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## Publications

Publications (44)

Switching common-mode voltage (CMV) generated by the pulse width modulation (PWM) of the inverter causes common-mode currents, which lead to motor bearing failures and electromagnetic interference problems in multiphase drives. Such switching CMV can be reduced by taking advantage of the switching states of multilevel multiphase inverters that prod...

Multiphase (MP) induction machines (IMs) provide important advantages over three-phase (3P) ones. Sensorless speed estimation makes it possible to obtain highperformance control and monitoring without the inconveniences of speed sensors. In 3P IMs, the speed estimation methods based on rotor slot harmonics (RSHs), normally on the principal RSHs (PS...

Rigorous analysis and design of the current control loop in voltage source converters (VSCs) requires an accurate modeling. The loop behavior can be significantly influenced by the VSC working conditions. To consider such effect, converter losses should be included in the model, which can be done by means of an equivalent series resistance. This pa...

Low-order odd current harmonics arise in practical multiphase drives due to machine and converter nonlinear behavior (e.g., deadtime and flux saturation). If the windings are distributed, some harmonics cause torque ripple, while others produce losses. The latter is aggravated by the small impedance in the no-torque subspaces. Current harmonics can...

Precise knowledge of the plant time constant L/R is essential to perform a thorough analysis and design of the current control loop in voltage source converters (VSCs). From the perspective of the current controller dynamics in the low frequency range, such plant time constant is also suitable for most cases in which an LCL filter is used. As the l...

Current controller performance is key in grid-connected power converters for renewable energy applications. In this context, a challenging scenario is arising in multi-MW wind turbines, where sampling and switching frequencies tend to be lower and lower as power ratings increase. This strongly affects achievable control time constant. With this per...

Precise knowledge of the plant time constant is essential to perform a thorough analysis of the current control loop in voltage source converters (VSCs). As the loop behavior can be significantly influenced by the VSC working conditions, the effects associated to converter losses should be included in the model, through an equivalent series resista...

This paper deepens on the transient response analysis of the so-called vector proportional-integral (VPI) controllers and compares them with the popular proportional-resonant (PR) controllers for grid-connected applications. The employed methodology is based on the study of the error signal roots: both reference tracking and disturbance rejection a...

Implementation of proportional-integral controllers in synchronous reference frame is a well-established current control solution for electric machines. Nevertheless, their gain selection is still regarded to be poorly reported, particularly in relation to the influence of the computation and modulation delay. To fill this gap, a design procedure t...

The use of multiphase motor drives is an increasingly important strategy nowadays. These multiphase machines are usually modeled by a reference frame transformation to avoid the cross-coupling of variables. This transformation decomposes the original n-dimensional vector space into orthogonal subspaces. Mapping the voltage and current harmonics int...

It has been previously suggested to use multiple reference frame (MRF) structures, based on proportional-integral controllers in synchronous reference frames (SRFs), to suppress current harmonics caused by nonlinearities in multiphase drives. However, the rotational transformations are computationally demanding. In Part 1, the three-phase strategy...

Low-order odd harmonics arise in practical multiphase drives because of the machine and converter nonlinear behavior (e.g., deadtime and saturation). If the windings are distributed, some of the harmonics cause torque ripple, while others cause losses. The latter is aggravated by the small impedance in the no-torque subspaces. The harmonics can be...

The multi-motor drive concept is based on the use of the additional degrees of freedom available in multiphase motors to independently control a group of series-connected machines fed from a single voltage source inverter. To achieve this independent control, the motors should have a perfectly sinusoidal distribution of the stator windings. However...

Current control performance is key in some ac power conversion applications, such as renewable energies and motor drives. This paper presents a method for accurate assessment of dq-PI current controllers dynamics. The proposed methodology is based on linear control for multivariable systems. First, the plant and controller matrices are modeled incl...

Implementation of proportional-integral controllers in synchronous reference frame is a well-established current control solution for electric machines. Nevertheless, their gain selection is still regarded to be poorly reported, particularly in relation to the influence of the computation and the modulation delay. To fill this gap, a design procedu...

Low-order odd harmonics are particularly problematic in multiphase drives, due to the small impedance in the no-torque subspaces. The harmonics can be compensated by proportional-integral controllers in multiple synchronous reference frames (SRFs). In three-phase systems, the computational burden of such scheme is often avoided by implementing inst...

Proportional-integral (PI) controllers in a single synchronous reference frame (SRF) are popular for current control in voltage source converters. The most common technique to decouple the cross-coupling between its axes is to add/subtract at the output of the PI controller in each axis the current of the orthogonal axis, multiplied by the plant re...

Optimization of the current control loop in voltage source converters (VSCs) requires an accurate modeling. The VSC behavior can be significantly influenced by its working conditions. To consider such effect, converter losses should be included in the model, which can be done by means of an equivalent series resistance. This paper proposes a method...

The increasing number of distributed power generation systems (DPGSs) is changing the traditional organization of the electrical network. An important part of these DPGSs is based on renewable energy sources. In order to guarantee an efficient integration of renewable-based generation units, grid codes must be fulfilled. Their most demanding requir...

