Voltage signal acquisition and processing method based on charged display coupling capacitor

Abstract

The invention belongs to the technical field of voltage signal acquisition, and discloses a voltage signal acquisition and processing method based on a coupling capacitor of an electrified display, which comprises the following steps of: 1, acquiring a voltage signal; 2, calculating the frequency of the voltage signal; 3, calculating the phase of the voltage signal; and step 4, non-voltage detection and synchronization reclosing detection are realized. According to the invention, on the premise of not additionally adding a voltage transformer, the electrified display of the switch cabinet is utilized to realize the acquisition of a line voltage signal, and the non-voltage detection and synchronization detection judgment of the line are realized through the cooperation with the protection device. The device is very suitable for transforming a transformer substation which is put into operation, the requirement for the space of a switch cabinet is low, the transformation cost is low by adopting a combined power amplifier mode, the whole device can be highly integrated with an electrified display, and the acquisition of a three-phase voltage signal of a line can be realized; according to the scheme, repeated wiring or equipment adding on the high-voltage side is not needed, and the operation is completed on the secondary low-voltage side without influencing the insulation design of the high-voltage switch cabinet.

Description

Technical Field

[0001] The present invention belongs to the technical field of voltage signal acquisition, and in particular relates to a voltage signal acquisition and processing method based on a charged display coupling capacitor. Background Art

[0002] Traditional distribution networks usually adopt a closed-loop design and open-loop operation mode. They are radial networks with unidirectional power flow and adopt a three-stage current protection configuration scheme coordinated by timing. The access of distributed power sources changes the distribution of fault currents in the distribution network. The original current protection may malfunction, reduce sensitivity or even refuse to operate. In addition, the access of a high proportion of distributed power sources also brings new problems to the reclosing switch configured based on the radial distribution network. When the distribution network line fault trips, since there is no voltage transformer (PT) on the line side, it is impossible to achieve reclosing by detecting no voltage. Direct unconditional reclosing may lead to asynchronous reclosing. The transient overvoltage generated by asynchronous reclosing will damage the insulation inside the electrical equipment, seriously affecting the service life of the equipment, and even causing downtime for maintenance, affecting the normal operation of the power grid. Asynchronous reclosing will also cause changes in parameters such as frequency and voltage of the power system, seriously affecting the stability of the power grid. In severe cases, it may trigger a chain reaction, leading to large-scale power outages.

[0003] Therefore, in order to avoid the harm caused by asynchronous reclosing of high-voltage lines, it is very important to check that the line is voltage-free for reclosing. The voltage measurement method commonly used in medium-voltage power grids is to use traditional PT to isolate the voltage and reduce it to a range that the measuring meter can bear, and obtain voltage information through the voltmeter on the secondary side. However, the traditional PT is large in size. In the built 10kV substation, due to space and renovation cost limitations, it is impossible to install PT in the switch cabinet, which makes it impossible to accurately obtain the voltage signal of the line.

[0004] In summary, the prior art has the following problems:

[0005] (1) Due to space and renovation cost limitations, it is not possible to install PTs in existing switch cabinets and obtain line voltage signals.

[0006] (2) Some non-contact voltage sensors currently available on the market have high costs, varying degrees of accuracy, high modification costs, and unknown stability.

[0007] (3) The coupling capacitance of the charged display is about 100 pF, which is very small and cannot be directly connected to the sampling device, so further modification is required.

[0008] (4) Currently there is no feasible voltage signal acquisition solution based on a live display. Summary of the invention

[0009] The object of the present invention is to provide a method for collecting and processing voltage signals based on a charged display coupling capacitor to solve the above-mentioned technical problems.

[0010] In order to solve the above technical problems, the specific technical solution of a voltage signal acquisition and processing method based on a charged display coupling capacitor of the present invention is as follows:

[0011] A method for collecting and processing voltage signals based on a coupled capacitor of a charged display comprises the following steps:

[0012] Step 1: Acquisition of voltage signal;

[0013] Step 2: Calculation of voltage signal frequency;

[0014] Step 3: Calculation of voltage signal phase;

[0015] Step 4: Check for no pressure and check for synchronous reclosing.

