Contactor coil current control circuit and on-off device

Abstract

The invention discloses a contactor coil current control circuit and an on-off device, and the circuit comprises an execution circuit which is used for connecting and disconnecting a main loop under the control of a PWM signal; the current sampling circuit is used for acquiring a first voltage signal representing the current of the contactor coil; the comparison circuit is used for comparing the first voltage signal with a set value and outputting a duty ratio adjusting signal, and after the power supply voltage is switched on, when the first voltage signal is smaller than the set value, the duty ratio adjusting signal is invalid; when the first voltage signal is increased to a set value, the duty ratio adjusting signal is automatically switched to be effective; the self-locking circuit is used for locking the duty ratio adjusting signal when the duty ratio adjusting signal is automatically switched to be effective; and the PWM control circuit is used for outputting a PWM signal according to the received duty ratio adjusting signal, and the duty ratio when the duty ratio adjusting signal is invalid is greater than the duty ratio when the duty ratio adjusting signal is valid. According to the invention, the coil current can be rapidly and adaptively adjusted and reduced, and useless loss is reduced.

Description

Technical Field

[0001] The invention relates to the field of contactor coil control, in particular to a control circuit of a contactor coil current and a control method and switching device thereof. Background Art

[0002] Contactors and other coil control instruments are indispensable in our lives. They are devices that generate current in the coil by energizing the coil, which then generates a magnetic field and attracts the built-in armature to operate through magnetic force. Such devices are widely used in industrial control and civilian life, and have the advantages of convenience, speed, and automatic control.

[0003] As the demand for energy consumption becomes higher and higher, more and more attention is paid to the energy saving of contactors. Traditional contactors are composed of coils and iron cores, and the working process is divided into three stages: the pull-in stage, the holding stage, and the shut-off stage. In the pull-in stage, the coil generates a large enough electromagnetic force to pull the contactor contacts in through a large pull-in current. In the holding stage, the holding current of the coil only needs to be one-tenth of the pull-in current. Excessive holding current will increase the loss of the coil. There are two existing energy-saving methods on the market, one is the double-coil energy-saving method, and the other is the electronic energy-saving method.

[0004] The electronic energy-saving method is to add a large current at the moment the contactor is closed, and keep the large current for a period of time to ensure that the contactor contacts are reliably closed; after the high current is maintained for a period of time, the coil current automatically switches to a small current to keep the contactor contacts closed. Under high temperature, the internal resistance of the coil of the contactor with this technology will increase, causing the coil current to decrease, which may cause the contactor to fail to work properly. Under low voltage input conditions, the coil current will be lower than the normal set current, which may also cause the contactor to fail to operate normally. Therefore, the high current closing stage time is set to be relatively long. In fact, when the contactor is input at rated voltage, its coil is still in a high current state for a long time after closing, such as Figure 4 As shown in the coil current, after the contactor is closed, the high current lasts for a long time. The loss during this period is useless loss, which will greatly increase the temperature rise of the coil when it is closed. Especially when the contactor is frequently turned on and off, the temperature rise of the coil is greatly affected by the closing current.

[0005] In recent years, some solutions have been proposed for this part of the loss. The contactor has auxiliary contacts that can reflect the state of the contactor contact closing and opening. The auxiliary contacts are used as signals to the controller to convert the large coil current into a small current. This method must be coordinated with auxiliary contacts, so the scope of application is limited, and the cost of auxiliary contacts is high. There is also a method of detecting the decrease in coil current through a single-chip microcomputer (contact movement, increased inductance, and decreased current). This method is feasible when DC voltage is input, but when AC input is used, the AC voltage itself will pass zero, causing the coil current to decrease as the input voltage decreases, resulting in this method being unable to detect. Summary of the invention

[0006] In view of this, the technical problem to be solved by the present invention is to provide a contactor coil current control circuit and a switching device, which can at least solve one of the technical problems existing in the prior art to a certain extent.

