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13Estimation of Power Losses Caused by Supraharmonics
A. Novitskiy*, S. Schlegel, D. Westermann Ilmenau University of Technology, Ilmenau, Germany
Abstract — Nowadays, the number of power electronic devices in electrical distribution networks rapidly increases. Modern generation and consumption units use high switching frequency power converters for the network connection and therefore cause voltage and current distortion at frequencies higher than 2 kHz (so-called supraharmonics) in addition to conventional harmonics. Supraharmonics cause additional power losses in electrical equipment. The objective of this paper is to estimate the power losses caused by supraharmonics. The focus is on the method of assessing the supraharmonic power losses, which combines the analytic determination of AC cable resistances at supraharmonic frequencies and the use of supraharmonic currents measured in a real MV/LV cable network. The paper shows that the supraharmonic power losses in an MV cable can reach the values of several percent of power losses at the fundamental frequency and can exceed ten percent of power losses caused by conventional current harmonics.
Index Terms. Power losses, power quality, supraharmonics.
I. Introduction
The increase in the number of power electronic devices in electrical distribution networks has been a characteristic trend in the development of electric power supply for many years. Modern generation and consumption units use high switching frequency power converters for the network connection, which leads to voltage and current distortion at frequencies higher than 2 kHz (so-called supraharmonics) in addition to conventional harmonics.
* Corresponding author. E-mail: Alexander.Novitskiy@TU-Ilmenau.de
http://dx.doi.org/10.38028/esr.2020.04.0004
Received September 15, 2020. Revised October 14, 2020.
Accepted November 10, 2020. Available online February 01, 2021.
This is an open access article under a Creative Commons Attribution-NonCommercial 4.0 International License.
© 2020 ESI SB RAS and authors. All rights reserved.
The harmonic and supraharmonic distortion in electrical networks directly influence the power and energy losses in the electrical equipment. The harmonic and supraharmonic currents cause additional Joule heating of conductors and therefore increase the total power losses in these conductors.
The conductor resistance grows with a rise in the frequency and, therefore, relatively small harmonic or supraharmonic currents can cause notable power losses.
The studies presented in [1-3] show that additional power losses in LV cables and HV transmission lines caused by conventional current harmonics can be up to thirty percent of power losses at the fundamental frequency. The influence of supraharmonics on the additional power losses can be illustrated using the simplified assumption that the values of the line conductor resistances are proportional to the root of the frequency [2-5]:
RA = R 4h , (1)
where Rsh, R1 are resistance values at the supraharmonic frequency fsh and at the fundamental frequency f1 respectively, h = f h /f is the harmonic order.
Using the calculation formula for the Joule heating and taking into account (1), one can calculate the relative values of additional power losses caused by supraharmonics as follows:
PLh /= (I h / A)2>/h , (2)
where PLsh, PL1 are power losses caused by the supraharmonic current I sh at the frequency fsh and by the current I1 at the fundamental frequency f1, respectively.
The dependences (2) are presented in Figure 1 for some ratios of 1 sh /11.
As seen from Figure 1, additional power losses caused by a supraharmonic can be, for example, ten percent of the power losses at the fundamental frequency and higher, and consequently, they cannot be neglected in the calculation of total power losses in electrical networks. The exact values of additional power losses depend on the supraharmonic frequency and the ratio of I sh /11.
It is worth noting that (1) and (2) are valid mainly for overhead transmission lines.
50 45
5 40 S 35 " 30 25 20 15 10 5 0
ft
cc
— - Rsh/Ri Plsh/Pll (Ish/ll = 2.5%) - Plsh/Pll (Ish/ll = 5.0%) — PLsh/Pu (Ish/ll =7.5%) — Plsh/Pli (Ish/ll = 10.0%)
_ ' ■ ::--"t-—'-
42 36 30 24 18 12 6 0
2 9 16 23 30 37 44 51 58 65 72 79 86 93 100 Frequency (kHz) Fig. 1. Relative supraharmonic power losses (2) and the corresponding ratio of Rsh /Rr
The estimation of power losses caused by supraharmonics in a cable feeder under real operating conditions is presented below. The estimation is based on the measurement results obtained in a real MV/LV network in Germany [6].
II. Measurements of Supraharmonics
Results of the measurements carried out in the real MV / LV electrical network presented in Figure 2 were used to estimate the effect of supraharmonics on power losses in MV cable feeders.
