Constantin Radoi

The advantages, limitations and disadvantages of Z-source inverter

A Z-source converter is an unique x-shaped impedance network called Z-source impedance network that couples the converter main circuit to the power source. The converter may be of all conversion types - if it is of ac-to-dc type, the z-source converter is called z-source inverter. Since 2003 when this recently conversion concept appeared [1], it proved able to solve many conversion problems. In this paper its superiority compared to traditional solutions are shown. There are also small disadvantages and limitations revealed.

The analysis of the solutions for harmonic elimination PWM bipolar waveform with a specialized differential evolution algorithm

The selective harmonic elimination pulse-width modulation (SHE-PWM) offers multiple solutions depending of the number of switching angles or problem formulation, each one with different harmonic performance. This paper proposes a novel approach to the SHE-PWM problem, using a minimization technique based on a specialized evolutionary algorithm that can find all solutions for a given modulation index. The algorithm, based on the Differential Evolution (DE), is tested on the bipolar waveform with quarter-wave symmetry for three-phase inverters. In order to provide a complete analysis of the solutions, four performance indicators are used: a harmonic distortion factor that takes into account the first two (HDF2) and the first four (HDF4) significant harmonics, the total harmonic distortion (THD) and weighted THD (WTHD) of the output line voltage. The distribution of the switching angles in the first quarter-period is also analyzed and a general formulation that allows the identification of the best solution from the ones found for N switching angles is proposed.

Microcontroller-based Walsh function PWM modulation with harmonic injection technique

An improved pulse width modulation (PWM) method for three-phase inverters using the Walsh function harmonic elimination method with harmonic injection technique is presented, together with a noniterative algorithm that produces a set of linear equations that relates switching angles with the output phase voltage fundamental. The approach used gives a set of solutions with a near-linear trajectory which can be approximated by straight-line curve fitting. Thus, on-line control of fundamental amplitude and frequency is possible with a microcontroller-based implementation. The novel use of harmonic injection technique maximizes the output line voltage fundamental. The theoretical predictions are confirmed by computer simulation and DSC-based hardware implementation.

Implementation of simple MPPT algorithms using low-cost 8-bit microcontrollers

The fundamental topologies like buck and boost are commonly used in low-cost PV systems combined with simple maximum power point tracking (MPPT) algorithms like the perturb-and-observe (P&O) and incremental conductance (INC). This paper presents the influence of the operating modes (Continuous/Discontinuous Current Mode) of converter over the P&O and INC algorithms. A typical architecture that avoids the topology-induced effects is presented and his performance is evaluated in a low-cost PV charger controlled by an 8-bit microcontroller.

Performance analysis of slope and frequency modulated carrier PWM methods for grid connected converters

A detailed analysis of two Pulse-Width Modulation (PWM) methods is performed in this paper for grid connected converters. The considered methods are: sinusoidal carrier regulated by the slope of a trapezoidal waveform PWM (SLPWM) and frequency modulated triangular carrier PWM (HIPWM-FMTC). The analysis of the two PWM methods is realized with four performance indicators: standard and weighted total harmonic distortion (THD and WTHD), fulfillment of the grid connection requirements and minimum pulse width. The results are compared with those obtained for the Space Vector Modulation (SVPWM) and Selective Harmonic Elimination PWM (SHE-PWM). Experimental results are presented for a 1 kVA inverter prototype to validate the paper conclusions.

A simple method for power loss estimation in PWM inverter-fed motors

This paper presents a simple power loss estimation method for inverter-fed low power AC asynchronous and synchronous motors. The method uses a simulation based DC/AC converter power loss estimation based on datasheet parameters and load characteristics like measured phase resistance and current phase delay. A current control scheme is used to impose a constant current at various speeds. Using this approach both asynchronous and synchronous motors can be used as a load. Total power loss is measured as the DC Link current by an amperemeter avoiding the use of complicated measurement systems.

Design optimization methods of an intelligent controller from a speed control system

The paper presents fuzzy logic simple and combined with evolution strategies and neuro-fuzzy designs of a duty-cycle compensation controller in order to linearize the nonlinear external characteristics family of a step-down or forward DC-DC converter that supplies DC motors. The controller is additionally introduced in high precision speed control systems. Comparisons between classical PI controllers and fuzzy controllers are made. Advantages of combined methods of computational intelligence domain are revealed.

Power Conversion and Energy Management for Mission-Critical Systems

The need for high power density has been the trend of the power conversion industry for many years. The key to obtain a high power density is to increase system’s efficiency. In the case of space applications, there is the same need for high power density but with the very important note that the reliability of the system must not be compromised. In order to increase system’s efficiency while maintaining reliability, the latest soft switching converter topologies, high power density packaging, improved heat extraction and planar magnetics are used. Other key parameters are: the digital loop control and the digital energy management through microcontrollers, and digital signal controllers.

Power Architectures and Power Conditioning Unit for Very Small Satellites

Space agencies all over the world are interested today in very small satellites because of their advantages compared to heavier satellites. This chapter starts with the general characteristics, Earth orbits, eclipses and current missions of very small satellites. It continues with a brief summary of the component parts of the electrical power system: the array of solar cells, batteries for space applications, 3 power architectures and 19 maximum power point tracker’s algorithms. Authors’ attention is mainly focused on designing, simulation and practical demonstration of a prototype with a flexible hybrid proposed architecture of the power conditioning unit for very small satellites, whose component blocks are the battery charge unit (BCU) including the dc–dc converter, the digital controller, the BCU sensors circuitry and the BCU prototype) and the battery charge/discharge monitor unit (BCDMU) including the microcontroller, the BCDMU sensors circuitry, the battery switch, the battery heater and the telemetry system.

Single-phase power factor correction circuit with Proportional-Resonant control

This paper propose the use of “Proportional-Resonant” (PR) controllers for Power Factor Correction (PFC) circuits used in front-end converters for grid-connected applications. The performance of the PFC converter with PR control is analyzed using simulations and the advantages and disadvantages of this kind of control are discussed. The classical PI controllers and the PR controllers are evaluated on the same operating conditions, under severe distorted grid voltages.