Within a power converter, multiple currents are usually measured for control, protection, and/or monitoring. They are therefore important sources of information, which must unquestionably be measured accurately to maintain continuous and reliable operation of the power converter. Accurate current measurement has however become tougher with the introduction of wide band-gap (WBG) devices with switching frequency tending toward the megahertz (MHz) range. Because of that, the installed current sensors must have a significantly widened bandwidth. Moreover, they must be nonintrusive and compact, in order not to degrade fast switching characteristics and high power density of the WBG converter. Presently, these features are not collectively obtainable from existing commercial current sensors. Consequently, many new current sensing techniques have surfaced in the literature for usage with the more demanding MHz power converter. These new techniques, some classical techniques, and their hybrid integrations are now reviewed, after overviewing functionalities made possible by current sensors in a power converter. Last but importantly, some future developmental trends aimed at matching MHz current sensors with MHz power converters are described, before concluding the article.

https://ieeexplore.ieee.org/ielx7/63/9714885/09658157.pdf

A Review of Megahertz Current Sensors for Megahertz Power Converters

An quasi-online equivalent series resistance (ESR) identification method that considers the impact of capacitance based on variational mode decomposition (VMD) of forward converters is proposed in this letter. First, the capacitance impact is included in ESR derivation. Subsequently, VMD is adopted to process characteristic signals for harmonic analysis, filter out noise, and simplify circuits design. The experiments and simulation are employed to verify the proposed method. In addition, in order to overcome the disadvantages of using ideal capacitors in the traditional simulation, fractional-order capacitors are constructed to describe the nonideal characteristics of the capacitor. Meanwhile, the identification result is compared with the LCR meter measurement. Thus, the superiority of the proposed ESR quasi-online identification method and the construction method of fractional-order capacitors are confirmed through comparative analysis. 

An ESR Quasi-Online Identification Method for the Fractional-Order Capacitor of Forward Converters Based on Variational Mode Decomposition

Aluminum electrolytic capacitors (Al-Caps) are widely used in the dc-link of ac/dc applications, however, they are one of the weakest components in power electronic converters. With the degradation of Al-Cap, its capacitance (C) decreases, and the equivalent series resistance (ESR) increases. Based on this, many efforts have been made to realize condition monitoring (CM) of Al-Caps. Unfortunately, additional hardware (including current sensors and sampling circuits), and/or powerful data processing tools are usually required, which increases the cost and would bring new reliability risks. Considering this issue, this paper presents a transient-based CM scheme for dc-link capacitors in digital-controlled boost power factor correction (PFC) converters, which does not need additional sampling devices. By analyzing the relationship between large-signal transient voltage profile and dc-link capacitance, a calculation model is established. Based on the sampled voltage and current signals used for digital control, the dc-link capacitance can be online estimated. Its feasibility is validated in simulation with a boost PFC operating in continuous conduction mode (CCM) and discontinuous conduction mode (DCM). Furthermore, taking a 1-kW boost PFC operating in CCM as a case study, experimental results illustrate that the estimation errors of the dc-link capacitance are less than 3.5% (error of a single test) and 1.5% (average error of multiple tests).

Online DC-Link Capacitance Monitoring for Digital-Controlled Boost PFC Converters without Additional Sampling Devices

Online monitoring of Lithium-ion (Li-ion) battery internal temperature by electrochemical impedance spectrum (EIS) is important for the system safe and reliable operation. However, it is challenging in the high temperature region due to the limited thermal sensitivity. Moreover, additional signal injection or disturbance for online EIS measurement may interact with the operating system. To address these challenges, a Li-ion battery internal temperature continuous monitoring method using the self-excited ultrahigh frequency (UHF) PWM switching oscillations (e.g., several hundred kHz) is proposed in this article. First, the UHF EIS characteristics of a Li-ion battery are explored to find a novel thermal sensitive electric parameter applicable for high temperature measurement. Then, an PWM switching oscillation based online battery temperature monitoring scheme is presented, including the UHF oscillation sensor, resonance impedance extraction algorithm, and battery internal temperature estimation procedure. Finally, experimental work was carried out, and the results demonstrate an excellent performance, such as high sensitivity over 90 °C, ms-level fast response, and noncontract continuous monitoring.

