Siamak Mehrnami

An Analytical Solution for Tracking Photovoltaic Module MPP

In this paper, a new method for estimating the maximum power point (MPP) of a solar array based on its characteristic equation is introduced. The proposed method is simple fast and returns the MPP accurately. Moreover, the sensitivity of the introduced scheme to the model parameters is analyzed. Finally, the practicability of the proposed method is demonstrated by both simulation and experimental results on REC-AE220 solar modules.

Discontinuous Modulation Scheme for a Differential-Mode Ćuk Inverter

The differential-mode Ćuk inverter (DMCI) is a single-stage inverter with low device count. It offers advantages over other topologies because of compactness, higher power density, and reduced cost. It is a promising topological configuration for renewable-/alternative-energy applications with isolated as well as nonisolated structures. The continuous modulation scheme (CMS), which was introduced originally for this inverter, activates all the modules of the DMCI. The new discontinuous modulation scheme (DMS) deactivates one module in each half line-cycle leading to discontinuous operation of modules. This paper outlines the DMS and a mechanism to realize it. The experimental open-loop and closed-loop results of the DMCI using CMS and DMS are provided along with a comparison of their performances. It is shown that, the DMS reduces the circulating power and hence mitigates the losses. The voltage ratings of the devices also are reduced with the DMS. In contrast, the CMS has wider linearity in its normalized dc-voltage gain and yields reduced harmonic distortion of the output voltage. For DMS, to achieve comparable linearity in normalized dc-voltage gain and distortion, harmonic compensation under closed-loop control is a pathway that has been demonstrated.

A low-device-count single-stage direct-power-conversion solar microinverter for microgrid

This paper covers the design and analysis of a compact inverter for photovoltaic (PV) and fuel-cell applications. The inverter is made up of two isolated Ćuk converters working differentially to create a 60-Hz sinusoidal output. This enables direct dc/ac conversion with low device count and yields a simple drive-circuitry. This configuration will lower converter cost and size and can achieve an estimated efficiency of ≥ 95%. Key topics covered in this paper include analysis of the inverter topology and its design.

Modulation scheme of the differential-mode Ćuk inverter for loss mitigation

Among the various isolated inverter topologies for grid connection of the renewable energies, the differentialmode Ćuk inverter has several outstanding features. It has lower number of devices, which are low-side driven. It has lower high-frequency ripple on the both ac and dc sides. This paper introduces a new modulation technique intended to eliminate the power circulation by manipulating just one module at a time which leads to a better efficiency.

Closed-loop control of switching transition of SiC MOSFETs

This paper presents a novel closed-loop active-gatecontrol (AGC) circuit for high-voltage SiC MOSFETs, used in the high-voltage, high-frequency and high-power-density applications. The proposed controller independently adjusts the switching di/dt and dv/dt by closed-loop control of the gate current and enables one to reach optimal performance in terms of loss, device stress, and EMI. The di/dt is adjusted to control the overvoltage stress and peak reverse recovery current while the dv/dt is adjusted to control the common mode (CM) noise and switching loss. The dv/dt is the primary source of the common mode noise in power electronics converters. Dynamic control of switching dv/dt has been somewhat overlooked in the state-of-the art works based on Si based power semiconductor devices (PSDs), and maximum achievable dv/dt is used to decrease the switching loss. However, the magnitude of generated dv/dt in the high-voltage SiC-based applications is appreciable because of the exceptionally higher switching speed of the SiC MOSFETs as compared to Si IGBTs. In contrast to other works, the proposed controller dynamically and independently controls the turn-off di/dt and dv/dt of a SiC MOSFET using closed-loop control of the gate current. Independent control of turn-off di/dt and dv/dt is achieved using a delay compensation circuit. This circuit compensates the total delay in the feedback loop and predicts the onset of transition between dv/dt and di/dt control regions. The proposed control circuit operation and advantages are presented and verified by experimental results.

