Low-cost driving circuit for variable frequency water pump

Abstract

The utility model discloses a low-cost drive circuit for a variable frequency water pump, which comprises a DSP (Digital Signal Processor) chip, a half-bridge drive circuit and an overcurrent detection circuit, and the half-bridge drive circuit comprises a half-bridge drive chip U4, a half-bridge drive chip U7 and a half-bridge drive chip U8; the overcurrent detection circuit comprises a two-way operational amplifier U31A and a comparator U31B; the DSP chip outputs SPWM signals UH, UL, VH, VL, WH and WL to the half-bridge driving chip U4, the half-bridge driving chip U7 and the half-bridge driving chip U8. According to the utility model, overcurrent of the motor driving circuit can be protected, and the situation that a faucet and a water conveying pipeline are damaged due to overlarge current in the use process can be effectively reduced, so that the risk of waste of electric energy and water resources is reduced.

Description

Technical Field

[0001] The utility model relates to the technical field of drive circuits, in particular to a low-cost drive circuit for a variable-frequency water pump. Background Art

[0002] The shortage of water resources and energy is an important factor restricting the economic development of our country. Saving water and energy is the basic national policy for the sustainable development of our social economy. Since the 1990s, the United States has applied variable-frequency water-saving and energy-saving technologies to systems such as translational, shaft-rotating sprinklers and pipeline irrigation, but their prices are expensive. At that time, in the urban and rural water supply and water pump pumping systems in our country, the motor operated at the rated speed and supplied water at the rated water output.

[0003] The variable-frequency water pump drive circuit in the prior art lacks the function of overcurrent automatic protection. When the water consumption decreases or during the low water consumption period, the current is too high. When the current of the drive motor circuit is large, overcurrent protection cannot be carried out in time, so the faucets and water delivery pipes are often damaged, which also causes waste of electric energy and water resources and cannot meet the use requirements. Considering the above situation, we have proposed a low-cost drive circuit for a variable-frequency water pump. Content of the Utility Model

[0004] The purpose of the utility model is to solve the defects existing in the prior art, and to propose a low-cost drive circuit for a variable-frequency water pump.

[0005] In order to achieve the above purpose, the utility model adopts the following technical scheme:

[0006] A low-cost drive circuit for a variable-frequency water pump includes a DSP chip, a half-bridge drive circuit and an overcurrent detection circuit. The half-bridge drive circuit includes a half-bridge drive chip U4, a half-bridge drive chip U7 and a half-bridge drive chip U8;

[0007] The overcurrent detection circuit includes a dual-channel operational amplifier U31A and a comparator U31B;

[0008] The DSP chip outputs SPWM signals UH, UL, VH, VL, WH, WL to the half-bridge drive chips U4, U7 and U8.

[0009] Preferably, one end of a capacitor C3, a 15V power supply, and the positive electrode of a diode D2 are electrically connected to pin 1 of the half-bridge drive chip U4. The other end of the capacitor C3 is grounded. The negative electrode of the diode D2 is electrically connected to one end of a resistor R4. The other end of the resistor R4 is electrically connected to pin 8 of the half-bridge drive chip U4. Pins 2 and 3 of the half-bridge drive chip U4 are respectively electrically connected to SPWM signals UH and UL. Pin 4 of the half-bridge drive chip U4 is grounded. One end of a resistor R7 and the negative electrode of a diode D5 are electrically connected to pin 7 of the half-bridge drive chip U4. One end of a bootstrap capacitor E1 is electrically connected to the other end of the resistor R4. The other end of the bootstrap capacitor E1 is electrically connected to pin 6 of the half-bridge drive chip U4. Pin 6 of the half-bridge drive chip U4 is also electrically connected to one end of a resistor R8, one end of a capacitor C19, pin 3 of an IGBT single transistor Q1, and the U phase of the drive motor. Pin 1 of the IGBT single transistor Q1 is electrically connected to the other end of the capacitor C19, the other end of the resistor R8, the positive electrode of the diode D5, and the other end of the resistor R7. One end of a resistor R14 and the negative electrode of a diode D13 are electrically connected to pin 5 of the half-bridge drive chip U4. One end of a resistor R21, one end of a capacitor C22, and pin 1 of an IGBT single transistor Q6 are electrically connected to the other end of the resistor R14 and the positive electrode of the diode D13. Pin 2 of the IGBT single transistor Q6 is electrically connected to pin 3 of the IGBT single transistor Q1. One end of the same resistor R31 is electrically connected to the other end of the resistor R21, the other end of the capacitor C22, and pin 3 of the IGBT single transistor Q6. The other end of the resistor R31 is electrically connected to one end of a resistor R27, one end of a resistor R29, and one end of a resistor R30. The other ends of the resistor R27, the resistor R29, and the resistor R30 are all grounded.