[0007] As a first aspect of the present invention, the embodiment and technical solution of the contactor coil current control circuit provided is as follows:

[0008] A contactor coil current control circuit, wherein the contactor coil is used to be connected in series in a main loop between a power supply voltage and a ground, and one end is used to be connected to the power supply voltage and the other end is used to be connected to the ground, wherein the contactor coil current control circuit comprises:

[0009] An execution circuit, connected in the main circuit, for switching the main circuit on and off under the control of a PWM signal;

[0010] A current sampling circuit, one end of which is used to be connected to the other end of the contactor coil through the execution circuit, and the other end is used to be grounded, and the current sampling circuit is used to obtain a first voltage signal representing the current size of the contactor coil;

[0011] A comparison circuit is used to compare the first voltage signal with a set value and output a duty cycle adjustment signal. When the power supply voltage is turned on, when the first voltage signal is less than the set value, the duty cycle adjustment signal is invalid; when the first voltage signal increases to the set value, the duty cycle adjustment signal automatically switches to be valid; before the contactor is closed, the peak value of the contactor coil current is a first current, and after the contactor is closed, the peak value of the contactor coil current is a second current. The set value is set so that when the first voltage signal increases to the set value, the contactor coil current is greater than the first current and less than the second current;

[0012] A self-locking circuit, used for locking the duty cycle adjustment signal to a valid state when the duty cycle adjustment signal automatically switches to a valid state;

[0013] A PWM control circuit, whose receiving end is connected to the output end of the comparison control circuit, and the PWM control circuit is used to output the PWM signal according to the received duty cycle adjustment signal: when the duty cycle adjustment signal is invalid, the duty cycle of the PWM signal is a first duty cycle; when the duty cycle adjustment signal is valid, the duty cycle of the PWM signal is a second duty cycle; the first duty cycle is greater than the second duty cycle.

[0014] Preferably, the execution circuit includes a controllable switch tube.

[0015] Preferably, the controllable switch tube is a MOS tube or an IGBT.

[0016] Preferably, the current sampling circuit comprises a resistor or a current sensor.

[0017] Preferably, the comparison circuit includes TL431 and a first bias circuit, the anode of the TL431 is connected to the other end of the current sampling circuit, and the reference end is connected to one end of the current sampling circuit, one end of the first bias circuit is used to input the power supply voltage, and the other end is connected to the cathode of the TL431 to output the duty cycle adjustment signal.

[0018] Preferably, the first bias circuit comprises a resistor.

[0019] Preferably, the duty cycle adjustment signal is low level effective, the self-locking circuit includes an NMOS tube Q1, a PMOS tube Q2, a second bias circuit and a third bias circuit, one end of the second bias circuit and the source of the PMOS tube Q2 are connected together for inputting a power supply voltage, the other end of the second bias circuit, the gate of the PMOS tube Q2 and the drain of the NMOS tube Q1 are all connected to the output end of the comparison control circuit, the drain of the PMOS tube Q2 is simultaneously connected to the gate of the NMOS tube Q1 and one end of the third bias circuit, and the source of the NMOS tube Q1 and the other end of the third bias circuit are both used to be connected to the ground.

[0020] Preferably, the second bias circuit comprises a resistor; and / or the third bias circuit comprises a resistor.

[0021] Preferably, the PWM control circuit includes a control chip SCM1501.

[0022] As a second aspect of the present invention, the technical solution of the embodiment of the on-off device provided is as follows:

[0023] A switching device includes a contactor, wherein the contactor coil is used to be connected in series in a main circuit between a power supply voltage and a ground, and one end is used to be connected to the power supply voltage and the other end is used to be connected to the ground, wherein: it also includes the contactor coil current control circuit described in any one of the first aspects above.

