Jorge G. Cintron-Rivera

Modeling and Control of Quasi-Z-Source Inverter for Distributed Generation Applications

The voltage-fed Z-source inverter/quasi-Z-source inverter (qZSI) has been presented suitable for photovoltaic (PV) applications mainly because of its single-stage buck and boost capability and improved reliability. This paper further addresses detailed modeling and control issues of the qZSI used for distributed generation (DG), such as PV or fuel cell power conditioning. The dynamical characteristics of the qZSI network are first investigated by small-signal analysis. Based on the dynamic model, stand-alone operation and grid-connected operation with closed-loop control methods are carried out, which are the two necessary operation modes of DG in distributed power grids. Due to the mutual limitation between the modulation index and shoot-through duty ratio of qZSI, constant capacitor voltage control method is proposed in a two-stage control manner. Minimum switching stress on devices can be achieved by choosing a proper capacitor voltage reference. Experimental results are presented for validation of the theoretical analysis and controller design.

A Switched-Capacitor DC–DC Converter With High Voltage Gain and Reduced Component Rating and Count

This paper proposes a bidirectional switched-capacitor dc-dc converter for applications that require high voltage gain. Some of conventional switched-capacitor dc-dc converters have diverse voltage or current stresses for the switching devices in the circuit, not suitable for modular configuration or for high efficiency demand; some suffer from relatively high power loss or large device count for high voltage gain, even if the device voltage stress could be low. By contrast, the proposed dc-dc converter features low component (switching device and capacitor) power rating, small switching device count, and low output capacitance requirement. In addition to its low current stress, the combination of two short symmetric paths of charge pumps further lowers power loss. Therefore, a small and light converter with high voltage gain and high efficiency can be achieved. Simulation and experimental results of a 450-W prototype with a voltage conversion ratio of six validate the principle and features of this topology.

Quasi-Z-Source inverter with energy storage for Photovoltaic power generation systems

In this paper the Quasi-Z-Source Inverter (QZSI) with Energy Storage for Photovoltaic Power Generation Systems is presented. The energy storage device was integrated to QZSI topology with no need for an extra charging circuit. This upgraded topology acquires the operating characteristics from the traditional QZSI, plus the capability of operating under very low PV power conditions. Its main operating points are classified into two modes, the low PV power mode, where the battery is discharged and the high power mode, where the battery is charge up. An extended input power operating range is achieved since the lack of Photovoltaic power can be compensated by the battery. Quasi-Z-Source inverters are very suitable for Photovoltaic power generation systems and this upgrade makes them even more suitable for this type of applications. To obtain the experimental data, a prototype was built and used to demonstrate that the Quasi-Z-Source inverter is capable of managing the State of Charge of a battery and the AC output voltage in each operating mode.

Controller design for quasi-Z-source inverter in photovoltaic systems

The voltage-fed quasi-Z-source inverter (qZSI) has been presented advantageous for photovoltaic (PV) applications. This paper further develops the closed-loop controller for the qZSI operating in both stand-alone and grid-connected modes. Regarding to the limitation between the modulation index and shoot-through duty ratio, guideline of the reference selection for capacitor voltage to minimize the voltage stress imposed on switching legs has been illustrated. A two-stage control method operating in both stand-alone and grid-connected mode is presented. Closed-loop control for the output voltage/current has been performed; simultaneously, capacitor voltage in the qZSI-network is fed back for different purpose under the two operation modes. MPPT has been implemented in the grid-connected qZSI through the proposed controller. Both stand-alone and grid-connected operations of the qZSI have been implemented and their simulation and experimental results are presented for theoretical validation.

Mitigation of Turn-to-Turn Faults in Fault Tolerant Permanent Magnet Synchronous Motors

This study presents a method to mitigate and alleviate the effects produced by a turn-to-turn short in a fault tolerant permanent magnet synchronous motor with single-layer concentrated windings. The rotor magnets are capable of inducing a high voltage across the fault contact point; this voltage has the potential to generate a high circulating current that promotes the rapid propagation of the fault due to the thermal stress created by the increased localized fault power losses. The scope of this study is for applications where postfault operation is desired, even if it means operating at reduced power capacity and lower speeds. Upon quick detection of a fault, the proposed technique can be used to decelerate the propagation of the fault and extend the machines postfault life span. The technique consists of a magnetic field-weakening strategy at speeds below nominal, to reduce the voltage induced in the faulted portion. The concept is validated through finite element analysis, modeling, and experimental data. It is demonstrated that the proposed technique reduces the fault current magnitude and winding temperature.

