inverters use three-resistance sampling, that is, the three-phase currents of the inverter (phase A, phase B, and phase C) are sampled independently. Although this scheme can accurately obtain the current information of each phase, it also has many problems, such as high hardware cost. Three-resistance sampling requires three sampling resistors and three high-precision differential amplifier circuits, as well as complex three-phase overcurrent protection circuits, resulting in high hardware complexity, occupying more PCB area, and increasing system cost. Traditional three-resistance sampling usually cannot take into account both three-phase load overcurrent protection and three-phase inverter bridge direct short-circuit protection.

[0003] The existing three-phase inverter overcurrent protection also has a single resistor sampling circuit structure. Since there is only one sampling resistor, the circuit design of the system is simplified, but the control algorithm is complex and the calculation is large. The short duration of direct sampling of one phase current in a unit cycle leads to large measurement errors, resulting in inaccurate sampling current data, affecting the system control performance. In addition, the signal processing of this method requires the microcontroller to read the analog signal. When an overcurrent fault occurs, the program needs to perform the complete process of sampling-judgment-response, which slows down the response speed of this overcurrent protection and reduces safety. Traditional single resistor sampling is usually unable to take into account both three-phase load overcurrent protection and three-phase inverter bridge direct short-circuit protection.

[0004] Therefore, simplifying the three-phase current sampling circuit, reducing system cost, and improving the overcurrent protection performance of the three-phase inverter have become important technical challenges in inverter design. Summary of the invention

[0005] The purpose of the present invention is to provide a three-phase inverter control system and method to overcome the technical problems of the existing three-phase inverter sampling circuit using a complex three-resistance sampling structure, a complex single-resistance sampling algorithm, and large measurement errors.

[0006] To solve the above problems, the present invention adopts the following technical solutions: A three-phase inverter control system comprises a main control chip circuit, a power drive chip circuit and a three-phase inverter two-resistance sampling circuit connected in sequence; The output end of the two-resistance sampling circuit of the three-phase inverter is respectively connected to the input end of the voltage sampling circuit and the input end of the overcurrent protection circuit, and the output end of the voltage sampling circuit and the output end of the overcurrent protection circuit are respectively connected to the input end of the main control chip circuit; The input end of the main control chip circuit is also connected to a magnetic encoder interface circuit; The three-phase inverter two-resistance sampling circuit comprises three-phase inverter bridge arms, wherein the lower bridge arm of one phase inverter bridge arm is connected in series with a first sampling resistor, and the lower bridge arms of the other two phase inverter bridge arms are connected in series with a second sampling resistor, and the first sampling resistor and the second sampling resistor are grounded respectively.

[0007] Furthermore, the first sampling resistor and the second sampling resistor are respectively connected in parallel with a filter capacitor.

[0008] Furthermore, the overcurrent protection circuit includes a comparison circuit, a protection current value setting circuit and an output filter circuit, the input end of the comparison circuit is respectively connected to the output end of the two-resistance sampling circuit of the three-phase inverter and the protection current value setting circuit, and the output filter circuit is connected to the output end of the comparison circuit.

[0009] Further, the comparison circuit includes a voltage comparator and a resistor connected to an input terminal of the voltage comparator; The protection current value setting circuit includes a voltage dividing resistor and a filter capacitor connected in parallel with the voltage dividing resistor.

[0010] Furthermore, the output end of the voltage comparator is also connected to a pull-up resistor.

[0011] Furthermore, the main control chip circuit and the power driving chip circuit, and the main control chip circuit and the magnetic encoder interface circuit all communicate via SPI.

[0012] Furthermore, the main control chip circuit includes a main control chip, and the main control chip is connected to a crystal oscillator circuit, a reset circuit and a voltage-stabilized power supply.

[0013] Furthermore, the voltage sampling circuit includes a DC bus voltage sampling circuit and an inverter three-phase output voltage sampling circuit.

[0014] Furthermore, the magnetic encoder interface circuit includes a magnetic encoder chip, and the magnetic encoder chip is connected to a voltage stabilizing diode and a decoupling capacitor connected in parallel with the voltage stabilizing diode.

[0015] In a second aspect, a three-phase inverter control method is provided, comprising the following steps: The three-phase current of the inverter is collected through the first sampling resistor and the second sampling resistor of the two-resistance sampling circuit of the three-phase inverter respectively, and fed back to the main control chip circuit through the power drive chip circuit; The motor rotor position is collected through the magnetic encoder interface circuit, and the inverter three-phase output voltage is collected through the voltage sampling circuit and fed back to the main control chip circuit; The main control chip circuit outputs a PWM control signal to control the inverter according to the collected three-phase current of the inverter, the motor rotor position and the three-phase output voltage information of the inverter; When the three-phase current of the inverter exceeds the safety threshold, the overcurrent protection circuit outputs a feedback signal to the main control chip circuit, and the main control chip circuit controls the three-phase inverter to stop working.

