E. Aldabas

A New High-Efficiency Single-Phase Transformerless PV Inverter Topology

There is a strong trend in the photovoltaic inverter technology to use transformerless topologies in order to acquire higher efficiencies combining with very low ground leakage current. In this paper, a new topology, based on the H-bridge with a new ac bypass circuit consisting of a diode rectifier and a switch with clamping to the dc midpoint, is proposed. The topology is simulated and experimentally validated, and a comparison with other existing topologies is performed. High conversion efficiency and low leakage current are demonstrated.

Novel direct torque control (DTC) scheme with fuzzy adaptive torque-ripple reduction

Investigations were carried out on a novel direct torque control system, which not only reduces the undesirable torque ripple by up to 98% by means of introducing a modulation between the selected active state and a zero state, but also maintains constant switching frequency. Additionally, this two-state modulator is fuzzy adaptive and may be applied to any induction motor. Simulation and the results of experiment illustrate the operation and performance of the proposed fuzzy-logic-based controller.

Fuzzy logic direct torque control

A brief review of the different induction motor drives is done and its reason of being such a high matter of interest is summarised. Next, the direct torque control (DTC) in induction motors with its fundamental principles and schemes is described. Once the DTC is described, its main drawbacks are introduced. One of the goals of the paper is to overcome one of the worst disadvantages of the DTC, which is the existence of a considerable ripple in its torque response. The previously explained DTC limitations involve plenty of nonlinear functions. Therefore, artificial intelligence is suggested to overcome the DTC limitations. Hence, a fuzzy logic DTC controller, which is based on the classical DTC but includes a fuzzy logic controller, is described. Finally an optimised method of calculating the stator reference flux value is presented, which can be applied in any kind of induction motor drive. This optimised stator flux reference value not only improves the torque ripple, but also reduces the power consumption from the mains. Simulated results are shown to corroborate all the presented work and the updated workbench where all the experimentation is realised is also described.

Improvements in high frequency modelling of induction motors for diagnostics and EMI prediction

This paper shows that it is possible to apply in on-line conditions a proposed procedure to diagnosis induction motors or predict the EMI due to them. This procedure is based in high frequency measurements to obtain a high frequency model whose parameters are linked with some characteristics of the motors (ball bearing performance and others). The authors have been exploring the use of measurements of common mode impedance up to 30 MHz to adjust a Z/sub CM/ expression and identify the parameters of that model. Two different measuring methods have been described in former papers and the obtained results showed the reliability of that procedure. In this paper, measurements of common mode impedance obtained by using a third method (simply, by using standard instrumentation: an impedance analyzer working in a range of only up to 1 MHz) are presented. Firstly, these results confirm the former ones. Secondly, motor speed influence is analyzed. Being the procedure for adjusting Z/sub CM/ based on knowing resonance maximum frequencies, measurements of frequency of a particular resonance maximum for different motor speeds have been made. Results show that motor speed does not affect the frequency of this resonance maximum in the considered range of speed. Thirdly, on-line measurements of high frequency data show a strong impact of EMI from the environment. This paper shows how this noise can be filtered in an efficient way. In conclusion this paper shows that the proposed procedure to diagnose the induction motor or predict the EMI due to that load could be applied in on-line conditions.

A simple fuzzy adaptive speed controller

The authors present an adaptive fuzzy controller for AC motor speed regulation with a very low computational algorithm. The control continuously measures the dynamic characteristics of the system, given by total accumulated error between set value and real speed, and uses it to vary fuzzy system parameters, in this case physical shape of the membership fuzzy functions. The developed controller has been compared with other classical controls, and it has shown very fast learning features and very good tracking characteristics even under severe variations of the systems parameters. The fuzzy logic adaptive strategy can be readily implemented. The experimental results obtained over a real system built up using a PC-DSP as CPU, 1.35 hp induction motor and PWM power inverter demonstrate the robustness of the suggested algorithm in contending with varying load and torque disturbance.

Efficiency analysis of DCM-232 three-phase PV topology

In this paper the losses of the DCM-232 topology for a particular modulation strategy has been analyzed. This modulation has as particular that no common mode currents are presented. Some simulation and experimental results are given in order to prove the good behavior of the topology regarding common mode voltage (CMV), the converter efficiency and the THD.

Symmetrical ripple constant common mode voltage modulation strategy for DCM-232 three-phase PV topology

In this paper a modulation strategy for the DCM-232 power converter is proposed. This modulation has as particular a symmetrical ripple and that no common mode currents are presented. Some simulation and experimental results are given in order to prove the good behavior of the topology regarding common mode voltage (CMV).

Current controller for low switching frequency by means of increasing the null vectors time application

This paper presents a new software-implemented current regulator for three phase loads based on orthogonal two-phase /spl alpha/-/spl beta/ system. The controller uses the module of the error for defining two control situations, called of steady state and transitory, which depend on the position of the current error inside or outside of the hysteresis margin. In the steady state, a new active vector voltage application strategy is used for assuring the nearest trajectory to the diameter of the current error within the circular boundary hysteresis when a null vector is applied. Moreover, this null vector is chosen between V(0) and V(7) for reducing the number of inverters switches commutations. On the other hand, in the transitory zone the control applies only active vectors, for reducing quickly the error inside the hysteresis margins. Computer simulations were carried out in order to investigate the performance of the regulator, and results show the effectiveness of the proposed control scheme.

DCM-232 converter: A PV transformerless three-phase inverter

Nowadays transformerless PV converters are widely used in the energy conversion stage of a PV plant, because their good characteristics regarding efficiency, size, cost and weight. The main problem in transformerless PV systems is the common mode voltage variations that can generate leakage ground currents (LGC) through the parasitic capacitance formed between the PV panels and ground. These LGC are a risk for the users in a PV system therefore they should be avoided. The LGC has a clear origin on the pulse width modulation (PWM) strategy and the converter structure. In this paper a three-phase inverter with constant common mode voltage (CMV) is proposed. Simulation results are also provided.

Supervisory fuzzy control of non-linear motion system

High performance AC drives requiring good position command tracking and load regulation responses are increasingly demanded in industrial applications. The adaptive control methods that take plant disturbances suppression into account are being used for driving either nonlinear systems or nonconstant parameters systems. Generally, the adaptation is achieved by using the model reference approach or recursive plant parameter identification. Instead of this paper proposes a single self-tuning control based on supervisory fuzzy adaptation. The supervisor changes the integral term of a standard PDF controller for adapting it to the plant evolution according to the dynamics of the system. The fuzzy logic adaptive strategy has been readily implemented, with very good tracking and regulation characteristics. Stability of the developed controller has been also established in the Lyapunov sense, and computing simulations and experimental results demonstrate the robustness of the suggested algorithm in contending with varying load and torque disturbance.