[0016] Further, the step 1 includes two methods:

[0017] Method 1: Direct connection to high-voltage power amplifier mode: The voltage follower is constructed through a high-voltage power amplifier to output a voltage signal in a 1:1 ratio, keeping the voltage signal unchanged while improving its load capacity, and directly connecting the switch input of the protection device to provide the device with a line voltage signal;

[0018] Method 2: Combined power amplifier mode: The voltage signal from the high-voltage sensor is first reduced to about 10V through the capacitor dividers C1 and C2, and then connected to the voltage follower composed of a conventional power amplifier with an input-output ratio of 1:1. It is then connected to the step-up transformer T1 to increase the voltage and then connected to the protection device to realize the detection of the line voltage signal.

[0019] Furthermore, in the second method, the high-voltage sensor has a withstand voltage level of 12kV, a capacitance of 115pF, and a tap output voltage of 110V; a capacitor voltage divider is connected in series, wherein C1 is 1nF, with a withstand voltage of 300V, and C2 is 10nF, with a withstand voltage of 300V; the power amplifier is composed of an OP07 operational amplifier, with an input-output ratio of 1:1, V+ is +15V, and V- is -15V; and the transformation ratio of T1 is 12V / 120V.

[0020] Furthermore, the step 2 includes the following specific steps:

[0021] Step 2.1: The voltage signal input to the protection device through the combined power amplifier mode is first sampled by AD with a sampling rate of 4000 Hz, converted into the actual voltage value, and stored in the ring data buffer;

[0022] Step 2.2: The DSP task cycle is set to 250 μs. In each task cycle, two sampling cycles of data, i.e. 160 points, are taken from the circular data buffer. The obtained data points are first processed by a second-order bandpass filter, and the upper and lower limits of the bandpass filter are set to 55 Hz and 45 Hz respectively.

[0023] Step 2.3: Find the zero-crossing point: Calculate whether the product of the current data point value[i] and the next data point value[i+1] is less than 0 to determine whether the data crosses zero, that is, determine whether value[i]*value[i+1]<0;

[0024] If there is a zero crossing point, the next step is divided into the following cases: If the first data point is a zero crossing point, that is, value[0]*value[1]<0, then take the four data points of value[0], value[1], value[2], and value[3] to calculate the exact position of the zero crossing point; If the second data point is a zero crossing point, that is, value[1]*value[2]<0, then take the four data points of value[0], value[1], value[2], and value[3] to calculate the exact position of the zero crossing point; If the 159th data point is a zero crossing point, that is, value[0]*value[1]<0 e

[158] *value

[159] <0, then take the four data points of value

[156] , value

[157] , value

[158] , and value

[159] to calculate the exact position of the zero-crossing point; when the zero-crossing point does not belong to the above three cases, assuming value[i]*value[i+1]<0, then take the four points of value[i-2], value[i-1], value[i], and value[i+1] to calculate the exact position of the zero-crossing point, calculate the data points of the two cycles respectively, and find out the positions of all zero-crossing points and the corresponding four calculated data points;

[0025] Step 2.4: Calculate the exact position of the zero-crossing point: Use the four data points for calculating the zero-crossing point determined above to construct the difference function using three Lagrange difference methods, then use the bisection method to solve the exact position of the zero-crossing point, calculate the data points of the two cycles obtained respectively, and find out the exact position of all the zero-crossing points;

[0026] Step 2.5: Calculate the frequency: Calculate the time difference Δt between the two most recent zero-crossing points respectively, then the frequency of the voltage signal is 1 / 2Δt; calculate the time difference between all zero-crossing points and calculate the average frequency as the final signal frequency.

[0027] Furthermore, the phase of the voltage signal collected in step 3 is calculated by FFT.

