Welcome to the

Smart Power Electronics & Control Systems (SPECS) Research Group

The Mike Wiegers Department of Electrical and Computer Engineering

Kansas State University

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Welcome to the Smart Power Electronics and Control Systems (SPECS) Research Group. We are a research group with the state-of-the-art laboratories located in the Engineering Hall on the campus of Kansas State University in Manhattan, Kansas. Our labs are located at room 2186 and room 2187 at the second floor of the Carl R. Ice College of Engineering. These newly developed labs are equipped with various modern equipment and are growing.

We are conducting research on smart inverters with grid-forming and grid-following modes of operation implementing self-governing, self-adapting, self-security, and self-healing features. Furthermore, we design and control WBG converters for powertrains in more electric mobile systems. The present website includes highlights of our research outcomes, current research staff, and ongoing research projects.

We are always looking for opportunities to establish a working relationship. Prospective students should apply to the Electrical and Computer Engineering Department graduate program.

SPECS Research Highlights


Weak Grid Impacts on the Stability of Grid-Tied Inverters

SPECS research group studied the impacts of circuit and control parameters on the stability of voltage source inverters using a small-signal state-space model in the synchronously rotating dq-frame of reference.

The full-order state-space model is directly extracted from the pulse width modulation switching pattern and enables the stability analysis of concurrent variations in the three-phase circuit and control parameters. The system stability is a function of both the grid R/X ratio and grid inductance. Despite the grid-side inductor of the LCL filter is in series with the grid impedance, they have different impacts on the stability of a grid-tied PQ-controlled VSI, i.e., an increase in the filter inductance may improve the system stability in a weak grid. These findings are verified through simulated and experimentally obtained data.

Dynamic Performance of Variable-Frequency AC-DC Converters

Variable-frequency schemes have increased their presence in aerospace applications while maintaining their popularity in hybrid electric vehicles.

The dynamic performance under parameter mismatch of a variable-frequency ac-dc converter is analyzed. A Lyapunov-based adaptive parameter estimation algorithm is developed, and included in the control scheme to address the performance degradation that occurs from the parameter mismatch between the hardware and the controller due to the variable-frequency and ambient operating conditions. Because of this adaptive parameter estimation technique, the proposed controller can effectively regulate the output dc-bus voltage and maintain a unity power factor. The validity and performance effectiveness of the proposed controller are verified experimentally through a laboratory-scaled three-phase 1.5 kW 270 V SiC-based two-level voltage-source-converter using a variable-frequency programmable grid emulator. The results demonstrate that by including the developed adaptive parameter estimation algorithm in the control scheme, the performance of the ac-dc converter can be improved under rapid input frequency changes and filter parameter variations.


Ultra fast Rectifier for Variable Frequency Applications

SPECS research group developed a dynamic Performance of Variable-Frequency AC-DC Converters. Variable-frequency schemes have increased their presence in aerospace applications while maintaining their popularity in hybrid electric vehicles.

The dynamic performance under parameter mismatch of a variable-frequency ac-dc converter is analyzed. A Lyapunov-based adaptive parameter estimation algorithm is developed, and included in the control scheme to address the performance degradation that occurs from the parameter mismatch between the hardware and the controller due to the variable-frequency and ambient operating conditions. Because of this adaptive parameter estimation technique, the proposed controller can effectively regulate the output dc-bus voltage and maintain a unity power factor. The validity and performance effectiveness of the proposed controller are verified experimentally through a laboratory-scaled three-phase 1.5 kW 270 V SiC-based two-level voltage-source-converter using a variable-frequency programmable grid emulator. The results demonstrate that by including the developed adaptive parameter estimation algorithm in the control scheme, the performance of the ac-dc converter can be improved under rapid input frequency changes and filter parameter variations.


High Frequency Models for Magnetic Circuits and Motors

A three-phase universal motor model depicting the motor behavior from low to high frequencies is developed. The universal model is derived by extending low-frequency standard T-equivalent circuit (IEEE Standard 112), and thus high-frequency effects caused by common-mode and differential-mode can be included in the motor model.

In motor-drive systems, which generally consist of an ac–ac converter, a cable, and an ac electric motor, fast semiconductor devices (e.g., IGBTs, SiC MOSFETs, and recently GaN Transistors) are desirable in order to reduce switching losses and consequently obtain higher efficiency in a compact package. Fast switching means shorter voltage rise time, which can lead to the reflected wave phenomenon as well as high-frequency leakage currents through the system’s stray capacitors. Reflected waves cause voltage spikes at the motor terminals, and the high-frequency leakage currents cause electromagnetic interference (EMI). These two phenomena are commonly modeled as two decoupled single-line circuits, namely, differential mode (DM) and common-mode (CM). Herein, low-to-high frequency model is presented, where both differential and common mode phenomena can be studied. For more information, one may check:

  • B. Mirafzal, G. Skibinski, and R. Tallam, “Determination of parameters in the universal induction motor model,” IEEE Transactions on Industry Applications, vol.45, no. 1, pp. 142 - 151, January/February 2009.

  • B. Mirafzal, G. Skibinski, R. Tallam, D. Schlegel, and R. Lukaszewski, “Universal induction motor model with low-to-high frequency response characteristics,” IEEE Transactions on Industry Applications, vol.43, no. 5, pp. 1233 - 1246, September/October 2007. (IEEE Transactions IEEE IAS Society Paper Award)

  • B. Mirafzal, G. Skibinski, and R. Tallam, “A failure mode for PWM inverter-fed AC motors due to the antiresonance phenomenon,” IEEE Transactions on Industry Applications, vol. 45, no. 5, pp. 1697-1705, September/October 2009.


SPECS Spotlights

For details, please visit "Research" section!

Grid of Nanogrid (GNG) Testbed

SPECS research group will develop "grid of nanogrid (GNG) testbed" funded by National Science Foundation (NSF).

The proposed testbed provides the capability to examine various hypotheses and research ideas on nanogrid controls, hardware, software, communications and security protocols, and standards, under all possible envisioned operating conditions of the power distribution grid, including faults and anomalies in both islanded and networked modes.

"Care-PV" Project

SPECS research group will investigate technologies to enhance distributed grid resiliency and cybersecurity with high penetration of photovoltaics.

U.S. Department of Energy (DOE), Solar Energy Technologies Office (SETO) selected "CARE-PV" project proposed by Kansas State University (KSU) power group to advance solar energy’s role in strengthening resiliency and cybersecurity of the electricity grid.

Smart Three-Phase Power Converters for More Electric Powertrains

SPECS research group is developing and testing "Smart Three-Phase Power Converters for More Electric Powertrains" to seamlessly regulate the output DC voltage while maintaining unity power factor with very low total harmonic distortion in three-phase input currents.

Different control techniques are proposed for this application such as a Lyapunov-based adaptive parameter estimation algorithm, a multi-variable direct model reference adaptive control, and step-ahead predictive control. 1.5 kW SiC-MOSFET two-level voltage-source converter topology is used.