Port Voltage Research Articles

Modulation strategy design method for single-inductor multi-port converter based on reinforcement learning

Single-inductor multi-port converters have the characteristics of "more silicon and less magnetism" and have great application potential in many fields. However, single-inductor multi-port converters have many switching modes and the modulation strategy design is complex. The current design method is to manually select the switching mode sequence and perform modal analysis. The design process requires power electronics expertise and experience. This paper proposes a modulation strategy design method for single-inductor multi-port converters based on reinforcement learning. This method uses a neural network to generate the modulation strategy and adopts a set of simple rules to provide rewards for training the neural network. Through reinforcement learning, the neural network can summarize experience in trial and error without human intervention and finally generate the optimal modulation strategy. This method has many advantages: (1) It only requires known conditions such as port voltage and converter structure as input, and some simple constraints as rewards, avoiding complicated manual design; (2) It can use a neural network to generate the optimal modulation strategy under different operating conditions, and has strong adaptability. Based on this method, a modulation strategy design for a single-inductor multi-port converter is carried out, and the effectiveness of the method is verified by experiments.

Adaptive control strategy for microgrid inverters based on Narendra model

In recent years, microgrid technology has been widely studied and applied. However, with times developing, the installed capacity of distributed power generation devices has been improved, and work is being carried out in increasingly complex situations, resulting in a decline in the control performance of microgrids. In view of this, to effectively improve inverter’s control performance, research is conducted on the fusion of Narendra model and adaptive control strategies for real-time voltage correction and compensation in complex situations. Compared to traditional inverters, inverters under research methods have faster voltage recovery speed when encountering load switching, and can recover in about one cycle, with good control performance. In the comparison between the improved inverter adaptive control system and the inverter adaptive system, the improved inverter voltage recovery speed is faster, can be restored within one cycle, and the control effect of the inverter is better. The harmonic rate of the port voltage has decreased from 10.43 to 1.92%. The applicability of the research method was verified. It indicats that the research method can improve inverter’s control effect and solve problems such as voltage deviation, three-phase asymmetry, harmonic pollution, etc. that are easily generated by the output terminal voltage. Simultaneously, research has provided theoretical basis and data support for the research of microgrids.

A novel multi‐slice electromagnetic field‐circuit coupling method for transient computation of long‐distance gas‐insulated transmission lines

AbstractAccurate calculation of short‐circuit electromagnetic force is crucial for both mechanical strength check and the optimal design of gas‐insulated transmission lines (GIL). Since the full 3D numerical simulation method is highly time‐consuming, a novel lightweight 2D multi‐slice electromagnetic field‐circuit coupled method for computing transient electromagnetic force is proposed, where appropriate port voltage degrees of freedom (DoFs) are introduced for the solid GIL conductor terminals. When the transient magnetic field equations are combined with the constraint equations of circuit part, including nodal voltage and loop current DoFs, a direct field‐circuit coupling scheme is thus derived. The proposed method can simultaneously consider the effect of interphase‐shunts and ground wires, as well as the skin effect and proximity effect. It can accurately capture the transient electromagnetic characteristics of GIL spanning from several to tens of kilometers under different short‐circuit conditions. The transient electromagnetic forces, as well as the induced voltages and currents of the enclosure, are analysed by the proposed method for both single‐phase and three‐phase enclosed GIL under various short‐circuit conditions. The proposed method has the advantages of high accuracy and lightweight computational cost, and thus it is also suitable for conducting important simulation tasks such as mechanical strength checks during the design optimisation phase of long‐distance GIL.

