Fullscreen HTML5Med Res (??MB)HTML4

More 1.5kW Induction Speed Controller Revis The revised Induction Motor Speed Controller design presented in the December 2012 issue was clearly an improvement over the original circuit and PCB presented in the April & May 2012 issues. It has since been built by quite a few readers and its operation on 3-phase motors is much improved. However, a few readers built the modified design or performed the mods on the original PCB and still managed to blow it up on their particular pump or motor.   Note: the changes described in this article have already been applied to the online versions of the two original articles on the Induction Motor Speed Controller, in the April 2012 and May 2012 issues. W e asked the designer, Andrew Levido, to help us come up with some changes to further protect the unit against damage and to fix a few small bugs in operation. The changes he has come up with can be accommodated on the revised PCB presented in the December 2012 issue. The main problem that constructors have run into appears to be that the overload protection was too slow to prevent damage when running in single-phase mode with heavy loads and high heatsink temperatures. We have taken a two-pronged approach to solving this problem which involves a faster switch-off of the IGBT bridge if the current level rises beyond its normal operating limits and we have incorporated better cooling as well. To speed up the switch-off under fault conditions, the shunt RC filter components involved with monitoring the load current have been changed to 100Ω and 10nF (originally 2.2kΩ and 1.5nF). This reduces the short circuit trip time from around 3.3µs to 1µs, providing much better protection for the IGBT bridge. This will also result in a faster switch-off under excessive load conditions, which we believe will make the unit more rugged and also lowers the filter impedance to improve noise immunity. In addition, we have reduced the 82  Silicon Chip over-temperature trip threshold from 95° to 85°. This gives a little more headroom to the over-current protection since if the IGBT junctions are already at about 100°, the withstand time at peak current will be reduced. This change has been done in the software; the thermistor itself is unchanged. Also, a special condition has been added to the software so that if the heatsink temperature is over 60° when power is applied, the unit will wait for it to cool down first before applying power to the motor. This is to provide extra protection as the highest currents are normally drawn at start-up, especially when starting under load (eg, with a pool pump) and a hotter heatsink means less margin for the IGBTs under highcurrent conditions. Normally this should not be a problem since the heatsink will usually have time to cool between motor runs in this type of situation and besides, we are also improving the cooling which should result in a reduced operating temperature. Note that we have also changed the value of the 1kΩ resistor feeding zener diode ZD1 to 470Ω. This is not strictly necessary but operates ZD1 closer to its rated power. With the previous value resistor, in a small percentage of cases the reference voltage was lower than expected. It isn’t critical but you might as well replace this resistor when you change the other components. Fan cooling A number of readers reported a failure of the controller while starting a motor when it was already quite hot. Hence, we decided to add fan cooling. This has been provided by fitting a small fan (Jaycar YX2505) and grille (Jaycar YX2550) in the bottom of the box and by drilling a row of 6.5mm holes along the top edge of the box to provide airflow. The fan is mounted on the inside of the box and blows the air through and across the heatsink fins. This has effectively negated the advantage of the sealed IP65 plastic case but we regard the need for cooling as paramount. The fan is wired to the unregulated input to REG1 (about 6-7V) and so will run quite slowly (and hence, quietly). While it could also be wired across the 15V HOT rail for more efficient cooling, we are not satisfied that the insulation of the fan is adequate. Adding the fan meant we had to move the output mains connector to the right hand side of the case. We decided to replace the flush 250VAC socket with a surface-mount type which is more sturdy; the type we used originally is only held in with a single screw and they can come apart if