The network supplies power to different settlements with mainly residential and commercial loads and contains a lot of decentralized renewable energy generating units. The network contains a MV wind plant and several MV
Fig. 2. MV/LV network under study and location of measuring devices.
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Frequency (kHz) Fig. 3. Measured current spectrum, 95% quantiles of 1 min. average values, 200 Hz groups, measurement time 24 h, MP2
10 9 8 7 6 5 4
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Frequency (kHz)
Fig. 4. Measured current spectrum, 95% quantiles of 1 min. average values, 200 Hz groups, measurement time is one week, MP2
PV plants distributed throughout the whole network and connected to the MV grid via dedicated transformers. Several powerful wind parks are located in the upstream HV network. Numerous LV PV power plants are connected to the downstream LV distribution networks together with other power electronic devices using high switching frequency power converters such as charging stations, consumer electronics, and others, via local area step-down MV / LV transformers.
Measurement devices SIRIUSi-HS [7] were located at the measurement points MP1 - MP3 and operated with a sampling rate of 100 kHz. Supraharmonic voltage and current 200 Hz groups (according to [8, 9]) were recorded as 1 min. average values over the measurement interval of 2 weeks.
Power quality (PQ) parameters were additionally measured at MP1 - MP3.
Instantaneous voltage values (a sampling rate of 10.240 kHz) and some PQ parameters as 1 sec average values were recorded at the measurement points W1-W24 (LV network) using measuring devices WeSense [10].
The effects of renewable energy sources on the supraharmonic distortion and the propagation of the supraharmonic distortion in the network under study were analyzed in [6, 11, and 12].
Power losses in the supraharmonic frequency range can be estimated using the supraharmonic currents measured in the MV feeder at the distribution station. This is the measurement point MP2 (Fig. 2).
Measuring device at MP2 was connected to the secondary winding of the current transformer via current clamps. Current clamps were certified for the measurements at a frequency up to 100 kHz.
The applicability of the standard MV current transformer to the measurements in the supraharmonic frequency range was assessed given the IEC Technical Report 61869-103 [13] and investigation results [14, 15].
Supraharmonic frequency range is divided into several subranges. The supraharmonics in the frequency subrange of 2 to 9 kHz are the subject of special consideration in the IEC standards for compatibility levels for conducted disturbances and signaling in public medium-voltage [16] and low-voltage [17] power supply systems. Technical requirements for the operation of customer installations and their connection to the MV network in Germany contain admissible values for the supraharmonic currents in a frequency range of 2 to 9 kHz [18]. Therefore, special attention should be paid to the transfer characteristics of MV current transformers in the frequency range of 2 to 9 kHz.
In [13], inductive current transformers are noted to be suitable for the use in the supraharmonic frequency range of 2 to 9 kHz. Given the measured frequency dependences
— 10 mm2 16 mm2 25 mm2 —35 mm2 —50 mm2 70 mm2 —95 mm2 —120 mm2—150 mm2
— 185 mm2 —240 mm2 - 300 mrn^, —400 mm2 - -Xp = 2.8
3 4 5 6 Frequency (kHz)
Fig. 5. Factors XS and Xp for cable solid aluminum conductors at the operating temperature of 20°C.
18
16
14
a 12 X » 10 X
8 6 4 2 0
— 10 — 35 —95 mm2 mm2 mm2 16 mm2 —50 mm2 —120 mm2 25 mm2 70 mm2 —150 mm2
—185 mm' —400 mm2 —240 mm2 - -Xp = 2.8 300 mm2
0123456789 Frequency (kHz)
Fig. 6. Factors XS and Xp for cable solid aluminum conductors at the operating temperature of 90°C
B 2.503e-002 : >2.635e-002 2.37U-002 : 2.503e-002 2.240e-002 : 2.37U-002 2.108e-002 : 2.240e-002 1.976e-002 : 2.108e-002 1.844e-002 : 1.976e-002 1.713e-002 : 1.8445-002 1.58U-002 : 1.713e-002 1.449e-002 : 1.581e-002 1.317e-002 : 1.449e-002 1.186e-002 : 1.317e-002 1.054e-002 : 1.186e-002 9.222e-003 : 1.054e-002 7.905e-003 : 9.222e-003 6.587e-003 : 7.905e-003 5.270e-003 : 6.587e-003 3.952e-003 : 5.270e-003 2.635e-003 : 3.952e-003 1.317e-003 : 2.635e-003
I_] <0.000e+000 : 1.317e-003
Density Plot: 131, MA/m~2
Fig. 7. Current density distribution in the aluminum conductors and copper screens of the MV cable 3x1x150/25 caused by the supraharmonic current 0.54 A (r.ms. value) at the frequency of 2.5 kHz
E
3
0,03
0,025 >. 0,02
® 0,015
O
0,01
0,005
-40 -20 0 20 40
Position (mm)
Fig. 8. Current density distribution J along the straight line crossing the centers of two neighboring conductors and screens of the MV 3x1x150/25 cable caused by the supraharmonic current 0.54 A (r.ms. value) at the frequency 2.5 kHz
for ratio and phase errors of the MV current transformers presented in [14] and [15], one can conclude that the supraharmonic currents can be measured with the standard MV current transformers with sufficient accuracy (an error amplitude of up to several percent) for the simplified estimation of power losses in the frequency range of 2 to 9 kHz.
