Power supply and sampling circuit of low-voltage electrical appliances and its control method

Abstract

A power supply and sampling circuit for a low-voltage electrical appliance and its control method, comprising a current transformer, a rectifier circuit, a sampling circuit, a voltage stabilization energy storage circuit, a step-down energy storage circuit and a control unit. The current transformer, the rectifier circuit, the voltage stabilization energy storage circuit and the step-down energy storage circuit are connected in sequence. The sampling circuit is connected between the rectifier circuit and the control unit. The control unit is connected to the voltage stabilization energy storage circuit to obtain the voltage value of the voltage stabilization energy storage circuit. The voltage stabilization energy storage circuit includes a voltage stabilization switching element. The control unit outputs a control signal based on the obtained voltage value to turn on or off the voltage stabilization switching element. Each time the control unit collects signals through the sampling circuit, it is during the period when the voltage stabilization switching element is turned on, or each time the control unit collects signals through the sampling circuit, it is during the period when the voltage stabilization switching element is turned off, ensuring the accuracy of current sampling and the power supply effect.

Description

Technical Field

[0001] The present invention relates to the field of low-voltage electrical appliances, and specifically relates to a power supply and sampling circuit for a low-voltage electrical appliance and a control method therefor. Background Art

[0002] A circuit breaker is an important switching electrical appliance in the power system, which can connect and disconnect normal load currents, overloaded circuits, and can also connect and disconnect short-circuit currents. As a type of circuit breaker, an electronic low-voltage circuit breaker has a power supply and sampling circuit. Usually, a core current transformer is provided in the power supply and sampling circuit, so that while collecting current signals, it also provides a working power supply for the controller circuit in the circuit breaker. The greater the current input to the current transformer, the greater the voltage induced and converted at the secondary side. When the voltage reaches a certain threshold, a voltage-regulating switching tube will be turned on to discharge the current. However, in the existing power supply and sampling circuit, the voltage-regulating switching tube is controlled by a hardware circuit. When collecting current signals, the voltage-regulating switching tube is sometimes in the on state and sometimes in the off state, which is easily interfered by the on or off of the voltage-regulating switching tube, resulting in difficulty in improving the current sampling accuracy, and the hardware discharge frequency is high and difficult to control. Summary of the Invention

[0003] The purpose of the present invention is to overcome the defects of the prior art and provide a power supply and sampling circuit for a low-voltage electrical appliance and a control method therefor, which have low cost, high current measurement accuracy, and good power supply effect.

[0004] To achieve the above purpose, the present invention adopts the following technical solutions:

[0005] A power supply and sampling circuit for a low-voltage electrical appliance includes a current transformer, a rectifier circuit, a sampling circuit, a voltage-regulating energy storage circuit, and a control unit. The current transformer is connected to the main line of the low-voltage electrical appliance, and the current transformer, the rectifier circuit, and the voltage-regulating energy storage circuit are connected in sequence. The sampling circuit is connected between the rectifier circuit and the control unit. The control unit obtains the voltage value of the voltage-regulating energy storage circuit. The voltage-regulating energy storage circuit includes a voltage-regulating switching element controlled by the control unit. The control unit outputs a control signal to the voltage-regulating energy storage circuit based on the obtained voltage value to control the on and off of the voltage-regulating switching element. Each time the control unit collects a signal through the sampling circuit, it is during the period when the voltage-regulating switching element is turned on, or each time the control unit collects a signal through the sampling circuit, it is during the period when the voltage-regulating switching element is turned off.

[0006] Preferably, it further includes a comparator circuit. The comparator circuit obtains the voltage value from the voltage-regulating energy storage circuit and compares it with a reference voltage to control the on and off of the voltage-regulating switching element.

[0007] Preferably, the comparator circuit includes a voltage comparator capable of controlling the conduction or cutoff of a voltage stabilizing switch element. When the control unit is operating normally, the voltage comparator is not triggered. When the control unit fails, the voltage comparator will be triggered to control the conduction of the voltage stabilizing switch element.

[0008] Preferably, the voltage stabilizing energy storage circuit includes a voltage stabilizing switch element, an isolation diode, and an energy storage capacitor.

[0009] Preferably, it further includes a signal conditioning circuit and a step-down energy storage circuit. The control unit is connected to the sampling circuit through the signal conditioning circuit. The step-down energy storage circuit is connected between the control unit and the voltage stabilizing energy storage circuit, and the step-down energy storage circuit provides a working power supply for the control unit.

