$35 is a weeks wages here. just for the record, suggestions to buy 'cheap' stuff to finish the project falls on poor and deaf ears. to put this into perspective, just add a 0 to anything that seems cheap, and that what it is for me...if i can even source the part or the cash. in days where i had more $ than i could spend, i also just bought random cool stuff hoping it may come in useful in the future. thats the stuff i am working with now. even so, it kind of defeats the idea of a hobby and learning experience to just buy modules and wire them up.The cost of the driver board with LCD display showing Volts Current & Freq was quite cheap, about $35 hardly worth copying.
Induction motor flux is determined by voltage to frequency ratio, often called V/F ratio. If you change the frequency it is best to change the voltage too so that V/F is constant and therefore motor flux is constant. Induction motor runs well on smaller than nominal frequency in v/f mode (also called scalar mode). On the start from standstill in v/f mode, voltage drop in stator resistance is big when compared to supplied voltage. Outcome of this is reduced starting torque. Voltage can be increased on the start to get better starting torque. This is often called IR compensation but it should not be required on the water pump as breakaway torque is not big.Chris Blizzard said:what happens if i run that type of ac pump motor on a higher or lower frequency? could i vary the power of the pump, or water flow? or speed it up and have it pump more (it will run nowhere near its maximum head)
It is best to have a driver circuit made with discrete transistors or using specific drives ic.Chris Blizzard said:can i feed igbt modules direct from the pic, or will it need buffering?
On this case current being switched off is so small that perhaps negative supply is not necessary. 500w is about 5A peak and the IGBT is 400A. If the motor is started like direct online manner then current can be 30 A peak so not that small anymore. Gate threshold voltage of MG06400D-BN1MM is about 5V so not that small either. Driver M57959L recommends -7 to -10V.Chris Blizzard said:the junction likes a hefty negative pull down to switch off
Some multimeters can measure frequency. Perhaps multimeter can measure the pwm frequency from the pic output pin.Chris Blizzard said:i dont know what the pwm frequency is for the hex file i blew to the pic and i would like to try and calculate
M57959L is for single IGBT and can't provide dead time. Some bridge drivers that have low side and high side driver has deadtime function.Chris Blizzard said:s being tristate to protect the igbt from shorting the supply for a nanosecond from risetimes, maybe my driver modules have this protection.
Recommended Vin of M57959L drives is 5 V but can work with 3.3 V too. Current requirement is 16mA with 5V. There is 185 ohm resistor in series with the opto-coupler. Recommended IGBT module size is upto 200A for 600V IGBT. This is not a problem if you will use 500W motor even when the IGBT is 400A rated.Chris Blizzard said:what do you think of the driver hybrid modules i bought? will they do the job? interface to the pic/olinuxino drive levels?
Most of industrial variable speed drives/motors are run with pwm voltage. Inductance of the motor will filter the current to acceptable level provided there is enough high switching frequency, lets say 2-3 kHz minimum. Usually extra losses are just taken account by derating the motor for example 10%. High rise time of the voltage can cause high voltage peaks on the motor windings destroying them. It is possible to reduce voltage rise time on the inverter output with du/dt or LC filter. One possibility is to use a bigger gate resistor (about 10 ohm used on the IGBT data sheet) to make switching slower. It would create more switching losses but on this case IGBT is really big.Chris Blizzard said:if it ran in switch mode the induction motor wont like it, may overheat from the energy on the squarewaves corners cant be put to use.
If you get 2x 400V (or 325-400V) it should work ok. With this method gate driver is easier to make as it does not require a high side driver.also i am considering using the solar in 2x3 series parallel with centre tap instead of a full bridge or transformer, then keep adding capacitors to the input until i get maximum power out. i would only need a single igbt half bridge would this have any disadvantages?
With pic or Linux control it is possible to run the pump in V/F mode. It would make it easy to adjust frequency -and therefore power- according to available power from the solar panel. Start of the pump would also be easy. Direct online start of the small motor takes about 7 times nominal current. Power factor is low but there is quite some extra active power requirement too. It is no problem if solar panels can supply it or there is enough capacitors on the supply. In V/F mode power demand is small during start.i do like the idea of having a pic or linux control on the igbt bricks so i can reprogram them to do other stuff like driving a tesla coil or vlf radio now the spectrum has been released for hams.
serious thanks dude! so many answers and all at once. so my drivers are not so good for bridge because of deadtime. i will need to either find another pic file that uses 4 gpio lines or linux on the sbc and hope not for a crash that switches both on.Here are my comments to some of the questions on this thread. Perhaps too late but anyway...
Induction motor flux is determined by voltage to frequency ratio, often called V/F ratio. If you change the frequency it is best to change the voltage too so that V/F is constant and therefore motor flux is constant. Induction motor runs well on smaller than nominal frequency in v/f mode (also called scalar mode). On the start from standstill in v/f mode, voltage drop in stator resistance is big when compared to supplied voltage. Outcome of this is reduced starting torque. Voltage can be increased on the start to get better starting torque. This is often called IR compensation but it should not be required on the water pump as breakaway torque is not big.