Examples of measured current spectra in the MV feeder (MV distribution station, measurement point MP2) are presented in Figs. 3 and 4.
As seen in Figures 3 and 4, the current spectra are characterized by the domination of the supraharmonic components of 2.5 kHz. In [6, 12], the authors show that these components in the considered network are mainly caused by the operation of the MV wind plant.
The components of 5.9 and 6.1 kHz are caused by the daily operation of solar plants, the components of 4.3 and 4.5 kHz result from the changes at the connection points of operating units.
The measurement point MP2 is the connection point of the MV 3x1x150/25 cable to the busbar of the distribution station. This MV cable connection contains three single-core cables with 150 mm2 aluminum conductors and 25 mm2 copper screens for each of them.
Determination of the frequency dependences for the cable resistances is considered below.
III. Determination of the frequency dependences for the cable resistances
A. Analytic calculation method
Calculation of AC resistance of a conductor is part of the IEC standard [19]. The standard states that the AC cable conductor resistance depends on the skin and the proximity effects. The following formula can be used:
Rsh = RDC (1+Y + Y > (3)
where Rsh is a conductor resistance at the supraharmonic frequency fh, R'DC is a DC resistance of conductor at the maximum operating temperature 0, YS is a skin effect factor, and Yp is a proximity effect factor.
The values of YS and Yp depend on the values of the factors XS and Xp as follows:
(4)
XS =(1/RD C )8f 10-7 ks
and
XP =(1/RDC ) 8f10-7 kp, (5)
where kS, kp are coefficients, e.g. kS = 1 and kp = 1 for cables with solid copper or aluminum conductors [19].
Analytic (Ys) —Analytic (Ys+Yp) —Analytic (Ys+Yp+Ysc)
0
2 9 16 23 30 37 44 51 58 65 72 79 86 93 100 Frequency (kHz) 9. Analytically and numerically (using the FEMM software) determined frequency dependences Rsh / R1 for the MV3x1x150/25 cable in a supraharmonic frequency range
Fig.
a.
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Frequency (kHz) Fig. 10. Relative power losses in a 20 kV cable feeder, 95% quantiles of 1 min. values, 200 Hz groups, measurement time is 24 h, MP2
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Frequency (kHz) Fig. 11. Relative power losses in a 20 kV cable feeder, 95% quantiles of 1 min. values, 200 Hz groups, measurement time is one week, MP2
The skin effect factor YS is given by the following equations [19]:
for 0 < Xs < 2.8
YS = X4S/ (192 +0.8 XS ),
(6)
for 2.8 < X, < 3.8
for 3.8 < X.
YS = -0.136- 0.0177XS + 0.056X2, (7)
YS = 0.354XS - 0.733.
(8)
The proximity effect factor Y according to [19], can be calculated only if factorXp does not exceed 2.8.
As seen from (4) and (5), on the assumption that kS = kp = 1, for the cables with solid conductorsXp = XS [19].
The values of Xp and XS calculated according to (4) and (5) for the cables with solid aluminum conductors are presented in Figures 5 and 6. The values R'DC in (4) and (5) were determined for each cross-sectional area according to [20], based on the standard formula [19]:
R'dC = RDC (1 + «20 (0 - 20)) ,
(9)
where RDC is a DC resistance of conductor at 20°C, R'DC is a DC resistance of conductor at the maximum operating temperature 0, a20 is the constant mass temperature coefficient at 20°C per Kelvin.
