CN115020153A

CN115020153A - Control method and control circuit for minimum on-time

Info

Publication number: CN115020153A
Application number: CN202210613119.0A
Authority: CN
Inventors: 胡涛; 康博
Original assignee: Mornsun Guangzhou Science and Technology Ltd
Current assignee: Mornsun Guangzhou Science and Technology Ltd
Priority date: 2022-05-31
Filing date: 2022-05-31
Publication date: 2022-09-06

Abstract

The invention relates to the field of contactor control equipment, and provides a control method for self-adaptive minimum on-time in a contactor control scheme. Namely, in the case of adopting contactors with different specifications and different switching tubes, the controller can adaptively generate the optimal minimum conduction time. The problems that in the prior art, when the input voltage range is enlarged and the input voltage is continuously increased, the coil loss is increased and the power factor is reduced due to unreasonable minimum conduction time are solved, and the possibility that the whole system generates audio noise is increased due to the fact that the frequency reduction mode is controlled to enter in advance due to the improper minimum conduction time. The invention further expands the input voltage range by self-adapting to the minimum conduction time, provides an accurate frequency reduction control signal and simultaneously meets the requirements of low power consumption and high power factor of the contactor.

Description

Control method and control circuit for minimum on-time

Technical Field

The invention relates to the field of contactor control equipment, in particular to a control method and a control circuit for minimum conduction time in a control circuit of a contactor.

Background

At present, in a control circuit of the contactor, a PWM mode is generally adopted to control a current in a coil of the contactor, so that the magnitude of the current in the coil of the contactor can be maintained at a constant value in a holding stage of the contactor within a narrow input voltage range, thereby effectively reducing loss. For different types of contactors, a conventional PWM control scheme generally sets a fixed minimum on-time to ensure complete turn-on of a switching tube in a control circuit. In the scheme, the set minimum conduction time cannot reach the most appropriate time under the influence of factors such as the turn-on delay of a switching tube of the control part, the output junction capacitance, the coil turn-to-turn capacitance of a coil of the contactor and the like. When the preset minimum conduction time is too long, when the input voltage rises, and the conduction time reaches the minimum conduction time, the coil current is increased along with the rise of the input voltage due to the limitation of the minimum conduction time, and the power consumption is also increased; when the preset minimum conduction time is too short, and when the input voltage is increased, and the conduction time reaches the minimum conduction time, because the control port of the switch tube has the input capacitor, according to the capacitor charge-discharge relation:

it can be seen that, when the capacitor C and the charging current i are fixed, the voltage U of the capacitor varies in proportion to the charging time t, and the switching tube, such as a MOSFET, is a voltage control type device, and has a threshold value of saturation conduction, and when the control voltage is lower than the threshold value, the MOSFET operates in a linear region. When the minimum conduction time is too short, the control voltage of the switch tube cannot reach the threshold value of saturated conduction, and the switch tube enters a linear working area, so that the loss of the switch tube is increased, and the power consumption of the whole machine is also increased. And the control circuit of the contactor is brought into the down mode in advance by an inappropriate minimum on-time, thereby risking audible noise to the contactor.

Disclosure of Invention

In view of the defects of the energy-saving control circuit of the contactor, the invention provides an adaptive minimum on-time control method and a control circuit in the control circuit of the contactor. Namely, under the condition that contactors with different specifications and different switching tubes are adopted, the controller can generate the optimal minimum on-time in a self-adaptive mode.

In order to achieve the purpose, the invention adopts the following technical scheme:

a control method of minimum on-time is used in a control circuit of a contactor, the minimum on-time is used for controlling the minimum time for switching on a switching tube in the control circuit, and the control method comprises the following steps:

in the holding stage of the contactor, determining the starting moment of the minimum conduction time based on a clock signal output by a control chip of a control circuit;

in the holding stage of the contactor, a voltage signal generated in the initial stage of switching on of a switching tube in the control circuit is detected, the voltage signal is compared with a set threshold value, and the end moment of the minimum on-time is determined based on the comparison result of the voltage signal and the threshold value. When the detector does not detect the voltage signal, the default minimum on-time is the initial set value t.

Preferably, the start time of the minimum on-time is determined based on a clock signal output by a control chip of the control circuit, and the start time of the minimum on-time is determined based on a rising edge of the clock signal output by the control chip of the control circuit.

Preferably, the voltage signal generated at the initial stage of the switching tube in the detection control circuit is specifically a voltage corresponding to a waveform falling edge of a spike pulse generated at the initial stage of the switching tube, and when a comparison result of the voltage corresponding to the falling edge of the spike pulse and a threshold is that the voltage corresponding to the falling edge of the spike pulse is lower than a set threshold, the end time of the minimum on-time is determined.

Preferably, the voltage signal is a current signal representing an initial stage of the switching tube being turned on.

