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An overmodulation method is proposed for an in-wheel system where two motors are coupled to a sum gear. In the dual-motor dual-inverter single shaft systems, the output voltage magnitudes of two inverters are not the same in the overmodulation range due to the angle offset between two motors. In this article, to maintain torque balance in the overmodulation region, holding vectors are defined between adjacent vertices of two voltage hexagons. Around these vectors, the holding region is also defined by the holding angle. If a reference voltage vector is in the holding region, it is modulated to the holding vector; otherwise, it is modulated to the vector on the arc of inscribed circle. For a given the modulation index (MI), the holding angle is obtained based on the Fourier series expansion. The proposed method keeps the output voltages of two inverters the same even if two motors have the angle offset. Further, it has the characteristic of maintaining the linearity between the reference and output MI to the maximum MI. The proposed overmodulation method is demonstrated by simulation and experimental results. [ABSTRACT FROM AUTHOR]

This paper presents a design strategy of an induction motor (IM) for a wide constant power speed range (CPSR). The stator inductance is a key parameter that determines a CPSR, because it affects the voltage limit and the torque simultaneously. Low inductance allows a wide CPSR under a voltage limit. However, it results in torque reduction. On the other hand, if inductance is high, the opposite results take place; high torque and narrow CPSR. Therefore, there is a tradeoff between the power level and the speed range. The classical design process does not consider the CPSR, but provides a guideline to calculate core dimensions and the winding number for a nominal operation point. Thereby, the machine inductance is determined passively. This classical procedure is not appropriate for widening the CPSR. To extend the speed range under a voltage limit, a proper inductance must be chosen in the first place. In this work, a different IM design process is pursued with the objective of widening CPSR: An optimal inductance is obtained that minimizes the maximum current under a constant power condition. In the secondary part, an IM design method is proposed, which determines the winding number and the core dimension under a given inductance. Finally, the proposed analytic design is compared with the design optimized by finite-element-analysis. Based on the design results, a real IM (130 kW, 14 000 r/min) is constructed and tested. The experimental results are in good agreement with the design data. [ABSTRACT FROM AUTHOR]

A copper-loss-minimizing torque control method is considered for wound synchronous machines (WSMs) in the field-weakening region. In general, the current-minimizing solutions are often found at the intersection of the torque and voltage curves. However, those curves change depending on the rotor field current in WSM. This complicates the problem of obtaining an analytic loss-minimizing solution. In this study, a hybrid approach is suggested: analytic method, iterative computation, and curve fitting. The Ferrari's method is repeatedly applied for each field current to find intersections between the voltage limit and torque curves. Then, a loss-minimizing current set is found at the minimum of a second-order function fitted to three Ferrari's solutions. At each step, inductance changes are reflected. In the cost function, the field-winding copper loss is included along with the stator copper loss. The results show that the total loss is minimized at a point where the power factor is slightly lower than unity. Simulations and experiments were carried out for a 60-kW WSM to show the usefulness of the algorithm. [ABSTRACT FROM PUBLISHER]

Electrically excited synchronous motors are designed to have high power density for electric vehicle applications. During a high-torque operation, severe nonlinearities associated with a saturation are observed: change of inductances, emergence of cross-coupling effects, variation of back EMF coefficient, etc. A flux linkage map over the current plane is obtained via finite-element analysis (FEA), and it is fitted by a third-order polynomial with the use of the least square method. Then, by grouping terms of the polynomial, the inductances are expressed as functions of currents. The validity of inductance fitting is shown by comparing with FEA and experimental results. This enables us to predict inductances online instead of using premade lookup table. The torque equation is expanded by incorporating the cross-coupling inductances, for which an extended maximum torque per ampere (MTPA) is developed by using Ferrari's method to a quartic equation. The extended MTPA locus is compared with the experimental optimal results. [ABSTRACT FROM PUBLISHER]