The torque and flux of sinusoidally distributed multiphase machines can be controlled by using only two stator d-q components. Thus, in these machines there exist additional degrees of freedom, which in multimotor drive systems are used to independently control a group of series-connected multiphase machines. Series connected machines share stator...

Multilevel multiphase inverters are a promising practical solution for high-power applications. In applications where high switching frequency cannot be accommodated due to the increased switching losses associated to the pulse-width modulation techniques, the space vector control modulation technique is a feasible alternative. The space vector con...

Grid codes force generation units based on renewable sources to act similarly to conventional power plants: when a fault is detected, they must remain connected and support the grid. To fulfill these requirements, the transient response of the current controllers is critical. This paper applies a recently proposed methodology which assesses and opt...

Proportional-integral (PI) controllers in a positive-sequence (PS) synchronous reference frame (SRF) are widely employed for ac machines. Resonant controllers (RCs) in stationary frame are equivalent to PI ones in a positive- and a negative-sequence SRF simultaneously. However, as shown in this work, the additional open-loop pole at the negative-se...

Power quality is a very important topic nowadays. Sensitive industrial equipment should be protected against steady-state distortions and temporary transients in the distribution lines. Typical disturbances that affect the voltage waveform quality are harmonics, imbalances and sags. This paper presents a solution to protect sensitive loads against...

Resonant filters implemented in the control of grid-connected power converters should adapt their coefficients in real time using a grid frequency estimation, for example, obtained by a phase-locked loop (PLL). Otherwise, perfect reference tracking and total disturbance rejection of ac signals are not achieved. An optimised implementation of resona...

Three-phase four-leg voltage-source converters are used in inverter, rectifier and active filter applications to control the neutral current caused by unbalanced or nonlinear loads. From the modulation point of view, a four-leg converter can be considered as a four-phase system. Hence, the modulation task can be carried out with a generic multiphas...

This paper proposes a modified weighted least square estimation (WLSE) technique used in combination with a phase locked loop for fast and accurate reference generation, a key part in the control of ac power converters. Simulation and real-time implementation (dSpace DS1103) tests emulating realistic (distorted) environments have been performed. Th...

Resonant control is one of the highest performance alternatives for ac current/voltage control. The implementations based on two integrators are a widely employed choice in order to provide frequency adaptation to these regulators without substantial computational burden. However, the discretization of these schemes causes a significant error both...

This paper analyzes the suitability of the weighted least square estimation (WLSE) technique for reference generation. The original WLSE is modified in order to estimate non fundamental sequences and improve dynamics. Specific details of implementation and tuning are provided in the paper. Experimental and simulation results prove the high performa...

For low-power grid-connected applications, a single-phase converter can be used. In photovoltaic (PV) applications, it is possible to remove the transformer in the inverter to reduce losses, costs, and size. Galvanic connection of the grid and the dc sources in transformerless systems can introduce additional ground currents due to the ground paras...

The increasing demand for non-sinusoidal currents affects the quality of distribution networks. Harmonic detection is a crucial step in the cancellation of those components by active power filters. In this paper, the discrete cosine transform (DCT) is compared with different implementations based on Fourier transforms, demonstrating their equivalen...

Grid synchronization is an important part in the control of grid-connected power electronic converters. The fundamental phase-angle at the point of common coupling should be tracked on-line in order to control energy transfers. Digital implementation allows to implement high performance algorithms, which are robust in the presence of power quality...

Harmonic detection is a very important factor in control of active power filters, since it generates the reference signal for the current controller. The performance of the whole system will be affected by the suitability of the implemented harmonic identification method. In this work, the equivalences and advantages of the discrete cosine transfor...

This paper presents the particularization of a recent multilevel multiphase space vector pulse-width modulation algorithm for three-phase converters. This modulation technique takes advantage of the switching state redundancy, which permits to achieve different goals like extending the modulation index range and reducing the number of switchings. T...

Current control is crucial in active power filters. The current controller should provide perfect tracking of reference and total rejection of disturbance (grid voltage). The use of resonant controllers has been often proposed as one of the highest performance alternatives for alternating current and voltage control. In this work it is studied the...

The actual lines have many operation problems like power flow distribution, oscillations, etc. A bad power flow distribution on the network lines appears for example during a fault, in this case is possible that some lines of the network would be overloaded and other lines under their thermal value. A possible solution of the problem is using serie...

The power grid in most of the countries is aging and under increasing stress. The modern industrial infrastructure demands increasing amounts of affordable and reliable electricity. Solutions based on Flexible AC Transmission Systems (FACTS) can be used to control power flow on the grid. Shunt VARs compensators provide grid voltage support, while s...

The power grid in most of the countries is aging and under increasing stress. The modern industrial infrastructure demands increasing amounts of affordable and reliable electricity. Solutions based on flexible AC transmission systems (FACTS) can be used to control power flow on the grid. Shunt VARs compensators provide grid voltage support, while s...

Non-sinusoidal back electromagnetic forces cause torque ripple in permanent magnet synchronous motors. These harmonics should be reduced by means of an appropriate current control to improve performance. Good results have been obtained with linear regulators such as repetitive controllers in synchronous reference frame (SRF) and resonant controller...