1 introduction
Along with national economy’s rapidly expand, 10 kV power distribution network is getting more and more complex, the distribution line are getting more and more, how to monitor and the control distribution line, guaranteed that the distribution network power supply security and stability reliability service becomes the power distribution automation the key. In the power distribution automated system, the feed line automation is the power distribution automation foundation, but the core equipment’s feed line end instrument becomes the power distribution automated system success implementation as the feed line automated system in the key. The feed line end instrument is called FTU (Feeder Terminal Unit) [1], installs on 10 kV feeder, on the paired columns the switch carries on the monitoring, completes the telemetering, the remote control, the remote letter, the failure detection function, and with the power distribution automation master station correspondence, provides the electrical power distribution system operational aspect and each kind of parameter is the monitor control needs the information, including time on-off state, the electrical energy parameter, the interaction breakdown, the earth fault as well as the breakdown parameter, and carries out the order which the power distribution master station after-crops, carries on the adjustment and the control to the switching equipment, realizes the fault location, the failure isolation and the non-breakdown region quick recovery power supply function.
This system uses the advanced DSP technology, by TI Corporation’s TMS320LF2407 controller, completes the feed line terminal unit primarily the research and the design. TMS320LF2407 uses 3.3 V voltage power supplies, reduced controller’s power loss, 40 MI/s carries out the speed, 32 K×16 position internal procedure Flash. 2.5 K×16 position procedure/data internal RAM, but also has the PWM channel, the capture unit, a/D switch, 4 level of assembly line technology and the special 16 hardware multiplier, the processing speed is high. Is suitable in processes the big operand the real-time task. TMS320LF2407 internal integrated the massive system resources, reduced system’s designed cost.
2 system hardware designs
The system hardware design divides into FTU the top and bottom two plywood. The lower level is the information acquisition and the control panel, including PT, CT, electro-optical coupler, control relay, serial port level switch and so on modules and so on composition data acquisitions, digital signal control and correspondence; The upper formation is the CPU board, including DSP, latch and so on modules and so on composition data processing, switch quantity input, output. Such FTU structure has the hierarchization, the modulation, the anti-jamming strong and the convenient system debugging.
2.1 system’s system designs
The system mainly divides into the simulation quantity data acquisition and the transformation module, the switch quantity input output module, the connection module, the clock module, the keyboard display module, outside expands the memory module, the power source module and so on. System composition diagram as shown in Figure 1.
2.2 simulated signal gathering and switching circuit
The simulation quantity input uses the exchange sampling technique. In electrical network’s network voltage and the electric current first transform into 0 V~100 after scene high efficiency PT and CT V and 0 A~5 A exchange electric quantity, then passes through two time PT and CT again transforms into 0 V~5 V voltage signal, eliminates the higher harmonic and the noise signal again after filter processing carries on the power amplification again, then sees somebody off the MD switch. Simulated signal recuperation electric circuit as shown in Figure 2.
In order to realize to the electric current, the voltage as well as between the two phase relation correct measurement, has used the synchronization sampling technique. Uses two piece of MAX125 to complete the simulation quantity input the synchronized sampling, to DSP carries on processing from the MAX125 output’s data direct input. MAX125 has the synchronized sampling function 14 A/D switch, may eliminate the electric current which and the voltage phase difference, because the non-at the same time sampling causes. Two piece of MAX125 constitution’s sampling circuit as shown in Figure 3.
The various phase voltages’ simulation quantity inlet connection first piece of MAX125 A group of first three channels, the various interphase currents’ simulation quantity inlet connection second piece of MAX125 A group of first three channels, on the surplus channel meet MAXl25 the output reference voltage 2.5 V, uses in carrying on a/D self-checking. Two piece of MAXl25 transformation start signal CONVST realizes by the TMS320LF2407 timer 3 interrupts, two piece of MAX125 transformations complete signal INT to receive TMS320LF2407 through the NAND gate XINT2. DSP reads the transformation result in the interrupt routine from MAXl25 RAM, then carries on the real-time processing to the result. Because the MAX125 digital signal is 5 V levels, cannot the direct drive TMS320LF2407 3.3 V levels, must therefore carry on the level switch through 74LVC4245.
