N. Muntean

• PhD
• Professor (Full) at Polytechnic University of Timişoara

The paper presents a synthesis of the author contributions in developing a new class of DC-DC hybrid converters (HDC) with large voltage conversion ratio. The HDC structures are obtained by introducing commutated inductive and capacitive cells in the classical DC-DC converters. With these topologies, the voltage conversion ratio is larger, at the s...

Electrical energy conversion and storage in DC systems, with increasing importance in industry, requires DC–DC power electronic converters with performances adapted to today’s requirements. In recent years, the applications of DC–DC converters have expanded, including energy storage management strategies, due to the use of supercapacitors for energ...

This paper presents the structure, analytical description, simulation results, and rather extended laboratory scale experiments on a minibus electric drive, using a supercapacitor (SC) as a storage element. The traction is implemented by a single interior permanent magnet synchronous motor (IPMSM), with Bonded-NdFeB Spoke PMs in axis d and flux bar...

Abstract A bidirectional hybrid switched inductor converter (BHSI) is proposed in this paper. The converter uses an inductor switching cell in order to achieve a wide voltage conversion range, smaller passive components, and lower stress on the active devices. Apart from these advantages, the introduction of the additional inductor in the switching...

This paper proposes a hybrid micro grid system for critical consumers like military disaster intervention, health or municipality. The solution is based on a multiple level of redundancy DC micro grid. The solution is projected to provide critical functionalities like stability, power quality, coordinated control, grid support capability. The confi...

This work is focused on a step-down switched-inductor hybrid dc-dc converter (SIHDC) integrated in a small power wind energy conversion system (WECS). The converter has two roles, to maintain the wind turbine at the maximum power point by controlling the electric generator loading, and to charge a high power density supercapacitor, which is part of...

"High voltage DC power systems (HVDC) provide essential technical advantages in relation with the AC classical distribution networks: increasing the capacity and the stability in a natural and efficient way, simultaneously with the decoupling of some local disturbances that may occur in their subsystems and the easy interconnection of power AC grid...

This paper presents a bidirectional converter (BHSI) with a hybrid structure based on a switched inductive cell which helps to achieve a higher conversion ratio. The switched inductive cell has two inductors which are connected in series and in parallel so that an additional current doubling/division is obtained. Bidirectional high ratio converters...

This paper proposes a new energy management strategy (EMS) used for charging and discharging a supercapacitor (SC). The method is based on a nonlinear impedance and resembles the droop control applied in microgrid structures. The droop control has the advantage of being decentralized so the proposed EMS also benefits this characteristic. Usually a...

This book describes a theoretical and experimental study which was intended to introduce a low cost (PM less), wide-speed-range operation with reduced capacity of the static power controller, low power electric wind or hydro generators. It reports the key design equations, preliminary optimal design aspects, FEM analysis, control design model and t...

Renewable energy conversion systems require high performance DC-DC power converters, for power flow control between the primary energy sources, storage elements, different DC buses and loads. For high conversion voltage ratio, new hybrid structures can be used for energy conversion in single or bidirectional power flow, obtained by introducing comm...

This paper focuses on a bidirectional hybrid DC-DC converter suitable as an interface between two DC voltage buses in various applications including microgrids. The switched-capacitor cell, incorporated in the converter topology, gives the advantage of high voltage conversion ratio without using a transformer. The paper analyses the converter opera...

This paper proposes a novel topology of a power flyback inverter, which is intended to be used in a microgrid system, as an interface between a low DC voltage line bus and a part of 230 V AC loads. In addition to galvanic isolation, this topology offers other advantages like high conversion ratio and a low number of power switches. Moreover, only t...

In microgrid systems, a high power density storage unit is needed in order to take quick bursts of power provided by the renewable sources. A supercapacitor (SC) is ideal for this purpose therefore a charge/discharge regulation is needed for the energy management system. This paper presents a novel nonlinear droop control strategy used for this pur...

The microgrid concept is widely adopted due to its facilities to mixt the renewable and conventional energy sources with loads and storage elements, in an intelligent energy management system. Though, before it can be fully implemented in a real system, the microgrid solutions must be studied and tested in various conditions. This paper presents a...

