CN109946554B - Single-phase alternating current grounding real-time detection circuit and detection method thereof - Google Patents
Single-phase alternating current grounding real-time detection circuit and detection method thereof Download PDFInfo
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Abstract
The invention discloses a single-phase alternating-current grounding real-time detection circuit, which comprises a live wire, a zero line and a protective ground, and also comprises a rectification filter circuit, wherein the live wire and the zero line are connected to the input end of the rectification filter circuit, the output end of the rectification filter circuit is sequentially connected with a first resistor, a second resistor and a third resistor, the common end of the third resistor and the second resistor is connected with an AD port of a singlechip, the other end of the third resistor is connected with the protective ground, the single-phase alternating-current grounding real-time detection circuit and a switching power supply of a control system where the single-phase alternating-current grounding real-time detection circuit is positioned share one rectification filter circuit, and the singlechip is a main control CPU in the control system. The invention can simplify the hardware of the grounding detection circuit, reduce the increase of fault rate caused by multiple devices and improve the detection efficiency.
Description
Technical Field
The invention relates to the technical field of alternating current grounding detection, in particular to a single-phase alternating current grounding real-time detection circuit.
Background
The electrical equipment with the metal shell is required to be reliably installed to be grounded through safety protection, but the requirement of the safety protection on the ground is often not up to the standard due to various reasons, so that electrification of the electrical equipment is easy to cause, damage to the electrical equipment is caused, and even an electric shock accident occurs. For new energy pure electric vehicles, because the charging is inconvenient, the private wire is very common, the charging can only be ensured, and the safety grounding wire can be saved. In the prior art, various grounding detection circuits or instruments exist, but various application conditions cannot be met due to various reasons such as high manufacturing cost, inconvenient operation, troublesome installation and the like, so that the device cannot be popularized.
As shown in FIG. 1, the grounding detection circuit commonly used in the prior art needs to divide the voltage of the L line and the N line by two paths of resistors and then respectively connect the L line and the N line to diode ends of two paths of optical couplers, the two diodes provide diode reverse voltage protection of the optical couplers, and outputs of the two paths of optical couplers are connected to the point A and the point B of the detection circuit, and the detection circuit is generally a singlechip.
The current ground detection system has four conditions as follows:
1. l line connects live wire, N line connects zero line, PE ground connection: point a has a duty cycle of about 50%, a frequency of 50hz, and point b is constantly high;
2. l line connects the zero line, and N line connects live wire, PE ground connection: point B has a duty cycle of about 50%, a frequency of 50hz, and point a is constantly high;
3. l line connects live wire, and N line connects zero line, and PE is unsettled: the duty cycle of the point A and the point B is about 50%, the frequency is 50HZ, and the phases AB are opposite;
4. l line connects the zero line, and N line connects the live wire, and PE is unsettled: the duty cycle of points a and B is about 50%, the frequency 50HZ, and the AB phase is opposite.
The singlechip distinguishes whether PE is effectively grounded or not through the states, and executes corresponding actions through output driving.
The detection circuit described above has some drawbacks, however, such as: 1. the technology is complex, two IO ports of the singlechip are consumed, and the internal resource CCP module of the singlechip is occupied; the duty cycle, frequency and phase are measured, and the state can be determined by calculating the information; 2. the cost is high, and two paths of optical lotus roots are needed to be isolated.
Disclosure of Invention
The invention aims to solve the problems and provide a single-phase alternating-current grounding real-time detection circuit.
In order to achieve the above purpose, the present invention adopts the following technical scheme:
the utility model provides a single-phase AC ground connection real-time detection circuit, includes live wire, zero line and protection ground, still includes rectification filter circuit, live wire and zero line connect in rectification filter circuit's input, rectification filter circuit's output has connected gradually first resistance, second resistance and third resistance, the public end of third resistance and second resistance is connected in the AD mouth of singlechip, the other end of third resistance connect in the protection ground.