Comparison between a spoke-type PMSM and a PMASynRM using ferrite magnets

Increasing concerns over costs and supply of rare earth magnets have introduced more attention to Permanent Magnet Synchronous Machine (PMSM) designs that can work with ferrite magnets. Ferrite magnets are weaker in comparison to rare earth magnets which makes it a challenge to achieve high torque density. In light of this, literature has introduced several PMSM designs that show an improved performance despite the challenges of ferrite magnets. This paper presents a comparison between the spoke-type PMSM design and the Permanent Magnet Assisted Synchronous Reluctance Machine (PMASynRM), both using ferrite magnets. The spoke type PMSM is based on an existing design, whereas the PMASynRM is designed by changing the configuration of the magnets in the rotor and using a lower number of poles. The PMASynRM design also incorporates some of the best practices from literature that are used to improve its performance. The objective is to determine which rotor configuration gives the best performance. In addition, a design used for quick implementation is presented. Finite Element Analysis (FEA) is used to analyze both designs, and some experimental results are shown.

A zero-current-switching multilevel switched capacitor DC-DC converter

This paper introduces a zero-current-switching multilevel switched capacitor dc-dc converter for use in high voltage gain and high temperature applications. This circuit has a reduced charge path, low switch count and low device ratings compared to many similar topologies. Furthermore, switching losses and component size are greatly reduced. Zero-current-switching is achieved using small inductances in the circuit to resonate in series with the capacitors. In this way, the current is made to go to zero at the beginning and end of each switching cycle. A simulation is used to then verify the proposed converter.

A multilevel dc-dc converter with high voltage gain and reduced component rating and count

This paper proposes a bidirectional multilevel dc-dc converter for applications that require high voltage gain. Some of conventional multilevel dc-dc converters have diverse voltage or current stresses for the switching devices within the circuit, not suitable for modular configuration or for high efficiency demand; some suffer from relatively high power loss or large device count for high voltage gain, even if the device voltage stress could be low. By contrast, the proposed dc-dc converter features low component (switching device and capacitor) power rating, small switching device count and low output capacitance requirement. In addition to its low current stress, the combination of two short symmetric paths of charge pumps further lowers power loss. Therefore, a small and light converter with high voltage gain and high efficiency can be achieved. Simulation and experimental results of a 450-W prototype with a voltage conversion ratio of six validate the principle and features of this topology.

Evaluation of a Parameter Identification Method for Permanent Magnet AC Machines Through Parametric Sensitivity Analysis

In this paper, the effectiveness of a simplified characterization method for permanent magnet machines is evaluated through performance sensitivity analysis. Performance sensitivity analysis is a novel way to evaluate the effectiveness of any identification method, as it investigates the effects of parametric errors upon the output performance of a machine. Parametric errors are due to inaccuracies during the identification process. This evaluation tool was validated using a 10-kW SmCo interior permanent magnet machine characterized using two different identification methods. A detailed identification procedure is used as the basis for evaluating a simplified method. The performance experimental data were collected using torque controllers based on the parameters extracted with both approaches. This information is used to perform the sensitivity analysis over the operating range of the machine. Finally, the results are compared and analyzed to determine the effectiveness of the simplified characterization method and its implications on the control performance.

High performance controllers for Interior Permanent Magnet Synchronous Machines using look-up tables and curve-fitting methods

Interior Permanent Magnet Synchronous Machines (IPMSM) used in hybrid powertrain applications are required to deliver high efficiency over wide speed and torque ranges. The performance of any control algorithm is directly dependent on the accuracy of the parameters. Saturation and cross-saturation of permanent magnet synchronous machines are well recognized phenomena. Developing a controller utilizing either a two-dimensional look-up table or linear approximation of the machine parameters generated from characterization data will include the effects of saturation and cross-saturation and thereby achieve the desired performance. Both the look-up table and curve-fitting methods are implemented on a microcontroller. A 125kW IPMSM drive is used to experimentally evaluate both methods. The work presented here demonstrates that both the look-up table and curve-fitting methods provide satisfactory performance over the entire operating range. A comparison of the complexity of implementing both methods is included.