Preferably, when the control circuit adopts a PWM peak current control mode, the current of the coil of the contactor is controlled by controlling the duty ratio of the switching tube, and the down-conversion trigger point of the switching tube in the control circuit is set according to the minimum on-time. When a PWM peak current control mode is adopted, the real-time duty ratio of the switching tube is gradually reduced along with the gradual rise of the input voltage, and when the actual time conduction time of the switching tube is close to the minimum conduction time, the control duty ratio is kept unchanged.

Preferably, when the control circuit adopts a voltage control mode, the input voltage of the control circuit is sampled, the duty ratio of the switch tube is controlled according to the input voltage, and the frequency reduction trigger point of the switch tube in the control circuit is set according to the minimum on-time.

Preferably, the minimum on-time varies with the type of contactor and the parasitic parameters of the switching tube.

Preferably, the sampling circuit samples the voltage signal, the sampling circuit comprises a resistor R1 and a resistor R2, one point of the resistor R1 is connected with the source of the switching tube, the other end of the resistor R1 is connected with one end of the resistor R2, the other end of the resistor R2 is connected with the ground, and the connection point of the resistor R1 and the resistor R2 is used as a sampling point of the voltage signal.

According to another aspect of the embodiments of the present invention, there is also provided a control circuit of a contactor, including: a main circuit and a control chip for executing the control method; the main circuit comprises an alternating current power supply, a rectifier tube, a switching tube, a coil, a capacitor, a diode, a resistor R1 and a resistor R2, wherein the alternating current power supply passes through the rectifier tube, the anode of the rectifier tube is connected with the ground, the cathode of the rectifier tube is connected with the anode of the capacitor, the connection point of the cathode of the rectifier tube and the anode of the capacitor is used as a first connection port, one end of the diode cathode and one end of the coil are respectively connected with the first connection port, the cathode of the capacitor is connected with the ground, the anode of the diode is connected with the other end of the coil, the connection point of the anode of the diode and the coil is used as a second connection port, the drain of the switching tube is connected with the second connection port, the source of the switching tube is connected with one end of a resistor R1, the other end of the resistor R1 is connected with one end of a resistor R2, the other end of the resistor R2 is connected with the ground, the gate of the switching tube is connected with a control chip, and the gate of the switching tube is connected with a control signal.

The contactor power-saving control method and the control circuit thereof have the beneficial effects that:

when the contactor works in the holding stage, the most appropriate minimum conduction time in the switch tube is obtained by detecting the minimum conduction time of the switch tube of the control circuit in real time, the problems that the coil loss is increased and the power factor is reduced due to unreasonable minimum conduction time when the input voltage range is enlarged and the input voltage is continuously improved in the prior art are solved, and the probability that the whole contactor generates audio noise is increased due to the fact that the control enters a frequency reduction mode in advance due to the improper minimum conduction time. The invention further expands the input voltage range by self-adapting the minimum conduction time, provides an accurate frequency reduction control signal and simultaneously meets the requirements of low power consumption and high power factor of the contactor.

Drawings

FIG. 1 is a flow chart of a method for controlling minimum on-time of the present invention;

FIG. 2 is a schematic diagram of the control circuit of the contactor of the present invention;

FIG. 3 is a control timing diagram of minimum on-time according to the present invention.

Detailed Description

Referring to fig. 1, fig. 1 is a flowchart illustrating a minimum on-time control method according to the present invention. The method is used in a control circuit of a contactor as shown in fig. 2, the minimum conduction time is the minimum time for controlling a switch tube Q1 in the control circuit to be switched on, and the control method comprises the following steps:

step S101, in the holding stage of the contactor, determining the starting time of the minimum conducting time based on a clock signal CLK output by a control chip of a control circuit;

step S102, in the holding stage of the contactor, detecting a voltage signal CS generated in an initial stage of turning on the switching tube Q1 in the control circuit, comparing the voltage signal CS with a set threshold, and determining an end time of the minimum on-time based on a comparison result of the voltage signal CS and a threshold.

In the control method, the starting time of the minimum on-time is the starting time of the minimum on-time based on the rising edge of the clock signal output by the control chip of the control circuit, that is, the rising edge generating time of the clock signal is determined as the starting time of the minimum on-time; the voltage signal CS generated at the initial stage of the switching transistor Q1 in the detection control circuit is specifically a voltage corresponding to the falling edge of the spike pulse generated at the initial stage of the switching transistor Q1, and when the comparison result between the voltage corresponding to the falling edge of the spike pulse and the threshold is that the voltage corresponding to the falling edge of the spike pulse is lower than the threshold, the end time of the minimum on-time is determined.