[0024] Compared with the prior art, this application has the following beneficial effects:

[0025] (1) The embodiment of the present invention utilizes that the peak current of the contactor coil before the contactor is closed is smaller than the peak current of the contactor coil after the contactor is closed, and reasonably sets the comparison threshold of the first voltage signal, so that the comparison circuit can automatically identify that the contactor contacts are closed. After the contactor contacts are closed, the coil current can be quickly and adaptively adjusted to be reduced, the power consumption of the coil is greatly reduced, and the temperature rise of the contactor coil when the machine is frequently turned on and off is significantly improved.

[0026] (2) In the embodiment of the present invention, the duty cycle adjustment signal automatically switches to be valid and is maintained by the self-locking circuit, which can be implemented by a simple hardware circuit, thereby eliminating the need for single-chip microcomputer processing, and has low cost, strong anti-interference and high reliability. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Figure 1 It is a principle block diagram of the contactor coil current control circuit of the present invention;

[0028] Figure 2 A specific circuit diagram of the contactor coil current control circuit of the present invention;

[0029] Figure 3 The coil current waveform of the control circuit of this application;

[0030] Figure 4 Conventional control circuit coil current waveform. DETAILED DESCRIPTION

[0031] It should be noted that, in the absence of conflict, the embodiments and features in the embodiments of the present application may be combined with each other.

[0032] In order to enable those skilled in the art to better understand the solution of the present application, the technical solution in the embodiments of the present application will be clearly and completely described below in conjunction with the drawings in the embodiments of the present application. Obviously, the described embodiments are only part of the embodiments of the present application, not all of the embodiments. Based on the embodiments in the present application, all other embodiments obtained by ordinary technicians in this field without creative work should fall within the scope of protection of the present application.

[0033] It should be noted that the terms "first", "second", etc. in the specification and claims of the present application and the above-mentioned drawings are used to distinguish similar objects, and are not necessarily used to describe a specific order or sequential order. It should be understood that the data used in this way can be interchanged where appropriate, so that the embodiments of the present application are described here. In addition, the terms "including" and "having" and any of their variations are intended to cover non-exclusive inclusions, for example, the process, method, system, product or equipment comprising a series of steps or units is not necessarily limited to those steps or units clearly listed, but may include other steps or units that are not clearly listed or inherent to these processes, methods, products or equipment.

[0034] It should be understood that, in the specification, claims and drawings, when a step is described as being connected to another step, the step may be directly connected to the other step, or be connected to the other step through a third step; when an element / unit is described as being "connected" to another element / unit, the element / unit may be "directly connected" to the other element / unit, or be "connected" to the other element / unit through a third element / unit.

[0035] In addition, the drawings of the present disclosure are only schematic diagrams of the present disclosure and are not necessarily drawn to scale. The same symbols in the drawings represent the same or similar parts, and thus repeated descriptions thereof will be omitted. Some of the block diagrams shown in the drawings are functional entities and do not necessarily correspond to physically or logically independent entities. These functional entities can be implemented using software, or implemented in one or more hardware modules or integrated circuits, or implemented in different networks and / or processor devices and / or microcontrollers.

[0036] Figure 1 For the principle block diagram of the contactor coil current control circuit of the present invention, please refer to Figure 1 , wherein the contactor coil L1 is used to be connected in series in the main circuit between the power supply voltage VIN and the ground, and one end is used to be connected to the power supply voltage VIN and the other end is used to be connected to the ground, and the role of the diode D1 is to carry out the coil current freewheeling, wherein the contactor coil current control circuit includes:

[0037] An execution circuit is used to be connected in the main circuit and to switch the main circuit on and off under the control of a PWM signal;

[0038] A current sampling circuit, one end of which is used to be connected to the other end of the contactor coil through the execution circuit, and the other end is used to be grounded, and the current sampling circuit is used to obtain a first voltage signal representing the current size of the contactor coil;

[0039] A comparison circuit is used to compare the first voltage signal with a set value and output a duty cycle adjustment signal. When the power supply voltage is turned on, when the first voltage signal is less than the set value, the duty cycle adjustment signal is invalid; when the first voltage signal increases to the set value, the duty cycle adjustment signal automatically switches to be valid; before the contactor is closed, the peak value of the contactor coil current is the first current, and after the contactor is closed, the peak value of the contactor coil current is the second current. The set value is set so that when the first voltage signal increases to the set value, the contactor coil current is greater than the first current and less than the second current;

