Automatic load selection and switching device based on single chip microcomputer control

Abstract

The present invention relates to a load automatic selection and switching device based on single-chip microcomputer control. It includes an AC voltage sampling and transmission circuit, a single-chip microcomputer processor and an output control circuit that are electrically connected in sequence. The AC voltage sampling and transmission circuit is connected to three-phase lines respectively. The AC voltage sampling and transmission circuit includes a current limiting resistor, a high-precision current transformer, a precision current detection amplifier and an A / D converter that are electrically connected in sequence. The single-chip microcomputer processor is a 51 single-chip microcomputer. The output control circuit includes an optocoupler, an anti-short circuit, a solid relay and a leakage protector that are electrically connected in sequence. The present invention provides a load automatic selection and switching device based on single-chip microcomputer control. Based on the mature C51 single-chip microcomputer processor, the present invention adjusts the client load, balances the three-phase current of the three-phase four-wire low-voltage power line and the three-phase output load of the transformer, thereby reducing the neutral line current, reducing power loss, improving power supply quality, and extending the service life of the equipment.

Description

Technical Field

[0001] The invention belongs to the field of electric power equipment, relates to three-phase load adjustment, and in particular to an automatic load selection and switching device based on single-chip microcomputer control. Background Art

[0002] At present, most of the residential electricity in my country adopts the 220V / 380V, 50Hz three-phase four-wire low-voltage power supply mode, and most of the residential electricity adopts the 220V single-phase two-wire power supply mode, which causes the load obtained by users from the three-phase power line to be inconsistent, resulting in the imbalance of the three-phase current of the line and the transformer that supplies it, and this imbalance is random and real-time, which is difficult to control manually. According to statistics, the three-phase load balance rate of rural low-voltage power supply stations is unqualified by more than 30%, and the three-phase load balance rate of urban areas is also unqualified by more than 17%.

[0003] The following hazards exist when the three-phase load is unbalanced: 1. The three-phase load unbalance will increase the loss of the transformer and the low-voltage line, wasting precious electric energy: the loss of the transformer includes no-load loss and load loss. The load loss changes with the change of the transformer operating load and is proportional to the square of the load current. When the three-phase load of the transformer is balanced under the condition of unchanged load, the loss of the transformer is the smallest. When the three-phase output load of the transformer is unbalanced, its loss will increase exponentially. In the three-phase four-wire power supply line, when the three-phase current is balanced, the neutral line current is zero, and its power loss is: ΔP1=3I2R. When the maximum imbalance occurs, that is, one phase is 3I and the other two phases are zero, the neutral line current is also 3I, and the power loss is: ΔP2=2(3I)2R=18I2R=6(3I2R); that is, the power loss at the maximum imbalance is 6 times that at the balanced state.

[0004] 2. Unbalanced three-phase load may cause serious consequences such as burning transformers and supporting equipment: When the above imbalance occurs, the heavy load phase current is too large, and the overload is too much, which may cause overheating of the winding and transformer oil. Overheating of the winding accelerates insulation aging; overheating of the transformer oil causes oil quality deterioration, rapidly reduces the insulation performance of the transformer, reduces the life of the transformer, and even burns the winding. Unbalanced operation of the three-phase load will cause excessive zero-sequence current of the transformer and increase the temperature rise of local metal parts: When the transformer is under unbalanced operation of the three-phase load, zero-sequence current will be generated, and the existence of zero-sequence current inside the transformer will generate zero-sequence flux in the iron core. The hysteresis and eddy current losses caused by this will cause these components to heat up, causing the temperature of local metal parts of the transformer to rise abnormally, which will lead to transformer operation accidents in severe cases. When the above imbalance occurs, the heavy load phase current is too large, which may cause the temperature of the phase conductor to overheat and burn out, and since the cross-section of the neutral line conductor is generally 50% of the cross-section of the phase line, the probability of the neutral line burning out is higher. The burning out of the neutral line will cause the neutral point voltage to shift, thereby burning out equipment and causing personal injury.

[0005] 3. This results in insufficient transformer output. As long as one phase reaches full load, the transformer is operating at full load, and other low-load phases will not be able to operate at full load.

[0006] 4. The three-phase load is unbalanced, and one or two phases are abnormally heavy, which will inevitably increase the voltage drop in the line, reduce the quality of power, and affect the normal use of users' electrical appliances.

[0007] Currently, there is still a lack of a device on the market that can effectively adjust the three-phase imbalance in real time. Summary of the invention

[0008] In view of the lack of effective equipment for adjusting three-phase imbalance in real time, the present invention proposes a load automatic selection and switching device based on single-chip microcomputer control which has reasonable design, simple structure and can automatically and real-time adjust three-phase imbalance.

