1,720,973 research outputs found
Permanent Magnet Synchronous Motors Control: Sensorless and Field-Weakening Operation
Full text linkThe Permanent Magnet Synchronous Motor (PMSM) has been adopted since the 1980s, mainly in low and medium power high accuracy servo drives, thanks to its high power density. Moreover, the possibility of using powerful digital controllers has allowed to exploit its inherent accuracy in torque production. In the recent years, industry has shown a renewed interest in this class of machines, mainly related to the higher efficiency achievable with respect to other kinds of motor. In fact, following an increasing trend in the energy cost, the higher initial cost represented by the purchase and installation of a PMSM with respect to typical solutions (e.g. induction and DC) has started to be covered by the lifetime consumption. This, together with the improved environmental consciousness, opened the way to new applications, characterized by lower accuracy and slower dynamics, where different requirements are set, like lower production and maintenance costs, higher reliability, energy optimized control and wider speed ranges. Among these applications, industrial ones are maybe the most relevant (e.g. fans and pumps), while emerging ones are electric and hybrid vehicles and home appliances. The impact of the adoption of these machines could be very important in the future, as most of the electrical energy consumption at present is represented by relatively low efficiency motors, and even few percentage units of increased efficiency would lead to huge savings.
This thesis describes the work in the years 2010-2012, during the PhD course at the Electric Drives Laboratory of the University of Udine. The topics studied are mainly two, both regarding the digital control of electric drives for Permanent Magnet Synchronous Motors (PMSMs): the sensorless control and the flux-weakening control. Although the two topics have been an object of the research in electric drives for many years, and a strong development has started from that research, still many issues are open, and the industrial need for higher performances and efficiency of these drives keeps posing interesting challenges to researchers worldwide.
“Sensorless control” is the name under which the motor control techniques aiming at the avoiding the use of mechanical sensors usually adopted. For the case of PMSM, different techniques have been considered, and some improvements have been proposed both to the analytical approach and to the techniques adopted.
Different flux-weakening control feedback schemes have been compared, and a proposal for the non linearity compensation of the loop dynamics has been proposed for a class of these, mainly applicable to Interior PMSM.
A perspective on the practical implementation issues has been kept all over the work, favoring simpler schemes with the less possible parameter dependence, in order to avoid the need for extensive off line tests on the single machine
General-Purpose Full-Speed-Range Sensorless SPM Drive: Low-Frequency Injection and Robustness Improvement
No full textSpeed control accuracy and robustness of sensorless drives based on non-salient PMSMs in the low-speed region are critical issues due to the low amplitude of back-EMF. Although open-loop control is commonly adopted up to a sufficiently high speed, it results in low accuracy and poor robustness against load torque and inertia variations or random initial rotor position conditions. Thus, extension of the closed-loop operating range towards zero is strongly desired. An integrated approach based on low-frequency current injection technique and a more general speed control stabilization technique based on reactive current superimposition is shown in this paper, allowing both initial position detection and closed-loop speed control at low-speed. Analytical development, simulation and experimental investigation results will be reported, considering an actual sensorless industrial drive system
Systematic Current Measurement Error Due to Back-EMF in PMSM Drives Adopting Synchronous Sampling
No full textStand-Still Self-Identification of Flux Characteristics for Synchronous Reluctance Machines Using Novel Saturation Approximating Function and Multiple Linear Regression
No full textMotor characterization has a fundamental role in dynamics, torque accuracy, and efficiency of vector controlled Synchronous Reluctance Machine (SynRM) drives. Control performances and robustness in the whole speed/torque range, including the flux-weakening region, and in sensorless operation strongly rely on the knowledge of machine flux versus current characteristics. A convenient flux saturation approximating function is proposed in this paper, together with an efficient parameters self-identification procedure. The adopted strategy is very simple and can be performed at stand-still by injecting a proper voltage stimulus (current control is not involved), and does not require any additional hardware (motor can be either connected or disconnected from mechanical load). Nevertheless, an excellent fitting for the flux curves on both axes is obtained, using reasonable memory and computational resources. These features make the technique very suitable to motor self-identification in industrial drives. Experimental results based on a commercial drive and two SynRMs are reported to demonstrate the effectiveness of the proposal. Extensions of the method to the evaluation of the whole flux map (including cross-saturation effects) or to interior permanent-magnet machines is also investigated and verified. © 2016 IEEE
Hybrid Modulation and Optimal Neutral-Point Voltage Control for Three-Level NPC Inverters
No full textA preliminary review of advanced carrier based modulation techniques for three-phase three-level NPC inverter is reported, focusing the attention to double signal and hybrid modulations. The problem of the neutral-point balancing is considered and reference to previous proposals recalled. A general analytical approach for the calculation of conduction and switching losses in NPC 3-level inverter is proposed, emphasizing the role of the adopted modulation strategy on the calculations. Finally simulation results are reported based on the model of a grid-connected three-phase three-level neutral-point-clamped inverter
