The presence of harmonics in the electricity distribution grid is set to become an increasing concern as the penetration of EV increases. This article in our Learning series aims to answer basic questions about ‘Harmonic Pollution’ and its relevance to the subject of EV charging.
We would like to thank Chandana Sasidharan for explaining the concept for our readers.
1. What is meant by harmonics and supraharmonics?
The electricity grid supplies AC power in the form of a smooth sinusoidal wave as shown in Figure 1. This wave is said to have a frequency of 50 Hertz (Hz) as it repeats itself over itself fifty times in a second. The AC power generated by machines in thermal or hydropower stations is quite smooth in nature. However, electronic components alter the shape of this AC power and cause distortion to the sine wave as shown in Figure 2. The distortions are what constitutes harmonics.
Any device with power electronic equipment can lead to harmonic issues. This includes inverter driven air conditioners and washing machines. Most common household equipment like television, microwaves etc also causes some amount of harmonics. This happens for any non-linear load, that is, a load where the current wave is distorted. The current drawn by a non-linear load will fluctuate as the impedance or opposition to current changes, and cause harmonics.
To study the harmonics, we break down the distorted sine wave into smaller component waveforms, which are at different frequencies than the original sine wave. If the frequency of the component sine wave is thousands of times higher than the original frequency, then it is called supraharmonics, ie. these wave components repeat themselves thousands of times in a second. The frequencies in the range of 2-150 kilo Hz is classified as supraharmonics.
2. Why is it called harmonic pollution?
Harmonics is an undesirable effect. It is not a phenomenon with any positive impact and causes problems to the electric equipment. The most significant footprint left by harmonics is in the decrease in the quality of power supplied. Harmonics impacts the Electromagnetic compatibility (EMC) of electrical equipment, that is the ability of the equipment and the system to function properly. Harmonics disturbs this ability and causes losses and damage to components. It also causes problems to the electricity grid operation because it can cause faults in the operation of protection relays. As it is an outcome that is not wished for and creates challenges, it is called as pollution.
3. How is harmonic pollution relevant to the subject of EV charging?
The presence of harmonics in the electricity distribution grid is an increasing concern as the penetration of EV is increasing. This is because EVs have a lot of power electronics equipment which help to convert the grid AC power to DC power needed for batteries. In simple terms, all EV chargers cause harmonics as they are electronic equipment. These harmonic distortions can be injected into the electricity grid if it is not monitored and controlled.
The harmonic pollution associated with EVs dependent on the number of EVs and the charging method. If a large number of EVs are charging in the same area, then the harmonic pollution in that area will be more. Similarly fast charging at high powers will lead to a considerable increase of harmonics in the local grid.
4. What are the implications of harmonic pollution?
The implication of harmonic pollution is that it is damaging to the electricity grid, any equipment that is connected to it, including the EV components. The end results of harmonic pollution for equipment are increased failures and losses, which has a financial implication. In the case of the electricity grid, its impact is much more disruptive in nature as it can lead to malfunctions of the protection system. This can lead to power failures, and power quality issues in the distribution grid.
5. What are the standards for monitoring harmonic pollution?
Harmonics are subject to various standards and regulations, which include limits to the total harmonics that can be injected by equipment and compatibility standards for the electricity grid.
Most of the international standard organisations have developed standards on power quality. These standards specify some limits to harmonic pollution, and its different impacts such as flicker, voltage swell. The most common of them are IEC 61000 and IEEE 519.
6. Is there a regulatory framework around measurement and testing of harmonic pollution causes by EV chargers?
As the penetration of EV is increasing, new standards are introduced to control harmonic pollution from electric vehicles. One of such upcoming standards is the IEC 61851 which is associated with the onboard chargers. In the absence of standards specific to EVs, the limits to harmonics given by the existing standards like IEC 61000 will apply.
7. What can Charging solution providers do to cut harmonic pollution?
Charging service providers can take adequate care in the selection of chargers, and monitoring them. Low-quality products, which do not conform to any standards may be economical. However, they may cause problems in the long run to all equipment. It makes sense to invest in creating quality checks and ensuring proper maintenance. More often than not, a faulty operation can lead to an increase in harmonics. The second step is to periodically monitor the amount of harmonics that is caused by the chargers so that the service provider can take adequate preventive actions to limit the increase in harmonics.
A good charger design can reduce harmonics. Using a PFC (power correction factor) section in front of the EV charger can help reduce the harmonic distortion. A well-designed quality charger would come with built-in EMI (electromagnetic interference) filters that suppress the high-frequency noise and interference with other devices.
Disclaimer – The views and opinions expressed here are that of the author (Chandana Sasidharan) and do not necessarily reflect the official position of her employer – Alliance for an Energy Efficient Economy.