In the above-mentioned single-phase ac ground connection real-time detection circuit, the rectifying and filtering circuit includes a rectifying bridge and a filtering capacitor, the live wire and the zero line are connected to two input ends of the rectifying bridge, two output ends of the rectifying bridge are connected to two ends of the filtering capacitor, and one of the output ends of the rectifying bridge is connected to the first resistor.
In the single-phase ac grounding real-time detection circuit, the single-phase ac grounding real-time detection circuit and the switching power supply of the control system where the single-phase ac grounding real-time detection circuit is located share one rectifying and filtering circuit.
In the single-phase alternating-current grounding real-time detection circuit, the singlechip is a main control CPU in the control system.
In the single-phase ac grounding real-time detection circuit, the resistance value of the first resistor is greater than or equal to 5000kΩ.
In the single-phase ac grounding real-time detection circuit, the resistance value of the second resistor is greater than or equal to 5000kΩ.
In the foregoing single-phase ac grounding real-time detection circuit, the resistance value of the third resistor is selected according to a resistance value determination formula (1):
U11*R3/(R1+R2+R3)<U22 ①
wherein, the liquid crystal display device comprises a liquid crystal display device,
r1, a first resistance value; r2, the second resistance value; r3 is a third resistance value; u11, highest input voltage; u22, the AD port receives the highest voltage.
A detection method of a single-phase alternating-current grounding real-time detection circuit comprises the following steps:
s1, acquiring a pulse voltage average value;
s2, judging whether the average value of the pulse voltage is smaller than a threshold value, if yes, judging that the pulse voltage is abnormally grounded, and if not, judging that the pulse voltage is normally grounded.
In the above detection method of the single-phase ac ground real-time detection circuit, in step S1, the pulse voltage average value is obtained by:
s11, detecting AD values at intervals of a preset time, and continuously detecting the AD values for set times;
s12, adding all detected AD values within set times to obtain AD sum values;
s12, dividing the AD sum value by the set times to obtain a pulse voltage average value.
In the above detection method of the single-phase ac ground real-time detection circuit, in step S2, the threshold value is determined by: intermediate value-30 < = threshold value < = intermediate value +30; the intermediate value is an intermediate pulse voltage value between the pulse voltage average value at normal grounding and the pulse voltage average value at abnormal grounding.
The invention has the advantages that: 1. the hardware of the grounding detection circuit is simplified, and the increase of fault rate caused by multiple devices is reduced; 2. the BOM cost can be effectively reduced, the occupied PCB area is reduced, the occupied 3 of the detection circuit to the internal data of the singlechip is greatly reduced, and the grounding detection can be realized only by using one more low-speed low-resolution AD port on the basis of the original system.
Drawings
FIG. 1 is a prior art ground detection circuit diagram;
FIG. 2 is a circuit diagram of a single phase AC ground real-time detection circuit according to the present invention;
FIG. 3 is a circuit diagram of a switching power supply on the original control system;
FIG. 4 is a voltage waveform diagram of the AD port measured by the singlechip;
FIG. 5 is a schematic flow chart of the detection method of the present invention.
In the figure: a live wire L; zero line N; a protected area PE; a first resistor R1; a second resistor R2; a third resistor R3; a singlechip U1; a rectifier bridge DB1; a wave capacitance C1; and a rectifying and filtering circuit 2.
Detailed Description
The invention will be described in further detail with reference to the drawings and the detailed description.
The following description of the embodiments of the present invention will be made clearly and completely with reference to the accompanying drawings, in which it is apparent that the embodiments described are only some embodiments of the present invention, but not all embodiments. All other embodiments, which can be made by those skilled in the art based on the embodiments of the invention without making any inventive effort, are intended to be within the scope of the invention.
As shown in fig. 2, the single-phase ac grounding real-time detection circuit comprises a live wire L, a zero wire N, a protection ground PE and a rectifying and filtering circuit 2, wherein the live wire L and the zero wire N are connected to the input end of the rectifying and filtering circuit 2, the output end of the rectifying and filtering circuit 2 is sequentially connected with a first resistor R1, a second resistor R2 and a third resistor R3, the common end of the third resistor R3 and the second resistor R2 is connected to an AD port a of the single-chip microcomputer U1, and the other end of the third resistor R3 is connected to the protection ground PE and the grounding end of the single-chip microcomputer U1.
