Open circuit voltage distortion in salient pole synchronous generators with damper windings

Converters are used in the utility interface of renewable energy system to reduce harmonic contents in line current/voltage and to increase reliability. These converters suffer from high level of Total Harmonic Distortion (THD) in the utility line currents/voltages which creates a lot of problems in the power system. In this paper selective harmonics are eliminated to reduce the THD, that is, the problem is to determine optimal switching angles for eliminate harmonics while maintaining the required fundamental currents/ voltages. The THD reduction is achieved by the help of multilevel inverter with equal separate dc sources using particle swarm optimization technique. This technique can be applied to multilevel inverters with any number of levels; as an example in this paper, an 11-level inverter is considered. Theoretical results are verified by experiments and simulations for an 11- level H-bridge inverter. Results show that the proposed method does effectively eliminate a great number of specific harmonics, and the output voltage is resulted in low total harmonic distortion.

This paper proposes an improved harmonic distorted modified triangular carrier-based multicarrier pulse width modulation for generating the switching pulses of a multilevel inverter. This modified triangular wave consists of a triangular wave bearing a close resemblance to an ‘M’ shaped wave. The design of this carrier signal has been optimized to maintain a low level of total harmonic distortion (THD), while increasing the fundamental o/p voltage to ensure the effective DC voltage utilization. Moreover, this optimization reduces the switching losses and improve the efficiency of the power inverter. With the help of this carrier signal, High-frequency alternative phase opposition disposition pulse width modulation (APODPWM) is generated. This new control scheme has been applied to seven levels of conventional cascaded H-bridge with reduced switch multilevel inverter. The output is compared with conventional carrier-based APODPWM. The comparison is made in terms of THD, fundamental output voltages and inverter losses. To ensure quality performance, conventional carrier and modified carrier-based multicarrier PWM topologies are used for the Cascaded seven-level inverter with reduced switch seven-level inverter having a carrier frequency of 2 kHz and modulation index of 0.8-1.30. According to the simulation results, by using the proposed modulation scheme the THD and the switching loss were reduced by 9.64[%] and 4.2[%] respectively. Besides, the proposed modulation technique increases the fundamental output voltages. The total simulation process is done in MATLAB Simulink environment.
 GUB JOURNAL OF SCIENCE AND ENGINEERING, Vol 6(1), Dec 2019 P 12-19

In this work, a comprehensive analysis of the influence of higher harmonics generated by a frequency converter on a three-phase power supply system of an electric drive was carried out. Attention was paid to determining the level of harmonic distortion in the input current of the converter. For experimental research, a scheme of a specialized experimental setup was developed and implemented, which provides the possibility of measuring the operating parameters of the frequency converter in real time. Experimental tests of the Altivar 71 frequency converter were carried out in three operating modes: idle, rated load and overload by 25%. The measured values ​​of current and relative line voltage were processed in the Mathcad 14 environment and presented in the form of graphs demonstrating the change in electricity parameters under different operating conditions. Analysis of the obtained spectra of harmonic components showed that the system contains mainly odd harmonics, among which the 5th and 7th harmonics have the greatest influence, especially under load conditions. It was found that increasing the load of the converter contributes to a decrease in the harmonic distortion factor, while reducing the output frequency of the frequency converter, on the contrary, leads to an increase in the level of distortion. One of the most effective methods of reducing the level of harmonic distortion, as well as increasing the power factor of the system, is the use of power factor correctors (PFC). These devices, which are based on the use of highly efficient pulse circuits with low energy losses, not only improve the current shape and increase the power factor, but also provide voltage stabilization in the DC circuit even under conditions of sharp voltage drops. As a result of the study, the levels of harmonic distortion factors for different operating modes of the frequency converter were determined, and the use of PFC was also proposed to minimize the negative impact of higher harmonics on the power supply system of the electric drive. The implementation of such measures allows to increase the efficiency of electric drive systems, ensure improved electricity quality indicators and stable operation of inverters.