[0010] Preferably, one end of a capacitor C4, a 15V power supply, and the positive electrode of a diode D3 are electrically connected to pin 1 of the half-bridge drive chip U7. The other end of the capacitor C4 is grounded. The negative electrode of the diode D3 is electrically connected to one end of a resistor R5. The other end of the resistor R5 is electrically connected to pin 8 of the half-bridge drive chip U7. Pins 2 and 3 of the half-bridge drive chip U7 are respectively electrically connected to the SPWM signals VH and VL. Pin 4 of the half-bridge drive chip U7 is grounded. One end of a resistor R9 and the negative electrode of a diode D8 are electrically connected to pin 7 of the half-bridge drive chip U7. One end of a bootstrap capacitor E2 is electrically connected to the other end of the resistor R5. The other end of the bootstrap capacitor E2 is electrically connected to pin 6 of the half-bridge drive chip U7. Pin 6 of the half-bridge drive chip U7 is also electrically connected to one end of a resistor R10, one end of a capacitor C20, pin 3 of an IGBT single transistor Q2, and the V phase of the drive motor. Pin 1 of the IGBT single transistor Q2 is electrically connected to the other end of the capacitor C20, the other end of the resistor R10, the positive electrode of the diode D8, and the other end of the resistor R9. One end of a resistor R15 and the negative electrode of a diode D14 are electrically connected to pin 5 of the half-bridge drive chip U7. One end of a resistor R22, one end of a capacitor C26, and pin 1 of an IGBT single transistor Q7 are electrically connected to the other end of the resistor R15 and the positive electrode of the diode D14. Pin 2 of the IGBT single transistor Q7 is electrically connected to pin 3 of the IGBT single transistor Q2. One end of the same resistor R33 is electrically connected to the other end of the resistor R22, the other end of the capacitor C26, and pin 3 of the IGBT single transistor Q7. The other end of the resistor R33 is electrically connected to one end of a resistor R27, one end of a resistor R29, and one end of a resistor R30.

[0011] Preferably, one end of a capacitor C17, a 15V power supply, and the positive electrode of a diode D4 are electrically connected to pin 1 of the half-bridge drive chip U8. The other end of the capacitor C17 is grounded. The negative electrode of the diode D4 is electrically connected to one end of a resistor R6. The other end of the resistor R6 is electrically connected to pin 8 of the half-bridge drive chip U8. Pins 2 and 3 of the half-bridge drive chip U8 are respectively electrically connected to SPWM signals WH and WL. Pin 4 of the half-bridge drive chip U8 is grounded. One end of a resistor R12 and the negative electrode of a diode D12 are electrically connected to pin 7 of the half-bridge drive chip U8. The other end of the resistor R6 is electrically connected to one end of a bootstrap capacitor E3. The other end of the bootstrap capacitor E3 is electrically connected to pin 6 of the half-bridge drive chip U8. Pin 6 of the half-bridge drive chip U8 is also electrically connected to one end of a resistor R13, one end of a capacitor C21, pin 3 of an IGBT single transistor Q3, and the W phase of a drive motor. Pin 1 of the IGBT single transistor Q3 is electrically connected to the other end of the capacitor C21, the other end of the resistor R13, the positive electrode of the diode D12, and the other end of the resistor R12. One end of a resistor R16 and the negative electrode of a diode D15 are electrically connected to pin 5 of the half-bridge drive chip U8. The other end of the resistor R16 and the positive electrode of the diode D15 are electrically connected to one end of a resistor R24, one end of a capacitor C27, and pin 1 of an IGBT single transistor Q8. Pin 2 of the IGBT single transistor Q8 is electrically connected to pin 3 of the IGBT single transistor Q3. The other end of the resistor R24, the other end of the capacitor C27, and pin 3 of the IGBT single transistor Q8 are electrically connected to one end of the same resistor R34. The other end of the resistor R34 is electrically connected to one end of a resistor R27, one end of a resistor R29, and one end of a resistor R30.

