Understanding EMC and EMI Regulations in Power Electronic Design
In power electronics, engineers must understand the concepts of electromagnetic interference (EMI) and electromagnetic compatibility (EMC) and how to manage the issues they create.
In this article, we’ll explain the fundamentals of EMC/EMI, the relevant standards and regulations, and practical design techniques to achieve compliance.
Just what is EMC anyway?
Electromagnetic fields are all around us. Whenever a current flows through a conductor and varies over time, unwanted electromagnetic fields (which we call interference or EMI) are generated. The energy in these fields can be physically conducted to or absorbed through induction by any nearby cables or PCB tracks, interpreted by sensitive electronic systems as noise, and can often cause problems[2]. EMC means building systems that have some built-in immunity to the problems the electrical noise may cause.
There are diverse sources of EMI, particularly in complicated electronic systems. The EMI they generate can be an issue within the system itself, as well as any nearby circuits or systems.
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Switching power supplies are a major source of EMI in the form of energy conducted or radiated by the switching signals. Signals with higher frequencies have more energy which can include clocks, analogue signal inputs, relays and microcontroller interfaces.
When loads are connected to the power network, they typically draw current out of phase with the voltage. This generates additional currents, called harmonics, which occur at multiples of the network frequency (50 Hz in Europe, 60 Hz in the US). These lower-frequency distortions can conduct or emit EMI noise at frequencies typically up to around 2.5 or 3 kHz and are a key contributor to reduced power quality.
Managing harmonics is essential for maintaining grid efficiency and is typically achieved through power factor correction (PFC) and harmonic filtering. While both harmonics and EMI involve unwanted electrical disturbances, they occupy different parts of the frequency spectrum and are addressed using different techniques. Harmonics tend to affect waveform quality at lower frequencies and are mitigated using PFC circuits and passive or active filters. Higher-frequency EMI, by contrast, is managed using shielding, careful PCB layout, and EMI filters such as ferrite beads and common-mode chokes.
Other circuit components functioning at much higher frequencies also generate EMI, such as computers and communication equipment that may operate in the gigahertz range. Overall, EMI signals can be generated over a wide frequency range, from 50 Hz conducted mains harmonics to 40 GHz for radiated emissions from some telecoms equipment.
Figure 1: transfer mechanisms of unwanted EMI noise (source: https://www.avnet.com/americas/resources/article/the-importance-of-emi-emc-in-evs/)
There are four main routes, known as ‘coupling mechanisms’, that enable EMI from a source to be transmitted to another circuit (see Figure 1):
- Conductive: where a path is formed by direct contact with a conductor
- Capacitive: where a varying electric field occurs between two conductors, inducing a voltage change in the receiver
- Inductive (also called magnetic): where a varying magnetic field occurs between two conductors, also inducing a voltage change in the receiver
- Radiative: where the source and recipient act like radio aerials, to emit and absorb an electromagnetic wave
In addition to these technical standards, there are different legal requirements around the world. For example, EU Directive 2014/30/EU defines the legal framework for EMC for equipment to be used and sold in the European Union (EU) and the UK. The EU directive sets the EMC requirements for electric and electronic equipment, and these requirements are often met by demonstrating compliance with the relevant standards in the IEC EN 61000 family.
Also relevant is EN 50160, the European power quality standard. This specifies the voltage characteristics in an electricity supply network, including frequency, magnitude, waveform and symmetry.
Regulations and standards
Industry standards define the rules for EMC, both in terms of the level of emissions and the immunity to emissions from other devices. They also specify how products and devices should be tested to ensure compliance.
Since the introduction of the first EMC regulation in the 1980s, its scope has grown. Today, there are many versions around the world. They define requirements from the broad fundamentals to more specialised regulations for applications such as automotive, medical, radio transmitters, and electronic alarms.
Some of the most important and wide-ranging standards include the following:
- IEC (International Electrotechnical Commission) EN 61000: the main family of European EMC standards, including application-specific standards such as IEC EN 60601 (medical).
- FCC standards: in the US, radio frequency transmissions, including unintentional EMI emissions, are regulated by Federal Communications Commission (FCC) Part 15. Before they can be sold in the US, electronic devices must be reviewed to check compliance with this.
- CISPR (International Special Committee for Radio Protection of IEC) standards: aimed at protecting radio reception from electromagnetic interference, in the frequency range from 9 kHz to 400 GHz. There are multiple standards covering emission and immunity requirements, which define test methods and equipment.
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SEE OVERVIEWAs well as these technical standards, there are different legal requirements around the world. For example, EU Directive 2014/30/EU defines the legal framework for EMC for equipment to be used and sold in the European Union (EU) and the UK. The EU directive sets the EMC requirements for electric and electronic equipment, and these requirements are often met by demonstrating compliance with the relevant standards in the IEC EN 61000 family.
Also relevant is EN 50160, the European power quality standard. This specifies the voltage characteristics in an electricity supply network, including frequency, magnitude, waveform and symmetry.
Minimising EMC problems
There are two related aspects to consider: minimising the EMI that a circuit generates, and protecting it against EMI generated by another circuit. In both cases, some practical design techniques can be followed to achieve compliance with EMC regulations.
Firstly, design engineers need to find and analyse EMI hotspots, using a spectrum analyser or specialist EMI receiver to locate where the circuit is generating EMI. They can also use software modelling and simulation to investigate your circuit’s EMI emissions and its susceptibility to EMI.
Once the potential problems are identified, there are suitable mitigation methods that can be applied, including:
- Metal shielding from an enclosure and shielded interconnects, to block emissions both generated by your circuit and arriving from elsewhere.
- Passive filters and ferrite cores, to absorb EMI emissions. An EMI filter is a low-pass filter, thus blocking higher frequencies above a pre-defined range. Cables and connections can have built-in filters, such as ferrite beads and common-mode chokes.
- Decoupling capacitors, which can suppress voltage skips, transient current surges and magnetic fields.
- Ground planes, which can shunt EMI and reduce loop inductance.
Cabling needs to be considered, with long cable runs avoided, and any crossings of two cables arranged at 90 degrees to keep inductive coupling to a minimum. PCB design is also important to minimise EMC problems, with signal traces kept short where possible, and routed carefully to reduce the chances of capacitive coupling to nearby components, particularly with high-speed signals. Minimising the number and the size of vias can avoid inducing parasitic capacitances and inductances.
Wide bandgap (WBG) semiconductors and their higher switching frequencies can bring new benefits, but not without EMC challenges. For example, in GaN HEMT power transistors, induced voltages and currents can produce EMI at tens or hundreds of MHz, which can bypass EMI filters. In practice, this can often be addressed by slowing down switching rates, without a major impact on efficiency. Alternatively, using SiC at relatively low frequencies, instead of GaN, can also help reduce EMI problems[2].
How to ensure compliance
Understanding which standards are applicable can be complex and time-consuming, with different variations by country, product and application type. Once the goalposts have been located, products need to be tested to demonstrate compliance with the relevant regulations.
EMC is a complex subject that needs to be considered from day one of a design project. Design engineers can work towards successful EMI compliance by considering the noise sources in the design and identifying which circuits are susceptible to EMI.
Expert advice from a partner, such as Avnet Silica, can ensure you are designing to the right standards and provide support to pick the best components to minimise any EMC issues.
References
- https://www.avnet.com/americas/resources/article/the-importance-of-emi-emc-in-evs/
- https://my.avnet.com/silica/resources/article/when-gan-is-too-fast-for-your-application-consider-sic-instead/
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