Control of Asymmetric Permanent Magnet Synchronous Generator Systems

The thesis focuses on the control of asymmetric permanent magnet synchronous generator (PMSG) system, with particular reference to the suppression of its second harmonic (2h) power, DC bus voltage and torque ripples. The asymmetries include the unbalanced resistances, unbalanced inductances, and unbalanced 3-phase back-electromotive forces (EMFs). The mathematical model of the general asymmetries in the PMSG system is firstly presented. The power ripple and torque ripple due to the asymmetries without/with negative-(N-) sequence currents are then analysed in detail. It shows that there are 2h impedances in the synchronous dq-axis frame. Consequently, the N-sequence currents emerge under the conventional current proportional and integral (PI) control, which will result in undesired 2h power, DC bus voltage and torque ripples. To suppress the 2h torque resulted from the N-sequence currents, three typical methods aiming for balanced currents without N-sequence currents are reviewed, evaluated and their relationship is revealed. It shows that all these three methods are capable of suppressing the N-sequence currents as verified by experiments. However, the 2h power and DC bus voltage cannot be suppressed. To suppress the undesired 2h power and DC bus voltage, an improved power control without any sequential component decomposers under general unbalanced conditions is proposed. Its effectiveness is validated by elaborated experiments on a prototype PMSG with inherent asymmetry and deliberately introduced asymmetries. However, the 2h torque is compromised. To solve the 2h torque, power and DC bus voltage simultaneously, the compensation in parallel with the DC bus is investigated in the PMSG system with asymmetric impedances. The undesired 2h power from the PMSG is compensated by the 2h power from the compensation unit. Two topologies of the compensation unit and corresponding control methods are investigated, while the compensation effectiveness is validated by experiments. Furthermore, the compensation unit with external circuits in series with the asymmetric PMSG is investigated. By the compensation in series, the original unbalanced system is modified to a balanced system in theory. Therefore, the N-sequence currents, 2h power, DC bus voltage, and torque ripple can be naturally suppressed. The feasibility of this compensation method is verified by experiments at different speeds and load conditions, although the effectiveness may be slightly affected by the non-linearity of the compensation inductors in practice. Finally, the research of suppressing the 2h DC bus voltage and torque ripple is extended to the dual 3-phase PMSG system with one channel failed. By utilizing the windings, rectifier or inverter in the faulty channel which are still functional, three methods designated as two sets in parallel, two DC buses in parallel and N-sequence currents compensation are investigated, which require minimum extra hardware investment compared with the compensation in parallel and in series

Torque Enhancement of Dual Three-Phase PMSM by Harmonic Injection

The torque enhancement of dual three-phase permanent magnet synchronous machine (DT-PMSM) drive system by full exploitation of flux-linkage and current harmonics are comparatively studied in this paper. The torque capability of DT-PMSM is previously evaluated with strategies of harmonics utilization, i.e. Strategy-1 of 3rd harmonic utilization and Strategy-2 of 5th and 7th harmonic utilization, which can extend the torque capability by 18.2% and 9.0% respectively. However, the full exploitation of harmonics including 3rd, 5th and 7th harmonics in the dual three-phase system are not addressed. In this paper, the Strategy-3 of 3rd, 5th and 7th harmonic utilization is also included. Its corresponding harmonic current control is proposed and the average torque and harmonic torque are analyzed in detail. Based on a test rig with existing prototype DT-PMSM, the torque with Strategy-3 is increased up to 26.5%, which is superior to the previous strategies

Sensorless Control of Dual Three-Phase IPMSM Based on Frequency Adaptive Linear Extended State Observer

The sensorless control of interior permanent magnet synchronous motor (IPMSM) based on the conventional linear extended state observer (LESO) does not have sufficient capability to eliminate the steady-state position estimation error. To solve this issue, a frequency adaptive LESO (FA-LESO) is proposed to estimate the back electromotive force (BEMF) accurately. The gains of the proposed observer are designed according to the pre-designed transfer function of a second-order complex-coefficient filter, whose stability is guaranteed by the generalized Routh criterion. The linearized model of the proposed FA-LESO is established and the design guideline of the observer gains is presented. Compared with the conventional LESO, the proposed FA-LESO can eliminate the steady-state position estimation error without any phase compensation. Meanwhile, it exhibits better high-frequency noise immunity without additional filters being required. The feasibility and effectiveness of the proposed FA-LESO are verified by the comparative experiments on a dual three-phase IPMSM platform

Flux-Weakening Control of Dual Three-Phase PMSM Based on Vector Space Decomposition Control

This paper proposes a flux-weakening (FW) control for dual three-phase ermanent magnet synchronous machine (DT-PMSM) based on vector space decomposition (VSD) control, where the output voltage in αβ sub-plane is employed for voltage feedback in the flux-weakening control loop. As the fundamental components are mapped to αβ sub-plane while the 5th and 7th harmonics are projected to harmonic z1z2 sub-plane, the flux-weakening current from this new control in αβ sub-plane is sixth harmonic-free regardless of the 5th and 7th harmonics being resulted from the non-sinusoidal back EMF or inverter non-linearity. The proposed control is compared with the conventional FW feedback control extended for DT-PMSM, where the FW control is applied to the two sets of three-phase windings separately. The experimental results show that the proposed FW control based on VSD is superior to the conventional FW control in terms of reduction in current unbalance and harmonic currents