[0012] Preferably, one end of a resistor R26 and one end of a resistor R35 are electrically connected to pin 3 of the dual operational amplifier U31A. The other end of the resistor R35 is grounded. One end of a resistor R39 and one end of a resistor R38 are electrically connected to pin 2 of the dual operational amplifier U31A. The other end of the resistor R39 is grounded. The other end of the resistor R38 is electrically connected to pin 1 of the dual operational amplifier U31A. One end of a capacitor C45 is electrically connected to pin 1 of the dual operational amplifier U31A. The other end of the capacitor C45 is grounded. One end of a capacitor C28 and one end of a capacitor C35 are electrically connected to pin 8 of the dual operational amplifier U31A. The other end of the capacitor C28, the other end of the capacitor C35, and pin 4 of the dual operational amplifier U31A are all grounded.

[0013] Preferably, one end of a resistor R40 and one end of a resistor R42 are electrically connected to pin 5 of the comparator U31B. The other end of the resistor R42 is grounded. The other end of the resistor R40 is electrically connected to a 3.3V voltage. One end of a resistor R41 is electrically connected to pin 7 of the comparator U31B. The other end of the resistor R41 is electrically connected to a 3.3V voltage.

[0014] Preferably, the resistors R7 and R14 are the gate drive resistors of the IGBT single transistors Q1 and Q6, and the size of the resistors can be adjusted according to the actual effect; the diodes D5 and D13 can accelerate the discharge speed of the GS junction capacitance when the IGBT single transistors Q1 and Q6 are turned off.

[0015] Preferably, the resistors R31, R33 and R34 are all current detection resistors. By sampling the voltage across the resistors, the currents of the U phase, V phase and W phase of the drive motor can be calculated respectively. The overcurrent protection function of the circuit can be realized by setting the resistance value after the parallel connection of the resistors R27, R29 and R30.

[0016] Compared with the existing technology, the beneficial effects of the present utility model are as follows:

[0017] 1. By setting the half-bridge drive circuit, the phase current of the motor can be calculated by sampling the voltage across the resistors, so that the overcurrent protection function of the circuit can be realized;

[0018] 2. By setting the overcurrent detection circuit, the overcurrent protection function of the motor drive circuit can be realized. Through the above two overcurrent protections, the situation that the faucet and the water delivery pipeline are damaged due to excessive current during use can be effectively reduced, thereby reducing the risk of waste of electric energy and water resources;

[0019] The present utility model can protect the overcurrent of the motor drive circuit, effectively reduce the situation that the faucet and the water delivery pipeline are damaged due to excessive current during use, thereby reducing the risk of waste of electric energy and water resources. Description of the Drawings

[0020] Figure 1 is the circuit diagram of a half-bridge drive circuit for a low-cost variable-frequency water pump drive circuit proposed by the present utility model;

[0021] Figure 2 is the circuit diagram of a half-bridge drive chip U4 for a low-cost variable-frequency water pump drive circuit proposed by the present utility model;

[0022] Figure 3 is the circuit diagram of a half-bridge drive chip U7 for a low-cost variable-frequency water pump drive circuit proposed by the present utility model;

[0023] Figure 4 is the circuit diagram of a half-bridge drive chip U8 for a low-cost variable-frequency water pump drive circuit proposed by the present utility model;

[0024] Figure 5Circuit diagram of a dual operational amplifier U31A and a comparator U31B with low cost for a variable frequency water pump drive circuit proposed by the present utility model. Specific implementation manner

[0025] The following will clearly and completely describe the technical solutions in the embodiments of the present utility model with reference to the accompanying drawings in the embodiments of the present utility model. Obviously, the described embodiments are only a part of the embodiments of the present utility model, rather than all of the embodiments.