[0009] In order to achieve the above-mentioned purpose, the technical solution adopted by the present invention is that the present invention provides a load automatic selection switching device based on single-chip microcomputer control, comprising an AC voltage sampling and transmission circuit, a single-chip microcomputer processor and an output control circuit electrically connected in sequence, the AC voltage sampling and transmission circuit is connected to three-phase lines respectively, the AC voltage sampling and transmission circuit comprises a current limiting resistor, a high-precision current transformer, a precision current detection amplifier and an A / D converter electrically connected in sequence, the single-chip microcomputer processor is a 51 single-chip microcomputer, and the process of processing by the single-chip microcomputer processor comprises the following steps:

[0010] a. Store the data of the three A / D converters into the corresponding registers, compare the three data, select the phase with the largest data, and assign the highest phase identification register as the phase identification code;

[0011] b. Then read the data from the three A / D converters and replace the values ​​of the corresponding registers, and give them to the

[0012] Numerical weighting of the row phase;

[0013] c. Compare the weighted value with the other two phases, select the largest phase, and determine whether it matches the identification signal.

[0014] Memory consistent;

[0015] d. If the maximum phase value is consistent with the identification register, if they are consistent, return to step b. If they are not consistent, enter the delay subroutine. The delay subroutine is for the single-chip processor to take the value again after a delay of 5 minutes, weight it, judge the maximum phase, and compare it with the identification code in the identification register. If they become consistent, return to step b. If they are inconsistent, re-assign the identification register. The single-chip processor is not the highest relative

[0016] The corresponding output interface is set to 0, and the highest corresponding output interface is set to 1;

[0017] e. After the highest corresponding output interface is set to 1, the weighted subroutine is entered and runs for one hour, and then step b is re-entered. The weighted subroutine performs secondary weighting on the running phase;

[0018] The output control circuit includes a photoelectric coupler, an anti-short circuit, a solid relay and a leakage protector which are electrically connected in sequence.

[0019] Preferably, in step b, the weighted value is 5 volts.

[0020] Preferably, in the step e, the secondary weighted value is 20 to 30 volts.

[0021] Preferably, the single-chip processor is an AT89C51 chip.

[0022] Preferably, the anti-short circuit is arranged between the input and output terminals of each solid state relay.

[0023] Preferably, the output control circuit is further provided with a 12V independent power supply, and the 12V independent power supply is electrically connected to the photoelectric coupler.

[0024] Compared with the prior art, the advantages and positive effects of the present invention are:

[0025] 1. The present invention provides a load automatic selection and switching device based on single-chip microcomputer control. Based on the mature C51 single-chip microcomputer processor, it adjusts the client load, balances the three-phase current of the three-phase four-wire low-voltage power line and the three-phase output load of the transformer, thereby reducing the neutral line current, reducing power loss, improving power supply quality, and extending the service life of the equipment.

[0026] 2. The present invention uses an AC voltage sampling and transmission circuit to amplify small current changes with high precision, thereby obtaining a voltage change signal with very high linearity, and senses the load changes of the three-phase line through slight voltage changes, thereby facilitating operation and control by the C51 single-chip processor.

[0027] 3. The present invention provides an output control circuit and uses a solid-state relay with a thyristor as the core component as the main circuit breaker, thereby ensuring that the waveform distortion time during the switching process is less than 10 milliseconds, which is consistent with the switching time of the backup UPS, and all existing civilian electrical equipment can withstand the operation. At the same time, a photoelectric coupler with an independent power supply system is used for isolation to avoid electromagnetic interference between the front and rear stages and improve reliability. In addition, an original anti-short circuit protection circuit is used to avoid the phase-to-phase short circuit phenomenon during the switching process. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the following briefly introduces the drawings required for use in the description of the embodiments. Obviously, the drawings described below are some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without creative work.

[0029] Figure 1 A circuit diagram of the AC voltage sampling and transmitting circuit provided in Example 1;

[0030] Figure 2 A control schematic diagram of the single-chip processor provided in Example 1;

[0031] Figure 3 The operation logic diagram of the single-chip processor provided in Example 1;

[0032] Figure 4 This is a circuit diagram of the output control circuit provided in Example 1. DETAILED DESCRIPTION

[0033] In order to more clearly understand the above-mentioned purpose, features and advantages of the present invention, the present invention is further described below in conjunction with the accompanying drawings and embodiments. It should be noted that the embodiments of the present application and the features in the embodiments can be combined with each other without conflict.

[0034] In the following description, many specific details are set forth to facilitate a full understanding of the present invention. However, the present invention may also be implemented in other ways than those described herein. Therefore, the present invention is not limited to the specific embodiments of the following disclosure.