A control mechanism to compensate nonlinearity of discontinuous modulation based grid-connected differential-mode ĆUK inverter

The differential-mode Ćuk inverter (DMCI), with outstanding features, has a good chance to replace the conventional topologies in grid connected application for renewable energies. Two modulation schemes have been introduced for the inverter in literature. Discontinuous-modulation scheme (DMS) uses one module in each half line cycle, whereas the continuous-modulation scheme (CMS) continuously uses both the inverter modules. The DMS suits the switched mode power supply applications because of better efficiency and lower device ratings. But, the DMS shows nonlinear control-to-output relation, which translates to more current distortion or need for complicated controller in grid-connected mode. This paper introduces a static-linearized DMS (SLDMS) scheme. It mitigates the control-to-output nonlinearity of the DMCI. It uses the input and output voltages as feed forward to generate the needed modulating signal. The results demonstrated in this digest provide the validity to the new mechanism.

Modulation Scheme for Three-Phase Differential-Mode Ćuk Inverter

Three-phase differential-mode inverters are single-stage inverters, which have the potential to reduce the number of devices and cost with higher power density. Among such inverter topologies, differential-mode three-phase Ćuk inverter (DTCI) has some advantage over other topologies, including modularity, lower number of switches, bidirectional power flow capability, and galvanic isolation. DTCI is a promising configuration for renewable-/alternative-energy applications with isolated and nonisolated structures. The continuous modulation scheme (CMS), which was introduced originally for the DTCI, activates all of three modules of the inverter. CMS increases the circulating power in modules and hence increases inverter power loss. This paper describes a discontinuous modulation scheme (DMS) for the DTCI which deactivates one module at a time resulting in a discontinuous operation of the inverter modules. The experimental open- and closed-loop results of DMS- and CMS-based DTCI are provided and compared. DMS reduces the circulating power, device voltage ratings, and mitigates the DTCI losses. The DTCI exhibits a nonlinear voltage gain with both DMS and CMS. It has been demonstrated that by feed-forwarding the input voltage and incorporating a static linearization method, the harmonic distortion of the output voltage is considerably reduced.

Harmonic-compensation based control of a nonlinear differential-mode Ćuk inverter

There are different topologies for realization of the inverter. The differential-mode Ćuk inverter, with features such as reduced number of devices, reduced power dissipation, and reduced ripple on the both the ac and the dc sides is a good candidate for renewable-energy applications and micro-inverters. The voltage gain of the differential-mode Ćuk inverter is nonlinear for which compensation scheme needs to be appropriately designed. This paper shows that, a proportional-resonant (PR) harmonic compensator can be used to control this nonlinear inverter. Experimental results of the inverter using 3rd, 5th, 7th, and 9th order harmonic compensators yields voltage total-harmonic distortion (THD) less than 5% in standalone mode of operation with resistive load.

New single-bias all-optical ETO configuration for a 15 kV-100A SiC thyristor eliminating the turn-on leakage current

In this paper a new single-bias optically-triggered (OT) emitter-turn-off (ETO) configuration for a 15kV-100A SiC thyristor, used in the next generation high-voltage high-frequency and high-power-density applications is outlined. Optical turn-off and turn-on of the OT ETO is achieved using an auxiliary optically-triggered power transistor (OTPT) in the anode path of the SiC thyristor. Leakage current during the turn-on transition of OT ETO is caused by the undesired activation of the turn-off path of the gate of the thyristor. This undesired activation is due to parasitic inductances and high di/dt in the commutation path, resulting in additional switching loss and electro-magnetic noise. In contrast to other works, the proposed method removes the leakage current enhancing the switching performance, reducing the switching loss and EMI. The other feature of the proposed work is using a single high-voltage bias eliminating the need for low-voltage (LV) control bias and devices in conventional methods. The system reliability is increased via using optical link to turn the SiC thyristor on and off, precluding the susceptibility to external noise. The proposed method and the OTPT are respectively verified through simulation and experimental results.

Optical power-electronic technology

In this paper, a top-level outline on the work related to optically-switched power semiconductor devices that have been carried out at the University of Illinois, Chicago (UIC) or those in which UIC has been involved has been outlined. In addition, an outline on optical control that affects the switching dynamics of the power semiconductor devices is provided.