[0026] Refer to Figures 1-5 , a low-cost variable frequency water pump drive circuit, comprising a DSP chip, a half-bridge drive circuit and an overcurrent detection circuit. The half-bridge drive circuit includes a half-bridge drive chip U4, a half-bridge drive chip U7 and a half-bridge drive chip U8. The DSP chip outputs SPWM signals UH, UL, VH, VL, WH, WL to the half-bridge drive chips U4, U7 and U8.

[0027] One end of the capacitor C3, the 15V power supply, and the positive electrode of the diode D2 are electrically connected to the pin 1 of the half-bridge drive chip U4. The other end of the capacitor C3 is grounded. The negative electrode of the diode D2 is electrically connected to one end of the resistor R4. The other end of the resistor R4 is electrically connected to the pin 8 of the half-bridge drive chip U4. The pins 2 and 3 of the half-bridge drive chip U4 are respectively electrically connected to the SPWM signals UH and UL. The pin 4 of the half-bridge drive chip U4 is grounded. One end of the resistor R7 and the negative electrode of the diode D5 are electrically connected to the pin 7 of the half-bridge drive chip U4. The other end of the resistor R4 is electrically connected to one end of the bootstrap capacitor E1. The other end of the bootstrap capacitor E1 is electrically connected to the pin 6 of the half-bridge drive chip U4. The pin 6 of the half-bridge drive chip U4 is also electrically connected to one end of the resistor R8, one end of the capacitor C19, the pin 3 of the IGBT single transistor Q1, and the U phase of the drive motor. The pin 1 of the IGBT single transistor Q1 is electrically connected to the other end of the capacitor C19, the other end of the resistor R8, the positive electrode of the diode D5, and the other end of the resistor R7. One end of the resistor R14 and the negative electrode of the diode D13 are electrically connected to the pin 5 of the half-bridge drive chip U4. The other end of the resistor R14 and the positive electrode of the diode D13 are electrically connected to one end of the resistor R21, one end of the capacitor C22, and the pin 1 of the IGBT single transistor Q6. The pin 2 of the IGBT single transistor Q6 is electrically connected to the pin 3 of the IGBT single transistor Q1. The other end of the resistor R21, the other end of the capacitor C22, and the pin 3 of the IGBT single transistor Q6 are electrically connected to one end of the same resistor R31. The other end of the resistor R31 is electrically connected to one end of the resistor R27, one end of the resistor R29, and one end of the resistor R30. The other ends of the resistor R27, the resistor R29, and the resistor R30 are all grounded. The resistors R7 and R14 are the gate drive resistors of the IGBT single transistors Q1 and Q6, and the size of the resistors can be adjusted according to the actual effect; the diodes D5 and D13 can accelerate the discharge speed of the GS junction capacitance when the IGBT single transistors Q1 and Q6 are turned off;

[0028] One end of a capacitor C4, a 15V power supply, and the positive electrode of a diode D3 are electrically connected to pin 1 of a half-bridge drive chip U7. The other end of the capacitor C4 is grounded. The negative electrode of the diode D3 is electrically connected to one end of a resistor R5. The other end of the resistor R5 is electrically connected to pin 8 of the half-bridge drive chip U7. Pins 2 and 3 of the half-bridge drive chip U7 are electrically connected to SPWM signals VH and VL respectively. Pin 4 of the half-bridge drive chip U7 is grounded. One end of a resistor R9 and the negative electrode of a diode D8 are electrically connected to pin 7 of the half-bridge drive chip U7. One end of a bootstrap capacitor E2 is electrically connected to the other end of the resistor R5. The other end of the bootstrap capacitor E2 is electrically connected to pin 6 of the half-bridge drive chip U7. Pin 6 of the half-bridge drive chip U7 is also electrically connected to one end of a resistor R10, one end of a capacitor C20, pin 3 of an IGBT single transistor Q2, and the V phase of a driving motor. Pin 1 of the IGBT single transistor Q2 is electrically connected to the other end of the capacitor C20, the other end of the resistor R10, the positive electrode of the diode D8, and the other end of the resistor R9. One end of a resistor R15 and the negative electrode of a diode D14 are electrically connected to pin 5 of the half-bridge drive chip U7. The other end of the resistor R15 and the positive electrode of the diode D14 are electrically connected to one end of a resistor R22, one end of a capacitor C26, and pin 1 of an IGBT single transistor Q7. Pin 2 of the IGBT single transistor Q7 is electrically connected to pin 3 of the IGBT single transistor Q2. The other end of the resistor R22, the other end of the capacitor C26, and pin 3 of the IGBT single transistor Q7 are electrically connected to one end of the same resistor R33. The other end of the resistor R33 is electrically connected to one end of a resistor R27, one end of a resistor R29, and one end of a resistor R30;