[0040] A self-locking circuit is used to lock the duty cycle adjustment signal into a valid state when the duty cycle adjustment signal automatically switches to a valid state;

[0041] A PWM control circuit, whose receiving end is connected to the output end of the comparison control circuit, is used to output a PWM signal according to a received duty cycle adjustment signal: when the duty cycle adjustment signal is invalid, the duty cycle of the PWM signal is a first duty cycle; when the duty cycle adjustment signal is valid, the duty cycle of the PWM signal is a second duty cycle; the first duty cycle is greater than the second duty cycle.

[0042] The inventor of this application proposes the following theoretical basis for the present invention:

[0043] The contactor electromagnetic system has the following voltage balance equation:

[0044]

[0045] Among them: U is the voltage across the coil L1; i is the current in the coil L1; R is the actual resistance value of the coil L1; L is the inductance of the coil L1; t is the time; ν is the movement speed of the contact; χ is the travel of the contact.

[0046] The inventor of the present application noticed that when the contactor is closed, it no longer has kinetic energy, that is, the third voltage component on the right side of Formula 1 is zero. Since the power supply voltage VIN remains unchanged, that is, U in Formula 1 remains unchanged, the sum of the first voltage component and the second voltage component on the right side of Formula 1 will increase. It is thus speculated that i in Formula 1 will inevitably increase, so that the maximum value of the coil L1 current of the contactor before the contacts are attracted must be smaller than the maximum value of the coil L1 current after they are attracted.

[0047] After building a prototype, it was measured Figure 4 In the waveform shown, the horizontal axis is time, and the vertical axis is the current in coil L1. The current values ​​of the four scale lines on the vertical axis are 140mA, 2.14A, 4.14A, and 6.14A from small to large. The waveform on the left side of the vertical line is the current waveform in coil L1 before the contactor is closed, and the waveform on the right side of the vertical line is the current waveform in coil L1 after the contactor is closed. The peak value on the left side is smaller than the peak value on the right side, which verifies the above guess.

[0048] According to the above verification conclusion, the inventor of the present application uses the fact that the peak current of the contactor coil before the contactor is closed is smaller than the peak current of the contactor coil after the contactor is closed to reasonably set the comparison threshold of the first voltage signal so that the comparison circuit can automatically identify the contactor contact closure. The prototype was rebuilt for testing and the following results were obtained. Figure 3 The waveform shown is based on Figure 3 As can be seen from the waveform, after the power supply voltage VIN is turned on, the circuit starts and the control timing is as follows:

[0049] Before the contactor is closed, the contactor coil current is always less than or equal to the first current. Due to the setting of the set value, when the first voltage signal increases to the set value, the contactor coil current is greater than the first current and less than the second current. Therefore, the first voltage signal is always less than the set value at this stage, and the duty cycle adjustment signal is always invalid. The PWM control circuit drives the execution circuit with a larger duty cycle. After the coil L1 is excited, the current gradually increases, generating electromagnetic force and causing the contactor to close. The waveform diagram is shown in Figure 3 The waveform to the left of the middle vertical line;

[0050] After the contactor is closed, when the first voltage signal increases to the set value, under the action of the comparison circuit, the duty cycle adjustment signal automatically switches to valid and is maintained in this valid state by the self-locking circuit. The PWM control circuit outputs a small duty cycle to drive the execution circuit. At this time, the contactor coil L1 is continuously excited with a small current, and the contactor adaptively enters the holding stage. The waveform diagram is shown in Figure 3 The waveform to the right of the middle vertical line.

