variable speed drives

Asynchronous motors are capable of developing significantly higher starting torque than synchronous motors. It has everything to do with the slip. Two pole motors are also an issue at start, due to a significantly lower starting torque capability than 4 or more pole motors.

An encoder of some type is typically used for hoisting applications when the hoist has no mechanical load brake in the gear case. Generally, when we build flux vector hoist controls, we employ 1024 PPR, 24 VDC, ...

For a hoist application
1) You can make a sensorless VFD (variable frequency drive) work on a Hoist however... If an encoder is not used and the VFD doesn't properly sense that there is a problem (it might be a rare occurrence but I've seen it), you could potentially drop the load. It only takes once to seriously damage equipment, hurt someone or worse.


2) With an encoder, and proper br ...

A variable frequency drive (VFD) will improve the system power factor to which it is connected, primarily because the motor reactive current is supplied by the DC bus, rather than the supply system. This will only improve the displacement power factor. Modern VFDs with AFE draw almost sinusoidal current from the supply, so power factor on the source side can be controlled up to unity and the generated harmonics are ...

Q:
I'm looking for ways to estimate the supply current to variable frequency drive (VFD) when an asynchronous motor is running under different torque and speed outputs.

Motor manufacturers usually provide the rated torque, rated current and rated speed of the motor, but when the motor is not running at the rated conditions, how can one estimate the supply current to the VFD from the actual speed and torque output of the motor?

A: ...

I had an oil filled motor start capacitor blow once. What I think happened was when someone replaced it, rather than putting it back in its holder, they duct taped it to the side of the squirrel cage motor that it was starting. They started the motor up and walked away. The motor was a continuous duty motor so it wasn't turned off for a long time. One day, someone shut it off to do some servicing. They notice ...

Induction motor with squirrel cage rotor has two different speeds. The synchronous speed refers to the stator rotating magnetic field, which depends on the number of poles and frequency. The other speed is the rotor's. The rotor speed will be always slower than the stator speed, we call it slip. Without the slip, the squirrel cage induction motor doesn't have torque. Even without load the motor has slip. It increases with the load, according to the current x torque curves you can check it out ...

I have a question regarding protecting a variable frequency drive (VFD). I have read that the important part to protect of the variable frequency drive is the active front end (prior to the IGBT's). I also am under the impression that the VFDs themselves protect the motors from faults. So my questions are as follows:

1. Do you need an overload to protect the motor? And if so do you put in on the PWM output side?
2. How should I protect the variable frequency drive and Motor? ...

Q: What will happen if shaft earthing brushes are not provided for VFD driven motor? Is it acceptable? Motor is of 50 hp, 415 V, and is at 200 m from VFD panel.

A: More than likely it will work just fine. Think of the shaft brushes as cheap insurance. They will make sure the bearings are protected from discharge current to equipment ground. On the other hand, the brushes will also ensure a long useful life from the motor by preventing eve ...

Basically, there are two types of chillers - constant speed and variable speed. The demand on the chiller varies all over the map depending on several factors that are beyond your control. Suffice to say that the load can range anywhere from 25-100 percent of rated capacity.

With a "constant" speed chiller design, we can either cycle the chiller more frequently or close the valve for light loading conditions requiring less flow. This is inherently less energy efficient than a "var ...

This question is a little more complex than it seems on the surface. Let's start with understanding the reason you believe you need to provide some form of braking in the first place. Do you need to stop very quickly under either normal or emergency stop conditions? Does your process need to be able to decelerate quickly when changing from a higher speed to a lower speed? If none of these conditions exist you may not need to provide any form of braking at all. The system friction and windage ...

The variable frequency drive (VFD) has the capacity of 11kW, it's a rotogravure printing machine which is used in packaging industry (plastic web films). The data is collected from the VFD display when the motor was running:

The set speed or speed command given was 100 m/min via HMI (Touchscreen LCD)
Frequency Reference: 48.83 Hz
Output Frequency: -50.10 Hz to -50.82 Hz (Not stable, fluc ...

The vast majority of variable frequency drives (VFDs) are the "voltage-source inverter" (VSI) type with a diode front-end. These non-regenerative VSI-type VFDs, do not contribute to upstream fault current as the input diodes block any current that might flow from the dc bus to the mains.

For regenerative VSI VFDs, the actual front-end regenerative circuit can be either transistors (IGBT, etc.) or thyristors. The VFD controls will respond very quickly. The controls will sense eithe ...

Most manufacturers have separate product families for "servo drives" and "variable frequency drive" or "inverter". However, if we take one of the many VFDs that support PM motors with sensor and a PM servo drive, the control, is the same up to the speed loop. Both servo and VFD (except for DTC) need an inner vector current control loop, which means torque control, and a speed control regulator. They also need a self-tuning p ...

One operational point is to leave a surge buffer at the top of the tank, based on maximum possible input flow. I would eliminate the control valve, to use the VFD, but you may need a stop valve if the discharge of the pump allows gravity flow, when the pump is stopped for Low-Low Level, for instance. A stop valve is easier to apply and more reliable than a vacuum breaker on the discharge line.

The VFD provides significant energy s ...

Every engineer has good points about variable frequency drive (VFD) failure reasons. Some of the phenomenons occur more frequently and some are rarer.

The sizing of VFD is important. Also the application and demands of application should be studied carefully. In some case it might be better to use soft starter than use VFD. Thus VFD is suitable for wide range of applications, some parameters should be examined before installin ...

JOG - a small change in rotational position. A "jog" command is essentially an energy "pulse". A very quick ramp up and down of voltage and/or current is commanded with the idea that it will generate enough torque to overcome static friction and move the rotor some arbitrary fraction of a revolution. Since the duration and amplitude of the pulse are programmable, the resulting angle of the move is also variable. A drive train which contains large inertia components (either in the driven equip ...

As for the good performance of a well-controlled variable frequency drive (VFD) system tank capacity is not an issue, my own criteria is to dimension them as expansion tanks, to take water hammering, and expansion due to temperature raises -if pipes are exposed to the sun for e.g., or water heating tanks are in the line.

For domestic and small civilian uses, a bigger tank will prevent start-stop cycles due to small leakages, but this will highly depend on relationship between set ...

Continuous level control, using a level sensor, would allow for cost-savings if applied using a properly-sized variable frequency drive (VFD). The VFD would allow more consistent level control, improve reliability in not requiring a control contactor and decrease operational costs. Employing a non-contact level sensor will supply a feedback to the VFD and would allow the pump to ramp up/down as the inflow increases/decreases. If the level goes too low, you could put the motor in an off state ...

The rotating speed of the stand was nowhere near enough, so we made an emergency plan with a Variable Speed Drive on the original (4 pole) motor - up to about 200 Hz. This was still not fast enough (we reached the constant power flux limit) so we procured a new 2 pole (22 kW) motor.

I must emphasize that this was an absolutely standard off-the-shelf (Chinese manufacture actually) motor from our sister company who supplies these motors. There was absolutely nothing special about it ...

Every motor driven application needs to be evaluated and the starting and control method properly chosen to meet those needs. If variable speed is not required for the process and the power and mechanical systems are robust the direct-on-line (DOL) starting may be the best choice. If the power system and / or the mechanical system are weak and only fixed speed is required for the process then a reduced voltage starter with bypass may be the best choice as long as the reduced starting torque t ...