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.

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.

This paper investigates a dual three-phase permanent magnet synchronous machine supplied by two independent three-phase voltage source inverters (VSIs). Dual three-phase machines have many important advantages compared with their conventional three-phase counterparts. Instead of six-phase converters and special vector controls, it would be a very interesting alternative to supply these machines by two conventional three-phase VSIs since they are readily commercially available. This paper shows that the proposed supply method can be used successfully although it suffers from a decrease in the dynamic performance and an error in the estimation of torque. On the other hand, two independent VSIs do not cause low-frequency current harmonics and guarantee balanced current sharing between the winding sets thus avoiding the two most common problems with dual three-phase machines. Experimental results are provided to verify the conclusions. The results suggest that the simple supply method of two conventional VSIs could be a feasible alternative for many industrial applications.

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.

This paper introduces a research site for a low-voltage direct current (LVDC) distribution system. The research site was established to enable practical studies concerning different areas of the LVDC distribution. Because the LVDC distribution is a novel approach to public electricity distribution, the objective is to combine a fully functional LVDC system and a flexible research platform, where various measurements and tests can be conducted. The scope of this paper is to discuss the design, structure, functionalities, and operation of the site. Experiences of use and measurement results are provided to demonstrate the major functionalities and other important system properties. Finally, future research tasks and the development of the site towards the LVDC μGrid are presented.

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.