CN114384315A - Voltage fluctuation and flicker tester based on FPGA and ARM9 - Google Patents

Abstract

The invention takes an embedded ARM9 controller and an FPGA as processing cores, designs a handheld voltage fluctuation and flicker tester, and can simultaneously measure the short-time flicker value of a plurality of paths of alternating voltage signalsP _stAnd long time flicker valueP _lt. In order to simplify the operation process, the square root mean value operation is carried out once on each half cycle of the voltage, the obtained square root mean value sequence is subjected to fast Fourier transform, the corresponding instantaneous flicker value under each frequency is solved, and the short-time flicker is solved by utilizing a probability large value method. By alternately receiving data in 2 groups of memories in the FPGA and utilizing a ping-pong mode to realize a 32-bit FFT algorithm, the operation speed and the accuracy can be greatly improved. The actual measurement result shows that the calculation precision of the tester for the root mean square value reaches 2%, and the flicker measurement precision reaches 2%. The software and hardware platform can conveniently expand the application of other electric energy quality measurement such as harmonic waves, interharmonic waves and the like, and has better popularization value.

Description

A voltage fluctuation and flicker tester based on FPGA and ARM9

technical field

The invention belongs to the technical field of electronic measurement, and relates to a monitoring device for power quality, in particular to a voltage fluctuation and flicker tester based on FPGA and ARM9.

Background technique

With the rapid development of my country's industry and national economy, the load of the power grid has increased sharply, especially the proportion of impact and nonlinear loads has been increasing, which makes the power supply voltage fluctuate and flicker, which seriously affects the power quality of the power grid. At present, the digital flicker meter based on the flicker measurement principle given by the IEC61OOO-3-7 standard has come out, but its measurement method is complicated and the cost is high. The voltage flicker detection method based on the parallel filter needs to use two parallel filters to analyze the spectrum and follow the amplitude, which is difficult to implement. The measurement of voltage flicker by the square detection method based on virtual instrument requires the cooperation of a computer, which is not convenient for hand-held or installed applications.

SUMMARY OF THE INVENTION

In view of the problems existing in the prior art, the present invention provides a hand-held voltage fluctuation and flicker tester, which takes FPGA and ARM as the control core and combines the FFT algorithm, which can measure the multi-channel voltage fluctuation and flicker in real time and with high precision. The voltage rms value curve can be recorded and stored, which is convenient for viewing and analysis, and ensures high measurement accuracy.

A voltage fluctuation and flicker tester based on FPGA and ARM9, including signal preprocessing circuit, synchronous A/D converter, FPGA and ARM microcontroller system;

The signal preprocessing circuit detects and processes 4 channels of AC voltage signals, and then performs pre-operation and AD conversion circuit conversion processing through FPGA, and then transmits it to the ARM control system for post-operation to realize human-computer interaction and network communication functions;

The signal preprocessing circuit is composed of a voltage transformer, an adjustable amplifier circuit composed of an analog switch and an operational amplifier, and an RC low-pass filter, which converts the measured voltage signal into a signal suitable for the A/D range, and filters the signal. remove high frequency components;

The FPGA contains 43661 logic units, 2088Kb of block RAM, and 401Kb of distributed RAM. The device provides 218 I/Os; the FPGA is responsible for controlling the A/D converter for sampling, and according to ARM9 instructions Control the analog switch to switch the range, sample the keyboard action and transmit the key code to the ARM controller;

The core operation of the tester is completed by the FPGA, including half-wave RMS calculation and FFT transformation, and the operation results and waveform data are transmitted to the ARM controller for subsequent processing;

The A/D converter has a 4-channel simultaneous sampling function, the sampling rate is 200KSPS. 16-bit precision, there are two output modes of serial and parallel, and the input range of ±5V or ±10V is selected to expand the phase difference The measurement function is connected to the FPGA in the parallel port mode, and the input range of ±5V is selected, and the data and control bus of the A/D converter are directly connected to the I/O of the FPGA;

The ARM control system, running at a speed of 200MHz, as the control core of the system, completes the initialization of the operating system and assignment of tasks, and performs post-operation on the results of the FFT to obtain the final results of voltage fluctuation and flicker.

Further, in the signal preprocessing circuit, the voltage transformer is a 2mA: 2mA miniature transformer, and the adjustable amplifier circuit is composed of rail-to-rail integrated operational amplifiers and 4-way analog switches, providing 4-level magnification to improve the voltage measurement. range, the RC low-pass filter cutoff frequency is selected as 3000Hz.

Further, the connection between the FPGA and the ARM adopts the bus interface, and the IP core tool is used to generate a 4KB FIFO using the block RAM inside the FPGA to transmit data between the FPGA and the ARM.

Further, the ARM control system has built-in LINUX operating system and QT graphic file system, and supports TCP/IP network protocol stack, externally expands NAND FLASH memory with a capacity of 128MB; externally expands DRAM chip with a capacity of 16M×32bit; externally expands SPI bus FLASH chip for parameter storage, the capacity is 128KB.

