Motor zero-cross detection circuit

Abstract

The utility model discloses a motor zero-cross detection circuit in the technical field of motor zero-cross detection, which comprises three drive circuits, each drive circuit is correspondingly connected with a protection circuit, each protection circuit is correspondingly connected with a detection circuit, and the drive circuits are connected with a motor M through the protection circuits. One protection circuit, one driving circuit and one detection circuit form one group, the three groups are respectively connected with the A, B and C phases of the three-phase power supply and are respectively connected with the three phase ends of the asynchronous motor, the protection circuits can effectively protect electronic devices of the whole circuit, the detection circuit detects the current zero crossing point of each phase of the motor, the circuit structure is simple, and the cost is low. Control is convenient and reliability is high.

Description

Technical Field

[0001] The utility model relates to a zero-crossing detection circuit in the technical field of motor zero-crossing detection. Background Art

[0002] To prevent current oscillation during the soft-start and energy-saving operation of asynchronous motor energy-saving control devices, real-time detection of the measurable power factor angle and a rational control strategy are necessary to suppress current oscillation. Therefore, the system must perform zero-crossing detection when the waveform transitions from the positive half-cycle to the negative half-cycle and passes through zero. Existing technologies typically use bidirectional thyristors or two thyristors connected in anti-parallel, and require bulky components such as pulse transformers. This results in a relatively complex circuit structure and low reliability. Utility Model Content

[0003] The utility model aims to provide a motor zero-crossing detection circuit with a simple circuit structure, convenient control and high reliability.

[0004] To achieve the above-mentioned purpose, the present invention provides a motor zero-crossing detection circuit, including three drive circuits, each drive circuit is correspondingly connected to a protection circuit, each protection circuit is correspondingly connected to a detection circuit, and the drive circuit is connected to the motor M via the protection circuit.

[0005] Compared with the prior art, the beneficial effect of the present invention lies in that one protection circuit, one drive circuit and one detection circuit form a group, with a total of three groups, which are respectively connected to the A, B, C phases of the three-phase power supply and are also respectively connected to the three terminals of the asynchronous motor. The protection circuit can effectively protect the electronic devices of the entire circuit, and the detection circuit detects the zero-crossing point of the current of each phase of the motor. The circuit structure is simple, the control is convenient, and the reliability is high.

[0006] As a further improvement of the present utility model, the drive circuit includes an optocoupler U1 and an optocoupler U2, pin 1 of the optocoupler U1 is connected to a +5V power supply, pin 3 of the optocoupler U1 is connected to pin 1 of the optocoupler U2, pin 2 of the optocoupler U2 is connected to the collector of the transistor Q1 via a resistor R2, the emitter of the transistor Q1 is grounded, the base of the transistor Q1 is connected to the soft start controller via a resistor R1, resistors R5 and R6 are connected in series between pin 6 and pin 4 of the optocoupler U2, pin 6 of the optocoupler U2 is connected to pin 4 of the optocoupler U1, and resistors R4 and R3 are connected in series between pin 6 and pin 4 of the optocoupler U1. Resistors R5 and R6 are connected in series between pin 6 and pin 4 of the optocoupler U2; pin 6 of the optocoupler U1 is connected to the gate of the thyristor T2 via resistor R7, the anode of the thyristor T2 is respectively connected to the motor, the cathode of the thyristor T1 and the detection circuit, the cathode of the thyristor T2 is respectively connected to the anode of the thyristor T1 and the three-phase power supply, the anode of the thyristor T1 is connected to one end of the resistor R9, the other end of the resistor R9 is connected to one end of the capacitor C1, the other end of the capacitor C1 is respectively connected to the cathode of the thyristor T1 and the anode of the thyristor T2, and the gate of the thyristor T1 is connected to pin 4 of the optocoupler U2.

[0007] During the positive half-wave of phase A, current flows through A+ and R7 to U1's pin 6, while thyristor T2 remains off. If the controller sends a high-level signal to the base of transistor Q1, Q1 turns on, and the connection between U1's pin 6 and U2's pin 4 is in conduction. At this point, the gate and cathode of thyristor T1 are forward biased, turning it on. Similarly, during the negative half-wave of phase A, T2 should be turned on, enabling subsequent zero-crossing detection.

[0008] As a further improvement of the present invention, the protection circuit includes diodes D1 and D2, the cathode of the diode D1 is connected to the gate of the thyristor T1, the anode of the diode D1 is connected to the cathode of the thyristor T1, and a resistor R8 is connected between the gate and cathode of the thyristor T1; the gate of the thyristor T2 is connected to the cathode of the diode D2, the anode of the diode D2 is connected to the cathode of the thyristor T2, and a resistor R10 is connected between the gate and cathode of the thyristor T2.

[0009] In this way, during the positive half-wave, the voltage drop of D2 applies a reverse voltage between the gate and cathode of thyristor T2, so thyristor T2 can reliably remain in the off state during this period, and can also effectively protect the thyristor.