[0010] Preferably, the rectifier circuit includes a rectifier bridge D1, the sampling circuit includes a resistor R1 for sampling, the voltage stabilizing energy storage circuit includes a voltage stabilizing switch tube Q2, diodes D2, D3, D4, a capacitor C1, resistors R2 and R3, the comparator circuit includes a comparator U1A, and the control unit is an MCU;

[0011] The primary side of the current transformer is connected to the main line, and the secondary side of the current transformer is connected to the input end of the rectifier bridge D1. One output end of the rectifier bridge D1 is connected to one end of the resistor R1, and the other output end of the rectifier bridge D1 is connected to the drain of the voltage stabilizing switch tube Q2 and the anode of the diode D2. The source of the voltage stabilizing switch tube Q2 is connected to the other end of the resistor R1 and is connected to GND. The gate of the voltage stabilizing switch tube Q2 is connected to the cathodes of the diodes D3 and D4. The anode of the diode D3 is connected to the output end of the comparator U1A, and the anode of the diode D4 is connected to the MCU. The positive input end of the comparator U1A is connected to one ends of the resistors R2 and R3. One ends of the resistors R2 and R3 are connected to the MCU. The negative input end of the comparator U1A is connected to the reference voltage Vref. The other end of the resistor R2 and the positive electrode of the capacitor C1 are connected to the cathode of the diode D2.

[0012] A control method for the power supply and sampling circuit of a low-voltage electrical appliance based on the above, obtaining the voltage value of the voltage stabilizing energy storage circuit every 0.5N power frequency cycles of alternating current, and adjusting the pulse width time of the control signal periodically output to the voltage stabilizing energy storage circuit based on the obtained voltage value, so that the voltage stabilizing switch element is periodically conducted or cutoff under the drive of the control signal;

[0013] Based on the pulse width time of the control signal output by the voltage stabilizing energy storage circuit, determining the period of the signal collected by the acquisition circuit within the 0.5N power frequency cycles of alternating current, so that each signal acquisition is during the conduction period of the voltage stabilizing switch element, or each signal acquisition is during the cutoff period of the voltage stabilizing switch element;

[0014] Calculate the effective value of the current based on multiple collected signals after the power frequency period of 0.5M alternating currents, where N is a non-zero natural number and M is a non-zero natural number.

[0015] Further, proportionally adjust the pulse width time of the control signal according to the voltage value of the voltage stabilizing energy storage circuit, so that when the voltage stabilizing energy storage circuit outputs a higher voltage value, the conduction time of the voltage stabilizing switch element is long, and when the voltage value output by the voltage stabilizing energy storage circuit is low, the conduction time of the voltage stabilizing switch element is short.

[0016] Further, the control unit controls the voltage stabilizing switch element and the collected signal through the interrupt control method, sets the pulse timer interrupt and the current sampling timer interrupt based on the pulse width time of the control signal output to the voltage stabilizing energy storage circuit, and makes the pulse timer program executed by the pulse timer interrupt enter the interrupt program earlier than the current sampling timer program executed by the current sampling timer interrupt. After controlling the voltage stabilizing switch element to conduct in the pulse timer program, collect the signal through the collection circuit in the current sampling timer program, and after completing the sampling, then control the voltage stabilizing switch element to turn off.

[0017] Further, control the voltage stabilizing switch element to conduct, collect the signal through the collection circuit, and control the voltage stabilizing switch element to turn off after reaching the pulse width time.

[0018] A power supply and sampling circuit and its control method for a low-voltage electrical appliance according to the present invention, compared with the existing circuit, by adding a control unit to output a control signal to control the conduction or turn-off of the voltage stabilizing switch element, so that the control unit collects signals during the conduction period of the voltage stabilizing switch element or during the turn-off period of the voltage stabilizing switch element, ensuring the consistency of the collected signals, thus avoiding interference from the conduction or turn-off of the voltage stabilizing switch element during signal collection, ensuring the accuracy and linearity of current sampling, and at the same time cooperating with the power supply hardware circuit to ensure power supply reliability. Therefore, the circuit of the present invention has the advantages of small size, low cost, high measurement accuracy, and good power supply effect. At the same time, the low-voltage electrical appliance applying the present invention, especially the low-voltage circuit breaker, also has the advantages of small circuit size, low cost, high measurement accuracy, and good power supply effect. Description of the Drawings

[0019] Figure 1 is a schematic diagram of a power supply and sampling circuit for a low-voltage electrical appliance according to the present invention;

