Abstract: Used the high integration rate special-purpose chip SA866 and intelligent power module PS21255 has developed one kind of low power general frequency changer. The experiment and the practical application indicated that this frequency changer performance is good, the price is low, the reliability is high.
Key word: Frequency changer; Sine wave pulse-duration modulation; Specific IC; Intelligent power module
Introduction
As a result of the electric power electronic technology’s swift development, the exchange frequency conversion velocity modulation rose for the electric drive mainstream, is substituting for traditional gradually the direct-current transmission. But looking from the performance-to-price ratio angle, the exchange frequency conversion speeder already surpassed the cocurrent speeder.
Asynchronous machine’s frequency conversion velocity modulation not only may realize the stepless regulation, but also has many other exchange velocity modulation system incomparable merit: The exchange frequency conversion velocity modulation in the frequency range, the dynamic response, the velocity modulation precision, the low frequency torque, slips aspect and so on compensation, correspondence function, intelligent control, power factor, working efficiency, easy to operate superiority is other exchange velocity modulation way achieves with difficulty, and is small by the volume, the weight is light, the versatility is strong, the protection function consummates, the reliability to be high, the operation simple and so on merits, the depth profession and so on steel and iron, metallurgy, mine, petroleum, chemical industry, medicine, spinning and weaving, machinery, electric power, light industry, papermaking, printing, cigarette, running water welcome, the social efficiency is been remarkable.
Although the frequency conversion velocity modulation has its superiority in each aspect, but its early expensive construction cost and the reliable question cause many users to shrink back at the sight. Reduces the construction cost and enhances the reliability exchanges the frequency conversion velocity modulation important topic.
In the late-1990s this article in view of the general low power exchange asynchronous motor frequency conversion velocity modulation’s request, used multi-purpose high integration rate special-purpose SPWM which only then promoted control chip SA866 and intelligent power module PS21255 has developed one kind of new general frequency changer. Its entire? The structure is succinct, has the quite perfect function, has satisfied air conditioning, washer industry and so on and so on electrical appliances and small spinning and weaving, plastic processing automatic production lines to the frequency changer low cost, redundant reliable, the high performance request, and already in Guangdong, Jiangsu and so on many plant productions obtained the application.
1 SA866 and PS21255 function introduction
1.1 SA866 function synopsis
1.1.1 function characteristics
SA866 is uses in exchanging the asynchronous machine SPWM control integrated circuit specially. It besides produces according to the setup parameter conforms with the request the SPWM pulse, but also integrated many kinds of protection functions, and may when the emergency case, like the short circuit and the overload shuts off the SPWM pulse fast, protects the invertor and the electrical machinery. Its most major characteristic is may move independently, does not need the microprocessor control. Its output frequency as well as accelerates to decelerate the frequency to be possible online to adjust continuously by the external connection potentiometer. Must define the parameter like carrier frequency, the dead time, the minimum pulse width, the modulation waveform, the V/f curve and so on save when external connection inexpensive EEPROM, on the electricity reads in automatically SA866. SA866 has 6 kind of working patterns, with the microprocessor coordination use, has achieved the low price basically multi-purpose.
1.1.2 base pin explanations
This chip uses the PLCC seal, altogether has 32 base pins, various base pins arrangement as shown in Figure 1.
Various base pins function is as follows.
1) power source VDDD and VDDA respectively be digital power source and simulation power source; VSSADC is a/D transformation power source, they meet 5V the power source; VSSD and VSSA respectively and simulate power source’s place be the digital power source; VREFIN is a/D transformation reference voltage ( 2.5V).
2) serial interface SDA, SCL and CS use from the EEPROM gain data, respectively is the data, the clock and selects patches or strips of land as worth saving for seed the signal.
3) controls and outputs SETPOINT is the frequency gives the fixed end, this foot’s input voltage will decide system’s operating frequency; RACC and RDEC determined separately accelerates time which and decelerates; RPHT, YPHT, BPHT, RPHB, YPHB and BPHB are the bridge arm signal impulse outputs, RPHT, YPHT and BPHT correspond the three-phase output separately on bridge arm; RPHB, YPHB and BPHB correspond the three-phase output separately under bridge arm; DIR controls the three-phase order, this foot correspondence height level has two direction PWM waves for the user choice.
what 4) the active status chooses the SERIAL decision and the SA866 connection is EEPROM or the microprocessor, high level expression and EEPROM connection; What PAGE0 and the PAGE1 decision uses is which page of parameters EEPROM.
