Minimum on-time control method and control circuit

Abstract

The present invention relates to the field of contactor control equipment, and proposes a control method for an adaptive minimum on-time in a contactor control scheme. That is, when using contactors of different specifications and different switching tubes, the controller can adaptively generate the optimal minimum on-time. This overcomes the problems in the prior art of increased coil loss and decreased power factor due to unreasonable minimum on-time as the input voltage range expands and the input voltage continues to increase, as well as the problem that the control enters the frequency reduction mode prematurely due to the inappropriate minimum on-time, which increases the possibility of audio noise being generated by the entire system. The present invention further expands the input voltage range through adaptive minimum on-time, and provides an accurate frequency reduction control signal, while meeting the requirements of low power consumption and high power factor of the contactor.

Description

Technical Field

[0001] The present invention relates to the field of contactor control equipment, and in particular to a method for controlling the minimum on-time in a control circuit of a contactor and a control circuit. Background Art

[0002] At present, the control circuit of the contactor generally uses PWM to control the current in the contactor coil, so that within a narrow input voltage range, the current in the contactor coil can be maintained at a constant value during the contactor's holding phase, effectively reducing losses. For different types of contactors, traditional PWM control schemes generally set a fixed minimum on-time to ensure that the switch tube in the control circuit is fully turned on. In this scheme, the set minimum on-time cannot reach the most appropriate time due to factors such as the turn-on delay of the switch tube in the control part, the output junction capacitance and the coil turn capacitance of the contactor coil. When the preset minimum on-time is too long, when the input voltage increases, after the on-time reaches the minimum on-time, due to the limitation of the minimum on-time, the coil current will increase with the increase of input voltage, and the power consumption will also increase; when the preset minimum on-time is too short, when the input voltage increases, after the on-time reaches the minimum on-time, due to the presence of input capacitance at the control port of the switch tube, according to the capacitor charging and discharging relationship:

[0003]

[0004] It can be seen that when the capacitor C and charging current i are fixed, the change in the capacitor voltage U is proportional to the charging time t. Switches, such as MOSFETs, are voltage-controlled devices and have a saturation conduction threshold. When the control voltage is lower than this threshold, the MOSFET operates in the linear region. When the minimum on-time is too short, the control voltage of the switch cannot reach the saturation conduction threshold, and the switch enters the linear operating region, resulting in increased losses in the switch and increased power consumption of the entire device. Furthermore, an inappropriate minimum on-time causes the contactor's control circuit to enter frequency reduction mode prematurely, which introduces the risk of audible noise in the contactor. Summary of the Invention

[0005] In view of the shortcomings of the aforementioned contactor energy-saving control circuit, the present invention proposes a method and circuit for adaptively controlling the minimum on-time in a contactor control circuit. Specifically, the controller can adaptively generate the optimal minimum on-time when using contactors of different specifications and different switching transistors.

[0006] In order to achieve the above-mentioned object of the invention, the present invention adopts the following technical solutions:

[0007] A minimum on-time control method is used in a control circuit of a contactor. The minimum on-time is the minimum time for controlling the switching of a switch in the control circuit. The control method includes:

[0008] During the holding phase of the contactor, the starting time of the minimum on-time is determined based on the clock signal output by the control chip of the control circuit;

[0009] During the holding stage of the contactor, the voltage signal generated in the initial stage of the switching tube in the control circuit is detected, and the voltage signal is compared with a set threshold value. The end time of the minimum conduction time is determined based on the comparison result of the voltage signal and the set threshold value; when the detector does not detect the voltage signal, the default minimum conduction time is the initial set value t.

[0010] Preferably, the starting moment of the minimum on-time is determined based on the clock signal output by the control chip of the control circuit, and the starting moment of the minimum on-time is determined based on the rising edge of the clock signal output by the control chip of the control circuit;

[0011] The voltage signal generated in the initial stage of turning on the switch tube in the detection control circuit is specifically the voltage corresponding to the falling edge of the spike pulse generated in the initial stage of turning on the detection switch tube. When the comparison result of the voltage corresponding to the falling edge of the spike pulse and the set threshold is that the voltage corresponding to the falling edge of the spike pulse is lower than the set threshold, it is determined as the end time of the minimum conduction time.

[0012] Preferably, the voltage signal is a current signal representing the initial stage of turning on the switch tube.