Toward a Comprehensive Evaluation on the Online Methods for Monitoring Transformer Turn-to-Turn Faults

Transformer winding turn-to-turn fault is the prominent cause of transformer total failure, so detecting the winding fault in real time to stop the failure development in advance is imperative. However, existing techniques entailing periodic offline inspections fail to continuously monitor transformer winding states while causing extra costs due to the outage during inspections. This has driven researchers to consider effective continuous online monitoring methods from several technical perspectives, including typically port voltage current analysis, online frequency response analysis, and vibration analysis. Since these methods are conventionally evaluated with qualitative comparisons focusing only on feasibility, quantitative assessments indispensable for the targeted improvement of the methods and the most suitable method decision in specific scenarios are still missing. To this end, we conduct a comprehensive evaluation on the three methods by leveraging both experiment and theoretical analysis. Specifically, a customized experiment platform has been designed to support data acquisition under different operating conditions. As conventional feature mining algorithms cannot process the monitoring data produced by different methods in a uniform manner, a feature extraction algorithm leveraging image mining is proposed to extract data features after mapping the test data into a high-dimensional image. This novel algorithm allows us to fully assess several fundamental aspects (i.e., sensitivity, repeatability, and anti-interference capability) of these monitoring methods.

High-Frequency Three-Port DC–DC Converter With Zero-Voltage Switching Operation

In this paper, an isolated zero voltage switching three-port DC-DC converter (TPC) using a planer transformer is proposed and operated for the frequency of 1MHz. The proposed converter has a bidirectional operation. In the proposed converter, the main transformer is used to isolate low dc voltage ports from the high dc voltage port and to increase the voltage conversion ratio of the secondary side port, which supplies the load. The proposed converter is partially isolated TPC and has the advantage of galvanically isolation between one of the ports which are interfaced to the main load and the other two ports (input and storage-side ports) are non-isolated and common-grounded. The proposed converter is compared with other recent converters of the same type, and it is concluded that the proposed converter has achieved the capabilities of having an isolated structure with lower volume, interfacing three different dc voltages in the three dc ports, having the bidirectional operation, high voltage gain, zero voltage switching operation of all four switches, simple switching pattern, achieving simple controlling way for all ranges of duty cycles both step-up and step-down operations, utilizing a nonlinear digital controlling system, smaller size, higher operating frequency, higher efficiency, and high power density.

Active Power Allocation Strategy for a Novel Wireless Open-Winding Motor System With Improved Antimisalignment Capability

This paper proposes a wireless open-winding motor (WOWM) system, where noncontact operation can be achieved with the magnetic coupler. Thus, the flexibility and reliability of the WOWM system can be improved. Two isolated DC voltage ports for the open-winding motor can be obtained with only one DC voltage source, which facilitates the application of the system. The zero-sequence current in the motor winding can be suppressed and the DC link voltage utilization rate can be maximized owing to the isolated DC link structure. Besides, the operation characteristics of the WOWM system are analyzed in detail. The decoupled dual-receivers are designed, which ensures that the ratio of DC link voltages is load-independent. Moreover, the influences of misalignment on the WOWM system, including the overmodulation and increased phase current ripple are presented. The DC link voltage regulation (DVR) and active power allocation (APA) strategy are further proposed. The DC link voltage reference is identified based on the operating state of the motor for high performance operation. The allocation coefficient, <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">k</i> is adjusted according to the extent of misalignment, which improves the anti-misalignment capability. The feasibility of the WOWM system and the effectiveness of the DVR and APA strategy are verified by experiments.

A comparative analysis of power pulsating buffer architectures for mitigating high‐frequency and low‐frequency ripple in PV microinverter applications

AbstractThis study provides a comparative analysis of feasible architectures of Power Pulsating Buffer (PPB) as an actively controlled energy storage solution alternative to the electrolytic capacitors in a single‐stage isolated, single‐phase 120 V AC 60Hz grid‐connected photovoltaic (PV) microinverter for a 400 W rated system with 20–40 V input range. The comparison encompasses key factors including energy density, volume reduction, efficiency, frequency operation, and system stability. The findings shed light on the primary advantages and disadvantages of the buck‐ and boost‐derived PPB under study. The results indicate that the boost PPB exhibits enhanced stability, a more compact design, and higher power efficiency compared to the buck PPB. However, for low switching frequency operations, the buck PPB proves to be more effective in mitigating DC port voltage ripple and ensuring controller over microinverter load variation.