[0016] Compared with the prior art, the present invention has the following beneficial technical effects: The invention provides a three-phase inverter control system. A complete current detection, overcurrent protection and control feedback system is formed by organically combining a main control chip circuit, a power drive chip circuit, a magnetic encoder interface circuit, a two-resistance sampling circuit of a three-phase inverter, an overcurrent protection circuit and a voltage sampling circuit. The three-phase bridge arm current of the three-phase inverter is sampled by two resistors, the number of sampling resistors and operational amplifiers used is reduced in hardware, the PCB layout area of ​​the three-phase inverter is reduced, and the system cost is reduced; the overcurrent protection of the three-phase inverter simplifies the peripheral circuit, reduces signal interference, improves the sampling accuracy of the sampling current, improves the accuracy of the control algorithm, and reduces the probability of fault occurrence; through signal acquisition, signal amplification and processing, overcurrent detection, bus voltage monitoring to protection action, the invention simplifies the circuit on the existing basis, the hardware overcurrent protection response speed is fast, the sampling delay error is reduced, the damage of overcurrent to the motor and the power device can be effectively prevented, and the safe operation of the system is guaranteed.

[0017] Preferably, two sampling resistors in the two-resistance sampling circuit of the three-phase inverter are respectively connected in parallel with filter capacitors, which can effectively filter out high-frequency noise, stabilize the voltage, and improve signal quality.

[0018] Preferably, in the overcurrent protection circuit, an output filter circuit is connected to the output end of the voltage comparator for filtering.

[0019] Preferably, the main control chip communicates with the power driver chip via the SPI interface, adjusts the gain value of the differential current amplifier circuit, and periodically reads the value of its fault status register. If a FAULT signal is detected, the main control chip can stop outputting the PWM signal and shut down the inverter.

[0020] The present invention provides a two-resistance sampling and overcurrent protection method for a three-phase inverter. Two resistors are used to sample the three-phase inverter. The three-phase bridge arm current of the three-phase inverter is sampled through the two resistors. While completing the three-phase load current sampling, the current signal obtained through sampling is connected to the overcurrent protection circuit to ensure that the system responds to the blocking output pulse in time when overload occurs and the inverter is short-circuited and directly connected, so as to avoid equipment damage and protect the circuit. The main control chip performs coordinated control of the two-resistance sampling of the three-phase inverter and the overcurrent protection circuit, thereby realizing the three-phase load current sampling of the three-phase inverter, the three-phase load current overload protection and the three-phase inverter bridge arm direct current protection. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 A structural diagram of a three-phase inverter control system in an embodiment of the present invention; Figure 2 This is a schematic diagram of the circuit structure of the main control chip STM32F411RE of the present invention; Figure 3 The schematic diagram of the serial communication and JTAG program download circuit structure of the main control chip STM32F411RE of the present invention; Figure 4 This is a schematic diagram of the circuit structure of the power driver chip DQ5402 of the present invention; Figure 5 This is a schematic diagram of the interface circuit structure of the magnetic encoder MT6826GT-AKD-R of the present invention; Figure 6 This is a schematic diagram of the structure of a two-resistance three-phase inverter sampling circuit of the present invention; Figure 7 This is a schematic diagram of the structure of the overcurrent protection circuit of the present invention; Figure 8 It is a schematic diagram of the structure of a DC bus voltage sampling circuit in the voltage sampling circuit of the present invention; Fig. 9 It is a schematic diagram of the structure of the three-phase output voltage sampling circuit of the inverter in the voltage sampling circuit of the present invention; Fig.10 The present invention is a flow chart of a three-phase inverter control method.

[0022] In the figure, 1. main control chip circuit; 2. power drive chip circuit; 3. three-phase inverter two-resistance sampling circuit; 4. torque motor; 5. voltage sampling circuit; 6. magnetic encoder interface circuit; 7. overcurrent protection circuit. DETAILED DESCRIPTION

[0023] In order to make the technical problems, technical solutions and beneficial effects solved by the present invention more clearly understood, the present invention is further described in detail in the following specific embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not used to limit the present invention.

[0024] In order to make the purpose, technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are part of the embodiments of the present invention, not all of the embodiments. Generally, the components of the embodiments of the present invention described and shown in the drawings here can be arranged and designed in various different configurations.