[0013] Preferably, when the control circuit adopts PWM peak current control mode, the current in the contactor coil is controlled by controlling the duty cycle of the switch, and the frequency reduction trigger point of the switch in the control circuit is set according to the minimum on-time. When adopting PWM peak current control mode, as the input voltage gradually increases, the real-time duty cycle of the switch gradually decreases. When the actual on-time of the switch approaches the minimum on-time, the control duty cycle remains unchanged.

[0014] Preferably, when the control circuit adopts the voltage control mode, the input voltage of the control circuit is sampled, and the duty cycle 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.

[0015] Preferably, the minimum on-time varies with the type of contactor and the parasitic parameters of the switch tube.

[0016] Preferably, the voltage signal is sampled by a sampling circuit, the sampling circuit includes a resistor R1 and a resistor R2, one end of the resistor R1 is connected to the source of the switching tube, the other end of the resistor R1 is connected to one end of the resistor R2, the other end of the resistor R2 is connected to the ground, and the connection point between the resistor R1 and the resistor R2 serves as the sampling point of the voltage signal.

[0017] According to another aspect of an embodiment of the present invention, a control circuit for a contactor is further provided, comprising: a main circuit and a control chip for executing the above-mentioned control method; wherein the main circuit comprises an AC power supply, a rectifier, a switch tube, a coil, a capacitor, a diode, a resistor R1, and a resistor R2, the AC power supply passes through the rectifier tube, the anode of the rectifier tube is connected to the ground, the cathode of the rectifier tube is connected to the positive electrode of the capacitor, and the connection point between the cathode of the rectifier tube and the positive electrode of the capacitor serves as a first connection port, the cathode of the diode and one end of the coil are respectively connected to the first connection port, the negative electrode of the capacitor is connected to the ground, the anode of the diode is connected to the other end of the coil, and the connection point between the anode of the diode and the coil serves as a second connection port, the drain of the switch tube is connected to the second connection port, the source of the switch tube is connected to one end of the resistor R1, the other end of the resistor R1 is connected to one end of the resistor R2, the other end of the resistor R2 is connected to the ground, the gate of the switch tube is connected to the control chip, and the gate of the switch tube receives a control signal.

[0018] The beneficial effects of the contactor power saving control method and control circuit of the present invention are:

[0019] When the contactor is operating in the holding phase, the minimum on-time of the control circuit's switching tube is detected in real time to determine the optimal minimum on-time for the switching tube. This overcomes the existing problems of increased coil loss and decreased power factor caused by an unreasonable minimum on-time as the input voltage range expands and the input voltage continues to rise. Furthermore, this inappropriate minimum on-time causes the control circuit to enter frequency reduction mode prematurely, increasing the likelihood of audible noise generated by the entire contactor. By using an adaptive minimum on-time, the present invention further expands the input voltage range and provides an accurate frequency reduction control signal, while meeting the contactor's requirements for low power consumption and high power factor. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 Flowchart of the method for controlling the minimum on-time of the present invention;

[0021] Figure 2 Schematic diagram of the control circuit of the contactor of the present invention;

[0022] Figure 3 This is a control timing diagram of the minimum on-time of the present invention. DETAILED DESCRIPTION

[0023] Please refer to Figure 1 , Figure 1This is a flow chart of the method for controlling the minimum on-time of the present invention. Figure 2 In the control circuit of the contactor shown, the minimum on-time is the minimum time for controlling the switch tube Q1 in the control circuit to be turned on. The control method includes the following steps:

[0024] Step S101, in the holding phase of the contactor, determining the starting time of the minimum on-time based on the clock signal CLK output by the control chip of the control circuit;

[0025] In step S102, during the holding phase of the contactor, a voltage signal CS generated during the initial stage of turning on the switch Q1 in the control circuit is detected, the voltage signal CS is compared with a set threshold, and the end time of the minimum on-time is determined based on the comparison result of the voltage signal CS and the set threshold.

[0026] In the above control method, the starting moment of the minimum on-time is the starting moment 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 of the clock signal is determined as the starting moment of the minimum on-time; the voltage signal CS generated in the initial stage of the switch tube Q1 in the detection control circuit is specifically the voltage corresponding to the falling edge of the spike pulse generated in the initial stage of the detection switch tube Q1. When the comparison result of 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, it is determined as the end moment of the minimum on-time.