The calculation results for the operating temperature of 20°C are presented in Figure 5, the calculation results for the maximum operating temperature of 90°C are presented in Figure 6.
It can be clearly seen from Figures 5 and 6 that the cable solid aluminum conductors with the standard cross-sectional areas starting with 16 mm2 and larger are characterized by the values of Xp higher than 2.8 at least at some frequencies in the frequency range of 2 to 9 kHz.
Cable solid aluminum conductors with the standard cross-sections of 70 mm2 and larger are characterized by the values of Xp higher than 2.8 in the entire frequency range of 2 to 9 kHz.
This means that the method for the analytic calculation of frequency-dependent cable resistances [19] is not applicable to the calculation of resistances at supraharmonic
frequencies in many practical cases due to the constraints on the combination of parameters considered in [19].
A more common analytic method for the calculation of frequency-dependent cable resistances is presented in [21].
The analytic method for the calculation of the skin effect factor YS in [21] is identical with the method [19] described above.
The following formula is suggested in [21] for the calculation of the proximity effect factor Yp for three single-core cables:
YP = my2Gf / (2 - 5y2Hf /12),
(10)
where m = 3 for three single-core circular cables; y is a spacing ratio; Gp, Hp are coefficients.
The coefficients Gp, Hp are given by the following equations [21]:
for 0 <Xp < 2.8
for 2.8 <Xp < 3.8
for 3.8 < Xp
for 0 <Xp < 2.8
GP = llXP / (704 +20X4f ), (11)
GP = -0.08Xp + 0.72XP -1.04, (12)
GP = XP / (472) -1/8, (13)
H P = (1/3) (l+0.0283XAP ) / (l + 0.0042X4P ) , (14)
for 2.8 < Xp < 3.8
HD
for 3.8 < X,
: 0.0384X; + 0.119Xp + 0.095
„ 2XP -4.69
HP =-
P XP -1.16
(15)
(16)
The spacing ratio y = dc/s, where s is the spacing between conductor axes, dc is the diameter of an equivalent circular conductor.
The construction of the MV 3x1x150/25 cable suggests that each cable conductor is surrounded by a cable screen.
The AC currents flowing in the cable conductors cause induced currents in the screens surrounding the cable and therefore cause some additional power losses in the screens. This means an increase in the equivalent cable resistances at the frequencies of the AC currents (fundamental frequency, harmonic and supraharmonic frequencies).
Therefore, formula (3) can be extended to consider the influence of power losses in cable screens on the conductor resistance as follows:
RSh = RDC (1+Y + Y + YSC ),
(17)
where YSC is the screen losses factor.
It is worth noting that each cable containing axial conductor surrounded by a cable screen can be considered as a pipe-type cable. Taking into account the relation given in [22] to consider the increase in losses in the phase
conductors due to the proximity of the pipe, we can use the following formula for the screen loss factor:
Ysc = 0.5 (Ys + YP ).
(18)
These considerations are in compliance with the recommendation [19] for the calculation of AC cable conductor resistances for pipe-type cables. The following formula can be used according to [19]:
Rsh = R'dC (1 + 1.5(Ys + Yp)). (19)
Using (4) - (16), (19), one can analyticly determine the values of the conductor resistances at the supraharmonic frequencies Rsh and the relations Rsh / Rj for the MV 3x1x150/25 cable under study.
B. Numerical calculation method
The use of the finite element method (FEM) is a popular approach to the numerical calculation of frequency dependences for cable resistances.
The advantages of this method are the exact modeling of the cable geometry, the simulation of properties of the materials used in the cable construction, and the simultaneous consideration of all influencing effects named above: the skin effect, the proximity effect, the influence of cable screens and all other metallic elements (for example, cable armor, pipes, ducts, trays, and others), which can affect the AC resistances of the cable conductors.
The FEM approach makes it possible to calculate the current density distribution in all parts of the simulated cable construction. Taking into account the cable geometry and the electrical conductivities of simulated constructive materials, one can determine power losses in all elements of the cable construction.
The equivalent AC resistance of the cable conductor Rsh at the supraharmonic frequency fsh can be calculated considering the following formula:
P = 12 R
1 Lsh sh sh
(20)
where PLsh is the average value of total power losses caused by the simulated supraharmonic conductor current Ish at the frequency fsh in each phase of the three-phase cable system.