The invention obtains the most appropriate minimum conduction time of the switch tube Q1 by detecting the minimum conduction time of the switch tube Q1 in the control circuit of the contactor in real time, overcomes the problems that the loss of a coil L of the contactor is increased and the power factor is reduced due to unreasonable minimum conduction time when the input voltage is continuously improved along with the expansion of the input voltage range in the prior art, and increases the possibility that the system where the whole contactor is positioned generates audio noise due to the fact that the control enters a frequency reduction mode in advance due to the improper minimum conduction time. The invention further expands the input voltage range by self-adapting the minimum conduction time, provides an accurate frequency reduction control signal and simultaneously meets the requirements of low power consumption and high power factor of the contactor.

Fig. 2 is a schematic diagram of the control circuit of the contactor according to the present invention, and the control circuit includes a main circuit and a control chip (not shown): wherein the main circuit comprises a rectifier tube D1, a switch tube Q1, a coil L1 and an alternating current power supply AC, a capacitor C1, a diode D2, a resistor R1 and a resistor R2, wherein an alternating current power supply AC passes through a rectifier tube D1, the anode of a rectifier tube D1 is electrically connected with the common ground, the cathode of a rectifier tube D1 is electrically connected with the anode of a capacitor C1, the connection point of the cathode of the rectifier tube D1 and the anode of a capacitor C1 is used as a first connection port, the cathode of a diode D2 and one end of a coil L1 are respectively and electrically connected with the first connection port, the cathode of the capacitor C1 is electrically connected with the common ground, the anode of a diode D2 is electrically connected with the other end of the coil L1, the connection point of the anode of a diode D2 and the coil L is used as a second connection port, the drain of a switch tube Q1 is electrically connected with the second connection port, the source of the switch tube Q1 is electrically connected with one end of the resistor R1, the other end of a resistor R1 is electrically connected with one end of a resistor R2, and the other end of the resistor R2 is electrically connected with the common ground; the control chip is connected with the gate of the switching tube Q1, and is used for outputting a control signal for controlling the switching tube Q1 to turn on and off to the switching tube Q1. When the switch tube Q1 is turned on, the coil L1 generates current, so that the armature of the contactor is attracted, and the contact SW1 of the contactor is turned on.

The timing diagram of the minimum on-time control of the present invention is shown in fig. 3, when the clock signal CLK outputted from the control chip arrives, the rising edge of the clock signal CLK triggers the start time of the minimum on-time; the ending time of the minimum on-time is determined according to the voltage signal CS generated by the switching tube Q1 in the initial stage of turning on, where the voltage signal CS is specifically a voltage corresponding to the falling edge of the spike pulse generated in the initial stage of turning on the switching tube Q1.

In this embodiment, a sampling circuit composed of a resistor R1 and a resistor R2 samples a current signal generated by the switching tube Q1 at the initial stage of turn-on, the current signal is converted into a voltage signal CS (the voltage signal CS represents a current signal turned on by the switching tube Q1) through the resistor R1 and the resistor R2 and is input to a detector arranged inside a control chip, when the detector detects that the voltage signal CS (i.e., a voltage corresponding to a falling edge of a spike pulse) is lower than a set threshold, a turn-off time is generated, and a time from the initial time to the turn-off time is a minimum turn-on time. The minimum on-time generated here can be used as the minimum clamping duty ratio of the switching tube Q1 when the control circuit adopts a PWM peak current control mode or a voltage control mode, and the minimum on-time can be used as a frequency reduction reference signal under two modes, and the minimum on-time here is the duty ratio which is most reasonably set by the switching tube Q1 in the control circuit, so that the input voltage range can be greatly and effectively improved, the loss problem of the contactor due to the fixed minimum duty ratio under high voltage is reduced, the problem that the contactor is mistakenly judged to enter the frequency reduction mode due to the fixed minimum on-time is solved, and the risk of audio noise is brought to the system where the contactor is located.

The working principle of the embodiment is as follows: the contactor is in the pull-in stage, the current flowing through the coil L of the contactor can be controlled by controlling the duty ratio of the switch tube Q1, when the switch tube Q1 is switched on, the current flows through the coil L of the contactor to form the excitation stage, the current in the coil L is gradually increased, when the switch tube Q1 is switched off, the current of the coil L cannot suddenly change, the current flows through the diode D2, the current in the coil L shows the descending trend due to the diode drop and the internal resistance in the coil L of the contactor, and when the switch tube Q1 is switched on again, the current in the coil L is increased on the previous basis. In the pull-in stage, because the armature needs to be pulled down, the required electromagnetic force is large, and therefore the current in the coil L in the pull-in stage is large, the PWM duty ratio of the switch of the control switch tube Q1 is large, different contactor types and the required duty ratio are different, and the problem that the duty ratio is limited does not exist in the pull-in stage.

