Foreword
Because the production automation and each kind of automatic control, the sequential control equipment’s appearance, requests the electrical machinery to move in the frequent starting, the brake, the pro and con biography, the intermittence as well as changes frequently the load and so on each way. Electrical machinery’s movement request is getting higher and higher. At the same time, because electrical machinery and necessary machinery continually in the same place, when the electrical machinery breaks down, affects the production system frequently. Therefore, implements the effective protection to the electrical machinery is guarantees the production system normal work an important task.
Along with science’s and technology’s development, in the electrical machinery protective device has used the electron protective device gradually. In overseas, at present the electron protective device already has obtained the widespread application in the electrical power system and in the electrical machinery protective device, domestic also starts to promote [1]. The electron protective device’s merit is: Basically is composed of the static part. Its acting speed is quick, does not have the mechanical displacement and the attrition, the precision and the life has the electronic contact relay to be higher than generally, bears the impact and the vibration, the reliability is good. Moreover, the electronic circuit movement power is small, the sensitivity is high.
Digital signal processor (DSP) has the streamline form operating function and the monocycle completes the multiplication the structure, is composed the system by it to be able real-time to carry on the spectral analysis. High speed 14 A/D switch MAX126 belt multiway switches and sampling retainer, very suitable electrical machinery signal gathering. In order to realize to electrical machinery’s reliable protection, what proposed by TMS320LF2407 is the core, to the overload, the underloading, not balanced, breaks, has pressed with the undervoltage and so on common breakdown has the synthesis examination protection function intelligent electrical machinery protector.
1 system basic principle and design concept
In the electrical machinery movement will have not the normal running status frequently. These not normal running status includes: The overload, stops up the extension, the short circuit, the underloading, not balanced, to break, the pressure, the undervoltage and the leakage. The electrical machinery protection is in examines three phase voltage UA, UB, UC, three interphase current IA, IB, IC and leak electric current IL in the foundation to make. The concrete process is as follows:
(1) establishes each parameter, sends out the control signal by PC machine;
(2) sampling three phase voltages, three interphase currents and leak the electric current, obtains the real-time value;
(3) carries on processing and the computation using the FFT algorithm to the data, obtains three phase voltages, the electric current effective values, the active power, the reactive power as well as the power factor;
(4) judges the electrical machinery whether to be at not the normal running status;
(5) transmits through the RS-485 connection the data to the demonstration part, demonstrates on LCD.
System’s hardware diagram as shown in Figure 1. CPU selects TI Corporation’s TMS320LF2407, its rich hardware source obtained the full application in the system, in addition the few periphery component, constituted a function to consummate, the simple suitable system.
Figure 1 hardware diagram
2 system hardware designs
2.1 TMS320LF2407
TMS320LF2407 is also called the DSP controller, is TI Corporation aims at [2-4] which specially controls and so on electrical machinery, invertor, robot, numerically-controlled machine tool design. TMS320LF2407 uses the high performance static state CMOS technology, causes the power line voltage to reduce to 3.3V, reduced controller’s power loss; 30MIPS carries out the speed to cause the instruction cycle to reduce to 33ns (30MHZ), thus sharpened controller’s real-time control ability. It has included two event supervisor module EVA and EVB, can realize: Three phase reverser controls; PWM symmetry and asymmetrical profile; 3 capture units; 16 channel A/D switch. The event supervisor module is suitable for the control exchange asynchronous machine, not brushes the direct current machine, the switch magnetic resistance electrical machinery, to step-by-step the electrical machinery, the multistage electrical machinery and the invertor.
2.2 TMS320LF2407 and MAX126 interface circuits
Although the TMS320LF2407 chip interior contains the pair of 10 A/D transformation module, but can only simultaneously the sampling and transforms two input channels, does not satisfy at the same time the electrical machinery supervisory system the sampling multi-channel requests. MAX126 is the high speed 14 gradually comparison A/D transformation chip which MAXIM Corporation produces, 4 group synchronized sampling/retainer may to 4 channel’s signals at the same time the sampling.
This systematic sampling 7 groups signals, therefore uses two piece of MAX126 chips, and works Yu AZU the multiway switches, 4 groups sampling, the switching time is 12ms. DSP and MAX126 interface circuit as shown in Figure 2 [5]. May control the MAX126 normal work through the different I/O operation.
Figure 2 DSP and MAX126 connection
2.3 display circuits
The display circuit take AT89S52 as the core, the liquid crystal display module uses MGLS240128T, interface circuit as shown in Figure 3.
Liquid crystal display module controller T6963C data bus DB0~DB7 and at89S52 P0 mouth is connected. T6963C read-write control signal RD/WD separately by AT89S52 exterior ROM read-write control signal RD/WD control. CE selects patches or strips of land as worth saving for seed the signal, by AT89S52 P2.7 control, when low level selects. C/D is the register selection signal, inputs the low level to express what this read-write is the data; Inputs the high level to express what this time writes is the order, what reads is the T6963C condition. 