The authors carried out a theoretical and experimental study of dual stator winding squirrel cage asynchronous generator (DSWA) behaviour in the presence of saturation regime (non-sinusoidal) due to the variable speed operation. The main aims are the determination of the relations of calculating the equivalent parameters of the machine windings, FE...

This paper presents an attempt to design a high efficiency (90%) 3kW, 3000/3600rpm, 220/240Vrms, 50/60Hz, around (8+2) kg, one phase ac autonomous generator with simplified voltage control of max. (+/-5%) steady state error. A two salient pole stator, PM rotor configuration with heavily saturated stator core was necessary to reduce the machine reac...

This paper is focused on a control method to improve the THD factor of a bidirectional flyback inverter. The inverter structure, presented in a previous paper of the authors, contains a DC-DC converter tracking a rectified sinusoidal voltage waveform, and a full-bridge to obtain the AC waveform. The flyback inverter has a zero in the right half pla...

In power electronic converters working with PWM discontinuous control loops is very often used. This paper analyses the implementation of a valley current mode (VCM) control in a bi-directional hybrid DC-DC converter (HBDC) used in renewable energy applications. Analytical descriptions, digital simulation and experimental results performed on a lab...

This paper presents an attempt to design a high efficiency (90%) 3kW, 3000/3600rpm, 220/240Vrms, 50/60Hz, around (8+2) kg, one phase ac autonomous generator with simplified voltage control of max. (+/-5%) steady state error. A two salient pole stator, PM rotor configuration with heavily saturated stator core was necessary to reduce the machine reac...

The paper presents a Hardware in the Loop (HIL) emulator for a wind turbine system, developed for the testing in the microgrid laboratory of a PMSM generator and the associate power electronics and control. The emulator includes: a LabVIEW real time model of the wind turbine, an induction machine drive with direct torque control (the wind turbine m...

This paper develops a single-phase voltage source inverter mainly containing a high frequency flyback bidirectional DC-DC converter-as a previous stage, and a full-bridge module. The flyback bidirectional converter generates a rectified sinusoidal voltage waveform across the output capacitor. The full bridge transistors switch two times in one AC p...

The paper presents a double stator winding induction generator (DSWIG) used in renewable energy systems. The generator has a squirrel-cage rotor and a two separate stator windings. The main winding is connected to a DC bus through an inverter. The auxiliary winding is connected to a capacitor bank, in order to ensure a part of the necessary reactiv...

The paper presents experimental results related to the application of series inductors and detuned filters in different industrial power systems where AC Variable Speed Drives based on induction motors and frequency converters are used. The aim is to validate through experimental results part of the equipment designed, developed and produced within...

In an effort to reduce the initial cost of a cage-rotor (robust) variable speed induction generator with full (100%) power PWM inverter, for a dc link local power bus, a novel dual stator winding configuration with a 50% rating PWM inverter and a capacitor and 50% diode rectifier (for additional active power delivery at high speeds capable of soft-...

This paper proposes a bi-directional DC-DC converter used as interface between the battery stack and the DC bus in a microgrid application, highlighting its main feature that permits a large conversion rate, with a low number of semiconductors and without using transformers. Analytical descriptions, design aspects, digital simulation and preliminar...

This papers presents a complete study of the boundary conduction mode (BCM) for a dual input hybrid buck DC-DC converter (HBLC). It includes the operating principles and the analytic expressions for the key currents and voltages. A numerical method is used for solving the BCM equations in order to find the proper values of the converter inductances...

This paper presents and discusses design considerations and efficiency investigation of a conventional step-down and a hybrid switched-capacitor DC-DC converter. Three MOSFETs with low on-resistance have been tested for each converter in order to find the most adequate switch for this application. The experimental results and comparative efficiency...

The paper presents a high voltage conversion ratio DC-DC step-down topology obtained from a classical buck converter associated with an input switched-capacitor cell and an output switched-inductor cell. Analytical descriptions, the voltage and current limits of the main components are synthesized in a comparative form, related to the classical buc...