Online Monitoring of Lithium-Ion Battery Internal Temperature Using PWM Switching Oscillations

Online monitoring of Lithium-ion (Li-ion) battery internal temperature by electrochemical impedance spectrum (EIS) is important for the system safe and reliable operation. However, it is challenging in the high temperature region due to the limited thermal sensitivity. Moreover, additional signal injection or disturbance for online EIS measurement may interact with the operating system. To address these challenges, a Li-ion battery internal temperature continuous monitoring method using the self-excited ultrahigh frequency (UHF) PWM switching oscillations (e.g., several hundred kHz) is proposed in this article. First, the UHF EIS characteristics of a Li-ion battery are explored to find a novel thermal sensitive electric parameter applicable for high temperature measurement. Then, an PWM switching oscillation based online battery temperature monitoring scheme is presented, including the UHF oscillation sensor, resonance impedance extraction algorithm, and battery internal temperature estimation procedure. Finally, experimental work was carried out, and the results demonstrate an excellent performance, such as high sensitivity over 90 °C, ms-level fast response, and noncontract continuous monitoring. 

Online monitoring of dc-link capacitor's equivalent series resistance (ESR) could provide valuable and timely information for power converter failure prognosis and predictive maintenance. The conventional ESR estimation methods are mainly based on pulsewidth modulation (PWM) voltage and current ripples (ESRaΔ u c/Δ i c), but the performance is affected by operating conditions (especially at light-load), quasi-resonance effect and sensor amplitude error. To overcome these difficulties, an online ESR monitoring method is proposed using the damping characteristic of dc capacitor switching ringings. The intrinsic high-frequency (HF) resonance incidents between the power device fast switching and converter parasitic parameters are utilized in this article. First, the mechanism of dc capacitor switching ringing is analyzed by the HF resonance equivalent circuit. The analytic relationship between the damping characteristic and the ESR is established. Then, the condition monitoring (CM) scheme, noncontact HF sensor, and half-power bandwidth algorithm for ESR estimation are presented. Finally, an experimental study is carried out to validate the feasibility and effectiveness. The damping of switching ringing is inherently sensitive to the ESR of dc capacitor under the condition of resonance. Both theoretical analysis and experimental results confirm that the proposed method can achieve mΩ-level accuracy and good robustness under different conditions.

Online ESR Monitoring of DC-Link Capacitor in Voltage-Source-Converter Using Damping Characteristic of Switching Ringings

The invention relates to a DC capacitor ESR on-line monitoring method and system. The method comprises the following steps: 1) obtaining an absorption capacitor capacitance parameter Cs; 2) detectinga PWM high-frequency oscillation signal Sosc on line when a converter system operates normally; 3) conditioning the PWM high-frequency oscillation signal Sosc to obtain a high-frequency resonance signal Sres; 4) extracting the resonant frequency f0 and the attenuation time constant tau of the PWM resonant circuit from the high-frequency resonant signal Sosc; 5) calculating the total resistance Rtot of the PWM resonant circuit according to the resonant frequency f0 and the attenuation time constant tau of the high-frequency resonant signal Sosc; and 6) subtracting the total resistance Rtot of the PWM resonance circuit from the initial value Rtot0 of the total resistance of the resonance circuit to obtain a change value deltaESR of the DC capacitor ESR. Compared with the prior art, the method has the advantages of high sensitivity, high accuracy, simplicity and convenience in implementation, safety and the like.

Zheng Jingnan

Papers

Online ESR Monitoring of DC-Link Capacitor in Voltage-Source-Converter Using Damping Characteristic of Switching Ringings

DC capacitor ESR on-line monitoring method and system