Supply Voltage Harmonics Research Articles

Derating of Squirrel-Cage Induction Motors Due to High Harmonics in Supply Voltage

This paper presents the results of load capacity calculations for three-phase squirrel-cage induction motors supplied with distorted voltage with rotating harmonics. The calculations were made on the basis of a commonly used model of an induction machine. The difference from many papers is that the parameters of the equivalent circuit of each motor were precisely determined in terms of power losses in the motor. The load capacity of the motors was made dependent on the load power losses in the rotor cage. These losses were determined on the basis of short-circuit measurements of motors, made for frequencies equal to harmonic frequencies. Measurements and calculations were made for low-voltage squirrel-cage motors with rated powers of 4–65 kW and various efficiency classes. Calculations have shown that the calculated derating curves do not match the curves given in IEC 60034-17 and NEMA MG1. The differences are up to 15% for IE1 and IE2 motors and more than 50% for IE3 motors.

An Approach to Control SCR Bridge Rectifier to Suppress the Effect of Even Ordered Supply Voltage Harmonics on DC-Bus Capacitor of Adjustable Speed Drives

Electrolytic capacitors used in adjustable speed drives (ASDs) are affected more by low-frequency currents than high frequency. It is shown in this article that even-ordered harmonics in the supply voltage create a 150 Hz current component in the dc bus, and impact the heating in the capacitor. It is further shown that the total harmonic distortion of the current drawn by the ASD is adversely affected due to the even-ordered harmonics. This article discusses a cost-effective approach based on suitable triggering of the silicon controlled rectifiers (SCRs) in the bridge of ASD to suppress the effect of even-ordered harmonics on capacitor ripple current and source current. Using parameters taken from capacitor datasheets, and the supply voltage characteristics from field studies, exhaustive simulation studies are presented to identify an approach to the determination of various thresholds required. The applicability of the method to the ASDs of various power levels is also presented. The proposed strategy is analyzed by simulations under different grid impedance and harmonic combination cases and validated by a hardware test setup.

Waveform Variation Defined Model for Harmonic Current Emissions Including Cross-Order Supply Voltage Harmonics Influence

The paper reports an experimental non-linear load evaluation regarding current harmonics sensitivity to supply voltage harmonics. A base for the model is proposed relying on the time-domain waveform variations, rather than impedance or conductance approach. The proposed Waveform Variation Defined Model is able to detail to provide improved correspondence for the actual load physical operation on the emergence of cross-order coupling between the supply voltage and current harmonics variations. Model proposal specifies to implement non-impedance relation and separated phase and magnitude response components, in empirical outcome of the voltage-to-current harmonic variation relation. It will be shown that the model proposed is able to provide an accurate estimation on cumulative influence of different supply voltage harmonics included, for the most probable supply voltage harmonics in the residential grid, for the low order odd harmonics. Model results present outstanding match of the harmonic voltage influence estimations on the load current harmonics levels measured, phase and magnitude values included.

Single-Phase Transfer Delay FLL With Enhanced Performance for Power System Applications

This article proposes a gradient descent-based transfer delay frequency-locked loop (FLL) (GDTD FLL) to effectively address the challenges of existing transfer delay-based FLLs in terms of unacceptable frequency and phase angle overshoots during variations in the supply voltage amplitude and distorted voltage conditions. In the proposed GDTD FLL, a linear model of the distorted single-phase supply voltage is developed and the error term is constructed. Consequently, the gradient descent algorithm is employed to drive the error term to zero and provide an estimate of the FLL expression from which frequency estimation is achieved. By designing the learning rate employed in the gradient descent algorithm, a degree of freedom is introduced in the proposed GDTD FLL, giving it the ability to achieve improved performance during variations in the supply voltage amplitude. Furthermore, a delay-based harmonic cancellation approach is developed to reject supply voltage harmonics in the FLL’s phase angle estimation. The effectiveness of the proposed GDTD FLL is verified in comparison with other single-phase FLL schemes through experimental studies where it is shown that the proposed GDTD FLL effectively addresses the challenges of existing delay-based FLLs in terms of peak frequency and phase angle overshoots, especially when the supply voltage undergoes amplitude variation or distortion.

Failure analysis of a high-speed induction machine driven by a SiC-inverter and operating on a common shaft with a high-speed generator

Due to ongoing research work, a prototype test rig for testing high speed motors/generators has been developed. Its design is quite unique as the two high speed machines share a single shaft with no support bearings between them. A very high maximum operating speed, up to 80,000 rpm, was required. Because of the need to minimise vibration during operation at very high rotational speeds, rolling bearings were used. To eliminate the influence of higher harmonics of supply voltage and current on the formation of torque oscillations on the shaft and excessive losses in the form of heat, a voltage source inverter with high switching silicon carbide (SiC) power transistors characterizing high precision of the output voltage generation with a fundamental harmonic frequency of several kilohertz has been used. During the first start-ups, it turned out that the system was not stable, and a failure occurred. The paper presents the consequences that may arise when a machine operating at a speed of about 70,000 rpm fails. The article contains pictures of a generator failure that occurred at a high rotational speed.

