A power control method

Abstract

This invention discloses a power control method, including a zero-crossing detection module, an MCU control module, a thyristor module, and a storage module. The zero-crossing detection module detects the zero-crossing point of the AC power supply and transmits high and low level signals to the MCU control module. The MCU control module obtains the zero-crossing frequency based on the zero-crossing detection module. The MCU control module obtains the PWM wave duty cycle value according to a PWM wave duty cycle calculation method and stores the appliance power ratio and the PWM wave duty cycle value in the storage module. The MCU control module reads the PWM wave duty cycle value and PWM wave frequency from the storage module, configures the PWM wave, and then outputs high and low levels to the thyristor module according to the PWM wave control method. This invention uses a PWM wave method to control the switching angle of the thyristor through the MCU control module, resulting in low processor resource consumption. By obtaining the AC power supply frequency through the zero-crossing detection module and adjusting the PWM wave period according to the AC power supply frequency, the control becomes more reliable, and the power control cost is lower and the accuracy is higher.

Description

Technical Field

[0001] This invention belongs to the field of thyristor power control technology, and particularly relates to a power control method. Background Technology

[0002] Currently, the control methods for commonly used AC series motors, induction cookers, and other electrical appliances mostly employ the software / hardware timer of an MCU to delay and control the opening and closing angle of the thyristor, thereby achieving the purpose of controlling the power of the appliance.

[0003] Currently, most electrical appliances use a thyristor + MCU delay method for power control. Taking the 220V 50Hz AC power grid in China as an example, 100 zero-crossing points are generated per second, corresponding to 100 control cycles (T) for the thyristor. Within one control cycle, the MCU applies a high level to the thyristor after a delay of t1, turning it on and allowing the appliance to operate. After another delay of t2, a low level is applied to the thyristor, and it turns off at the next zero-crossing point, stopping the appliance. Therefore, each control cycle requires two timer operations from the MCU processor, totaling 200 operations per second. This places high demands on the MCU's performance. If a low-cost, low-performance MCU is used, the large amount of data processing can easily lead to inaccurate timing, causing problems such as abnormal appliance control. Using a high-performance MCU, however, requires a higher cost.

[0004] If the PWM method is used to control the thyristor directly, the zero-crossing cycle is unstable due to the fluctuation of the power grid frequency. The PWM wave is difficult to match with the zero-crossing cycle, which can easily lead to abnormal control of electrical appliances.

[0005] To address this, a power control method is proposed, which uses a variable PWM period to control the thyristor and periodically detects the zero-crossing period to calibrate the PWM wave control period. The PWM wave and the zero-crossing period are accurately matched, achieving low-cost and high-precision control of the thyristor, thereby regulating the power of the electrical appliance. Summary of the Invention

[0006] The purpose of this invention is to provide a power control method that addresses the problems of high cost and instability in existing thyristor control methods described in the background section. To achieve this objective, the technical solution adopted by this invention is as follows:

[0007] A power control method includes a zero-crossing detection module, an MCU control module, a SCR module, and a storage module. The zero-crossing detection module detects the zero-crossing point of the AC power supply and transmits high and low level signals to the MCU control module.

[0008] The MCU control module obtains the zero-crossing frequency f from the zero-crossing detection module, then the PWM wave frequency is f′=f+1;

[0009] The power ratio p of the electrical appliance is set, and p is between 0 and 100%. The MCU control module obtains the duty cycle value D of the PWM wave according to the PWM wave duty cycle calculation method, and stores the power ratio p of the electrical appliance and the duty cycle value D of the PWM wave into the storage module.

[0010] The MCU control module reads the PWM wave duty cycle value D and the PWM wave frequency f′ from the storage module, configures the PWM wave, and then outputs high and low levels to the thyristor module according to the PWM wave control method.

[0011] The thyristor module switches on and off according to the high and low levels output by the MCU control module, changing the current and thus the power.

