Advantages of high frequency PWM in AC motor drive applications (2024)

FAQs

Advantages of high frequency PWM in AC motor drive applications? ›

There are many advantages of using high frequency PWM (in the range of 50 to 100 kHz) in motor drive applications. High motor efficiency, fast control response, lower motor torque ripple, close to ideal sinusoidal motor current waveform, smaller filter size, lower cost filter, etc. are a few of the advantages.

AC drives that use PWM techniques have varying levels of performance based on control algorithms. There are four basic types of control for AC drives today. These are Volts per Hertz, Sensorless Vector Control, Flux Vector Control, and Field Oriented Control. variable frequency drive for applications like fan and pump.

Motors as a class require very high currents to operate. Being able to vary their speed with PWM increases the efficiency of the total system by quite a bit. PWM is more effective at controlling motor speeds at low RPM than linear methods.

Hence this is where the term Pulse Width Modulation comes from (figure 1). Frequency as it relates to PWM is the number of times per second that we repeat the on and off cycle (figure 2). If we pulse the solenoid on and off at a given duty cycle 30 times a second, we have a frequency of 30 Hz.

High frequency refers to motors which run at a higher frequency than the conventional 50 or 60 Hz. High frequency power tools have much higher efficiency, meaning higher output for the same current input, and superior performance with lighter weight.

There are many advantages of using high frequency PWM (in the range of 50 to 100 kHz) in motor drive applications. High motor efficiency, fast control response, lower motor torque ripple, close to ideal sinusoidal motor current waveform, smaller filter size, lower cost filter, etc. are a few of the advantages.

Typically at least 50 kHz is recommended for maxon motors. All maxon's ESCON and EPOS4 product types have a PWM frequency in between 50 ... 100 kHz. Choose a modern controller with a "3-level PWM" scheme.

Pulse-width modulation (PWM) offers several advantages for power electronics systems, such as reducing harmonic distortion and noise in the output waveform, thus improving power quality and reducing electromagnetic interference (EMI).

PWM allows motors to have more torque at low speeds.” Such thinking would suggest that PWM is superior to applying a variable dc voltage, and that the experience with trains and sewing machines provides confirmation.

Using PWM causes the average DC value of the signal to change when passed through a low pass filter. If such a signal is fed to a DC motor, we can change the speed of the motor by changing the duty cycle of the PWM signal.

What is the disadvantage of PWM? ›

Disadvantages of pulse width modulation :

The system requires a semiconductor device with low turn ON and turn OFF times. Hence they are very expensive. Radiofrequency interference. Electromagnetic noise.

With 43 MHz as the input clock to the PWM and 65535 as the period, the maximum supported frequency is 656 Hz. (43,000,000/65536 = 656). The PWM cannot achieve the desired 20 KHz maximum frequency.

PWM is used in many applications, ranging from communications to power control and conversion. For example, the PWM is commonly used to control the speed of electric motors, the brightness of lights, in ultrasonic cleaning applications, and many more.

A frequency higher than the rated frequency usually improves the power factor but decreases locked-rotor torque and increases the speed and friction and windage loss. At a frequency lower than the rated frequency, the speed is decreased, locked-rotor torque is increased, and power factor is decreased.

With the use of Variable Frequency Drives (VFD), motors can be run at higher than 60 Hz, known as an overspeed condition, typically as direct drive fan wall/plenum fans (per NIH DRM 6.2. 4.2, the maximum operating speed is 90 Hz).

In induction motor, speed is function of supply frequency. Frequency increases the speed. For power to change, product of torque and speed has to change. So, in general, if frequency is increased, speed increases.

Any other voltage or current that changes over time can be called AC so a PWM signal is AC as long as it isn't a 0 % (exactly) or 100% (exactly) PWM signal because those signals are constant and thus they're DC.

The other common method of generating AC power in electronic power converters is pulse width modulation (PWM). PWM is used extensively as a means of powering AC devices with a DC power source. A DC voltage source can be made to look like an AC signal across a load by altering the duty cycle of the PWM signal.

The process involved in inverting the DC voltage to the variable voltage variable frequency (VVVF) AC voltage in the inverter section of the VFD is called pulse width modulation or PWM.

Pulse-width modulation (PWM) or duty-cycle variation methods are commonly used in speed control of DC motors. The duty cycle is defined as the percentage of digital 'high' to digital 'low' plus digital 'high' pulse- width during a PWM period. Above fig shows the 5V pulses with 0% through 100% duty cycle.