[0028] Furthermore, step 4 includes the following steps:

[0029] Step 4.1: Check for no-pressure overlap:

[0030] The protection device determines whether the voltage signal of the line input is less than 30% of the rated voltage. Under the rated voltage of the line, its tap output voltage is 110V. After capacitor voltage division and 1:1 voltage follower, and then through the 12V / 120V transformer, its rated voltage is 100V. Therefore, if the line voltage signal is less than 30V, it is judged as "line no pressure", and if it is greater than 30V, it is judged as "line pressure"; Step 4.2: Check synchronization coincidence:

[0031] Requirements for inspection:

[0032] Determine the voltage difference on both sides of the circuit breaker, which is required to be within ±5% to 10% of the rated voltage;

[0033] Determine the frequency difference of the voltage on both sides of the circuit breaker, which is required to be within ±0.2~0.5Hz;

[0034] Determine the phase angle difference of the voltage on both sides of the circuit breaker, which is required to be within 20°;

[0035] The protection device calculates whether the voltage difference, frequency difference and phase difference on both sides of the circuit breaker meet the synchronization requirements. If the above three requirements are met at the same time, it is judged as "synchronous", otherwise it is judged as "asynchronous".

[0036] The voltage signal acquisition and processing method based on the live display coupling capacitor of the present invention has the following advantages: the present invention can use the live display of the switch cabinet to obtain the line voltage signal without adding an additional voltage transformer, and realize the line voltage detection and synchronization judgment by cooperating with the protection device. It is very suitable for the transformation of the substation that has been put into operation. It has low requirements for the space of the switch cabinet and the transformation cost is low by using the combined power amplifier mode. The whole set of equipment can be highly integrated with the live display, with small size and low cost, and can realize the acquisition of the three-phase voltage signal of the line; and this solution does not require repeated wiring or additional equipment on the high-voltage side, and it is completed on the secondary low-voltage side without affecting the insulation design of the high-voltage switch cabinet, and can realize non-stop modification and easy maintenance, safe and reliable. The scheme proposed by the present invention is particularly suitable for solving the problem of unknown line status due to the lack of voltage transformer on the line side of the distribution network reclosing under the current new energy access. BRIEF DESCRIPTION OF THE DRAWINGS

[0037] Figure 1 This is the wiring diagram for the DXN type live display;

[0038] Figure 2 This is the structural diagram of the high pressure sensor;

[0039] Figure 3 This is a schematic diagram of a direct-connected high-voltage power amplifier mode of the present invention;

[0040] Figure 4 It is a schematic diagram of the combined power amplifier mode of the present invention;

[0041] Figure 5 A curve diagram of a verification voltage signal constructed according to the present invention. DETAILED DESCRIPTION

[0042] In order to better understand the purpose, structure and function of the present invention, the following is a further detailed description of a voltage signal acquisition and processing method based on a charged display coupling capacitor of the present invention in conjunction with the accompanying drawings.

[0043] like Figure 1 As shown in the figure, the traditional DXN type live display mainly uses the capacitor core rod in the high-voltage sensor to sense the voltage signal of the high-voltage bus, and connects it to a neon lamp or light-emitting diode to identify the live state of the line through the light signal. Figure 2 As shown. Selecting the commonly used 12kV voltage level, the extraction voltage is 110V, and the adaptation capacitance is 115 (±15) pF, the calculated electrical energy capacity of the sensor is 0.000437VAR, which shows that the capacity of the sensor is very small. The field test results also show that if it is directly connected to the measurement and control device with a sampling PT, the live display cannot work normally and cannot glow, which means that the sensor capacity of the live display is too small to meet the load requirements of the measurement and control device.

[0044] Based on this, the present invention further processes the signal output by the charged display to enhance its load capacity:

[0045] Step 1: Obtaining voltage signal

[0046] The present invention is implemented by two technical solutions:

[0047] Method 1: Direct connection to high voltage amplifier mode, such as Figure 3 As shown in the figure, the direct connection high-voltage power amplifier mode requires a high-voltage power amplifier. For a 10kV line, the sensor output voltage is about 110V. The high-voltage power amplifier can be used to construct a voltage follower 1:1 to output the voltage signal, keep the voltage signal unchanged and improve its load capacity. It is directly connected to the switch input of the protection device to provide the device with a line voltage signal. The high-voltage power amplifier required for this mode needs to have an output voltage greater than 110V, which is relatively expensive.