Compared with the prior art, the beneficial effects of the present invention are as follows: a handheld voltage fluctuation and flicker tester is designed on the ARM9 and FPGA platforms, and the FFT algorithm in the FPGA is used to realize the measurement of the flicker, with high precision and high speed. Quick advantage. The method of LINUX+QT+FATFS makes the development of ARM convenient, the graphical interface is friendly, the storage is easy, and the introduction of the network interface is convenient for remote communication and control.

Description of drawings

FIG. 1 is a hardware structural diagram in an embodiment of the present invention.

FIG. 2 is a diagram of a network communication interface for connecting an Ethernet control chip DP83848YB to realize 10M/100M self-adaptation in an embodiment of the present invention.

FIG. 3 is a flow chart of calculation of flicker in an embodiment of the present invention.

FIG. 4 is a block diagram of each module in the FPGA in the embodiment of the present invention.

Detailed ways

The technical solutions of the present invention will be further described in detail below with reference to the accompanying drawings.

A handheld device composed of signal preprocessing circuit, synchronous A/D converter, FPGA and ARM microcontroller system. The 4-channel AC voltage signal is detected and processed by the signal preprocessing circuit, and then the FPGA is used for pre-operation and AD conversion circuit conversion processing, and then transmitted to the ARM control system for post-operation to realize human-computer interaction and network communication functions.

The signal preprocessing circuit is composed of a voltage transformer, an adjustable amplifier circuit composed of an analog switch and an operational amplifier, and an RC low-pass filter, which can convert the measured voltage signal into a signal suitable for the A/D range (the system is designed as -5 ~﹢5V), and filter out high frequency components. Among them, the voltage transformer is a 2mA: 2mA miniature transformer, and the adjustable amplifier circuit is composed of rail-to-rail integrated operational amplifiers and 4-way analog switches, providing 4-level magnification to improve the voltage measurement range (the system is designed to be 0.5-500V ), the cut-off frequency of RC low-pass filter is selected as 3000Hz.

FPGA, which contains 43661 logic units, block RAM up to 2088Kb, also contains 401Kb distributed RAM, this device can provide 218 I/Os, and the power consumption is only 50% of the commonly used FPGA, which is suitable for hand-held design. The FPGA is responsible for controlling the A/D converter to sample, and controls the analog switch to switch the range according to the ARM9 instruction, samples the keyboard action and transmits the key code to the ARM controller. The core operation of the tester is completed by the FPGA, including half-wave RMS calculation and FFT transformation, and the operation results and waveform data are transmitted to the ARM controller for subsequent processing. The connection between the FPGA and the ARM adopts the bus interface, and the IP core tool is used to generate a 4KB FIFO using the block RAM inside the FPGA to transmit data between the FPGA and the ARM.

A/D converter, with 4-channel simultaneous sampling function, the highest sampling rate is 200KSPS. 16-bit precision, there are two output modes of serial and parallel, optional ±5V or ±10V input range can be used to expand phase difference measurement In the present invention, the parallel port is used to connect with the FPGA, and the input range of ±5V is selected, and the data and control bus of the A/D converter can be directly connected with the I/O of the FPGA.

The ARM control system, with a running speed of 200MHz and rich user interface functions, is the control core of the system. It completes the initialization of the operating system and assignment of tasks, and performs post-operation on the results of the FFT to obtain the final voltage fluctuation and flicker. result. Because the ARM control system needs to have built-in LINUX operating system and QT graphics file system, and needs to support the TCP/IP network protocol stack, the program space is required to be larger, so the NAND FLASH memory is expanded externally with a capacity of 128MB. And expand the DRAM chip, the capacity is 16M × 32bit. External expansion of SPI bus FLASH chip for parameter storage, the capacity is 128KB. The present invention is described in further detail below in conjunction with specific embodiments:

First, use a standard harmonic signal source to provide the input signal to the system, and set the 2nd to 6th harmonics to 2% of the fundamental wave, then perform the first-order RMS value operation on each half-cycle of the voltage, and perform a fast-Four-Four (FFT) on the obtained RMS value sequence. Lie transform is used to solve the instantaneous flicker value corresponding to each frequency, and the short-term flicker is solved by using the maximum probability method. The 32-bit FFT algorithm is realized by using the ping-pong method to receive data alternately between two sets of memories in the FPGA, which can greatly improve the operation speed and accuracy.

The first step is to calculate the voltage root mean square value every half cycle, and obtain the voltage root mean square value sequence U(N).

The second step is to perform FFT operation on the sequence U(N) to obtain its discrete spectrum. Since the time span is 10.24s, the spectral resolution of U(N) is 1/10.24=0.097656Hz.

The third step is to divide twice the frequency spectrum amplitude corresponding to each frequency by the decomposed DC component amplitude to obtain the voltage fluctuation d _i at this frequency, using the formula S _i =[d(i)/d _i ] ² can obtain the instantaneous flicker value S _i at this frequency.

