A contactor coil current control circuit and on-off device

Abstract

The application discloses a contactor coil current control circuit and a contactor, and belongs to the field of contactor control technology. The contactor coil current control circuit comprises an execution circuit, a current sampling circuit, a comparison circuit, a self-locking circuit and a PWM control circuit. The execution circuit is used for turning on and off a main circuit under the control of a PWM signal. The current sampling circuit is used for obtaining a first voltage signal representing the size of the contactor coil current. The comparison circuit is used for comparing the first voltage signal with a set value and outputting a duty cycle adjustment signal. When the power supply voltage is turned on, the duty cycle adjustment signal is invalid when the first voltage signal is less than the set value, and the duty cycle adjustment signal is automatically switched to be valid when the first voltage signal increases to the set value. The self-locking circuit is used for locking the duty cycle adjustment signal when the duty cycle adjustment signal is automatically switched to be valid. The PWM control circuit is used for outputting the PWM signal according to the received duty cycle adjustment signal. The duty cycle when the duty cycle adjustment signal is invalid is greater than the duty cycle when the duty cycle adjustment signal is valid. The application can quickly and adaptively adjust and reduce the coil current and reduce the useless loss.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of contactor coil control, in particular to a control circuit for contactor coil current and a control method thereof. BACKGROUND

[0002] Contactor coil control instruments are indispensable in our life. Such devices are devices that generate a magnetic field through the energization of a coil to produce current in the coil, and then the current produces a magnetic field to attract the built-in armature to act. Such devices are widely used in industrial control and civilian life, and have the advantages of convenience, speed, control automation, etc.

[0003] With the increasing demand for energy consumption, more and more attention is paid to the energy saving of contactors. The traditional contactor is composed of a coil and a core, and the working process is divided into three stages: attraction stage, holding stage and off stage. In the attraction stage, the coil passes through a large attraction current to generate a large enough electromagnetic force to attract the contactor contact. In the holding stage, the holding current of the coil only needs to be one tenth of the attraction current, and the excessive holding current will increase the loss of the coil. The existing energy-saving methods on the market are divided into two types: one is a double-coil energy-saving method, and the other is an electronic energy-saving method.

[0004] The electronic energy-saving method is to add a large current at the moment of contactor attraction, and keep the large current for a period of time to ensure that the contactor contact is reliably attracted and closed. After a period of time, the coil current is automatically switched to a small current to keep the contactor contact closed. The coil current of the contactor will become small due to the increase of the coil resistance caused by the heat generated by the coil at high temperature, which may cause the contactor to malfunction. In addition, the coil current will be lower than the normal set current under low voltage input conditions, which may also cause the contactor to malfunction. Therefore, the time of the large current attraction stage is set relatively long. In fact, when the contactor is under rated voltage input, the coil still has a long time in the large current state after attraction, as shown in the coil current. The loss of this period of time is a useless loss, which will greatly increase the temperature rise of the coil during attraction, especially in the case of frequent on-off of the contactor, the temperature rise of the coil is greatly affected by the attraction current. Figure 4

[0005] ​In recent years, some solutions have been proposed to address the loss of this part. The auxiliary contact of the contactor can reflect the state of the contactor contact closing and opening. The auxiliary contact sends a signal to the controller to convert the large current of the coil into a small current. This method has limited application range due to the need for auxiliary contact cooperation, and the cost of auxiliary contact is high. Another method is to use a single-chip microcomputer to detect the decrease in coil current (contact movement, inductance increases, current decreases). This method is feasible when used in direct current voltage input, but in alternating current input, the alternating current voltage itself will zero, causing the coil current to decrease with the input voltage, making this method undetectable. SUMMARY

[0006] Therefore, the technical problem to be solved by the present application is to provide a contactor coil current control circuit and a on-off device, which at least partially solves one of the technical problems in the prior art.

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

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

[0009] An execution circuit is used to connect in the main loop and turn on and off the main loop under the control of a PWM signal;

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

[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 is automatically switched to valid; the peak value of the contactor coil current before the contactor is attracted is a first current, and the peak value of the contactor coil current after the contactor is attracted is a second current, and 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 is used to lock the duty cycle adjustment signal to the valid state when the duty cycle adjustment signal is automatically switched to valid;

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

[0014] Preferably, the execution circuit comprises 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 comprises a TL431 and a first bias circuit, an anode of the TL431 is connected to the other end of the current sampling circuit, a reference end of the TL431 is connected to one end of the current sampling circuit, one end of the first bias circuit is used to input a supply voltage, and the other end of the first bias circuit and a cathode of the TL431 are connected together to output the duty ratio adjustment signal.

