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This configuration, sometimes referred to as a "shoebox on the wall" is the least expensive option of the three major types. It features a basic frequency inverter connected between the line and the load. Speed control is generally operator initiated either through a front panel keypad or speed potentiometer. Functionality and features on this type of frequency inverter are generally limited. It should be noted that an external disconnect is required and that this type of frequency inverter may not be suitable for filter room applications due to the harsh environment and the lack of a secondary enclosure. One major issue with this type of frequency inverter is that being the sole load driving component, a failure of the frequency inverter will bring the entire system down until the frequency inverter is removed from service for repair or replacement.
Tags: inverter, Frequency inverter
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
Inverter is capable to smoothly starting AC motors (ramp from 0 up to 100% of the load) as well as the energy saving will be achieved, accordingly. Also may I confirmed that frequency inverter also acting as AC Motor starting means among (Star/Delta, Soft Starter, Auto Transformer, Electrolyte, series resistance - wound rotor- etc,). The starting factor of frequency inverter is usually 1 up to 1.2 with respect to the rated load current while for Direct On line about 5-6.
Moreover and as you know the inverter can control the speed of the AC motors in accordance to the formula N=120f/P rpm
where f = the supply frequency and P = number of the Poles.
According to this formula, Motor Speed can be changed either by changing/control the frequency or by changing the number of Poles of the Motor by which step changed in the RPM will be given, while the former gives continuous variable speed as per application demand.
However, as per newly developed power Semi Conductor IGCT based on PWM frequency inverter became the most smart, effective and efficient control device in Industries since is associated also with protective and monitoring means.
Moreover and as you know the inverter can control the speed of the AC motors in accordance to the formula N=120f/P rpm
where f = the supply frequency and P = number of the Poles.
According to this formula, Motor Speed can be changed either by changing/control the frequency or by changing the number of Poles of the Motor by which step changed in the RPM will be given, while the former gives continuous variable speed as per application demand.
However, as per newly developed power Semi Conductor IGCT based on PWM frequency inverter became the most smart, effective and efficient control device in Industries since is associated also with protective and monitoring means.
High Voltages in the range of 10kV to 100kV and at low power finds use in a number of industrial equipment such as ionizers. Special electronic circuits are required to generate this high voltage from the relatively lower and safer to handle voltages available. The most straight forward method would be to use a voltage step-up transformer that would convert the lower voltage alternating current on the primary side to a high voltage alternating current on the secondary side. For a compact and lower cost solution, a multi stage voltage multiplier circuit fed by a high frequency AC voltage is used.
Voltage Multipliers
Voltage Multipliers are circuits consisting of a network of capacitors and diode rectifiers. They work on the basic principle of an AC voltage charging sets of capacitors to a peak voltage. The output would be the sum of voltages across a string of such capacitors. The diodes form valves that enable charging in a particular direction and prevent the discharge during the negative of the AC voltage. Voltage multipliers can be used to generate bias voltages of a few hundred volts to millions of volts.
Various types of multiplier circuits, each having a particular advantage, are available. The most simple and common of these is the Half Wave Cockcroft-Walton (CW) Multiplier. The figure below gives the basic schematic for a CW multiplier. This circuit is preferred if the output ripple and voltage drop are not as much critical as the cost and size of the unit.
Voltage Multipliers
Voltage Multipliers are circuits consisting of a network of capacitors and diode rectifiers. They work on the basic principle of an AC voltage charging sets of capacitors to a peak voltage. The output would be the sum of voltages across a string of such capacitors. The diodes form valves that enable charging in a particular direction and prevent the discharge during the negative of the AC voltage. Voltage multipliers can be used to generate bias voltages of a few hundred volts to millions of volts.
Various types of multiplier circuits, each having a particular advantage, are available. The most simple and common of these is the Half Wave Cockcroft-Walton (CW) Multiplier. The figure below gives the basic schematic for a CW multiplier. This circuit is preferred if the output ripple and voltage drop are not as much critical as the cost and size of the unit.
Tags: inverter
Noise radiated from a frequency inverter cable is proportional to the amount of varying electric current within it. As cable lengths grow, so does the magnitude of reflected voltage. This transient over voltage, combined with the high amplitudes of current associated with frequency inverters, creates a significant source of radiated noise. By shielding the frequency inverter cable, the noise can be controlled. In the tests presented in this paper, relative shielding effectiveness was observed by noting the magnitude of noise coupled to 10 ft. of parallel unshielded instrumentation cable for each frequency inverter cable type examined. The results of the shielding effectiveness testing are documented in the Figure.
As demonstrated by its trace in that figure, foil shields are simply not robust enough to capture the volume of noise generated by frequency inverters. Unshielded cables connected between a frequency inverter and a motor can radiate noise in excess of 80V to unshielded communication wires/ cables, and in excess of 10V to shielded instrumentation cables. Moreover, the use of unshielded cables in conduits should be limited, as the conduit is an uncontrolled path to ground for the noise it captures. Any equipment in the vicinity of the conduit or conduit hangers may be subject to an injection of this captured, common- mode noise. Therefore, unshielded cables in conduit are also not a recommended method for connecting frequency inverters to motors.
