A Zero-Crossing Trigger PWM Control Method for SCR with Power Equalization

Abstract

The present invention provides a thyristor zero-crossing trigger PWM control method for power balancing. First, a thyristor zero-crossing trigger PWM control circuit is built. During the control process, the control unit sends a control signal CTRL to the heating unit to control the conduction of the thyristor Q1, so as to control the heating component RL to generate heat. The control signal is obtained by evenly splitting the number of consecutive conduction cycles of the AC power supply voltage within a PWM control period and is alternately controlled with the number of off cycles. The thyristor zero-crossing trigger PWM control method for power balancing provided by the present invention evenly splits the number of consecutive conduction cycles of the AC power supply voltage within a PWM control period and alternately controls it with the number of off cycles, achieving balanced output of the AC power supply power within the PWM control period and reducing the load flicker phenomenon.

Description

Technical Field

[0001] The invention relates to the field of power electronics and automatic control, and in particular to a power-balanced silicon controlled rectifier zero-crossing trigger PWM control method. Background Art

[0002] With the rapid development of e-commerce and logistics industries, online shopping has become an indispensable part of people's lives. There are many kinds of online shopping products. In addition to clothing, daily necessities, home appliances and other commodities, fresh food has also become the mainstream of online shopping. In the warehouse constant temperature system, it is necessary to continuously collect and feedback the temperature, and then control the temperature.

[0003] PID (Proportional Integral Derivative) is a commonly used temperature control method, which is often used to control the conduction of the heating unit to achieve temperature control. Thyristor is a commonly used heating unit.

[0004] There are generally two ways to control thyristors: phase-shift triggering and zero-crossing triggering. Phase-shift triggering is to change the starting position or ending position of the cycle conduction to adjust its output power or voltage. That is, the conduction amount of the thyristor is controlled by controlling the conduction angle of the thyristor. This thyristor control method is prone to electromagnetic interference due to the non-zero voltage or zero current conduction or shutdown. Zero-crossing triggering is to trigger the conduction and shutdown of the thyristor when crossing the zero point. The AC power supply voltage output has positive and negative half cycles. When the positive half cycle to the negative half cycle or from the negative half cycle to the positive half cycle, it must pass through the zero point. The conduction frequency is changed within a certain period of time to change the output average power of the thyristor to achieve the effect of adjusting the load power. This control method is zero voltage and zero current control because the control time of the thyristor is zero point, and the electromagnetic interference is small, but it is easy to cause load flickering. Summary of the invention

[0005] In order to address the deficiencies in the prior art, the present invention provides a power-balanced thyristor zero-crossing triggered PWM control method, in which a control signal is obtained by evenly splitting the continuous conduction frequency of the AC power supply voltage output within a PWM control cycle, and is alternately controlled with the shutdown frequency to achieve balanced output of the AC power supply power within the PWM control cycle and reduce load flickering.

[0006] The technical solution adopted by the present invention to solve the technical problem is: to provide a power balanced thyristor zero-crossing trigger PWM control method, comprising the following steps:

[0007] S1. Build a thyristor zero-crossing trigger PWM control circuit. The thyristor zero-crossing trigger PWM control circuit includes a control unit, a heating unit, a zero-crossing detection unit, and an AC power supply. Among them, the control unit is connected to the live wire L of the AC power supply through the heating unit, and the control unit is also connected to the neutral wire N of the AC power supply through the zero-crossing detection unit;

[0008] S2. The control unit sends a control signal CTRL to the heating unit to control the conduction of the thyristor Q1, so as to control the heating component RL to generate heat. The timing of the control unit sending the control signal CTRL follows the following rule: Let T be the number of cycles within one period of the PWM signal that the control unit can send, m be the number of cycles that the thyristor Q1 should conduct within one period obtained according to the PID control method, and Aon k be the position of the kth thyristor conduction cycle when the control signal CTRL is sent within the period. Then for each period, the position of the kth thyristor conduction cycle when the control signal CTRL is sent is:

[0009]

[0010] The calculation of m is obtained by the PID regulation control method, that is, the temperature value to be adjusted is periodically obtained according to the PID control method, and the temperature value to be adjusted is converted into the ratio of the thyristor conduction time per period to the total time per period, and then the number of cycles that the thyristor Q1 should conduct within one period is obtained.

