Muhammad Ali Masood Cheema

Modified direct thrust control of linear permanent magnet motors with sensorless speed estimation

A modified direct thrust control of linear permanent magnet motor with sensorless estimation of mover position and speed is presented. The improved direct thrust control is based on decoupled control of thrust and flux in the stator flux frame using space vector modulation. The thrust regulation loop in the stator flux reference frame is developed using a linearized relation between thrust and load angle. The thrust and flux errors are used as inputs to two PI controllers to generate the orthogonal components of the reference voltage in the stator flux reference frame. These orthogonal components are further converted to stationary frame of reference by using the stator flux vector angle so that required voltage vector can be generated using space vector modulation instead of the conventional switching table. This scheme retains all the inherited advantages of classical direct thrust control. In this research the flux vector angular position and the mover speed is estimated from the orthogonal components of stator flux vector without using any position or speed sensor. The proposed approach is experimentally validated by its application to a prototype linear permanent magnet motor drive system in the laboratory. Practical results prove that excellent thrust and flux response with minimized ripple is achieved by the proposed technique. These practical results also demonstrate the effectiveness of sensorless position and speed estimation. Moreover a constant switching frequency is achieved due to space vector modulation.

A Direct Thrust Control Scheme for Linear Permanent Magnet Synchronous Motor Based on Online Duty Ratio Control

Linear permanent magnet synchronous motors, especially those with low inductance and short pole pitch, exhibit significant ripple in flux and thrust force under conventional direct thrust force control. Aimed at reducing ripple in the flux and the force, a duty ratio control scheme for direct thrust force control of linear permanent magnet synchronous motors is proposed. The effect of inverter voltage vectors on the flux and the thrust force is analyzed. Subsequently, a precise expression for the online computation of the required duty ratio is derived. Compared to the state-of-the-art duty ratio control, the proposed approach eliminates the need to tune gains. The proposed online duty ratio calculation is based on the selected voltage vector from the switching table and takes into account the movers speed. The proposed approach retains the characteristics of the conventional direct thrust control in terms of fast transient and steady-state responses for both flux and thrust force. Experimental results demonstrate a faster transient response and negligible steady-state error for flux, force, and speed responses under the proposed approach when compared to the state of the art.

A Practical Approach for the Global Optimization of Electromagnetic Design of 3-Phase Core-Type Distribution Transformer Allowing for Capitalization of Losses

A new approach which integrates multiple nonlinear constrained optimization algorithms in conjunction with an improved heuristic algorithm is presented. The approach includes capitalization of losses in the global design optimization process of three-phase oil-immersed distribution transformers. In addition, the proposed technique incorporates finite element-based electromagnetic analysis for losses, short circuit impedance and forces, in order to assess the globally optimum design produced by the approach against design specifications. We present practical results from a range of distribution transformers designed using existing techniques and the new approach. The practical results demonstrate the significant improvements in design when compared with existing techniques.

A Novel Approach to Investigate the Quantitative Impact of Harmonic Currents on Winding Losses and Short Circuit Forces in a Furnace Transformer

A novel approach based on the finite element method is proposed to calculate accurately the winding losses and short circuit forces caused by harmonic currents in a furnace transformer. The technique derives the appropriate partial differential equation required to determine the harmonic currents. The technique is validated by its application to a benchmark furnace transformer where experimental results demonstrate the accuracy of the developed technique. The contribution of harmonic currents to winding losses is shown to be significant in the benchmark furnace transformer, whereas the contribution of harmonic currents to short-circuit forces is limited.

Sensorless control of linear permanent magnet synchronous motors using a combined sliding mode adaptive observer

A novel combined sliding mode adaptive observer for flux and speed estimation of direct thrust controlled surface mounted Linear Permanent Magnet Synchronous Motor (LPMSM) without using position sensors is proposed. The observer comprises a linear state observer combined with a novel nonlinear sliding mode component. The sliding mode component is improved by using two boundary layers which reduce the chattering without compromising the robustness. The novel observer is experimentally validated. The flux, speed and position estimation errors are small resulting in reliable observer performance.