[0048] Method 2: Combined Amplifier Mode

[0049] In order to reduce the cost, the present invention proposes another combined power amplifier mode, such as Figure 4As shown, the voltage signal derived from the high-voltage sensor is first reduced to about 10V through the capacitor dividers C1 and C2, and then connected to the voltage follower composed of a conventional power amplifier with an input-output ratio of 1:1. It is then connected to the step-up transformer T1 to increase the voltage and then connected to the protection device to realize the detection of the line voltage signal.

[0050] Specific implementation:

[0051] The high-voltage sensor has a withstand voltage of 12kV, a capacitor of 115pF, and a tap output voltage of 110V; a series capacitor voltage divider is used, where C1 is 1nF, withstand voltage 300V, and C2 is 10nF, withstand voltage 300V; the power amplifier is composed of OP07 op amps, with an input-output ratio of 1:1, V+ is +15V, and V- is -15V; the transformation ratio of T1 is 12V / 120V. Through this transformation, the secondary side rating of the traditional voltage transformer can be kept consistent with 100V, which is convenient for subsequent detection of no-voltage and synchronous reclosing.

[0052] Step 2: Calculation of voltage signal frequency

[0053] The above method can be used to extract the line voltage signal. In order to realize synchronous closing, the line voltage signal frequency needs to be calculated. The present invention provides a method for calculating the power frequency voltage frequency:

[0054] Step 2.1: The voltage signal input to the protection device through the combined power amplifier mode is first sampled by AD with a sampling rate of 4000 Hz, converted into the actual voltage value, and stored in the ring data buffer.

[0055] Step 2.2: The DSP task cycle is set to 250μs. Each task cycle takes data of two sampling cycles, i.e. 160 points, from the circular data buffer. The data points are first processed by a second-order bandpass filter, and the upper and lower limits of the bandpass filter are set to 55Hz and 45Hz respectively.

[0056] Step 2.3: Find the zero-crossing point: Calculate whether the product of the current data point value[i] and the next data point value[i+1] is less than 0 to determine whether the data crosses zero, that is, determine whether value[i]*value[i+1]<0.

[0057] If there is a zero crossing point, the next step is processed according to the following situations: If the first data point is a zero crossing point, that is, value[0]*value[1]<0, then take the four data points of value[0], value[1], value[2], and value[3] to calculate the exact position of the zero crossing point; If the second data point is a zero crossing point, that is, value[1]*value[2]<0, then take the four data points of value[0], value[1], value[2], and value[3] to calculate the exact position of the zero crossing point; If the 159th data point is a zero-crossing point, that is, value

[158] *value

[159] <0, then take value

[156] , value

[157] , value

[158] , and value

[159] to calculate the exact position of the zero-crossing point; when the zero-crossing point does not belong to the above three cases, assuming value[i]*value[i+1]<0, then take value[i-2], value[i-1], value[i], and value[i+1] to calculate the exact position of the zero-crossing point. Calculate the data points of the two cycles obtained respectively, and find the positions of all zero-crossing points and the corresponding four calculated data points.

[0058] Step 2.4: Calculate the exact position of the zero-crossing point: Use the three Lagrange difference methods to construct the difference function through the four data points for calculating the zero-crossing point determined above, and then use the bisection method to solve the exact position of the zero-crossing point. Calculate the data points of the two cycles obtained respectively to find the exact position of all zero-crossing points.

[0059] Step 2.5: Calculate the frequency: Calculate the time difference Δt between the two most recent zero-crossing points respectively, then the frequency of the voltage signal is 1 / 2Δt; calculate the time difference between all zero-crossing points and calculate the average frequency as the final signal frequency.

[0060] test:

[0061] Construct a voltage signal containing multiple harmonics in Matlab:

[0062] y=20+220*sin(2*pi*f*t)+10*sin(2*pi*3*f*t)+

[0063] 5*sin(2*pi*5*f*t)+12*sin(2*pi*11*f*t); such as Figure 5 shown.