[0020] Figure 2 is a circuit diagram of a power supply and sampling circuit for a low-voltage electrical appliance according to the present invention;

[0021] Figure 3 is a current sampling waveform diagram in a power supply and sampling circuit for a low-voltage electrical appliance according to the present invention;

[0022] Figure 4 is Figure 3Partial enlarged view;

[0023] Figure 5 Circuit diagram of the existing power supply and sampling circuit. Detailed implementation manners

[0024] The following embodiments given in conjunction with the drawings further illustrate the detailed implementation manners of a power supply and sampling circuit and its control method for a low-voltage electrical appliance according to the present invention. The power supply and sampling circuit and its control method for a low-voltage electrical appliance according to the present invention are not limited to the descriptions of the following embodiments.

[0025] A power supply and sampling circuit for a low-voltage electrical appliance includes a current transformer, a rectification circuit, a sampling circuit, a voltage stabilization and energy storage circuit, and a control unit. The current transformer is connected to the main circuit of the low-voltage electrical appliance, and the current transformer, the rectification circuit, and the voltage stabilization and energy storage circuit are connected in sequence. The sampling circuit is connected between the rectification circuit and the control unit. The control unit obtains the voltage value of the voltage stabilization and energy storage circuit. The voltage stabilization and energy storage circuit includes a voltage stabilization switch element controlled by the control unit. The control unit outputs a control signal to the voltage stabilization and energy storage circuit based on the obtained voltage value to control the conduction and cutoff of the voltage stabilization switch element. Each time the control unit collects a signal through the sampling circuit, it is during the period when the voltage stabilization switch element is conducting, or each time the control unit collects a signal through the sampling circuit, it is during the period when the voltage stabilization switch element is cutoff.

[0026] For a power supply and sampling circuit and its control method for a low-voltage electrical appliance according to the present invention, compared with the existing circuit, by adding a control unit to output a control signal to control the conduction or cutoff of the voltage stabilization switch element, the control unit collects signals during the period when the voltage stabilization switch element is conducting, or collects signals during the period when the voltage stabilization switch element is cutoff, ensuring the consistency of the collected signals. Thus, interference caused by the conduction or cutoff of the voltage stabilization switch element during current signal collection is avoided, ensuring the accuracy and linearity of current sampling. At the same time, in cooperation with the power supply hardware circuit, the power supply reliability is ensured. Therefore, the circuit of the present invention is small in volume, low in cost, high in measurement accuracy, and good in power supply effect. At the same time, the low-voltage electrical appliance applying the present invention, especially the low-voltage circuit breaker, also has the advantages of small circuit volume, low cost, high measurement accuracy, and good power supply effect.

[0027] Combined with Figures 1-4 A preferred embodiment of the present invention will be introduced in detail. In this embodiment, it is illustrated by taking the control unit collecting the main circuit current signal during the period when the voltage stabilization switch element is conducting as an example.

[0028] The power supply and sampling circuit of the low-voltage electrical appliance includes a current transformer, a rectification circuit, a sampling circuit, a voltage stabilization energy storage circuit, a step-down energy storage circuit, a signal conditioning circuit, and a control unit. The primary side of the current transformer is connected to the main line of the low-voltage electrical appliance, and the secondary side of the current transformer is connected to the rectification circuit. The rectification circuit is respectively connected to the sampling circuit and the voltage stabilization energy storage circuit. The voltage stabilization energy storage circuit is connected to the step-down energy storage circuit. The voltage stabilization energy storage circuit serves as the primary power supply. The voltage stabilization energy storage circuit can provide a stable voltage and prevent the circuit load voltage from being too high through discharging. In addition, the voltage stabilization energy storage circuit can also supply power to some operating mechanisms in the low-voltage electrical appliance. The step-down energy storage circuit serves as the secondary power supply. After the current signal induced by the current transformer passes through the rectification circuit, the voltage stabilization energy storage circuit, and the step-down energy storage circuit for rectification, voltage stabilization, and step-down processing, the step-down energy storage circuit can provide a working power supply to the control unit. The sampling circuit is connected to the control unit through the signal conditioning circuit. The control unit is preferably an MCU and has the functions of signal acquisition and processing. The control unit is connected to the voltage stabilization energy storage circuit to obtain the voltage value of the voltage stabilization energy storage circuit. The voltage stabilization energy storage circuit includes a voltage stabilization switching element controlled by the control unit. The voltage stabilization switching element conducts or turns off under the control signal output by the control unit. The voltage stabilization switching element is preferably a triode or a field effect transistor. After the control unit obtains the voltage value of the voltage stabilization energy storage circuit, when the voltage value reaches a certain threshold, the voltage stabilization switching element is turned on to discharge the current. In this embodiment, the control unit controls the conduction and turn-off of the voltage stabilization switching element by adjusting the pulse width, that is, the pulse width time is the time for discharging the current. The control unit adjusts the pulse width of the control signal according to the voltage value and outputs the control signal to the voltage stabilization energy storage circuit.