5) protects VMON is the overvoltage signal input end, in the moderating process this end level, if is bigger than 2.5V, the start overvoltage protection movement, will output the frequency fixing in the current value; IMON is the electric current signal input end, in the vertical speed process, if the level is bigger than 2.5V, the internal overflow protection on the movement, no longer continues the vertical speed, until overflow loss of signal; SETTRIP is the urgent stopping signal, but forbids the PWM pulse output fast; The TRIP end expression output disable condition, the low level is effective, this signal only then can relieve under reset signal RESET.
1.2 PS21255 function synopsis
1.2.1 function characteristics
Compares with the conventional IGBT module, PS21255 has the following characteristic:
1) contained driving circuit IPM to establish the internal IGBT best actuation condition, the driving circuit has been near to IGBT, might reduce the signaling impedance greatly, and is been small the external interference, therefore could not add the reverse bias, simultaneously, this module used the bootstrap circuit, thus got rid of the control supply not altogether place limit, used a power source, then realized the convenience control;
because 2) contains each kind of protection to cause internal IGBT the breakdown damage probability to reduce greatly, these protections protect (SC) including the short circuit, the control circuit undervoltage protect (UV) and so on;
3) the internal warning outputs (FO) this signal to deliver controls the PWM producer, the blockade pulse output, then stop system work;
4) radiates the effect well to use the ceramic insulator structure, the flat packaging, may the immediate packing on the radiator;
5) the post layout is reasonable, is advantageous for the installment strong and the weak electricity the output input end to arrange separately in the module both sides, achieves reduces the disturbance as far as possible.
1.2.2 base pin explanations
This module’s contour and post distribution as shown in Figure 2. IPM(PS21255) module exterior post the strong and the weak electricity separates in the layout, P and N are direct current the input end, P are the end, N are negative ends; U, V, W is the invertor three-phase out-port; UP, VP, WP is on the bridge arm U, V, W each signal impulse input end; UN, VN, WN is under the bridge arm U, V, W each signal impulse input end; VP1 and VPC are on the bridge arm work power source input end, VP1 are the end, VPC are negative ends; VN1 and VNC are under the bridge arm work power source input end, VN1 are the end, VNC are negative ends; CIN is the electric current detection signal input end; FO is the breakdown out-port (low level effective); CFO is the breakdown output pulse width control end; VUFB and VUFS are the U bootstrap circuit both sides, VUFB are the high-end, VUFS are the low ends; VVFB and VVFS are V bootstrap circuit both sides, VVFB are the high-end, VVFS are the low ends; VWFB and VWFS are the W bootstrap circuit both sides, VWFB are the high-end, VWFS are the low ends.
2 system designs
2.1 hardware circuits
We develop the low power general frequency changer, uses the single phase AC power supply, after rectification filter sends in the contravariant bridge, inverts again by the contravariant bridge this direct current three-phase VVVF (variablevoltagevariablefrequency) the power source, actuates the electrical machinery. The overall system divides into the main circuit and the control circuit two parts. System constitution diagram as shown in Figure 3.
The main circuit uses the diode rectification, the large capacity electrolysis electric capacity filter, the IPM module electric circuit’s hard core, it contains 6 IGBT to constitute the three-phase contravariant bridge primarily, and has own driving circuit and the protection circuit respectively, the entire module also has the short circuit and the control circuit undervoltage protection function. Its input may the compatible TTL level input.
The control circuit mainly has the control supply and as the core SPWM wave has and the driving circuit take SA866. The control supply uses 7805 and 7815 provides the cocurrent voltage-stabilized source. SA866AE through 10 d/as converter and the external connection forward and reverse direction foot, may realize the rotational speed continual adjustment and the forward and reverse cut. All operational factor, including the carrier frequency, the profile, the minimum pulse width, the dead area pulse width and the V/f curve and so on is through the external connection EEPROM programming. Because the input voltage and the feedback energy will directly reflect on the direct-current link, therefore, overall system’s voltage electric current examination and the protection sample concentrate in the direct-current link. The actuation inversion bridge must the PWM signal provides by ASIC chip SA866, after reverse gives the IPM module.