In the fourth step, the instantaneous flicker S _i corresponding to the sequence U(N) is equal to the sum of the instantaneous flicker corresponding to each frequency on its frequency spectrum, S _i =s _0.5 +s ₁ +s _1.5 +...+s ₂₅ .

即可求解出10min内的短时闪变值P_st。The fifth step is to calculate 60 instantaneous flicker values according to the above steps, and then solve the 5 specified values of P _0.1 , P ₁ , P ₃ , P ₁₀ and P ₅₀ by sorting them, which are the S sequences in this period of time respectively. 99.9%, 99%, 97%, 90% and 50% of the probability of large value, substitute into the formula

The short-term flicker value P _st within 10 minutes can be solved.

即可求解出2h内的长时闪变P_lt。In the sixth step, the above steps are performed 12 times, and 12 short-term flicker values are obtained, using the formula

The long-term flicker P _lt within 2h can be solved.

View the result after the FPGA performs the FFT operation:

The calculation shows that the relative error of each harmonic and the fundamental wave percentage is less than 2%. Comparing the measured root mean square value with the given value, the error is less than 2%. Analysis shows that the error is caused by signal source error, A/D sampling error, rounding error during FFT operation, etc. At the same time, the voltage fluctuation and flicker tester was used to measure the 380V distribution network in the school area. The test results show that the short-term flicker value P _st is the minimum value of 0.096, the maximum value is 0.473, and the long-term flicker value P _lt is 0.178 , far below the national standard limit of 1.0. The results are more in line with the actual situation in the school area.

The above descriptions are only the preferred embodiments of the present invention, and the protection scope of the present invention is not limited to the above-mentioned embodiments, but any equivalent modifications or changes made by those of ordinary skill in the art based on the contents disclosed in the present invention should be included in the within the scope of protection described in the claims.

Claims (4)

1. a voltage fluctuation and flicker tester based on FPGA and ARM9, comprise signal preprocessing circuit, synchronous A/D converter, FPGA and ARM microcontroller system, it is characterized in that: The signal preprocessing circuit detects and processes 4 channels of AC voltage signals, and then performs pre-operation and AD conversion circuit conversion processing through FPGA, and then transmits it to the ARM control system for post-operation to obtain the final operation result, realizing human-computer interaction and network communication functions; The signal preprocessing circuit is composed of a voltage transformer, an adjustable amplifier circuit composed of an analog switch and an operational amplifier, and an RC low-pass filter, which converts the measured voltage signal into a signal suitable for the A/D range, and filters the signal. remove high frequency components; The FPGA contains 43661 logic units, 2088 Kb of block RAM, and 401 Kb of distributed RAM. The device provides 218 I/Os; the FPGA is responsible for controlling the A/D converter for sampling, and according to the ARM9 The command controls the analog switch to switch the range, samples the keyboard action and transmits the key code to the ARM controller; The core operation of the tester is completed by the FPGA, including half-wave RMS calculation and FFT transformation, and the operation results and waveform data are transmitted to the ARM controller for subsequent processing; The A/D converter has the function of 4-channel simultaneous sampling, and its sampling rate is up to 200KSPS. 16-bit precision, there are two output modes of serial and parallel, and the input range of ±5V or ±10V is selected for phase expansion. Difference measurement function, use parallel port to connect with FPGA, and select ±5 V input range, the data and control bus of A/D converter are directly connected to I/O of FPGA; The ARM control system, running at a speed of 200 MHz, as the control core of the system, completes the initialization of the operating system and assignment of tasks, and performs post-operation on the results of the FFT to obtain the final results of voltage fluctuation and flicker. 2. a kind of voltage fluctuation and flicker tester based on FPGA and ARM9 according to claim 1, is characterized in that: in signal preprocessing circuit, voltage transformer selects 2mA: the miniature transformer of 2mA, adjustable amplifier circuit It is composed of rail-to-rail integrated operational amplifier and 4 analog switches. It provides 4-level magnification to improve the voltage measurement range. The cut-off frequency of RC low-pass filter is selected as 3 000 Hz. 3. a kind of voltage fluctuation and flicker tester based on FPGA and ARM9 according to claim 1, it is characterized in that: the connection of FPGA and ARM adopts bus interface, uses IP core tool to use block RAM inside FPGA to generate a 4 KB FIFO is used to transfer data between FPGA and ARM. 4. a kind of voltage fluctuation and flicker tester based on FPGA and ARM9 according to claim 1, is characterized in that: ARM control system built-in LINUX operating system and QT graphic file system, and support TCP/IP network protocol stack, Externally expand NAND FLASH memory, with a capacity of 128 MB; externally expand DRAM chip, with a capacity of 16 M×32 bit; externally expand SPI bus FLASH chip for parameter storage, with a capacity of 128 KB.

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