[0029] Preferably, the control signal output by the control unit is divided into a high level and a low level. When the control unit outputs a high-level control signal, the voltage stabilization switching element is turned on to discharge the current, making the secondary load of the current transformer light and the output stable. The control unit outputs a low-level control signal to turn off the voltage stabilization switching element. At this time, no current is discharged, making the secondary load of the current transformer heavy and the output small.

[0030] The control unit outputs a high-level control signal to turn on the voltage stabilization switching element. During the period when the voltage stabilization switching element is turned on, the control unit collects the current signal of the main line of the low-voltage electrical appliance through the signal conditioning unit, the sampling circuit, and the rectification circuit. The signal conditioning circuit inputs the sampling signal output by the sampling circuit to the control unit after completing A / D conversion. After the current signal is collected and reaches the pulse width time for discharging the current, the control unit outputs a low-level control signal to turn off the voltage stabilization switching element. Of course, according to needs, the signal conditioning unit can also not be set, and the MCU of the control unit is integrated with an ADC interface for analog-to-digital conversion.

[0031] During the period when the control unit of this embodiment controls the voltage-stabilizing switch element to conduct, the circuit signal is collected through the sampling circuit. During the period when the voltage-stabilizing switch element is turned off, the current signal is not collected, so that each sampling point is located when the voltage-stabilizing switch tube conducts, avoiding being affected by the discharge current sometimes and not being affected by the discharge current sometimes when collecting the current signal, ensuring the consistency of the collected signal, and improving the sampling accuracy. After a power frequency cycle of an alternating current, the control unit calculates the effective current value based on the current signals collected at multiple sampling points in this power frequency cycle to obtain an accurate effective current value. Calculating the effective current value based on the collected multiple current signals belongs to the prior art in this field and will not be elaborated here.

[0032] The control unit of this embodiment collects signals during the period when the voltage-stabilizing switch element conducts. Of course, as another embodiment, it is also possible that the control unit collects signals during the period when the voltage-stabilizing switch element is turned off. The control unit controls the pulse width time of the voltage-stabilizing switch element to conduct through pulse width. During the period when the high level is output to control the voltage-stabilizing switch element to conduct, the current signal is not collected through the sampling circuit. During the period when the low level is output to control the voltage-stabilizing switch element to turn off, the current signal is collected through the sampling circuit.

[0033] Furthermore, the power supply and sampling circuit of the low-voltage electrical appliance further includes a comparator circuit. The comparator circuit obtains the voltage value from the voltage-stabilizing energy storage circuit and compares it with the reference voltage to control the on-off of the voltage-stabilizing switch element. When the control unit cannot control the voltage-stabilizing switch element, the comparator circuit works to realize the conduction or cut-off of the voltage-stabilizing switch element. For example, when the control unit fails or other accidents occur, the comparator circuit is triggered to control the voltage-stabilizing switch element. By controlling the voltage-stabilizing switch element in two ways, the reliability of the power supply is ensured.

[0034] In this embodiment, preferably, the sampling circuit includes a sampling resistor, and the sampling resistor converts the collected current into a voltage signal; the rectifying circuit includes a rectifier bridge circuit, the voltage-stabilizing energy storage circuit includes a voltage-stabilizing switch element, an isolation diode and an energy storage capacitor, the comparator circuit includes a voltage comparator capable of controlling the conduction or cut-off of the voltage-stabilizing switch element, and the voltage comparator can be a comparator or an operational amplifier; the step-down energy storage circuit includes a DC / DC BUCK circuit or an LDO circuit for step-down and an energy storage capacitor.

[0035] Combined with Figure 2Provide a specific connection method for the power supply and sampling circuit. Taking the connection to a low-voltage circuit breaker as an example, the rectifier circuit includes a rectifier bridge D1, the sampling circuit includes a resistor R1 for sampling, the voltage stabilization and energy storage circuit includes a voltage stabilization switching tube Q2, diodes D2, D3, D4, a capacitor C1, resistors R2 and R3, the comparator circuit includes a comparator U1A, and the control unit is an MCU. Among them, resistor R1 = 2Ω, the voltage stabilization switching tube Q2 is an STD60NF06T4 tube, diodes D2, D3, D4 are all SS14 diodes, comparator U1A is an LM293, capacitor C1 = 100UF, resistor R2 = 100KΩ, resistor R3 = 15KΩ, and R5 in the figure is an equivalent load.