As demonstrated by its trace in that figure, foil shields are simply not robust enough to capture the volume of noise generated by frequency inverters. Unshielded cables connected between a frequency inverter and a motor can radiate noise in excess of 80V to unshielded communication wires/ cables, and in excess of 10V to shielded instrumentation cables. Moreover, the use of unshielded cables in conduits should be limited, as the conduit is an uncontrolled path to ground for the noise it captures. Any equipment in the vicinity of the conduit or conduit hangers may be subject to an injection of this captured, common- mode noise. Therefore, unshielded cables in conduit are also not a recommended method for connecting frequency inverters to motors.
Frequency inverters require an acceptable electrical supply for safe, successful and reliable operation.
Single phase inverters have standardized voltages of 120 and 240 volts. Three phase motors have standardized voltages of 200, 230, 460 and 575 volts.
The nominal supply voltage of the distribution system is normally higher than the inverter nameplate voltage to allow for voltage drops from the distribution transformer to the point of utilization.
Rated frequency is usually 60Hz (hertz or cycles per second) in North America.
Harmonics
Harmonic distortion of voltage and current is produced in electrical systems by non-linear loads such as frequency inverters, welders, rectifiers, Uninterruptible Power Supplies (UPS), arc furnaces etc. Harmonics cause electrical waveform distortion that can propagate through the entire power system and even outside of the plant. The source of harmonic distortion in frequency inverters is the solid-state power switching devices used to generate the varying supply frequencies.
These effects, known as "line harmonic currents", are multiples of the fundamental 60 Hz supply current. For example, a frequency of 180 Hz is called the third harmonic. These currents generate harmonic voltage distortions which often exceed acceptable levels.
For more information, refer to the CEATI Power Quality Energy Efficiency Reference Guide.
Harmonic Components
Harmonic Amplitudes
The odd harmonic amplitudes usually decrease with increasing frequency, so the lowest order harmonics are the most significant. Even numbered harmonics are not normally generated by frequency inverter systems.
Harmonics occur as long as the harmonic generating equipment is in operation and tend to be of a steady magnitude.
Harmonics may be greatly magnified by power factor correction capacitors. The supply system inductance can resonate with capacitors at certain harmonic frequencies developing large currents and voltages, which can damage equipment.
Single phase inverters have standardized voltages of 120 and 240 volts. Three phase motors have standardized voltages of 200, 230, 460 and 575 volts.
The nominal supply voltage of the distribution system is normally higher than the inverter nameplate voltage to allow for voltage drops from the distribution transformer to the point of utilization.
Rated frequency is usually 60Hz (hertz or cycles per second) in North America.
Harmonics
Harmonic distortion of voltage and current is produced in electrical systems by non-linear loads such as frequency inverters, welders, rectifiers, Uninterruptible Power Supplies (UPS), arc furnaces etc. Harmonics cause electrical waveform distortion that can propagate through the entire power system and even outside of the plant. The source of harmonic distortion in frequency inverters is the solid-state power switching devices used to generate the varying supply frequencies.
These effects, known as "line harmonic currents", are multiples of the fundamental 60 Hz supply current. For example, a frequency of 180 Hz is called the third harmonic. These currents generate harmonic voltage distortions which often exceed acceptable levels.
For more information, refer to the CEATI Power Quality Energy Efficiency Reference Guide.
Harmonic Components
Harmonic Amplitudes
The odd harmonic amplitudes usually decrease with increasing frequency, so the lowest order harmonics are the most significant. Even numbered harmonics are not normally generated by frequency inverter systems.
Harmonics occur as long as the harmonic generating equipment is in operation and tend to be of a steady magnitude.
Harmonics may be greatly magnified by power factor correction capacitors. The supply system inductance can resonate with capacitors at certain harmonic frequencies developing large currents and voltages, which can damage equipment.
Tags: inverter, Frequency inverter
Energy Savings with inverters
if you have an AC motor-driven application that does not need to be run at full speed, then you can cut down energy costs by controlling the motor with an inverter (frequency inverter, aka variable frequency drive). Inverters allow you to match the speed of the motor-driven equipment to the process requirement. There is no other method of AC motor control that allows you to accomplish this.
Example of an Excellent inverter Candidate
Example of a Decent inverter Candidate
Example of a Poor inverter Candidate
Variable Torque Versus Constant Torque
inverters, and the loads they are applied to, can generally be divided into two groups: constant torque and variable torque. The energy savings potential of variable torque applications is much greater than that of constant torque applications. Variable torque loads include centrifugal pumps and fans, which make up the majority of HVAC applications. Constant torque loads include vibrating conveyors, punch presses, rock crushers, machine tools, and other applications where the drive follows a constant V/Hz ratio.