[0029] Pin 1 of the half-bridge drive chip U8 is electrically connected to one end of the capacitor C17, the 15V power supply, and the positive electrode of the diode D4. The other end of the capacitor C17 is grounded. The negative electrode of the diode D4 is electrically connected to one end of the resistor R6. The other end of the resistor R6 is electrically connected to pin 8 of the half-bridge drive chip U8. Pins 2 and 3 of the half-bridge drive chip U8 are respectively electrically connected to the SPWM signals WH and WL. Pin 4 of the half-bridge drive chip U8 is grounded. Pin 7 of the half-bridge drive chip U8 is electrically connected to one end of the resistor R12 and the negative electrode of the diode D12. The other end of the resistor R6 is electrically connected to one end of the bootstrap capacitor E3. The other end of the bootstrap capacitor E3 is electrically connected to pin 6 of the half-bridge drive chip U8. Pin 6 of the half-bridge drive chip U8 is also electrically connected to one end of the resistor R13, one end of the capacitor C21, pin 3 of the IGBT single transistor Q3, and the W phase of the drive motor. Pin 1 of the IGBT single transistor Q3 is electrically connected to the other end of the capacitor C21, the other end of the resistor R13, the positive electrode of the diode D12, and the other end of the resistor R12. Pin 5 of the half-bridge drive chip U8 is electrically connected to one end of the resistor R16 and the negative electrode of the diode D15. The other end of the resistor R16 and the positive electrode of the diode D15 are electrically connected to one end of the resistor R24, one end of the capacitor C27, and pin 1 of the IGBT single transistor Q8. Pin 2 of the IGBT single transistor Q8 is electrically connected to pin 3 of the IGBT single transistor Q3. The other end of the resistor R24, the other end of the capacitor C27, and pin 3 of the IGBT single transistor Q8 are electrically connected to one end of the same resistor R34. The other end of the resistor R34 is electrically connected to one end of the resistor R27, one end of the resistor R29, and one end of the resistor R30. The resistors R31, R33, and R34 are all current-sensing resistors. By sampling the voltage across the resistors, the currents of the U phase, V phase, and W phase of the drive motor can be calculated respectively. By setting the resistance value of the parallel connection of the resistors R27, R29, and R30, the over-current protection function of the circuit can be realized. Among them, the 6 IGBT single transistors Q1, Q2, Q3, Q6, Q7, and Q8 all adopt the TO-263 surface mount package, which can greatly simplify the production process flow and improve the production efficiency;

[0030] The overcurrent detection circuit includes a dual operational amplifier U31A and a comparator U31B. One end of a resistor R26 and one end of a resistor R35 are electrically connected to pin 3 of the dual operational amplifier U31A. The other end of the resistor R35 is grounded. One end of a resistor R39 and one end of a resistor R38 are electrically connected to pin 2 of the dual operational amplifier U31A. The other end of the resistor R39 is grounded. The other end of the resistor R38 is electrically connected to pin 1 of the dual operational amplifier U31A. One end of a capacitor C45 is electrically connected to pin 1 of the dual operational amplifier U31A. The other end of the capacitor C45 is grounded. One end of a capacitor C28 and one end of a capacitor C35 are electrically connected to pin 8 of the dual operational amplifier U31A. The other end of the capacitor C28, the other end of the capacitor C35, and pin 4 of the dual operational amplifier U31A are all grounded.

