Abstracts:This letter proposes a new modeling framework for stability assessment in grid-forming virtual synchronous generator. Specifically, the mechanism of self-stability and induced-stability have been clarified with frequency and voltage magnitude. The models of frequency self-loop, voltage self-loop, frequency induced-loop, and voltage induced-loop are derived to comprehensively identify whether the mechanism of the oscillation is caused by the self-stabilizing loop or by oscillation transferring. By mathematical derivation combined with logical judgment of physical significance, it is found that frequency has the same closed-loop transfer function with that of active-power. Finally, analysis is validated by experiments.

Abstracts:The development of dc grids requires compact, economical, and efficient means of dc–dc integration. The parallel hybrid converter (PHC) is a suitable candidate for dc–dc integration due to its low energy storage requirement (ESR), soft switching, low submodule (SM) and switch count. However, the requirement of large dc side filtering and harmonic voltage injection (HVI) have been crucial limitations of the PHC. This article proposes a new modulation scheme to eliminate the need of dc filter inductor. The design steps and comparison with existing modulation scheme are briefed. The effectiveness of the proposed modulation scheme is validated on a developed three-phase front-to-front experimental setup.

Abstracts:As a critical power electronic device in dc transmission systems, thyristors are highly favored for their low conduction loss, excellent surge capability, economic efficiency, and reliable current-carrying performance. However, in key applications such as commutation converters, active inverters, and circuit breakers, accurately determining the off-state of thyristors remains a significant challenge for the reliable operation of these systems. The traditional method relies on detecting the reverse recovery current flowing through the thyristor to determine its off-state. This method is often plagued by detection difficulties, high costs, and insufficient accuracy, and no new methods for detecting the off-state of thyristors have been proposed for decades. To address the difficulty in recognizing the off-state of thyristors, this article proposes a novel method for identifying the reverse recovery state of thyristors based on the gate voltage of the thyristor. This method eliminates the need to measure the high current on the primary side, requiring only the measurement of a small voltage on the secondary side to accurately determine the thyristor's reverse recovery state. Experimental validation confirms the feasibility of this approach. The proposed method offers advantages such as low cost and ease of integration, providing an effective solution for identifying the reverse recovery state of thyristors in existing equipment.

Abstracts:Noninvasive, real-time monitoring of large-span currents in power grid and electric vehicles remains a challenge. A resonant galvanometer (RGM) achieving multiple measurement ranges with a single sensing unit is proposed in this article. An electromagnetic torque introduced theory for ac measurement is established to analyze the deviated output voltages, which have not been well physically interpreted and theoretically characterized so far. The deviated output voltages are defined as two asymmetric subpeaks for the first time. According to the Euler–Bernoulli beam theory, two asymmetric subpeaks have the potential to achieve multirange measurement with the main peak, which is at the magnetic field gradient extremum and directly opposite to the cable. A multirange sensing mechanism is proposed with three peaks, comprised of two newly defined asymmetric subpeaks and one main peak. Measurement ranges of the two subpeaks are two and five times than that of the main peak, respectively. Geometrical design of the sensing unit is analyzed to further adjust the multiranges via three peak values. A prototype with a single sensing unit is designed and fabricated to achieve multiple measurement ranges, and its practical applications in power grid and electric vehicles are also considered.

Abstracts:A major challenge towards enabling energy autonomous microsystems is cold-starting, especially in real use case environments which are often uncertain and involve long inactivity periods. In this article, a dual supercapacitor storage power management architecture is proposed, with the primary storage capacitor providing fast start-up and the secondary providing a large energy buffer. The circuit introduces a combination of a MOSFET switch and a buck converter that can handle efficient charge transport and eliminate leakage between the two storage capacitors, leading to faster cold starting. A start-up time reduction of more than two orders of magnitude over conventional solutions is experimentally demonstrated, for a 1.5 mF/470 mF supercapacitor combination, without a compromise in overall efficiency. The various functional modes of the system are experimentally analyzed, using an inductive power line energy harvester with currents that correspond to an industrially defined aircraft sensor use case. For example, 11 mW and 32 mW regulated output was measured from a 10 A and 15 A rms, 500 Hz power line, respectively. The architecture is configurable and can be dynamically parametrized and controlled to optimize power routing according to functional priorities by the microcontroller of the powered system.