Switching Network Loss Minimization Through Multivariable Modulation in a Multiactive Bridge Converter

This paper presents a unified and generalized modeling, circuit analysis and power flow optimization techniques for a n-port multi-active bridge (MAB) dc-dc converter comprised of n active full bridges and a multi-winding transformer. The work aims at improving the efficiency of the MAB converter for a wide load and port voltage gain range by proposing an optimal phase-duty control variable-based modulation strategy. The loss optimization technique constitutes of two stages: firstly, both the switching and conduction loss objective functions are equivalently formulated by relating them to the transformer winding current peaks and RMSs that are synthesized by employing the proposed generalized harmonic approximation (GHA) based computational model; secondly, a multivariable multi-constrained optimization technique is adopted in order to minimize the converter power loss for wide load-gain range. Moreover, the universal zero-voltage switching (ZVS) criteria for any MAB port is also derived by proposing a port-equivalent converter model. A 600W quadruple active bridge (QAB) converter proof-of-concept is designed and tested to validate the theoretical analysis, claims, thus verifying the applicability of the generic MAB loss optimization technique for any converter candidate under the MAB family. With the implementation of proposed optimal phase-duty control, the experimental results show efficiency increment up to 17% at non-unity voltage gain and 10% loading condition, when compared to the conventional phase modulation technique.

Generalized Architecture of a GaN-Based Modular Multiport Multilevel Flying Capacitor Converter

This paper proposes a generalized Gallium Nitride (GaN) based modular multiport multilevel flying capacitor architecture. In other words, the attractive flying capacitor multilevel (FCML) design and the full-bridge unfolding circuit are employed to develop a multiport multilevel converter architecture that fits various applications. Each module can be designed to contain any combination of AC and DC ports connected through DC-to-DC and DC-to-AC power conversion paths. These conversion paths are FCML topologies that can be designed with any number of levels; the DC-to-AC paths incorporate the full-bridge unfolding circuit. Two example prototypes with open-loop control, three-port and four-port, have verified this generalized architecture. A single module 3 kW three-port four-level prototype with two DC ports and an AC port has achieved a compact size of 11.6 in <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sup> (4.8 in ×4.3 in × 0.56 in) and a high power density of 258.6 W/in <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sup> . The three ports are connected through DC-to-AC and DC-to-DC paths that have achieved peak efficiencies of 98.2% and 99.43%, respectively. The total harmonic distortion (THD) of the AC port's voltage and current are 1.26% and 1.23%, respectively. It operates at a high switching frequency of 120 kHz because of the GaN switches and has an actual frequency (inductor's ripple frequency) of 360 kHz thanks to the frequency multiplication effect of the FCML. The four-port prototype contains three DC ports and an AC port and achieved similar high figures of merit. These experimental results of the two prototypes of high efficiency, power density, and compact size are presented in this article and highlight this architecture's promising potential. The choice of the number of modules, ports, and levels depends on the application and its specification; therefore, this proposed generalized structure may serve as a reference design approach for various applications of interest.

Bifurcation Behavior Analysis and Stability Region Discrimination for Series-Parallel Architecture Electric Energy Router