[0012] Further description of the above scheme, where the PWM wave duty cycle is calculated as follows: N zero-crossing cycles constitute one control cycle, and the relationship between the PWM wave duty cycle value D and the power ratio p can be calculated using the following formula:

[0013]

[0014] Further describing the above scheme, the method for calculating the PWM wave frequency is as follows: obtain t, the time required for m consecutive zero-crossing signals, and take... For zero-crossing period time, As the zero-crossing frequency, the PWM wave frequency f′=f+1. To ensure that there is a complete PWM wave within one zero-crossing cycle, the PWM wave period is slightly shorter than the zero-crossing cycle time.

[0015] Further describing the above scheme, the PWM wave control method uses N zero-crossing cycles as one PWM wave control cycle, which contains N PWM waves, to control the thyristor module, and includes the following steps:

[0016] The first step is to detect the PWM wave duty cycle value D and the PWM wave frequency f′. If the PWM wave duty cycle value D and the PWM wave frequency change, the PWM wave is reconfigured. If there is no change, reconfiguration is not required.

[0017] The second step is that when the MCU control module detects that the first zero-crossing cycle has started, it immediately starts to output a high level of PWM wave. At this time, the first PWM wave is immediately output to the thyristor module.

[0018] Third, when the MCU control module detects the start of the Nth zero-crossing cycle, it stops the PWM wave output, sets the PWM output port to a low level, and turns off the SCR module.

[0019] Alternatively, the PWM wave duty cycle calculation method can be replaced by the following method: taking f′=f, the calculation formula for the PWM wave duty cycle value D and the power ratio p is:

[0020] Even better, the result of the PWM wave duty cycle value D corresponding to the power ratio p is pre-input into the storage module for storage. During the power adjustment process, the MCU control module does not need to perform complex calculations and can directly retrieve the PWM wave duty cycle value D from the storage module. This results in low resource consumption of the MCU control module and fast response speed.

[0021] Compared with the prior art, the present invention has the following beneficial effects:

[0022] 1. The opening and closing angle of the thyristor is controlled by the MCU control module using PWM wave, which has low processor resource consumption;

[0023] 2. The AC power frequency is obtained through the zero-crossing detection module, and the PWM wave period is adjusted according to the AC power frequency, making the control more reliable, the power control cost lower, and the accuracy higher.

[0024] 3. By controlling the duty cycle of the PWM wave through the MCU control module to control the motor power, soft start of the motor can be achieved, avoiding the motor from shaking due to excessive instantaneous power. Attached Figure Description

[0025] Figure 1 This is a schematic diagram of the principle block provided for an embodiment of the present invention;

[0026] Figure 2 This is a schematic diagram of the PWM wave control signal provided in an embodiment of the present invention;

[0027] Figure 3 This is a schematic diagram of the PWM wave control method provided in an embodiment of the present invention;

[0028] Figure 4 This is a schematic diagram of the workflow provided for an embodiment of the present invention. Detailed Implementation

[0029] To facilitate understanding of the present invention, a more complete description will be given below with reference to the accompanying drawings. Preferred embodiments of the invention are shown in the drawings. However, the invention can be implemented in many different forms and is not limited to the embodiments described herein. Rather, these embodiments are provided to provide a thorough and complete understanding of the disclosure of the invention.

[0030] The technical solution of this patent will be further described in detail below with reference to specific embodiments.

[0031] like Figure 1-4As shown, a power control method includes a zero-crossing detection module, an MCU control module, a thyristor module, and a storage module. The zero-crossing detection module detects the zero-crossing point of the AC power supply and transmits high and low level signals to the MCU control module. The MCU control module obtains the zero-crossing frequency f based on the high and low level signals from the zero-crossing detection module, and the PWM wave frequency is f′=f+1. The user sets the power ratio p of the appliance, where p is between 0 and 100%. The MCU control module obtains the PWM wave duty cycle value D according to the PWM wave duty cycle calculation method and stores the appliance power ratio p and the PWM wave duty cycle value D in the storage module. The MCU control module reads the PWM wave duty cycle value D and the PWM wave frequency f′ from the storage module, configures the PWM wave, and then outputs high and low levels to the thyristor module according to the PWM wave control method. The thyristor module switches on and off accordingly based on the high and low levels output by the MCU control module, changing the current magnitude and thus changing the power.