Abstracts:Modular multilevel cascade converters (MMCCs) have emerged as one of the most attractive topologies for medium and high-voltage applications due to their modularity, scalability, redundancy, and high power quality. Voltage balancing in power submodule (SM) capacitors plays a critical role in the internal energy balancing of the MMCC, making monitoring SM capacitor voltages a crucial task. However, achieving higher operating voltages requires a substantial increase in the number of voltage sensors and communication lines. This escalation in hardware complexity renders the system more reliant on sensors, reducing its reliability. Several techniques for estimating capacitor voltages have been presented to address this control and design burden. This work proposes an extended Kalman filter (EKF)-based observer for capacitor voltage estimation of all SMs in a triple-star bridge converter (TSBC). The proposed approach operates effectively under both open-loop and closed-loop conditions during transients and steady-state operation, enabling a decoupled controller using just one voltage and one current sensor per cluster. Experiments conducted in a TSBC composed of 27 SMs demonstrate the effectiveness of the proposed approach during transients and steady-state operation.

Abstracts:Transformerless inverters are widely used to integrate the photovoltaic (PV) source into the distributed generation system. Within the converter, an open-circuit (OC) switch fault may lead to the partial or total failure of the converter. To address this issue, a new technique for detecting and localizing OC switch faults based on pole-to-pole voltage (voltage measured across the inverter output terminals) is proposed. The proposed variables for fault detection and localization (FDL) are continuously generated with every sampled pole-to-pole voltage and are compared with threshold values which are immune to parameter variation. As a result, OC is detected and located within a switching cycle for the ac side bypass switches. For localizing the OC fault in the H-bridge, the converter is reconfigured once the fault in the H-bridge switch is detected using pole-to-pole voltage. The input voltage required for the maximum power point tracking (MPPT) is estimated from the voltage measured with the new sensor arrangement for pole-to-pole voltage measurement. This makes the number of sensors the same as in a conventional converter. The viability and effectiveness of this approach are demonstrated through simulation studies on the highly efficient and reliable inverter concept (HERIC) inverter, a popular transformerless inverter topology. Additionally, a laboratory prototype is developed to validate the practical applicability of the method.

Abstracts:The main function of pulse-width modulation (PWM) converters in many applications is to control the dc-link voltage with good dynamic performance and strong disturbance rejection capability. Finite-control-set model predictive control (FCS-MPC) is known for its merits in both the above aspects, especially the noncascaded FCS-MPC control structure. However, as to be discussed in this article, the noncascaded FCS-MPC cannot be used to directly control the dc-link voltage of PWM converters, due to the problem of multiequilibrium points caused by the essential nonlinear characteristic of PWM converters. Hence, a quasi-noncascaded dc-link voltage predictive control structure is proposed for the first time, which keeps the outstanding dynamic performance and strong disturbance rejection capability of noncascaded FCS-MPC while avoids overcurrent caused by the unexpected equilibrium points. In addition, the proposed method can inherently handle the parameter mismatch issue, which is an important merit for MPC. Experimental results validate the theoretical analysis and performance of the proposed control strategy.

Abstracts:Single-inductor dual-output (SIDO) buck converter has been widely applied in fields of portable electronic products and smart homes due to their advantages of small size and multiple outputs. However, cross regulation seriously deteriorates the stability of the converter. In addition, parasitic parameters of circuit components reduce the conversion efficiency of the converter and have a significant impact on cross regulation. To suppress the cross regulation and improve the conversion efficiency of the nonideal SIDO buck converter, a multiobjective optimization control strategy is proposed. Considering the parasitic parameters of circuit components, a large signal model of the converter is established, and a predictive equation is constructed based on the model predictive control theory. Furthermore, an objective function for optimizing output error is established based on weighting the output voltage error and inductor current error. Then, a method is proposed to achieve real-time correction of the state variable reference values. The power loss of the system is analyzed and weighted onto the objective function to improve the conversion efficiency. Compared with the common mode voltage-differential mode voltage control method, simulation and experimental results show that the proposed strategy provides smaller cross regulation and better dynamic performance. The conversion efficiency is improved by 6.6%.

Abstracts:Hybrid active neutral-point-clamped (HANPC) converters comprising silicon and silicon carbide devices are promising topologies in middle-low power conversion systems. The reliable operation of such converters is highly desirable, which depends on effective fault-tolerant schemes. However, existing schemes do not provide HANPC converters with the ability to tolerate the failures of multiple outer-switches with satisfactory fault-tolerant performance in terms of neutral-point voltage balancing and rated output voltage. To address this issue, the shared redundant unit is configured into HANPC converters. The matched fault-tolerant control strategy is proposed with rearranged switching sequences by utilizing the available space vector. In this context, the feasible region of the designed vector sequence (FRDVS) for fault-tolerant operation of HANPC converters is defined. Subsequently, the boundaries of FRDVS are quantitatively analyzed under different power factors. The improved fault-tolerant scheme allows the continuous operation of HANPC converters at rated capacity during the fault period, even up to open-circuit faults at all outer-switches. Experimental results are presented to verify the effectiveness of the proposed fault-tolerant scheme.