Electric energy routers (EERs) can effectively deal with the energy management issues caused by the access of multi-sources and multi-loads. Different from the energy transmission form in the existing series architecture EER (SA-EER) for low-voltage distribution networks, a new series-parallel architecture EER (SPA-EER) has the advantages of high-power transmission capability and reactive power flexible operation. However, if controller parameters change beyond their critical stability boundaries, SPA-EER will produce slow- and fast-scale bifurcation behaviors, which are manifested as low- and high-frequency oscillations of port voltages or port currents in varying degrees. To avoid the system instability caused by controller parameter changes, how to discriminate the stability regions of controller parameters for SPA-EER is a key research content in this paper. To this end, the stroboscopic mapping discrete model of SPA-EER system is first established, and system bifurcation behaviors are analyzed based on bifurcation theory. Furthermore, the critical stability boundaries of controller parameters are discriminated by using Jacobian matrix, root locus and bifurcation diagram. After that, a time delay feedback control (TDFC) is employed to suppress system bifurcation behaviors. Finally, the correctness of bifurcation analysis and the effectiveness of TDFC are verified by a hardware-in-the-loop (HIL) experimental platform.

The Closed-Loop Control of the Half-Bridge-Based MMC Drive with Variable DC-Link Voltage

The modular multilevel converter (MMC) based on half-bridge modules is a power converter topology suitable for high-power medium-voltage variable-speed drives. However, the voltage of its flying capacitors is negatively affected when low frequencies appear at the AC port. This paper analyzes the influence of using a variable DC port voltage in a machine-side MMC by implementing a closed-loop approach, ensuring a constant voltage fluctuation in the capacitors of the MMC during the whole operating range. The effectiveness of the proposed control scheme is demonstrated through simulation studies and experimental validation tests conducted using a 7.5 kW experimental prototype composed of an induction machine fed by an MMC with 18 half-bridge cells.

Improved SEM Current Ringing Suppressor for Maglev Trains

In electromagnetic suspension (EMS) systems, the air gap between the suspension electromagnet (SEM) and steel track is adjusted by changing the electromagnetic attraction force, which is accomplished by controlling the maglev chopper (MC). When switching the power electronic devices of the MC, SEM current ringing tends to occur, which is harmful to the whole EMS system. A conventional current ringing suppressor (CRS) deteriorates the SEM port voltage ringing, which may accelerate the aging process of SEM insulation or even directly result in a breakdown fault. Herein, to explore the generation mechanism of SEM current ringing, a third-order equivalent circuit model of the suspension electromagnet-maglev chopper (SEM-MC) system is established by using the field-circuit coupling analysis technique. A series of simulations and experiments have been undertaken to verify the validity of the built circuit model, and the deviation between the simulation and experimental results is acceptable. As the influencing factors of SEM current ringing are analyzed based on this third-order equivalent circuit model, an improved CRS, i.e., hybrid inductor-resistor CRS, is proposed to avoid deteriorating the SEM port voltage ringing and protect the SEM insulation. Finally, the feasibility of the proposed hybrid inductor-resistor CRS is verified by corresponding experiments.

A unified black‐box macro model for analog circuit based on artificial neural network

SummaryA novel unified black‐box macro model for analog circuits is presented. This black‐box macro model enables the creation of a high‐accuracy DC and AC macro model by modeling the port voltages and currents of analog circuits using an artificial neural network (ANN). The modeling process for different analog circuit blocks is the same, as the model can be modeled by extracting only the port values. The operational amplifier (OPAMP), which is an important module of the analog circuit, is taken as an example for the verification of the model proposed in this work. The black‐box macro model of OPAMP is used for DC, AC, and transient simulations. The simulation speed of the black‐box macro model is much better than that of the transistor‐level model, and the trade‐off between accuracy and speed can be freely adjusted. The black‐box macro model of OPAMP is also validated by bandgap and low dropout regulators (LDO). To verify the accuracy of the model, the experimental measurement results of the LDO circuit fabricated in the 0.18 μm process have been obtained. Compared with the measurement results, the simulation results of both transistor and black‐box macro models have high accuracy. Those results demonstrate the great potential of the black‐box macro model in analog circuit design and simulation.

