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Multiphase electric machines are known to have problems with stator current harmonics. The harmonics can be eliminated by various current harmonic compensation methods. However, using the active harmonic compensation can increase the required output voltage of the inverter supplying the machine. Because the maximum voltage is limited, complete elimination of the current harmonics may not always be possible. For such cases, this paper introduces a strategy for a partial compensation of the current harmonics. The aim of the proposed strategy is to provide a maximum reduction in the magnitude of the harmonics when the available voltage is limited. The strategy is verified by experimental results. [ABSTRACT FROM AUTHOR]

Multiphase electric machines can provide significant advantages over conventional three-phase machines. Unfortunately, multiphase machines also have a notable disadvantage that even a small voltage excitation of certain frequency components can cause large stator current harmonics. This paper presents an inverse-based current harmonic controller to eliminate the current harmonics. A detailed theoretical analysis of the proposed harmonic controller is given including a comprehensive set of analytical design principles. The robustness of the method is studied with a multi-input multi-output approach based on a structured singular value and H8 norm analyses. In addition to the theoretical work, the performance of the harmonic controller is investigated with experimental results from a dual three-phase permanent magnet synchronous machine (PMSM). The analysis and results of this paper show that the inverse-based current harmonic controller provides a robust and high-performance method to eliminate the current harmonics in multiphase PMSMs. [ABSTRACT FROM AUTHOR]

Dual three-phase electric machines are known to offer many important advantages compared with their conventional three-phase counterparts. However, these machines also suffer from a significant disadvantage of easily occurring large stator current harmonics. To solve this problem, this paper introduces a current harmonic elimination method based on a disturbance observer (DOB). The study provides a detailed analysis and design principles for the DOB. The performance of the proposed method is verified by experimental results. The results show that nearly complete elimination (> 99% reduction) of harmonic components is achieved. In addition, it is shown that the method is robust against uncertainties. The method provides a simple yet effective alternative for solving the issue of stator current harmonics in dual three-phase drives, and the results of this paper can be easily applied also to other multiphase machine types. [ABSTRACT FROM AUTHOR]

Accurate and updated knowledge of the electric machine parameters provides benefits in many applications, such as model-based control methods. This paper presents an online parameter estimation method for double-star interior permanent-magnet (IPM) machines supplied with voltage-source inverters (VSI). The estimation method is based on a decoupled D–Q model of the machine and a recursive least-squares (RLS) algorithm. Initial machine parameters are estimated at a standstill. Then, in the rotating operating state, the inductances and the flux linkage produced by the PMs are updated. The estimation in the operating state is performed with a flux-linkage-based approach. The experimental results are compared with the corresponding values obtained from finite-element analyses. The results show an acceptable agreement and demonstrate the feasibility of the estimation scheme to estimate the parameters of double-star PM machines. The parameters are validated by comparing experimental and simulated open-loop responses and steady-state torques. [ABSTRACT FROM PUBLISHER]

Dual three-phase electric machines have many advantages compared with conventional three-phase machines. However, the properties of such machines present challenges for current control that make it difficult to produce sufficient performance for the electric drive. This paper introduces an improved vector control scheme for dual three-phase permanent magnet synchronous machines. The study includes detailed solutions for key parts of the control such as reference frame transformations, decoupling of the current control loops, and modulation. The performance of the suggested control scheme is evaluated using finite-element analyses and experimental results. The results show that the scheme can produce desired dynamics for the current control and guarantees balanced current sharing between the winding sets. In addition, the proposed solution is capable of reducing current harmonics produced by the internal structure of the machine. This problem is, however, only partly solved since complete elimination of harmonic components is not achieved. Nevertheless, the suggested control scheme overcomes many of the disadvantages found with other control solutions. Improved control performance allows the full benefits of dual three-phase drives to be utilized even in demanding applications. [ABSTRACT FROM PUBLISHER]

Analytical models are the key tools in the model‐based control design of electric drives. The inductances together with the stator resistance are the fundamental parameters of these models. In this study three methods to determine the inductances of the decoupled d–q model of double‐star permanent‐magnet (PM) synchronous machines are studied. These methods have commonly been used to determine the inductances of conventional three‐phase PM machines. Two of the evaluated methods are based on the phase‐variable inductance waveforms and flux linkages and are thus analysed with finite‐element analyses only. The third method, based on the analytical stator voltage equations, can be applied straightforwardly with the real drive system supplied with voltage‐source inverters (VSIs). This method requires only the knowledge of the rotor position and the existing current measurements of the VSIs that are used for the current control. Experimental results are provided to verify the applicability of the voltage‐equation‐based method to determine the inductances. On the average, the presented methods provide similar values, but also some discrepancies between the obtained values can be observed. The measured inductance parameters are validated using model‐based closed‐loop controllers. [ABSTRACT FROM AUTHOR]

This paper describes a d– q transformation to be applied to double-star permanent-magnet synchronous machines with interior magnets. The d– q model consists of two d–q reference frames decoupled with respect to each other and applies to a generic angular displacement between the winding sets. The decoupled d–q model simplifies the analysis of the machine behavior and the drive control implementation. Machine parameters are determined by a sequence of finite-element (FE) analyses. The effectiveness of the proposed modeling method is verified by a comparison with the results related to measurements on a test machine and FE simulations. It was assumed that the mutual inductances between the two winding sets can be represented with two coefficients. Although such an assumption inevitably leads to inaccuracy in the machine model, the simulation results with the proposed d–q model agree remarkably well with the experimental results and FE simulations. [ABSTRACT FROM PUBLISHER]