[0025] In the description of the embodiments of the present invention, it is also necessary to explain that, unless otherwise clearly specified and limited, the terms "set", "install", "connect", and "connect" should be understood in a broad sense, for example, it can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection or an electrical connection; it can be a direct connection, or it can be indirectly connected through an intermediate medium, or it can be the internal connection of two components. For ordinary technicians in this field, the specific meanings of the above terms in the present invention can be understood according to specific circumstances.

[0026] A three-phase inverter control system, such as Figure 1 As shown, it includes a main control chip circuit 1, a power drive chip circuit 2, a magnetic encoder interface circuit 6, a two-resistance three-phase inverter sampling circuit 3, an overcurrent protection circuit 7, and a voltage sampling circuit 5; The main control chip circuit 1 is responsible for the PWM drive signal generation, current detection signal processing, overcurrent protection response and system fault management of the three-phase inverter, including the main control chip, which is connected to a crystal oscillator circuit, a reset circuit and a voltage-stabilized power supply. The main control chip adopts; The power driver chip circuit 2 and the main control chip circuit 1 communicate via SPI, and have a wide power supply voltage range, high drive capability, and multiple protection functions, including MOSFET drive, overcurrent protection, undervoltage protection, and dead time control. Supporting SPI communication, register configuration can be used to change the amplification factor of the differential amplifier circuit, and functions such as state monitoring and parameter adjustment can be realized; the magnetic encoder interface circuit 6 and the main control chip circuit 1 communicate through SPI to realize motor rotor position reading and state monitoring; the three-phase inverter two-resistance sampling circuit 3 is connected to the power drive chip circuit 2 for measuring the three-phase current of the inverter; the three-phase inverter two-resistance sampling circuit 3 is connected to the input end of the voltage sampling circuit 5, and the voltage sampling circuit 5 includes a DC bus voltage sampling circuit and an inverter three-phase output voltage sampling circuit; the three-phase inverter two-resistance sampling circuit 3 is connected to the input end of the overcurrent protection circuit 7, and the overcurrent protection circuit 7 includes a comparison circuit, a protection current value setting circuit and an output filter circuit. The input end of the comparison circuit is respectively connected to the output end of the three-phase inverter two-resistance sampling circuit 3 and the protection current value setting circuit, and the output filter circuit is connected to the output end of the comparison circuit; the output end of the voltage sampling circuit 5 and the output end of the overcurrent protection circuit 7 are connected to the input end of the main control chip circuit 1.

[0027] like Figure 6 As shown, the three-phase inverter two-resistance sampling circuit 3 includes MOS transistors Q1, MOS transistors Q2, MOS transistors Q3, MOS transistors Q4, MOS transistors Q5, MOS transistors Q6, sampling resistors R28, and sampling resistors R29. The MOS transistors Q1 and MOS transistors Q2, MOS transistors Q3 and MOS transistors Q4, MOS transistors Q5 and MOS transistors Q6 respectively form three-phase inverter bridge arms. The MOS transistors Q1, MOS transistors Q3, and MOS transistors Q5 are upper bridge arm switch tubes of the three-phase inverter. The source electrodes S of the MOS transistors Q1, MOS transistors Q3, and MOS transistors Q5 correspond to the output terminals PHASE_A, PHASE_B, and PHASE_C of the three-phase inverter respectively. The MOS transistors Q2, MOS transistors Q4, and MOS transistors Q6 are lower bridge arm switch tubes of the three-phase inverter. The sampling resistor R28 is connected in series between the source S of the MOS tube Q2 and the power ground PGND, the sampling resistor R28 is connected in parallel with the filter capacitor C15, and the sampling resistor R28 independently measures the current flowing through the MOS tube Q2, which is used to measure the A-phase current of the three-phase inverter. The source S of the MOS tube Q4 and the source S of the MOS tube Q6 are short-circuited, the sampling resistor R29 is connected in series between the source S of the MOS tube Q4 and the power ground PGND, the sampling resistor R29 is connected in parallel with the filter capacitor C16, and the sampling resistor R29 simultaneously measures the current flowing through the MOS tube Q4 and the current flowing through the MOS tube Q6, which are used to measure the B-phase current and the C-phase current of the three-phase inverter respectively.

[0028] The controller samples the two resistors of the three-phase inverter and coordinates the overcurrent protection circuit to achieve efficient and safe control of the three-phase inverter. The control system circuit of the present invention together constitutes a complete and efficient motor drive system, which not only ensures the safety of motor operation, saves device costs, but also improves control accuracy and response speed.