[0051] From the above waveform analysis, it can be seen that the contactor coil current control circuit of this embodiment utilizes the fact that the contactor coil current peak value before the contactor is attracted is smaller than the contactor coil current peak value after it is attracted, and reasonably sets the comparison threshold of the first voltage signal, so that the comparison circuit can automatically identify that the contactor contact is closed, so that the contactor coil current control circuit can quickly and adaptively switch to a small current to maintain, thereby greatly reducing the coil temperature rise.

[0052] As a specific implementation circuit of the contactor coil current control circuit of the present invention, please refer to Figure 2 , wherein the execution circuit includes a controllable switch tube K1.

[0053] Preferably, the controllable switch tube K1 is a MOS tube or an IGBT.

[0054] As a specific implementation circuit of the contactor coil current control circuit of the present invention, please refer to Figure 2 , wherein the current sampling circuit includes a resistor R1 or a current sensor.

[0055] As a specific implementation circuit of the contactor coil current control circuit of the present invention, please refer to Figure 2The comparison circuit includes TL431 and a first bias circuit, wherein the anode of TL431 is connected to the other end of the current sampling circuit, and the reference end is connected to one end of the current sampling circuit. One end of the first bias circuit is used to input the power supply voltage, and the other end is connected to the cathode of TL431 to output the duty cycle adjustment signal.

[0056] Furthermore, the first bias circuit includes a resistor R2.

[0057] As a specific implementation circuit of the contactor coil current control circuit of the present invention, please refer to Figure 2 , wherein the duty cycle adjustment signal is low level effective, the self-locking circuit includes an NMOS tube Q1, a PMOS tube Q2, a second bias circuit and a third bias circuit, one end of the second bias circuit and the source of the PMOS tube Q2 are connected together for inputting a power supply voltage, the other end of the second bias circuit, the gate of the PMOS tube Q2 and the drain of the NMOS tube Q1 are all connected to the output end of the comparison control circuit, the drain of the PMOS tube Q2 is simultaneously connected to the gate of the NMOS tube Q1 and one end of the third bias circuit, and the source of the NMOS tube Q1 and the other end of the third bias circuit are both used to be connected to the ground.

[0058] Further, the second bias circuit includes a resistor R3; and / or the third bias circuit includes a resistor R4.

[0059] As a specific implementation circuit of the contactor coil current control circuit of the present invention, please refer to Figure 2 The PWM control circuit includes a control chip SCM1501, which is a contactor power-saving control chip developed by Goldensun Corporation.

[0060] Figure 2 The working principle of the circuit is analyzed as follows:

[0061] The power supply voltage VIN is powered on, and the resistor R1 continuously samples the current. When the current of the coil L1 does not reach the set current (that is, when the first voltage signal does not reach the set value), the control chip U1 outputs a large duty cycle to drive the MOS tube, and the coil current continues to increase. Before the contactor contacts are closed, the coil current will not reach the set current due to the continuous increase in the kinetic energy of the contactor contacts. After the contactor contacts are closed, the contactor contacts no longer move, and the coil current rises. When the set current is reached, the voltage across the resistor R1 is greater than the reference voltage of TL431, and TL431 is turned on, and the level of its cathode changes from a high level to a low level. The MOS tube Q2 in the self-locking circuit is turned on, and the voltage across the resistor R4 is pulled up. The MOS tube Q1 is turned on, and the voltage of the cathode of TL431 is continuously pulled down. After receiving the low-level signal, the control chip reduces the duty cycle to reduce the coil current. Through this control method, the contactor contact closure is automatically identified, and the small current is quickly and adaptively switched to maintain, which greatly reduces the temperature rise of the coil.

[0062] The present invention also provides an on-off device, including a contactor, wherein the contactor coil is used to be connected in series in a main circuit between a power supply voltage and ground, and one end is used to be connected to the power supply voltage and the other end is used to be connected to the ground, wherein: it also includes any of the above-mentioned contactor coil current control circuits.

[0063] The above are merely implementation modes of the present invention. It should be particularly pointed out that the above implementation modes should not be regarded as limitations of the present invention. For ordinary technicians in this technical field, several improvements and modifications can be made without departing from the spirit and scope of the present invention. These improvements and modifications should also be regarded as within the scope of protection of the present invention.

