Marco Tursini

Adaptive sliding mode observer for speed sensorless control of induction motors

This paper presents an adaptive sliding mode observer for speed sensorless field-oriented control of induction motors. The observer detects the rotor flux components in the two-phase stationary reference frame by the motor electrical equations. The motor speed is identified by an additional relation obtained by a Lyapunov function. The analytical development of the sliding observer and the speed identification algorithm is fully explained. Experimental results are presented, based on a TMS320F240 DSP controller implementation, showing the system performance with different observer gains and the influence of the motor parameters deviations.

Initial rotor position estimation method for PM motors

This paper presents a method to detect the rotor position of PM motors at standstill. It is suitable to avoid temporary reverse rotation or starting failure. The basic approach is the well-known method to estimate the rotor position by using the inductance variation as a function of the magnets position and the stator currents: a suitable sequence of voltage pulses is applied to the stator windings and the evaluation of the peak value of the current leads to the rotor position estimation. Actually, the current measurements show significant uncertainties which affect the rotor detection. In order to avoid these problems, the authors propose a novel procedure which combines an iterative sequence of voltage pulses with a fuzzy logic processing of the current responses and phase currents derivation based on the DC link current measurements. The proposed method has been implemented on a /spl mu/C DSP (TMS320F240). The obtained results confirm the effectiveness of the proposed solution. It is consistent with sensorless or nonabsolute position transducers drives, a wide range of motors and it does not require the knowledge of any of the motor parameters.

Real-time gain tuning of PI controllers for high-performance PMSM drives

In this paper, a new and practical real-time gain-tuning method for proportional plus integral (PI) controllers has been formulated and implemented, using the speed control of a permanent-magnet synchronous motor drive system as a testbed. While the novel strategy enhances the performance of traditional PI controller greatly and proves to be a completely model-free approach, it also preserves the simple structure and features of PI controllers. The essential idea is as follows: (1) according to the system dynamics to step variation, define a performance index to evaluate the system response; (2) based on the monotonous relationship between the performance index and an intermediate PI gain parameter, this latter parameter is estimated with a modified binary search algorithm in order to improve the performance index; and (3) finally, PI gains are calculated and renewed according to the estimated intermediate gain parameter. Experiments have been thoroughly carried out to test the proposed method under different conditions. Besides being simple and easy to implement for real-time applications, the proposed method also possesses features such as versatility, stability, and effectiveness.

High Reliability Permanent Magnet Brushless Motor Drive for Aircraft Application

Reliability is a fundamental requirement in aircraft safety-critical equipments. Its pursuing involves the adoption of protective design concepts such as fault-tolerant or redundant approaches, aiming to minimize mission failure probabilities. Multi-phase motor drives are gaining a growing interest to this extent, because they permit a boost in torque and power density, allowing the design of very compact high efficiency drives with intrinsic fault-tolerant capabilities. This paper presents a five-phase permanent magnet brushless motor drive developed for an aircraft flap actuator application. The motor is designed to satisfy the load specifications with one or two phases open or with a phase short circuited, while a failure in the rotor position sensors is remedied through a sensorless strategy. Design studies aiming to predict the faulty mode performance in case of different remedial strategies are presented. Experimental tests on the drive prototype are included, which confirm its capability to satisfy the planned degraded modes of operation.

Feedforward Flux-Weakening Control of Surface-Mounted Permanent-Magnet Synchronous Motors Accounting for Resistive Voltage Drop

This paper deals with the flux-weakening control of surface-mounted permanent-magnet synchronous motors, taking into account the influence of the resistive voltage drop in the stator windings, whose effect is usually neglected in similar studies. First, the motor equations exploiting the optimal torque-speed limits in the flux-weakening region are evaluated and discussed. Then, the influence of the resistive voltage drop is pointed out, highlighting its effect on the setup of the flux-weakening strategy. Hence, a simplified approach to flux-weakening motor control is presented, useful for the practical implementation in microcontrolled drives. Finally, experimental results are shown, using a position tracking application as a test case.