[0011] The heating unit includes an optocoupler N1, a thyristor Q1, and a heating component RL. The second pin of the optocoupler N1 is electrically connected to the output terminal of the control unit. The first pin of the optocoupler N1 is electrically connected to the power supply VCC through the first resistor R1. The fourth pin of the optocoupler N1 is respectively connected to the first pin of the thyristor Q1 and the live wire of the AC power supply through the series-connected second resistor R2 and third resistor R3. The third pin of the optocoupler N1 is connected to the third pin of the thyristor Q1. The second pin of the thyristor Q1 is connected to the first capacitor C1 between the second resistor R2 and the third resistor R3. The second pin of the optocoupler N1 is also electrically connected to the neutral wire N of the AC power supply through the heating component RL.

[0012] The zero-crossing detection unit includes an optocoupler device N2 and a bridge rectifier Q2. The fourth pin of the optocoupler device N2 is electrically connected to the input terminal of the control unit. The fourth pin of the optocoupler device N2 is also electrically connected to the power supply VCC through the fourth resistor R4. The first pin of the optocoupler device N2 is electrically connected to the positive electrode of the bridge rectifier Q2. The second pin of the optocoupler device N2 is electrically connected to the negative electrode of the bridge rectifier Q2. The third pin of the optocoupler device N2 is grounded. The first input terminal of the optocoupler device N2 is electrically connected to the neutral wire N of the AC power supply. The second input terminal of the optocoupler device N2 is electrically connected to the live wire L of the AC power supply through the fifth resistor R5.

[0013] The beneficial effects of the present invention based on its technical solution are as follows: A thyristor zero-crossing trigger PWM control method with power balance provided by the present invention uses a third resistor R3 and a first capacitor C1 for filtering; a resistor R2 and a resistor R3 are used for current limiting; an AC power supply 40 obtains a positive 100 Hz half-wave signal after passing through a resistor R5 and a bridge rectifier Q2. The half-wave signal controls the on-off of an optocoupler device N2, and a 100 Hz AC zero-crossing signal ZERO is obtained from the output of the optocoupler device N2. The power of the load is evenly distributed within the control period, greatly improving the flashing phenomenon of the load. Description of the Drawings

[0014] Figure 1 It is a schematic connection diagram of a thyristor zero-crossing trigger PWM control circuit.

[0015] Figure 2 It is a schematic diagram of the waveform of the AC power supply voltage Vi.

[0016] Figure 3 It is a schematic diagram of the waveform of the zero-crossing detection signal ZERO.

[0017] Figure 4 It is a schematic diagram of the waveform of the control signal CTRL. Detailed Embodiment

[0018] The present invention will be further described below with reference to the drawings and embodiments.

[0019] The present invention provides a thyristor zero-crossing trigger PWM control method with power balance, including the following steps:

[0020] S1. Build a thyristor zero-crossing trigger PWM control circuit. The thyristor zero-crossing trigger PWM control circuit includes a control unit, a heating unit, a zero-crossing detection unit, and an AC power supply. Among them, the control unit is connected to the live wire L of the AC power supply through the heating unit, and the control unit is also connected to the neutral wire N of the AC power supply through the zero-crossing detection unit.

[0021] Refer to Figure 1 , the heating unit includes an optocoupler N1, a thyristor Q1, and a heating component RL. The second pin of the optocoupler N1 is electrically connected to the output end of the control unit. The first pin of the optocoupler N1 is electrically connected to the power supply VCC through a first resistor R1. The fourth pin of the optocoupler N1 is respectively connected to the first pin of the thyristor Q1 and the live wire of the AC power supply through a series-connected second resistor R2 and a third resistor R3. The third pin of the optocoupler N1 is connected to the third pin of the thyristor Q1. The second pin of the thyristor Q1 is connected to the second resistor R2 and the third resistor R3 through a first capacitor C1. The second pin of the optocoupler N1 is also connected to the neutral wire N of the AC power supply through the heating component RL.