This paper describes the development of a fuzzy logic based maximum power point tracking (MPPT) strategy for a variable speed wind turbine system (VSWT). For this scope, a fuzzy logic controller (FLC) was described, simulated and tested on a real time "hardware in the loop" wind turbine emulator. Simulation and experimental results show that the co...

Many applications require a high step-down ratio in DC-DC converters. Hybrid structures, using switched-capacitors and/or switched-inductors, have been reported as an alternative to high frequency transformer converters. The object of this paper is a comparative study of a switched-capacitor hybrid buck DC-DC converter (HBDC) and a classical buck D...

A small power, mixed wind and PV array generation system (WPVGS) working in off-grid regime, that comprises a dual input hybrid buck LC converter (HBLC) with high ratio of the input/ output voltage, a battery bank and a corresponding energy management control is presented in this paper. Analytical description, digital simulation and experimental re...

The proposed dual input hybrid buck L/hybrid buck C (HBLC) DC-DC converter, suitable to be used in renewable energy, telecom, automotive applications, etc., consists of two hybrid step down converters with a high ratio of the input/output voltage, connected to a single output. Operation modes, analytical description and digital simulations, validat...

For a higher step down ratio hybrid structures of buck DC-DC converters (HBDC), using switched-capacitors or switched-inductors, were presented in the literature. A comparative study of a switched-capacitor HBDC and classical buck DC-DC converters (BDC), in order to have a practical guide needed to a correct choice of these structures for various a...

The proposed, small power, mixed wind and PV energy conversion system (MWPV) consists of a dual input hybrid buck L/ hybrid buck C, DC-DC converter (HBLC), made by two hybrid step down converters with a high ratio of the input/output voltage (the main part), a battery bank as a storage element, and a DC-AC inverter for AC loads supplied with, or wi...

Hybrid structures of buck DC-DC converters, using commutated capacitors or inductors, in order to obtain a higher step-down ratio, were presented in the literature. The paper is focused on a comparative study of classical buck converter (BDC) and a hybrid buck “switched inductor” DC-DC converter (HBDC), in continuous conduction mode (CCM), and at t...

This paper describes the design of a maximum power point tracking (MPPT) strategy for a variable speed, small scale, wind turbine systems based on a fuzzy logic controller (FLC). The FLC has as input variables the change in mechanical power (ΔPm), the change in rotor speed (Δω), and the sign of ΔPm/Δω. The change of reference generator current (ΔI*...

Modern process control systems are used in industrial automation for flexibility, modularity and reliability, employing state of the art technology based on three concepts: Distributed Control System (DCS), Programmable Logic Controller (PLC) and Supervisory Control and Data Acquisition (SCADA). This paper deals with design and implementation of a...

The paper presents a “hardware in the loop” emulator for a wind turbine system, used to tune and test in the laboratory the generator and the associate power electronics and control. The emulator includes: a Matlab/Simulink model of the wind turbine, an a.c. drive with direct torque control (the wind turbine equivalent) coupled with the real genera...

The proposed dual input hybrid buck C/ hybrid buck L (HBCL) DC-DC converter, is suitable for power conversion in renewable energy, automotive and telecom power systems. It extends the use of the hybrid DC-DC converters in a dual-input structure, with high voltage-conversion ratio. Operation modes, analytical description, digital simulations and tes...

The paper reviews the main multi-input converter and systems topologies for power flow control in renewable energy systems, with more than one energy generation unit. The multi-input converters/systems are synthesized from two or more single input converters, which have only one output filter and one control system, coordinated by a common energy m...

The multi-input converters are synthesized from two or more single input converters in order to obtain a compact structure with one output filter and one control system. The proposed configurations are obtained mixing buck hybrid DC- DC converters and classical buck structure. Preliminary theoretical analyses, validated by digital simulations, come...

The two-level bipolar current controlled three phase reluctance motor drive distinguishes itself from other types by having a single coil/pole/phase (q = 1) three phase uniformly distributed winding. Furthermore the motor has a distributed-anisotropy rotor with axial laminations for high saliency ratio and a two-level current control triggered by a...

