Pulse-width modulation (PWM) control of electric motors

Learn the basics of PWM for electric drives and the requirements this places on measurement technology

What exactly is pulse width modulation (PWM)?

Pulse width modulation (PWM) is a digital control method in which a constant DC voltage is rapidly switched on and off to simulate a variable average analogue voltage. The resulting signal consists of a square wave with a constant frequency, the ratio of the on-time (pulse width) to the period – known as the duty cycle – can be varied. If, for example, this duty cycle is 50 per cent, the voltage is switched on for half the time, meaning that a connected load receives, on average, only half the maximum power.

As modern semiconductor switches such as MOSFETs either conduct fully or are completely off, this method operates extremely efficiently and minimises power loss in the form of heat compared to analogue linear regulators. The inertia of the controlled system – such as the inductance of a motor or the thermal inertia of a heater – smooths out the rapid voltage fluctuations, so that the load responds as if to a genuine analogue voltage. The main applications of PWM are speed control of DC motors, LED dimming, and signal transmission and voltage regulation in switching power supplies.

What is meant by pulse-width-modulated control?

Pulse-width modulation is a highly efficient method for precisely controlling the speed and torque of electric motors. Instead of linearly regulating the voltage—which would result in high losses—the supply voltage is switched on and off extremely rapidly. By varying the duty cycle (the ratio of on-time to off-time within a cycle), the average voltage applied to the motor can be continuously adjusted. This enables low-loss control, which is essential for modern electric drives.

Why is PWM so important for electric drives?

PWM is the key to the efficiency of modern electric drives in e-mobility and industrial applications. Without PWM, energy-efficient torque and speed control would be virtually impossible. Thanks to the high switching frequency, electrical energy is modulated so that the motor delivers exactly the required power without losing excess energy as heat. This maximizes the range of electric vehicles and the service life of drive components.

What specific requirements does PWM place on measurement technology?

Measuring PWM signals is a major challenge because the resulting voltage and current waveforms are not clean sine waves, but rather steep-edged square-wave signals.

High switching frequencies: To capture the signal correctly, the measurement system must have an extremely high sampling rate.
Steep switching edges: The analysis of power data requires high bandwidth to accurately capture the physical processes occurring during the switching edges.
Low distortion: Due to the high harmonic content, the measurement technology must have extremely low distortion to correctly perform power calculations (active power, reactive power).

Why is the LTTsmart the ideal measurement system?

The LTTsmart Power Analyzer was specifically developed to meet these complex power measurement requirements:

Maximum sampling rate & 24-bit resolution: With a sampling rate of up to 4 MHz per channel and a resolution of 24 bits, the LTTsmart captures even transient processes in the switching edges with the highest level of detail.
High-precision power characteristics: Thanks to the synchronous nature of the inputs, the LTTsmart provides mathematically precise data on efficiency and losses that cannot be achieved with conventional systems.
Ruggedness: The combination of high-voltage inputs and high precision makes it the ideal tool for the standards-compliant development and testing of inverters and powertrains.

It is precisely these technical features that make the LTTsmart so popular with our customers. Are you interested and have questions? Just give us a call at +49 931 359 610 or fill out the contact form. We would also be happy to schedule a demo appointment for you.