A novel integrated monitoring method for MPPF capacitor and IGBT junction temperature of half‐bridge modules

AbstractCapacitance and Insulated gate bipolar transistor (IGBT) junction temperature are two critical healthy parameters for modular multilevel converters (MMC) sub‐modules (SMs) condition monitoring. This paper proposes an integrated monitoring method for capacitance degradation and IGBT junction temperature variation. By measuring multiple characteristics of the same port voltage, the capacitance and the junction temperature can be obtained simultaneously, which greatly simplifies the measurement unit required for condition evaluation and realizes the submodule‐level condition monitoring at a lower cost. The capacitance is characterized by voltage changes during capacitor discharging and the junction temperature is monitored by capacitor voltage overshoot (peak value) during IGBT turn‐off. Theoretical analysis and experimental results verify the effectiveness of the proposed method and articulated the influence of load current, SM capacitor pre‐discharge voltage, and junction temperature. Moreover, an online data‐acquisition circuit for time‐specific capacitor voltage characterization is devised.

A Dual-Inductor-Connected Isolated DC–DC Converter With Direct Current Control and Low Current Harmonics

Renewable energy sources such as fuel cells and photovoltaics (PV) modules are widely installed in recent years. Due to these sources&#x2019; characteristics such as low port voltage, current-harmonic-sensitive and weak short-circuit withstanding capability, their interface converters usually require high voltage gains, low high-frequency (HF) current harmonics and short-circuit protection. At present, the existing step-up isolated dc-dc converters are usually combined with two capacitor-connected terminals or one capacitor-connected terminal plus one inductor-connected terminal, failing to obtain the low HF current harmonics and convenient direct current control (DCC) on both ports. Hence, a dual-inductor-connected (DIC) isolated dc-dc converter is proposed in this paper with the inductor connection on both ports. Then, low HF current harmonics and convenient DCC capability can be realized simultaneously through the connected inductors. Meanwhile, the proposed converter can also achieve voltage spike suppression and soft-switching operation without snubber circuits, and its inherent voltage boost function makes it suitable for high voltage-gain applications. Subsequently, the modulation scheme, topology characters and control scheme are elaborated in this paper. The experimental results based on a scale-down laboratory prototype are presented to verify the steady-state and transient-state performance of the proposed converter.

Research on DC Power Supply for Electrolytic Water to Hydrogen Based on Renewable Energy

Hydrogen production from electrolytic water based on Renewable Energy has been found as a vital method for the local consumption of new energy and the utilization of hydrogen energy. In this paper, the hydrogen production power supply matching the working characteristics of electrolytic water production was investigated. Through the analysis of the correlation between the electrolysis current and temperature of the proton exchange membrane electrolyzer and the electrolyzer port voltage, energy efficiency, and hydrogen production speed, it was concluded that the hydrogen production power supply should be characterized by low output current ripple, high output current, and wide range voltage output. To meet the requirements of the system of hydrogen production from electrolytic water based on new energy, a hydrogen production power supply scheme was proposed based on Y which is the type three, is the phase staggered parallel LLC topology. In the proposed scheme, the cavity with three is the phase staggered parallel output is resonated to meet the operating characteristics (high current and low ripple) of the electrolyzer, and pulse frequency control is adopted to achieve resonant soft in the switching operation and increase conversion efficiency. Lastly, a simulation model and a 6kW experimental prototype were built to verify the rationality and feasibility of the proposed scheme.

Cascaded AC-DC Power Conversion Interface for Charging Battery

This paper develops a cascaded AC-DC power conversion interface (CADPCI) to convert AC power to charge the battery set. The proposed CADPCI is composed of a cascaded converter (CC) and a dual-input buck converter (DIBC). The CC is formed by connecting a full-bridge converter (FBC) and a bridgeless rectifier (BLR) in series. The CADPCI generates an 11-level input voltage and performs unity power factor correction. The switching loss is reduced because only the FBC with a lower DC port voltage is switched at a high frequency. The DIBC uses a buck converter and a selection switch set to generate a two-level DC voltage on the DC port of the BLR. By controlling the DC input voltage of the buck converter, the injected power of the BLR can match the input power of the utility. Therefore, the FBC does not require to handle the real power, saving an isolated converter for regulating the DC port voltage of the FBC, thus simplifying the power circuit of the CC. The buck converter also acts as a DC active filter to filter out low-frequency ripples of the charging current. A prototype is constructed to verify the performance of the proposed CADPCI.