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

[0019] Preferably, the duty ratio adjustment signal is low-level valid, and the self-locking circuit comprises 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 a source of the PMOS tube Q2 are connected together to input a supply voltage, the other end of the second bias circuit, a gate of the PMOS tube Q2 and a drain of the NMOS tube Q1 are all connected to the output end of the comparison circuit, a drain of the PMOS tube Q2 is connected to a gate of the NMOS tube Q1 and one end of the third bias circuit at the same time, a 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 comprises a control chip SCM1501.

[0022] As a second aspect of the present application, an embodiment technical scheme of a switch device is provided as follows:

[0023] A kind of on-off device, including contactor, contactor coil is used to be connected in series in the main circuit between power supply voltage and ground, and one end is used to be connected with the power supply voltage, the other end is used to be connected with the ground, wherein: it further includes the contactor coil current control circuit of any one of the above first aspect.

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

[0025] (1) The embodiment of the present application utilizes that the contactor coil current peak value before contactor attraction is less than the contactor coil current peak value after attraction, reasonably sets the comparison threshold of first voltage signal, so that the comparison circuit can automatically identify the contactor contact closure, after the contactor contact closure, can quickly self-adapting adjustment reduces coil current, greatly reduces the coil power consumption, significantly improves the temperature rise when the contactor coil frequently switches on and off.

[0026] (2) The embodiment of the present application can be realized by simple hardware circuit that duty cycle adjustment signal automatic switching is effective and is kept by self-locking circuit, so as to not need single-chip microcomputer processing, low in cost, strong in anti-interference and high in reliability. BRIEF DESCRIPTION OF DRAWINGS

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

[0028] Figure 2 It is a specific circuit diagram of the contactor coil current control circuit of the present application;

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

[0030] Figure 4 The coil current waveform of the traditional control circuit. DETAILED DESCRIPTION

[0031] It should be noted that the embodiments in the present application and the features in the embodiments can be combined with each other without conflict.

[0032] In order to enable the personnel in the art to better understand the present application scheme, the technical solutions in the embodiments of the present application will be described clearly and completely in conjunction with the drawings in the embodiments of the present application. Obviously, the described embodiments are only a part of the embodiments of the present application, not all. Based on the embodiments in the present application, all other embodiments obtained by the person skilled in the art without creative labor should belong to 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 drawings are used to distinguish similar objects, and do not necessarily have to describe a specific order or sequence. It should be understood that the data thus used can be interchanged under appropriate circumstances, so as to describe the embodiments of the present application. In addition, the terms "include" and "have" and any variations thereof are intended to cover non-exclusive inclusion, for example, a process, method, system, product or device including a series of steps or units does not have to be limited to only those steps or units clearly listed, but can include other steps or units not clearly listed or inherent to these processes, methods, products or devices.

[0034] It should be understood that, in the specification, claims and drawings, when it is described that a step is connected to another step, the step can be directly connected to the other step, or connected to the other step through a third step; when it is described that an element / unit is "connected" to another element / unit, the element / unit can be "directly connected" to the other element / unit, or "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 reference signs in the drawings represent the same or similar parts, and thus repeated description thereof will be omitted. Some block diagrams shown in the drawings are functional entities, which do not necessarily have to correspond to physically or logically independent entities. These functional entities can be implemented by software, or in one or more hardware modules or integrated circuits, or in different network and / or processor devices and / or microcontroller devices.

[0036] Figure 1 For the principle block diagram of the contactor coil current control circuit of the present application, please refer to Figure 1 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 with the power supply voltage VIN and the other end is used to be connected with the ground. The diode D1 is used to make the coil current freewheeling. The contactor coil current control circuit comprises:

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

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

[0039] The comparison circuit is used for comparing the first voltage signal with a set value and outputting a duty cycle adjustment signal, when the power 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 is automatically switched to be valid; the peak value of the contactor coil current before the contactor is attracted is the first current, the peak value of the contactor coil current after the contactor is attracted is the second current, and 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] The self-locking circuit is used for locking the duty cycle adjustment signal to be in the valid state when the duty cycle adjustment signal is automatically switched to be valid.