A Linear Quadratic Regulator-Based Optimal Direct Thrust Force Control of Linear Permanent-Magnet Synchronous Motor

Linear permanent-magnet machines are often characterized by low inductance and short pole-pitch which leads to a small operational range of load angles. The resultant control performance using conventional direct thrust force control (DTFC) techniques is poor with high force ripple. This research improves this aspect of DTFC. A novel multiple-input multiple-output (MIMO) state-space model, independent of the movers speed, having stator flux and thrust force as states, is formulated for the linear permanent-magnet synchronous motor (PMSM). An optimal linear state feedback control scheme is then designed using the optimal linear quadratic regulator technique. Integral action is added to the designed control scheme by state augmentation to minimize the steady-state error and reduce the force ripple. Experimental results clearly prove that the proposed optimal control scheme results in a faster transient response of speed and force with improved steady-state regulation of force and flux when compared to the state of the art.

Combined Speed and Direct Thrust Force Control of Linear Permanent-Magnet Synchronous Motors With Sensorless Speed Estimation Using a Sliding-Mode Control With Integral Action

A sliding-mode-based control scheme with integral action for combined speed and direct thrust force control of a linear permanent-magnet synchronous motor is proposed. A nonlinear state-space model for the combined dynamics of speed and thrust force as system states is utilized for the synthesis of the sliding-mode control law. Direct integral action is also included in the control law to eliminate the steady-state error in the speed tracking. The sensorless speed estimation is performed by using an adaptive flux observer with a modified dual boundary layer sliding-mode component. Lyapunov stability analysis to prove the global asymptotic stabilities of both the controller and observer is provided. The effectiveness of the proposed method is validated experimentally and demonstrates excellent transient and steady-state speed control performance.

Optimal, Combined Speed, and Direct Thrust Control of Linear Permanent Magnet Synchronous Motors

An optimal control scheme synthesized using a linear quadratic regulator-based approach for combined speed and direct thrust force control of permanent magnet synchronous motor (PMSM) is proposed. A novel multiple-input-multiple-output state space model, having stator flux, thrust force, and movers speed as states, is formulated for the linear PMSM where the state transition matrix is independent of movers speed. An optimal linear state feedback control scheme is designed using the optimal linear quadratic regulator technique. Integral action is added to the designed control scheme by state augmentation to minimize the steady-state error. Experimental results clearly prove that the proposed optimal control scheme results in a faster transient response of speed and force with improved steady-state regulation of force and flux when compared with the state of the art.

Detailed Analytical Modeling of Fractional-Slot Concentrated-Wound Interior Permanent Magnet Machines for Prediction of Torque Ripple

Electromagnetic torque in interior permanent magnet machines is a function of their inductances and permanent magnet (PM) flux linkages, which are assumed sinusoidal in the standard dq model of the machine. This assumption is flawed when a fractional-slot concentrated-wound stator is utilized, because its nonsinusoidal winding function leads to harmonics in the machine parameters. In order to address this deficiency, the nonsinusoidal machine parameters are modeled in this paper, based on which, a modified extended dq model is proposed. The harmonics in the machine parameters are included in the proposed modified extended dq model and their effects on the machine operational characteristics are accounted for. Detailed equations for the average torque and torque ripple are then derived based on the proposed modified extended dq model. Experimental tests are also described for the measurement of the proposed modified extended dq model parameters. The estimated torque and torque ripple by the proposed model are validated through experimental tests on a prototype fractional-slot concentrated-wound interior permanent magnet machine.

Detailed analytical modelling of fractional-slot concentrated-wound interior permanent magnet machines for prediction of torque ripple

The standard dq model of interior permanent magnet machines is based on the assumption of sinusoidal machine parameters. This assumption is flawed especially when a fractional-slot concentrated-wound stator is utilized. In order to address this deficiency, in this paper the non-sinusoidal machine parameters are modelled in the abc-system. An extended dq-model is then proposed based on the derived non-sinusoidal machine parameters. New parameters are introduced in the proposed model and experimental tests are described for their determination. Based on the proposed extended dq-model, detailed equations for the average torque and torque ripple are proposed that specify the parameters involved in the production of different torque components. The proposed extended dq-model is used to predict the performance of a prototype fractional-slot concentrated-wound interior permanent magnet machine.