[0022] The zero-crossing detection unit includes an optocoupler device N2 and a bridge rectifier Q2. The 4th pin of the optocoupler device N2 is electrically connected to the input end of the control unit. The 4th pin of the optocoupler device N2 is also electrically connected to the power supply VCC through a fourth resistor R4. The 1st pin of the optocoupler device N2 is electrically connected to the positive electrode of the bridge rectifier Q2. The 2nd pin of the optocoupler device N2 is electrically connected to the cathode of the bridge rectifier Q2. The 3rd pin of the optocoupler device N2 is grounded. The first input end of the optocoupler device N2 is electrically connected to the neutral line N of the AC power supply. The second input end of the optocoupler device N2 is electrically connected to the live wire L of the AC power supply through a fifth resistor R5.

[0023] S2. The control unit sends a control signal CTRL to the heating unit to control the conduction of the thyristor Q1, so as to control the heating of the heating component RL. In this embodiment, the control signal CTRL controls the conduction angle of the thyristor Q1 through the optocoupler N1 to control the heating component RL of the temperature control device; the resistor R3 and the capacitor C1 are used for filtering; the resistor R2 and the resistor R3 are used for current limiting. The AC power supply obtains a positive 100Hz half-wave signal after passing through the resistor R5 and the bridge rectifier Q2. The half-wave signal controls the on-off of the optocoupler device N2, and a 100Hz AC zero-crossing signal ZERO is obtained from the output of the optocoupler device N2. The waveforms of the AC power supply voltage and the zero-crossing detection signal ZERO are respectively as Figure 2 and Figure 3 shown.

[0024] The timing of the control unit sending the control signal CTRL follows the following rule: Let T be the number of cycles within one period of the PWM signal that the control unit can send, m be the number of cycles that the thyristor Q1 should conduct within one period obtained according to the PID control method, and Aon k be the position of the kth thyristor conduction cycle when the control signal CTRL is sent within the period. Then for each period, the position of the kth thyristor conduction cycle when the control signal CTRL is sent is:

[0025]

[0026] The calculation of m is obtained by the PID adjustment algorithm, that is, according to the PID control method, the temperature value to be adjusted is periodically obtained, and the temperature value to be adjusted is converted into the proportion of the thyristor conduction time in the total time of each period, so as to obtain the number of cycles that the thyristor Q1 should conduct within one period.

[0027] Referring to Figure 3 in (2), taking the PWM control period T as 10 cycles and the PWM duty cycle m, that is, the number of cycles of thyristor conduction are 0 to 10 as an example, there are:

[0028] (1) When m = 0, the thyristor is turned off at all cycle positions within the PWM period.

[0029] (2) When m = 1, the thyristor conduction position:

[0030] The thyristor conduction position is in the 1st cycle.

[0031] (3) When m = 2, the thyristor conduction position:

[0032] The thyristor conduction position is in the 1st and 6th cycles.

[0033] (4) When m = 3, the thyristor conduction position:

[0034] The thyristor conduction position is in the 1st, 4th, and 7th cycles.

[0035] (5) When m = 4, the thyristor conduction position:

[0036] The thyristor conduction position is in the 1st, 3rd, 6th, and 8th cycles.

[0037] (6) When m = 5, the thyristor conduction position:

[0038] The thyristor conduction position is in the 1st, 3rd, 5th, 7th, and 9th cycles.

[0039] (7) When m = 6, the thyristor conduction position:

[0040] The thyristor conduction position is in the 1st, 2nd, 4th, 6th, 7th, and 9th cycles.

[0041] (8) When m = 7, the thyristor conduction position:

[0042] The thyristor conduction position is in the 1st, 2nd, 3rd, 5th, 6th, 8th, and 9th cycles.

[0043] (9) When m = 8, the thyristor conduction position:

[0044] The thyristor conduction position is in the 1st, 2nd, 3rd, 4th, 6th, 7th, 8th, and 9th cycles.

[0045] (10) When m = 9, the thyristor conduction position:

[0046] The thyristor conduction position is in the 1st, 2nd, 3rd, 4th, 5th, 6th, 7th, 8th, and 9th cycles.

