J. Peracaula

Voltage Balancing Control of Diode-Clamped Multilevel Converters With Passive Front-Ends

In the previous literature, it has been reported that it is not possible to guarantee the balance of the DC-link capacitor voltages of multilevel three-phase diode-clamped DC-AC converters with passive front-ends for high modulation indices, especially for more than three levels. This paper proposes a novel closed-loop control approach capable of guaranteeing such balance for all operating conditions of the converters without the need for additional hardware. Three different phase duty-ratio perturbation schemes are proposed. They are compared through simulation for the case of a four-level three-phase diode-clamped DC-AC converter operated with a virtual-vector-based modulation. The most simple and effective perturbation scheme, only requiring the sensing of all DC-link capacitor voltages, is tested experimentally in the same four-level converter. The results demonstrate the feasibility of guaranteeing the dc-link capacitor voltage balance for all converter operating conditions.

D-Q modeling and control of a single-phase three-level boost rectifier with power factor correction and neutral-point voltage balancing

This paper deals with the analysis, design and operation of a control system for a single-phase three-level rectifier with a neutral-point-clamped (NPC) topology. Usually the desired operating conditions for this type of converter are: unity displacement factor, output DC voltage regulation and neutral point voltage balancing. A d-q reference frame has been used in this work to model the rectifier behaviour in order to exploit the results obtained in the field of three-phase converters. In this way, a space vector modulation PWM method has been used, with the possibility of using redundant switching states to achieve charge balancing of the capacitors. The time assignment of each redundant switching state is accomplished by utilizing a closed-loop control system. Validity of the modeling and control strategies are confirmed by the transient and steady state simulation and experimental results.

Voltage Balancing Control of Diode-Clamped Multilevel Converters with Passive Front-Ends

In the previous literature, it has been reported that it is not possible to guarantee the balance of the DC-link capacitor voltages of multilevel three-phase diode-clamped DC-AC converters with passive front-ends for high modulation indices, especially for more than three levels. This paper proposes a novel closed-loop control approach capable of guaranteeing such balance for all operating conditions of the converters without the need for additional hardware. Three different phase duty-ratio perturbation schemes are proposed. They are compared through simulation for the case of a four-level three-phase diode-clamped DC-AC converter operated with a virtual-vector-based modulation. The most simple and effective perturbation scheme, only requiring the sensing of all DC-link capacitor voltages, is tested experimentally in the same four-level converter. The results demonstrate the feasibility of guaranteeing the dc-link capacitor voltage balance for all converter operating conditions.

Fuzzy logic based improvements in efficiency optimization of induction motor drives

Induction motors are, without any doubt, the most used in industry. Motor drive efficiency optimization is important for two reasons: economic saving, and reduction of environmental pollution. In this paper, advantages of using fuzzy logic in steady-state efficiency optimization for induction motor drives are described. Experimental results of a fuzzy logic based optimum flux search controller are presented. For transient states a new original idea is introduced: a fuzzy logic based controller actuating as a supervisor is proposed to work with reduced flux levels during transients to optimize efficiency also in dynamic mode. Two different rule tables are designed, for torque transitions and for reference speed changes. With this controller efficiency can be improved in transients, and also search controller convergence speed is increased. Experimental results with a 1.5 kW induction motor drive demonstrate the validity of the proposed methods.

Neural network flux optimization using a model of losses in induction motor drives

This paper focuses on loss minimization in induction motor (IM) drives. In many applications Induction Motor drives work below the nominal torque most of the time. In these circumstances the IM efficiency can be improved lowering the flux. For a given torque, this decreases iron looses and increases copper losses. With appropriate algorithms an optimum point for the flux can be achieved in order to minimize IM total power losses. Using an IM model, a neural network (NN) based approach is used to improve efficiency in a vector control of the induction motor drive. A complex loss model of the motor, including magnetic and thermal deviations of its parameters, is used to estimate losses. Based on this model, the neural network is trained to estimate the optimum rotor flux. Inputs to the NN are torque, speed and rotor resistance of the IM and the output is the rotor flux. Analysis, modeling and simulation results are presented to demonstrate the validity of the proposed method. method.

Induction motor optimum flux search algorithms with transient state loss minimization using a fuzzy logic based supervisor

A review of different optimum flux search algorithms for loss minimization in a vector-controlled induction motor drive is presented. A fuzzy logic controller, actuating as a supervisor, is proposed to work with reduced flux levels during transients and also to optimize efficiency in dynamic modes. Experimental results demonstrate the validity of the proposed methods.

Neural network based efficiency optimization of an induction motor drive with vector control

In this paper an efficient optimization controller for a vector control induction motor drive is studied using a neural network. A 2-5-7-1 neural network has been designed to estimate the optimum rotor flux for the motor. The network has been trained using a complete motor loss model, taking into account the magnetic deviations of the motor parameters. Simulation results are shown to demonstrate the validity of the proposed methods.

A novel control approach of three-level VSIs using a LQR-based gain-scheduling technique

Three-Level VSIs present multivariable structure. Thus, control of these converters is interesting to be implemented using multivariable techniques. This work introduces a novel and simple method for the design of a controller using LQR and gain-scheduling techniques. The method allows the control of any state variables and the controller can operate in large-signal mode. Simulation results confirm the validity of the proposed controller design.

Analysis and design of a resonant battery charger for photovoltaic systems

A solar battery charger using a DC/DC resonant converter with 3 reactive elements operating over a wide load range is presented. This charger is based on a half bridge inverter structure and it can be fed by a solar panels system configured as two current sources, An experimental 100 W/250 kHz unit was built and tested in the laboratory. The operation has been verified with a rechargeable lead-acid battery of 12 V and 1.2 Ah and a HP 6030A DC current source of 200 V and 17 A controlled by a personal computer. The current source follows the characteristic curve of the solar panels.

Dynamic analysis of three-level voltage-source inverters applied to power regulation

The dynamic characteristics of three-level voltage-source inverters are analyzed, in order to control the power delivered to the load in closed-loop operation. A model of the three-level voltage-source inverter is presented. The dynamics of the complete system is considered, including the DC-link and the load side. The model uses D-Q transformation. An open-loop dynamic analysis is done first. An LQR controller is designed to improve the dynamic response of the system for the closed-loop operation. The simulation results confirm the improvement of dynamic behavior in closed-loop operation.