[0031] One end of a resistor R40 and one end of a resistor R42 are electrically connected to pin 5 of the comparator U31B. The other end of the resistor R42 is grounded. The other end of the resistor R40 is electrically connected to a 3.3V voltage. One end of a resistor R41 is electrically connected to pin 7 of the comparator U31B. The other end of the resistor R41 is electrically connected to a 3.3V voltage. The utility model can protect the motor drive circuit from overcurrent, effectively reduce the damage of the faucet and the water delivery pipeline caused by excessive current during use, and thus reduce the risk of waste of electric energy and water resources.

[0032] Working principle: During use, the half-bridge drive chips U4, U7, and U8 are powered by a 15V voltage. The DSP chip outputs SPWM signals UH, UL, VH, VL, WH, and WL to the half-bridge drive chips U4, U7, and U8 to drive the U, V, and W three-phase electricity of the motor respectively. Taking the U-phase drive circuit as an example, after power-on, the IGBT single transistor Q6 is controlled to conduct, and the 15V power supply will charge the bootstrap capacitor E1 through the current loop composed of the diode D2, the resistor R4, the bootstrap capacitor E1, the IGBT single transistor Q6, the resistor R31, the resistor R27, the resistor R29, and the resistor R30. The resistors R7 and R14 are the gate drive resistors of the IGBT single transistors Q1 and Q6, and the size of the resistor can be adjusted according to the actual effect.

[0033] Meanwhile, diode D5 and diode D13 can accelerate the discharge speed of the GS junction capacitance of IGBT single transistor Q1 and IGBT single transistor Q6 when they turn off. The 6 IGBT single transistors Q1, Q2, Q3, Q6, Q7, and Q8 all adopt TO-263 surface mount packages, which can greatly simplify the production process flow and improve production efficiency. Resistors R31, R33, and R34 are current sensing resistors. The motor phase current can be calculated by sampling the voltage across the resistors. The overcurrent protection function of the circuit can be realized by setting the resistance value of the parallel connection of resistors R27, R29, and R30.

[0034] Among them, comparator U31B is used as a comparator. The voltage at pin 6 of comparator U31B is compared with the voltage after voltage division by resistor R40 and resistor R42 from the 3.3V power supply. When the voltage at pin 6 is higher than the voltage at pin 5, pin 7 of comparator U31B will output a low level, otherwise pin 7 is set to a high level through pull-up resistor R41.

[0035] In addition, dual operational amplifier U31A is used as an amplifier. The voltage values on resistors R27, R29, and R30 are used as the input signals of the amplifier. The amplification factor of the amplifier is set by setting the resistance values of resistors R26, R35, R38, and R39. Capacitor C45 is a filter capacitor. The amplified voltage signal of dual operational amplifier U31A is filtered and then sent to comparator U31B for comparison. The FLT signal output by comparator U31B can be used as the input of the DSP chip to realize the overcurrent protection function of the motor drive circuit. Through the above two kinds of overcurrent protection, the situation that the faucet and the water delivery pipeline are damaged due to excessive current during use can be effectively reduced, thereby reducing the risk of waste of electric energy and water resources.

[0036] The above is only the preferred specific implementation mode of the present invention, but the protection scope of the present invention is not limited thereto. Any person skilled in the art within the technical scope disclosed by the present invention, according to the technical solution of the present invention and its inventive concept, makes equivalent substitutions or changes, and all should be covered by the protection scope of the present invention.

Claims

1. A low-cost variable frequency water pump drive circuit, including a DSP chip, a half-bridge drive circuit and an overcurrent detection circuit, characterized in that: The half-bridge driving circuit includes a half-bridge driving chip U4, a half-bridge driving chip U7 and a half-bridge driving chip U8; The overcurrent detection circuit includes a dual operational amplifier U31A and a comparator U31B; The DSP chip outputs SPWM signals UH, UL, VH, VL, WH, and WL to half-bridge driver chips U4, U7, and U8.