[0027] The present invention detects the minimum on-time of the switch Q1 in the contactor's control circuit in real time to determine the optimal minimum on-time for the switch Q1. This overcomes the prior art issues of increased coil L losses and decreased power factor in the contactor due to an unreasonable minimum on-time as the input voltage range expands and the input voltage continues to rise. Furthermore, this inappropriate minimum on-time causes the control system to enter frequency reduction mode prematurely, increasing the likelihood of audible noise in the entire contactor system. By using an adaptive minimum on-time, the present invention further expands the input voltage range and provides an accurate frequency reduction control signal, while simultaneously meeting the contactor's requirements for low power consumption and high power factor.

[0028] The embodiment of the present invention further provides a control circuit for a contactor. Figure 2The schematic diagram of the control circuit of the contactor of the present invention includes a main circuit and a control chip (not shown): wherein the main circuit includes a rectifier tube D1, a switch tube Q1, a coil L1, an AC power supply AC, a capacitor C1, a diode D2, a resistor R1 and a resistor R2, the AC power supply AC passes through the rectifier tube D1, the anode of the rectifier tube D1 is electrically connected to the common ground, the cathode of the rectifier tube D1 is electrically connected to the positive electrode of the capacitor C1, the connection point between the cathode of the rectifier tube D1 and the positive electrode of the capacitor C1 is used as the first connection port, the cathode of the diode D2 and one end of the coil L1 are respectively connected to the first connection port. The first terminal is electrically connected to the first terminal, the negative terminal of capacitor C1 is electrically connected to the common ground, the anode of diode D2 is electrically connected to the other end of coil L1, and the connection point between the anode of diode D2 and coil L serves as a second connection port. The drain of switch Q1 is electrically connected to the second connection port, the source of switch Q1 is electrically connected to one end of resistor R1, the other end of resistor R1 is electrically connected to one end of resistor R2, and the other end of resistor R2 is electrically connected to the common ground. The control chip is connected to the gate of switch Q1 and is used to output a control signal to switch Q1 for turning switch Q1 on and off. When switch Q1 is turned on, coil L1 generates current, which causes the armature of the contactor to be attracted, and the contactor's contact SW1 is turned on.

[0029] The minimum on-time control timing diagram of the present invention is as follows: Figure 3 When the clock signal CLK output by the control chip arrives, the rising edge of the clock signal CLK triggers the start time of the minimum on-time; and the end time of the minimum on-time is determined by the voltage signal CS generated by the switch tube Q1 in the initial stage of turning on. The voltage signal CS is specifically the voltage corresponding to the falling edge of the spike pulse generated in the initial stage of turning on the switch tube Q1.

[0030] In this embodiment, a sampling circuit composed of resistors R1 and R2 samples the current signal generated by switch Q1 during its initial turn-on phase. This current signal is converted by resistors R1 and R2 into a voltage signal CS (which represents the current signal when switch Q1 is turned on) and input into a detector within the control chip. When the detector detects that voltage signal CS (i.e., the voltage corresponding to the falling edge of the spike pulse) is lower than a set threshold, a turn-off moment is generated. The time from the start moment to the turn-off moment is the minimum on-time. The minimum on-time generated here can be used as the minimum clamping duty cycle of switch Q1 when the control circuit adopts PWM peak current control mode or voltage control mode, and this minimum on-time can be used as a reference signal for frequency reduction in both modes. The minimum on-time here is the most reasonable duty cycle setting for switch Q1 in the control circuit. This can significantly increase the input voltage range, reduce the loss problem caused by the fixed minimum duty cycle of the contactor at high voltage, and eliminate the risk of the contactor mistakenly entering frequency reduction mode due to the fixed minimum on-time, which introduces audible noise to the system in which the contactor is located.

[0031] The working principle of this embodiment is as follows: During the contactor's pull-in phase, the current flowing through the contactor coil L can be controlled by controlling the duty cycle of the switch tube Q1. When the switch tube Q1 is turned on, current flows through the contactor coil L, forming an excitation phase, and the current in the coil L gradually increases. When the switch tube Q1 is turned off, since the current in the coil L cannot change suddenly, it is continued through the diode D2. Due to the diode voltage drop and the internal resistance in the contactor coil L, the current in the coil L shows a downward trend. When the switch tube Q1 is turned on again, the current in the coil L increases based on the previous level. During the pull-in phase, since the armature needs to be pulled down, the required electromagnetic force is large, so the current in the coil L is large during the pull-in phase, which controls the PWM duty cycle of the switch tube Q1. Different contactor types require different duty cycles, so there is no problem of duty cycle limitation during the pull-in phase.