[0036] The primary side of the current transformer (marked as T1 in the figure) is connected to the main line, and the secondary side of the current transformer is connected to the input end of the rectifier bridge D1. One output end of the rectifier bridge D1 is connected to one end of the resistor R1, and the other output end of the rectifier bridge D1 is connected to the drain of the voltage stabilization switching tube Q2 and the anode of the diode D2. The source of the voltage stabilization switching tube Q2 is connected to the other end of the resistor R1 and is connected to GND. The gate of the voltage stabilization switching tube Q2 is connected to the cathodes of the diodes D3 and D4. The anode of the diode D3 is connected to the output end of the comparator U1A, and the anode of the diode D4 is connected to the MCU. The positive input end of the comparator U1A is connected to one ends of the resistors R2 and R3. One ends of the resistors R2 and R3 are connected to the MCU. The negative input end of the comparator U1A is connected to the reference voltage Vref. The reference voltage can be provided by a reference chip or resistor voltage division and operational amplifier following, etc. The other end of the resistor R2, the positive pole of the capacitor C1 are connected to the cathode of the diode D2. One end of the equivalent load R5 is connected to the cathode of the diode D2. The cathode of the diode D2 outputs the voltage as the VP terminal for power supply. The other end of the equivalent load R5, the other end of the resistor R3, and the negative pole of the capacitor C1 are connected to the other end of the resistor R1. The capacitor C1 can supply power to the magnetic flux tripping circuit of the circuit breaker through energy storage.

[0037] In this embodiment, the MCU obtains the voltage value from the resistors R2 and R3. When the voltage value reaches a certain threshold, it turns on the voltage stabilization switching element to discharge the current; at the same time, the comparator U1A also controls the conduction of the voltage stabilization switching element based on the comparison of the voltage value obtained from the resistors R2 and R3 with the reference voltage Vref. The voltage stabilization switching element is controlled by both software and hardware methods to ensure the reliability of the power supply. In actual use, when the MCU is working normally, the comparator U1A will not be triggered, and basically the MCU is in control. When the MCU fails or there are other accidents, the comparator U1A will be triggered to control the conduction of the voltage stabilization switching element. As another degraded embodiment, of course, the comparator U1A can also not be set.

[0038] Based on the above power supply and sampling circuit of the low-voltage electrical appliance, the control process specifically applied to the circuit breaker is as follows, including the following steps:

[0039] Step S1: Power on the main circuit of the circuit breaker and the power supply and sampling circuit;

[0040] Step S2: The current transformer inductively outputs a current signal. After being rectified by the rectification circuit, regulated by the voltage regulation energy storage circuit, and stepped down by the step-down energy storage circuit, the current signal is used as the working power supply of the control unit;

[0041] Step S3: The control unit collects the voltage value of the voltage regulation energy storage circuit. Based on the obtained voltage value, the control unit adjusts the pulse width time of the control signal output to the voltage regulation energy storage circuit, so that the voltage regulation switching element is periodically turned on or off under the drive of the control signal to discharge the current; for example, when the control unit outputs a high level, the voltage regulation switching element is turned on, and when it outputs a low level, the voltage regulation switching element is turned off;

[0042] Step S4: The control unit collects the current signal of the main circuit during the period when the voltage regulation switching element is turned on. After the collection is completed and the pulse width time for discharging the current is reached, the control signal is output to turn off the voltage regulation switching element; or the control unit collects the current signal of the main circuit during the period when the voltage regulation switching element is turned off. For example, when the control unit outputs a high level to turn on the voltage regulation switching element, and after reaching the pulse width time for discharging the current, it outputs a low level to collect the current signal of the main circuit, and then during the period of waiting for the next turn-on of the voltage regulation switching element, that is, during the period when the voltage regulation switching element is turned off, the current signal of the main circuit is collected;

[0043] Step S5: Repeat steps S3 - S4 after every 0.5N power frequency cycles of alternating current, where N is a non-zero natural number, that is, every half, one, one and a half, or two power frequency cycles, etc., re-adjust the pulse width time of the control signal output to the voltage regulation energy storage circuit according to the obtained voltage value of the voltage regulation energy storage circuit to accurately discharge the current and ensure the stability of the power supply circuit; calculate the effective value of each phase current based on multiple collected signals after 0.5M power frequency cycles of alternating current, where M is a non-zero natural number, that is, calculate the effective value of each phase current after every half, one, one and a half, or two power frequency cycles of alternating current. However, calculating after half a power frequency cycle cannot guarantee accuracy, and calculating after more than one power frequency cycle will affect timeliness and cannot meet some protection requirements. It is preferably to calculate the effective value of each phase current after one power frequency cycle.

