Presence Of Low-order Harmonics Research Articles

A Cascaded Nine-Level Inverter Topology With T-Type and H-Bridge With Increased DC-Bus Utilization

This article introduces a hybrid nine-level inverter topology with extended dc-bus utilization for operation at over modulation range without the presence of lower order harmonics (predominantly fifth and seventh) when compared to conventional two-level and multilevel inverter with hexagonal voltage space vector structure. The proposed inverter is a cascade of a five-level T-type unit and an H-bridge (HB) unit. An increase in the dc-bus utilization is possible by increasing the pole voltage levels to $\pm (V_{\text{dc}}/2+V_{\text{dc}}/8)$ using the HB capacitor voltage and also the capacitor voltages are balanced by adding a offset to sine reference. The aforementioned pulsewidth modulation strategy allows us to increase the peak phase fundamental voltage from $0.577V_{\text{dc}}$ to $0.625V_{\text{dc}}$ in case of unity power factor (p.f) load and to $0.637V_{\text{dc}}$ for 0.82 p.f load with the proposed nine-level inverter. The limiting factor on increasing the dc bus utilization such as p.f, HB capacitor balancing are analysed broadly in this article. The proposed inverter scheme and its claim of increasing the peak phase fundamental voltage is experimentally validated in a laboratory prototype.

Sensorless Predictive Current Control of PMSM EV Drive Using DSOGI-FLL Based Sliding Mode Observer

Conventional back electromotive force (EMF) estimation based active flux concept for sensorless control has various limitations due to pure integrator problems and performance deterioration at low speeds. The fundamental back EMF component extraction with a conventional low pass filter, is difficult due to the presence of lower order harmonics, dc offset, saturation, etc., and causes significant phase delay in the estimated position and speed. This article deals with a sensorless speed and position estimation technique for a surface mounted permanent magnet synchronous motor (SPMSM) based electric vehicle (EV) drive using a sliding mode observer (SMO) with a dual second order generalized integrator frequency locked loop (DSOGI-FLL). A novel method of utilizing the DSOGI-FLL, along with feedforward term is shown to achieve better harmonic elimination of estimated back EMF components and faster dynamic speed estimation. A delay compensated predictive current controller-based PMSM EV drive with the presented estimation technique is used for improved dynamic response. This system is simulated using Simulink and its efficacy is experimentally validated using dSPACE 1202. Test results show that the DSOGI-FLL-based SMO has better performance compared to the conventional technique.

Investigation on Extending the DC Bus Utilization of a Single-Source Five-Level Inverter With Single Capacitor-Fed H-Bridge Per Phase

Enhancement of dc bus voltage utilization for a five-level inverter with single dc source and capacitor-fed H-bridge (CHB) units is investigated in this paper. A carrier-based modulation technique is used for boosting the dc bus utilization, which is established by providing detailed mathematical analysis. The five-level inverter used here is realized by cascading a CHB unit to each phase of a three-level neutral point clamped inverter. The increase in dc bus voltage utilization owes to the pole voltage redundancies offered by CHB units. The floating capacitors of H-bridge units are balanced within a quarter fundamental cycle using the switching state redundancies of pole voltage levels. The aforementioned modulation technique allows the inverter to enhance the dc bus utilization from 0.577 $\text{V}_{\text{dc}}$ to 0.63 $\text{V}_{\text{dc}}$ under unity power factor. This enhancement is obtained in the linear modulation range without increasing the dc bus voltage, and thus, the inverter can operate without the presence of low-order harmonics in its phase voltages. The strength of this paper lies in its detailed mathematical analysis for finding out the limiting modulation index and power factor condition in the light of floating capacitor voltage balancing issue. Simulation as well as experimental verification of the modulation scheme is carried out on an induction motor drive under various operating conditions. It is shown that this carrier-based modulation technique is suitable for any single source inverter topology with one CHB unit per phase.

