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2. PWM strategies fo multilevel multiphase AC drives

Author

Dordevic, Obrad

Subjects
621.3133, TK Electrical engineering. Electronics. Nuclear engineering
Abstract

Pulse width modulation (PWM) strategies for multilevel multiphase ac drives have been analysed in this thesis. The large amount of published work in the area of multiphase drives recognises their advantages compared to the standard three-phase solutions. Some of them arc improved power sharing capabilities, increased reliability and fault tolerance. However, in the most of these works two-level inverters were used for supply of multiphase machine. Also, huge amount of research has been done in the area of multi level inverters. Nowadays, three-phase multilevel inverters are in use in high-power applications. However. the ideal scenario for high-power applications is supply of a multi phase machine from the multilevel inverters. So far no negative consequences of combination of these two topologies, apart from increased complexity of the system, have been identified, and this topology is the subject of this thesis.

Published
2013
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4. Memory-Based Model Predictive Control for Parameter Detuning in Multiphase Electric Machines

Author

Gonzalez-Prieto, Angel, Gonzalez-Prieto, Ignacio, Dordevic, Obrad, Aciego, Juan Jose, Montenegro, Jorge, Duran, Mario Javier, and Khan, Mohammad Umar

Abstract

Model predictive control (MPC) is a popular control technique to regulate multiphase electric drives (EDs). Despite the well-known advantages of MPC, it is sensitive to parameter detuning and lacks the capability to eliminate steady-state errors. The appearance of an offset between the reference and measured currents can significantly jeopardize the performance of the ED. This article suggests the use of a memory-based model predictive control (MB-MPC) that activates a compensation term when the parameter mismatch is detected. The suggested MB-MPC is universal for any multiphase machine if spatial harmonics are neglected since the proposed method does not consider any of the secondary x–y planes. Experimental results in two different rigs with six- and nine-phase induction motors prove this universality as well as its capability to eliminate current and speed offsets.

Published
2024
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11. DC‐link low‐frequency current and voltage ripple analysis in multiphase voltage source inverters with unbalanced load.

Author

Vujacic, Marija, Dordevic, Obrad, Mandrioli, Riccardo, and Grandi, Gabriele

Subjects
*PULSE width modulation inverters, *IDEAL sources (Electric circuits), *SWITCHING circuits, *MECHANICAL loads, *IMPEDANCE control
Abstract

Inverter's performance and operating mode may be negatively affected by inverter input (dc‐link) current and voltage ripple. It is a common experience that even theoretically balanced loads with perfectly balanced supply voltages, such as multiphase ac motors supplied by pulse‐width modulation (PWM) inverters, in practice show a certain degree of current unbalance, in the range of a few percent, which introduces a low‐frequency instantaneous power oscillation. This reflects in current and voltage low‐frequency ripple on the dc‐link inverter side (i.e. at the double‐fundamental frequency). A possible method to analyse this matter is through the symmetric sequence components. In particular, based on the first negative current sequence component and by considering the equivalent dc‐link impedance calculated at the dominant double‐fundamental frequency, the amplitude of the corresponding dc‐link voltage ripple component is calculated in this work for a general multiphase load. Finally, the design of the dc‐link capacitor in multiphase inverters is proposed considering requirements referred to the double‐fundamental dc voltage ripple. The feasibility of the proposed developments has been verified for three‐, five‐ and seven‐phase inverters by both numerical simulations and comprehensive experimental tests, always showing a good matching. [ABSTRACT FROM AUTHOR]

Published
2022
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26. Regenerative Test for Multiple Three-Phase Machines With Even Number of Neutral Points.