EEPROM selects 93LC46, it only need the 5V voltage then work. But repeatedly scratches writes 106 times. This chip’s seal form is DIP-8, VCC and VSS respectively are the 5V mains input positive and negative ends, CLK is the clock signal input end, DI is the data input end, DO is the data out-port, ORG is the internal data memory structure, carries on 8 or 16 choices. Will need to establish the parameter reads in EEPROM, the system when on electricity automatically from EEPROM senate digital read-in SA866, rests on the senate digit which establishes, the system produces the corresponding pulse waveform to use for to control in the main circuit the module to open or the pass.
2.2 parameter computations and hypothesis
1) the carrier frequency (CFS) carrier frequency is the external connection clock rate and a percentage coefficient N function, the N decimal base value by an initialization register’s in 3 CFS character decision. Carrier frequency fCARR (1) decided by the type.
fCARR=fCLK/(512×2 n 1) (1)
In the formula: fCLK is the clock input frequency, this system selects the crystal oscillator is 20MHz. Takes n=1, CFS=001, actual fCARR==9.766kHz.
2) output the supply frequency scope (FRS) frequency range to give the output frequency on limiting value. The frequency range fRANCE=fCARR×2m/384, takes m=1, namely FRS=(001)B.
3) dead time (tpdy) tpdy= (63-PDY)/(fCARR×512); PDY between 0~63, takes PDY=37= (100101) B; Then actual tpdy=(26/26.2144)5μs=4.959μs.
4) the pulse cancels time (PDT) after the modulation the SPWM pulse width may be very small, but in fact, too small pulse width not useful, because the time is excessively short, the power tube has not had opens completely with enough time has shut down, only increased power tube’s loss, cut system’s efficiency. The pulse cancels the time tpd=(127-PDT)/(fCARR×512); According to this formula, if defines the minimum width as 3μs, the minimum pulse width is tpd-tpdy actually, then tpd=7.959μs, may result in PDT=85.272, takes PDT=85= (1010101) B, therefore, actual tpd=8.01μs, pulse minimum width for tpd-tpdy=8.01μs-4.959μs=3.051μs.
5) the profile chooses SA866AE to have three kind of standard wave patterns to supply the choice, namely pure wave, sine wave band triple frequency (enlargement mode) and belt dead area triple frequency (highly effective). The profile uses the symmetrical technology to guarantee that each power tube’s clear angle is the same. This system selects the belt triple frequency the sine wave to take the modulating wave, namely has: WS= (01) B.
6) the V/f curve controls FC to use for to determine that is the linear law or the ventilator law, this system hypothesis work in linearity curve condition, namely FC=0. Figure 4 is the straight characteristic which SA866AE/AM provides. PED is 8 parameters, uses for to determine when the frequency is 0 on electrical machinery’s voltage. If establishes PED=255, then the VVVF straight characteristic is useless. Pedestal(%)=PED×100/255, this system’s starting value hypothesis is 10%, may result in PED=25.5, takes 25, actual Pedestal(%)=9.8. GRAD is a 8 binary number, decides the permanent torque area curve the slope, according to base frequency and PED value computation: GRAD=(255-PED)×fRANGE/(16×fbase); GRAD255, takes fbase=50Hz; Then has GRAD=15= (1111) B.
7) other parameters, because in the linearity curve does not use KAY, in this KAY= (0000000) B; A/D transforms zero threshold value controlled variable ZTH= (00) B; Results in CHKSUM= the above all senate digit after the statistics (001) B. AWS= (0000) B.
May obtain the parameter distribution list like table by the above computation 1 to arrange in order.
Table 1 parameter distribution list
|
ADDRESS |
MSB(15~8) |
LSB(7~0) |
|
001100 |
00001111 |
00011001 |
|
001101 |
10010100 |
10101010 |
|
001110 |
00101001 |
00000000 |
|
001111 |
11111110 |
******** |
In table “*” expression willfully item, when read-in wrote 01010101
4 experimental application result and conclusion
General frequency changer which makes according to the design, has carried on the velocity modulation, the starting, the stop, reverse, the overload adjustment and adds experiments and so on deceleration time adjustment, the experiment indicated that this frequency changer each performance is good, meets the design requirements, and already successively in places the such as Guangdong and Jiangsu air conditioning refrigerators, the compressor, the textile production line and on the plastic products production line obtains the application. This frequency changer structure is succinct, the cost is low, the reliability high, has the high performance-to-price ratio and the nimble compatibility, is actuates the low power electrical machinery and this kind of production line most ideal choice.