After the pull-in stage is finished, the pull-in stage is started, the principle is the same as that of the pull-in stage, the duty ratio of the switching tube Q1 is controlled, the current in the coil L of the control contactor is controlled, the pull-in stage only needs to keep the armature contact state, the current required in the stage is small, when the required current is small, the duty ratio of the switching tube Q1 is controlled to be small, and when the pull-in stage works at high pressure, low power consumption needs to be kept, and the duty ratio needs to be small.

Based on this, in this embodiment, the adaptive minimum on-time is set, a sampling circuit composed of a resistor R1 and a resistor R2 is used to sample the voltage signal CS of the drain of the switching tube Q1, so as to detect the voltage corresponding to the falling edge of the spike pulse of the switching tube Q1 at the initial stage of switching on (specifically, at the moment of switching on), and compare the voltage corresponding to the falling edge with the set threshold, where the voltage corresponding to the falling edge is lower than the set threshold, that is, the turn-off time of the minimum on-time; and the starting time is the corresponding time generated by the rising edge of the clock CLK output by the control chip. Based on the influence of parasitic parameters of different types of contactors and different switching devices in the control circuit, the most appropriate minimum conduction time under the contactors of different specifications is obtained, and the minimum conduction time is used as a reference point of a frequency reduction signal, so that the control system is prevented from entering an unreasonable frequency reduction stage in advance due to the fixed minimum conduction time, and the risk of audio noise brought to the system where the contactor is located is avoided.

Claims

1. A control method of minimum conduction time is used in a control circuit of a contactor, and the minimum conduction time is the minimum time for controlling a switch tube in the control circuit to be switched on, and is characterized by comprising the following steps:

in the holding stage of the contactor, determining the starting moment of the minimum conduction time based on a clock signal output by a control chip of the control circuit;

in the holding stage of the contactor, detecting a voltage signal generated in the initial stage of the switching tube in the control circuit, comparing the voltage signal with a set threshold value, and determining the end time of the minimum conduction time based on the comparison result of the voltage signal and the threshold value.

2. The control method of claim 1, wherein determining the starting time of the minimum on-time based on a clock signal output by a control chip of the control circuit determines the starting time of the minimum on-time based on a rising edge of the clock signal output by the control chip of the control circuit.

3. The control method according to claim 1, wherein the detecting of the voltage signal generated in the initial stage of the switching on of the switching tube in the control circuit is specifically detecting a voltage corresponding to a falling edge of a spike generated in the initial stage of the switching on of the switching tube, and when a comparison result between the voltage corresponding to the falling edge of the spike and the threshold value is that the voltage corresponding to the falling edge of the spike is lower than the threshold value, determining the ending time of the minimum on-time.

4. The control method of claim 1, wherein the voltage signal is a current signal indicative of an initial stage of the switching tube turning on.

5. The control method according to claim 1, characterized in that: when the control circuit controls to adopt a PWM peak current control mode, the current of the coil of the contactor is controlled by controlling the duty ratio of the switching tube, and the frequency reduction trigger point of the switching tube in the control circuit is set according to the minimum conduction time.

6. The control method according to claim 1, characterized in that: when the control circuit adopts a voltage control mode, the input voltage of the control circuit is sampled, the duty ratio of the switch tube is controlled according to the input voltage, and the frequency reduction trigger point of the switch tube in the control circuit is set according to the minimum conduction time.

7. The control method according to claim 1, characterized in that: the minimum conduction time varies with the type of the contactor and the parasitic parameters of the switch tube.

8. The control method according to claim 1, characterized in that: the voltage signal is sampled through a sampling circuit, the detection circuit comprises a resistor R1 and a resistor R2, one point of the resistor R1 is connected with the drain electrode of the switching tube, the other end of the resistor R1 is connected with one end of the resistor R2, the other end of the resistor R2 is connected with the ground, and the connection point of the resistor R1 and the resistor R2 serves as the sampling point of the voltage signal.

9. A control circuit for a contactor, comprising: a main circuit and a control chip for performing the control method of any one of claims 1 to 4, the main circuit comprising: the high-voltage direct current rectifier comprises an alternating current power supply, a rectifier tube, a switch tube, a coil, a capacitor, a diode, a resistor R1 and a resistor R2, wherein the alternating current power supply passes through the rectifier tube, the anode of the rectifier tube is connected with the ground, the cathode of the rectifier tube is connected with the anode of the capacitor, the connection point of the cathode of the rectifier tube and the anode of the capacitor is used as a first connection port, one end of the diode and one end of the coil are respectively connected with the first connection port, the cathode of the capacitor is connected with the ground, the anode of the diode is connected with the other end of the coil, the connection point of the anode of the diode and the coil is used as a second connection port, the drain of the switch tube is connected with the second connection port, the source of the switch tube is connected with one end of the resistor R1, the other end of the resistor R1 is connected with one end of the resistor R2, and the other end of the resistor R2 is connected with the ground, and the grid electrode of the switching tube is connected with the control chip.