As shown in fig. 2 and 3, in the prior art, the switching power supply part of the control system comprises a rectifying and filtering circuit 2, the rectifying and filtering circuit 2 comprises a rectifying bridge DB1 and a filtering capacitor C1, the rectifying and filtering circuit 2 has the function of rectifying AC220V alternating current into 300V direct current in the switching power supply, and supplying the flyback power supply consisting of a switching tube Q1, a transformer T1 and the control part in fig. 2, so as to generate direct current power supply required by each path of the control system, and it is noted that a U4 in fig. 3 is a flyback power supply chip, and the switching tube Q1 in fig. 2 is integrated inside. In addition, the singlechip U1 in this embodiment adopts a main control CPU in a control system.
The single-phase alternating-current grounding real-time detection circuit and the switching power supply of the control system where the single-phase alternating-current grounding real-time detection circuit and the switching power supply share a rectifying and filtering circuit, and the singlechip directly uses all main control CPUs of the system. The use of additional components is saved. The specific way of applying the rectifying and filtering circuit 2 and the main control CPU to the invention is as follows: the live wire L and the zero line N are connected to two input ends of the rectifier bridge DB1, two output ends of the rectifier bridge DB1 are connected to two ends of the filter capacitor C1, and one output end of the rectifier bridge DB1 is connected to the first resistor R1. The first resistor R1, the second resistor R2 and the third resistor R3 are all high-voltage resistors with large resistance values, and are connected to the singlechip U1 after voltage division, namely the AD port A of the main control CPU. Specifically, the first resistor R1 and the second resistor R2 are preferably resistors with withstand voltage of 1500V AC or more and power of 2W or more, and the resistance values of the first resistor R1 and the second resistor R2 are both greater than or equal to 5000kΩ; the resistance value of the third resistor R3 is selected according to the resistance value determination formula (1): U11R 3/r1+r2+r3; < U22 (1)
Wherein R1 is the resistance of the first resistor; r2, the second resistance value; r3 is a third resistance value; u11, highest input voltage; u22, the AD port receives the highest voltage.
In general, the highest withstand voltage of the AD port a of the main control CPU is 5V, so the U22 here may be 5V, and the input voltage is generally 220V, but the input voltage generally fluctuates up and down, so the highest input voltage is 1.3 times 220V, namely 285VAC, and the corresponding dc voltage is 285V, so the U11 here may be 285V. When the first resistor R1 and the second resistor R2 are both 5000KΩ, the resistance value selected by the third resistor R3 is 125KΩ, the partial pressure ratio of R1+R2 to R3 is approximately 80:1, and when the highest input voltage is 285V, the voltage at the third resistor R3 is approximately 3.5V, and the voltage is within the tolerance 5V of the AD port A, so that the requirement is satisfied. Of course, in addition to this selection, the first resistor R1, the second resistor R2, and the third resistor R3 having other resistance values may be selected, so long as the peak voltage generated in the third resistor R3 after the voltage division by the first resistor R1 and the second resistor R2 does not exceed the highest withstand voltage of the AD port a when the highest voltage input is satisfied.
Specifically, the detection principle of the single-phase alternating-current grounding real-time detection circuit is as follows:
in normal grounding, the live wire L has 220V alternating current voltage to the protective ground PE, and the voltage of the zero wire N to the protective ground PE is basically 0V. The alternating current voltage of the live wire L is rectified into direct current through a rectifier bridge DB1, and the direct current voltage of 300V is filtered by a filter capacitor C1. After the direct-current voltage is divided by the first resistor R1 and the second resistor R2, a fixed direct-current voltage is formed and is connected into the singlechip U1 through the AD port A for analog-digital conversion so as to be used for grounding judgment. And finally, connecting the load with alternating current 220VAC through an output pipe foot control relay, and realizing real-time detection and control of the grounding state.