[0041] The PWM control circuit is connected to the output end of the comparison circuit, and the PWM control circuit is used for outputting a 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 the first duty cycle; when the duty cycle adjustment signal is valid, the duty cycle of the PWM signal is the second duty cycle; the first duty cycle is greater than the second duty cycle.

[0042] The inventor of the present application proposes the theoretical basis of the present application as follows:

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

[0044] (Formula 1);

[0045] Wherein: 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; v is the movement speed of the contact; χ is the stroke of the contact movement.

[0046] The inventor of the present application notices 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 voltage VIN is constant, that is, U in formula 1 is constant, therefore the sum of the first and second voltage components on the right side of formula 1 will increase, thereby it is guessed that i in formula 1 must increase, so that the maximum value of the coil L1 current before the contact is attracted must be less than the maximum value of the coil L1 current after the contact is attracted.

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

[0048] Based on the above verification conclusions, the inventors of this application, by utilizing the fact that the peak current of the contactor coil before contactor engagement is less than the peak current of the contactor coil after engagement, reasonably set the comparison threshold of the first voltage signal, enabling the comparison circuit to automatically identify contactor contact closure. They then rebuilt the prototype for testing and obtained the following results. Figure 3 The waveform shown is based on Figure 3 As can be seen from the waveform, the circuit starts after the power supply voltage VIN is turned on, and the control timing is as follows:

[0049] Before the contactor engages, 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 but less than the second current. Therefore, during this stage, the first voltage signal is always less than the set value, and the duty cycle adjustment signal is always ineffective. The PWM control circuit drives the execution circuit with a larger duty cycle. After the coil L1 is energized, the current gradually increases, generating electromagnetic force and causing the contactor to engage. See the waveform diagram below. Figure 3 The waveform to the left of the central vertical line;

[0050] After the contactor engages, when the first voltage signal increases to the set value, the duty cycle adjustment signal automatically switches to active under the action of the comparator circuit and is maintained in this active 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 energized with a small current, and the contactor adaptively enters the holding stage. See the waveform diagram below. Figure 3 The waveform to the right of the vertical line.

[0051] As can be seen from the waveform analysis above, the contactor coil current control circuit of this embodiment utilizes the fact that the peak value of the contactor coil current before the contactor is energized is less than the peak value of the contactor coil current after energization, and reasonably sets the comparison threshold of the first voltage signal so that the comparison circuit can automatically identify the contactor contact closure. Thus, the contactor coil current control circuit can quickly and adaptively switch to low current holding, which greatly reduces 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 The execution circuit includes a controllable switching transistor K1.

[0053] Preferably, the controllable switch K1 is a MOSFET 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 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 comprises a TL431 and a first bias circuit, the anode of the TL431 is connected to the other end of the current sampling circuit, the reference end is connected to the one end of the current sampling circuit, and the one end of the first bias circuit is used for inputting the power supply voltage, and the other end is connected to the cathode of the TL431 to output a duty cycle adjustment signal.

[0056] Further, the first bias circuit comprises a resistor R2.

[0057] As a specific implementation circuit of the contactor coil current control circuit, please refer to Figure 2 The duty cycle adjustment signal is low level effective, the self-locking circuit comprises an NMOS tube Q1, a PMOS tube Q2, a second bias circuit and a third bias circuit, the one end of the second bias circuit and the source of the PMOS tube Q2 are connected together to input the 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 circuit, the drain of the PMOS tube Q2 is connected to the gate of the NMOS tube Q1 and the 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 for being connected to the ground.

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

[0059] As a specific implementation circuit of the contactor coil current control circuit, please refer to Figure 2 The PWM control circuit comprises a control chip SCM1501, which is a contactor power saving control chip developed by Jinshengyang Company.