Moreover a system expanded two piece of IS61LV6416 the SRAM memory, because TMS320LF2407 is the undervoltage device, therefore selects the low voltage 3.3 V power supplies IS61LV6416, the wiring is simple. A piece serves as the data-carrier storage, another piece serves as the debugging stage the program memory. Because in the research and development debugging stage, loads generally the procedure to RAM in moves, like this programs the speed and the efficiency can have the enhancement. The exterior memory selection uses 74HC32, each or gate two input termination
TMS320LF2407 STRB and RD, WE, if both are the low levels, then read-write selection. Selects patches or strips of land as worth saving for seed signal CE and the TMS320LF2407 PS connection in debugging stage IS61LV6416, after the debugging had ended, CE meets the high level.
2.3 switch quantity signal input output circuit
The remote letter input’s signal and the remote control output’s signal is the switch quantity. The switch quantity takes when the supply oscillator itself disturbs is quite big. This system uses the electro-optical isolation elimination disturbance, designs 8 group switch quantity remote letter input signal, mainly to the feeder column on switch’s current position as well as corresponds to be whether normal and the stored energy completes the situation and so on important state to carry on gathering, carries on the remote letter to the feeder protection movement situation. Switch quantity after electro-optical isolation, receives DSP directly: I/O mouth. Designs 3 group switch quantity output control signal, the control relay realizes the protection function.
2.4 clock circuits
Because the overall system needs fixed time to gather the data, the record surpasses the threshold value the time, counts the total power failure time, must therefore have the online system real-time clock. This system used real-time clock integrated circuit module DS12887, DS12887 to have information and so on second, minute, hour, Japan, week, month and year, and had the leap year compensatory function. The DS12887 interior has 128 byte non-volatility RAM and the lithium battery, even if the exterior power failure may also guarantee that the internal RAM content will not lose and internal clock work normal [2], had like this guaranteed FTU when power cut can also continue to time. Because the TMS320LF2407 read-write succession and the DS12887 read-write succession is completely different, therefore takes DS12887 DSP on the I/O address memory peripheral device, uses DSP general. The I/O port produces DS12887 to select patches or strips of land as worth saving for seed, to read, writes, enables the signal. Because the DS12887 power line voltage is 5 V, must therefore adds voltage switch 74LVC4245 in it and between DSP. DSl2887 and DSP interface circuit as shown in Figure 4.
2.5 power circuits
The FTU voltage class are many, CPU uses 3.3 V voltage power supplies, but the periphery component mostly uses 5 V voltage power supplies. When design must consider when the power cut how to work, this design has used the double-end power source cut electric circuit. Takes the emergency power supply with the accumulator cell. When normal work the FTU power source provides by the feed line transformation, but time breakdown situation supplies power by the accumulator cell [3]. Matches the net high pressure through the PT supplies power source module 220 V or 100 V exchange input, 220 V/100 V alternating currents after transformer, rectification block and three end manostat the transformation is 24 V direct currents, inputs to the battery charger for the battery charging. 24 V direct currents after the DC-DC transformation, the output ±5 V voltage supply the system various modules use again. Moreover through as1117 component 5 V TTL level switch is 3.3 V voltages. As DSP electric power supply.
2.6 keyboard demonstrations
For ease of operates and has the friendly man-machine connection, but also has designed the keyboard and liquid crystal display, uses in inputting each kind of parameter as well as the display system running status and so on. Uses the MG-12232 liquid crystal display module coordination keyboard operation, the demonstration related information, like electricity parameter data demonstration, parameter installation, breakdown information demonstration and so on. Uses DSP the digital I/O mouth simulation succession hardware interface plan. Realizes through the software control DSP I/O mouth with the slow peripheral device succession match, the hardware circuit is simple.
2.7 correspondence connections
TMS320LF2407 has a SCI module, may use this module to realize CPU and RS232 conveniently between serial port correspondence [4]. Uses the MAX232 achievement to actuate the component to carry on the serial communication. Because TMS320LF2407 uses 3.3 V supply voltage power supply, therefore between TMS320LF2407 and MAX232 needs to carry on the level switch, uses the 4N35 low speed light pair to isolate the component to carry on the electro-optical isolation and the level switch control. The RS232 connection mainly provides a debugging connection, debugs the personnel only to is connected the computer and FTU, may through computer’s COM mouth read data or the establishment operational parameter. Interface circuit as shown in Figure 5.