And, no matter the live wire L and the zero wire N are connected positively or reversely, the rectified voltage is a direct current voltage, and the third resistor R3 can detect the direct current voltage for judging the grounding state of the singlechip.
When the protection ground PE is disconnected, the system is in a non-grounding state, the reference ground of the singlechip U1 is floating, 300V direct-current voltage on the filter capacitor C1 cannot form a loop through the first resistor R1/the second resistor R2/the third resistor R3, voltage cannot be formed on the third resistor R3, and the direct-current voltage detected by the singlechip is close to 0. After the processing of the singlechip, the connection between the load and alternating current 220VAC is cut off through an output pipe foot control relay, so that the real-time detection and control of the grounding state are realized.
Further, the method for detecting based on the single-phase ac grounding real-time detection circuit in this embodiment is as follows:
s1, acquiring a pulse voltage average value;
s2, judging whether the average value of the pulse voltage is smaller than a threshold value, if yes, judging that the pulse voltage is abnormally grounded, and if not, judging that the pulse voltage is normally grounded.
Further, in step S1, the pulse voltage average value is obtained by:
s11, detecting AD values at intervals of a preset time, and continuously detecting the AD values for set times;
s12, adding all detected AD values within set times to obtain AD sum values;
s12, dividing the AD sum value by the set times to obtain a pulse voltage average value.
The preset time may be 1ms, and the preset number of times is 50, that is, one control period signal acquisition is completed every 50 mm. Each acquisition period is controlled to be 50mm, so that power frequency interference can be filtered.
The following is a brief description of why the acquisition period is used with 50 mm: fig. 4 is a waveform obtained by measuring the point D in fig. 2 from the protected ground when normally grounded and 230VAC is input, and the alternating current is rectified by a rectifier bridge into a direct current of a single phase pulse 50 HZ. The square frame in fig. 4 is any 50mm waveform, and as can be seen from fig. 4, any 50ms can contain 2.5 waveforms, so that by measuring any 50mm analog quantity, adding up by the AD value of 50ms, and dividing by 50, the average value of pulse voltage across 2.5 waveforms can be obtained, and then the average value of pulse voltage can be approximated. The method does not need to synchronize the waveform detection deliberately, and is simple and easy to realize. Of course, in actual operation, time different from 50mm, for example 60mm,80mm, etc. can be selected, 50mm is preferable in this embodiment, and not only power frequency interference can be filtered, but also real-time detection can be ensured.
Further, the present embodiment adopts the acquisition accuracy of 10 bits, that is, 10 th power of 2=1024. For example, when the input signal is an analog signal of 5V, a digital quantity of 1024 is converted. In addition, the lowest input of the system is 80% of 220VAC, namely 220×0.8=176 VAC, when the input is the lowest input 176VAC and the input is the lowest input 176VAC, the voltage at the third resistor is 2.173V after voltage division, and the detected AD value is 2.173/5×1024=445. That is, at the lowest input voltage, the converted AD value is around 445 when the ground is good.
When the system is grounded and disconnected, the current at the alternating current side cannot return to form a loop through the first resistor R1, the second resistor R2 and the third resistor R3, and no voltage can be generated on the third resistor R3, so that the AD port A of the singlechip U1 can hardly detect a numerical value, only a bit of noise can be actually detected, and the AD value fluctuates by about 10.
Thus, the lower limit value 10 of the control parameter is the average value of the pulse voltage at abnormal ground, and the upper limit value 445 is the average value of the pulse voltage at normal ground. For reliability, take the median of two numbers, i.e. (445-10)/2=217, so in step S2 the threshold may be: intermediate value-30 < = threshold value < = intermediate value +30, e.g. 200. Meaning that grounding is considered effective as long as the converted filtered AD value is greater than 200. Through a large number of tests, the value can reliably distinguish whether the grounding is good or not when being connected with different types of different power loads. Fig. 5 is a flowchart of a method for detecting the ground of the circuit when the intermediate value is selected 200, the preset time is selected 1ms, and the preset times are selected 50 times.
