If the converter side dc-link current is made equal to the inverter side dc-link current in a pulsewidth modulation (PWM) converter-inverter system, no current will flow through the dc-link capacitor. As a result, no dc-link voltage variation occurs. This leads to the possibility of making a large reduction in the size of dc-link capacitors, which are expensive, bulky, and have a lifetime limit. However, a converter current control loop inherently involves a delay in supplying the required current. In this paper, a capacitor current is nullified with a feedforward compensation term. To minimize the response delay, the authors calculate the compensation amount in terms of voltage and inject it at the voltage node. In calculating the compensation term, a differentiator is incorporated with a one-step predictor developed from converter and inverter dynamics. Simulation and experiments are performed with only 40 /spl mu/F of dc-link capacitance for a 9-kW motor, and the results support the validity of the proposed scheme.

In this study, interturn short fault models of permanent magnet synchronous motors (PMSMs) employing series and parallel winding connections are developed using deformed flux models based on both fault winding flux information and inductance variations caused by cross flux linkages that depend on the distribution of same phase windings. As these models take into account fault winding within a three-phase winding dynamics analysis, they constitute fourth-order assessments. In the parallel-winding model, an additional dynamical analysis is used to describe variations in current distribution caused by the parallel connection between fault and healthy windings. Based on deformed flux modeling and positive sequence current assumptions, the proposed model is derived in both positive and negative sequence synchronous reference frames. A finite-element method-based simulation is applied to validate the proposed PMSM model.

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.

In this study, the interturn fault (ITF) models of interior permanent magnet synchronous motors (IPMSMs) employing series and parallel winding connections were developed through the addition of saliency modeling to the surface-mounted permanent magnet motor models presented in a previous work. The saliency model was obtained by using deformed flux models based on both the fault winding flux information and inductance variations caused by cross-flux linkages that depend on the distribution of same-phase windings. By assuming a balanced three-phase current injection, positive and negative sequence voltages, and the fault current are obtained in the positive and negative synchronous reference frames. The output torque models were developed by adding the magnet and reluctance torques, which were derived from the developed models. To verify the proposed IPMSM models with an ITF, a finite element method-based simulation and experimental measurements were performed; the results are presented in this paper.

This paper is a continuation of part I, which presented interturn fault (ITF) models for interior permanent magnet synchronous motors (IPMSMs). ITFs are defined by two ITF parameters: the healthy turn ratio and the fault contact resistance. First, this paper presents a proof that the two fault parameters defining a given ITF condition cannot be individually estimated from motor information and drive information (applied voltage, phase current, rotor speed, etc.) because they have multiple solutions. However, it is also shown that the additional Ohmic loss, which is the most important factor in heat generation and deterioration due to ITFs, is not dependent on these solutions. Thus, after arbitrarily setting one fault parameter, the other can be estimated for a given ITF condition; this model can be used to represent the effect of an ITF, particularly its Ohmic power loss. In this paper, an online fault parameter estimation method for IPMSMs is proposed after presenting one of the two fault parameters. The proposed method utilizes a searching algorithm that finds the fault parameter that has the minimum negative-sequence voltage error between the applied voltage and the ITF models (presented in part I). An experiment was performed to verify the proposed fault parameter estimation method.

In this paper, a new offline interturn fault (ITF) diagnosis method for induction motors is presented. The proposed method is based on impedance imbalance in the stationary d-q plane. First, to show the impedance imbalance, an induction motor model is presented with an ITF circuit loop and fault resistance. Then, six impedance components in the stationary d-q plane are defined, depending on the excited phase windings. With fast Fourier transform (FFT) filtering applied to the six impedance components in the d-q plane, the second-order impedance magnitudes are obtained. From the magnitude, the ITF and the faulty phase can easily be detected. Moreover, a specific faulty winding among the faulty phase windings can be identified. To verify the proposed method, finite-element analysis (FEA) and experimental results are presented for an induction motor having an ITF.