You can speed the motor above nominal motor frequency but not huge amount especially when the motor is loaded. Typically DC voltage is selected so that about nominal motor voltage can be reached with pwm. Above nominal frequency v/f ratio decreases (also called field weakening) and maximum torque of the motor drops rapidly. At the same time power increases cube of speed on the water pump.
Reducing the frequency below nominal frequency reduces the power a lot on the water pump. Power is proportional to cube of motor speed on a pump. It would be easy to adjust power demand from solar panel by changing frequency. Motor shaft cooling fan is less effective on smaller frequency but the load is much smaller too so it doesn't matter.
It is best to have a driver circuit made with discrete transistors or using specific drives ic.
On this case current being switched off is so small that perhaps negative supply is not necessary. 500w is about 5A peak and the IGBT is 400A. If the motor is started like direct online manner then current can be 30 A peak so not that small anymore. Gate threshold voltage of MG06400D-BN1MM is about 5V so not that small either. Driver M57959L recommends -7 to -10V.
Some multimeters can measure frequency. Perhaps multimeter can measure the pwm frequency from the pic output pin.
M57959L is for single IGBT and can't provide dead time. Some bridge drivers that have low side and high side driver has deadtime function.
Recommended Vin of M57959L drives is 5 V but can work with 3.3 V too. Current requirement is 16mA with 5V. There is 185 ohm resistor in series with the opto-coupler. Recommended IGBT module size is upto 200A for 600V IGBT. This is not a problem if you will use 500W motor even when the IGBT is 400A rated.
Most of industrial variable speed drives/motors are run with pwm voltage. Inductance of the motor will filter the current to acceptable level provided there is enough high switching frequency, lets say 2-3 kHz minimum. Usually extra losses are just taken account by derating the motor for example 10%. High rise time of the voltage can cause high voltage peaks on the motor windings destroying them. It is possible to reduce voltage rise time on the inverter output with du/dt or LC filter. One possibility is to use a bigger gate resistor (about 10 ohm used on the IGBT data sheet) to make switching slower. It would create more switching losses but on this case IGBT is really big.
Common mode voltage can also cause bearing currents. I don't if common mode voltage/current can be a problem on single phase inverter. Common mode chokes are often used on various single phase power supplies so it would be good to use common mode choke in inverter too.
Industrial motors are three phase. Single phase motor can have a starting capacitor or running capacitor. Typically (based on google images) capacitor is in series with a winding and does not see pwm voltage directly. At least if there is a running capacitor it would be good to measure if there are peaks on the current because of pwm. Or just use LC filter to have more sinusoidal output voltage.
If you get 2x 400V (or 325-400V) it should work ok. With this method gate driver is easier to make as it does not require a high side driver.
With pic or Linux control it is possible to run the pump in V/F mode. It would make it easy to adjust frequency -and therefore power- according to available power from the solar panel. Start of the pump would also be easy. Direct online start of the small motor takes about 7 times nominal current. Power factor is low but there is quite some extra active power requirement too. It is no problem if solar panels can supply it or there is enough capacitors on the supply. In V/F mode power demand is small during start.
Do you have an example how pulse timings are calculated on the fly? I have heard selective harmonic elimination only but I think for example sine triangle comparison is better on this low power level. It is easy to use high enough switching frequency.if i go the linux route (olinuxino imx233 micro with arch) will i be able to compute the sine on the fly with pulse width overall adjusted with feedback?
I can't say about processing power but to my understanding normal Linux kernel can start to do some housekeeping and during that time there is no new switching commands. Over current will happen very soon.would 450mhz cpu be fine, or will i need rtos or assembler level code?
Tables on the micro controller gives a benefit that it's easier to control what table row (pulse timings) to use. If solar panel voltage varies 50 V it would be good to change the switching pattern too. One option I think of is to use reference sine wave and compare it to timer to find out switching moments. It reduces amount of data in tables.a lot of websites discuss using pointers and tables, but i thinks thats for arduino level stuff rather than a real computer.
if im using tables i might as well scrap the cpu and have a counter and rom chip.
rather have something i can telnet in to though
Google image search with term deadtime shows several circuits that typically have RC network and some logic chip. If you have those components you can make a deadtime generator and use existing PIC program.i will need to either find another pic file that uses 4 gpio lines or linux on the sbc and hope not for a crash that switches both on.
Required dead time is on micro seconds range. 1/3 kHz is about 330 us cycle time. 10 us should be on the safe side if you have negative gate turn off voltage, about recommended turn on gate voltage and gate resistor is similar that was used on the datasheet tests.i like the idea of a millisecond delay from cr and logic.
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