[0035] Embodiment 1, as Figure 1 , Figure 2 , Figure 3 , Figure 4 As shown, this embodiment provides a load automatic selection and switching device based on single-chip microcomputer control, including an AC voltage sampling and transmission circuit, a single-chip microcomputer processor and an output control circuit that are electrically connected in sequence. The AC voltage sampling and transmission circuit mainly uses a current and voltage detection method of a high-precision current transformer in conjunction with a current-limiting resistor. Through a microampere-level resolution, the tiny current change is amplified with high precision, thereby obtaining a voltage change signal with very high linearity, and the load change of the three-phase line is sensed through subtle voltage changes. And it is converted into a digital signal through an A / D converter and provided to the single-chip microcomputer processor for processing. As shown Figure 1As shown, CT1\CT2\CT3 are 2mA / 2mA high-precision current transformers, R10\R20\R30 are current-limiting resistors, and the input AC voltage signal will be converted into a 0-2mA current signal through the high-precision current transformer. The precision current detection amplifier composed of the operational amplifier and resistors R11(21)(31) / R12(22)(32) / R13(23)(33) / R14, and the voltage-stabilizing diode D1(2)(3)5 converts the current signal into an AC voltage signal. After rectification and filtering, it is transmitted to the A / D converter ADC8040 to be converted into a digital signal and sent to the subsequent single-chip processor for processing.

[0036] The single-chip processor uses a 51 single-chip processor, the specific model is the AT89C51 chip, which has a simple structure, low cost, mature and reliable, strong anti-interference ability, and fast response rate. It is an 8-bit 8051 core chip, containing 9 EPROMs, an internal storage space of 4K, an internal ROM of 512B, and a maximum external frequency of 40MHz. Its performance can fully meet the use requirements. This processor contains 4 I / O interfaces, P1 as the output interface, and the output interface is isolated by a photoelectric coupler to enhance the anti-interference ability. P0 and P1 ports are used as data acquisition interfaces.

[0037] When working, the initialization program is started and the data of the three A / D converters are stored in the corresponding registers in turn. The microcontroller processor compares the three data, selects the largest phase, and assigns the highest phase identification register with the identification code, and sets the interface corresponding to P1 to 1. The program enters the next cycle mode. First, the data of the three A / D converters are read again and the values ​​of the corresponding registers are replaced. The value of the running phase is weighted. The value is adjustable and is generally set to 5 volts to prevent frequent switching of the equipment. The weighted value is compared with the other two phases, and the largest phase is selected to determine whether it is consistent with the identification register. If it is consistent, it returns. If it is inconsistent, the delay subroutine is run. After a delay of 5 minutes, the value is taken, weighted, and the largest phase is judged again. It is compared with the identification code in the identification register. If it becomes consistent, it returns. If it is inconsistent, the identification register is re-assigned, P1 is set to 0, and the highest corresponding P1 port is set to 1. The weighted subroutine is run for one hour, and the running phase is weighted twice. It is generally set to 20-30V. The purpose is to keep the running phase as stable as possible and avoid frequent switching. The program returns to enter the cycle monitoring. This program design takes into account the weighting of the running phase to avoid frequent switching of equipment due to short-term or intermittent heavy loads, thereby extending the service life of the equipment and avoiding the occurrence of harmonics during the switching process.

[0038] By setting the output interface to 0 or 1, the user's single-phase equipment load is controlled to switch on and off in the three-phase line.

[0039] In order to realize the switching of the line, the present embodiment also provides an output control circuit, which is composed of a photoelectric coupler, an anti-short circuit, a solid relay, a leakage protector, and an independent 12 volt power supply. The function of the photoelectric coupler is to completely electrically isolate the electrical AC part from the single-chip processor to avoid the interference of the harsh electromagnetic environment on the single-chip processor. The anti-short circuit is installed between the input and output terminals of each solid relay. Only when the solid relay is completely disconnected and sufficient isolation voltage is generated between the two terminals, the corresponding photoelectric coupler will be turned on, and the solid relay of the newly put into operation phase will be triggered to turn on, avoiding the short circuit caused by the simultaneous conduction of the two phases during the switching process. The solid relay adopts a small current triggering property, with a triggering voltage of 3-36V and a triggering current of less than or equal to 10 mA. Reliable triggering is guaranteed.

[0040] Working process: When the single-chip microcomputer is changing phases, first the P1 port is set to zero. At this time, the photoelectric coupler is cut off, and the solid-state relay of the operating phase is cut off at zero crossing. At this time, all three solid-state relays are cut off, and the voltage between the input and output terminals of the solid-state relay rises to 220V. The 6 photoelectric couplers of the anti-short-circuit circuit are all turned on. At this time, the corresponding port of the newly operated P1 port is set to 1, and the solid-state relay of the newly put into operation phase is triggered and turned on. The voltage between its output and input terminals becomes the turn-on voltage of the thyristor, which is less than 1V. At this time, the corresponding photoelectric coupler is cut off, and the trigger circuits of the other two phases are open and will not be turned on, avoiding short circuit.