[0029] In this embodiment, the main control chip is STM32F411RE, the power driver chip is DQ5402, and the magnetic encoder is MT6826GT-AKD-R; Specifically, Figure 2 , Figure 3 As shown, the single-chip microcomputer system includes a system chip, a crystal oscillator circuit, a reset circuit, a JTAG program download interface, a voltage-regulated power supply, a digital input port PB12 and six PWM output terminals; the crystal oscillator circuit, the reset circuit, the digital input port PB12 and the six PWM output terminals are respectively connected to the system chip; the crystal oscillator circuit is composed of an 8MHz passive crystal oscillator Y1 and two 20pF capacitors C22 and a capacitor C23; the reset circuit is composed of a button S1, a resistor R40 and a capacitor C21; the digital input port PB12 is connected to an isolated overcurrent protection signal DI0; the six PWM output terminals include PA8, PA9, PA10, PB13, PB14 and PB15, which drive the three-phase inverter switch elements MOS tubes Q1, MOS tubes Q2, MOS tubes Q3, MOS tubes Q4, MOS tubes Q5 and MOS tubes Q6 through the power driver chip DQ5402.

[0030] like Figure 2 , Figure 3As shown in the figure, the main control chip STM32F411RE is the core processor of the system, responsible for the PWM drive signal generation, current detection signal processing, overcurrent protection response and system fault management of the three-phase inverter. The main control chip STM32F411RE is powered by +3.3V voltage. The VDD pin of the main control chip STM32F411RE is connected to the +3.3V power supply. The analog voltage required by the main control chip STM32F411RE is provided by the REF terminal of the power driver chip DQ5402. The terminal voltage is connected to the VDDA / VREF+ pin of the main control chip STM32F411RE after passing through the filter capacitor. The +3.3V power supply required by the main control chip STM32F411RE is provided by the output voltage VCC of the BUCK circuit inside the power driver chip DQ5402. The NRST pin is connected to an external pull-up resistor of 10kΩ and a button in series to form a manual reset circuit. At the same time, it is connected to the ground through a 100nF capacitor C55 to eliminate reset jitter. The main control chip STM32F411RE uses an external 8MHz crystal oscillator, which is grounded through 20pF capacitors C43 and C45 for frequency stabilization. At the same time, the crystal oscillator signal is connected to the PH0_OSC_IN and PH1_OSC_OUT pins for generating the main frequency clock.

[0031] like Figure 4 As shown in the figure, DVDD and AVDD of the power driver chip DQ5402 circuit are connected to the +3.3V power supply, and are decoupled and filtered through 1µF capacitor C32 and 1µF capacitor C36 respectively. The high and low side drive input signals UH, UL, VH, VL, WH, and WL of each phase of the power driver chip DQ5402 circuit are respectively controlled by the PWM output of the main control chip STM32F411RE, and together with the EN_GATE signal of the power driver chip DQ5402, determine the on and off state of the inverter.

[0032] The power driver chip DQ5402 integrates overcurrent detection and fault signal output functions. The SPI communication of the power driver chip DQ5402 is connected to the SPI communication of the main control chip STM32F411RE, using pins SPI1_CS, SPI1_MOSI, SPI1_MISO and SPI1_SCK to configure protection parameters and obtain fault status. The DC_CAL and NOCTW pins of the power driver chip DQ5402 are used to detect the bus voltage and thermal protection status to ensure that the circuit operates within a safe range. The two-resistance sampling current IA+, IA-, IBC+, and IBC- of the three-phase inverter are connected to SN1, SP1, SN2, and SP2 of the power driver chip DQ5402, which can realize the current acquisition and signal processing for overcurrent control and protection.

[0033] When the power driver chip DQ5402 detects internal overvoltage and overcurrent signals, the fault protection mechanism is triggered, the FAULT signal is output immediately, and the power switch MOSFETs of all bridge arms are turned off, thereby cutting off the current path and protecting the circuit and load from further damage.

