FPGA-based implementation of the back-EMF symmetric-threshold-tracking sensorless commutation method for brushless DC-machines

The operation of brushless DC permanent-magnet machines requires information of the rotor position to steer the semiconductor switches of the power-supply module which is commonly referred to as Brushless Commutation. Different sensorless techniques have been proposed to estimate the rotor position using current and voltage measurements of the machine. Detection of the back-electromotive force (EMF) zero-crossing moments is one of the methods most used to achieve sensorless control by predicting the commutation moments. Most of the techniques based on this phenomenon have the inherit disadvantage of an indirect detection of commutation moments. This is the result of the commutation moment occurring 30 electrical degrees after the zero-crossing of the induced back-emf in the unexcited phase. Often, the time difference between the zero crossing of the back-emf and the optimal current commutation is assumed constant. This assumption can be valid for steady-state operation, however a varying time difference should be taken into account during transient operation of the BLDC machine. This uncertainty degrades the performance of the drive during transients. To overcome this problem which improves the performance while keeping the simplicity of the back-emf zero-crossing detection method an enhancement is proposed. The proposed sensorless method operates parameterless in a way it uses none of the brushless dc-machine parameters. In this paper different aspects of experimental implementation of the new method as well as various aspects of the FPGA programming are discussed. Proposed control method is implemented within a Xilinx Spartan 3E XC3S500E board

Initial rotor position estimation and sensorless direct torque control of surface-mounted permanent magnet synchronous motors considering saturation saliency

For a practical direct torque-controlled (DTC) permanent magnet synchronous motor (PMSM) drive system, the information of the initial rotor position, which is usually obtained by a mechanical position sensor, is essential for starting under the full load. To avoid the disadvantages of using mechanical position sensors, great efforts have been made on the development of sensorless control schemes. An initial rotor position estimation strategy is presented for a DTC PMSM drive based on a nonlinear model of PMSM incorporating both structural and saturation saliencies. In the new scheme, specially designed high-voltage pulses are applied to amplify the saturation saliencies. The peak currents corresponding to the voltage pulses are used, in combination with the inductance patterns, to determine the d-axis position and the polarity of the rotor. The presented initial rotor position identification strategy has been implemented in a sensorless DTC drive for a surface-mounted PMSM. Experiments are conducted to confirm the effectiveness of the method and the performance of the drive system. © The Institution of Engineering and Technology 2008

High-resolution rotor-position detection for green vehicle drives at halt condition with statistical view

Considerations around environmental pollution and green energy usage have led to environmentally-friendly machines being used in many industrial applications. Permanent magnet (PM) machines are the best solution to substitute the pollutant diesel-powered machines. In such machines, rotor position detection is crucial for safe startup operating. Meanwhile, encoderless controllers have become more reliable, over the years, in supporting the operation of PM machines. The key point, presented by this paper, is to introduce an improved positioning model to detect the rotor-position of interior permanent magnet synchronous machine at halt condition. To verify this objective, only two short duration pulses were injected into the stator windings. Then, the corresponding terminal voltage and current responses were measured and employed to create two memory address lines. Thereby, the memory cells, which contain the rotor position information, could be accessed. This detection model makes a significant improvement in rotor positioning detection of high resolution (1 degree) which represents lower value than most verified results in literature. The model was simulated and tested in a MATLAB/Simulink environment and shows an approximate accuracy 95%. Additionally, the statistical analysis was also employed to support the work outcomes

High-frequency issues using rotating voltage injections intended for position self-sensing

The rotor position is required in many control schemes in electrical drives. Replacing position sensors by machine self-sensing estimators increases reliability and reduces cost. Solutions based on tracking magnetic anisotropies through the monitoring of the incremental inductance variations are efficient at low-speed and standstill operations. This inductance can be estimated by measuring the response to the injection of high-frequency signals. In general however, the selection of the optimal frequency is not addressed thoroughly. In this paper, we propose discrete-time operations based on a rotating voltage injection at frequencies up to one third of the sampling frequency used by the digital controller. The impact on the rotation-drive, the computational requirement, the robustness and the effect of the resistance on the position estimation are analyzed regarding the signal frequency

A practical approach to HFI based sensorless control of PM-assisted synchronous reluctance machines applied to EVs and HEVs

