How Do VFDs Work

How Do VFDs Work?A variable frequency drive is also known as a VFD, variable speed drive, adjustable speed drive, electronic motor controller, or an inverter. How do VFDs work? Every VFD is unique with its own component characteristics so how each VFD works is dependent upon components within the VFD. Most VFDs integrate a solid state electronics controller consisting of a bridge rectifier, a converter, and an inverter module.

Voltage-source inverter drives are the most common type of VFDs. These drives convert AC line input to AC inverter output.There are some applications that use common DC bus and solar applications. These type of drives are configured as DC to AC drives. The bridge rectifier converter for volts per hertz drives is configured for 3 phase AC electric motors. Volts per hertz drives usea capacitor to smooth out the converter DC output ripple and provides a solid input to the inverter.

This filtered DC voltage is converted to AC voltage output using the inverter’s active switching elements. VSI drives provide higher power factor and lower harmonic distortion (noise) than phase controlled current source inverters and load commutated inverters drives. The drive controller can also be configured as a phase converter having single-phase converter input and three-phase inverter output.Controller advances have allowed increased voltage and current ratings and switching frequency of solid-state power devices over the past 50 years. VFDs were first introduced in 1983, and the insulated gate bipolar transistor has in the past 20 years become the standard for VFDs as an inverter switching device.

In variable-torque applications using Volts per Hertz (V/Hz) drive control, AC motor specifications require that the voltage magnitude of the inverter’s output to the motor be adjusted to match the required load torque in a corresponding V/Hz relationship. For 460 VAC, 60 Hertz electric motors, this V/Hz relationship would be 460/60 = 7.67 V/Hz. While acceptable in a wide range of different applications, V/Hz control is sub-optimal in high performance applications. High performance applications requiring low speed control, demanding high torque, dynamic speed regulation, positioning, and reversing load demands, there are open loop VFDs and closed loop VFDs would be desired over V/Hz VFDs.

How Do VFDs Work In Manufacturing

Many manufacturers will apply variable frequency drivesto rotating equipment to reduce amperage spikes upon start up of large electric motors. Choosing the right VFD for an application will benefit rotating equipment by providing less wear on the electric motors where applied. Adjusting the acceleration and deceleration time of electric motors can extend the lifespan of an electric motor. Variable frequency drives provide the ability to control the frequency of starting and stopping of an AC electric motor. This ability allows an AC electric motor to only operate when needed for the equipment its rotating, and electric motors have a longer lifespan if they are only running when they need to be.

Approximately one third of the worlds electrical energy is supplied by electric motors in fixed-speed centrifugal pump, fan, and air compressor applications. These fixed-speed applications hardly ever require the full load speed (RPM) of the electric motor in which theyre operating. By installing a VFD to these applications, electric motor speeds are reduced, and power costs can be reduced by 50% or more. Technology has allowed cost and physical size reduction of variable frequency drives, and has improved performance through advances in semiconductor switching devices, simulation, control techniques, and control hardware and software.

How Do VFDs Work For Power Savings

The majority of variable frequency drives in the market today contain electronic circuitry that converts 60 Hertz Line power into direct current. The variable frequency drive converts this line power into a pulsed output voltage that duplicates varying alternating current to a desired frequency (speed). A properly applied VFD when paired with the correct electric motor will significantly reduce operating costs for manufacturers. This is particularly true for variable torque loads such as fans, blowers, and pumps. Blowers are often used with dampers to control air flow; these dampers may operate either manually or automatically. When dampers are closed, 50% of the electric motor current will drop to approximately 60% of full load nameplate current. By utilizing variable frequency drives in blower applications, the current draw of the motor will be reduced 30% for every 10% drop in speed. The same electric motor operating from an AC variable frequency drive at 50% speed, will draw approximately 20% of the full load current.

Are you still asking yourself, How Do VFDs Work? Please watch our YouTube Video,or contact us via email. For VFD repair and replacement quotes, contact Precision Electric, Inc.

Magnetek VFD Repair

Most Magnetek VFDrepair can be prevented with routine maintenance. Magnetek VFDrepair costs and lead times can also be reduced with routine maintenance. Magnetek VFD repair can be expensive and also cost manufacturers production downtime while the Magnetek VFD repair is in process.Most manufacturers stock spare Magnetek VFD modulesto prevent production downtime in the event of a Magnetek VFD failure.Components used for Magnetek VFDmodules are often cheaply made and prone to failure. Knowledgeable repair shops should replace cheaply made components with high quality components during the repair process. Using high quality components during a MagnetekVFDrepair ensures a longer lifespan of the VFD during production.