Adaptive Balancing by Reactive Compensators of Three-Phase Linear Loads Supplied by Nonsinusoidal Voltage from Four-Wire Lines

A method of the design of an adaptive balancing reactive compensator in four-wire systems with linear loads and nonsinusoidal voltage is described in this article. The method of compensation is founded on the Currents’ Physical Components (CPC) – based power theory of three-phase systems with nonsinusoidal voltages and currents. The compensator is built of two sub-compensators of Y and  structure, respectively. The Y compensator reduces the reactive current and the zero sequence symmetrical component of the unbalanced current. The  compensator reduces the negative sequence symmetrical component of the unbalanced current. The positive sequence symmetrical component of the unbalanced current and the scattered current remain uncompensated. It is because shunt reactive compensators do not have any capability for that. Thyristor Switched Inductors (TSIs) enable the susceptance control of the compensator branches, referred to in the article as Thyristor Controlled Susceptance (TCS) branches. Periodic switching of thyristors in these branches causes the generation of harmonic currents, in particular the third-order harmonic. Moreover, in the presence of the supply voltage harmonics, a resonance of the equivalent capacitance of the compensator with the distribution system inductance can occur. These two harmful phenomena in the compensator suggested were reduced by the selection of a special structure of the TCS branches and their LC parameters. The presented method of the adaptive compensator synthesis was verified in the article with a numerical example and results of computer modeling of the load with an adaptive compensator.

3D Electromagnetic Field Analysis Applied to Evaluate the Accuracy of a Voltage Transformer under Distorted Voltage

Voltage transformers (VTs) are an important element of the measuring system that allows measuring the energy flow in medium and high voltage networks. Additional problems with the accuracy of the measurement introduced by the appearance of sources and nonlinear receivers cause deformation of the voltage shape in the energy system. Due to the high metrological requirements, the design of voltage transformers requires high accuracy (for class 0.2 ΔU ≤ 0.2, phase displacement ≤10 min), which is not possible with the use of analytical methods using approximate models. Therefore, only the application of numerical modeling by the finite element method, taking into account real three-dimensional phenomena, allows achieving high modeling accuracy. The article concerns the phenomenon of the influence of voltage higher harmonics of supply voltage on the accuracy (up to the 100th harmonic) of the measuring inductive voltage transformer (IVT). The applied modeling method takes into account the phenomena in the transformer core and the circuit equations resulting from the winding arrangement, which allows for the study of the deformation voltage transformation. Experimental tests on a real model to evaluate the method used were necessary. The article presents simulations for a model transformer, and results have been confirmed by experimental tests.

Impact of Supply Voltage Unbalance and Harmonics on dc Bus Electrolytic Capacitor of Adjustable Speed Drives

Among the various supply voltage abnormalities, unbalance and distortion are some of the major threats to the dc bus capacitor of adjustable speed drives. The effect of supply voltage unbalance on the dc bus capacitor changes in the presence of supply voltage harmonics. Further, the value of grid impedance and the load on the drive influences the response of these supply voltage abnormalities on the dc bus capacitor. This article analyzes the impact of unbalance, distortion, and simultaneous presence of unbalance and distortion in the supply voltage, on the dc bus capacitor, along with the effect of grid impedance and the load on the drive. As a result of the analysis, the article proposes the derating of load required to keep the capacitor current within the safe value irrespective of the level of abnormalities and grid impedance. The effects are analyzed by simulations and validated by the hardware test setup.

Supply Voltage and Grid Current Harmonics Compensation Using Multi-Port Interfacing Converter Integrated Into Two-AC-Bus Grid

A modified multi-port converter topology is proposed for active power quality control of two-ac-bus grid while maintaining a flexible integration of distributed dc energy sources. In this system, the lower converter cells work in voltage controlled mode to supply power to autonomous local critical loads with reduced harmonic distortions. At the same time, the upper converter cells working in current controlled mode are placed in between the main grid and the lower cells, to block the harmonic current from the local nonlinear loads to pollute the higher voltage grid current. In this proposed system, the upper and lower power cells harmonic control are well decoupled with minimal interferences. This features reduced computational load as there is no need to use any harmonic components extractions in the whole compensation process. In addition, the proposed harmonic compensation method has no interference with the interphase power flow control through zero sequence voltage injection. It has been examined that the proposed power quality control method works well in various conditions including that with large grid impedance and dc rail voltage variations.