Why Variable Torque Loads Offer Great Energy Savings
in variable torque applications, the torque required varies with the square of the speed, and the horsepower required varies with the cube of the speed, resulting in a large reduction of horsepower for even a small reduction in speed. The motor will consume only 25% as much energy at 50% speed than it will at 100% speed. This is referred to as the Affinity Laws, which define the relationships between speed, flow, torque, and horsepower. The following diagram illustrates these relationships.
if you have an AC motor-driven application that does not need to be run at full speed, then you can cut down energy costs by controlling the motor with an inverter (frequency inverter, aka variable frequency drive). Inverters allow you to match the speed of the motor-driven equipment to the process requirement. There is no other method of AC motor control that allows you to accomplish this.
Example of an Excellent inverter Candidate
Example of a Decent inverter Candidate
Example of a Poor inverter Candidate
Variable Torque Versus Constant Torque
inverters, and the loads they are applied to, can generally be divided into two groups: constant torque and variable torque. The energy savings potential of variable torque applications is much greater than that of constant torque applications. Variable torque loads include centrifugal pumps and fans, which make up the majority of HVAC applications. Constant torque loads include vibrating conveyors, punch presses, rock crushers, machine tools, and other applications where the drive follows a constant V/Hz ratio.
Why Variable Torque Loads Offer Great Energy Savings
in variable torque applications, the torque required varies with the square of the speed, and the horsepower required varies with the cube of the speed, resulting in a large reduction of horsepower for even a small reduction in speed. The motor will consume only 25% as much energy at 50% speed than it will at 100% speed. This is referred to as the Affinity Laws, which define the relationships between speed, flow, torque, and horsepower. The following diagram illustrates these relationships.
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
Anyways, please read the paper and form your own opinions, but my take on this paper is that it sets the minimum benefit of module level MPPT, and ANY additional variables will increase the benefit. Soiling, variable aging, and variable irradiance (shading) are very real considerations for any site which can have very significant effects on harvest. Additionally, without module level monitoring, there is no way to determine whether or not a modules are even meeting their standard deviation specifications.
Soiling and aging effects are especially hard to model, and the paper references establishes some techniques to quantify the potential benefit of microinverters under these conditions through measurements at an actual test site. Although the study did not use any global MPPT inverters, nonmonotoic conditions which "fooled" the inverter were excluded from the results.
Soiling and aging effects are especially hard to model, and the paper references establishes some techniques to quantify the potential benefit of microinverters under these conditions through measurements at an actual test site. Although the study did not use any global MPPT inverters, nonmonotoic conditions which "fooled" the inverter were excluded from the results.
100% failure is not an outlier in my experience. It may not be mechanical failure, but comms instead. I have seen very close to if not 100% of systems installed have some sort of issue, or multiple failure issues. No one really has the communications side of these things down yet. Communication, or inverter malfunction errors are typical on any micro installation I have seen. The costs of micro inverter versus central inverter replacement and micro service calls are much more expensive. I cannot imagine deploying micros on a commercial scale until a few things happen. The price per unit would have to fall dramatically in order to make up for the increased labor costs, and the communication issues would need to be orders of magnitude better.
We have installed a 140kw micro inverter system and it was at the customer request. The saving grace of the installation is that it is a carport structure and the micros are accessible via an 8' extension ladder. No modules have to be pulled in order to service a micro. I do not recommend micro inverters to anyone looking for more than a kw or so. That is also changing with newer small HF style central inverters with low MPPT ranges. That being said, the customer base Loves micro inverters. Many customers are sold on them before speaking to a sales rep, so someone on the micro side is doing something right! The shading argument is a little off in my opinion and there is a fine line between selling someone a system that has incremental shading, and selling someone a shady system..... System design with a micro can be more simple for a non technical sales person, but it can also lead to poor array placement if left unchecked by the technical support and engineering staff. There is a lot of, oh look a big roof with shade on it, lets use micros inverters happening out there right now. I am in agreement that they have a place in the pv world, but due diligence and robust system design should remain prime drivers on site selection.
We have installed a 140kw micro inverter system and it was at the customer request. The saving grace of the installation is that it is a carport structure and the micros are accessible via an 8' extension ladder. No modules have to be pulled in order to service a micro. I do not recommend micro inverters to anyone looking for more than a kw or so. That is also changing with newer small HF style central inverters with low MPPT ranges. That being said, the customer base Loves micro inverters. Many customers are sold on them before speaking to a sales rep, so someone on the micro side is doing something right! The shading argument is a little off in my opinion and there is a fine line between selling someone a system that has incremental shading, and selling someone a shady system..... System design with a micro can be more simple for a non technical sales person, but it can also lead to poor array placement if left unchecked by the technical support and engineering staff. There is a lot of, oh look a big roof with shade on it, lets use micros inverters happening out there right now. I am in agreement that they have a place in the pv world, but due diligence and robust system design should remain prime drivers on site selection.