Sensorless control is a promising alternative for controlling Electric Vehicle (EV) and Hybrid Electric Vehicle (HEV) propulsion systems without the need of complex devices, such as resolvers or encoders. As the usage of a physical sensor is avoided, this allows significant cost reductions of the drive, and the reliability of the system is also improved. EVs require an operation range from standstill to high speeds. At low speeds, the back-EMF of the electric machine is low, and signal injection techniques are required in order to estimate the position and speed of the machine. This paper presents practical implementation details of the High Frequency Injection (HFI) technique, giving special attention to signal processing, offset compensation due to filtering delays and robust speed estimation. The approach is validated in an automotive Permanent Magnet Assisted Synchronous Reluctance Machine (PM-assisted SynRM) of 51 kW.This work has been supported by the Government of the Basque Country within the research program ELKARTEK as the project KT4TRANS (KK-2015/00047 and KK- 2016/00061), by the Ministerio de Econom´ıa y Competitividad of Spain within the project DPI2014-53685-C2-2-R and FEDER funds, by the Department of Education, Linguistic Policy and Culture of the Basque Government within the fund for research groups of the Basque university system IT978-16 and partially by the “Ministerio de Econom´ıa y Competitividad” from Spain under the ENE2012-36871-C02- 01 and DPI2013-41224-P Research Projects

Automatic Tuning for Sensorless Commissioning of Synchronous Reluctance Machines Augmented with High Frequency Voltage Injection

Sensorless control of synchronous reluctance motors relies on the knowledge of the machine current-to-flux maps. Previous work demonstrated the feasibility of sensorless identification of the flux maps, performed by exciting the machine with square-wave voltage pulses at standstill, and without the need of rotor locking. The rotor position was initially estimated and then used throughout the identification, in open-loop fashion. In some cases, rotor oscillation and eventually position drift led to stop the identification before the programmed dq current domain was covered entirely. In this paper, the rotor position is closed-loop tracked during the motor commissioning to counteract the occurrence of rotor movement. The hysteresis-controlled excitation voltage is augmented with a high-frequency square-wave voltage component, and the position is tracked through demodulation of the current response to such high-frequency component. The proposed approach is experimentally verified on a 2.2 kW synchronous reluctance motor prototype. The results show that the id, iq commissioning domain is substantially extended, resulting in more accurate flux maps. Moreover, self-tuning of the method is addressed and possible causes of error are analyzed and commented

Low-cost, high-resolution, fault-robust position and speed estimation for PMSM drives operating in safety-critical systems

In this paper it is shown how to obtain a low-cost, high-resolution and fault-robust position sensing system for permanent magnet synchronous motor drives operating in safety-critical systems, by combining high-frequency signal injection with binary Hall-effect sensors. It is shown that the position error signal obtained via high-frequency signal injection can be merged easily into the quantization-harmonic-decoupling vector tracking observer used to process the Hall-effect sensor signals. The resulting algorithm provides accurate, high-resolution estimates of speed and position throughout the entire speed range; compared to state-of-the-art drives using Hall-effect sensors alone, the low speed performance is greatly improved in healthy conditions and also following position sensor faults. It is envisaged that such a sensing system can be successfully used in applications requiring IEC 61508 SIL 3 or ISO 26262 ASIL D compliance, due to its extremely high mean time to failure and to the very fast recovery of the drive following Hall-effect sensor faults at low speeds. Extensive simulation and experimental results are provided on a 3.7 kW permanent magnet drive

Rotor-position detection in permanent-magnet wheel motor to ensure smooth startup from standstill

In this paper, an innovative rotor-position-detection method for a permanent-magnet wheel motor (PMWM) that operates from standstill to low speed is presented. The neutral voltage, which is sensed through phaseshifted pulse width modulation, overcomes the limitations of the conventional back electromotive force (EMF)-based position-detection method, which is more suitable for high-speed operation. In addition, a technique that ensures a transition between the two position-detection methods is presented to cover the full speed range. Computer simulations are employed to design and assess the neutral-voltage-based and EMF-based position-detection methods. The results of the position detection and angle error are presented starting from standstill to low speed. A step current (iq) corresponding to motor torque demand is applied for the starting process in the two position-detection methods. The experimental studies of the new position-detection method are conducted. The method is successfully applied to drive a 60-kW PMWM that operates from standstill to high speed. This demonstrates the effectiveness and performance of the presented method