[0010] As a further improvement of the present utility model, the detection circuit includes a resistor R11, one end of the resistor R11 is connected to the anode of the diode D2, the other end of the resistor R11 is respectively connected to the anode of the diode D3 and the cathode of the diode D4, the cathode of the diode D3 is connected to the cathode of the diode D5 and pin 2 of the high-gain coupler U3, the anode of the diode D4 is connected to the anode of the diode D6 and pin 3 of the high-gain coupler U3, the anode of the diode D5 is connected to the cathode of the diode D6 and the anode of the thyristor T2, pins 6 and 8 of the high-gain coupler U3 are connected, pin 8 of the high-gain coupler U3 is respectively connected to one end of the resistor R12 and one end of the capacitor C2, the other end of the resistor R12 is connected to the +5V power supply, the other end of the capacitor C2 is connected to pin 5 of the high-gain coupler U3, and pin 7 of the high-gain coupler U3 is grounded via the resistor R13.

[0011] In this way, the current zero crossing point can be accurately captured by the high-speed optocoupler U3. BRIEF DESCRIPTION OF THE DRAWINGS

[0012] Figure 1 This is the circuit block diagram of the utility model.

[0013] Figure 2 This is the circuit diagram of the utility model. DETAILED DESCRIPTION

[0014] The present invention is further described below with reference to the accompanying drawings:

[0015] like Figure 1-2 The motor zero-crossing detection circuit shown includes three drive circuits, each drive circuit is correspondingly connected to a protection circuit, each protection circuit is correspondingly connected to a detection circuit, and the drive circuit is connected to the motor M.

[0016] The drive circuit includes optocoupler U1 and optocoupler U2. Pin 1 of optocoupler U1 is connected to a +5V power supply, pin 3 of optocoupler U1 is connected to pin 1 of optocoupler U2, pin 2 of optocoupler U2 is connected to the collector of transistor Q1 via resistor R2, the emitter of transistor Q1 is grounded, and the base of transistor Q1 is connected to the soft start controller via resistor R1. Resistors R5 and R6 are connected in series between pin 6 and pin 4 of optocoupler U2, pin 6 of optocoupler U2 is connected to pin 4 of optocoupler U1, resistors R4 and R3 are connected in series between pin 6 and pin 4 of optocoupler U1, and resistors R5 and R6 are connected in series between pin 6 and pin 4 of optocoupler U2.

[0017] Pin 6 of the optocoupler U1 is connected to the gate of the thyristor T2 via the resistor R7. The anode of the thyristor T2 is connected to the motor, the cathode of the thyristor T1 and the detection circuit respectively. The cathode of the thyristor T2 is connected to the anode of the thyristor T1 and the three-phase power supply respectively. The anode of the thyristor T1 is connected to one end of the resistor R9. The other end of the resistor R9 is connected to one end of the capacitor C1. The other end of the capacitor C1 is connected to the cathode of the thyristor T1 and the anode of the thyristor T2 respectively. The gate of the thyristor T1 is connected to pin 4 of the optocoupler U2.

[0018] The protection circuit includes diodes D1 and D2. The cathode of diode D1 is connected to the gate of thyristor T1, the anode of diode D1 is connected to the cathode of thyristor T1, and a resistor R8 is connected between the gate and cathode of thyristor T1; the gate of thyristor T2 is connected to the cathode of diode D2, the anode of diode D2 is connected to the cathode of thyristor T2, and a resistor R10 is connected between the gate and cathode of thyristor T2.

[0019] The detection circuit includes a resistor R11, one end of which is connected to the anode of the diode D2, the other end of which is respectively connected to the anode of the diode D3 and the cathode of the diode D4, the cathode of the diode D3 is connected to the cathode of the diode D5 and pin 2 of the high-gain coupler U3, the anode of the diode D4 is connected to the anode of the diode D6 and pin 3 of the high-gain coupler U3, the anode of the diode D5 is connected to the cathode of the diode D6 and the anode of the thyristor T2, pins 6 and 8 of the high-gain coupler U3 are connected, pin 8 of the high-gain coupler U3 is respectively connected to one end of the resistor R12 and one end of the capacitor C2, the other end of the resistor R12 is connected to the +5V power supply, the other end of the capacitor C2 is connected to pin 5 of the high-gain coupler U3, and pin 7 of the high-gain coupler U3 is grounded via the resistor R13.

[0020] In the present invention, the zero-crossing detection circuit is divided into three paths, which are respectively connected to the A, B, C phases of the three-phase power supply, and are correspondingly connected to the three-phase connectors of the motor, and are also connected to the soft start controller.

[0021] During the positive half-wave of phase A, the current flows through A+, diode D, and R to pin 6. Due to the voltage drop of D, a reverse voltage of about 0.7V is applied between the gate and cathode of thyristor T, so thyristor T can reliably remain in the off state. If the controller sends a high-level signal to the base of transistor Q at this time, Q is turned on, and the connection between pin 6 of IC and pin 4 of IC is in the on state. At this time, the gate and cathode of I are forward biased, meeting the conduction condition of the thyristor, and T is turned on. Because the thyristor is a unidirectional conducting device, T should be turned on when triggered during the negative half-wave of phase A.