[0034] like Figure 5 As shown in the figure, the magnetic encoder MT6826GT-AKD-R interface circuit includes the magnetic encoder chip MT6826GT-AKD-R U6, SPI communication interface SPI2_MISO, SPI communication interface SPI2_MOSI, SPI communication interface SPI2_SCK, SPI communication interface MT6826_CS, voltage stabilizing diode D8, decoupling capacitor C17, encoder signal input ENCODER-A+, encoder signal input ENCODER-B+, encoder signal input ENCODER-Z+, and the voltage stabilizing diode D8 and decoupling capacitor C17 are used to ensure the stability of the encoder working voltage. The SPI protocol is used to communicate data with the encoder through the main control chip STM32F411RE controller to realize position reading and status monitoring. The three encoder signals MT_A, MT_B, and MT_Z are connected to the encoder through the current limiting resistors R31, R32, and R33, and the current limiting resistors are all 120Ω. CAL_EN and TEST_EN are used for encoder calibration and testing, which are suitable for the initialization stage. The magnetic encoder is used to provide the motor rotor position signal to the main control chip STM32F411RE, which can detect the rotor position in real time and facilitate control.

[0035] like Figure 7As shown, the overcurrent protection circuit 7 includes a comparison circuit, a protection current value setting circuit and an output filter circuit. The comparison circuit includes a voltage comparator U11, an input resistor R70, an input resistor R71, an input resistor R72 and an input resistor R74; the protection current value setting circuit includes voltage divider resistors R67 and R68 and a filter capacitor C62 connected in parallel with the voltage divider resistors; the voltage comparator U11 uses a single-channel chip LMV331 powered by a single power supply, the resistor R69 is the output pull-up resistor of the comparator U11, and the output filter circuit includes a resistor R73 and a capacitor C64; when the current flowing through the sampling resistor R28 or the sampling resistor R29 is higher than the set protection current, the voltage comparator The potential of terminal 3 of U11 is higher than that of terminal 1, and the potential of terminal 4 of the voltage comparator U11 is a low-level signal. After filtering by the filtering circuit, the overcurrent protection signal BKIN is output. The overcurrent protection signal BKIN is connected to the PB12 terminal of the main control chip STM32F411RE. When the PB12 terminal signal of the main control chip STM32F411RE is at a low level, the PWM pulse is blocked to turn off MOS tubes Q1, Q2, Q3, Q4, Q5 and Q6, and stop the inverter output to realize the overcurrent protection function and prevent equipment damage. The whole process is realized by hardware circuits, and the overcurrent protection response speed is fast.

[0036] like Figure 6As shown, the two-resistance sampling circuit of the three-phase inverter includes MOS tube Q1, MOS tube Q2, MOS tube Q3, MOS tube Q4, MOS tube Q5, MOS tube Q6, sampling resistor R28, sampling resistor R29, and a driving current limiting and voltage limiting circuit. MOSFET tube Q1 and MOS tube Q2, MOS tube Q3 and MOS tube Q4, MOS tube Q5 and MOS tube Q6 respectively form a three-phase inverter bridge arm. MOS tube Q1, MOS tube Q3, MOS tube Q5 are three-phase upper bridge arm switch tubes, MOS tube Q2, MOS tube Q4, MOS tube Q6 are three-phase lower bridge arm switch tubes, and form a path with the corresponding upper bridge arm. The two-resistance sampling circuit is used to collect the phase current information of the inverter respectively. The sampling resistor R28 is connected in series between the source S terminal of the MOS tube Q2 and the power ground PGND. The sampling resistor R28 is connected in parallel with the filter capacitor C15. The sampling resistor R28 independently measures the current flowing through the MOS tube Q2, which is used to measure the A phase current of the three-phase inverter. The source S of MOS tube Q4 and the source S of MOS tube Q6 are short-circuited, the sampling resistor R29 is connected in series between the source S of MOS tube Q4 and the power ground PGND, the sampling resistor R29 is connected in parallel with the filter capacitor C16, and the sampling resistor R29 simultaneously measures the current flowing through MOS tube Q4 and the current flowing through MOS tube Q6, which are respectively used to measure the B-phase current and the C-phase current of the three-phase inverter. MOS tube Q1, MOS tube Q2, MOS tube Q3, MOS tube Q4, MOS tube Q5, MOS tube Q6 are all connected to the driving current limiting and voltage limiting circuit. The output phase voltages PHASE_A, PHASE_B, and PHASE_C of the three-phase inverter are respectively drawn from the connection points of MOS tube Q1 and MOS tube Q2, MOS tube Q3 and MOS tube Q4, and MOS tube Q5 and MOS tube Q6, which are the three-phase output terminals of the inverter.

