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Frequency inverter, or frequency converter, is a power electronics based device which converts a basic fixed frequency, fixed voltage sine wave power (line power) to a variable frequency, variable output voltage used to control speed of induction motor(s). It regulates the speed of a three phase induction motor by controlling the frequency and voltage of the power supplied to the motor.
Primary function of frequency inverter in industry is to provide smooth control along with energy savings. The frequency inverter system is more efficient than all other flow control methods including valves, turbines, hydraulic transmissions, dampers, etc. Energy cost savings becomes more pronounced in variable-torque ID fan and pump applications, where the load's torque and power is directly proportional to the square and cube of the speed respectively.
Primary function of frequency inverter in industry is to provide smooth control along with energy savings. The frequency inverter system is more efficient than all other flow control methods including valves, turbines, hydraulic transmissions, dampers, etc. Energy cost savings becomes more pronounced in variable-torque ID fan and pump applications, where the load's torque and power is directly proportional to the square and cube of the speed respectively.
The early-break contact should break around 500ms before the main legs to be effective. Typically-available 10ms early-break aux-contact isolators are ineffective as the residual motor field will not have decayed, resulting in an inductive kick 10ms later when the 3 main legs open. Pffff! goes the frequency inverter output! It is unclear in this situation what a suitable isolator could be. The only practical solution is a lockable isolator, the expectation being that the person with the key understands the need for care.
If one is expecting a lot of switching on the input, then this could be a problem. If an early-break contact on the contactor is used to panic-stop the inverter first, then that may be okay. It depends on the timing and also how the inverter responds to this sort of treatment. Some are more tolerant than others. Consult the manufacturers of the inverter.
In the case of an emergency, nothing can stop the motor faster than the inverter itself (most inverters having an E-Stop input anyway). How the frequency inverter handles the emergency condition is usually a programmable function: ramp down at max or coast. This assumes, of course, that the inverter is undamaged, one would be wise to tie in a line or load contactor to the NO (normally open) output of the inverter-status relay. If it's an emergency, break it on the load side (inverter output). Nobody at the inquiry is going to sympathize with your concerns to pamper the thyristors when weighed against the potential risk to human life.
If one is expecting a lot of switching on the input, then this could be a problem. If an early-break contact on the contactor is used to panic-stop the inverter first, then that may be okay. It depends on the timing and also how the inverter responds to this sort of treatment. Some are more tolerant than others. Consult the manufacturers of the inverter.
In the case of an emergency, nothing can stop the motor faster than the inverter itself (most inverters having an E-Stop input anyway). How the frequency inverter handles the emergency condition is usually a programmable function: ramp down at max or coast. This assumes, of course, that the inverter is undamaged, one would be wise to tie in a line or load contactor to the NO (normally open) output of the inverter-status relay. If it's an emergency, break it on the load side (inverter output). Nobody at the inquiry is going to sympathize with your concerns to pamper the thyristors when weighed against the potential risk to human life.
Tags: inverter, Frequency inverter
Frequency inverter also known as variable frequency drive, VFD, VSD or PWM inverter, the frequency inverter provides direct control of the speed of an electric motor whilst maintaining high levels of motor torque. Frequency inverters achieve this speed control by varying the frequency applied to the motor. Using a PWM (Pulse Width Modulated) control system the output is controlled to vary the voltage and frequency to the motor.
Process automation and productivity improvements
A frequency inverter offers total control of motor speed without sacrificing torque. The speed can be controlled locally (manually), remotely or automatically using internal or external controls. The optimum speed for a process can be adjusted quickly and easily by an operator or process controller.
Energy savings and improved resource management
A frequency inverter enables a reduction in speed when operation at full power or capacity is not required. On variable torque loads such as fans and pumps a reduction in speed can result in substantial energy savings. Pumping water becomes more efficient. Energy costs and carbon footprint are reduced.
Process automation and productivity improvements
A frequency inverter offers total control of motor speed without sacrificing torque. The speed can be controlled locally (manually), remotely or automatically using internal or external controls. The optimum speed for a process can be adjusted quickly and easily by an operator or process controller.
Energy savings and improved resource management
A frequency inverter enables a reduction in speed when operation at full power or capacity is not required. On variable torque loads such as fans and pumps a reduction in speed can result in substantial energy savings. Pumping water becomes more efficient. Energy costs and carbon footprint are reduced.