Sensorless Control of IPM Motors in the Low-Speed Range and at Standstill by HF Injection and DFT Processing

In this paper, a sensorless controller for an interior permanent-magnet synchronous motor is presented based on well-known high-frequency signal injection techniques. The issue of the demodulation process is the key point of this paper. A novel approach based on discrete Fourier transform and nonconventional reference frame transformation is presented, allowing a simple and robust noncoherent demodulation, i.e., in which no information about the carrier phase is needed. In the classically adopted coherent approaches, in fact, uncertainty about carrier phase reflects in uncertainty in the demodulated signal amplitude, affecting observer gains and signal-to-noise ratio and definitively providing a degradation of the performance of the estimator. Analytical development of the sensorless algorithm, including the demodulation technique, is provided. A complete investigation by simulation is carried out aiming at showing the performance of the proposed method. Finally, experimental results are presented based on a prototype motor drive for city scooters.

Sensorless speed control of a PM synchronous motor by sliding mode observer

This paper presents a sensorless speed control of a permanent magnet synchronous motor using a sliding mode observer. A vector control strategy is considered, for a motor with sinusoidal flux distribution. The sliding mode observer detects the voltages induced by the magnet flux on the stator windings. These signals are used to calculate the rotor position and speed needed for vector control. Due to the sliding mode operation, filters are used to smooth the estimated variables. A speed-dependent compensation is also proposed, in order to achieve an accurate estimation of the rotor position. As the observed variables are not available below a limit frequency, an open loop starting procedure is implemented. The resulting observer has been fully analyzed by simulations, in order to test the performance both in steady-state and transient operations. Experimental results based on a DSP TMS320C50 controller are presented, showing the performance of the sensorless drive over a wide range of operating conditions.

Sensorless speed control of a PM synchronous motor based on sliding mode observer and extended Kalman filter

In this paper a method for rotor speed and position detection in permanent magnet synchronous motors is presented, suitable for applications where low speed and standstill operations are not required. The approach is based on the estimation of the motor back-EMF through a sliding mode observer and a cascaded Kalman filtering. Due to its characteristics, the technique can be applied to motors having distorted and whatever shaped back-EMF waveform. The equation error for the rotor position estimation is derived and discussed. Test results are presented, which show the system performance including start-up capability, which is one of the most critical conditions in back-EMF based sensorless schemes.

Speed measurement algorithms for low-resolution incremental encoder equipped drives: a comparative analysis

Precise motion control requires high-accuracy and high- bandwidth feedback speed information, often calculated by direct measurement of the rotor position available through the incremental encoder equipping the drive. The resolution of the encoder heavily affects the cost of the drive and the accuracy and bandwidth of the calculated speed. The limitations introduced by a low resolution encoder can be partially reduced by a proper speed calculation (or estimation) algorithm, that therefore plays a key role in modern drive systems. In this paper a comparative analysis of state-of-art speed measurement and estimation algorithms suitable for low-resolution incremental encoder equipped drives is presented, aiming at highlighting the specific feature of each one, both from the performance point of view, and from the computational requirements needed for actual implementation. The paper proposes itself as a guide for engineers in the complex choice of the best solution for each application.

Low cost phase current sensing in DSP based AC drives

This paper presents the implementation of two techniques for phase current sensing based on a low cost last generation /spl mu/C DSP (TMS320F24x). The first one is based on the measurement of the current flowing in a shunt resistor put in the DC bus of the inverter, the second one is based on the measurement of the current flowing in shunt resistors put in series to the emitter of the IGBT for each lower leg of the inverter. The information provided by these sensors, together with the pulse width modulation (PWM) information, is used to reconstruct the motor phase currents. After a description of the two methods and the limitations they present, an application in case of an induction motor drive is illustrated in which the adjacent vector-space vector pulse width modulation (AV-SVPWM) technique is used to drive the inverter. Some aspects involving the non ideal behaviour of different parts of the system (presence of dead time, power switches driver delay, rise and settling time of the current, A/D conversion module sampling time) are investigated in details and the specific hardware implementation is discussed. Experimental results and comparisons between the two methods are presented.