In respect to the considered MV 3x1x150/25 cable construction:
(21)
P
= P + P
Lsh cond Lsh sc
where PLsh cond is an average value of power losses in each phase conductor and PLsh sc is an average value of power losses in each conductor screen. The frequency dependence for the equivalent AC cable resistance can be determined through a series of simulations at different frequencies. The frequency dependence can be determined from the following relations:
P / P
Lsh L1
■■ li Rsh /( I2 Ri).
(22)
The values Ish and I1 can be taken, for example, from the measurement results.
Taking into account the FEM simulation of the heating processes, the cable operating temperature can be determined and the temperature effect on the electrical conductivity can be considered additionally [23-25]. To simplify the calculations, it is sufficient to assume that Ish = I1. In this case, it is enough to calculate the power losses (21) for each frequency under consideration. Formula (22) will be simplified as follows:
PLsh / Pli = Rsh R
(23)
The frequency dependence for the equivalent AC cable resistance can be determined using (23).
It is noteworthy that the electrical conductivity of the cable insulation is very small in comparison with the conductivities of cable conductors and metallic screens. Therefore, it is sufficient to simulate only metallic parts of the cable configuration to simplify the estimation of power losses (20) and to calculate the equivalent AC resistance of the cable conductor.
Figure 7 presents a simulation example for the MV 3x1x150/25 cable. The trefoil formation with a spacing between conductor axes of 40 mm was simulated. Both aluminum conductors and copper screens were simplified and represented as solid objects.
The simulation was carried out using the FEMM software package [26].
The calculated current density distribution J in the aluminum cable conductors and in the copper cable screens is shown in Figure 7. The supraharmonic phase conductor currents of Ish = 0.54 A (r.m.s. value) at the frequency fh = 2.5 kHz were simulated as the origin of the magnetic field in the cable. This value of the conductor current was measured as a 1 min value during the measurement campaign at the measurement point MP2.
The conductor currents were simulated as a three-phase set of balanced phasors with a 120° difference in phase angles between two neighboring phasors.
Figure 8 presents the line plot of the current density for the straight-line contour crossing the centers of two neighboring conductors with screens. The coordinates of centers in the "position" axis are - 20 mm and + 20 mm, respectively. The Figure also indicates skin effect, proximity effect, and influence of cable screens. Calculated frequency dependences for the MV cable under study
The analyticly calculated frequency dependences Rsh / R1 for the MV 3x1x150/25 cable are presented in Figure 9. These are the frequency dependence calculated taking into account only the skin effect (parameter YS), the frequency dependence calculated taking into account both the skin effect and the proximity effect (parameters YS and Yp), the frequency dependence calculated taking into account the skin effect, the proximity effect, and the influence of power losses in the conductor screens (parameters 7S, Yp, Ysc).
The frequency dependence Rsh / R1 determined with the FEMM software package for numerical calculations is presented for comparison in Figure 9.
The corresponding reference values Rsh / R1 = 1 were calculated for each presented dependence, in terms of the fundamental frequency of 50 Hz.
Figure 9 shows that the skin effect is the dominating factor in the increase in the equivalent AC resistance of the cable conductor Rsh with a rise in the frequency in the supraharmonic frequency range.
As seen in Figure 9, the influence of power losses in conductor screens on the increase in the equivalent AC resistance of the cable conductor Rsh with a rise in the frequency is much higher in comparison with the influence of the proximity effect for the MV cable under study.
Based on the comparison of the analyticly and numerically calculated frequency dependences presented in Figure 9, we can conclude that the analytic formula (17), parameterized according to (18), or the direct formula (19) are most suitable for the analytic characterization of the increase in the equivalent AC resistance of the cable conductor Rsh when the frequency for the MV cable under study goes up in the supraharmonic frequency range of 2 to 100 kHz.
Given the frequency dependence (1) presented graphically in Figure 1, it can be concluded that the frequency dependences calculated by (19) or using FEMM simulations for the MV cable under study are characterized by lower values of the relations Rh / Rj than the square root of the harmonic order h = fsh / fv
For the supraharmonic frequency range of 2 to 9 kHz, the following formula can be suggested for a simplified representation of the frequency dependence of Rsh / R1 for the MV cable under study:
Rsh /R » 0.484h . (24)
Deviations of (24) from the FEMM calculation results do not exceed several percent points in the range of 2 to 9 kHz.