siliconchip.com.au Motor sions by Nicholas Vinen Externally, the differences are the addition of a small fan, necessitating the moving of the mains output socket (which is changed to a more robust type). you are rough in inserting and removing the 3-pin mains plug. Hence, we are taking the opportunity to replace it with a better one. If you are using the unit with a three-phase motor then you can use the same connection arrangement as before but you may need to move it across to make room for the fan. Users may also consider a 240VAC 120mm fan if they will operate for long periods at full load in high ambient temperatures – if nothing else, it will increase the lifetime of the large electrolytic capacitors. However, a large fan will also require a larger case. A further change to the software has corrected a bug in the 3-phase reversing logic. Now if the reverse switch is changed while the motor is spinning, it will ramp down to zero, change direction and ramp back up again. Some users also asked for a variation on pool pump mode, where the motor spends less time at full power before dropping to the set speed (half a second rather than 30s). This feature can be useful for lathes or other equipment which start off-load and is activated with Pool Pump enabled and a shorting block across pins 3 & 4 of the ICSP header. In this case, the ICSP header must be soldered to the PCB, not just held in by friction. We have also expanded the available ramp time range to 1-33 seconds, allowing faster ramp rates than were possible before. Making the changes If you are building the Induction Motor Speed Controller from scratch, you can simply fit 100Ω and 10nF RC filter components rather than the previously specified 2.2kΩ and 1.5nF. If you have already built the unit, you can either remove the PCB from the heatsink and change both of these components or alternatively, clip the 2.2kΩ resistor off (leaving as much lead as possible) and solder a 680Ω resistor across those leads, to give a similar time constant. However, this will not give anywhere near as much noise immunity and may lead to false trips at start-up, so it is better to change both components. If you do solder this resistor to the top of the board, make sure it’s wellanchored as the last thing you want is for this critical component to come loose and possibly cause a shortcircuit in the high-voltage section of the unit. Now is also a good time to change the resistor feeding the zener diode to a value of 470Ω. Sleeve the fan leads with a continu- There’s also a row of holes drilled across the rear of the case to allow airflow from that fan on the front. siliconchip.com.au August 2013  83 EARTH 4004 4004 4004 470mF 1.5kW Induction Motor Speed Controller 4.7k 5W + 47nF X2 10105122 4.7k 5W + + + 4004 D9 + 180W + 16k siliconchip.com.au + + + 4004 470m 10W 4.7k 5W OPTO2 HCPL2531 470mF 400V (UNDER) 100nF OPTO3 HCPL2531 620k THESE COMPONENTS 8.2k CHANGED 8.2k D5 100nF 10 VR1 10k 1 47k 8.2k 1.5k OPTO1 4N35 620k 10mF ZD1 100nF ARRIER 10mF 10mF 100nF 10mF 8.2k 4.7k 5W 100W 10nF 1 100nF 5.1V 470mF 400V (UNDER) CHANGED CHANGED IN VALUE 15W W 220nF X2 470W T2 6V+6V 5VA (UNDER) ISOLATION BARRIER 4004 IC1 STGIPS20K60 (UNDER) 10k 9 4004 110W CON7 ICSP 4004 PP Ext O/S Flt Fault N2 A Rev Run A A 100nF 470mF 470mF 10mF S1– 4 Fig. 1: the PCB overlay shown with the revised component values with the section of the board (Fig.2, right) showing their exact locations. ous length of 5mm diameter heatshrink tubing. Before fitting the fan, you must first remove the mains socket and enlarge the hole to suit the fan, as well as drilling four 3mm holes for the fan mounting screws (if necessary, use the grille as a template). The fan goes right in the middle of the panel, orientated so that it blows air into the case; the airflow direction is 470mF 400V (UNDER) 100W 4004 LM317T dsPIC33FJ64MC802 470W 100W 100W 100nF 100W 100nF 100nF REG1 D5 D6 D7 D8 100W IC3 680W 100W HCPL2531 100W 100nF 1.5k OPTO2 HCPL2531 10W 100nF 100W 15V BC337 Q1 CON6 ZD2 NYLON CABLE TIES GND 100W 8.2k OPTO3 OPTO1 4N35 100nF 100nF 4.7k 47k 10mF ZD1 4.7k EST 100nF CON5 100W 10mF 10mF 100nF 10mF RUN + 1 RAMP SUP SLEE PRESSIO VE N 100nF VR1 VR2 10k 100nF 10k CON4 SPEED FE RRIT E (GPO MAINS OUTLET MOUNTED ON OUTER SURFACE) 100nF 620k 8.2k 1.5k ISOLATION BARRIER 4.7k 5W 100W 100nF U 5.1V GND 16k 620k 8.2k 8.2k 470W 470mF 400V (UNDER) 0.015W 2W CON2 V 10k IC2 LM319 +3.3V 10nF IC1 STGIPS20K60 (UNDER) 0.5W 84  Silicon Chip 470mF 400V (UNDER) TH1 SL32 10015 BR1 GBJ3508 (UNDER) NE-2 NEON W MINI MUFFIN FAN NYLON CABLE TIES 1.1M REV + FUSE1 10A (COVERED) 150k 150k WARNING! DANGEROUS VOLTAGES NYLON CABLE TIE 47nF X2 220nF X2 Vin T1 6V+6V 5VA (UNDER) D1 D2 D3 D4 FLT1 YF10T6 CON3 NYLON CABLE CLAMP Neutral Earth Active BOX FRONT PANEL (INSIDE VIEW) CABLE GLAND (REAR VIEW) 4004 This photo shows the component changes along with the revised positioning for the mains outlet to accommodate the new fan. You can also see the row of vent holes drilled along the rear of the case. It is absolutely vital that our layout is followed to the letter – including keeping component lengths short – and that your soldering, especially (but not limited!) to the IGBT, is exemplary. We’ve found several “faults” which weren’t faults at all, due to poor soldering and dress. indicated with arrows moulded into the plastic housing. When drilling the holes, make sure the fan (when mounted internally) will sit all the way down against the bottom of the case; this is so that the lid will still fit. With the fan in place, mark out the three hole positions for the socket to its right. If you use a surface-mount socket like we did, you will need to rotate it about 45°, ie, with screw holes at upper-left and lower right. The screw holes are 4mm while the central hole needs to be large enough to comfortably fit four mains-rated wires through (about 12mm diameter) and should be smooth, ie, no jagged edges. siliconchip.com.au While you’re making holes in the box, drill a row of 6.5mm holes along the top edge, near the heatsink, to allow fresh air to be blown out of the box by the pressure differential generated when the fan is running. The more holes you drill, the better the airflow will be (to a point) but there’s a limit to how many you can put in before the case starts looking like Swiss cheese! We would recommend drilling at least as many holes as you can see in our photos and try to keep them in a neat row. Fitting the new parts Having done that, route the fan power cable around the right-hand side of the board and solder the leads to the cathode of D6 (red) and anode of D7 (blue or black) – see the wiring diagram. Use the hole for the thermistor wires and the lower-right corner mounting post as cable tie points to clamp the fan cable. This is important as otherwise, the solder joints could break and the wire could easily float around inside the case and cause havoc. Before mounting the new mains socket, the earth wire of the input lead must be long enough to reach it. To lengthen it, undo the P-clamp holding the input cable in place, disconnect the Active and Neutral leads, loosen the August 2013  85 FLT1 EMI FILTER FUSE1 ACTIVE +325V (NOMINAL) TH1 SL32 10015 BR1 4.7k 5W θ 10A ~ EARTH ~ NEUTRAL 470 µF 400V 470 µF 400V 470 µF 400V K T1 A A K 6V + 6V 5VA 100nF 100nF K D1 D4 T2 D6 A A + K A +3.3V OPTO1 4N35 470Ω OUT IN ADJ 1 5 110 λ 4 470 µF 100nF 2 100nF D8 D7 6V + 6V 5VA _ K A REG1 LM317T 12V DC FAN 470 µF 6V 1.5k 100nF D9 K ADDED (OFFBOARD) K D5 6V K A ~7V K 10k ZD1 5.1V A A CHANGED VALUE 470Ω 0.5W D3 470 µF 25V 6V NE-2 K D2 6V 150k 4.7k 5W – CON3 150k 4.7k 5W + 180 ISOLATION BARRIER A ALL CIRCUITRY AND COMPONENTS IN THIS AREA ARE ISOLATED FROM MAINS & FLOATING WITH RESPECT TO EARTH LEDS +3.3V Vin K A GND 1 3 C LM317T ESTOP OUT ADJ IN ZD1, ZD2 K D1– D9: 1N4004 A OUT GND 3 HEATSINK THERMISTOR TH2 1 100nF 100nF CON7 2 3 100nF K ZD2 15V CON6 A C Q1 BC337 B 680Ω E K A λ LED1 K SC 2012 100nF 100Ω CON5 GND 100nF SPEED 100Ω 2 REV VR1 10k 1.5k 1 RUN RAMP θ E A 4.7k 4.7k B VR2 10k 100nF +3.3V CON4 BC337 OUT 100Ω 2 A λ LED2 K A λ LED3 K 1.5KW INDUCTION MOTOR SPEED CONTROLLER Fig.3: for the benefit of those who don’t have access to the original article(s), we are reproducing the circuit diagram in full. The three changed components are identified on this circuit, along with the new 12V DC fan. All other changes are in software which, of course, means that the IC3 will need to be re-programmed with a free download from our website. 