Miguel Angel Rodriguez

Direct Power Control of Doubly-Fed-Induction-Generator-Based Wind Turbines Under Unbalanced Grid Voltage

In this paper, the behavior of a doubly fed induction generator (DFIG) is studied under unbalanced grid voltage conditions. It is shown that if no special control efforts are employed, the behavior of the generator is deteriorated, basically due to two reasons: electromagnetic torque oscillations and nonsinusoidal current exchange with the grid. These phenomena are first analyzed theoretically as a function of the stator active and reactive instantaneous power exchange by the stator of the DFIG and the grid-side converter (GSC). This analysis provides the main ideas for generation of the active and reactive power references for the rotor-side converter (RSC) and the GSC, controlled by means of direct power control techniques. Therefore, this paper proposes a new algorithm that generates the RSC power references, without the necessity of a sequence component extraction, in order to eliminate torque oscillations and achieve sinusoidal stator currents exchange. On the contrary, the GSC power references are provided by means of voltage and current sequence extraction. Finally, simulation and experimental results successfully validate the proposed power reference generation methods.

Two-Level VSC Based Predictive Direct Torque Control of the Doubly Fed Induction Machine With Reduced Torque and Flux Ripples at Low Constant Switching Frequency

In this paper, a new predictive direct torque control (DTC) strategy of the doubly fed induction machine (DFIM) is presented. It is especially designed to operate at a considerably low constant switching frequency, reducing the electromagnetic torque and rotor flux ripples, in order to provide good steady-state and fast dynamic performances. This control is convenient for high power drive and generator applications, with restricted switching frequency. The DFIM is connected to the grid by the stator and the rotor is fed by a two level voltage source converter. In addition, this control method allows to implement a technique that reduces the switching power losses of the converter. Finally, experimental results show that the proposed DTC method effectively reduces the torque and flux ripples at low switching frequency, even under variable speed operation conditions.

Two-Level VSC-Based Predictive Direct Power Control of the Doubly Fed Induction Machine with Reduced Power Ripple at Low Constant Switching Frequency

In this paper, a new predictive direct power control (DPC) technique is presented for the doubly fed induction machine (DFIM). Based on this predictive control, the strategy is able to operate at considerably low constant switching frequencies and allows it to perform a power ripple minimization technique, in order to improve the steady-state and transient response behaviors of the machine. In addition to the control technique definition, this paper includes a conceptual analysis of DPC. On the other hand, to validate the control strategy, it will be experimentally compared to the well-known voltage frequency control, the vector control, and the nonpredictive DPC strategy. The comparison will be carried out in terms of the steady-state behavior and transient response capacity, and it will be shown that the proposed predictive DPC technique allows to obtain the combination of the quick dynamic response of direct control techniques, and the benefits of constant switching-frequency-based control techniques.

Three-Level NPC Converter-Based Predictive Direct Power Control of the Doubly Fed Induction Machine at Low Constant Switching Frequency

This paper presents a new application of the predictive direct power control (P-DPC) for the doubly fed induction machine. The P-DPC deals with several main characteristics which makes it very suitable for high power-medium voltage generation systems where total harmonic distortion of the generating power is relevant: a three-level NPC converter presenting low and constant switching frequency feeds the rotor by means of an intermediate inductive filter. The developed P-DPC takes into account the inductive filter in the prediction stage as a part of the plant model, deals with the different sectors and regions of converter available voltage vectors and the balancing of the bus capacitors voltages. This way, it creates a sequence of 3 + 3 vectors that generates an active and reactive power trajectory which minimizes the next sample time predicted error. In addition, the P-DPC is specially designed to maintain the real-time implementation structure and simplicity of the ldquoclassicrdquo direct control strategies. Experimental results in a 15-kW test bench for the overall speed and power range are shown including synchronous speed, demonstrating that it is an attractive alternative to the conventional field-oriented control techniques.