Accuracy and robustness improvement in sensorless PMSM drives at low-speed by direct-axis current injection
No full textSpeed control accuracy and robustness in sensorless drives based on non-salient PMSMs, especially in the low-speed region, are critical issues mainly due to the low amplitude of the back-EMF, being the main information that state observers are normally exploiting, [1]-[4]. Open-loop control (e.g. constant amplitude rotating current space vector), is normally employed to start the motor up to an enough high speed, where sensorless closed-loop control is possible. Extension of the closed-loop control range towards zero is however strongly desired. Besides the adopted estimation techniques, it has been shown experimentally that adding an arbitrary direct-axis current component to the current reference leads to an important improvement in the feedback control capability, [2][5]. This phenomenon can be intuitively explained by considering that the rotor magnetic axis tends to align to the current vector angle, then the estimated direct-axis current forces convergence of estimated and actual position. In this paper, an unpublished analytical explanation of this effect is presented, while extensive simulation and experimental investigations demonstrate the effectiveness of the adopted approach and the resulting advantages in an actual sensorless industrial drive system
A Novel Proposal for Sensorless Speed Control of Non-Salient PMSMs at Standstill and Low-Speed Based on Current Injection and Constant Direct-Axis Current Stabilization Effect
No full textAccuracy and robustness in sensorless speed control of non-salient PMSMs at low-speed and standstill is a critical issue, due to the low amplitude of the back-EMF. The usually adopted open-loop control does not provide robustness against load torque, inertia variations and random initial position, making the extension of closed-loop operating range towards zero an important goal.
Where no relevant anisotropy is present in the considered class of machines, magnetic saliency cannot be exploited, but some methods based on the detection of torque produced by signal injection can be adopted, both for initial position detection and closed-loop control
Besides the adopted estimation technique, adding a constant direct-axis current has been shown experimentally to improve the feedback control capability. An analytical description of this effect has been obtained, yielding a means for the design of the proper d-axis current value.
A complete theoretical analysis, validated by simulations, is reported to show the features of the proposal. Experimental tests on a general-purpose industrial drive demonstrate the feasibility of full-speed range control, thanks to a proper integration of low-frequency injection and direct-axis current stabilization at low-speed and fundamental back-EMF at medium-high speeds
Flux-Weakening in IPM Motor Drives: Comparison of State-of-Art Algorithms and a Novel Proposal for Controller Design
No full textA review and comparison of some state-of-the-art flux-weakening algorithms for Interior Permanent Magnet Synchronous Motor (IPMSM) is presented in this paper, having voltage exploitation, dynamical performances and implementation efforts as key parameters of the comparison. Moreover an original proposal for the theoretical analysis of the overall dynamics of the voltage control loop is carried out, also taking into account non-linear effects and discrete-time implementation issues. All the considered algorithms have at least one feed-back path, thus providing steady-state voltage control even in presence of parameter errors, but different strategies are adopted leading to completely different behavioral characteristics. The approaches that will be analyzed are based on the control of the synchronous reference frame currents, the torque-flux characteristics and the voltage space vector angle. The effort for improving the voltage limitation performances, aiming at increasing dc bus voltage exploitation while still maintaining reasonable dynamical performances, is gaining importance due to both the efficiency demand (i.e. reducing the phase current magnitude for the required power) and some specific application issues, like the need for widening the speed-torque range given a relatively low voltage bus (e.g. in electrical or hybrid traction applications). A motor drive system for home appliances is considered in this paper as test bench for comparing the reviewed techniques. Simulation and experimental results are included
A Novel Approach to the Design of Back-EMF Observer Based Sensorless Control of non salient PMSM: Theoretical Analysis and Experimental Investigations
No full textA back-electromotive force (back-EMF) based sensorless technique for isotropic surface-mounted permanent magnet synchronous motor (SPMSM) drive systems is considered in this paper. Differently from the case of application specific drives, in general purpose ones tuning represents an important challenge, especially if low speed operation or relatively fast dynamics is desired. The trade off between dynamics and steady state performances introduced by estimation noise, and in particular by inverter non linearity, is discussed. The influence of the parameters in the speed and position estimation loop is characterized analytically and experimentally. As a result, a procedure for the design of each of the estimation processing blocks is derived, which is parametric on the desired speed regulation bandwidth, taken as an input from the application requirements. Finally, the stabilizing effect of a constant positive direct axis current reference is demonstrated, which allows to obtain consistent improvements in control accuracy performances at low speed, at the cost of very small additional losses
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