A new traction power supply system supplied by the Scott 3rd port and its partial compensation with current decomposition

To solve the reactive power and negative-sequence problems in electrified railways, this paper presents a novel railway power supply system, which synthesizes two secondary-side voltage ports of the Scott transformer to form the 3rd voltage port supplying the traction loads. The system can simultaneously ensure satisfactory power quality for the grids and cancel the neutral section out of the traction substation. The configuration and operation principle of the system are first explained, and a comparison with two other traction power supply systems is conducted. To reduce the operation currents and compensation capacity, a partial compensation strategy based on current decomposition is proposed. Compared with other strategies, the proposed strategy is characterized by a more intuitive physical mechanism and concise expressions, and hence has the advantage of smaller calculation and flexible application. On control, the reference detection based on this strategy is also explored to generate compensation currents instantaneously. In this paper, the mathematical relationships between the power quality indices and current components are established. And the capacity reduction analysis with partial compensation is given in detail. Both the simulation and experimental results are presented to show the feasibility and effectiveness of the proposed system and the strategy.

Research on Interferences of VFTO to Irregular Distributions of Secondary Side Cables

In the digital era, the secondary equipment of power system is becoming more and more sensitive to electromagnetic interference. Gas insulated switchgear (GIS) in substations will generate very fast transient overvoltage (VFTO) after switching action. The VFTO will generate transient electromagnetic fields and cause interferences to the secondary side cables. In recent years, the anti-interference measures for cable protection have been greatly improved. However, in the current cable trenches of some substations, there are still many irregular cable arrangements. It may have some influences on the electromagnetic interference to the cable generated by VFTO. This paper expresses a method for finding the exact interference areas of the cable and standardizing the wiring standard of the cable. Firstly, the relationship between the cable position variation and parameters is analyzed. Then, simulation experiments based on speculation are conducted to observe the effect of irregular cable arrangement on port voltage, and computer software simulation is performed for comparison. After that, an irregular cable is simulated and an interval type Ⅱ fuzzy neural network is used to predict the parameters of the shielding layer of the cable at each irregularly arranged point. Finally, the voltage and current at each point of the cable shield are calculated through the finite-difference time-domain (FDTD) algorithm. In this manner, the actual position of the higher interference voltage can be determined, which can provide a reference standard for cable arrangement.

Conducted Coupling Model and Anti-Interference Filter Design for Digital Control Circuit Under Electrical Fast Transient Noise

Control and protection equipment working in complex electromagnetic environment often suffers from electrical fast transient (EFT) noise, which easily leads to the failure of digital control circuits of the equipment. In order to realize low-cost and effective anti-interference solutions to the failure problem, it is necessary to study the anti-interference quantitative design method of the digital control circuit. In this article, a conducted interference coupling model of the digital control circuit under EFT noise is established. As an important part of the coupling path, the impedance model of the chip is built. A black-box impedance modeling method of voltage regulator chip is proposed based on online measurement. The equivalent impedance model of the digital signal processing (DSP) chip is represented by the high-frequency model of the inductor. The coupling model is validated by comparing the measured results and simulated results of the terminal load port voltage. Then, a measurement and analysis method is presented to obtain the circuit failure threshold. By analyzing EFT test results at different frequencies and amplitudes, the influencing factor of the circuit failure is clarified, and the circuit failure threshold is obtained. Finally, based on the coupling model and the circuit failure threshold, a quantitative design method of an anti-interference filter is developed. The method is validated through filter prototyping for a 5 kHz/+2.0 kV EFT test.