Economic assessment of non-sinusoidal energy in distorted distribution systems

PurposeThe purpose of this paper is to analyze annual energy expenditure in the presence of non-linear load and substation voltage harmonics in distribution systems. Economic assessment of non-sinusoidal energy is a challenging task that involves complex computations of harmonic load powers and harmonic line losses.Design/methodology/approachThe paper evaluates fundamental and non-sinusoidal components of electrical energy by applying backward/forward sweep technique in distorted distribution systems. This work involves harmonic power computations at the substation by including harmonic losses occurring in various lines of the distribution system.FindingsThe paper found that annual energy expenditure significantly depends upon the non-linear load, supply voltage harmonics and type of tariff structure considered in the distribution system. Impact of individual harmonic orders on the energy billing is also assessed.Originality/valueThe paper concludes that considering harmonic distortions in the distribution system analysis would help electricity regulators formulate adequate pricing structures, which would further generate appropriate economic signals for electricity utility and the consumers.

A laboratory application for teaching the effect of harmonics on transformer core saturation

Harmonics in supply voltage or load current in a transformer have undesirable effects on the core and windings. As the harmonic content increases, higher core loss and eddy current loss in the windings results in higher operating temperatures. It causes magnetic flux density in the core to increase and shifts the operating point through the saturated region. This phenomenon is mostly taught in undergraduate education as theoretical information. However, as a difficult concept to understand, harmonics phenomenon might be taught by using experiments for active learning, visualizing the effects in a laboratory setting, and making the connection between theoretical and practical applications for deeper and meaningful learning. In this study, a teaching method for effects of harmonics is proposed and phase shift between the fundamental and harmonic component of the supply voltage on the transformer B–H characteristic in a laboratory application is introduced by an experimental work performed on toroidal transformers. Feedback from students shows that the proposed method is very efficient and useful for students to better understand the effects of harmonics on the transformer cores.

ANN based control scheme for a three-level converter based unified power quality conditioner

Unified power quality conditioner (UPQC) has been used convincingly to mitigate most of the electric power quality issues. Conventional control schemes such as Synchronous Reference Fame (SRF) and P-Q theory based control involves abc to/from dq/αb transformations. Hence, they involve complex calculations and require DSPs/FPGAs which are costly. Employing Artificial Intelligent control schemes helps to reduce the control system size and complexity of operation. This paper proposes an ANN controller for UPQC for effective operation and control. The ANN controller reduces the cost and complexity of the system. The controller performance is analysed under various conditions like supply voltage and load current harmonics, load unbalances, voltage sag and swell. Results prove the superiority of the ANN controller over conventional controllers.

Effect of different methods of pulse width modulation on power losses in an induction motor

We consider the calculation of modulation power losses in a system “induction motor–inverter” for various pulse width modulation (PWM) methods of the supply voltage. Presented values of modulation power losses are the result of modeling a system “DC link - two-level three-phase voltage inverter - induction motor - load”. In this study the power losses in a system “induction motor - inverter” are computed, as well as losses caused by higher harmonics of PWM supply voltage, followed by definition of active power consumed by the DC link for a specified value mechanical power on the induction motor shaft. Mechanical power was determined by the rotation speed and the torque on the motor shaft in various quasi-sinusoidal supply voltage PWM modes. These calculations reveal the best coefficient of performance (COP) in a system of a variable frequency drive (VFD) with independent voltage inverter controlled by induction motor PWM.

Demand side management perspective on the interaction between a non-ideal grid and residential LED lamps

Lighting industries across the world are witnessing a rapid shift towards energy efficient LED (Light Emitting Diode) lightings. These lighting technologies can be seen asan alternative tool to the DSM (Demand Side Management) in residential, commercial as well as industrial sector. DSM has a strong linkage with the reliability and quality of power supply and any variations in supply conditions may significantly affect DSM strategies. As LED lighting technologies are penetrating the lighting market at a rapid pace, it is important to assess the different impacts of distribution grid conditions on the power quality and energy consumption performance of LEDs. This paper presents an extensive analysis of the consequences of sustained abnormal voltage, supply voltage harmonics, and supply frequency variations on LED lamps and its overall effect on the popular “LED lighting DSM Program” – being adopted worldwide. It was observed that under the variable grid conditions, some lamps’ technologies offer DSM like advantages without being actively engaged in DSM. Several parameters have been evaluated, analyzed and, recommendations have been made for LED-based passive DSM strategies which may encompass the LED manufacturers, the utilities, and the governments.

Multiple harmonic elimination‐based feedback controller for Shunt Hybrid Active Power Filter

This study presents a multiple harmonic elimination-based feedback controller for shunt hybrid active power filter (SHAPF) to perform an effective harmonic compensation performance in a wide harmonic frequency band. The conventional control methods presented for SHAPF cannot perform an adequate performance, because of the disturbances such as phase delays caused by controller methods and measurement circuitries, tolerances of passive filter components and supply voltage harmonics. In the proposed controller, the conventional feedback controller is improved by using supply side individual current harmonics which are extracted by the synchronous reference frame method. To prevent the performance degradation effects of disturbances, proportional–integral controllers are applied to each d and q components of individual current harmonics. The compensation performance of the proposed method is compared with conventional methods both theoretically and experimentally. The experimental results verify the advanced harmonic compensation performance of the proposed control method.