[0037] The voltage sampling circuit 5 includes a DC bus voltage sampling circuit, such as Figure 8 As shown, it includes a DC power supply PVDD, a power ground PGND, a +3.3V power supply, a filter capacitor C1, a filter capacitor C2, a filter capacitor C3, and a filter capacitor C4. The DC power supply PVDD is filtered by a capacitor, and the voltage is divided by voltage-dividing resistors R1 and R3. The DC bus voltage sampling signal UDC is connected to the PC5 terminal of the main control chip STM32F411RE. The main control chip STM32F411RE completes the periodic sampling of the DC bus voltage through the internal integrated analog-to-digital converter; it also includes an inverter three-phase output voltage sampling circuit, such as Fig. 9As shown, it includes three-phase power input PHASE_A, PHASE_B, PHASE_C, voltage dividing resistors R4, R5, R6, R7, R8, R9, and outputs VOLTAGE_A, VOLTAGE_B, and VOLTAGE_C. The three-phase output voltages PHASE_A, PHASE_B, and PHASE_C of the three-phase inverter are divided by voltage dividing resistors. The divided voltage signals are VOLTAGE_A, VOLTAGE_B, and VOLTAGE_C, respectively, and are connected to PC0, PC1, and PC2 of the main control chip STM32F411RE. The main control chip STM32F411RE completes the periodic sampling of the DC bus voltage through the internally integrated analog-to-digital converter.

[0038] The present invention also provides a three-phase inverter control method, such as Fig.10 As shown, the following steps are included: The three-phase current of the inverter is collected through the first sampling resistor and the second sampling resistor of the two-resistance sampling circuit 3 of the three-phase inverter respectively, and fed back to the main control chip circuit 1 through the power drive chip circuit 2; The motor rotor position is collected through the magnetic encoder interface circuit 6, and the inverter three-phase output voltage is collected through the voltage sampling circuit 5 and fed back to the main control chip circuit 1; The main control chip circuit 1 outputs a PWM control signal to control the inverter according to the collected three-phase current of the inverter, the motor rotor position and the three-phase output voltage information of the inverter; When the three-phase current of the inverter exceeds the safety threshold, the overcurrent protection circuit 7 outputs a feedback signal to the main control chip circuit 1, and the main control chip circuit 1 controls the three-phase inverter to stop working.

[0039] Specifically, the method of two-resistance sampling and overcurrent protection of the three-phase inverter is as follows: Through two sampling resistors connected in series in the three-phase bridge arm, the three-phase output current is sampled, and the detection of the direct fault current of the three-phase inverter bridge arm is taken into account. The specific implementation scheme is: the sampling resistor R28 is connected in series between the source S of the MOS tube Q2 of the lower bridge arm of phase A of the three-phase inverter and the power ground PGND to complete the independent sampling of the current of phase A. The source S of the MOS tube Q4 of the lower bridge arm of phase B of the three-phase inverter is directly connected to the source S of the MOS tube Q6 of the lower bridge arm of phase C, and the sampling resistor R29 is connected in series between the connection point and the power ground PGND. The main control chip STM32F411RE completes the sampling of the current of phase B and phase C through time-sharing sampling. The specific method of two-resistance sampling is: when the trigger signal of MOS tube Q2 is high level, the voltage signal of sampling resistor R28 is measured, and sent to the main control chip STM32F411RE after conditioning by differential amplifier circuit, which is the sampling value of phase A current of three-phase inverter; when the trigger signal of MOS tube Q4 is high level and the trigger signal of MOS tube Q6 is low level at the same time, the voltage signal of sampling resistor R29 is measured, and sent to the main control chip STM32F411RE after conditioning by differential amplifier circuit, which is the sampling value of phase B current of three-phase inverter; when the trigger signal of MOS tube Q6 is high level and the trigger signal of MOS tube Q4 is low level at the same time, the voltage signal of sampling resistor R29 is measured, and sent to the main control chip STM32F411RE after conditioning by differential amplifier circuit, which is the sampling value of phase C current of three-phase inverter.

[0040] In hardware design, the sampling resistor R28 and the sampling resistor R29 located in the lower bridge arm circuit of the three-phase inverter bridge arm are both 10mΩ power resistors connected in series in the lower bridge arm circuit of the three-phase inverter bridge arm. When the inverter is running, the load current will pass through the sampling resistor, and the parallel filter capacitor will filter out the high-frequency noise to ensure the accuracy of the sampling signals IA+ and IBC+. At this time, the sampling signals IA+ and IA-, IBC+ and IBC- are respectively input to the SN1 and SP1, SN2 and SP2 terminals of the power driver chip DQ5402, and the current sampling signals IA and IBC are output through the high-precision differential amplifier circuit inside the power driver chip DQ5402. The current sampling signals IA and IBC are connected to the terminals PC3 and PC4 of the main control chip STM32F411RE. The internal analog-to-digital converter of the main control chip STM32F411RE periodically samples the terminals PC3 and PC4 to complete the measurement of the three-phase current of the three-phase inverter.