[0044] The present invention also provides a control method for the power supply and sampling circuit of a low-voltage electrical appliance, which is executed by the MCU of the control unit, that is, the content of steps S3 - S5, including the following steps:

[0045] Obtain the voltage value of the voltage stabilizing energy storage circuit every half or one power frequency period of the alternating current, and adjust the pulse width time of the control signal periodically output to the voltage stabilizing energy storage circuit based on the obtained voltage value, so that the voltage stabilizing switch element is periodically turned on or off under the drive of the control signal;

[0046] Based on the pulse width time of the control signal output by the voltage stabilizing energy storage circuit, determine the period of collecting signals through the collecting circuit within the half or one power frequency period of the alternating current, so that each time of collecting signals is during the period when the voltage stabilizing switch element is turned on, or each time of collecting signals is during the period when the voltage stabilizing switch element is turned off;

[0047] Calculate the effective value of each phase current based on multiple collected signals after one power frequency period of the alternating current.

[0048] Preferably, the control unit is provided with an interrupt program, and the control unit controls the voltage stabilizing switch element and the collected signals through an interrupt control method. Taking the collection of current signals during the conduction period of the voltage stabilizing switch element as an example, the control unit collects the voltage value of the voltage stabilizing energy storage circuit, the control unit adjusts the pulse width time of the control signal output to the voltage stabilizing energy storage circuit based on the obtained voltage value, sets the pulse timer interrupt and the current sampling timer interrupt based on the pulse width time of the control signal output to the voltage stabilizing energy storage circuit, and makes the pulse timer program executed by the pulse timer interrupt enter the interrupt program earlier than the current sampling timer program executed by the current sampling timer interrupt. Control the voltage stabilizing switch element to conduct in the pulse timer program, then exit the pulse timer program, the control unit continues to run, collect signals through the collection circuit in the current sampling timer program, turn off the voltage stabilizing switch element after completing the sampling signal in the current sampling timer program, and then exit the current sampling timer program, and the control unit continues to run.

[0049] Specifically, in step S3, after the control unit collects the voltage of the voltage stabilizing energy storage circuit, the control unit proportionally adjusts the pulse width time of the control signal output to the voltage stabilizing energy storage circuit in the current sampling period according to the obtained voltage value. The higher the voltage value, the longer the pulse width time, and the longer the conduction time of the voltage stabilizing switch element is controlled. The pulse width time range is preferably 50US - 200US. The control unit adjusts the pulse width of the control signal through the voltage value of the voltage stabilizing energy storage circuit, making the conduction time of the voltage stabilizing switch element related to the voltage value of the voltage stabilizing energy storage circuit. In particular, the pulse width of the control signal is adjusted proportionally according to the voltage value. In this way, the conduction time of the voltage stabilizing switch element is related to the voltage value output by the voltage stabilizing energy storage circuit. That is, when the voltage stabilizing energy storage circuit outputs a higher voltage value, the conduction time of the voltage stabilizing switch element is long, and when the voltage value output by the voltage stabilizing energy storage circuit is low, the conduction time of the voltage stabilizing switch element is short. Then, the voltage stabilizing switch element is turned on in advance in cooperation with the pulse timer interruption, and the current is sampled when the voltage stabilizing switch element is turned on in cooperation with the current sampling timer, and the voltage stabilizing switch element is turned off after the sampling is completed. In this way, it is possible to avoid the situation where the power supply requirement of the secondary circuit load cannot be met due to improper discharge time, and at the same time, the accuracy of current sampling can be ensured. The relationship between the conduction time of the voltage stabilizing switch element and the voltage value output by the voltage stabilizing energy storage circuit can be obtained based on a linear function or based on an experimental data curve.

