TY - JOUR
T1 - Optimal Variable Switching Frequency Scheme to Reduce Loss of Single-Phase Grid-Connected Inverter with Unipolar and Bipolar PWM
AU - Xia, Yinglai
AU - Roy, Jinia
AU - Ayyanar, Rajapandian
N1 - Funding Information:
Manuscript received July 26, 2019; revised October 16, 2019; accepted November 23, 2019. Date of publication November 26, 2019; date of current version January 20, 2021. This work was supported in part by the Office of Energy Efficiency and Renewable Energy and in part by the U.S. Department of Energy with North Carolina State University, PowerAmerica Institute, under Award DE-EE0006521. Recommended for publication by Associate Editor Shuai Shao. (Corresponding author: Yinglai Xia.) Y. Xia and R. Ayyanar are with the School of Electrical, Computer and Energy Engineering, Arizona State University, Tempe, AZ 85287 USA (e-mail: yinglaixia@gmail.com).
Publisher Copyright:
© 2013 IEEE.
PY - 2021/2
Y1 - 2021/2
N2 - Reducing the power loss of a converter without increasing its volume or cost in hardware has always been a much sought-after but challenging goal. This article proposes a comprehensive variable switching frequency (VSF) scheme to improve the overall system efficiency while still meeting a given total harmonic distortion (THD) requirement without any hardware changes, achieved only by changes to the controller. In this article, it is analyzed that for the H-bridge inverter, the inductor copper loss and the switch conduction loss are independent of the switching frequency (SF), while the device switching loss and the inductor core loss are functions of the SF. This article aims at weighting the combined switching loss and inductor core loss for both the unipolar and bipolar modulation techniques, with the constraint on the output THD, which, for fixed passive components, is a function of inductor ripple current that in turn depends on the SF. An optimal VSF scheme is devised through rigorous mathematical analysis of the output ripple component and the SF-dependent losses. In each switching cycle, the inductor ripple current is predicted with the circuit parameters, such as duty cycle, switching period, inductance, and dc voltage, and by implementing the VSF scheme, the current ripple is optimally varied such as to satisfy the THD requirement while reducing the SF-dependent losses. A generalized method to design VSF schemes for any topology and specifications is also presented, which would help future users in designing the VSF controller. A 1-kW H-bridge inverter using SiC MOSFETs and powdered iron/ferrite core has been built to validate the theoretical analysis. Both constant SF (CSF) scheme (200 kHz) and optimal VSF scheme with simple controller modification have been implemented in the experimental prototype using DSP TMS320f28335. Compared with the CSF scheme, the optimal VSF scheme shows a significant improvement in the system efficiency at rated power from 94.7% to 95.4% with a corresponding saving of 16.5% in the SF-dependent loss in unipolar modulation and from 95.5% to 96.8% with a corresponding saving of 36.5% in the SF-dependent loss in bipolar modulation.
AB - Reducing the power loss of a converter without increasing its volume or cost in hardware has always been a much sought-after but challenging goal. This article proposes a comprehensive variable switching frequency (VSF) scheme to improve the overall system efficiency while still meeting a given total harmonic distortion (THD) requirement without any hardware changes, achieved only by changes to the controller. In this article, it is analyzed that for the H-bridge inverter, the inductor copper loss and the switch conduction loss are independent of the switching frequency (SF), while the device switching loss and the inductor core loss are functions of the SF. This article aims at weighting the combined switching loss and inductor core loss for both the unipolar and bipolar modulation techniques, with the constraint on the output THD, which, for fixed passive components, is a function of inductor ripple current that in turn depends on the SF. An optimal VSF scheme is devised through rigorous mathematical analysis of the output ripple component and the SF-dependent losses. In each switching cycle, the inductor ripple current is predicted with the circuit parameters, such as duty cycle, switching period, inductance, and dc voltage, and by implementing the VSF scheme, the current ripple is optimally varied such as to satisfy the THD requirement while reducing the SF-dependent losses. A generalized method to design VSF schemes for any topology and specifications is also presented, which would help future users in designing the VSF controller. A 1-kW H-bridge inverter using SiC MOSFETs and powdered iron/ferrite core has been built to validate the theoretical analysis. Both constant SF (CSF) scheme (200 kHz) and optimal VSF scheme with simple controller modification have been implemented in the experimental prototype using DSP TMS320f28335. Compared with the CSF scheme, the optimal VSF scheme shows a significant improvement in the system efficiency at rated power from 94.7% to 95.4% with a corresponding saving of 16.5% in the SF-dependent loss in unipolar modulation and from 95.5% to 96.8% with a corresponding saving of 36.5% in the SF-dependent loss in bipolar modulation.
KW - Conduction loss
KW - DSP controller
KW - Lagrange optimization
KW - inductor core loss
KW - loss optimization
KW - switching loss
KW - variable switching frequency (VSF)
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U2 - 10.1109/JESTPE.2019.2956034
DO - 10.1109/JESTPE.2019.2956034
M3 - Article
AN - SCOPUS:85076018551
SN - 2168-6777
VL - 9
SP - 1013
EP - 1026
JO - IEEE Journal of Emerging and Selected Topics in Power Electronics
JF - IEEE Journal of Emerging and Selected Topics in Power Electronics
IS - 1
M1 - 8913560
ER -