What are Supraharmonics?

Harmonic frequencies are integer multiples of the fundamental grid frequency and are generally defined within the range of 100 Hz ( 2nd harmonic ) to 2 kHz (40th harmonic). For instance, with a 50 Hz fundamental frequency, the third harmonic is 150 Hz, and the fifth harmonic is 250 Hz.

Variable frequency drives (VFD) featuring a diode-based rectifier input stage commonly employ a six-pulse bridge rectifier topology. As demonstrated in Figure 1, the current waveform generated by this structure is known to produce harmonics of the order 6n ±1. Consequently, the 5th, 7th, 11th, and 13th harmonics are particularly dominant in diode-based VFD.

Figure 1 shows a standard VFD circuit with a six-pulse diode rectifier stage.

Figure 1

Figure 2 shows the sinusoidal waveforms of the supply current iL(t) and voltage uLN(t) produced by a typical six-pulse diode rectifier with capacitive smoothing under uncontrolled operation.

Figure 2

Another topic that has attracted mounting interest in recent years is that of supraharmonics. These are voltage and current distortions in the frequency range from 2 kHz to 150 kHz. A primary source of these high-frequency components is the insulated-gate bipolar transistors utilised in the input stage of variable frequency drives, which operate at elevated switching frequencies. As the switching frequency increases, additional supraharmonic components are superimposed on classical harmonics and propagate into the power grid.

Rectifiers that employ Active Front End ( AFE ) technology, which utilise IGBTs, generate a more regulated and almost sinusoidal current waveform, as shown in Figure 2. However, given that these systems utilise pulse-width modulation (PWM)-based control, the generation of high-frequency supraharmonic components is unavoidable.

Figure 3 shows a typical variable frequency drive circuit with an IGBT-based rectifier stage.

Figure 3

Figure 4 shows the input current iL(t) and supply voltage uLN(t) waveforms of a typical PWM inverter with an Active Front End, capacitive smoothing, and no additional filtering.

Figure 4

For the past 30 years, harmonics in the frequency range of 50 Hz–2 kHz have been recognised as a well-known power quality problem in power systems, as they can be measured and mitigated using appropriate filter circuits.

However, over the last decade, with advancements in power electronics, a new power quality issue—referred to as supraharmonics—has emerged in the 2 kHz–150 kHz range. This phenomenon has become increasingly prevalent, and its effects have become more perceptible, in electrical networks.

Table 1 presents the frequency-based classification of interference types observed in transmission lines, along with the corresponding frequency ranges.

Supraharmonic-Induced Power Quality Issues :

Table 2 lists devices that may serve as sources of supraharmonics.

The supraharmonics generated by the devices presented in Table 2 correspond to power quality disturbances within the frequency range of 2 kHz to 150 kHz. In recent years, the rapid proliferation of electric vehicle charging infrastructure, photovoltaic (PV) inverters, and AFE-based variable frequency drives—utilizing PWM-controlled power electronic converters—has significantly increased the presence of these disturbances in modern power systems.

Supraharmonic-related power quality disturbances observed in field applications manifest through diverse effects, including flicker in power networks, accelerated ageing of cables and capacitors, audible noise, and interruptions in electric vehicle charging.

Further illustrative examples are provided in Table 3.

As shown in Table 3, supraharmonic components in the 2 kHz–150 kHz range not only impair overall power system performance but also trigger malfunctions across a wide array of field devices. Overheating of DC link capacitors in variable frequency drives (shortening their lifespan), unintended switching in street lighting and dimmer-controlled lamps, and erroneous signaling in traffic lights all underscore the severe, real-world impacts of these disturbances. Supraharmonics further erode system stability—particularly in inverter-dominated setups and “weak” microgrids—potentially leading to inverter failures, shutdowns, and interruptions in power supply.

Thus, the examples in Table 3 reveal that supraharmonics are far more than a theoretical concern; they pose a tangible threat to safety, reliability, and performance in industrial operations and everyday life, making them a critical factor in power system integrity.