2. A low-cost variable frequency water pump drive circuit according to claim 1, characterized in that: Pin 1 of the half-bridge driver chip U4 is electrically connected to one end of a capacitor C3, a 15V power supply and a positive electrode of a diode D2, the other end of the capacitor C3 is grounded, the negative electrode of the diode D2 is electrically connected to one end of a resistor R4, the other end of the resistor R4 is electrically connected to pin 8 of the half-bridge driver chip U4, pins 2 and 3 of the half-bridge driver chip U4 are electrically connected to SPWM signals UH and UL respectively, pin 4 of the half-bridge driver chip U4 is grounded, pin 7 of the half-bridge driver chip U4 is electrically connected to one end of a resistor R7 and a negative electrode of a diode D5, the other end of the resistor R4 is electrically connected to one end of a bootstrap capacitor E1, the other end of the bootstrap capacitor E1 is electrically connected to pin 6 of the half-bridge driver chip U4, pin 6 of the half-bridge driver chip U4 is also electrically connected to one end of a resistor R8, one end of a capacitor C19, pin 3 of an IGBT single tube Q1 and the U phase of the drive motor, IGBT Pin 1 of the single tube Q1 is electrically connected to the other end of the capacitor C19, the other end of the resistor R8, the positive electrode of the diode D5 and the other end of the resistor R7. Pin 5 of the half-bridge driver chip U4 is electrically connected to one end of the resistor R14 and the negative electrode of the diode D13. The other end of the resistor R14 and the positive electrode of the diode D13 are electrically connected to one end of the resistor R21, one end of the capacitor C22 and pin 1 of the IGBT single tube Q6. Pin 2 of the IGBT single tube Q6 is electrically connected to pin 3 of the IGBT single tube Q1. The other end of the resistor R21, the other end of the capacitor C22 and the pin 3 of the IGBT single tube Q6 are electrically connected to one end of the same resistor R31. The other end of the resistor R31 is electrically connected to one end of the resistor R27, one end of the resistor R29 and one end of the resistor R30. The other end of the resistor R27, the other end of the resistor R29 and the other end of the resistor R30 are all grounded.

3. A low-cost variable frequency water pump drive circuit according to claim 2, characterized in that: Pin 1 of the half-bridge driver chip U7 is electrically connected to one end of a capacitor C4, a 15V power supply and a positive electrode of a diode D3, the other end of the capacitor C4 is grounded, the negative electrode of the diode D3 is electrically connected to one end of a resistor R5, the other end of the resistor R5 is electrically connected to pin 8 of the half-bridge driver chip U7, pins 2 and 3 of the half-bridge driver chip U7 are electrically connected to SPWM signals VH and VL respectively, pin 4 of the half-bridge driver chip U7 is grounded, pin 7 of the half-bridge driver chip U7 is electrically connected to one end of a resistor R9 and a negative electrode of a diode D8, the other end of the resistor R5 is electrically connected to one end of a bootstrap capacitor E2, the other end of the bootstrap capacitor E2 is electrically connected to pin 6 of the half-bridge driver chip U7, and pin 6 of the half-bridge driver chip U7 is also electrically connected to one end of a resistor R10, one end of a capacitor C20, and the negative electrode of an IGBT single tube Q2. Pin 3 is electrically connected to the V phase of the drive motor, pin 1 of the IGBT single tube Q2 is electrically connected to the other end of the capacitor C20, the other end of the resistor R10, the positive electrode of the diode D8 and the other end of the resistor R9, pin 5 of the half-bridge drive chip U7 is electrically connected to one end of the resistor R15 and the negative electrode of the diode D14, the other end of the resistor R15 and the positive electrode of the diode D14 are electrically connected to one end of the resistor R22, one end of the capacitor C26 and pin 1 of the IGBT single tube Q7, pin 2 of the IGBT single tube Q7 is electrically connected to pin 3 of the IGBT single tube Q2, the other end of the resistor R22, the other end of the capacitor C26 and pin 3 of the IGBT single tube Q7 are electrically connected to one end of the same resistor R33, and the other end of the resistor R33 is electrically connected to one end of the resistor R27, one end of the resistor R29 and one end of the resistor R30.