[0064] Set f=49.00, 49.20, 49.55, 49.95, 50.05, 50.15, 51.25, 52.05 Hz respectively to verify the accuracy of the above frequency calculation algorithm. The calculation results are shown in the following table:

[0065]

[0066] Step 3: Calculation of voltage signal phase: The phase of the collected voltage signal is calculated by FFT (Fast Fourier Transform), which is a very mature algorithm and will not be described in detail.

[0067] Step 4: Check for no-pressure and synchronous reclosing

[0068] Through step 1: voltage signal acquisition, step 2: voltage signal frequency calculation and step 3: voltage signal phase calculation, it is possible to obtain the line voltage signal and obtain the voltage signal amplitude, frequency and phase through the switch cabinet's own live display without installing additional voltage transformers. Further, the line can be tested for no-voltage reclosing and synchronous reclosing based on the voltage signal:

[0069] Step 4.1: Check for no-pressure overlap:

[0070] The protection device determines whether the voltage signal of the line input is less than 30% of the rated voltage. Taking the voltage sensor used in the present invention as an example, its tap output voltage is 110V under the rated voltage of the line. After capacitor voltage division and 1:1 voltage follower, and then through a 12V / 120V transformer, its rated voltage is 100V. Therefore, if the line voltage signal is detected to be less than 30V at this time, it is determined as "the line has no voltage", and if it is greater than 30V, it is determined as "the line has voltage".

[0071] Step 4.2: Check synchronization:

[0072] Requirements for inspection:

[0073] (To determine the voltage difference on both sides of the circuit breaker, the voltage difference is generally required to be within ±5% to 10% of the rated voltage;

[0074] Determine the frequency difference of the voltage on both sides of the circuit breaker, which is generally required to be within ±0.2~0.5Hz;

[0075] Determine the phase angle difference of the voltage on both sides of the circuit breaker, generally requiring the phase difference to be within 20°.)

[0076] The protection device calculates whether the voltage difference, frequency difference and phase difference on both sides of the circuit breaker meet the synchronization requirements. If the above three requirements are met at the same time, it is judged as "synchronous", otherwise it is judged as "asynchronous".

[0077] It is to be understood that the present invention is described by some embodiments, and it is known to those skilled in the art that various changes or equivalent substitutions may be made to these features and embodiments without departing from the spirit and scope of the present invention. In addition, under the teachings of the present invention, these features and embodiments may be modified to adapt to specific circumstances and materials without departing from the spirit and scope of the present invention. Therefore, the present invention is not limited by the specific embodiments disclosed herein, and all embodiments falling within the scope of the claims of this application are within the scope of protection of the present invention.

Claims

1. A method for collecting and processing voltage signals based on a charged display coupling capacitor, characterized in that: The steps include: Step 1: Acquisition of voltage signal; Step 2: Calculation of voltage signal frequency; Step 3: Calculation of voltage signal phase; Step 4: Check for no pressure and check for synchronous reclosing.

2. The voltage signal acquisition and processing method based on the charged display coupling capacitor according to claim 1 is characterized in that: The step 1 includes two methods, Method 1: Direct connection to high-voltage power amplifier mode: The voltage follower is constructed through a high-voltage power amplifier to output a voltage signal in a 1:1 ratio, keeping the voltage signal unchanged while improving its load capacity, and directly connecting the switch input of the protection device to provide the device with a line voltage signal; Method 2: Combined power amplifier mode: The voltage signal from the high-voltage sensor is first reduced to about 10V through the capacitor dividers C1 and C2, and then connected to the voltage follower composed of a conventional power amplifier with an input-output ratio of 1:

1. It is then connected to the step-up transformer T1 to increase the voltage and then connected to the protection device to realize the detection of the line voltage signal.

3. The voltage signal acquisition and processing method based on the charged display coupling capacitor according to claim 2 is characterized in that: In the second method, the high-voltage sensor has a withstand voltage level of 12kV, a capacitance of 115pF, and a tap output voltage of 110V; a capacitor voltage divider is connected in series, wherein C1 is 1nF, with a withstand voltage of 300V, and C2 is 10nF, with a withstand voltage of 300V; the power amplifier is composed of an OP07 operational amplifier, with an input-output ratio of 1:1, V+ is +15V, and V- is -15V; and the transformation ratio of T1 is 12V / 120V.