[0032] The PWM duty cycle is calculated as follows: N zero-crossing cycles constitute one control cycle. The relationship between the PWM duty cycle value D and the power ratio p can be calculated using the following formula:

[0033]

[0034] The PWM wave duty cycle calculation method can also be replaced by the following method: Taking f′=f, the formula for calculating the PWM wave duty cycle value D and the power ratio p is:

[0035] Of course, to save the computing resources of the MCU control module and speed up the response time, the result of the PWM wave duty cycle value D corresponding to the power ratio p is pre-input into the storage module for storage. During the power adjustment process, the MCU control module does not need to perform complex calculations and directly retrieves the PWM wave duty cycle value D from the storage module. For example, when the power ratio p = 0, the PWM wave duty cycle value D = 0%; when the power ratio p = 0.1, the PWM wave duty cycle value D = 20%; when the power ratio p = 0.2, the PWM wave duty cycle value D = 29%, and so on. This achieves low resource consumption of the MCU control module and fast response speed.

[0036] The PWM wave frequency is calculated as follows: obtain t, the time required for m consecutive zero-crossing signals, and take... For zero-crossing period time, As the zero-crossing frequency, the PWM wave frequency f′=f+1. To ensure that there is a complete PWM wave within one zero-crossing cycle, the PWM wave period is slightly shorter than the zero-crossing cycle time.

[0037] like Figure 3As shown, the PWM wave control method uses N zero-crossing cycles as one PWM wave control cycle, which contains N PWM waves, to control the SCR module. The method includes the following steps:

[0038] The first step is to detect the PWM wave duty cycle value D and the PWM wave frequency f′. If the PWM wave duty cycle value D and the PWM wave frequency change, the PWM wave is reconfigured. If there is no change, reconfiguration is not required.

[0039] The second step is that when the MCU control module detects that the first zero-crossing cycle has started, it immediately starts to output a high level of PWM wave. At this time, the first PWM wave is immediately output to the thyristor module.

[0040] Third, when the MCU control module detects the start of the Nth zero-crossing cycle, it stops the PWM wave output, sets the PWM output port to a low level, and turns off the SCR module.

[0041] The PWM wave control method is explained, such as... Figure 2 As shown: With N=5, each 5 zero-crossing cycles constitute a control cycle. At the start of the first zero-crossing cycle, PWM wave output is initiated (i.e., the first PWM wave begins output). At the start of the fifth zero-crossing cycle, PWM wave output stops. Since the PWM wave period is slightly shorter than the zero-crossing cycle time, the output of the fifth PWM wave begins before the fifth zero-crossing cycle. After the fifth PWM wave output is complete, the PWM wave output terminates, and the PWM wave output port is set to low. Therefore, PWM wave output occurs in all 5 zero-crossing cycles, with PWM wave start and stop operations only occurring in the 1st and 5th zero-crossing cycles. Based on a domestic AC frequency of 50Hz, the MCU only performs 40 operations per second. Compared to the 200 delay operations per second achieved by software and hardware timer methods, the MCU saves 4 / 5 of its resource usage, significantly reducing its workload.

[0042] In practical applications, such as controlling AC motors:

[0043] The first step is for the zero-crossing detection module to detect the zero-crossing point of the AC power supply and transmit the high and low level signals to the MCU control module. The MCU control module obtains the zero-crossing frequency f based on the high and low level signals sent by the zero-crossing detection module, and then the PWM wave frequency is f′=f+1.

[0044] The second step involves the user setting the motor power ratio p, obtaining the duty cycle based on the PWM wave duty cycle calculation method, and storing the motor power ratio and PWM wave duty cycle values ​​into the storage module.

[0045] The third step is to obtain the PWM wave frequency according to the PWM wave frequency calculation method and store the PWM wave frequency in the storage module.

[0046] The fourth step is for the MCU control module to read the duty cycle and frequency of the PWM wave from the storage module, configure the PWM wave, and then start and stop the PWM wave according to the control rules.

[0047] Fifth, the thyristor module switches on and off according to the high and low levels output by the MCU control module, changing the current magnitude, and the motor changes its power due to the change in current.

[0048] When the motor starts, a soft-start method is used. Assuming the initial power corresponds to duty cycle D1, the target power corresponds to duty cycle D2, and the soft-start time is t seconds (meaning the duty cycle increases from D1 to D2 within t seconds), then the required increase in duty cycle for each PWM control cycle is ΔD.

