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    Control Technologies ManualPWM AC DrivesRevision 1.0Pulse Width Modulated (PWM)Figure 1.8 shows a block diagram of the power conversion unit in a PWM drive. In thistype of drive, a diode bridge rectifier provides the intermediate DC circuit voltage. In theintermediate DC circuit, the DC voltage...

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    PWMDrives01.docPage 2 of 13 PWM Output WaveformsAC drives that use a PWM type schemes have varying levels of performance based oncontrol algorithms. There are 4 basic types of control for AC drives today. These areVolts per Hertz, Sensorless Vector Control, Flux Vector Control, and Field Oriente...

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    PWMDrives01.docPage 3 of 13Volts/HertzVolt/Hertz control in its simplest form takes a speed reference command from an externalsource and varies the voltage and frequency applied to the motor. By maintaining aconstant V/Hz ratio, the drive can control the speed of the connected motor. V/Hz Block ...

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    PWMDrives01.docPage 4 of 13V/Hz Speed vs. TorqueThe plot above shows the steady state torque performance of a Volts/Hertz drive. Atorque transducer directly on the motor shaft supplied the data that is plotted. The drive isgiven a fixed speed/frequency reference. Then load on the motor is increas...

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    PWMDrives01.docPage 5 of 13torque. This only shows the ability of the drive to maintain torque output over a longperiod of time.The next type of control was developed to address some of these concerns.

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    PWMDrives01.docPage 6 of 13Sensorless VectorSensorless Vector Control, like a V/Hz drive, continues to operate as a frequency controldrive, with slip compensation keeping actual motor speed close to the desired speed.The Torque Current Estimator block determines the percent of current that is in ...

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    PWMDrives01.docPage 7 of 13Flux VectorThe flux vector control retains the Volts/Hertz core and adds additional blocks around thecore to improve the performance of the drive. A “current resolver” attempts to identify theflux and torque producing currents in the motor and makes these values ava...

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    PWMDrives01.docPage 8 of 13Sensorless Flux Vector Block DiagramFlux Vector Speed vs. TorqueThis graph shows the steady state torque capability of a flux vector drive. The speedcontrol has been improved. Second, the torque output capability is better. Note howeverthat there is still a decrease i...

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    PWMDrives01.docPage 9 of 13Field Oriented ControlWhat distinguishes a product using Field Oriented Control from a traditional vectorproduct is its ability to separate and independently control (or regulate) the motor fluxand torque. This will be explained in greater detail later in this presentat...

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    PWMDrives01.docPage 10 of 13Sensorless Field Oriented ControlAs with flux vector products the newest versions of Force Technology allow users tocontrol the motor without the use of a speed-sensing device. A major difference is thatthe drive continues to operate with Field Oriented control, inste...

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    PWMDrives01.docPage 11 of 13Performance ComparisonThe graph below shows a drive using Force Technology operating with and without anencoder, and a Volts/Hertz drive. Notice that there is very little difference in operationwith or without an encoder. You can clearly see the response to the step ...

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    PWMDrives01.docPage 12 of 13Field Oriented Control150% Load Acceleration to Base SpeedThis graph shows the ability of a drive using Force Technology to maintain control overtorque and speed, even under extreme conditions.The black trace shows actual shaft torque as the drive accelerates a 1.5 per...

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    PWMDrives01.docPage 13 of 13Torque per Ampere ComparisonThe result is that a motor run at low loads will dissipate higher losses when controlled by aVolts/Hertz drive. At slower speeds, this could cause unnecessary motor overheating.

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