Integral sliding mode‐improved adaptive MPPT control scheme for suppressing grid current harmonics for PV system

This study proposes a new control scheme for grid integration of a three-phase two-stage photovoltaic (PV) system by employing an integral sliding mode current control loop and an improved adaptive maximum power point tracking (MPPT) algorithm. Integral sliding mode control (ISMC) offers fast control action and is insensitive to plant parametric uncertainties. In a grid-connected PV system, ISMC suffers from steady-state error in tracking reference grid current signal due to disturbances in the dc-link voltage caused by the MPPT. To improve the performance of the ISMC, the authors propose a direct duty ratio control-based variable step size perturb and observe (P&O) MPPT algorithm for reducing the oscillations in the dc-link voltage. The efficacy of the proposed control scheme is verified by first simulating it using MATLAB/Simulink and then through real-time implementation on a prototype PV control setup. To evaluate the performance of this ISMC-improved adaptive P&O-based controller, its performance is compared with Lagrangian interpolation-based particle swarm optimisation MPPT, sliding mode controller and proportional–integral controller. From the comparison, it is observed that the former exhibits superior performance and suppresses the harmonic content in the grid current despite the presence of low-order harmonics in the utility grid voltage.

Implementation of Echo-State Network-Based Control for Power Quality Improvement

This paper proposes a new control algorithm for mitigation of power quality problems at the distribution level. The control algorithm is designed on the basis of echo-state network, which is a type of recurrent neural network. This technique is used to extract fundamental weight components from nonsinusoidal load currents. These weight components are used to evaluate reference grid currents and consequently generate switching logic for the voltage source converter used in the active filter. The shunt-connected active filter with the proposed control algorithm is used to overcome several current-related power quality problems and provides the load compensation. Problems such as the presence of lower order harmonics, insufficient reactive power, and load unbalancing are corrected using a shunt filter in both the power factor correction and voltage regulation modes. The proposed control algorithm is validated on a real time system which is a prototype of a shunt filter. The algorithm is tested in MATLAB using Sim Power Systems and SIMULINK and implemented on a digital signal processor.

Investigation of Line Current Harmonics in Cascaded Multi-level Inverter Based Induction Motor Drive and an Adaptive On-line Selective Current Harmonic Elimination Algorithm

Multilevel Inverters (MLIs) have drawn increasing attention in numerous applications, especially in drives, distributed energy resources area, utility etc. MLIs have the ability to synthesize a near sinusoidal output voltage wave with minimal Total Harmonic Distortion (THD) in low frequency switching. Even though they offer lower THD, the presence of lower order harmonics is objectionable and harmonics elimination in Multilevel Inverters (MLIs) has been receiving immense attention for the past few decades. Existing Selective Harmonic Elimination (SHE) techniques can eliminate the objectionable lower order voltage harmonics with low switching frequency by solving the Fourier non-linear transcendental equations of the output voltage. The line current harmonics has a direct role to play on the magneto-motive force and results in increase of mismatching of air-gap permeance, vibrations, acoustic noise etc. This study proposes Normalized Least Mean Squares (NLMS) algorithm based scheme to eliminate the selected dominant harmonics in load current using only the knowledge of the frequencies to be eliminated. The algorithm is simulated using MATLAB/SIMULINK tool for a three-phase VSI to eliminate the fifth and seventh harmonics. The informative simulation results verify the validity and effectiveness of the proposed algorithm. The system performance is analyzed based on the simulation results considering Total Harmonic Distortion (THD), magnitude of eliminated harmonics and frequency spectrum.

Analysis of Supply Voltage Distortion Effects on Induction Motor Operation

Many modem induction motor applications involve nonsinusoidal voltage supply. Under such operating conditions the motor performance can be seriously affected while the standard equivalent circuit is no more adequate for the motor analysis. In this paper, a modified equivalent circuit topology is introduced in order to account for the increased iron losses associated with the leakage flux and saturation in the motor, in presence of low-order harmonics in the supply waveform. This equivalent circuit allows the prediction of the motor performance under nonsinusoidal operation. The proposed results have been checked by means of an experimental setup comprising an inverter-fed 1.5 kW induction motor.