4. The voltage signal acquisition and processing method based on the charged display coupling capacitor according to claim 1 is characterized in that: The step 2 comprises the following specific steps: Step 2.1: The voltage signal input to the protection device through the combined power amplifier mode is first sampled by AD with a sampling rate of 4000 Hz, converted into the actual voltage value, and stored in the ring data buffer; Step 2.2: The DSP task cycle is set to 250 μs. In each task cycle, two sampling cycles of data, i.e. 160 points, are taken from the circular data buffer. The obtained data points are first processed by a second-order bandpass filter, and the upper and lower limits of the bandpass filter are set to 55 Hz and 45 Hz respectively. Step 2.3: Find the zero-crossing point: Calculate whether the product of the current data point value[i] and the next data point value[i+1] is less than 0 to determine whether the data crosses zero, that is, determine whether value[i]*value[i+1]<0; If there is a zero crossing point, the next step is divided into the following cases: If the first data point is a zero crossing point, that is, value[0]*value[1]<0, then take the four data points of value[0], value[1], value[2], and value[3] to calculate the exact position of the zero crossing point; If the second data point is a zero crossing point, that is, value[1]*value[2]<0, then take the four data points of value[0], value[1], value[2], and value[3] to calculate the exact position of the zero crossing point; If the 159th data point is a zero crossing point, that is, value[0]*value[1]<0 e[158]*value[159]<0, then take the four data points of value[156], value[157], value[158], and value[159] to calculate the exact position of the zero-crossing point; when the zero-crossing point does not belong to the above three cases, assuming value[i]*value[i+1]<0, then take the four points of value[i-2], value[i-1], value[i], and value[i+1] to calculate the exact position of the zero-crossing point, calculate the data points of the two cycles respectively, and find out the positions of all zero-crossing points and the corresponding four calculated data points; Step 2.4: Calculate the exact position of the zero-crossing point: Use the four data points for calculating the zero-crossing point determined above to construct the difference function using three Lagrange difference methods, then use the bisection method to solve the exact position of the zero-crossing point, calculate the data points of the two cycles obtained respectively, and find out the exact position of all the zero-crossing points; Step 2.5: Calculate the frequency: Calculate the time difference Δt between the two most recent zero-crossing points respectively, then the frequency of the voltage signal is 1 / 2Δt; calculate the time difference between all zero-crossing points and calculate the average frequency as the final signal frequency.

5. The voltage signal acquisition and processing method based on the charged display coupling capacitor according to claim 1 is characterized in that: The phase of the voltage signal collected in step 3 is calculated by FFT.

6. The voltage signal acquisition and processing method based on the charged display coupling capacitor according to claim 1 is characterized in that: The step 4 comprises the following steps: Step 4.1: Check for no-pressure overlap: The protection device determines whether the voltage signal of the line input is less than 30% of the rated voltage. Under the rated voltage of the line, its tap output voltage is 110V. After capacitor voltage division and 1:1 voltage follower, and then through the 12V / 120V transformer, its rated voltage is 100V. Therefore, if the line voltage signal is less than 30V, it is judged as "no voltage in the line", and if it is greater than 30V, it is judged as "voltage in the line". Step 4.2: Check synchronization: Requirements for inspection: Determine the voltage difference on both sides of the circuit breaker, which is required to be within ±5% to 10% of the rated voltage; Determine the frequency difference of the voltage on both sides of the circuit breaker, which is required to be within ±0.2~0.5Hz; Determine the phase angle difference of the voltage on both sides of the circuit breaker, which is required to be within 20°; The protection device calculates whether the voltage difference, frequency difference and phase difference on both sides of the circuit breaker meet the synchronization requirements. If the above three requirements are met at the same time, it is judged as "synchronous", otherwise it is judged as "asynchronous".

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