Tags: inverter, Frequency inverter
Frequency inverters are basically a green energy savings product that matches the amount of work or load on a motor to the amount of energy it needs to power that amount of work. This reduces excess energy from being wasted.
We use a lot of energy in this country and most of that energy is used to move air and water around a building. About half the electricity in commercial buildings is just used to move air and water around, so a frequency inverter is a big way to save energy there. If you look at a typical pump motor the life cycle cost of a pump, 90% of its life cycle costs is the energy it consumes and only 10% the actual cost of the pump motor… a frequency inverter can cut that in half.
Most motors are oversized to deal with your worst-case scenarios, your peak loads. A frequency inverter allows you to run that motor at the load it needs to be instead of running it at peak load all the time. Another benefit is it has a built-in soft start capability. So those combinations of things are going to give you savings; not only on energy, but also extending the life of the motor.
So what is a frequency inverter? Some of the different names that are used in the industry are a inverter, an adjustable frequency drive, a variable speed drive, or an adjustable speed drive. The technology has been around for quite a few years but only has started to make some headway in HVAC and pumping applications in the last several years. The size and cost of electronics has made frequency inverters applicable to a wider range of motors and increased the opportunity for savings.
All frequency inverters are going to take 3 phase AC power and convert that 3 phase power to DC power inside the drive and pulse it out in a simulated AC wave form to the motor. The motor still thinks it has AC power but the DC power conversion now lets us control the speed of the motor without harming it. Now we are in control to save energy and money.
The basic concept with the savings for frequency inverters is your speed and your flow are more or less proportional. But the energy consumption is cubed. If you're running your motor at full speed 60 Hertz, you don't have any savings- but any reduction pays the reduction cubed.
We use a lot of energy in this country and most of that energy is used to move air and water around a building. About half the electricity in commercial buildings is just used to move air and water around, so a frequency inverter is a big way to save energy there. If you look at a typical pump motor the life cycle cost of a pump, 90% of its life cycle costs is the energy it consumes and only 10% the actual cost of the pump motor… a frequency inverter can cut that in half.
Most motors are oversized to deal with your worst-case scenarios, your peak loads. A frequency inverter allows you to run that motor at the load it needs to be instead of running it at peak load all the time. Another benefit is it has a built-in soft start capability. So those combinations of things are going to give you savings; not only on energy, but also extending the life of the motor.
So what is a frequency inverter? Some of the different names that are used in the industry are a inverter, an adjustable frequency drive, a variable speed drive, or an adjustable speed drive. The technology has been around for quite a few years but only has started to make some headway in HVAC and pumping applications in the last several years. The size and cost of electronics has made frequency inverters applicable to a wider range of motors and increased the opportunity for savings.
All frequency inverters are going to take 3 phase AC power and convert that 3 phase power to DC power inside the drive and pulse it out in a simulated AC wave form to the motor. The motor still thinks it has AC power but the DC power conversion now lets us control the speed of the motor without harming it. Now we are in control to save energy and money.
The basic concept with the savings for frequency inverters is your speed and your flow are more or less proportional. But the energy consumption is cubed. If you're running your motor at full speed 60 Hertz, you don't have any savings- but any reduction pays the reduction cubed.
Implementing frequency inverter can pay back big benefits, and adopting them is easier than it might seem at first. You just have to follow a few basic guidelines:
- What are the torque demands of the loads or processes in your planned system? Will any of the loads be hard to start? Inverters have limited over-current capacity, so hard-to-start loads may require an over-sized unit to cover higher current demands.
- How many motors will the frequency inverter control? If it's more than one, will they start sequentially or simultaneously? Calculate the total peak currents of all motor loads under the worst operating conditions your planned system will see. Size the inverter according to this maximum current requirement.
- Will your applications require a quick start or an emergency stop of the load? If so, high currents will be demanded of the inverter. Over-sizing the frequency inverter may be necessary.
- Is motor overheating a potential concern for any of your planned inverter applications? It may be, for reduced-speed, constant-torque applications.
- What range of motor sizes will your process or processes require the inverter to handle? Remember, smaller motors aren't as efficient as larger ones, so improvements due to the inverter will likely be apparent. However, since large motors use much more power, even small increases in efficiency can produce appreciable savings over the life of the motor.
