H. J. Su

Accurate Assessment of Harmonic and Interharmonic Currents Generated by VSI-Fed Drives Under Unbalanced Supply Voltages

Applications of solid-state converters and inverters for adjustable speed drives (ASDs) are popular in industrial systems and lead to a significant amount of harmonic and interharmonic currents being injected into the connected system. This paper presents an accurate analytical approach for the assessment of the harmonic and interharmonic currents generated by the voltage-source inverter-fed ASDs operated under unbalanced supply voltages, where the commutaton effect of the ASD converter and the detailed motor circuit model with various load levels are included. To validate the accuracy of the proposed approach, simulation results are performed by comparing those obtained by a time-domain simulation tool and by laboratory tests. It is shown that the proposed method can effectively calculate the harmonic and interharmonic currents produced by the ASD, either under balanced or unbalanced supply-voltage conditions.

On Real-Time Simulation for Harmonic and Flicker Assessment of an Industrial System With Bulk Nonlinear Loads

This paper presents application experiences of real-time simulation (RTS) techniques for harmonic and flicker studies of an industrial power system, where the system and nonlinear loads are properly modeled. A PC-cluster-based real-time parallel simulator is implemented under MATLAB/SIMULINK, where the studied system consists of an ac electric arc furnace, dc and ac motor-drive loads, and the static var compensator. Guidelines for model partition of the studied system and the solver settings under an RTS environment are reported. In addition, the most commonly used offline simulation with variable-step solver and the actual field measurements are included for comparison. Results indicate that the RTS achieves satisfactory solution accuracy within much less execution time and can be applied for more complicated studies such as installing new nonlinear loads with different levels of model complexities or designing/tuning mitigation devices of power-quality disturbances, where the repeated time-consuming analysis is required.

Modelling VSI-Fed ASDs by Matlab/Simulink for harmonic and interharmonic assessment

This paper presents simulation results by using Matlab/Simulink for the assessment of harmonic and interharmonic currents generated by the voltage source inverter (VSI)-fed adjustable speed drives (ASDs). In the simulation, the commutation effects caused by source impedance and non-ideal supply voltages are included. The front-end converter, dc link, pulse-width modulated (PWM) inverter, and the induction moter of the ASD are modeled in detail. Results are then compared with those obtained by laboratory tests to show the solution accuracy. Numerical and measurement experiences show that the adopted simulation tool yields satisfactory results for harmonic and interharmonic current assessments of VSI-fed ASDs.

Development of power quality analysis platform for INER Microgrid

The deployment of ac microgrids including distributed energy resources (DERs) can reduce the investment cost of building new fossil-fuel based power plants, facilitate the carbon-oxide reduction, provide reactive power compensation and frequency regulation, and enhance the system stability. However, some undesired effects such as imbalance, voltage fluctuation, and harmonics accompanied with the operations of DERs and nonlinear loads may affect the power quality (PQ) within the microgrid system. It is thus crucial to maintain the power quality within the microgrid to a satisfactory level. This paper presents the development of a graphical user interface-based analysis platform to monitor the power quality of the INER AC microgrid.

Application of grey predictor model for forecasting flicker severity associated with electric arc furnace load

It is known that rapid voltage fluctuations caused by electric arc furnace loads may generate significant levels of flickers, which have negative impacts to human eyes and power system components. This paper proposes a grey predictor model for the forecast of flicker levels produced by an electric arc furnace load. Actual measured data are adopted to implement the predictor model. Test results based on the proposed model are compared with two other neural network methods. It shows that more accurate forecast is achieved for the flicker prediction based on the proposed method.

Feasibility study of SVC installation in a substation network for voltage fluctuation mitigation

The operation of electric arc furnaces (EAFs) with drastic and random voltage-current characteristics creates considerable power quality problems in the connected power network. Because of the nonlinear behaviors of the EAF loads during operations, serious voltage fluctuations have been observed at busses that connect the substation transformer and cause frequent operations of the on-load tap changer (OLTC) of the transformer, which may shorten the OLTC life and affect the voltage quality. To reduce the number of switching operations of the OLTC, it is necessary to adopt mitigation solutions. This paper presents a feasibility study of installing a static var compensator (SVC) in an actual substation network supplying two large EAF loads for mitigating the voltage fluctuation and the number of OLTC operations. The effectiveness of installing the SVC at selected busses and the corresponding size are then reported.

Modelling and simulation for INER AC microgrid control

A microgrid integrates renewable energy and other forms of distributed energy resources (DER) to serve its loads. The microgrid can increase the DER penetration and improve power quality and reliability through appropriate management. Under the normal operation, a microgrid is connected to the utility grid, and each DG provides a preset power to the network through active/reactive power control (PQ control), whereas the utility grid is responsible for supplying/absorbing any power discrepancy. When the microgrid is disconnected from the utility grid, at least one unit switches to droop control from PQ control in order to regulate the voltage and frequency in the microgrid and continue to supply power to local load. This paper adopts Matlab/Simulink to model and simulate an actual ac microgrid with proposed control strategies. Several operation conditions including grid connected mode, islanding mode and load variation are simulated. Results show that the proposed control strategies for the microgrid are effective.

A new method for flicker severity forecast

Precisely forecasting the flicker level is important for drastic voltage fluctuations associated with the rapid reactive power consumptions of electric arc furnace (EAF) loads. This paper presents a prediction model based on grey theory combined with radial basis function neural network (RBFNN) for the forecast of flicker severity caused by the operation of a dc and an ac EAF loads, respectively. Test results based on the proposed model are compared with two other neural network methods. It shows that more accurate forecast is achieved for the flicker prediction based on the proposed method.

A study of passive harmonic filter planning for an AC microgrid

A microgrid usually consists of small-scale of thermal generation sources and other distributed energy resources (DER) such as photovoltaic, wind power, and fuel cells to serve its loads. The microgrid can increase DER penetrations and operation reliability through appropriate control schemes and energy management. When the inverter-based DERs supply electric energy to nonlinear loads in the microgrid, harmonic currents are produced and resonances in the grid may occur and causes negative impacts on some critical loads or other equipment, as well as extra power losses. To mitigate the undesired harmonic effects and improve the microgrid performance, this paper presents a study of planning single-tuned passive harmonic filters for the microgrid. Simulation results show that the designed filters can effectively mitigate the harmonic currents in the microgrid.

IEEE standard 1459-based reference compensation current strategy for three-phase three-wire shunt active power filter control

This paper presents a study of applying the equivalent effective voltage concept according to IEEE Standard 1459-2010 for determining reference compensation currents of the three-phase three-wire shunt active power filter in the a-b-c reference frame. The APF reference current calculator is developed and is realized on the DSP board through processor-in-the-loop simulation for validating the effectiveness of the proposed APF control strategy.