Checkingconnections is a step many people miss or do incorrectly during the Magnetek VFDrepair process. Heat cycles and mechanical vibration can lead to sub-standard connections, as canpoorroutine maintenancepractices. Reusing torque screws is not a good Idea on connections, and further tightening an already tight connection can ruin the connection.Bad connections eventually lead to arcing. Arcing at the VFDinput can result in nuisance over voltage faults, clearing of input fuses, or damaging protective components. Arcing at the VFDoutput could result in over-current faults or damage to the power components.

Loose connections can also cause erratic operation. Loose START/STOP signal wires can cause uncontrollable inverterstarting and stopping. A loose speed reference wire can cause the VFDspeed to fluctuate, resulting in scrap, machine damage, injury or death.

Conduct Diode and IGBT Tests
There are a number of methods to test the input and output power sections during Magnetek VFD repair processes, and this step is essential prior to applying power to the VFDunit. If there’s a short on the input or output side of the VFD, further damage to the VFD may result if power is applied to it.

For this reason, Precision Electric uses meters to properly test the input and output power sections of the VFDprior to applying power to the unit. If a short is found, the unit can be disassembled and the cause of the short can be diagnosed and quoted for repair. If the repair is too costly, then a replacement is offeredto the customer.

Power Up Unit
If the input and output power sections test healthy during this step of the Magnetek VFDrepair process, Precision Electric will power the unit and perform amp reading and output frequency tests. Precision Electric prefers to slowly increase power voltage to the unit until the rated input voltage of the VFDis achieved.

Depending on whether or not the VFD provides a display will determine what further action(s) will be taken. If the VFD display is unavailable, dis assembly and diagnosis of the internal power supply of the control section of the VFD is likely necessary to further evaluate cause of failure and establish costand lead time of the VFDrepair.

Run A Motor
If the previous tests have passed during the Magnetek VFDrepair process, Precision Electric willrun a basic jog function of the VFDwith a simple template program. Often when Magnetek VFD repair jobscome into our facility, technicians will backup operation programs that are stored in the VFD prior to inputting a template program and running test procedures. Backing up the operation program will ensure that Precision Electric canreinstall the program once the Magnetek VFD repair is complete.

The best method for backing up an operation program depends on the manufacturerof drive, but after it has been backed up, Precision Electric will either reset the VFDto factory defaults through the keypad and recommission a basic start, stop function. If the VFD is closed loop requiring an encoder, the encoder is tested for faults prior to running the start, stop test function. If the motor will not run in factory default mode, the motor output voltages and motor current ratings are checked to see if the VFD is functioning properly for motor rotation.

Magnetek VFDrepair should be taken with extreme caution. VFDrepair should only be performed by technicians who have required training and experience to work with electrical equipment. Precision Electric strongly recommends consulting an expert in the field when repairing or installing industrial electrical equipment.Many VFD units have an internal DC bus that retains an electrical charge after power to the drive is turned off, which means it’s unsafe to work with. Technicians performingMagnetek VFD repair should always take extra precautions to ensure proper safety measures are taken to prevent injury or death.

For Magnetek VFDrepair and Magnetek VFDreplacement quotes, contact Precision Electric.

Eaton Overcurrent Protection

Eaton overcurrent protection and Eaton current control for the Eaton9000X drive is based on motor current measurement in all three phases. In the Frame 9/ Chassis 61 Eaton drives, the current sensors are built into the IGBT SKIP modules, and the current signals are combined and fed into a 14-bit A/D converter on the lower ASIC board. The ASIC board sends the current levels to the control board via a fiber optic serial link. In the smaller Eaton Frame 8 / Chassis 5 drives (and below), the measured current signal is fed directly to the control board. The EatonSVX9000drive has a 10-bit A/D converter and the EatonSPX9000drive has a 14-bit A/D converter.

Eaton overcurrent protection for the 9000X air-cooled frequency converter ratings are based on a High Overload (IH) capability. This means the drive can provide 150% rated output current for 1 minute if the drive was operating at rated output current (IH) for at least 9 minutes. To get continued 150% overcurrent capability, the average current over the duty cycle cannot exceed the rated output current. The maximum drive output current (IS) for starting produces approximately 200% rated motor torque but because the currents are vector sums, IS is less than 200% IH. The drive can deliver IS for 2 seconds every 20 seconds. The drive current limit can be set to 200% (2 x IH) to deliver IH but to reduce the chance of an overcurrent or IGBT over temperature trip, it is better to set the current limit to 150% (1.5 x IH) or less.

The actual drive output current available to the motor is dependent on ambient temperature at the intake to the drive, restrictions in airflow to the drive, and the drive frame size. Drive frames FR4FR9 can deliver rated current (IH) at 50C. Drive frames FR10 and above can deliver rated current (IH) at 40C except for the highest ratings of a drive frame, which may be limited to 35C. The Low Overload (IL ) rating is typically used for variable torque loads where an overload is not necessary even though a 1 (out of 10) minute overload of 110% is allowed. All drive frames are limited to 40C or less for the IL rating. The rated currents of each frame depend on a reduction of switching frequency when unit temperature reaches the warning level.