The paper proposes a new, high gain, power conversion system and an innovative speed-control strategy dedicated to optimize the efficiency and the delivered electric energy of small horizontal axis wind generators with non-regulated blades, in the frame of an European Economic Area (EEA) project, in partnership with “Politehnica” University from Ti...

The paper proposes a new architecture for a small off-grid wind-power generation, control, and storage system. This system employs a wind turbine, power electronic converters, supercapacitors, and operates with a variable d.c. voltage in the intermediate d.c. circuit. A significant amount of the generated energy is used to warm water, as an additio...

This paper presents an open loop dispatcher training simulator for boiler-turbine implemented in LabView for COLTERM heating power plant of Timisoara, Romania. The system employs real-time capability, graphical user interface (GUI), uninterrupted operator interaction, having as background a low order boiler-turbine model for dynamic simulation. The...

The paper presents an interleaved 3-phase step-down converter that can be used to charge the 12 V battery and to feed the corresponding loads from the 42 V bus, in automotive dual voltage system. The converter has a maximum 3 kW output power and efficiency above 93% at full load. The simulation results show good responses under various input and ou...

Modern process control systems are used in industrial automations for flexibility, modularity and reliability, employing state of the art technology based on three concepts: Distributed Control System (DCS), Programmable Logic Controller (PLC) and most importantly Supervisory Control and Data Acquisition (SCADA). This paper deals with design and im...

In the last few yearspsila literature the Z-Source network, as a DC-link energy storage sub-circuit, was proposed to be used in DC-AC power conversion circuits (inverter) due to its advantages compared to the traditional LC DC-link. In this paper a new modified Z-source (MZS) network is proposed in order to reduce the number of switches in a single...

This paper presents an industrial implemented technical solution to increase the efficiency of electrical energy utilization in the chemical industry, by using frequency converters for automatic control of water cooling tower fans, based on a feedback from the water temperature from the cooling circuit. There is presented a practical application an...

The Z-source network, as a DC-link energy storage sub-circuit, was proposed to be used in DC-AC power conversion circuits (inverters) due to its advantages compared to the traditional LC DC-link. In this paper a new modified Z-source (MZS) network is proposed in order to reduce the number of switches in a single-phase inverter, from four switches,...

The paper proposes a closed-loop modified carrier- based PWM modulation technique for a Z-source inverter, in order to maintain a desired average DC voltage value after the boost section. Extended digital simulations will be presented to demonstrate the features of this control method.

This paper introduces an offline deterministic method for identification of inertia moment, mechanical losses, and electrical parameters for large induction machines, based on direct-on-line starting and natural slowdown tests, performed under no-load conditions. The static characteristic of absorbed power is used for the validation of results. Com...

The paper presents variable speed drive (VSD) structures for automatic speed regulation of cooling tower fans, in order to maintain a constant temperature for the circulated technological water. Practical aspects of industrial implementations and the related benefits are also presented as a result of 10 years authors experience in the field.

The paper presents a case study on the harmonic distortion produced in an industrial power system by high power adjustable speed drives. A theoretical analysis based on experimental measurements of line voltage and current harmonic distortion for both: medium voltage side, and the low voltage side of the power transformer, is done. The measured res...

Abstract: - The paper presents a theoretical analysis and an experimental investigation of the harmonic distortion regime produced by high-power AC adjustable speed drives in an industrial electrical network, on a large chemical plant platform. There are investigated the voltage and current harmonic, both in the pimary-side and in the secondary-sid...

The paper includes solutions for increasing the efficiency of the electrical energy consumption in chemical industry using the frequency converters for the automatic speed regulation for the cooling tower fans application. The motivation in implementing a new solution and the structure of the electrical equipment, together with experimental results...

The paper presents an implementation of a low-cost robust digital-analogue (hybrid) speed (and position) vector controller for cageless-rotor reluctance synchronous motors. Separate control of i_d and i_s is performed with i_d* (reference value) constant up to the base speed and reducing gradually above the base speed....