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

[0061] When the power supply voltage VIN is powered on, the resistor R1 continuously samples the current, and when the coil current does not reach the set current (i.e., 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 continuously increases. Before the contactor contact is closed, the coil current does not reach the set current because the kinetic energy of the contactor contact is continuously increasing. After the contactor contact is closed, the contactor contact no longer moves, and the coil current rises to reach the set current. At this time, the voltage across the resistor R1 is greater than the reference voltage of the TL431, the TL431 is turned on, the level of the cathode of the TL431 is changed from high level to low level, the MOS tube Q2 in the self-locking circuit is turned on, the voltage across the resistor R4 is pulled up, the MOS tube Q1 is turned on, the voltage of the cathode of the TL431 is continuously pulled down, and the control chip receives a low level signal to reduce the duty cycle, so that the coil current is reduced. Through this control mode, the contactor contact closure is automatically identified, and the small current holding is quickly and adaptively switched, so that the coil temperature rise is greatly reduced.

[0062] The application also provides a kind of on-off device, including contactor, contactor coil is used for being connected in series in main circuit between power supply voltage and ground, and one end is used for being connected with power supply voltage, the other end is used for being connected with ground, it is special in: still including the contactor coil current control circuit of any one of the above.

[0063] The above is only the embodiment of the present application, it needs to be pointed out specially, the above embodiment should not be regarded as the limitation of the present application, for the ordinary skilled person in the art, without departing from the spirit and scope of the present application, can also make a number of improvements and refinements, these improvements and refinements should also be regarded as the protection scope of the present application.

Claims

1. A contactor coil current control circuit, the contactor coil being used in a main circuit which is connected in series between a power supply voltage and a ground, and one end of which is connected to the power supply voltage and the other end of which is connected to the ground, characterized by, The contactor coil current control circuit comprises: an execution circuit connected in the main circuit and used for turning on and off the main circuit under the control of a PWM signal; a current sampling circuit having one end connected to the other end of the contactor coil through the execution circuit and the other end grounded, and used for obtaining a first voltage signal representing the magnitude of the contactor coil current; a comparison circuit used for comparing the first voltage signal with a set value and outputting a duty cycle adjustment signal, wherein when the power voltage is turned on, the duty cycle adjustment signal is invalid when the first voltage signal is less than the set value, and the duty cycle adjustment signal is automatically switched to be valid when the first voltage signal increases to the set value; the peak value of the contactor coil current before the contactor is attracted is a first current, the peak value of the contactor coil current after the contactor is attracted is a second current, and the set value is set such that the contactor coil current is greater than the first current and less than the second current when the first voltage signal increases to the set value; a self-locking circuit used for locking the duty cycle adjustment signal to be valid when the duty cycle adjustment signal is automatically switched to be valid; a PWM control circuit having a receiving end connected to the output end of the comparison circuit, and used for outputting the PWM signal according to the received duty cycle adjustment signal, wherein the duty cycle of the PWM signal is a first duty cycle when the duty cycle adjustment signal is invalid, and the duty cycle of the PWM signal is a second duty cycle when the duty cycle adjustment signal is valid; and the first duty cycle is greater than the second duty cycle.

2. The contactor coil current control circuit of claim 1, wherein: The execution circuit comprises a controllable switch tube.

3. The contactor coil current control circuit of claim 2, wherein: The controllable switch tube is a MOS tube or an IGBT.

4. The contactor coil current control circuit of claim 1, wherein: The current sampling circuit comprises a resistor or a current sensor.

5. The contactor coil current control circuit of claim 1, wherein: The comparison circuit comprises a TL431 and a first bias circuit, wherein the anode of the TL431 is connected to the other end of the current sampling circuit, the reference end of the TL431 is connected to one end of the current sampling circuit, one end of the first bias circuit is used for inputting a supply voltage, and the other end of the first bias circuit and the cathode of the TL431 are connected together to output the duty cycle adjustment signal.

6. The contactor coil current control circuit of claim 5, wherein: The first bias circuit comprises a resistor.

7. The contactor coil current control circuit of claim 1, wherein: The duty cycle adjustment signal is low in level and valid, and the self-locking circuit comprises 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 to input a 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 circuit, the drain of the PMOS tube Q2 is 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 for being connected to the ground.

8. The contactor coil current control circuit of claim 7, wherein: The second bias circuit comprises a resistor, and / or the third bias circuit comprises a resistor.

9. The contactor coil current control circuit of claim 1, wherein: The PWM control circuit comprises a control chip SCM1501.

10. A switching device comprising a contactor, a coil of which is intended to be connected in series in a main circuit between a supply voltage and ground, one end for connection to said supply voltage and the other end for connection to said ground, characterized in that: The application further comprises the contactor coil current control circuit according to any one of claims 1 to 9.

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