[0049] In summary, this invention uses a PWM wave to control the opening and closing angle of the thyristor via an MCU control module, resulting in low processor resource consumption. The zero-crossing detection module acquires the AC power frequency, and the PWM wave period is adjusted accordingly, making control more reliable, lower in cost, and more precise. Furthermore, controlling the motor power by adjusting the PWM wave duty cycle via the MCU control module enables soft starting of the motor, preventing excessive instantaneous power from causing vibration.

[0050] It should be noted that when an element is referred to as being "fixed to" another element, it can be directly on the other element or there may be an intermediate element. When an element is considered to be "connected to" another element, it can be directly connected to the other element or there may be an intermediate element present. Conversely, when an element is referred to as being "directly on" another element, there is no intermediate element. The terms "vertical," "horizontal," "left," "right," and similar expressions used herein are for illustrative purposes only and do not represent the only possible implementations. The terms "upper end," "lower end," "left side," "right side," "front end," "rear end," and similar expressions used herein refer to the positional relationship with reference to the accompanying drawings.

[0051] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains. The terminology used herein in the description of the invention is for the purpose of describing particular embodiments only and is not intended to be limiting of the invention. The term "and / or" as used herein includes any and all combinations of one or more of the associated listed items.

[0052] The above embodiments are only used to illustrate the present invention and are not intended to limit the present invention. Those skilled in the art can make various changes and modifications without departing from the spirit and scope of the present invention. Therefore, all equivalent technical solutions also fall within the scope of the present invention, and the patent protection scope of the present invention should be defined by the claims.

Claims

1. A power control method, comprising a zero-crossing detection module, an MCU control module, a thyristor module, and a storage module, characterized in that: The zero-crossing detection module detects the zero-crossing point of the AC power supply and transmits the high and low level signals to the MCU control module. The MCU control module obtains the zero-crossing frequency f based on the high and low level signals of the zero-crossing detection module, and the PWM wave frequency is f′=f+1; The power ratio p of the electrical appliance is set, and the MCU control module obtains the duty cycle value D of the PWM wave according to the PWM wave duty cycle calculation method, and stores the power ratio p of the electrical appliance and the duty cycle value D of the PWM wave into the storage module; The MCU control module reads the PWM wave duty cycle value D and the PWM wave frequency f′ from the storage module and configures the PWM wave. The PWM wave control method uses N zero-crossing cycles as one PWM wave control cycle. The MCU control module outputs high and low levels to the SCR module according to the following steps: The first step is to detect the PWM wave duty cycle value D and the PWM wave frequency. If the PWM wave duty cycle value D and the PWM wave frequency change, the PWM wave is reconfigured. If there is no change, reconfiguration is not required. The second step is that when the MCU control module detects that the first zero-crossing cycle has started, it immediately starts to output a high level of PWM wave. At this time, the first PWM wave is immediately output to the thyristor module. Third, when the MCU control module detects the start of the Nth zero-crossing cycle, it stops the PWM wave output, sets the PWM output port to a low level, and turns off the SCR module; the SCR module opens and closes accordingly based on the high and low levels output by the MCU control module.

2. The power control method according to claim 1, characterized in that: The PWM wave duty cycle calculation method is as follows: N zero-crossing cycles constitute one control cycle. The relationship between the PWM wave duty cycle value D and the power ratio p can be calculated using the following formula:

3. The power control method according to claim 1, characterized in that: The method for calculating the PWM wave frequency is as follows: obtain t, which is the time required for m consecutive zero-crossing signals, and take... For zero-crossing period time, As the zero-crossing frequency, the PWM wave frequency f′=f+1, and the PWM wave period is less than the zero-crossing period.

4. The power control method according to claim 2, characterized in that: The PWM wave duty cycle calculation method can also be replaced by the following method: Taking f′=f, the formula for calculating the PWM wave duty cycle value D and the power ratio p is:

5. A power control method according to claim 2 or 4, characterized in that: The result of the PWM wave duty cycle value D corresponding to the power ratio p is pre-input into the storage module for storage.

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