[0041] In terms of device selection, the power MOSFET device STB60NF06LT4 is selected as the switching device of the inverter, and a sampling resistor R28 is connected between the source S of the MOS tube Q2 and the power ground PGND. The source S of the MOS tube Q4 and the source S of the MOS tube Q6 are directly connected, and a sampling resistor R29 is connected between the source S of the MOS tube Q4 and the power ground PGND. The sampling resistors R28 and R29 are high-precision power resistors with 10mΩ and 1% accuracy. The power driver chip DQ5402 is used to drive the power switch tube, and the magnetic encoder MT6826GT-AKD-R is used to realize the real-time detection of the motor rotor position signal, and the encoder speed signals ENCODER-A+, ENCODER-B+, and ENCODER-Z+ are generated and input into the main control chip STM32F411RE. The SPI2 serial communication interface of the main control chip STM32F411RE is connected to the SPI serial communication interface of the magnetic encoder MT6826GT-AKD-R, and the installation position of the magnetic encoder MT6826GT-AKD-R can be calibrated. The rotor position and rotor speed information detected by the magnetic encoder MT6826GT-AKD-R are combined with the three-phase current signal obtained by the two-resistance sampling method to achieve precise closed-loop control of the motor. Under the joint action of these modules, a complete control system is formed.

[0042] The basic principle of overcurrent protection is to detect the sampling current. When the detected current exceeds the preset safety threshold, protective measures are taken immediately to ensure that the main circuit is not affected, thereby improving the safety of the system. The overcurrent protection circuit 7 uses input resistors R71 and R74 to perform algebraic summation operations on the current sampling signals IA+ and IBC+, and sends the summation result to the inverting input terminal of the voltage comparator U11 through input resistor R72. The +3.3V voltage provides a reference voltage for the comparator through a voltage divider network composed of resistors R67 and R68, and is connected to the non-inverting input terminal of the voltage comparator U11 through input resistor R70. When the current signal value detected by the voltage comparator U11 exceeds the reference voltage setting value, the voltage comparator U11 outputs a low-level signal and generates an overcurrent protection signal BKIN after filtering by resistor R73 and capacitor C64, triggering the overcurrent protection mechanism. By adjusting the resistance value of resistor R68 and the capacitance value of capacitor C64, the response sensitivity and protection delay time can be changed. When the overcurrent protection signal BKIN is at a low level, the voltage of the PB12 terminal of the main control chip STM32F411RE connected to it is at a low level, and the internal hardware circuit of the main control chip STM32F411RE blocks 6 PWM signals, and turns off MOS tubes Q1, Q2, Q3, Q4, Q5 and Q6 through the power driver chip DQ5402, stops the inverter output, and realizes the overcurrent protection function.

[0043] The basic principle of three-phase inverter overload protection is: when the three-phase inverter is operating normally, through the above sampling method, the sampling resistor R28 measures the output current of phase A of the three-phase inverter. At the same time, the sampling resistor R29 measures the sampling current of phase B or phase C of the three-phase inverter. During normal operation, the three-phase current output by the three-phase inverter is approximately a three-phase symmetrical current, and its amplitude is approximately equal, and it satisfies Kirchhoff's current law, that is, the sum of the three-phase current is always equal to zero. Therefore, after algebraic summation of resistors R71 and R74, the output current is the B-phase or C-phase current of the three-phase inverter. When the three-phase inverter is overloaded, the amplitudes of the three-phase currents all exceed the specified current limit value, and the voltage comparator U11 outputs a low-level protection signal to complete the overload protection of the three-phase inverter.

[0044] The principle of the three-phase inverter bridge arm direct current protection is: when a phase bridge arm or multi-phase bridge arm of the three-phase inverter direct current occurs, the three-phase inverter A phase bridge arm direct current flows through the sampling resistor R28, and the B phase and C phase bridge arm direct current flows through the sampling resistor R29. When the three-phase inverter bridge arm direct current fault occurs, the direct current is much higher than the load current when the three-phase inverter is operating normally. After detection by the sampling resistors R28 and R29, the voltage comparator U11 outputs a low-level protection signal to complete the three-phase inverter bridge arm direct current protection.