Short circuit faults are a prevalent issue in power systems, causing disruptions to the grid's normal operation. Dynamic behaviours of the conventional power systems during short circuit faults have been extensively studied and understood. The bulk of ongoing research and development are focusing on the dynamic performance of grid-connected renewable energy systems under these fault conditions, due to changes in the grid code and a decrease in system inertia. The development of effective control strategies to enhance the system's reliability during fault conditions is of paramount importance. In this paper, a two-stages grid-connected photovoltaic system (GCPV) having a rated power of 2 MW was created in the MATLAB/Simulink environment. The dynamic behaviour of the presented system was evaluated in two scenarios: steady state conditions and short circuit faults. A line-to-ground short circuit fault was created at the grid side, and its effect on the PV system's operation was observed. An advanced control system was designed to maintain stability during fault conditions. The results demonstrated the efficiency of the designated control system in minimizing the effects of short circuit faults on the GCPV system's function, and restoring the system promptly after the fault was cleared. Furthermore, considering modifications in grid regulations, the low voltage ride through (LVRT) capability of the designed system was analysed and validated according to the UK standards. The Total Harmonic Distortion (THD) level at the common coupling point was also analysed for voltage and current, remaining below the acceptable level of 5% as specified in the IEEE Std. 519.

This paper purposely to examine and analyse the impact of the distribution capacitors banks operation to the transition of total harmonic distortion (THD) level in distribution network system. The main advantage of this work is the simplicity algorithm of the method and the system being analysed using free access open software which is known as electric power distribution system simulator (OpenDSS). In this paper, the harmonic current spectrum which is collected from the commercial site was injected to a node point on IEEE13 bus in order to provide the initial measurement of THD for the network. The proper sizing of the capacitors banks has been set and being deactivated and activated throughout the network to see the transistion in the THD level in the system. The results were achieved by simulation of the data on the configured IEEE13 bus. The simulation work was done by using the combination of C++ source codes, OpenDSS and Microsoft Excel software. From the output results, the THD current has increased up to two times from the initial value in certain phases and for the THD voltage, the THD has increased up to three times from its initial value in all phases.

<span>The development of active power filter (APF) using rectifier boost technique has been identified to compensate for the pulsating nature of the distorted supply current waveform of non-linear load. In this work, investigation is carried out on the operation of rectifier without any filters function. This is then extended to operate the rectifier converter with an active power filter function. APF function is implemented by enabling the closed-loop control using standard proportional integral control to rectify the distorted supply current to become continuous, sinusoidal and in-phase with the supply voltage waveform. Consequently, the total harmonic distortion (THD) level was reduced to meet the acceptable limit defined in the standard of IEEE-519 1992. The selected simulation results obtained from MATLAB/Simulink are presented to justify the proposed filter structure.</span>

This study presents an optimisation technique for proportional‐integral‐derivative (PID) controller to achieve maximum‐power‐point tracking (MPPT) of single‐ended primary‐inductor converter (SEPIC). A new weight function is developed to optimise the PID parameters based on gradient‐descent (GD) method by adding low‐pass filter term. The proposed optimisation method does not stick in the local minima, which happens frequently with the traditional weight function used in GD method, where the low‐pass filter term suppresses the noise and smooths the iteration process. The prototype of the proposed optimised PID‐based SEPIC converter for photovoltaic inverter applications is built using DSP‐based TMS320F28335. The performance of the proposed optimised PID‐based MPPT scheme is tested in both simulation and experiment at different operating conditions. A performance comparison of the proposed GD method with the conventional GD PID is also made in real‐time. It is found that the proposed optimised PID‐based SEPIC converter is superior to the conventional GD PID controller in terms of power transfer and efficiency. Furthermore, the proposed optimised PID controller for two‐level inverter can achieve a better total harmonic distortion (THD) level as compared to the multi‐level inverter frequently used by researchers for the same purpose.

Multi-pulse gate turn-off thyristor based voltage source converter (GTO-VSC) topology having a number of 6-pulse VSCs as elementary unit together with fundamental frequency mode of GTO gate control are widely used in STATCOM for dynamic reactive power compensation in electrical network. A 12-pulse topology generally produces an AC output voltage waveforms which contain 11/sup th/, 13/sup th/, etc. harmonics and hardly find its application due to higher total harmonic distortion (THD) level. In this paper, a new model of 2-level, 12-pulse, 132 kV, /spl plusmn/100 MVAr STATCOM employing 2/spl times/6-pulse GTO-VSCs, fundamental frequency gate switching, PI-control methodology, DC capacitor as an energy storage and two stages of magnetics, is designed and simulated to attenuate harmonics of the order of 5/sup th/, 7/sup th/, 11/sup th/, 13/sup th/ etc. by SimPowerSystems toolbox in MATLAB environment. The operating performance of the compensator is studied for regulating voltage and power factor correction in electrical network and results show the model acceptable for power system applications.

sampling times is presented in this paper. The purpose of the current controller is to regulate the load current within the set reference current. A simulation model of the five-level CHB inverter with Model Predictive current controller (MPC) has been built to demonstrate the CHB inverter system performance in terms of Total Harmonic Distortion (THD) level of the load current and reference current tracking for a step change with different sampling times. The simulation results are observed by using the MATLAB Simulink software to validate the proposed current control technique.