Despite their growing prevalence as a major power quality issue, many field investigations still rely exclusively on non Class A power quality analyzers. While adequate for fundamental harmonics and standard parameters, these devices lack the resolution and accuracy needed for supraharmonic measurements. As a result, 2 kHz–150 kHz disturbances often go undetected or yield unreliable data, obscuring root causes of equipment failures, user complaints, and anomalous system behavior. Without pinpointing the problem, solutions remain elusive, and issues persist.

Supraharmonic Measurement Techniques and Detection Methods :

With the rising switching frequencies of modern power electronic devices, supraharmonics are increasingly prevalent in the 2–150 kHz range, beyond the scope of traditional harmonic analysis. Consequently, their measurement, modeling, and mitigation have become essential, particularly amid the integration of renewable energy sources such as photovoltaic systems and electric vehicle charging infrastructure.

Consider, for instance, a highway installation comprising ten EV charging stations powered by a PV system that emits supraharmonics in the 16 kHz band. While vehicles charge via these PV-fed units, one charger may produce supraharmonics at 50 kHz, interrupting a neighboring vehicle’s process after about 20 seconds.

Measurements using non-Class A power quality analyzers may fail to detect this issue, as such devices typically limit harmonics to the 2–9 kHz range—insufficient for supraharmonics. Thus, the disturbance evades capture in results, leading investigators to pursue alternative faults while the root cause lingers undetected.

The IEC 61000-4-30 Ed. 3 and IEC 62586-2 Ed. 2 standards define accuracy classes, measurement methods, and comparability requirements for power quality instruments. Class A devices deliver high-precision, synchronized, and repeatable results, making them the choice for utilities, regulators, and large industrial sites in official monitoring.

To precisely pinpoint power quality issues—especially those involving supraharmonics—portable Class A instruments are essential. With proper hardware and software, they analyze components up to 150 kHz.

Moreover, reports should confirm compliance with IEC 61000-2-2 and IEC 61000-2-4 standards.

In conclusion, correct Class A instrumentation paired with sound methodology enables accurate problem identification and effective mitigation solutions.

Supraharmonic Filter :

The issue of supraharmonics has become a significant and increasingly complex power quality problem in modern electrical networks, particularly in the context of the widespread integration of renewable energy sources, electric vehicles, and variable frequency drives equipped with Active Front End technology. It has been established that high-frequency disturbances within the 2 kHz–150 kHz range produce effects that extend beyond conventional harmonics. The consequences of these disturbances include communication errors, false triggering of protection systems, performance degradation in sensitive equipment, and reduced equipment lifetime in both transmission and distribution systems.

In this context, broadband passive filters have emerged as an effective solution for suppressing supraharmonics at their source. These filters have been developed to attenuate supraharmonic components within specific frequency ranges and to isolate them from the system. The objective is to thereby minimise both the direct effects of supraharmonics and the secondary harmonic distortions triggered by them.

These low-cost and highly reliable passive filters are able to be readily incorporated into power systems, thus playing a critical role in modern energy infrastructures that are characterised by a high penetration of renewable energy and power electronics-based loads. Consequently, the lifespan of equipment is increased, failure rates are decreased, overall power quality is enhanced, and—most significantly—resonance risks are mitigated.

Figure 6: Serial Passive Harmonic Filter Circuit Diagram

In the highway example presented in the previous paragraph, the 16 kHz band supraharmonics emitted by the rooftop PV system and the approximately 50 kHz supraharmonic components generated by the vehicle charging units can be effectively attenuated using properly designed broadband passive filters. In this way, the rooftop-PV-equipped charging station can operate with stable and reliable performance without experiencing charging interruption faults.

FINAL OUTCOME :

In conclusion, accurate detection of supraharmonics necessitates the use of Class A power quality analyzers to measure the 2 kHz–150 kHz frequency band with sufficient accuracy and resolution. Once identified, these supraharmonic components can be effectively suppressed through the implementation of broadband passive filters, thereby markedly improving the facility’s overall power quality.

In order to ensure the safe, reliable and high-performance operation of modern electrical infrastructures, it is essential to combine advanced measurement technologies with properly designed passive filter solutions. The control of supraharmonics has been demonstrated to extend the lifetime of equipment and enhance system reliability, thus contributing to sustainable and uninterrupted energy operations.

Didem Ergun Sezer

Elektrik Mühendisi

Ergun Elektrik A.Ş.