Roberto Leidhold

Field-oriented controlled induction generator with loss minimization

In this paper, a strategy to control an induction generator (IG) working with variable speed and load is presented and discussed. An inverter and a field-oriented controller are used in order to excite the induction machine (IM) efficiently, minimizing copper and iron losses, and to regulate the generated voltage. The proposed IG system is a stand-alone (not grid connected) system. It is used to produce electrical DC energy, to charge a battery bank, and/or to supply DC loads with maximum efficiency. A laboratory setup, based on a conventional 4 kW squirrel-cage IM, has been implemented. Experimental results are presented in order to validate the proposed strategy.

Position Sensorless Control of PM Synchronous Motors Based on Zero-Sequence Carrier Injection

A position sensorless control method for PM synchronous motors is proposed in this paper. It relies on the magnetic saliencies to estimate the position of the rotor. In usual sensorless methods, a signal is injected in the αβ or dq components. In the proposed method, the signal is injected in the zero-sequence component. The high-frequency inherent zero-sequence component produced by a space-vector pulsewidth modulator (PWM) is used. In this way, no modification is required in the PWM, even at zero voltage, and the injected signal does not interact with the current controller. The response to the injected signal is obtained by a simple current derivative sensor. With this method, the position can be evaluated with high dynamics and with a high signal-to-noise ratio. The performance of the proposed method is evaluated with an experimental setup, using standard industrial servomotors with surface-mounted magnets.

Improved method for higher dynamics in sensorless position detection

Numerous methods have been published for sensorless detection of the rotor position in PM synchronous motors (PMSM) by evaluating the magnetic anisotropy. In this paper, the one based on the injection of an alternating voltage carrier is considered. It is able to detect the anisotropy, and by its means the rotorpsilas position, without any additional hardware or modifications on the samplings times. It will be shown that the observerpsilas dynamics is bounded by the carrier frequency. The carrier is usually sinusoidal and with a frequency of about 1/4 of the switching frequency or lower. As a measure to improve the dynamics of the position observation, a square wave carrier with the highest possible frequency, namely the switching frequency, will be used. In addition, the carrier response will be decoupled from the controlled q-current in order to avoid the usual bandpass filter. This filter would introduce a significant delay in the observer loop. The frequency increase, together with the removal of the filter allows a faster time response in the position estimation. Experimental results showing the improvements in the estimationpsilas dynamics are presented.

Speed Sensorless Control of a Long-Stator Linear Synchronous Motor Arranged in Multiple Segments

In the case of long-stator linear drives, unlike rotative drives for which speed or position sensors are a single unit attached to the shaft, these sensors extend along the carriage way, becoming a costly part of the system. Therefore, sensorless methods are of higher concern in linear motors than in rotative ones. For long carriage ways, the stator is usually divided in several independently fed segments in order to reduce the reactive power and to allow more than one vehicle to move on the same carriage way. This arrangement presents additional challenges in the implementation of sensorless methods because the position-dependent variables [as the electromotive force (EMF)] of each segment are nonperiodic signals. Moreover, the acquired speed and position information from one segment must be synchronized with the adjacent one when the mover passes over a segment transition. In this paper, a method to get a continuous estimation of the speed and position, even during the transition between segments, is proposed. This method uses an EMF observer for each active segment (i.e., where the mover is currently located, and the subsequent segment). Then, based on the addition of the observed EMF, a single speed and position observer is implemented for the mover. Using an experimental setup, validation results are attained and presented.

PMAC motor control strategy, based on the instantaneous active and reactive power, for ripple-torque and copper-losses minimization

A new strategy, based on the instantaneous reactive power theory, to control a permanent magnet AC motor (PMACM) is proposed. This strategy allows controlling the motoring torque and, simultaneously, minimizing ripple torque and copper-losses. Its practical implementation can be accomplished with a simple software and hardware scheme. To exemplify the proposal, the case of an axial-flux PMACM with a quasi-trapezoidal back-EMF is presented and some simulation results are shown.

