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GPS synchronized data acquisition card in the PCI Application

In Electronic Infomation Category: G | on November 10,2010

Abstract: The measurement of power angle data acquisition card is used Cygnal C8051F021 MCU to achieve the companys PCI bus interface card. The card port RAM via two pairs were realized with the GPS receiver board and EPM3064ATC100-10 datasheet and the host computer (PC) data exchange, in order to achieve high-speed, reliable data acquisition, processing and EPM3064ATC100-10 price and transmission. The data acquisition card with on-chip 12-bit high speed ADC and EPM3064ATC100-10 suppliers and supported by chip sample and hold circuit, sampling method is accurate by direct communication to achieve rapid sampling of voltage and current, ensuring real-time measurement of power system requirements.

Keywords: C8051F021 PCI GPS dual-port RAM AC power angle sampling

1 Introduction

Vice President Lu Yanchang State Power Corporation of China in the 26th running dispatching all closing remarks that the coming period of time the development of grid technology should focus on and solve problems, in the grid security, stability, and economic movement areas, interconnected power system real-time power angle measurement by increasing attention. Especially in the purpose to monitor the power dispatching automation system, how to quickly and accurately collecting and processing a variety of electrical parameters is very important. In the process of automation, the first link is the data acquisition. To this end we studied the development of power-angle wide-area power system monitoring and control system, which, with the C8051F021 MCU data acquisition card is not only to achieve an accurate, efficient, real-time data acquisition for AD and through the dual port RAM and PCI interfaces with the host computer exchange data, you can also communicate with the GPS receiver receives second pulse to achieve remote data acquisition synchronization.

2 power angle and its measurement

2.1 generator power angle

generator through the transformer, the output line and an infinite capacity system bus connection components of the transmission system shown in Figure 1.

if the graph G for the salient pole type generator, the generator active power output is

on the type also called generator power properties. Where XdΣ = Xd + XTL, where Xd is equivalent generator d-axis reactance, XTL for the generator and the connection between the infinite system reactance, Eq load for the generator potential, V, I for the system bus voltage reference and current, ψ is the bus voltage and current between the phase difference. When the generator potential and by Eq voltage V are constant, the transmission power P is the angle δ of the sine function, the angle δ is the phase difference between Eq and V angle. P due to the size of the power angle of cut associated with δ, so δ is called "power angle" or "power angle."

2.2 power angle measurement

for salient pole generators and salient-pole generator, The voltage and current vector as shown in Figure 2 (a), (b) below, shows the power angle vector δ is calculated as

where, XqΣ = Xq + XTL, Xq for the hair dryer in which the horizontal axis reactance. For a given system, XdΣ and XqΣ are constants, and therefore measured by computer, simply measure the voltage of the system bus is V, current I and power factor angle can be from (2) and (3) calculate the power angle. In addition, power systems described by a large disturbance in the electromechanical transient process is a set of nonlinear differential equations, can not be linear, so the general numerical integration method (such as Euler method, Runge - Kutta method, implicit integration) time domain analysis, the calculated results are plotted as operating parameters (such as the power angle) curves of time to determine power system transient stability. The slow curve of the system of calculation and are based on the precise power system AC signal acquisition can be achieved.

is through the data acquisition card samples the 3-phase AC voltage and current channels were collected after 6 to the computer for processing, that is, the signal for the exchange of power converters without directly to the transformer (PT / CT) secondary voltage and current measurement and then by a high-precision PT, CT is converted to a computer to measure the small signal (the data acquisition card is-2.5V ~ +2.5 V), then by A / D transform into the computer for processing, to calculate the voltage and current RMS and power factor angle and other electrical parameters and thus obtain the value of power angle and its change over time, and to provide power dispatching control center to power system stability monitoring.

3 capture card hardware design

mainly by the acquisition card C8051F021, A / D sample and hold filter circuit, dual-port RAM, GPS interfaces, PCI interface, and other components. From the field PT, CT over the voltage and current by the isolation transformer isolation transform input data acquisition card, and then after a second-order filter to the A / D converter front channels. Microcontroller through the GPS interface and dual-port RAM to obtain accurate second pulse and the corresponding time (year, month, day, hour, minute, second) and to achieve synchronization of the signal acquisition, digital conversion and then obtained by another dual-port RAM and PCI interfaces sent to the host computer for processing. System block diagram shown in Figure 3.

The acquisition card company using Cygnal C8051F021 MCU, the MCU is a fully integrated mixed-signal SoC (System On Chip), has the MCS-51 instruction set is fully compatible with high-speed CIP-51 core ; peak speeds of up to 25MI / S; in an integrated chip to form a single chip data acquisition or control system, almost all of the required analog and digital peripherals, and other features (including programmable gain amplifier PGA, ADC, DAC, voltage comparators, voltage references, UART, timers, programmable counter / timer array PCA, etc.). The instruction cycle is 83ns (3.3V, 12MHz); has a large capacity in the system (ISP) and in the application (IAP) programming of the FLASH memory; support meet IEEE 1194.1 standard JTAG debug and boundary scan, can be non-invasive , full-speed in-system debugging. As C8051F MCU 8-bit microcontroller and the other has a more excellent than performance, so a lot of available monitoring and control system design has become the preferred model.