Author

Abduallah, Ahmad Anad, Dordevic, Obrad, Jones, Martin, and Levi, Emil

Subjects
*MACHINING, *VECTOR spaces, *LOADERS (Machines), *INDUCTION machinery, *THERMAL efficiency, *COMPRESSOR blades, *TESTING
Abstract

Testing the high-power machines in general is not an easy task. One of the standard tests is the full-load test. This test typically requires another machine, of the same or higher power rating, to be coupled to the tested one. For multiphase machines, which are commonly designed for high-power applications, this test can be conducted in a different way. In order to simplify full-load test, this paper proposes a new method that is applicable for multiple three-phase machines with even number of neutral points. The method is based on indirect rotor-field oriented control. It enables evaluation of the efficiency and the thermal design in the case of synchronous machines and the segregation of the constant and stator variable losses for induction machines, without the need for coupling another machine as a load. In the presented method, the full-load test conditions on the stator are obtained by circulating the rated active power flow in a closed loop from one winding set to another. The only power used during the test is to cover machine and converter losses. The proposed control scheme is unique and is based around y-component from the vector space decomposition subspace. It is validated through the simulation and experimental results. [ABSTRACT FROM AUTHOR]

Published
2020
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38. Evaluation of DC-link Voltage Ripple in Seven-Phase PWM Voltage Source Inverters

Author

Marija Vujacic, Obrad Dordevic, Gabriele Grandi, IEEE, Vujacic, Marija, Dordevic, Obrad, and Grandi, Gabriele

Subjects
Physics, 020208 electrical & electronic engineering, Ripple, Modulation index, 020302 automobile design & engineering, 02 engineering and technology, AC motor, law.invention, Capacitor, 0203 mechanical engineering, law, Control theory, Voltage Ripple, multiphase inverters, pulse width modulation, space vector modulation, dc-link harmonics, 0202 electrical engineering, electronic engineering, information engineering, Voltage source, Pulse-width modulation, Space vector modulation, Voltage
Abstract

The analysis of dc-link inverter current and voltage ripple is important for the optimization of the input components, mainly the dc-link capacitor. In this paper reference is made to two-level seven-phase PWM voltage source inverters with balanced load, typically multiphase ac motor. The peak-to-peak amplitude of the dc-link voltage switching ripple within the fundamental period is analytically determined as a function of operating conditions: modulation index, output currents amplitude and phase angle. The maximum of voltage switching ripple is also derived in order to help with choice of the dc-link capacitor. The two most popular inverter modulation techniques are considered: sinusoidal PWM and centered PWM (CPWM, equivalent to space vector modulation, SVM). A comparison between them is made in terms of the dc voltage switching ripple envelope. Numerical simulations are carried out by Matlab/Simulink in order to verify the analytical results.

Published
2018

39. DC-link low-frequency current and voltage ripple analysis in multiphase voltage source inverters with unbalanced load

Author

Marija Vujacic, Gabriele Grandi, Riccardo Mandrioli, Obrad Dordevic, Vujacic, Marija, Dordevic, Obrad, Mandrioli, Riccardo, and Grandi, Gabriele

Subjects
Applications of electric power, TK, Ripple, DC-AC power converter, AC motor, multiphase systems, voltage-source inverter, law.invention, pulse-width modulation, law, Control theory, electric motor drive, DC-bus voltage ripple, DC‐bus voltage ripple, switching circuit, Voltage source, Electrical and Electronic Engineering, Electrical impedance, Physics, DC-link capacitor, multiphase system, TK4001-4102, Capacitor, pulse‐width modulation, DC‐link capacitor, DC‐AC power converters, Inverter, Pulse-width modulation, Voltage
Abstract

Inverter's performance and operating mode may be negatively affected by inverter input (dc‐link) current and voltage ripple. It is a common experience that even theoretically balanced loads with perfectly balanced supply voltages, such as multiphase ac motors supplied by pulse‐width modulation (PWM) inverters, in practice show a certain degree of current unbalance, in the range of a few percent, which introduces a low‐frequency instantaneous power oscillation. This reflects in current and voltage low‐frequency ripple on the dc‐link inverter side (i.e. at the double‐fundamental frequency). A possible method to analyse this matter is through the symmetric sequence components. In particular, based on the first negative current sequence component and by considering the equivalent dc‐link impedance calculated at the dominant double‐fundamental frequency, the amplitude of the corresponding dc‐link voltage ripple component is calculated in this work for a general multiphase load. Finally, the design of the dc‐link capacitor in multiphase inverters is proposed considering requirements referred to the double‐fundamental dc voltage ripple. The feasibility of the proposed developments has been verified for three‐, five‐ and seven‐phase inverters by both numerical simulations and comprehensive experimental tests, always showing a good matching.

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