The embodiment is simple to improve on the control system of the electrical equipment to obtain the single-phase alternating-current grounding real-time detection circuit, and can be realized by only adding a plurality of high-voltage large-resistance resistors on the original basis of the control system and then utilizing one AD port of the original control chip of the control system.
It will be evident to those skilled in the art that the invention is not limited to the details of the foregoing illustrative embodiments, and that the present invention may be embodied in other specific forms without departing from the spirit or essential characteristics thereof. The present embodiments are, therefore, to be considered in all respects as illustrative and not restrictive, the scope of the invention being indicated by the appended claims rather than by the foregoing description, and all changes which come within the meaning and range of equivalency of the claims are therefore intended to be embraced therein. Any reference sign in a claim should not be construed as limiting the claim concerned.
Furthermore, it should be understood that although the present disclosure describes embodiments, not every embodiment is provided with a separate embodiment, and that this description is provided for clarity only, and that the disclosure is not limited to the embodiments described in detail below, and that the embodiments described in the examples may be combined as appropriate to form other embodiments that will be apparent to those skilled in the art.
Claims (6)
1. The utility model provides a single-phase AC ground connection real-time detection circuit, includes live wire (L), zero line (N) and protection ground (PE), its characterized in that still includes rectification filter circuit (2), live wire (L) and zero line (N) connect in the input of rectification filter circuit (2), the output of rectification filter circuit (2) has connected gradually first resistance (R1), second resistance (R2) and third resistance (R3), the public end of third resistance (R3) and second resistance (R2) is connected in AD mouth (A) of singlechip (U1), the other end of third resistance (R3) connect in protection ground (PE);
the rectification filter circuit (2) comprises a rectification bridge (DB 1) and a filter capacitor (C1), wherein the live wire (L) and the zero wire (N) are connected to two input ends of the rectification bridge (DB 1), two output ends of the rectification bridge (DB 1) are connected to two ends of the filter capacitor (C1), and one output end of the rectification bridge (DB 1) is connected to the first resistor (R1);
the single-phase alternating-current grounding real-time detection circuit and a switching power supply of a control system where the single-phase alternating-current grounding real-time detection circuit is positioned share a rectifying and filtering circuit (2);
the resistance value of the first resistor (R1) is greater than or equal to 5000k omega.
2. The single-phase ac ground real-time detection circuit according to claim 1, wherein the single-chip microcomputer (U1) is a main control CPU in the control system.
3. The single-phase ac ground real-time detection circuit according to claim 2, wherein the resistance value of the second resistor (R2) is greater than or equal to 5000kΩ.
4. A single-phase ac ground real-time detection circuit according to claim 3, characterized in that the resistance value of the third resistor (R3) is selected according to a resistance value determination formula (1):
U11*R3/(R1+R2+R3)<U22 ①
wherein, the liquid crystal display device comprises a liquid crystal display device,
r1, the resistance value of the first resistor (R1); r2, the resistance value of the second resistor (R2); the resistance value of the third resistor R3; u11, highest input voltage; u22, AD port (A) highest withstand voltage.
5. A detection method based on the single-phase ac grounding real-time detection circuit as claimed in any one of claims 1 to 4, comprising:
s1, acquiring a pulse voltage average value;
s2, judging whether the average value of the pulse voltage is smaller than a threshold value, if yes, judging that the pulse voltage is abnormally grounded, and if not, judging that the pulse voltage is normally grounded;
the threshold is determined by: intermediate value-30 < = threshold value < = intermediate value +30;
the intermediate value is an intermediate pulse voltage value between the pulse voltage average value at normal grounding and the pulse voltage average value at abnormal grounding.
6. The method according to claim 5, wherein,
in step S1, a pulse voltage average value is acquired by:
s11, detecting AD values at intervals of a preset time, and continuously detecting the AD values for set times;
s12, adding all detected AD values within set times to obtain AD sum values;
s12, dividing the AD sum value by the set times to obtain a pulse voltage average value.
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