[0047] When m = 10, the thyristor conduction positions:

[0048] The thyristor conduction positions are in the 1st, 2nd, 3rd, 4th, 5th, 6th, 7th, 8th, 9th, and 10th cycles.

[0049] Figure 3 In (1), it is a schematic diagram of the thyristor control waveform controlled by the traditional thyristor zero-crossing trigger PWM method. Since the conduction and turn-off of the thyristor are continuous, within the control period, the load power is concentrated and not evenly distributed, and the load flicker phenomenon is obvious. In contrast, by using a thyristor zero-crossing trigger PWM control method with power balance provided by the present invention, the load power is evenly distributed within the control period, greatly improving the load flicker phenomenon.

[0050] A thyristor zero-crossing trigger PWM control method with power balance provided by the present invention, the control signal is obtained by evenly splitting the number of consecutive conduction cycles of the AC power supply voltage output within a PWM control period, and is alternately controlled with the number of turn-off cycles, achieving balanced output of the AC power supply power within the PWM control period and reducing the load flicker phenomenon.

Claims

1. A thyristor zero-crossing trigger PWM control method for power balancing, characterized in that It includes the following steps: S1. Build a thyristor zero-crossing trigger PWM control circuit. The thyristor zero-crossing trigger PWM control circuit includes a control unit, a heating unit, a zero-crossing detection unit, and an AC power supply. Among them, the control unit is connected to the live wire L of the AC power supply through the heating unit, and the control unit is also connected to the neutral wire N of the AC power supply through the zero-crossing detection unit; S2. The control unit sends a control signal CTRL to the heating unit to control the conduction of the thyristor Q1, so as to control the heating component RL to generate heat. The timing of the control unit sending the control signal CTRL follows the following rule: Let T be the number of cycles within one period of the PWM signal that the control unit can send, m be the number of cycles that the thyristor Q1 should conduct within one period obtained according to the PID control method, and Aon k is the position of the k-th thyristor conduction cycle when the control signal CTRL is sent within the period. Then, for each period, the position of the k-th thyristor conduction cycle when the control signal CTRL is sent is:

2. The thyristor zero-crossing trigger PWM control method for power balancing according to claim 1, wherein: The calculation of m is obtained by the PID regulation control method, that is, the temperature value to be adjusted is periodically obtained according to the PID control method, and the temperature value to be adjusted is converted into the proportion of the conduction time of the thyristor in each cycle to the total time of each cycle, and then the number of cycles that the thyristor Q1 should conduct in one cycle is obtained.

3. The thyristor zero-crossing trigger PWM control method for power balancing according to claim 1, characterized in that: The heating unit includes an optocoupler N1, a thyristor Q1, and a heating component RL. The second pin of the optocoupler N1 is electrically connected to the output terminal of the control unit. The first pin of the optocoupler N1 is electrically connected to the power supply VCC through the first resistor R1. The fourth pin of the optocoupler N1 is respectively connected to the first pin of the thyristor Q1 and the live wire of the AC power supply through the series-connected second resistor R2 and third resistor R3. The third pin of the optocoupler N1 is connected to the third pin of the thyristor Q1. The second pin of the thyristor Q1 is connected between the second resistor R2 and the third resistor R3 through the first capacitor C1. The second pin of the thyristor Q1 is also electrically connected to the neutral wire N of the AC power supply through the heating component RL.

4. The thyristor zero-crossing trigger PWM control method for power balancing according to claim 3, characterized in that: The zero-crossing detection unit includes an optocoupler device N2 and a bridge rectifier Q2. The fourth pin of the optocoupler device N2 is electrically connected to the input terminal of the control unit. The fourth pin of the optocoupler device N2 is also electrically connected to the power supply VCC through the fourth resistor R4. The first pin of the optocoupler device N2 is electrically connected to the positive electrode of the bridge rectifier Q2. The second pin of the optocoupler device N2 is electrically connected to the negative electrode of the bridge rectifier Q2. The third pin of the optocoupler device N2 is grounded. The first input terminal of the bridge rectifier Q2 is electrically connected to the neutral wire N of the AC power supply. The second input terminal of the bridge rectifier Q2 is electrically connected to the live wire L of the AC power supply through the fifth resistor R5.

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