Ilsu Jeong

Dynamic Modeling and Control for SPMSMs With Internal Turn Short Fault

A dynamic model for a faulted surface-mount permanent magnet synchronous motor (SPMSM) is derived using a deformed flux model. In reflecting the internal turn short into the dynamics, the variations in inductance and back EMF term were considered. Then, the faulted model was transformed into the two synchronous dq-models: one for the positive sequence and the other for the negative sequence. Also, a torque equation, which shows the relation between the ripple and the negative sequence current, is derived. The negative sequence current should be suppressed to eliminate the torque ripple. The dual current controller is utilized for this purpose: in the dual controller, the positive and negative sequences are controlled separately in their own synchronous frames. Notch filters are utilized in each synchronous frame to extract positive or negative sequence component. Experiments were performed with an SPMSM specially designed to make an internal turn short artificially. The experimental results coincide well with the corresponding simulation results, and exhibit a strength of the dual current controller in suppressing the negative sequence current.

Sensorless Control of PMSM in a High-Speed Region Considering Iron Loss

In a very high-speed operation (≥ 50 kr/min), the iron loss is not sufficiently small to be neglected. The iron loss alters the angle and magnitudes of the back electromotive force (EMF). The resistance representing the iron loss is calculated a priori from a finite-element analysis and incorporated into a lookup table, because it is dependent on the current magnitudes. Utilizing the extended EMF method, a sensorless control method is developed for a model that takes the iron loss into account. The proposed method overcomes the angle difference in the high-speed region, and the performance is demonstrated through simulation and experimental results.

Asymmetric duty control of the dual-active-bridge DC/DC converter for single-phase distributed generators

The dual-active-bridge (DAB) and a half-bridge inverter are integrated back-to-back for a converter/inverter system. The power source is isolated by a high frequency transformer, and a 60Hz inverter is directly connected to the secondary side of the converter via DC link capacitors. Thus, the proposed converter-inverter topology greatly reduces the size and the number of parts count, while providing isolation. But, the inverter causes the DC link voltage unbalance, leading to coupled dynamics between converter and inverter. In this work, a voltage balancing algorithm and a decoupling control algorithm are derived from the average model of the DAB converter. Its usefulness is validated by experimental results.

Extended MTPA with cross coupling inductances for electrically excited synchronous motors

Electrically excited synchronous motors (EESM) are designed to have high power density for electric vehicle (EV) applications. Thus, severe nonlinearity is observed during high torque operation. The nonlinearity associated with core saturation is modeled by incorporating the cross coupling inductances which also behave nonlinearly. The analytic torque equation with the cross coupling inductances yielded good results that matched well with FEM data and experimental data. Further, an extended maximum torque per ampere (MTPA) method was proposed for the EESM model with cross coupling inductances.

Inductance Estimation of Electrically Excited Synchronous Motor via Polynomial Approximations by Least Square Method

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 Ferraris method to a quartic equation. The extended MTPA locus is compared with the experimental optimal results.

Three-port full bridge converter application as a combined charger for PHEVs

The AC charger can be combined with the DCDC converter through the three-port full bridge topology for plug-in hybrid vehicles(PHEVs). During the driving mode, the main battery supplies energy to the 14V system through the DC-DC converter. At this time, the AC charger circuit should be disconnected. Otherwise, power flows in the AC charger circuit, resulting in a high voltage destruction. In this work, a virtual isolation method is proposed that prevents current flowing into the AC charger circuit, while a normal DC-DC converter operation is taking place. To realize the proposed control method, offset phase angles are calculated. A simulation evidence supports the feasibility of the proposed scheme.

Dynamic modeling for PMSM with internal turn short fault

If the stator winding of a permanent magnet synchronous motor (PMSM) has an internal turn winding fault, the symmetries in inductance and back emf collapse. As a result, negative sequence current is generated. The faulted PMSM dynamics are derived from a deformed flux model. The dynamics are developed in positive and negative sequence synchronous frames. Experiments was conducted with a specially wound SPSMS, and the results matches reasonably with the simulation results.

Fluctuating Current Control Method for a PMSM Along Constant Torque Contours

The dc-link voltage fluctuation problem is more serious for an inverter system which utilizes a single phase ac source. As an effort to reduce the dc-link capacitance, there is a tendency to make torque oscillate in synchronism with the input power. Then, the fluctuating motor power matches the converter power. The key idea is to enforce current oscillation along a constant torque line which only affects the reactive power of the motor. In other words, the proposed method uses the motor as inductive energy storage by controlling the motor flux by the reactive current component. Analytic method for obtaining the current bounds was derived. Also, a practical recursive algorithm was proposed. Simulation and experimental results support the effectiveness of the proposed method.

Analytic Expressions of Torque and Inductances via Polynomial Approximations of Flux Linkages

Due to slotting effects and non-sinusoidal flux distribution, permanent magnet synchronous motors have relatively large torque ripples. Furthermore, core saturation, along with armature reaction, intensifies the cross coupling between d-axis and q-axis dynamics, and causes changes in the rotor flux linkage. In this paper, it is attempted to develop a closed-form analytical torque equation and inductances, which are known to be uneasy due to the above non-linearities. This approach is based on the flux linkages obtained via finite-element analysis for all current sets in an operation area. First, a flux linkage is obtained for each phase coil as the rotor rotates over one electrical period. At this time, synchronous ac currents are injected to the stator coils. Then, the resulting flux linkages appear as sinusoidal curves with harmonics. They are transformed into a synchronous dq-frame and expanded by Fourier series. Then, the Fourier coefficients, reflecting high-order flux components caused by the permeance change associated with the rotor motion, are dependent on the magnitudes of current. Second, the Fourier coefficients of the same harmonic number are collected over many current samples and interpolated by polynomial functions in dq-axis current. In the interpolation process, the coefficients are obtained through a least square method. Then, an estimate of flux linkage is reconstructed analytically using the resulting interpolations. Analytic expressions for inductances and torque are obtained by dividing or by differentiating the flux linkage estimates. The accuracy is evaluated by comparing the results from finite element method (FEM) and the experimental results.

Sensorless control for electrically energized synchronous motor based on signal injection to field winding

A sensorless algorithm was developed for electrically energized synchronous motor(ESM). It is different from the techniques for PMSM to inject a carrier signal to the rotor winding. The relation between the angle estimation error and the rectified high frequency signal was derived straightforwardly with cross coupling inductances. And we develop compensation method for cross-coupling effect, and imply several advantages of proposed method in comparison with signal injection to stator winding. This method is much robust against magnetic saturation because it is not depend on saliency of rotor. Furthermore, proposed method does not need to check polarity at standstill. The experiments and simulation were performed to demonstrate improvement of compensation of cross coupling, robustness against magnetic saturation, and full load operation. We obtained accurate estimated position angle.