[0045] In the present invention, two resistors are used to sample the three-phase inverter, and an overcurrent protection circuit is added to ensure the safety of the system. The core principle of overcurrent protection is to monitor the sampled current in real time. When it is detected that the current exceeds a preset safety threshold, the hardware circuit immediately takes protective measures, and the circuit responds quickly. In order to simplify the circuit and reduce costs, the present invention adopts the "two-resistance sampling method". This method does not directly measure the three-phase load current, but samples the three-phase bridge arm current of the three-phase inverter through two resistors. While completing the three-phase load current sampling, the current signal obtained by sampling is connected to the overcurrent protection circuit to ensure that the system responds to the blocking output pulse in time when overload occurs and the inverter is short-circuited, avoiding equipment damage and protecting the circuit.

[0046] The preferred embodiments of the present invention are described in detail above, but the present invention is not limited thereto. Within the technical concept of the present invention, the technical solution of the present invention can be subjected to a variety of simple modifications, including the combination of various technical features in any other suitable manner, and these simple modifications and combinations should also be regarded as the contents disclosed by the present invention and belong to the protection scope of the present invention.

Claims

1. A three-phase inverter control system, characterized in that: It comprises a main control chip circuit (1), a power drive chip circuit (2) and a three-phase inverter two-resistance sampling circuit (3) which are connected in sequence; The output end of the two-resistance sampling circuit (3) of the three-phase inverter is respectively connected to the input end of the voltage sampling circuit (5) and the input end of the overcurrent protection circuit (7), and the output end of the voltage sampling circuit (5) and the output end of the overcurrent protection circuit (7) are respectively connected to the input end of the main control chip circuit (1); The input end of the main control chip circuit (1) is also connected to a magnetic encoder interface circuit (6); The three-phase inverter two-resistance sampling circuit (3) comprises three-phase inverter bridge arms, wherein the lower bridge arm of one phase inverter bridge arm is connected in series with a first sampling resistor, and the lower bridge arms of the other two phase inverter bridge arms are connected in series with a second sampling resistor, and the first sampling resistor and the second sampling resistor are grounded respectively.

2. A three-phase inverter control system according to claim 1, characterized in that: The first sampling resistor and the second sampling resistor are respectively connected in parallel with a filter capacitor.

3. A three-phase inverter control system according to claim 1, characterized in that: The overcurrent protection circuit (7) comprises a comparison circuit, a protection current value setting circuit and an output filter circuit, wherein the input end of the comparison circuit is respectively connected to the output end of the two-resistance sampling circuit (3) of the three-phase inverter and the protection current value setting circuit, and the output filter circuit is connected to the output end of the comparison circuit.

4. A three-phase inverter control system according to claim 3, characterized in that: The comparison circuit includes a voltage comparator and a resistor connected to an input terminal of the voltage comparator; The protection current value setting circuit includes a voltage dividing resistor and a filter capacitor connected in parallel with the voltage dividing resistor.

5. A three-phase inverter control system according to claim 4, characterized in that: The output end of the voltage comparator is also connected to a pull-up resistor.

6. A three-phase inverter control system according to claim 1, characterized in that: The main control chip circuit (1) and the power drive chip circuit (2), and the main control chip circuit (1) and the magnetic encoder interface circuit (6) communicate via SPI.

7. A three-phase inverter control system according to claim 1 or 6, characterized in that: The main control chip circuit (1) comprises a main control chip, to which a crystal oscillator circuit, a reset circuit and a voltage-stabilized power supply are connected.

8. A three-phase inverter control system according to claim 1, characterized in that: The voltage sampling circuit (5) comprises a DC bus voltage sampling circuit and an inverter three-phase output voltage sampling circuit.

9. A three-phase inverter control system according to claim 1, characterized in that: The magnetic encoder interface circuit (6) comprises a magnetic encoder chip, to which a voltage stabilizing diode and a decoupling capacitor connected in parallel with the voltage stabilizing diode are connected.

10. A three-phase inverter control method, characterized in that: The three-phase inverter control system according to any one of claims 1 to 9 comprises the following steps: The three-phase current of the inverter is collected through the first sampling resistor and the second sampling resistor of the two-resistance sampling circuit (3) of the three-phase inverter respectively, and fed back to the main control chip circuit (1) through the power drive chip circuit (2); The motor rotor position is collected through the magnetic encoder interface circuit (6), and the inverter three-phase output voltage is collected through the voltage sampling circuit (5) and fed back to the main control chip circuit (1); The main control chip circuit (1) outputs a PWM control signal to control the inverter according to the collected three-phase current of the inverter, the motor rotor position and the three-phase output voltage information of the inverter; When the three-phase current of the inverter exceeds the safety threshold, the overcurrent protection circuit (7) outputs a feedback signal to the main control chip circuit (1), and the main control chip circuit (1) controls the three-phase inverter to stop working.

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