Five ways to deal with heat in PWM

PULSE MODULATION Five ways to deal with heat in PWM

2024-06-05 From Venus Kohli 4 min Reading Time

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According to a universal law, heat generation is an effect of current. PWM is widely used in power electronics systems to control the output and deliver power to the load. But PWM ends up generating large amounts of heat in a system. The article explains the heat generation problem in PWM and lists ways to minimize it.

All devices in power electronic systems have high current ratings, which corresponds to high power and large amounts of heat generation. Learn more about ways to deal with it, in this article.(Source: Parkpoom - stock.adobe.com) — All devices in power electronic systems have high current ratings, which corresponds to high power and large amounts of heat generation. Learn more about ways to deal with it, in this article.
(Source: Parkpoom - stock.adobe.com)

Pulse width modulation (PWM) is the workhorse of power electronics, but its power comes with a hidden enemy: heat generation. This inefficiency can lead to system malfunctions and reduced lifespan. To combat this thermal challenge, we'll explore five key strategies – from component selection to advanced cooling techniques – to ensure your PWM applications run cool and efficient.

Why is heat generated in the PWM technique?

Several factors contribute to heat generation in PWM, including inefficiencies in the switching elements and the effects of operating frequency and duty cycles. Let's explore these reasons further.

Semiconductor switches

Pulse-Width Modulation is used with power semiconductor switches like MOSFETs and IGBTs. All these semiconductor switches are power transistors with high switching losses. Power transistors have a significant on-state resistance which hinders current flow during operation, resulting in more power consumption and heat dissipation.

High-frequency operation

The high operating frequency of PWM promotes various types of losses and the formation of parasitic capacitance. Rapid turning on and off action of PWM-based devices gives rise to current surges and introduces harmonic components that go on to consume more power.

Heavy duty cycles

PWM signals in power electronics have high-duty cycles of 50% or between 50-100%. In simple words, a PWM device is turned on for a long time. As a result, a PWM device consumes a lot of power and heats up.

Five ways to deal with heat generation in PWM

This section explores key strategies for mitigating thermal challenges in PWM applications. We'll examine component selection, sizing, and switching techniques to minimize heat generation. Additionally, we'll discuss the role of heat sinks and effective heat management practices.

Design smart

A smart design starts from the selection of appropriate components considering the thermal characteristics mentioned on data sheets. For example, you can select a MOSFET with low thermal resistance for your next design. Another example is to choose a slightly higher rated power supply for minimizing heavy load on the system during operation. The aim is to go for a minimized design that follows design rules, EMC constraints, and regulations to create better systems.

Select smaller components

Based on generalized examples of power electronic devices, smaller devices need less current to operate and consume less power. However, size is not always the indicator of power consumption. On the other hand, bigger devices need more current and consume high power. Select small motors and converters for your design that consume less power. Typically smaller motors have low current ratings and bigger motors have high current ratings. Hence, smaller components can minimize heat dissipation.

Implement soft switching

In hard switching, power devices are turned on and off when there is significant voltage and current in the circuit. In soft switching, the power device is turned on and off where there is either zero voltage or zero current in the circuit. To minimize heat, choose soft switching for your design. The magnitude of overall soft switching losses is lesser than hard switching losses. A less overall loss suggests low wastage of power and heat dissipation.

Use proper heat sink

Power electronic devices are mounted on large pieces of metals known as heat sinks. There is no electrical contact between the power device and the heat sink. Due to the presence of a heat sink, heat is radiated into the environment effectively. Heat sinks come in varying shapes and sizes. Combo heat sinks have their own blower to regulate temperature. Specialized heat sinks use liquid coolants. Choosing a proper heat sink reduces the operating temperature of a PWM device.

Implement heat management

In practical power electronics applications or any electronics/electrical application, heat cannot be completely avoided. After attempting to minimize heat, effective heat management is the key. Some effective heat management techniques are to ensure proper ventilation, regular cleaning of equipment and fans, and monitoring of temperature. At the time of overheating, cooling is necessary through fans and other equipment. Special sensors monitor temperature and are connected to control the projection of PWM signals in the power electronic system.

Conclusion

Heat is an inevitable effect of current. Where there is current, there is heat. However, heat reduction efforts are necessary in power electronics applications. Joule’s law of heating states that when a current “I” passes through a material with a resistance “R” for a time “t”, the amount of heat produced is equal to the product of resistance, time, and square of the current.

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H = I² x R x t

All devices in power electronic systems have high current ratings, which corresponds to high power and large amounts of heat generation. Hence, any power electronics system, PWM for that matter, will generate a significant amount of heat. The above-mentioned steps can help you reduce heat generation to some extent in your next project.

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