Naziha Ahmad Azli

Direct torque control of induction machines with constant switching frequency and improved stator flux estimation

Direct torque control (DTC) of induction machines is known to have a simple control structure yet has comparable performance to that of the field oriented control (FOC). To maintain this simple control structure while at the same time improving the performance of the DTC drive in terms of switching frequency and stator flux estimation, two simple techniques are proposed. The effectiveness of the proposed techniques are verified experimentally which is centered around a TMS320C31 digital signal processor.

Development of a DSP-based Fuzzy PI Controller for an Online Optimal PWM Control Scheme for a Multilevel Inverter

Previous work has presented the incorporation of a non conventional inverter topology known as multilevel inverter with an optimal PWM based control scheme for high voltage AC power supply applications. A Fuzzy Proportional Integral Controller (FPIC) takes a role in the control scheme in providing stronger control action for a large voltage error and a smoother control action for a small voltage error in the multilevel inverter output. This in turn ensures that high quality output voltage at a fixed frequency is always maintained on the inverter output while the transient response improved regardless of the loading conditions. This paper focuses mainly on the FPIC and its implementation using a digital signal processor (DSP) as part of the hardware implementation of the control scheme. A test conducted on the DSP-based FPIC operation shows response that is in good agreement to that obtained from a simulation study conducted using MATLAB/Simulink.

Design of a current mode PI controller for a single-phase PWM inverter

This paper presents the design of current mode PI controller for single-phase PWM inverter. The controller is comprised of inductor current as the inner loop and output voltage as the outer feedback loop. The control design is carried out using Sisotool, which is provided in Matlab. By using this tool, users can examine the effects of changing the gain control values to systems transient response and stability, simultaneously. Hence, simplify and speed up the control design process. To evaluate the performance of the designed controller, the inverter is simulated under several types of load disturbances. From the result, it is shown that the designed controller exhibits a good transient response i.e. fast rising and settling time with small overshoot when subjected to step load disturbance.

Application of fuzzy logic in an optimal PWM based control scheme for a multilevel inverter

Various circuit topologies and control techniques have been proposed on inverters for AC power supply applications but without much emphasis on very high power systems. Incorporation of a nonconventional inverter topology known as multilevel inverter with an optimal PWM based control scheme is proposed in this work for high voltage applications when the switching frequency of the inverter power devices is limited by the maximal power loss. A fuzzy proportional integral controller (FPIC) takes a role in the control scheme in providing stronger control action for a large voltage error and a smoother control action for a small voltage error in the multilevel inverter output. This in turn ensures that high quality output voltage at a fixed frequency is always maintained on the inverter output while the transient response improved regardless of the loading conditions. This paper focus on the development of this control scheme which is supported by some results based on a simulation study.

Sugeno-type fuzzy logic controller (SFLC) for a Modular Structured Multilevel Inverter (MSMI)

This paper presents a study on the performance of a Sugeno-type fuzzy logic controller (SFLC) as applied to a modular structured multilevel inverter (MSMI) to regulate its output voltage at a specified frequency. Simulation and analysis have been done, which includes comparison on the performance of the SFLC to that of the Mamdani-type fuzzy logic controller (MFLC), which has been conducted in a previous work. The proposed SFLC has shown good performance for closed-loop control of an MSMI during simulation using MATLAB/Simulink with higher execution speed compared to the MFLC.

Piecewise Linear Control Surface for Single Input Nonlinear PI-Fuzzy Controller

This paper presents an analysis on piecewise linear control surface for a single-input nonlinear PI Fuzzy controller. The analysis is carried out to determine the conditions that should be met in order for the piecewise linear control surface approximation to be validated. An equivalent two-input Pi-Fuzzy with conventional fuzzification, inference and deffuzification process is built for verification purpose and both controllers are then applied to a single phase inverter system. The dynamic response of both controllers are examined and compared. From the simulation results, it is shown that the approximation is valid.

Direct Torque Control with 5-level cascaded H-bridge multilevel inverter for induction machines

This paper presents a Direct Torque Control (DTC) utilizing a 5-level cascaded H-bridge multilevel inverter (CHMI) for induction machines. A multilevel hysteresis controller for flux and torque, with 12-sector stator flux angle detection and a precise look-up table for optimum vector selection is proposed to enhance DTC performances. A theoretical concept of the proposed DTC system in terms of flux and torque control and estimations and optimal voltage vector selection are studied in this work. The simulation results obtained from MATLAB/Simulink software showed that the proposed system significantly improved the DTC drive in terms of dynamic performance, smaller torque and flux ripple and lower THD.

Modular Structured Multilevel Inverter with Unified Constant-Frequency Integration Control for Active Power Filters

The increasing use of power electronics based loads in recent years has resulted in the generation of harmonic and reactive currents to the common point of coupling at which the loads are connected to. Besides the commonly used passive filters, active power filters (APFs) are gaining interest lately in canceling the reactive and harmonic currents from the nonlinear loads to ensure that the resulting total current drawn from the main incoming supply is sinusoidal. This paper presents a non-conventional inverter topology known as the Modular Structured Multilevel Inverter (MSMI) as an active power filter. With the MSMI, the harmonic content generated by the APF can be reduced as it can produce more levels of voltage than conventional inverters. Additionally, it can reduce the voltage and current ratings of the power devices used while providing the convenience for future expansion in order to achieve higher power ratings for the APF system. A Unified Constant-Frequency Integration (UCI) control technique is adopted for the MSMI APF which features constant switching frequency operation and simple analog circuitry. To demonstrate the capability of the proposed APF system, simulation results of a single-phase MSMI APF with UCI controller is presented and its performance analyzed.

Direct torque control of induction machines utilizing 3-level cascaded H-Bridge Multilevel Inverter and fuzzy logic

This paper proposes the use of a 3-level Cascaded H-Bridge Multilevel Inverter (CHMI) topology which results in further torque ripple minimization compared to the 2-level inverter-based Direct Torque Control (DTC). This is due to the increase in the inverter switching voltage vectors that allows minimization of the torque error. This in turn can reduce the Total Harmonic Distortion (THD) of the output voltage and current as well. This paper also presents two different control methods in selecting the appropriate output voltage vector for reducing the torque and flux error to zero. The first is based on the conventional DTC scheme using a pair of hysteresis comparators and look-up table to select the output voltage vector for controlling the torque and flux. The second is based on a new fuzzy logic controller (FLC) with Sugeno as its inference method to select the output voltage vector by replacing the hysteresis comparators and look-up table in the conventional DTC scheme. The latter has solved the problem of variable switching frequency which is the main characteristic of the former. By using FLC DTC not only the flux ripples reduce significantly but also the THD of the phase current decreases since a more sinusoidal current waveform is achieved. The simulation results have proven that by using the 3-level CHMI, torque ripple reduction is obtained compared to the 2-level inverter-based DTC while fuzzy DTC shows reduction in the stator flux ripples and the THD of the phase current.

A new optimum design for a single input fuzzy controller applied to DC to AC converters

In this paper, the design of an optimum single input Fuzzy controller for application in dc to ac converters is presented. Contrary to conventional Fuzzy controllers, the proposed controller has a smaller number of rules and tuning parameters but is capable of performing identically to a conventional controller. These benefits lead to a simpler controller design. The controller is designed as a PI controller for small-signal disturbances. However, for optimum large-signal performance, heuristic tuning is used. The tuning is less complicated and hence optimum large-signal performance is achievable. The system is simulated and a hardware prototype was developed for comparison purposes.