Figure 3 demonstration partial circuit diagrams
2.4 communication channels
This system uses always the linear distribution network structure. Network architecture as shown in Figure 4. Various protectors set up the RS485 communication main line through MAX485, between PC machine and the RS485 main line through the RS232/RS485 transformation card connection.
The PC machine function provides the good operation contact surface, allows the superintendent to revise the parameter. The superintendent through the operation contact surface may to various protectors transmission control command. The protector may receive main engine’s order, switches on or the trip according to the order actuation electrical equipment, as well as surveys each electrical parameter, and transmits the electrical parameter the display module demonstration.
The demonstration part uses the LCD module to demonstrate the electrical parameter.
Figure 4 communication structure drawing
Various protectors and 485 main line’s interface circuit as shown in Figure 5. The MAX485 chip is the RS485 chip, two control origin DSP two I/O mouth control, moreover is responsible for the data by a I/O mouth the direction of transmission choice.
Figure 5 RS485 interface circuit
2.5 protection actuating circuit
All protection circuit’s executive circuit as shown in Figure 6, is mainly completes through relay’s make-and-break. If the electrical machinery breaks down, then the DSP chip has the low level, urges the light pair breakover, thus causes the relay operation, has protected the electrical machinery.
Figure 6 protection circuit
3 system software designs
Had the hardware movement platform, must design the corresponding software to be able to display its application the effect. As a result of software’s flexibility, may act according to system’s request optional change, the fluctuation, therefore system’s intellectualized degree very major part is decided by the software architecture to be whether reasonable, the function is whether comprehensive.
The protector DSP part uses the C language programming, the control software mainly by the control procedure, the display sequence, the communication procedure and so on is composed.
4.1 control procedures
The intelligent electrical machinery protector’s through examination line in electric current and the voltage, after the computation, the analysis realizes each kind of protection function, and real time display line’s parameter and record malfunction.
This system through TMS320LF2407 internal timer interrupt enable inte A/D transformation. Establishes initial sampling frequency 2.56KHz, then sampling interval 390.625ms, namely 390.635ms triggers A/D. After the MAX126 12 group A/D transformation completes, transmission interrupt request signal to DSP XINT1 foot. Control procedure’s flow chart as shown in Figure 7.
Figure 7 control procedure flow chart
4.2 interrupt routines
Interrupt routine’s function is the sampling and the memory sampled data. In the electrical machinery protective system, the stored datum next step is generally carries on the FFT analysis to each voltage and the electric current sampling value, therefore in stored datum time must pay attention to the following two questions:
(1) although the voltage and the electric current sampling’s data is the separate real number sequence, but after carrying on FFT, turns the FFT plural number sequence, thus transforms after generally A/D the voltage and the electric current real number sequence regards as the imaginary component is zero plural number sequence, deposits the plural number with the continual memory space, the real part before, the imaginary component after.
(2) FFT input and output sequence existence “positive sequence - in reverse order” or “in reverse order - positive sequence” relations, therefore to simplify the following computation, when saves the sampled data the general use “reversion carrying adds the indexed address quantity” the indirect addressing way, in the DSP instruction is *BR0 .
Interrupt part’s program flow diagram as shown in Figure 8:
Figure 8 interrupt routine flow chart
4.3 display sequences
Demonstrated that the part program flow diagram as shown in Figure 9.
Figure 9 display sequence flow chart
4.4 communication procedures
The communication part is mainly two parts of compositions: 1st, between PC and DSP 485 communications; 2nd, between DSP and AT89S52 RS485 communication.
The PC machine part programs with Labview. Labview has provided function formidable VISA (Virtual Instrument Software Architecture) the storehouse, completes between the computer and instrument’s connection, with realizes to instrument’s programmed control.
AT89S52 from DSP receive data, then demonstration on LCD. The communication terms are F0 10data 0F, namely judges first whether to obtain start signal F0, if is, receives 11 data, then judgment last data whether is 0F, if is not, discards this group of data, receives.
4 experimental results
System test’s partial result as shown in Table 1.
Table 1 parameter test result
When test the electrical machinery voltage and the electric current actual value is 220V, 10A, according to the measurement result, A, B, the C three voltages and the current measurement precisions has met the requirements.
5 conclusions
This article proposed has used the DSP resources fully based on the TMS320LF2407 intelligent electrical machinery protector, constituted a function with the few periphery component to consummate, the performance fine inexpensive utility system, had guaranteed the production system reliability service, to realize the electrical machinery protection to equip the low cost development and the renewal has provided a practical and feasible way. This protector will have the very good application prospect in the electrical machinery protection.
Reference
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