86  Silicon Chip siliconchip.com.au 19 620k 220nF 250VAC X2 620k 22 47nF 250VAC X2 25 47nF 250VAC X2 16k CON2 0.015Ω 24 2W +15V HOT W 12 IC2a 4 V 18 8.2k 11 5 U 21 3 1 0 nF 100Ω +15V HOT CHANGED VALUES 1M 23 Vcc 5 2 Vboot-U 20 17 16 ALL CIRCUITRY IN SIDE THE PINK AREA OPERATES AT DANGEROUSLY HIGH VOLTAGES – CONTACT COULD BE LETHAL Cin 100nF IC2: LM319 OUT-U IC1 STGIPS20K60 15 SD/OD 3 Lin-U 4 Hin-U 9 Lin-V 10 Hin-V 13 Lin-W 14 Hin-W Vboot-V OUT-V Vboot-W OUT-W GND 1 7 6 12 11 10µF 25V MMC 10µF 25V MMC 10 µF 25V 10µF 25V MMC 8 10 7 IC2b 8 9 6 THIS SYMBOL INDICATES 'HOT' COMMON +15V HOT OPTO3 HCPL-2531 10Ω 100nF 2 3 4 5 6 7 28 AVdd 100nF 13 100Ω RB12 AN0 RB14 AN1 RB15 AN 2 RB13 RB1 RB11 RB2 23 100Ω 10 100Ω 11 100Ω 12 RA2 RB10 RB9 RB4 RB8 RB7 RA4 MCLR PGED AVss 27 siliconchip.com.au Vss 8 Vss 19 PGEC 8 λ 7 8.2k λ 8.2k 8.2k 6 5 26 24 22 OPTO2 HCPL-2531 100Ω 10 µF 6.3V MMC RA3 4 3 25 20 C1IN+ 1 2 Vdd IC3 dsPIC33FJ64MC802 9 100Ω +3.3V 21 17 18 16 1 14 15 1 2 100Ω 4 3 POOL 8 λ 7 λ 6 +3.3V 5 EXT O/S FLT 47k ICSP SOCKET 1 2 3 4 5 JUMPER FOR SHORT BOOST MODE NB: PARTS ARROWED CHANGED FROM VALUES SHOWN IN ORIGINAL CIRCUIT OF APRIL 2012 August 2013  87 cable gland nut and pull the cable out. You’ll have to guesstimate how much of the insulation to strip off it but perhaps another 150mm will be enough – remember that the earth wire will have to go over the fan and then some way into the back of the mains socket. Feed the cable back in through the gland but leave it loose. Ignore the extra-long Active and Neutral wires for now and feed the earth wire through the socket access hole. Twist its exposed copper together with the new, longer earth lead for the PCB and screw them tightly into the terminal in the rear of the socket. Similarly, connect up the new active and neutral wires too and feed them back into the case. All the socket terminals should be done up extra-tight with a flat-bladed screwdriver to ensure the wires can’t come loose. With the four wires in place, mount the socket using M4 machine screws and nuts, with a shakeproof washer under each head and nut. Make sure they too are done up tight. You can then cut the new motor connection wires to appropriate lengths and connect them to two of the motor output terminals; don’t forget to slip the ferrite suppression sleeve back over them before making this connection and use a cable tie to prevent it from moving around too much. The earth wire with the loose end is run to the earth point on the input screw terminal barrier at the left side of the PCB and this can be tied to the 88  Silicon Chip Additional parts required 1 60mm 12V DC fan (Jaycar YX2505) 1 60mm fan grille (Jaycar YX2550) 1 surface-mounting single mains (3pin) socket 1 100Ω 0.25W resistor 1 470Ω 0.5W resistor 1 10nF MKT metallised polyester capacitor 1 300mm length 6-8mm diameter heatshrink tubing 4 M3 x 20mm machine screws and nuts 4 M3 shakeproof washers 2 M4 x 20mm machine screws and nuts 4 M4 shakeproof washers 1 250mm length mains-rated earth wire (yellow/green striped), 10A+ 1 200mm length mains-rated neutral wire (blue) 1 200mm length mains-rated active wire (brown) 10 small cable ties other wires connecting to the PCB (see photos). It’s then just a matter of re-clamping the mains cable, doing the gland nut up and trimming the incoming active and neutral wires to length before re-connecting them to the respective power input terminals. Make sure all the wiring is properly tied down so that even if one of the wires breaks or becomes disconnected from the PCB, it can’t make contact with something that it shouldn’t – if in doubt, refer to the photos of our prototype. Updating the software To take advantage of the improved protection features, bug fixes and extended ramp setting range, you will need to re-program the microcontroller. Make sure the unit is completely unplugged from mains before doing this. It’s simply a matter of connecting the programmer (eg PICkit3) to the 5-pin in-circuit serial programming header, enabling the PICkit’s 3.3V power supply for the micro, loading the HEX file and re-flashing the chip. Alternatively, you can swap the dsPIC33 chip out for another one which has been pre-programmed with the latest version of the firmware (1010512B.HEX). This will be made available for download from the SILICON CHIP website, free of charge. Once the chip has been reprogrammed, go over the unit carefully to make sure all the changes have been made properly and nothing is loose, especially the mains wiring. You can then go through the test and set-up procedure from the previous article (May 2012). Essentially, this involves powering the unit up from mains with no load attached and checking that the neon lights up and the green LED flashes and then after a short period, goes solid. Assuming it checks out, you can switch off, connect a motor (ideally, unloaded) and power it back up to check that it is operating normally. SC siliconchip.com.au