Minimization of torque ripple and flux droop using optimal DTC switching and sector rotation strategy

Direct Torque Control (DTC) is a well-known AC control scheme for its robustness and simplicity. Although DTC provides excellent dynamic torque control performance, but it has several drawbacks. The digital implementation of the hysteresis band controller, which causes a delay action, may result in huge ripple and switching frequency inconsistency for DTC torque performance. Since the torque slope is already disturbed in the hysteresis bandwidth in various operating conditions, the limiting voltage vector of the two-level inverter in the conventional DTC limits the control switching frequency in the hysteresis controller. Another drawback of conventional DTC is that the presence of voltage drop in a stator resistance at low operating speeds causes a droop in stator flux performance. This problem occurs as the voltage vectors deviate from the usual state, where it manifests itself as a change in the boundary sector of the circular flux locus. Therefore, an optimal DTC switching strategy and an optimal DTC sector rotation strategy to overcome the problems in a three-phase induction motor have been proposed. A five-level cascaded H-bridge (CHB) inverter was used in the optimal DTC switching strategy because it had many voltage vectors and could be used for a variety of speed operations. Its objectives were to propose the optimal switching vector in minimizing torque ripple and controlling switching frequency at the steady-state of various speed operations. A modification torque error status and a look-up table of a five-level CHB inverter were used to implement the specified optimal voltage vectors. Another objective was to formulate and evaluate the optimal DTC sector rotation strategy that can reduce stator flux droop in the variation of torque and speed in steady-state and dynamic response. The optimal sector rotation strategy is determined using an analytical model of shifted angle that incorporates speed and torque variables which is dynamically tuned. Both proposed strategies were compared with conventional method and verified through simulation and experimentation works. MATLAB/Simulink software is used to simulate the proposed strategies while a complete setup system consists of a DS1104 digital signal processor (DSP)-board (to implement the DTC algorithm), Field-programmable Gate Arrays (FPGA) (to implement the blanking circuit), two-level and five-level (CHB) inverter circuit, gate driver circuit, and a 1.1 kW induction motor with 2 kW DC generator as a load is developed for testing and verification purpose. A compromise between simulation and experimentation works resulted in significant improvements; 1) a reduction of torque ripple up to 50% and a reduction of switching frequency up to 40%, 2) an ability to maintain a similar magnitude of stator flux by eliminating the droops. In conclusion, the method introduced demonstrates the effectiveness of DTC performance which maintains its simple structure as well as offers ease in modification for a desired control purpose

The simulation analysis of stator flux droop minimization in direct torque control open-end winding induction machine

Direct torque control (DTC) using dual-inverter technique is one of the best topologies for electric vehicle (EV) as it offers abundant selection of voltage vectors to drive the induction machine (IM). This dual-inverter technique also more reassuring as the system still workable even any of its voltage supply is disrupted or the power pack is drained. However, during the uneven voltage supply, the movement of voltage vectors is interrupted and will move obliquely especially in medium voltage vectors. This situation will lead to the faulty movement of the voltage vectors in the default sector definitions and lead to huge flux droop, which later could impose to distort phase current. This paper proposes an optimal sector definition based on the preset voltage ratio between the two inverters. The voltage vectors can be mapped tangentially to the flux vector, minimizing the flux droop and improving the phase current waveform when the proposed sector is utilized. The effectiveness of the proposed sector is tested using MATLAB/Simulink software and the exact parameter from the induction machine

Analysis Of Multiphase Transformer Supplying A Static And Dynamic Load

Transformers are able to step up or step down an output voltage from their input. It also can be used to directly supply an electrical motor when a constant frequency operation is required. Here, the research is focusing on designing a three-to-five phase transformer that acts as static phase converters for supplying a balance five-phase load. The designing process of the transformer is described based on the graphical phasor diagram that is flexible and easy to be implemented. At the end, the performances of the designed transformer are evaluated using a static and dynamic load. The designed three-to-five phase transformer is able to maintain a balance five phase voltage for several type and level of load as shown in experimental result