EMI Radiated Noise Measurement System Using the Source Reconstruction Technique

One of the requirements that electronics circuits must satisfy comprises conducted and irradiated noise specifications. Whereas conducted noise is well covered in the literature, radiated noise is not. Radiated noise regulations impose limits on the noise measured 3 or 10 m away from electronic equipment. These measurements are usually made in anechoic rooms, which are very expensive. Moreover, the measurement procedure is not a ldquoplug-and-playrdquo feature, but requires a strict measuring protocol. Once the electronic circuit has been tested, the designer remains ignorant of the source of the problem should the regulation not be met. Hence, the procedure to make an electronic circuit comply with regulations is usually one of trial-and-error, in which the experience of the designer is essential. A new radiated noise measurement technique is proposed in this paper with a twofold objective: to simplify the measurement procedure and to obtain more information about noise sources. The main idea is to scan the electric/magnetic field at two arbitrary although known distances. From these measurements, the source reconstruction technique enables the identification of the noise sources in the surface of the circuit and the field estimation at any distance and the assessment of compliance with regulations. Moreover, if regulations are not met, the effect of modifying the noise source can be tested in order to ascertain how the circuit should be modified to comply with regulations.

Predictive Direct Power Control - A New Control Strategy for DC/AC Converters

This paper proposes the predictive direct power control (P-DPC), a new control approach where the well-known direct power control (DPC) is combined with a predictive selection of a voltage-vectors sequence, obtaining both high transient dynamic and constant switching frequency. Two different P-DPC versions are developed based on two different types of voltage sequences: a two-vector one and a three-vector one. Simulation results of the three-vector sequence P-DPC are compared to standard voltage oriented control (VOC) strategies. Thanks to its high transient capability and its constant switching behaviour the P-DPC could become an interesting alternative of standard VOC techniques for grid-connected converters

Voltage Balancing control in 3-Level Neutral-Point Clamped Inverters Using Triangular Carrier PWM Modulation for FACTS Applications

In this paper, a novel technique to balance the voltage of the two split dc capacitors of a 3-Level Neutral-Point-Clamped inverter using triangular carrier PWM modulation is presented. This technique, suitable for reactive power compensation and for inverters operating with a relatively low switching frequency, consists in adding a square wave at six times the output frequency. Subsequently, the paper presents a comparison with two already known strategies in which a sinusoidal waveform at two and six times the output frequency are injected. The current contribution to the mid-point of the dc bus is then analysed for different modulation indexes and operating conditions. Based on this analysis, a small-signal averaged model, suitable for control design purposes is presented. Finally, simulation and experimental results on a 690 V AC, 120 kVA test bench that validate the theory are shown.

A Novel PWM Modulation Strategy for DC Voltage Balancing in Cascaded H-Bridge Multilevel Converters

This paper presents a novel Voltage Balancing PWM modulation strategy for Cascaded H-Bridge multilevel converters. These converters have been classically commu-tated at fundamental line-frequencies, but the evolution of Power Semiconductors has allowed to increase switching frequencies and the power ratings of these devices, permitting the use of PWM modulation techniques. This paper presents a new PWM modulation strategy that solves the DC Bus voltage balancing problems that appear in the cascaded converter working in reactive power compensation (STATCOM) applications.

Design, analysis and comparison of multilevel topologies for DSTATCOM applications

The aim of this paper is to present a design method of two different DSTATCOM multilevel topologies which are suitable to be used connected to the distribution grid. These devices have been classically commutated at fundamental line-frequencies, but the evolution of power semiconductors has allowed to increase switching frequencies and the power ratings of these devices, permitting the use of PWM modulation techniques. This paper mainly focuses the design issues of the NPC and cascaded H-bridge multilevel topologies for DSTATCOM applications, presenting a method for the dimensioning of the different elements that compose the device, paying special attention to the DC bus capacitor sizing and output filter inductance sizing

Direct Torque Control for Doubly Fed Induction Machine-Based Wind Turbines Under Voltage Dips and Without Crowbar Protection

This letter proposes a rotor flux amplitude reference generation strategy for doubly fed induction machine based wind turbines. It is specially designed to address perturbations, such as voltage dips, keeping controlled the torque of the wind turbine, and considerably reducing the stator and rotor overcurrents during faults. In addition, a direct torque control strategy that provides fast dynamic response accompanies the overall control of the wind turbine. Despite the fact that the proposed control does not totally eliminate the necessity of the typical crowbar protection for this kind of turbines, it eliminates the activation of this protection during low depth voltage dips.