Eaton overcurrent protection in the liquid-cooled drive has a Thermal maximum continuous rms current (Ith). Use this value for continuous or any overload requirements of the process. The liquid-cooled drive does not have a 1-minute overload current rating. The thermal current rating is dependent on proper coolant flow to each module and a module coolant inlet temperature of 30C. Current limit (software-function) The drive will attempt to limit drive output current to the current limit setting by overriding and lowering the frequency reference until current is within the current limit setting. If unit temperature nears the warning level, the drive will reduce the output frequency in an attempt to bring drive output current down to a continuous current that is approximately the Low Overload (IL ) current rating. The control will not allow any further overcurrent conditions until the average current over the duty cycle is less than the drives current rating. The liquid-cooled drive control will attempt to limit the output current to the current limit setting up to the drives thermal rating. The application should be designed to avoid using the current limiter for control.

The safest way to operate an Eatondrive is to keep the drive output current within ratings with appropriate ramp times or a controlled reference to the drive. If the drive software cannot prevent output current from exceeding 200% IH, a current cutter stops firing the IGBTs when the measured instantaneous value of the current exceeds 360% IH to reduce current quickly before an overcurrent trip occurs. They are re-fired on the next top of the triangle wave. The current cutter is active on select units FR8/CH5 and smaller. If the measured instantaneous value of current exceeds the trip limit value (260400% depending on drive size), all IGBTs are switched off and the drive displays an F1, overcurrent trip. The drive is protected from a short circuit at the motor if the motor leads are greater than 16 feet (5m) in length.

Only trained and experienced electricians should work withEaton overcurrent protection. For more safety information about Eaton overcurrent protection, visit the Eaton Website. For Eaton drive repair and Eaton drive replacement quotes, contact Precision Electric.

Eaton Low Voltage Drives

Eaton low voltage drives (also known as variable frequency drives) adjust an electric motor’s speed to closely match output requirements, resulting in a typical energy savings of 10 to 50 percent.

Eaton’s SVX9000 adjustable frequency drive offers sensorless vector control technology coupled with an adaptive motor model and sophisticated ASIC circuit features. This technology allows for steady speed error, fast torque rise time, high immunity to resonance vibrations and high starting torque and current. The SVX9000 is suitable for multiple motor drive systems and high-speed applications.EatonSPX9000 drives are designed specifically for high-performance applications. Eaton SPX9000 drives feature high processing power and the ability to use information from an encoder or a resolver to provide precise motor control. In addition, a fast microprocessor provides high dynamic performance for applications where good motor handling and reliability are required.

The Eaton DG1 General-Purpose drives are part of the Eaton next-generation PowerXL series of adjustable frequency drives specifically engineered for todays more demanding commercial and industrial applications. With an industry-leading energy efficiency algorithm, high short-circuit current rating and robust design, the Eaton DG1 General-Purpose drives offer increased efficiency, safety and reliability.Eaton’s LCX9000 drives are liquid-cooled products that utilize potable water or a water-glycol mixture as a cooling medium. Their compact size and low heat transfer rates allow the enclosure size to be greatly reduced, which is especially beneficial in UL Type 4X applications.

Eaton offers industry-leading technology for applications where harmonics are a concern. Eaton’s clean power drives significantly reduce line harmonics at the drive input terminals and provide some of the purest sinusoidal waveforms available.EatonPowerXL Enclosed Drivesis a next generation enclosed drive platform that packages Eatons PowerXL DG1 and SVX drive families in a versatile, fast, and reliable design solution.

EatonCFX9000 Clean Power Drivesuse tuned passive filters to significantly reduce line harmonics at the drive input terminals. These drives are an excellent choice for small and midsize applications where harmonics are a concern. EatonCPX9000 Clean Power Drivesare the clear choice for applications in the water, wastewater, HVAC, industrial and process industries where harmonics are a concern. They offer one of the purest sinusoidal waveforms available.

EatonCP to CPX Retrofit Kitsprovide an alternative to a complete drive and enclosure replacement for our existing CP customers. They provide a cost effective and time efficient solution only Eaton can provide. EatonAGSVX Irrigation Drive Panelis a single-phase to three-phase irrigation drive panel is an efficient and clean solution for three-phase power. EatonHVX9000 HVACvariable frequency drives use the most sophisticated semiconductor technology and a highly modular construction to provide flexibility for HVAC applications.

EatonMVX9000 Micro Drivesare sensorless vector variable frequency drives are designed to provide adjustable speed control of three-phase motors. EatonSLX9000 General Purposedrives are compact, yet powerful drive is based on the more robust SVX9000. It is designed to be the next generation of drives specifically engineered for modern commercial and light industrial applications.

To learn more about Eaton low voltage drives or for Eaton low voltage drives repair and replacement quotes, contact Precision Electric.