K. D. Hoang

Influence and Compensation of Inverter Voltage Drop in Direct Torque-Controlled Four-Switch Three-Phase PM Brushless AC Drives

This paper presents direct torque control (DTC) methodology for a four-switch three-phase (FSTP) inverter-fed permanent magnet brushless ac (PM BLAC) machine, with reference to a conventional six-switch three-phase (SSTP) inverter. It has been found that when derived from conventional voltage model flux estimation scheme, the predicted stator flux imbalance may be caused by unbalanced inverter voltage drop in the FSTP inverter, in which one phase winding is directly connected to dc-link midpoint. While this imbalanced problem does not adversely affect the performance of current-model-based DTC, it causes significantly nonsinusoidal current waveforms and considerably unbalanced current magnitudes in voltage-model-based DTC. A new compensation scheme taking into account the different forward voltage-drop values in the switching device and the freewheeling diode is proposed for the voltage-model-based DTC to correct for stator flux imbalance via the addition of corrective voltages to flux equations. The proposed scheme has significantly improved the shape of current waveforms with satisfactory balanced magnitudes, total harmonic distortion, and torque ripple factor, as verified by both simulation and experimental results. It has been shown that it is possible for an FSTP inverter to provide similar performance to an SSTP inverter when driving a PM BLAC machine.

Direct torque control of three-phase PM brushless AC motor with one phase open-circuit fault

In this paper, direct torque control (DTC) of a three-phase permanent magnet (PM) brushless AC (BLAC) motor having one phase open-circuit fault is described. An extra inverter leg is employed to provide the current path during the fault operation. The new flux estimation algorithm for the faulty motor is presented. The simulation results show that the proposed DTC yields satisfactory torque and flux control. The performance of the developed system is verified by experiments on a prototype system. In addition, the influence of low pass filter, sampling time delay, as well as the unbalanced phase back-emf waveforms is investigated, while the difference in DTC performance between healthy and faulty systems is also discussed and corresponding simulated and measured results presented.

Feed-forward torque control of interior permanent magnet brushless AC drive for traction applications

This paper presents a feed-forward torque control (FTC) technique for interior permanent magnet (IPM) brushless AC (BLAC) drives in traction applications. It is shown that by adopting the Newton-Raphson iterative method for solving the proposed high-order nonlinear relationship between the torque demand, flux-linkage and desirable dq-axis currents, FTC with due account of nonlinear machine parameters can be achieved for IPM BLAC drives. It is also proven that the comparison between the reference voltage magnitudes under maximum torque per ampere (MTPA) and field-weakening (FW) operations together with online base speed determination can be utilized for FW operation activation to achieve full exploitation of the available DC-link voltage during the transition between the constant torque and FW operation regions. Since both the dq-axis current references and the base speed for FW operation activation are computed online, the proposed FTC technique provides flexibility for online parameter update or estimation and is able to cope with wide DC-link voltage variation. The proposed FTC strategy is experimentally validated by measurements on a 10kW wide constant power speed range (CPSR) IPM BLAC machine drive.

Online Control of IPMSM Drives for Traction Applications Considering Machine Parameter and Inverter Nonlinearities

In this paper, an online control method of interior permanent magnet synchronous machine (IPMSM) drives for traction applications considering machine parameter and inverter nonlinearities is presented. It is shown that the conventional technique using parameter information instantly extracted from premeasured parameter look-up tables (LUTs) only determines the local maximum torque per ampere (MTPA) operating point associated with this specific parameter information without evaluating the global MTPA achievement. Therefore, global MTPA operation may not be achieved for conventional online control IPMSM drives with extreme nonlinear machine parameters (e.g., short-period overload operations). Thus, a model-based correction method using stator flux adjustment is proposed for an online quasiglobal MTPA achievement. It is also proven that in the flux weakening (FW) region, due to the inverter nonlinearities, a lower than expected maximum achievable torque for a demanded speed and a higher than expected current magnitude for a demanded torque may be obtained. Hence, an inverter nonlinearity compensation (INC) method exploiting the voltage feedback (FB) loop is introduced and its advantages over the conventional INC scheme are demonstrated. The proposed online control method is validated via measurements on a 10-kW IPMSM.

A rapid concept development technique for electric vehicle powertrains

This paper proposes a rapid concept development tool for electric vehicle (EVs) powertrains. The proposed method takes into consideration all the powertrain components (battery pack, DC/DC converter, DC/AC converter, electrical machine) together with optimum operation of the traction machine. The method mainly employs manufacturer data-sheets for the component parameters, and therefore exhibits high flexibility at the preliminary design stage of an EV drivetrain. It is shown that with limited computing resources, efficiency maps for the components of the Toyota Prius 2004 powertrain over the New European driving Cycle (NEDC) can be produced within several seconds.