Current Control for Dual Three-Phase Permanent Magnet Synchronous Motors Accounting for Current Unbalance and Harmonics

Personal use of this material is permitted. Permission from IEEE must be obtained for all other uses, in any current or future media, including reprinting/republishing this material for advertising or promotional purposes, creating new collective works, for resale or redistribution to servers or lists, or reuse of any copyrighted component of this work in other works.© 2014 IEEE.This paper proposes an improved vector space decomposition current control scheme for dual three-phase permanent magnet (PM) synchronous motors having two sets of three-phase windings spatially shifted by 30° electrical degrees. A proportional-integral (PI) and resonant (second) controller is developed for eliminating the current unbalance in αβ subplane, which is effective irrespective of the degree of current unbalance, while PI plus multifrequency resonant (second and sixth) control is employed to eliminate the current unbalance, fifth and seventh current harmonics in z1z2 subplane. Compared with existing methods only accounting for current unbalance in z1z2 subplane, the proposed method has considered the current unbalances in both z1z2 and αβ subplanes and can eliminate them simultaneously at the steady-state of operation. Consequently, the full compensation of current unbalance can be achieved, by which both the current unbalance between two sets and current unbalance between phase windings in each set are eliminated. Meanwhile, the fifth and seventh current harmonics caused by nonsinusoidal back electromotive force and inverter nonlinearity can also be fully compensated. The effectiveness of proposed method is verified by a set of comparative experiments on a prototype dual three-phase PM machine system. It shows that fully balanced currents without the fifth and seventh current harmonics at the steady state of operation can be achieved

Low-carbon Design Principles and Operational Strategies for Concrete Substation Buildings

As the economy continues to advance, and the populace's demand for material well-being grows, urban areas are witnessing an increasing need for electricity supply. Substations, playing a pivotal role in the power industry, are proliferating in terms of both quantity and construction scale. Reinforced concrete substation buildings are a common infrastructure that provides a suitable physical environment for the operation of power equipment. A thorough examination and analysis conducted through on-site investigations have unveiled deficiencies in the low-carbon design and operation of substation buildings, resulting in energy wastage and extra carbon emissions. Consequently, this study endeavors to introduce a method for calculating carbon emissions during the operational phase of reinforced concrete structure substations. It also presents corresponding strategies for low-carbon design and operation. These strategies encompass low-carbon design principles for the building envelope structure, the utilization of renewable energy, low-carbon design considerations for artificial lighting, and the implementation of intelligent environmental control systems. The strategies proposed in this research provide valuable ideas for making the power and construction industries more environmentally friendly and energy-efficient

Current control for dual three-phase permanent magnet synchronous motors accounting for current unbalance and harmonics

© 2014 IEEE.This paper proposes an improved vector space decomposition current control scheme for dual three-phase permanent magnet (PM) synchronous motors having two sets of three-phase windings spatially shifted by 30° electrical degrees. A proportional-integral (PI) and resonant (second) controller is developed for eliminating the current unbalance in αβ subplane, which is effective irrespective of the degree of current unbalance, while PI plus multifrequency resonant (second and sixth) control is employed to eliminate the current unbalance, fifth and seventh current harmonics in z1z2 subplane. Compared with existing methods only accounting for current unbalance in z1z2 subplane, the proposed method has considered the current unbalances in both z1z2 and αβ subplanes and can eliminate them simultaneously at the steady-state of operation. Consequently, the full compensation of current unbalance can be achieved, by which both the current unbalance between two sets and current unbalance between phase windings in each set are eliminated. Meanwhile, the fifth and seventh current harmonics caused by nonsinusoidal back electromotive force and inverter nonlinearity can also be fully compensated. The effectiveness of proposed method is verified by a set of comparative experiments on a prototype dual three-phase PM machine system. It shows that fully balanced currents without the fifth and seventh current harmonics at the steady state of operation can be achieved

Predictive Torque and Stator Flux Control for N*3-phase PMSM Drives with Parameter Robustness Improvement

In this study, a novel predictive torque and stator flux control (PTSF) method is proposed for N-segment three-phase PMSM (N*3-phase PMSM), which can effectively eliminate the influence of parameter mismatch on stator flux and torque. The proposed PTSF method has two loops, stator flux loop and torque loop, both implemented with robust predictive control algorithm. First, the stator flux predictive controller with parameter robustness is designed, and the sensitivity of its parameters is analyzed. In the dq stator flux space, the robust stator flux predictive control with one-step delay compensation is then proposed, which can effectively enhance robustness against parameters mismatch. Moreover, the robust torque predictive control based on unknown torque disturbance observer is developed, which can effectively strengthen the robustness against the load torque disturbance and parameter mismatch. Finally, the validity and feasibility of proposed PTSF method are verified by simulation and experiment. Excellent simulation and experimental results were achieved with respect to the stator flux tracking error, torque /flux ripple reduction, and stator current distortion over conventional predictive torque control (PTC)