[0041] Advantages of this output control circuit: 1. This circuit uses a solid-state relay with thyristor as the core component as the main circuit breaker, which has the advantages of fast switching speed, no arc extinguishing process, low power consumption, and long service life, thereby ensuring that the waveform distortion time during the switching process is less than 10 milliseconds, which is consistent with the switching time of the backup UPS, and all existing civilian electrical equipment can tolerate the operation.

[0042] 2. Adopting optocoupler isolation with independent power supply system, it avoids electromagnetic interference between the front and back stages and improves reliability.

[0043] 3. An original anti-short-circuit protection circuit is adopted to avoid phase-to-phase short-circuit during the switching process.

[0044] This embodiment is based on the mature C51 single-chip microcomputer system, which has a simple structure, low cost, mature and reliable, strong anti-interference ability, and fast response rate. The load automatic selection and switching device based on single-chip microcomputer control provided in this embodiment can balance the three-phase current of the three-phase four-wire low-voltage power line and the three-phase output load of the transformer by adjusting the client load, thereby reducing the neutral line current, reducing power loss, improving power supply quality, and extending the service life of the equipment.

[0045] The above description is only a preferred embodiment of the present invention and does not limit the present invention in other forms. Any technician familiar with the profession may use the technical content disclosed above to change or modify it into an equivalent embodiment with equivalent changes and apply it to other fields. However, any simple modification, equivalent change and modification made to the above embodiment based on the technical essence of the present invention without departing from the content of the technical solution of the present invention still falls within the protection scope of the technical solution of the present invention.

Claims

1. A load automatic selection and switching device based on single chip microcomputer control, characterized in that: The invention comprises an AC voltage sampling and transmitting circuit, a single-chip processor and an output control circuit which are electrically connected in sequence, wherein the AC voltage sampling and transmitting circuit is connected to three-phase lines respectively, and the AC voltage sampling and transmitting circuit comprises a current limiting resistor, a high-precision current transformer, a precision current detection amplifier and an A / D converter which are electrically connected in sequence, and the single-chip processor is a 51 single-chip microcomputer, and the process of processing by the single-chip processor comprises the following steps: a. Store the data of the three A / D converters into the corresponding registers, compare the three data, select the phase with the largest data, and assign the highest phase identification register as the phase identification code; b. Then read the data of the three A / D converters and replace the values ​​of the corresponding registers, and weight the values ​​in the running phase; c. Compare the weighted value with the other two phases, select the maximum phase, and determine whether it is consistent with the identification register; d. Determine whether the maximum phase value is consistent with the identification register. If they are consistent, return to step b. If they are inconsistent, enter the delay subroutine. The delay subroutine is for the single-chip processor to take values ​​again after a delay of 5 minutes, weight them, determine the maximum phase, and compare them with the identification code in the identification register. If they are consistent, return to step b. If they are inconsistent, re-assign the identification register, set the non-highest corresponding output interface of the single-chip processor to 0, and set the highest corresponding output interface to 1; e. After the highest corresponding output interface is set to 1, the weighted subroutine is entered and runs for one hour. Reenter step b, the weighting subroutine is to perform secondary weighting on the running phase; The output control circuit includes a photoelectric coupler, an anti-short circuit, a solid relay and a leakage protector which are electrically connected in sequence; When the single-chip microcomputer is changing phases, first the P1 port is set to zero. At this time, the photoelectric coupler is cut off, and the solid-state relay of the operating phase is cut off at zero crossing. At this time, all three solid-state relays are cut off, and the voltage between the input and output terminals of the solid-state relay rises to 220V. The 6 photoelectric couplers of the anti-short-circuit circuit are all turned on. At this time, the corresponding port of the newly operated P1 port is set to 1, and the solid-state relay of the newly put into operation phase is triggered to turn on. The voltage between its output and input terminals becomes the turn-on voltage of the thyristor, which is less than 1V. At this time, the corresponding photoelectric coupler is cut off, and the trigger circuits of the other two phases are open and will not be turned on, avoiding short circuit.

2. The load automatic selection and switching device based on single chip microcomputer control according to claim 1 is characterized in that: In step b, the weighted value is 5V.

3. The load automatic selection and switching device based on single chip microcomputer control according to claim 1 is characterized in that: In the step e, the secondary weighted value is 20 to 30 volts.

4. The load automatic selection and switching device based on single chip microcomputer control according to claim 1 is characterized in that: The model of the single-chip microcomputer processor is AT89C51 chip.

5. The load automatic selection and switching device based on single chip microcomputer control according to any one of claims 1 to 4, characterized in that: The short-circuit prevention circuit is provided between the input and output terminals of each solid-state relay.

6. The load automatic selection and switching device based on single chip microcomputer control according to claim 5 is characterized in that: The output control circuit is also provided with a 12V independent power supply, and the 12V independent power supply is electrically connected to the photoelectric coupler.

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