Simultaneous Microgrid Voltage and Current Harmonics Compensation Using Coordinated Control of Dual-Interfacing Converters

The growing installation of distributed generation (DG) units in low-voltage distribution systems has popularized the concept of nonlinear load harmonic current compensation using multifunctional DG interfacing converters. It is analyzed in this paper that the compensation of local load harmonic current using a single DG interfacing converter may cause the amplification of supply voltage harmonics to sensitive loads, particularly when the main grid voltage is highly distorted. To address this limitation, unlike the operation of conventional unified power quality conditioners with series converter, a new simultaneous supply voltage and grid current harmonic compensation strategy is proposed using coordinated control of two shunt interfacing converters. Specifically, the first converter is responsible for local load supply voltage harmonic suppression. The second converter is used to mitigate the harmonic current produced by the interaction between the first interfacing converter and the local nonlinear load. To realize a simple control of parallel converters, a modified hybrid voltage and current controller is also developed in the paper. By using this proposed controller, the grid voltage phase-locked loop and the detection of the load current and the supply voltage harmonics are unnecessary for both interfacing converters. Thus, the computational load of interfacing converters can be significantly reduced. Simulated and experimental results are captured to validate the performance of the proposed topology and the control strategy.

Voltage Sag, Swell and Harmonics Mitigation by Solar Photovoltaic fed ZSI based UPQC

This paper presents a solar photovoltaic (SPV) fed impedance or Z-source inverter (ZSI) based Unified Power Quality Conditioner (UPQC) for the alleviation of power quality events such as voltage sag, swell and harmonics with sudden addition or removal of a nonlinear load. The unit vector template (UVT) control technique is used to produce the reference voltage and current signals to control the operation of SPV fed ZSI-UPQC. A novel hybrid technique is also proposed for optimum maximum power point tracking (MPPT) with the combination of perturbation and observation (P&O) technique and incremental conductance (Inc) technique. The response of SPV fed ZSI-UPQC for mitigation of supply voltage sag, swell and harmonics are investigated and compared with SPV fed voltage source inverter (VSI) based UPQC (VSI-UPQC) and SPV fed current source inverter (CSI) based UPQC (CSI-UPQC).

Mathematical Modeling of Unified Power Quality Conditioner for Distribution Power System

This paper deals with the structure of unified power quality conditioner (UPQC), which is used to eliminate power quality problems such as supply voltage and current harmonics, compensate reactive power, voltage sag/swell compensation on distribution system. The performance of the inverters depends on the control strategy used to generate reference signals for its operation. The mathematical analysis of UPQC is done to see its characteristic performance in the distribution system. This analysis is very useful for the selection of device rating and placement based on its particular application area in the power system.

Electrical treeing in XLPE cable insulation at cryogenic temperature under harmonic AC voltages

The shape of electrical trees formed in XLPE cable insulation at low temperature under AC and harmonic voltages are fibrillar type. Life of cable insulation failure due to electrical treeing was analysed through Weibull distribution studies. It is observed that the voltage wave shape and peak factor exhibit high influence on the life of cable insulation due to electrical treeing. Harmonics with higher THD’s and the failure rate of cable insulation due to treeing are the same. The presence of 4th and 5th harmonics in supply voltage could cause early failure of cable insulation. Ultra High Frequency (UHF) signal radiated during tree growth process, under harmonic voltages lies in the range 0.5–1.5GHz. Phase Resolved Partial Discharge (PRPD) analysis using spectrum analyser has revealed that under 50Hz, discharges occur near zero crossing and in the presence of harmonics, it occurs when the rate of voltage rise is high. The discharge occurs at its peak under low frequency AC voltage of 1Hz.

A Disassembly-Free Offline Detection and Condition Monitoring Technique for Eccentricity Faults in Salient-Pole Synchronous Machines

A novel scheme to reliably monitor the condition of static and dynamic eccentricity (DE) faults in salient-pole synchronous machines (SPSMs) through the standard short-circuit test is proposed in this paper. The detection technique is based on offline current signature analysis that does not require machine disassembly. The procedure is unaffected by machine saturation or supply voltage harmonics. In this scheme, DE fault is monitored by exploiting the presence of inherent static eccentricity (SE), whereas SE fault monitoring is achieved using residual estimation technique. The proposed method is found to work for both star and delta-connected machines. Results obtained from an experimental three-phase 2-kW SPSM have been used to validate the proposed eccentricity condition monitoring method.