[0022] Taking phase A as an example, during the positive half-wave of phase A, current flows through A+ and R7 to pin 6 of U1. The voltage drop across D2 applies a reverse voltage between the gate and cathode of thyristor T2, reliably maintaining the OFF state. If the soft-start controller sends a high-level signal to the base of transistor Q1 at this time, Q1 turns on, and the area between pin 6 of optocoupler U1 and pin 4 of U2 is conductive. At this point, the gate and cathode of thyristor T1 are forward biased, turning on thyristor T1. Similarly, during the negative half-wave of phase A, when triggered, thyristor T2 turns on, while thyristor T1 turns off.

[0023] If thyristor T1 is turned on, the optocoupler U3 is turned off, and pin 6 of U3 outputs a high level. The current flow path is: A+, R11, D3, pin 2 of U3, pin 3 of U3, D6, A-; when T2 is turned on, the current flow path is: A-, D5, pin 2 of U3, pin 3 of U3, D4, R11, A+; if thyristors T1 and T2 are turned off, the optocoupler U3 is turned on, and pin 6 of U3 outputs a low level; in this way, the soft start controller can detect the level of pin 6 of U3 in real time to accurately detect the current zero crossing point.

[0024] The utility model has the advantages of simple circuit structure, convenient control and high reliability.

[0025] The present invention is not limited to the above-mentioned embodiments. On the basis of the technical solution disclosed herein, technicians in this field can make some substitutions and deformations of some technical features therein according to the disclosed technical content without creative labor, and these substitutions and deformations are all within the protection scope of the present invention.

Claims

1. A motor zero-crossing detection circuit, characterized in that: It includes three drive circuits, each drive circuit is correspondingly connected to a protection circuit, each protection circuit is correspondingly connected to a detection circuit, and the drive circuit is connected to the motor M.

2. A motor zero-crossing detection circuit according to claim 1, characterized in that: The drive circuit includes optocouplers U1 and U2. Pin 1 of optocoupler U1 is connected to a +5V power supply, pin 3 of optocoupler U1 is connected to pin 1 of optocoupler U2, pin 2 of optocoupler U2 is connected to the collector of transistor Q1 via resistor R2, the emitter of transistor Q1 is grounded, and the base of transistor Q1 is connected to a soft-start controller via resistor R1. Resistors R5 and R6 are connected in series between pin 6 and pin 4 of optocoupler U2, pin 6 of optocoupler U2 is connected to pin 4 of optocoupler U1, resistors R4 and R3 are connected in series between pin 6 and pin 4 of optocoupler U1, and resistors R5 and R6 are connected in series between pin 6 and pin 4 of optocoupler U2. Pin 6 of the optocoupler U1 is connected to the gate of the thyristor T2 via the resistor R7. The anode of the thyristor T2 is connected to the motor, the cathode of the thyristor T1 and the detection circuit respectively. The cathode of the thyristor T2 is connected to the anode of the thyristor T1 and the three-phase power supply respectively. The anode of the thyristor T1 is connected to one end of the resistor R9. The other end of the resistor R9 is connected to one end of the capacitor C1. The other end of the capacitor C1 is connected to the cathode of the thyristor T1 and the anode of the thyristor T2 respectively. The gate of the thyristor T1 is connected to pin 4 of the optocoupler U2.

3. A motor zero-crossing detection circuit according to claim 2, characterized in that: The protection circuit includes diodes D1 and D2. The cathode of diode D1 is connected to the gate of thyristor T1, the anode of diode D1 is connected to the cathode of thyristor T1, and a resistor R8 is connected between the gate and cathode of thyristor T1; the gate of thyristor T2 is connected to the cathode of diode D2, the anode of diode D2 is connected to the cathode of thyristor T2, and a resistor R10 is connected between the gate and cathode of thyristor T2.

4. A motor zero-crossing detection circuit according to claim 3, characterized in that: The detection circuit includes a resistor R11, one end of which is connected to the anode of the diode D2, the other end of which is respectively connected to the anode of the diode D3 and the cathode of the diode D4, the cathode of the diode D3 is connected to the cathode of the diode D5 and pin 2 of the high-gain coupler U3, the anode of the diode D4 is connected to the anode of the diode D6 and pin 3 of the high-gain coupler U3, the anode of the diode D5 is connected to the cathode of the diode D6 and the anode of the thyristor T2, pins 6 and 8 of the high-gain coupler U3 are connected, pin 8 of the high-gain coupler U3 is respectively connected to one end of the resistor R12 and one end of the capacitor C2, the other end of the resistor R12 is connected to the +5V power supply, the other end of the capacitor C2 is connected to pin 5 of the high-gain coupler U3, and pin 7 of the high-gain coupler U3 is grounded via the resistor R13.

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