Kennedy A. Aganah

A constant voltage maximum power point tracking method for solar powered systems

A constant voltage maximum power point (MPP) algorithm that automatically adjusts the reference voltage to account for varying environmental conditions is presented. A simple (and inexpensive) analog feedforward PWM controller is developed to continuously track the MPP of a solar cell array as the weather conditions vary. The solar array source is configured such that its open-circuit voltage is sampled without breaking the entire source from the load as is the case with other constant voltage MPP algorithms. MATLAB/Simulink simulations are presented to demonstrate the performance of the proposed MPP algorithm. The simulations correlated well with experimental results using a pure resistive load.

Pulsed-Width Modulation Technique for Family of (3N+3)-Switch Converters

This paper proposes a carrier-based pulse-width modulation (CBPWM) scheme for N independent three-phase loads using the general (3N+3)-switch converter. The proposed topology is derived from the nine-switch converter which is gaining considerable interest from researchers because it costs less due to its reduced number of active switches. The structure and limitations of the converter are elaborated; its modulation scheme is formulated in this paper. The generalized neutral voltages for the converter is derived for the first time and used as the offset voltages required by this type of topology to decouple the converters N outputs. The proposed algorithm is validated by both theoretical simulation and experimental results using the 9-switch and 12-switch topologies as case studies.

A cooperative game theory algorithm for distributed reactive power reserve optimization and voltage profile improvement

Modern power systems are continuously pushed to operate close to their limits due to economic and environmental constraints. As a result, the system voltage profile may seriously degrades, which can lead to voltage instability. The improvement of system voltage is thus of paramount importance for the reliability and stability of power grids. Several optimization techniques such as particle swarm optimization, artificial neural networks and non-cooperative game theory have been proposed to address the system voltage improvement and the related problem of reactive power maximization with varying levels of success. The framework of cooperative game theory is utilized in this work to propose novel models and algorithms for the joint optimization of reactive power reserve and voltage profile. We formulate a cooperative game with transferable utility to depict the interactions between system components during the operation of a power grid. First, a Shapley-value-based algorithm is developed to optimize system components locally (i.e., at the regional level). Second, we propose a cooperative game that adequately models the cooperation between independent regions within an interconnected power grid during power system operations. An algorithm is then developed to arrive at a global strategy that strives to optimize reactive power reserve and voltage profile at the regional level in a distributed manner. The proposed algorithms have been successfully validated using the IEEE-39 bus system and very encouraging results are reported.

A stochastic game framework for reactive power reserve optimization and voltage profile improvement

Voltage control and reactive power management are two critically important criteria for ensuring quality power delivery and system stability in the grid. As the two issues are coupled, they have been generally tackled simultaneously. In this paper, we utilize the concept of stochastic game modeling from game theory to develop a novel algorithm to solve the multi-objective optimization (MOO) problem of reactive power reserve maximization and voltage profile improvement. The MOO is first reduced to a single objective optimization (SOO) problem using the weighted-sum (or scalarization method). The solution to the SOO problem is then viewed as the equilibrium solution of a stochastic game. The algorithm that implements our proposed solution concept is validated in MATLAB/MATPOWER using the IEEE-39 (New England) bus system model, and very encouraging results are reported.

Single-phase multilevel inverter topology for distributed DC sources

In this paper, a new single-phase multilevel inverter topology suited for distributed DC sources is proposed. The proposed inverter is comprised of a voltage-level generator connected in series to the input of the classical H-bridge. The voltage-level generator is only able to generate positive DC voltage levels at its output. The H-bridge is used to generate the negative and zero voltage levels. The phase opposition disposition (POD) PWM method is used to generate the gate signals to drive the inverter. The basic unit of the inverter is comprised of two input DC sources, and can be used to generate 5-level (for equal DC sources) or 7-level (for unequal dc sources) voltage output. However, the proposed topology can be extended to an n-level inverter. MATLAB / Simulink simulations are presented to validate the operation of the proposed inverter. With a smaller device count, the proposed topology based on the results from the 5-level, achieves on average 50.98% reduction in average current THD, but a marginal 4.79% rise in the average voltage THD compared to the conventional 5-level topology.

Generalized Carrier-Based PWM Method for a 12-Switch Converter

Abstract This paper proposes a generalized carrier-based pulse-width modulation (CBPWM) method for a 12-switch converter feeding three independent loads. The converter topology is part of the (3N + 3)-switch converter family where N is the number of outputs (N = 3 for this special case). Its more famous sibling is the 9-switch converter which is gaining considerable interest from researchers because of its reduced-switch count architecture. The structure and limitations of the converter are elaborated; its modulation method applicable to both equal and different frequency (and/or amplitude) operations is formulated. The generalized neutral voltages for the converter is derived for the first time and used as the offset voltages required by this type of topology to decouple its three outputs. The proposed algorithm is validated by both theoretical simulations and experimental results.

The steady-state interaction of a grid-connected doubly-fed induction generator and the wind turbine

The generic expressions for the steady-state stability profile of a doubly-fed induction generator operating in maximum power tracking (MPT), power regulation, and rated output power modes are derived in this paper. This paper considers both mechanical and electrical dynamics in the derivation of the stability criterion. The contour plots using these expressions reveal a reduced stability region than previously reported in literature for both MPT and rated power modes. The paper further explores the sensitivity of the steady-state stability region to changes in rotor speed, wind speed, and blade pitch angle as to guarantee a good prediction of the steady-state stability region. Specifically, the simulations show that when operating in the sub-synchronous region, the effect of the pitch angle on the stability region is more prominent than its corresponding super-synchronous region when the mechanical dynamics are accounted for.