The increasing importance of power electronic converters in supplying electrical energy to utility grids places a higher priority to detect and protect against fault conditions. Fault detection and isolation are particularly important for inverters that provide black-start recovery for microgrids since these converters provide the energy source for restoration after a power outage. This paper presents a new fault detection and location method for Cascaded B-Bridge (CHB) multilevel inverters. The new fault detection method is based on monitoring the output voltage of each cell and output current directions along with each switch's state. By monitoring each cell's output voltage and current direction, the faulty cell can be detected and isolated. After the faulty cell is detected, the faulty switch can be located by comparing the current direction with the switching states. This technique is implemented with Level-Shifted Pulse Width Modulation (LS-PWM) in order to maintain acceptable total harmonic distortion (THD) levels at the converter. The proposed method can be implemented for a CHB with any number of cells, can operate with nonlinear loads, and offers very fast detection times. Simulation and experimental results verify the performance of this method.

This paper presents an implementation of controlled rectifier with power factor correction (PFC) using single-phase matrix converter (SPMC). A current control loop (CCL) using standard proportional integral control was used to implement PFC to correct the pulsating nature of the input current to almost unity power factor form with low total harmonic distortion (THD) level well below the acceptable limit that was defined in the standards of IEEE 519. Waveshaping of supply current is facilitated through the use of boost technique that could perform corrections making it continuous, sinusoidal and in phase with the supply voltage. Safe commutation strategy was implemented to avoid voltage spikes due to inductive load. Prior to its practical realization a computer simulation model is developed to investigate the behaviour of the SPMC using MATLAB/Simulink (MLS). An experimental test-rig was then constructed to verify the operation; incorporated with control electronics, gate drives, and power circuits. Selected simulations and experimental results are presented to verify proposed operation.

This paper presents the application of single-phase matrix converter (SPMC) as a single-phase AC-DC controlled rectifier incorporating active power filter as a battery charger. The output voltage of the charger should deliver a clean regulated voltage output with sinusoidal input current. A current control loop (CCL) using standard proportional integral control was used to correct the pulsating nature of the input current to almost unity power factor form with low total harmonic distortion (THD) level well below the acceptable limit that was defined in the standards of IEEE 519. Prior to its practical realization a computer simulation model is developed to investigate the behavior of the SPMC to the charging characteristic of lead-acid and lithium-ion battery using MATLAB/Simulink (MLS). Selected simulations results was presented to verify proposed operation.

Modern compact fluorescent lamps (CFLs) are reported to have very high levels of current total harmonic distortion, which may have strong negative impact on the quality of supply in distribution networks. This paper demonstrates how a novel circuit-based modelling approach can be used to investigate and quantify the effect of cancellation of harmonics between the groups of modern CFLs. The presented results are verified by measurements.

In this paper, we present an approach for Polymer Electrolyte Membrane Fuel Cell (PEMFC), drying out and flooding diagnosis. The present approach is signal-processing-based pattern recognition. The voltage signal is processed by a Fast Fourier Transform, in order to carry out a frequency analysis and to calculate the Total Harmonic Distortion (THD). The TDH is used, amoung other variables, as descriptor for a global Pattern Recognition approach (fault detection, and identification through a classification approach). In this work, a supervised and non-supervised classification, by means of the K-nearest neighbor and kmeans methods, are achieved to identify the fault. This work resulted in, first, the detection of defects, through the change in the total harmonic distortion level and the frequency spectrum, secondly in the fault identification, through supervised and non-supervised classification methods with, respectively, a good classification rate of 84% and 98.5%.

In this paper, the concept and the mathematical model of distribution network optimal operation are proposed, and a genetic algorithm based solution is presented. The objective is to minimize the system total power losses and harmonic distortion levels by properly adjusting the transformer taps changing the status of switches, capacitor banks and LC-filters, while satisfying bus voltage constraints, harmonic distortion constraints and security constraints of both capacitor banks and LC-filters. Test results on a 16-bus distribution network reveal the superiority and effectiveness of this method.