Speed sensorless control of a long-stator linear synchronous-motor arranged by multiple sections

Linear permanent magnet (PM) motors have become a viable alternative for material handling and processing systems in the industry, mainly because of its higher dynamic response, robustness and accuracy. For long stators, the position sensor, which extents along the carriageway, becomes a costly part of the system. In addition, for long carriageways, the stator is divided in several sections increasing sensing complexity. Therefore, sensorless methods are of higher concern than in rotative motors. In this paper, a speed sensorless control of a long-stator linear synchronous motor arranged by multiple sections is presented. This method uses an EMF observer for each active section (i.e. where the mover is and the subsequent). Then, based on the addition of the observed EMF a single speed and position observer is implemented for the mover. Finally, using an experimental setup, validation results are attained and presented.

Sensorless position-control method based on magnetic saliencies for a Long-Stator Linear Synchronous-Motor

A sensorless method based on evaluating magnetic saliencies by HF signal injection is investigated for long-stator linear synchronous-motors. For long carriageways, the stator is divided into several independently fed segments, in order to reduce the reactive power and to allow more than one vehicle to move on the same carriageway. This kind of linear motors present difficulties, not found in rotative ones, in order to implement the sensorless methods. For instance, due to the end-effect of the stator, stationary saliencies arise which interfere with the position detection. In addition, the position dependent inductance of each segment is non-periodic. Therefore the position information from one segment must be synchronized with the adjacent one when the mover passes over a segment transition. In this paper, a sensorless position-control method providing means to overcome the stationary saliencies and the segment transition is proposed. It was tested in an experimental setup and performance results are shown

Variable speed field-oriented controlled induction generator

In this work, a new induction generator system (IG), to work with variable speed and load, is proposed. The objective is to make it work as a stand alone (not grid connected) generator to produce constant voltage and variable frequency AC current. The IG is based on a three-phase induction machine (IM) exited, simultaneously, by a capacitor bank and a field-oriented controlled inverter. The inverter manipulates the IG excitation currents to control the generated voltage. The capacitor bank is used to minimize the inverter current and to filter voltage harmonics. A laboratory set up was mounted to experimentally validate the proposal. This prototype is based on a 4 kW conventional squirrel cage IM. The inverter uses IGBTs and the controller was implemented using a conventional PC and adequate interfaces. Experimental results are presented to validate the proposed strategy. This system can be used in variable-speed micro wind or hydro power plants where the prime mover operates within a variable speed range to obtain a better efficiency.

Sensorless position estimation by using the high frequency zero-sequence generated by the inverter

A method for sensorless position estimation in PM synchronous motors is proposed. The high frequency zero sequence voltage generated by the PWM is used as carrier source. It is applied to the motor by closing the neutral point to the DC-link through a filter. The anisotropy information, and consequently the position of the rotor, is evaluated from the resulting non-zero sequence current. When compared with the usual methods that inject the carrier in non-zero sequence, the proposed method provides a resulting anisotropy dependent signal four times higher for equal applied voltage. This advantage is useful in motors with weak saliencies as is the case of long-primary linear motors. An analysis of the method and experimental results, using a long-primary linear motor, are presented.

Losses minimization in a variable speed field-oriented controlled induction generator

A strategy to control an induction generator (IG), working with variable speed and load, is presented and discussed in this work. The objective of the proposed system is to make it work as a stand alone (not grid connected) generator to produce electrical DC energy, charging a battery bank and/or feeding DC loads with maximum efficiency. An inverter and a field-oriented controller are used to excite efficiently (minimizing system losses) the IM, regulating the generated voltage and rectifying the AC current. A laboratory set up was mounted to experimentally validate the proposal. This prototype is based on a conventional 4 kW squirrel cage IM. Simulation and experimental results were carried out to validate this proposal.