ADC converter chip 12-bit, 100ks / s the ADC, each conversion is only 10μs, fully satisfy the system of real time and fast requirements. F021 MCU ADC with 8 external inputs, internal or external reference voltage can be provided (2.5V), Programmable single-ended or differential input amplifier with programmable gain and the acquisition card with 6 single-ended input to complete the 3-phase voltage and current synchronous acquisition. Because the ADC can only be single-ended input signal to the 0 ~ 2.5V for AD conversion, so the PT, CT sent-2.5V ~ +2.5 V sinusoidal AC signal to be in the A / D conversion of the front walkway a DC bias voltage of 2.5V, so the input signal amplitude of 0V ~ 5V, the signal has now been on-chip programmable gain amplifier attenuation into 0V ~ 2.5V, and then complete the A / D conversion. Collection, through sample collection procedures to maintain order issued by the sample / hold device to maintain the value of the instant acquisition, acquisition of transient signals through the analog channel switch to select into the decay circuit that, through the A / D converter to convert 12-bit parallel data output to the dual-port read into the RAM for the host computer processing.

dual-port RAM is used in 32k, 8-bit high speed IDT7007S, MCU and PC respectively, from both sides of dual-port RAM read and write (but not at the same time write data unit of the same address), and dual-port RAM access the operating time is only 55ns, therefore, dual-port RAM by the microcontroller greatly improved data exchange between PC and the speed at which the data acquisition card in the power system control and the application of the field to provide a guarantee.

PCI interface, PCI interface, mainly by the completion of CH365. CH365 is a connected PCI bus interface circuit universal support I / O port mapping, memory mapping, extended ROM and interrupts. The main use of CH365 acquisition card memory mapping function, 32-bit high-speed PCI bus will be converted to 8-bit data, 16-bit address active parallel interface. CH365 dual-port memory through the microcontroller or DSP and external exchange of data, and then to transfer data to PC for further processing. If you read and write CH365 Strobe pulse width is set to 30ns, and the use of double-word units for data exchange, the actual data transmission speeds of up to 7M bytes per second. PCI bus, compared with the other major bus, faster, real-time better, better controllability, so CH365 especially for high-speed real-time I / O control card, communication interface cards and data acquisition cards.

addition to the above data acquisition and processing speed, accuracy, real-time transmission and other considerations, this acquisition card also considered separate ways in different places dependent synchronous acquisition, the designed with GARMINs GPS Receiver (GPS Receiver Board) GPS15L, Precision timing by satellite, by satellite to provide precise second pulse to achieve synchronous acquisition in different places. The board received at least 11 satellites to receive signals from the ASIC and processing software to extract the information received, and output two kinds of time signals: one second pulse 1PPS, with the Coordinated Universal Time UTC (international standard time) synchronization error is less than 1μs; the second is through the serial port and the 1PPS output pulse edge corresponding to the standard time code (year, month, day, hour, minute, second), the 1PPS the "time mark." Power within the system by the end of each sending end and the distribution of widely dispersed, the base along each end of the installation of a GPS receiver, the GPS, we can guarantee the global and high-precision time signals and UTC all over the relative error no more than 1μs. The global high-precision time synchronization in the power system in the detection and measurement of very high value in use. The data acquisition card that is provided through the GPS receiver board second pulse and its time stamp to synchronize data collection in different places, proved the effect is ideal.

4 capture card software

the capture card and software programs including GPS receiver board serial communication program, communication with the host computer PCI interface program and the data acquisition and processing procedures. Software flow chart shown in Figure 4.

capture card dual-port RAM can communicate with the host computer to change the sampling points, sampling frequency, such as a frequency cycle of 256 points divided into 40 samples, value of the sampling points and then converted to process and send the host computer for further processing, such as voltage, current and power angle of the amplitude curve shows a system to monitor and thereby fails to make timely and appropriate control measures.

Capture card features the following:

· As a result of second-order filter circuit, so you can better capture card, high harmonics of the shielding A / D conversion. C8051F021 mixed-signal models are high in 12MHz external crystal, its clock period is 83ns, so a wide range of adjustable sampling frequency. Sampling rate can be widely used in a variety of communication require a higher sampling monitoring device.

· can also enter the 8 single-input or 4 differential inputs PT / CT signal, high accuracy, high speed sampling.

· using on-chip 12-bit resolution, 100ks / s conversion speed of successive approximation A / D converter and external filter sample and hold circuit, capable of fast mode A / D conversion.

· by receiving the second pulse and the GPS time scale, can guarantee the synchronization of remote signal acquisition.

· dual-port RAM and a dedicated PCI interface allows the upper and lower computer communication and exchange of data more quickly.

5 Conclusion

development and debugging of the acquisition card has been used after the phase angle and reactive power system angle measurement device, the practice shows that C8051F021 MCU acquisition system based not only meet the demand for power system monitoring and control devices, also has good value for money, ideal for a variety of voltage levels of the transmission system monitoring and control devices and measuring instruments section.

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