Concurrent material selection of natural fibre filament for fused deposition modeling using integration of analytic hierarchy process/analytic network process

The employment of natural fibres in fused deposition modeling has raised much attention from researchers in finding a suitable formulation for the natural fibre composite filaments. Moreover, selection of suitable natural fibres for fused deposition modeling should be performed before the development of the composites. It could not be performed without identifying selection criteria that comprehend both materials and fused deposition modeling process requirements. Therefore, in this study, integration of the Analytic Hierarchy Process (AHP)/ Analytic Network Process (ANP) has been introduced in selecting the natural fibres based in different clusters of selection concurrently. The selection process has been performed based on the interdependency among the selection criteria. Pairwise comparison matrices are constructed based on AHP’s hierarchical model and super matrices are constructed based on the ANP’s network model. As a result, flax fibre has ranked at the top of the selection by scored 19.5% from the overall evaluation. Flax fibre has excellent material properties and been found in various natural fibre composite applications. Further investigation is needed to study the compatibility of this fibre to be reinforced with a thermoplastic polymer matrix to develop a resultant natural fibre composite filament for fused deposition modeling

Design And Analysis Of Bearingless Permanent Magnet Synchronous Motor

Bearingless permanent magnet synchronous motor (BPMSM) has the characteristic of both conventional permanent magnet synchronous motor and traditional magnetic bearings. In this paper, the design and analysis of BPMSM by using Matlab/Simulink and ANSYS Maxwell are presented. The principle of electromagnetic force is utilized to ensure a stable levitation operation of BPMSM. The BPMSM mathematical model that has established to represent the dynamic of motoring force and radial suspension force is simulated in Matlab/Simulink environment. The ANSYS Maxwell, as an accurate finite element method (FEM) software in solving static, frequency-domain, and time-varying electromagnetic and electric fields is used to assist the development of BPMSM model before the integration with the control system is performed. The excitation of motoring winding and suspension winding are independently controlled through separate PI controller. The applications of BPMSM are suitable for high speed electrical machines such as compressors, turbines, pumps, and mixers

An investigation of flux characteristic in direct torque control using sector rotation strategy

Stator flux fails to regulate at low operating speed condition is a common drawback for the conventional direct torque control (DTC). It is due to the inevitable of zero-voltage vector demagnetization that interrupts the controlling of stator flux in DTC. Hence, a fixed sector rotation strategy is one of the solutions to rectify the raised issue. The strategy is based on the decreasing stator flux droop, which is an easy technique to change the sector of flux locus at a specific angle. However, this strategy only focuses at low operating speed. Thus, the stator flux droop effect at the various speed needs to be analysed. In this paper, an investigation is conducted by using simulation (MATLAB/Simulink) and experimental setup (dSPACE board) where a good agreement has been achieved between the predicted and measured results. The analysis taking into account between the conventional method (without strategy) and the proposed method (with strategy). In conclusion, the influence of stator flux droop is inversely proportional to the operating speed

Bearingless Permanent Magnet Synchronous Motor using Independent Control

Bearingless permanent magnet synchronous motor (BPMSM) combines the characteristic of the conventional permanent magent synchronous motor and magnetic bearing in one electric motor. BPMSM is a kind of high performance motor due to having both advantages of PMSM and magnetic bearing with simple structure, high efficiency, and reasonable cost. The research on BPMSM is to design and analyse BPMSM by using Maxwell 2-Dimensional of ANSYS Finite Element Method (FEM). Independent suspension force model and bearingless PMSM model are developed by using the method of suspension force. Then, the mathematical model of electromagnetic torque and radial suspension force has been developed by using Matlab/Simulink. The relation between force, current, distance and other parameter are determined. This research covered the principle of suspension force, the mathematical model, FEM analysis and digital control system of bearingless PMSM. This kind of motor is widely used in high speed application such as compressors, pumps and turbines