[0032] After the pull-in stage ends, it enters the holding stage. The principle is the same as that of the pull-in stage. By controlling the duty cycle of the switch tube Q1, the current in the coil L of the contactor is controlled. Since the holding stage only needs to keep the armature in contact, the current required in this stage is relatively small. When the required current is small, the duty cycle of the control switch tube Q1 becomes smaller. When working at high voltage, a smaller duty cycle is required to maintain low power consumption.

[0033] Based on this, this embodiment sets an adaptive minimum on-time. A sampling circuit composed of resistors R1 and R2 samples the voltage signal CS at the drain of the switch Q1 to detect the voltage corresponding to the falling edge of the spike pulse during the initial turn-on phase (specifically, the moment of turn-on). The voltage corresponding to the falling edge is compared with a set threshold. When the voltage corresponding to the falling edge is lower than the set threshold, the minimum on-time is turned off. The starting time is the time corresponding to the rising edge of the clock CLK output by the control chip. Based on this, the effects of different types of contactors and the parasitic parameters of different switching devices in the control circuit are determined, and the most appropriate minimum on-time for contactors of different specifications is obtained. This minimum on-time is used as the reference point for the frequency reduction signal, thereby avoiding the risk of the control system prematurely entering an unreasonable frequency reduction phase due to a fixed minimum on-time, which would introduce audio noise into the system where the contactor is located.

Claims

1. A method for controlling a minimum on-time, used in a control circuit of a contactor, wherein the minimum on-time is the minimum time for controlling the switching of a switch in the control circuit, characterized in that: The control method includes: During the holding phase of the contactor, determining the starting time of the minimum on-time based on a clock signal output by a control chip of the control circuit; During the holding phase of the contactor, detecting a voltage signal generated in the initial phase of turning on the switch in the control circuit, comparing the voltage signal with a set threshold, and determining an end time of the minimum on-time based on the comparison result between the voltage signal and the set threshold; The starting time of determining the minimum on-time based on the clock signal output by the control chip of the control circuit is determining 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; Detecting the voltage signal generated in the initial stage of turning on the switch tube in the control circuit specifically involves detecting the voltage corresponding to the falling edge of the spike pulse generated in the initial stage of turning on the switch tube. When a comparison result between the voltage corresponding to the falling edge of the spike pulse and the set threshold shows that the voltage corresponding to the falling edge of the spike pulse is lower than the set threshold, the end time of the minimum on-time is determined.

2. The control method according to claim 1, characterized in that: The voltage signal is a current signal representing the initial stage of turning on the switch tube.

3. The control method according to claim 1, characterized in that: When the control circuit adopts the PWM peak current control mode, the current of the coil of the contactor is controlled by controlling the duty cycle of the switch tube, and the frequency reduction trigger point of the switch tube in the control circuit is set according to the minimum conduction time.

4. The control method according to claim 1, characterized in that: When the control circuit adopts the voltage control mode, the input voltage of the control circuit is sampled, and the duty cycle 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.

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

6. The control method according to claim 1, characterized in that: The voltage signal is sampled by a sampling circuit, which includes a resistor R1 and a resistor R2. One end of the resistor R1 is connected to the drain of the switching tube, the other end of the resistor R1 is connected to one end of the resistor R2, and the other end of the resistor R2 is connected to the ground. The connection point between the resistor R1 and the resistor R2 serves as the sampling point of the voltage signal.

7. A control circuit for a contactor, characterized in that: include: A main circuit and a control chip for executing the control method according to any one of claims 1 to 2, the main circuit comprising: an AC power supply, a rectifier, a switching tube, a coil, a capacitor, a diode, a resistor R1, and a resistor R2, the AC power supply passing through the rectifier, the anode of the rectifier being connected to ground, the cathode of the rectifier being connected to the positive electrode of the capacitor, the connection point between the cathode of the rectifier and the positive electrode of the capacitor serving as a first connection port, the cathode of the diode and one end of the coil being respectively connected to the first connection port, the negative electrode of the capacitor being connected to ground, the anode of the diode being connected to the other end of the coil, the connection point between the anode of the diode and the coil serving as a second connection port, the drain of the switching tube being connected to the second connection port, the source of the switching tube being connected to one end of the resistor R1, the other end of the resistor R1 being connected to one end of the resistor R2, the other end of the resistor R2 being connected to ground, and the gate of the switching tube being connected to the control chip.

Images