4. A low-cost variable frequency water pump drive circuit according to claim 3, characterized in that: Pin 1 of the half-bridge driver chip U8 is electrically connected to one end of a capacitor C17, a 15V power supply and a positive electrode of a diode D4, the other end of the capacitor C17 is grounded, the negative electrode of the diode D4 is electrically connected to one end of a resistor R6, the other end of the resistor R6 is electrically connected to pin 8 of the half-bridge driver chip U8, pins 2 and 3 of the half-bridge driver chip U8 are electrically connected to SPWM signals WH and WL respectively, pin 4 of the half-bridge driver chip U8 is grounded, pin 7 of the half-bridge driver chip U8 is electrically connected to one end of a resistor R12 and a negative electrode of a diode D12, the other end of the resistor R6 is electrically connected to one end of a bootstrap capacitor E3, the other end of the bootstrap capacitor E3 is electrically connected to pin 6 of the half-bridge driver chip U8, and pin 6 of the half-bridge driver chip U8 is also electrically connected to one end of a resistor R13, one end of a capacitor C21, and an IGBT single tube Q3 Pin 3 of the IGBT single tube Q3 is electrically connected to the W phase of the drive motor, pin 1 of the IGBT single tube Q3 is electrically connected to the other end of the capacitor C21, the other end of the resistor R13, the positive electrode of the diode D12 and the other end of the resistor R12, pin 5 of the half-bridge drive chip U8 is electrically connected to one end of the resistor R16 and the negative electrode of the diode D15, the other end of the resistor R16 and the positive electrode of the diode D15 are electrically connected to one end of the resistor R24, one end of the capacitor C27 and pin 1 of the IGBT single tube Q8, pin 2 of the IGBT single tube Q8 is electrically connected to pin 3 of the IGBT single tube Q3, the other end of the resistor R24, the other end of the capacitor C27 and pin 3 of the IGBT single tube Q8 are electrically connected to one end of the same resistor R34, and the other end of the resistor R34 is electrically connected to one end of the resistor R27, one end of the resistor R29 and one end of the resistor R30.

5. The low-cost variable frequency water pump drive circuit according to claim 1 is characterized in that: Pin 3 of the dual-channel operational amplifier U31A is electrically connected to one end of the resistor R26 and one end of the resistor R35, and the other end of the resistor R35 is grounded. Pin 2 of the dual-channel operational amplifier U31A is electrically connected to one end of the resistor R39 and one end of the resistor R38, and the other end of the resistor R39 is grounded. The other end of the resistor R38 is electrically connected to pin 1 of the dual-channel operational amplifier U31A. Pin 1 of the dual-channel operational amplifier U31A is electrically connected to one end of the capacitor C45, and the other end of the capacitor C45 is grounded. Pin 8 of the dual-channel operational amplifier U31A is electrically connected to one end of the capacitor C28 and one end of the capacitor C35, and the other end of the capacitor C28, the other end of the capacitor C35 and pin 4 of the dual-channel operational amplifier U31A are all grounded.

6. A low-cost variable frequency water pump drive circuit according to claim 1, characterized in that: Pin 5 of the comparator U31B is electrically connected to one end of a resistor R40 and one end of a resistor R42, the other end of the resistor R42 is grounded, the other end of the resistor R40 is electrically connected to a 3.3V voltage, and pin 7 of the comparator U31B is electrically connected to one end of a resistor R41, the other end of the resistor R41 is electrically connected to a 3.3V voltage.

7. A low-cost variable frequency water pump drive circuit according to claim 2, characterized in that: The resistor R7 and the resistor R14 are gate drive resistors of the IGBT single tube Q1 and the IGBT single tube Q6, and the size of the resistor can be adjusted according to the actual effect; the diode D5 and the diode D13 can accelerate the discharge speed of the GS junction capacitance when the IGBT single tube Q1 and the IGBT single tube Q6 are turned off.

8. A low-cost variable frequency water pump drive circuit according to claim 4, characterized in that: The resistors R31, R33 and R34 are all current-sensing resistors. By sampling the voltages at both ends of the resistors, the currents of the U-phase, V-phase and W-phase of the drive motor can be calculated respectively. By setting the resistance values ​​of the resistors R27, R29 and R30 in parallel, the circuit overcurrent protection function can be realized.

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