Claims

1. A contactor coil current control circuit, wherein the contactor coil is used to be connected in series in a main circuit between a power supply voltage and a ground, and one end is used to be connected to the power supply voltage and the other end is used to be connected to the ground, characterized in that: The contactor coil current control circuit comprises: An execution circuit, connected in the main circuit, for switching the main circuit on and off under the control of a PWM signal; A current sampling circuit, one end of which is used to be connected to the other end of the contactor coil through the execution circuit, and the other end is used to be grounded, and the current sampling circuit is used to obtain a first voltage signal representing the current size of the contactor coil; A comparison circuit is used to compare the first voltage signal with a set value and output a duty cycle adjustment signal. When the power supply voltage is turned on, when the first voltage signal is less than the set value, the duty cycle adjustment signal is invalid; when the first voltage signal increases to the set value, the duty cycle adjustment signal automatically switches to be valid; before the contactor is closed, the peak value of the contactor coil current is a first current, and after the contactor is closed, the peak value of the contactor coil current is a second current. The set value is set so that when the first voltage signal increases to the set value, the contactor coil current is greater than the first current and less than the second current; A self-locking circuit, used for locking the duty cycle adjustment signal to a valid state when the duty cycle adjustment signal automatically switches to a valid state; A PWM control circuit, whose receiving end is connected to the output end of the comparison control circuit, and the PWM control circuit is used to output the PWM signal according to the received duty cycle adjustment signal: when the duty cycle adjustment signal is invalid, the duty cycle of the PWM signal is a first duty cycle; when the duty cycle adjustment signal is valid, the duty cycle of the PWM signal is a second duty cycle; the first duty cycle is greater than the second duty cycle.

2. The contactor coil current control circuit according to claim 1, characterized in that: The execution circuit includes a controllable switch tube.

3. The contactor coil current control circuit according to claim 2, characterized in that: The controllable switch tube is a MOS tube or an IGBT.

4. The contactor coil current control circuit according to claim 1, characterized in that: The current sampling circuit includes a resistor or a current sensor.

5. The contactor coil current control circuit according to claim 1, characterized in that: The comparison circuit includes TL431 and a first bias circuit, wherein the anode of the TL431 is connected to the other end of the current sampling circuit, and the reference end is connected to one end of the current sampling circuit; one end of the first bias circuit is used to input a power supply voltage, and the other end is connected to the cathode of the TL431 to output the duty cycle adjustment signal.

6. The contactor coil current control circuit according to claim 5, characterized in that: The first bias circuit includes a resistor.

7. The contactor coil current control circuit according to claim 1, characterized in that: The duty cycle adjustment signal is effective at a low level. The self-locking circuit includes an NMOS tube Q1, a PMOS tube Q2, a second bias circuit and a third bias circuit. One end of the second bias circuit and the source of the PMOS tube Q2 are connected together for inputting a power supply voltage. The other end of the second bias circuit, the gate of the PMOS tube Q2 and the drain of the NMOS tube Q1 are all connected to the output end of the comparison control circuit. The drain of the PMOS tube Q2 is simultaneously connected to the gate of the NMOS tube Q1 and one end of the third bias circuit. The source of the NMOS tube Q1 and the other end of the third bias circuit are both used to be connected to the ground.

8. The contactor coil current control circuit according to claim 1, characterized in that: The second bias circuit includes a resistor; and / or the third bias circuit includes a resistor.

9. The contactor coil current control circuit according to claim 1, characterized in that: The PWM control circuit includes a control chip SCM1501.

10. A switching device, comprising a contactor, wherein the contactor coil is connected in series in a main circuit between a power supply voltage and a ground, and one end of the contactor coil is connected to the power supply voltage and the other end of the contactor coil is connected to the ground, characterized in that: It also includes the contactor coil current control circuit as described in any one of claims 1 to 9.

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