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Design-Oriented Stability of Outer Voltage Loop in Capacitor Current Controlled Buck Converters
Zhang, Xi,Zhang, Zhongwei,Bao, Bocheng,Bao, Han,Wu, Zhimin,Yao, Kaiwen,Wu, Jing The Korean Institute of Power Electronics 2019 JOURNAL OF POWER ELECTRONICS Vol.19 No.4
Due to the inherent feedforward of load current, capacitor current (CC) control shows a fast transient response that makes it suitable for the power supplies used in various portable electronic devices. However, considering the effect of the outer voltage loop, the stable range of the duty-cycle is significantly diminished in CC controlled buck converters. To investigate the stability effect of the outer voltage loop on buck converters, a CC controlled buck converter with a proportion-integral (PI) compensator is taken as an example, and its second-order discrete-time model is established. Based on this model, the instability caused by the duty-cycle is discussed with consideration of the outer voltage loop. Then the dynamical effects of the feedback gain of the PI compensator and the equivalent series resistance (ESR) of the output capacitor on the CC controlled buck converter with a PI compensator are studied. Furthermore, the design-oriented closed-loop stability criterion is derived. Finally, PSIM simulations and experimental results are supplied to verify the theoretical analyses.
Design-Oriented Stability of Outer Voltage Loop in Capacitor Current Controlled Buck Converters
Xi Zhang,Zhongwei Zhang,Bocheng Bao,Han Bao,Zhimin Wu,Kaiwen Yao,Jing Wu 전력전자학회 2019 JOURNAL OF POWER ELECTRONICS Vol.19 No.4
Due to the inherent feedforward of load current, capacitor current (CC) control shows a fast transient response that makes itsuitable for the power supplies used in various portable electronic devices. However, considering the effect of the outer voltageloop, the stable range of the duty-cycle is significantly diminished in CC controlled buck converters. To investigate the stabilityeffect of the outer voltage loop on buck converters, a CC controlled buck converter with a proportion-integral (PI) compensatoris taken as an example, and its second-order discrete-time model is established. Based on this model, the instability caused by theduty-cycle is discussed with consideration of the outer voltage loop. Then the dynamical effects of the feedback gain of the PIcompensator and the equivalent series resistance (ESR) of the output capacitor on the CC controlled buck converter with a PIcompensator are studied. Furthermore, the design-oriented closed-loop stability criterion is derived. Finally, PSIM simulationsand experimental results are supplied to verify the theoretical analyses.
Zhang, Xi,Xu, Jianping,Wu, Jiahui,Bao, Bocheng,Zhou, Guohua,Zhang, Kaitun The Korean Institute of Power Electronics 2017 JOURNAL OF POWER ELECTRONICS Vol.17 No.5
The constant on-time current-mode controlled (COT-CMC) switching dc-dc converter is stable, with no subharmonic oscillation in its current loop when a voltage ripple in its outer voltage loop is ignored. However, when its output capacitance is small or its feedback gain is high, subharmonic oscillation may occur in a COT-CMC buck converter with a proportional-integral (PI) compensator. To investigate the subharmonic instability of COT-CMC buck converters with a PI compensator, an accurate reduced-order asynchronous-switching map model of a COT-CMC buck converter with a PI compensator is established. Based on this, the instability behaviors caused by output capacitance and feedback gain are investigated. Furthermore, an approximate instability condition is obtained and design-oriented stability boundaries in different circuit parameter spaces are yielded. The analysis results show that the instability of COT-CMC buck converters with a PI compensator is mainly affected by the output capacitance, output capacitor equivalent series resistance (ESR), feedback gain, current-sensing gain and constant on-time. The study results of this paper are helpful for the circuit parameter design of COT-CMC switching dc-dc converters. Experimental results are provided to verify the analysis results.
Xi Zhang,Jianping Xu,Jiahui Wu,Bocheng Bao,Guohua Zhou,Kaitun Zhang 전력전자학회 2017 JOURNAL OF POWER ELECTRONICS Vol.17 No.5
The constant on-time current-mode controlled (COT-CMC) switching dc-dc converter is stable, with no subharmonic oscillation in its current loop when a voltage ripple in its outer voltage loop is ignored. However, when its output capacitance is small or its feedback gain is high, subharmonic oscillation may occur in a COT-CMC buck converter with a proportional-integral (PI) compensator. To investigate the subharmonic instability of COT-CMC buck converters with a PI compensator, an accurate reduced-order asynchronous-switching map model of a COT-CMC buck converter with a PI compensator is established. Based on this, the instability behaviors caused by output capacitance and feedback gain are investigated. Furthermore, an approximate instability condition is obtained and design-oriented stability boundaries in different circuit parameter spaces are yielded. The analysis results show that the instability of COT-CMC buck converters with a PI compensator is mainly affected by the output capacitance, output capacitor equivalent series resistance (ESR), feedback gain, current-sensing gain and constant on-time. The study results of this paper are helpful for the circuit parameter design of COT-CMC switching dc-dc converters. Experimental results are provided to verify the analysis results.