Tags: inverter, Frequency inverter
If the motor is designed for 60 Hz and you intend to use it at 50 Hz, you must reduce the voltage so that you don't overexcite the core (iron). To achieve this, you will have to reduce the voltage to 200 Vac (i.e., volts per hertz V/Hz = constant). By doing this, realize that the nameplate power, torque and speed ratings will all be reduced. The power will be 83%, the torque will be 69% and the speed will be 83%. Since this is an induction motor, there will be no pole slipping as stated above. As long as you don't exceed the temperature rise rating of the machine, the life span of the motor will not be reduced.
Tags: Power supply, 60Hz 50Hz
One reason why the converter is unable to feed the peak current directly is because of its own source (output) impedance limitations. One could consider feed-forward technique to address this problem.
Let me assume that this is Lsource, say it is predominantly inductive. In that case, the feed-forward voltage required to overcome this effect is dff, where
vff = Lsource*delta(Ipk)/deltat
Where delta(Ipk)/deltat is the rate of change of peak current.
dff = vff/Vdcmax
where
dff is the dutycycle required to produce vff
Thus,
Dtot = Derr+dff
Where
Dtot = total dutycycle fed to the switch
Derr = dutycycle from the error controller
Let me assume that this is Lsource, say it is predominantly inductive. In that case, the feed-forward voltage required to overcome this effect is dff, where
vff = Lsource*delta(Ipk)/deltat
Where delta(Ipk)/deltat is the rate of change of peak current.
dff = vff/Vdcmax
where
dff is the dutycycle required to produce vff
Thus,
Dtot = Derr+dff
Where
Dtot = total dutycycle fed to the switch
Derr = dutycycle from the error controller
Tags: Converter, Power supply
Constant Torque: This is where the torque required to run the load is the same no matter what speed it is running at. For example a conveyor with a 1000 lb load and a 1 foot radius head pulley would require 1000 ft. Lb. of torque at all speeds. Because these applications can be started under full load conditions the rule of thumb is to provide a frequency inverter drive with 150% overload capacity for 60 seconds in order to overcome the inertia at start up and for overload conditions. Further understanding of the application is required for situation such as an outdoor conveyor that has is fully loaded overnight with a wet gravel load which is now frozen. Starting this load might require 200% or more full load torque, current and HP just to get it running.
Variable Torque: This is where the power required to run the driven equipment increases to the cube of the speed. For example centrifugal pumps and fans. Because these applications start with no load and build up to full load they generally do not require more than 100% of full load torque, current and HP. Inverters with 110% overload capacity for 60 seconds can protect the driven equipment in the case of bearing failure etc. This is the type of application where energy savings are usually large. For example if you have a 300HP water cooling tower fan. To get the return water temperature that you desire in August may require full flow of air. In January you may only require 50% air flow and each month may be different. At 80% flow the horse power required would be about 52% providing saving of 48%.
Constant Horse Power: This is where the torque required to run the load changes with the process. An example here is a mixer used to make soap. The operator starts the mixer and has it running at full speed. He adds water, then other chemicals one after the other. As each chemical is added he reduces the speed but the soap gets thicker and thicker requiring more and more torque. Since the speed is reducing and the torque is increasing the horse power required might be constant or it might even require more horse power at the low speeds. The old variable pitch belt drives were very good for these applications because they provided constant HP from full to half speed.
Variable Torque: This is where the power required to run the driven equipment increases to the cube of the speed. For example centrifugal pumps and fans. Because these applications start with no load and build up to full load they generally do not require more than 100% of full load torque, current and HP. Inverters with 110% overload capacity for 60 seconds can protect the driven equipment in the case of bearing failure etc. This is the type of application where energy savings are usually large. For example if you have a 300HP water cooling tower fan. To get the return water temperature that you desire in August may require full flow of air. In January you may only require 50% air flow and each month may be different. At 80% flow the horse power required would be about 52% providing saving of 48%.
Constant Horse Power: This is where the torque required to run the load changes with the process. An example here is a mixer used to make soap. The operator starts the mixer and has it running at full speed. He adds water, then other chemicals one after the other. As each chemical is added he reduces the speed but the soap gets thicker and thicker requiring more and more torque. Since the speed is reducing and the torque is increasing the horse power required might be constant or it might even require more horse power at the low speeds. The old variable pitch belt drives were very good for these applications because they provided constant HP from full to half speed.
Tags: inverter, Frequency inverter