[0050] Generally, the current sampling frequency is related to the number of sampling points. If 32 sampling points are set within one power frequency cycle (20ms), then the interval between each sampling point is 625us. Among them, if the high level outputs for 50us, then the low level outputs for 575us. In addition, the time for the control unit to collect the current each time is calculated by the instruction cycle of the control unit itself, which is about several or more than ten microseconds. In addition, the relationship between the conduction time of the voltage stabilizing switch element and the voltage value is obtained through experiments, and a function graph with the voltage value on the x-axis and the discharge time on the y-axis is established, and the adjustment relationship is obtained according to the experimental curve.

[0051] From Figure 3 , 4 it can be seen that in Figure 3 , 4 the waveform above is the control signal pulse waveform, Figure 3 , 4 and the waveform below is the AD sampled current waveform. When the pulse signal outputs a high level ( Figure 4 the part marked 1 in the figure), the voltage stabilizing switch element is turned on, making the secondary load of the current transformer light and the output stable. In Figure 4 , when the pulse signal outputs a high level, the sampling signal has an obvious rise (the part corresponding to the label 4). When the control signal is at a low level ( Figure 4 the part marked 2 in the figure), the voltage stabilizing switch element is turned off, making the secondary load of the current transformer heavy and the output small. In Figure 4 , the sampling signal drops (the part corresponding to the label 3).Figure 4 The glitch of the lower AC signal is interference generated when the voltage stabilizing switch element switches.

[0052] In this embodiment, the voltage stabilizing switch element and the signal acquisition are controlled by the interrupt control method. Of course, the control unit may not be provided with an interrupt program and the current signal may not be sampled by the interrupt method. Instead, the current signal is sampled by the logic control method to ensure that the current signal is sampled during the period when the voltage stabilizing switch element is turned on at a high level output, so that the control unit can collect the current signal while performing other functions. For example, the control unit controls the voltage stabilizing switch element to turn on, then collects the signal through the acquisition circuit, and controls the voltage stabilizing switch element to turn off after reaching the pulse width time.

[0053] In this application, the power supply and sampling circuit can be applied to low-voltage electrical appliances, such as circuit breakers, contactors, relays, fuses, automatic switches, etc. It is preferably applied to low-voltage circuit breakers. It is connected to the main circuit of the low-voltage electrical appliance through a current transformer to collect the current signal of the main circuit of the low-voltage electrical appliance. At the same time, the power supply and sampling circuit can also supply power to the low-voltage electrical appliance, such as supplying power to the flux tripping circuit of the circuit breaker. Since the power supply and sampling circuit has a small circuit volume, low cost, high measurement accuracy, and good power supply effect, the circuit breaker also has the advantages of small circuit volume, low cost, high measurement accuracy, and good power supply effect.

[0054] The above content is a further detailed description of the present invention in combination with specific preferred embodiments. It cannot be determined that the specific implementation of the present invention is only limited to these descriptions. For those of ordinary skill in the technical field to which the present invention belongs, without departing from the concept of the present invention, several simple deductions or substitutions can be made, which should all be regarded as belonging to the protection scope of the present invention.

Claims

1. A power supply and sampling circuit for a low-voltage electrical appliance, comprising a current transformer, a rectifier circuit, a sampling circuit, a voltage-stabilizing energy storage circuit and a control unit, characterized in that: The current transformer is connected to the main circuit of the low-voltage electrical appliance. The current transformer, the rectifier circuit, and the voltage-stabilizing energy storage circuit are connected in sequence. The sampling circuit is connected between the rectifier circuit and the control unit. The control unit acquires the voltage value of the voltage-stabilizing energy storage circuit. The voltage-stabilizing energy storage circuit includes a voltage-stabilizing switching element controlled by the control unit. The control unit outputs a control signal to the voltage-stabilizing energy storage circuit based on the acquired voltage value to control the conduction and cutoff of the voltage-stabilizing switching element. Each time the control unit acquires a signal through the sampling circuit, it is during the period when the voltage-stabilizing switching element is conducting, or each time the control unit acquires a signal through the sampling circuit, it is during the period when the voltage-stabilizing switching element is cutoff.

2. The power supply and sampling circuit of a low-voltage electrical appliance according to claim 1, characterized in that: It further includes a comparator circuit. The comparator circuit acquires the voltage value from the voltage-stabilizing energy storage circuit and compares it with a reference voltage to control the on-off of the voltage-stabilizing switching element.

3. The power supply and sampling circuit of a low-voltage electrical appliance according to claim 2, characterized in that: The comparator circuit includes a voltage comparator capable of controlling the conduction or cutoff of the voltage-stabilizing switching element. When the control unit is operating normally, the voltage comparator is not triggered. When the control unit fails, the voltage comparator will be triggered to control the conduction of the voltage-stabilizing switching element.