TMS320LF20407 internal integrated the CAN controller module, may realize the CAN main line correspondence to turn conveniently, only need adds on the corresponding driver and the suitable antijamming electric circuit in DSP and between the CAN main line then. The CAN main line’s data communication has the redundant reliability, timeliness and the flexibility, obtained more and more widespread use in the distribution network correspondence.
3 system software designs
The software uses the C language programming, uses the assembly language to the timely request high part, raises the running rate. The C language development speed is quick, the readability, the probability are good, the DSP assembly language has suits FFT instructions and so on operation reverse addressing, cyclic addressing.
The system software completes major function: 6 groups voltages, current analogue quantity gathering. 8 group switch quantity signal gathering, 3 group switch quantity output control, system initialization, breakdown judgment, serial port correspondence and so on.
3.1 system master routine flow
In order to realize the FTU function as well as the hardware request. Software design master routine flow as shown in Figure 6.
On after system electricity, the first initialization establishment, to the internal peripheral device (event supervisor EVA, EVB, the I/O port, SCI module, watch-dog and so on) carries on the initialization in turn, reads the current calendar clock data from DS12887. After the initialization completes, opens the interrupt, carries on the MD data acquisition in the interrupt, TMS320LF2407 reads the data, then carries on the FIR filter, already the sampling stored DSP to DSP the signal to carry on the operation again, carries on the FFT operation to each group signal, calculates its scope, coexisting enters RAM. CPU carries on the judgment to the electric current. Looked whether to surpass the predetermined value, judges whether to break down, then the utilization fault location algorithm, locates the breakdown rapidly, issues the order according to the place above to carry on the minute to switch on the operation. Realizes through the signal procedure with the master station correspondence, mainly includes data reporting, the installation parameter value to after-crop and so on.
The software uses the modular design, by the master routine module, the interrupt service module and the function submodule three major part is composed. Including initialization module, data storage module, display module, connection module, parameter revision module and so on.
Master routine:
3.2 fundamental quantity computations
Uses 14 A/D exchange sampling, each cycle carries on 64 sampling, the survey meter figures out the electric current, the voltage, the active power, the reactive power power factor and so on.
Voltage u(n) which, electric current i(N) obtains according to the sampling, may calculate electrical network’s other parameters; Power mean value (active power), alternating voltage effective value U, alternating current effective value, I, active power P, apparent power S, power factor cosφ. The formula is as follows:
Voltage, electric current effective value:
In addition, because used the synchronization sampling technique, zero foreword magnitude of current has been possible to extract by the software. Each time the sampling will obtain three-phase current data summation then. Regarding the symmetrical electrical network, its value should be zero, but the actual electrical network is not the full symmetry, must therefore judge the single-phase earth fault, cannot simply compares the electric current effective value and zero, should act according to the actual electrical network movement to establish an installation value, this installation value may add an allowance by FTU in the normal condition zero foreword electric current effective value to obtain.
3.3 frequency measurements
In the exchange sampling system, usually is a cycle sampling N spot electric quantity value. Then carries on processing to these data. If the mains frequency is constant, then sampling interval t=T/N (T is a cycle, N is sampling point), but electrical network’s frequency has certain fluctuation generally, therefore wants the continual readjustment sampling interval.
The input signal the filter, then becomes the square-wave signal after the zero crossing comparator LM339 reshaping take the counter again the first gating signal. The counter carries on the accumulation in this gating signal working life to input pulse’s integer. After the counting completes, the lock saves the counting value and by the TMS320-LF2407 read, will count again by the software does a tour of duty the counter impulse cycle, then obtains is measured signal the cycle.
4 concluding remark
This article in view of the power distribution automated system’s in feed line end instrument, the union digital signal processing technology, studied and has designed based on TMS320LF2407 FTU, has realized the DSP peripheral circuit, the simulation quantity, the switch quantity gathering electric circuit, the communication circuit design and so on. Has compiled the FTU hardware circuit’s software routine, has realized the fault location, the isolation and the power supply restores and so on important function.