IV. Use of measurement results for the supraharmonic power loss estimation
The supraharmonic power losses in the MV cable under study can be determined using (22). For clarity, (22) can be represented similar to (2) and rewritten as follows:
PLsh / PL1 = (Ish /If)Rsh /R
Taking into consideration the calculated frequency dependences Rsh / R1 for the MV cable under study and the measurement results for the time series Ih / I1 obtained during the measurement campaign, we can determine the time series for the relative values of supraharmonic power losses PLsh / PL1.
Figures 10 and 11 show the supraharmonic spectra of relative power losses in the frequency range of 2 to 9 kHz in the 20 kV cable feeder under study determined
according to (25) for the measurement interval of 24 hours (Figure 10) and for the measurement interval of one week (Figure 11).
The spectra in Figures 10 and 11 are presented for the supraharmonic groups of 200 Hz in accordance with the obtained measurement results for the supraharmonic currents. For the centered frequencies of each group, the frequency dependences Rsh / R1 calculated according to (19) were taken into consideration.
It is worth noting that the sum of average values of 1 min. relative harmonic power losses (harmonics 2 to 40) for this day of measurement considered in Figure 10 is 24.4%, the sum of average values of 1 min relative supraharmonic power losses in the range of 2 to 9 kHz presented in Figure 10 is 2.4%. The sum of average values of 1 min relative harmonic power losses for the whole measurement week considered in Figure 11 is 12.9%, the sum of average values of 1 min relative supraharmonic power losses in the range of 2 to 9 kHz presented in Figure 11 is 1.6%.
This means that there are supraharmonic power losses in modern distribution networks and they can reach the values of several percent of power losses at the fundamental frequency. The analysis shows that the supraharmonic power losses can exceed ten percent of power losses caused by conventional current harmonics in the MV cable under study. Therefore, it can be recommended to consider supraharmonic power losses to correctly estimate the total power losses in modern distribution networks.
Conclusion
The paper has considered a method of estimating the supraharmonic power losses, which combines the analytic determination of AC cable resistances at the supraharmonic frequencies and the use of measurements of supraharmonic currents in a real MV/LV cable network.
The results of the analytic calculations of the AC cable resistances at supraharmonic frequencies have been verified and made more precise using the FEMM simulations for a MV cable chosen for the investigation. We have proposed a simplified formula for the estimation of the increase in the AC cable resistances with respect to the cable resistance at the fundamental frequency of the MV cable under study for the frequency range of 2 to 9 kHz.
The findings indicate that the estimation of the supraharmonic power losses in MV networks in the frequency range of 2 to 9 kHz can be simplified using the measurement results obtained by conventional current measuring instruments.
The study has shown that supraharmonic power losses in the considered MV cable operating in a real network can reach the values of several percent of power losses at the fundamental frequency and can exceed ten percent of the power losses caused by conventional current harmonics.
It can be recommended to consider supraharmonic power losses to correctly estimate the total power losses in networks with high presence of power electronic devices.
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Alexander Novitskiy received his Ph.D. degree in electrical engineering from St. Petersburg State Polytechnic University in 1993. In 1994-1995, he worked as a Researcher at Tianjin University of Technology, China. Since 1996, he has been a Researcher at Ilmenau University of Technology, Germany. In 2006, he received his Dr.-Ing. habil. (D.Sc.) degree from that University. Since 2007, he has been a Senior Scientist in the Power Systems Group, Department of Electrical Engineering and Information Technology. His research interests include power quality, electromagnetic compatibility and interferences, simulation and analysis of steady states and transients in electric power systems..
Steffen Schlegel received his Ph.D. degree in electrical engineering from Ilmenau University of Technology, Ilmenau, Germany, in 2015. He is Chief Engineer and Head of the research team "Vertical System Operation" at Power Systems Group. A special focus of his research is on system integration of transmission and distribution grid operation, new power system operation methodologies with an active interface between distribution and transmission grid operators.
Dirk Westermann received the Diploma in electrical engineering and the Ph.D. degree from the University of Dortmund, Dortmund, Germany, in 1992 and 1997, respectively. In 1997, he joined the ABB Switzerland Ltd., where he held several positions in R&D and Technology Management. He became a Full Professor of power systems at Ilmenau University of Technology in 2005. Since 2018, he has been the Director of the Thuringian Energy Research Institute.
His research interests include design, control and operation of power systems. He is an IEEE Senior Member, an active member of CIGRE and IEC working groups.