4. The power supply and sampling circuit of a low-voltage electrical appliance according to claim 1, characterized in that: The voltage-stabilizing energy storage circuit includes a voltage-stabilizing switching element, an isolation diode, and an energy storage capacitor.

5. The power supply and sampling circuit of a low-voltage electrical appliance according to claim 1, wherein: It further includes a signal conditioning circuit and a step-down energy storage circuit. The control unit is connected to the sampling circuit through the signal conditioning circuit. The step-down energy storage circuit is connected between the control unit and the voltage-stabilizing energy storage circuit. The step-down energy storage circuit provides a working power supply for the control unit.

6. The power supply and sampling circuit of a low-voltage electrical appliance according to claim 2, characterized in that: The rectifier circuit includes a rectifier bridge D1. The sampling circuit includes a resistor R1 for sampling. The voltage-stabilizing energy storage circuit includes a voltage-stabilizing switching tube Q2, diodes D2, D3, D4, a capacitor C1, resistors R2 and R3. The comparator circuit includes a comparator U1A. The control unit is an MCU. The primary side of the current transformer is connected to the main circuit. The secondary side of the current transformer is connected to the input end of the rectifier bridge D1. One output end of the rectifier bridge D1 is connected to one end of the resistor R1. The other output end of the rectifier bridge D1 is connected to the drain of the voltage-stabilizing switching tube Q2 and the anode of the diode D2. The source of the voltage-stabilizing switching tube Q2 is connected to the other end of the resistor R1 and grounded. The gate of the voltage-stabilizing switching tube Q2 is connected to the cathodes of the diodes D3 and D4. The anode of the diode D3 is connected to the output end of the comparator U1A. The anode of the diode D4 is connected to the MCU. The positive input end of the comparator U1A is connected to one ends of the resistors R2 and R3. One ends of the resistors R2 and R3 are connected to the MCU. The negative input end of the comparator U1A is connected to the reference voltage Vref. The other end of the resistor R2 and the positive electrode of the capacitor C1 are connected to the cathode of the diode D2.

7. A control method for the power supply and sampling circuit of a low-voltage electrical appliance according to any one of claims 1-6, characterized in that: Obtain the voltage value of the voltage-stabilizing energy storage circuit every 0.5N power frequency cycles of alternating current, and adjust the pulse width time of the control signal periodically output to the voltage-stabilizing energy storage circuit based on the obtained voltage value, so that the voltage-stabilizing switching element is periodically conducted or cutoff under the drive of the control signal. Determine the period of the signal collected by the acquisition circuit within the power frequency period of the 0.5N alternating currents based on the pulse width time of the control signal output by the voltage stabilizing energy storage circuit, so that each signal collection is during the conduction period of the voltage stabilizing switch element, or each signal collection is during the off period of the voltage stabilizing switch element; Calculate the effective current value based on multiple collected signals after 0.5M power frequency periods of the alternating current, where N is a non-zero natural number and M is a non-zero natural number.

8. The control method of the power supply and sampling circuit of the low-voltage electrical appliance according to claim 7, characterized in that: Proportionally adjust the pulse width time of the control signal according to the voltage value of the voltage stabilizing energy storage circuit, so that when the voltage stabilizing energy storage circuit outputs a higher voltage value, the conduction time of the voltage stabilizing switch element is long, and when the voltage stabilizing energy storage circuit outputs a lower voltage value, the conduction time of the voltage stabilizing switch element is short.

9. The control method of the power supply and sampling circuit of the low-voltage electrical appliance according to claim 7, characterized in that: The control unit controls the voltage stabilizing switch element and the signal acquisition through the interrupt control method. Based on the pulse width time of the control signal output to the voltage stabilizing energy storage circuit, the pulse timer interrupt and the current sampling timer interrupt are set, and the pulse timer program executed by the pulse timer interrupt enters the interrupt program earlier than the current sampling timer program executed by the current sampling timer interrupt. After the voltage stabilizing switch element is controlled to conduct in the pulse timer program, the signal is collected by the acquisition circuit in the current sampling timer program. After the sampling is completed, the voltage stabilizing switch element is then controlled to turn off.

10. The control method for the power supply and sampling circuit of the low-voltage electrical appliance according to claim 7, characterized in that: Control the voltage stabilizing switch element to conduct, collect the signal through the acquisition circuit, and control the voltage stabilizing switch element to turn off after reaching the pulse width time.

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