Modified Reference Signal Research Articles

Minimization of total harmonic distortion in neutral point clamped multilevel inverter using grey wolf optimizer

<span lang="EN-US">The inverter has been attracting researchers for their application in renewable energy. So far, multilevel inverter is considered as low distortion class, which produces multilevel output voltage imitating a pure sine waveform. However, the needs for free distortion of output voltage have been motivating to improve multilevel pulse width modulation PWM generation method. In this paper, the modified PWM technique is proposed to reduce the voltage total harmonics distortion (THD) of multilevel inverter. This modulation technique is then applied to control a single-phase threelevel neutral point clamped multilevel inverter (NPC-MLI). Grey wolf optimizer (GWO) algorithm is utilized to generate optimal amplitude and phase shift of modified reference signal. The GWO algorithm is then compared with other optimization algorithms such as differential evolution (DE), human psychology optimization (HPO), and particle swarm optimization (PSO) to evaluate their performance in harmonic minimization. The performance of the proposed work is validated through simulation and experimentation on a prototype. The results show that the modified PWM technique optimized with GWO can reduce THD on NPC-MLI output voltage.</span>

Voltage Balancing Control of Hybrid Stacked Multicell Converters Based on Modified Phase-Shifted PWM

The hybrid stacked multicell converter (HSMC) is a competitive converter in the low-voltage high-efficiency applications. Proper modulation and voltage balancing control are important for the operation of the HSMC, which may ensure the HSMC to obtain high-quality output and low power losses. A hybrid phase-shifted PWM (PS-PWM) with the modified reference signal is developed for nine-level HSMC (9L-HSMC), and the neutral point voltage can be naturally balanced in a fundamental cycle. Based on the hybrid PS-PWM, an active voltage balancing control is put forward for the flying capacitor (FC). The voltage balancing of FC is implemented by slightly modifying the reference signals to adjust the duty cycles of the high-frequency switches symmetrically. This method does not need complex calculations, and it can be easily extended to higher level HSMC and other FC-based configurations. The simulations are carried out to validate the merits of low power losses and superior power quality. A downscale experimental platform of a 9L-HSMC is a setup to verify the effectiveness of the proposed control strategy under both the steady state and the transient states.

New Fault-Tolerant Control Strategy of Five-Phase Induction Motor with Four-Phase and Three-Phase Modes of Operation

The developed torque with minimum oscillations is one of the difficulties faced when designing drive systems. High ripple torque contents result in fluctuations and acoustic noise that impact the life of a drive system. A multiphase machine can offer a better alternative to a conventional three-phase machine in faulty situations by reducing the number of interruptions in industrial operation. This paper proposes a unique fault-tolerant control strategy for a five-phase induction motor. The paper considers a variable-voltage, variable-frequency control five-phase induction motor in one- and two-phase open circuit faults. The four-phase and three-phase operation modes for these faults are utilized with a modified voltage reference signal. The suggested remedial strategy is the method for compensating a faulty open phase of the machine through a modified reference signal. A modified voltage reference signal can be efficiently executed by a carrier-based pulse width modulation (PWM) system. A test bench for the execution of the fault-tolerant control strategy of the motor drive system is presented in detail along with the experimental results.

Robust adaptive boundary control of semilinear PDE systems using a dyadic controller

SummaryIn this paper, we describe a dyadic adaptive control framework for output tracking in a class of semilinear systems of partial differential equations with boundary actuation and unknown distributed nonlinearities. The dyadic adaptive control framework uses the linear terms in the system to split the plant into 2 virtual subsystems, one of which contains the nonlinearities, whereas the other contains the control input. Full‐plant‐state feedback is used to estimate the unmeasured individual states of the 2 subsystems as well as the nonlinearities. The control signal is designed to ensure that the controlled subsystem tracks a suitably modified reference signal. We prove the well posedness of the closed‐loop system rigorously and derive conditions for closed‐loop stability and robustness using finite‐gain stability theory.

A gain‐scheduled control algorithm for input constrained systems to track time‐varying references using controller state resets

In this paper, we propose a control law for a discrete‐time linear system with actuator saturation to track time‐varying reference signals. The proposed control law consists of a feedback controller and a target recalculation mechanism. The feedback controller includes an integrator to achieve zero steady‐state error in the case where the reference signal is constant. The feedback gains of the controller are parameterized by a single scheduling parameter. In the proposed control algorithm, when the tracking error is large, a modified reference signal is computed by the target recalculation mechanism so that feasibility of the algorithm and stability of the control system are guaranteed at all times. At this stage, the controller state is modified online so that the tracking control performance is improved. Further, when the tracking error becomes small, the scheduling parameter and the controller state are updated simultaneously so that the tracking control performance is improved. The problems of determining the scheduling parameter, the controller state, and the modified reference signal are reduced to convex optimization problems with linear matrix inequality constraints. The effectiveness of the proposed control method is shown through an experiment. © 2016 Institute of Electrical Engineers of Japan. Published by John Wiley & Sons, Inc.

3D Non-destructive Imaging of Punctures in Polyethylene Composite Armor by THz Time Domain Spectroscopy

An ultra-high molecular weight polyethylene composite sample totally punctured by a projectile was examined by THz TDS raster scanning method in reflection configuration. The scanning results correctly match the distribution of delaminations inside the sample, which was proven with cross-sectional and frontal views after waterjet cutting. For further analysis, a signal-processing algorithm based on the deconvolution method was developed and the modified reference signal was used to reduce disturbances. The complex refractive index of the sample was determined by transmission TDS technique and was later used for the simulation of pulse propagation by the finite difference time domain method. These simulations verified the correctness of the proposed method and showed its constraints. Using the proposed algorithm, the ambiguous raw THz image was converted into a binary 3D image of the sample, which consists only of two areas: sample—polyethylene and delamination—air. As a result, a clear image of the distribution of delaminations with their spatial extent was obtained which can be used for further comparative analysis. The limitation of the proposed method is that parts of the central area of the puncture cannot be analyzed because tilted layers deflect the incident signal.

On reference governor in iterative learning control for dynamic systems with input saturation

Input saturation is inevitable in many engineering applications. Most existing iterative learning control (ILC) algorithms that can deal with input saturation require that the reference signal is realizable within the saturation bound. For engineering systems without precise models, it is hard to verify this requirement. In this note, a “reference governor” (RG) is introduced and is incorporated with the available ILC algorithms (primary ILC algorithms). The role of the RG is to re-design the reference signal so that the modified reference signal is realizable. Two types of the RG are proposed: one modifies the amplitude of the reference signal and the other modifies the frequency. Our main results provide design guidelines for two RGs. Moreover, a design trade-off between the convergence speed and tracking performance is also discussed. A simple simulation result verifies the effectiveness of the proposed methods.

Linearization of the Multi-Level SVPWM Signal Generation in the Over-Modulation Region Extending up to Six-Step Mode Using Only the Sampled Amplitudes of Reference Phase Voltages

A multi-level PWM signal generation with linear transfer characteristics between fundamental component of output voltage and modulation index is proposed in this paper for a n-level SVPWM signal generation. The reference signal to the PWM modulator is pre-scaled in over-modulation region, keeping the fundamental component of the modified signals same as the original signal. The modified reference signal is always confined within the carrier region. Thus linear transfer characteristics can be extended throughout the over-modulation region up to six-step mode to get the maximum utilization of DC link, for multi-level inverter drive control of any general n-level. In this paper, the principle of pre-scaling the reference signal, based on a look up table, for two-level PWM generation is extended to a general n-level SVPWM. The whole PWM signal generation is implemented using only the sampled amplitudes of reference phase voltages and the algorithm is very suitable for real time implementation on DSP processors. A five-level inverter configuration, using an open-end winding induction motor drive, is used for verifying the SVPWM generation scheme, experimentally.

Range migration algorithm for airborne squint mode spotlight SAR imaging

Since the reference signal based on the fixed reference range is used in the range migration algorithm (RMA), the RMA is not available to process an airborne squint-mode spotlight synthetic aperture radar (SAR) data. Thus, the modified reference signal to transform a squint-mode data to a broadside-mode data is introduced on the basis of the coordinate transformation and the extended Taylor approximation. Then, using the principle of the stationary phase, the presented formulation is analysed. Moreover, to compensate curvature errors, the proposed method is extended on the basis of the subarea technique. Finally, the effectiveness of the proposed method is demonstrated by some numerical simulations via a pulsed spotlight SAR simulator.

Compensated synchronous PI current controller in overmodulation range and six-step operation of space-vector-modulation-based vector-controlled drives

Overmodulation enhances the power utilization of the installed capacity of a voltage-source inverter. A space-vector strategy is used for constant-switching-frequency inverters. In order to achieve the overmodulation, a modified reference signal with nonuniform angular velocity is generated using a preprocessor. Such a reference wave produces low-frequency harmonics in currents. The presence of current harmonics restricts the bandwidth of the synchronous proportional plus integral current controller in the overmodulation range. A compensating current control is presented to allow for high-bandwidth current control in synchronous coordinates during overmodulation and six-step. The proposed scheme allows for an easy upgrade of a conventional vector control scheme to include overmodulation and, thus, reduce the design-to-market time.

Modification of the reference signal for fast convergence in LMS-based adaptive equalizers

In adaptive equalizers based on least mean squares (LMS) algorithms, the convergence rate is determined by the correlation matrix of an input signal. When the eigenvalue spread of the correlation matrix is close to unity, the convergence rate is quite fast. In this paper, for fast convergence of LMS-based adaptive equalizers we propose a modified reference signal pertinent to the given statistical channel. From the theoretical analysis and computer simulations, it is shown that the proposed modification method is guile effective for fast convergence of LMS-based adaptive equalizers. >

Method of controlling strainer screw press used in food industry using error signal, generated by comparing screw press motor current with modified reference signal to regulate tamper motor current : Sket Schwermasch MA GB 2242-042; 18 September 1991

Method of controlling strainer screw press used in food industry using error signal, generated by comparing screw press motor current with modified reference signal to regulate tamper motor current : Sket Schwermasch MA GB 2242-042; 18 September 1991