Multiple Voltage Levels Research Articles

A Real-Time Application of Modified Inductor Coupled KY Converter Topology in Speed Control of E-Bikes

Congested road network and traffic jam lead to vehicle idling and fuel wastage. An E-bike which is a solution to this is often available with Thumb Throttle Mechanism and single speed operation. A motor controller with multiple output voltage levels and Click Throttle Mechanism is presented in this paper which provides variable speed operation, better power utilization and is highly economical. Proposed modified KY converter utilizes the turns ratio of an On-Line Tap Changer (OLTC) to generate multiple output voltages for variable speed commutation. This possess a stable continuous conduction mode throughout its operation and reduced switching transients when compared to the existing topologies. Mutually independent control variables namely turns ratio and duty ratio, are used here for voltage conversion, which facilitates the flexible transition between multiple output voltage levels. A 15 W prototype of the proposed modified inductor coupled KY converter is realized using Arduino Uno Board.

Minimizing Ripples of Inductor Currents in Coupled SIDO Boost Converter by Shift of Gate Pulses

Single-input dual-output (SIDO) dc–dc converters have gained attention with the increasing need of multiple voltage levels. Magnetically coupled inductor SIDO (CI-SIDO) boost converter is the topology focused in this article. Ripples in inductor currents play important role in design of dc–dc converters and need to be as low as possible. The shift of one gate pulse with respect to another gate pulse has been used in converters, such as interleaved boost for reducing ripples. However, unlike interleaved boost, CI-SIDO boost has unequal output voltages and unequal inductances. The values of shifts, at which ripples are minimized, vary under different conditions of CI-SIDO boost. So, the analysis to reduce ripple in interleaved boost is not applicable for CI-SIDO boost. This article presents a detailed analysis of CI-SIDO boost converter for obtaining minimum ripples by shifting gate pulses. The analysis accounts for all permissible combinations of output voltages and inductances. Ranges of shifts in gate pulse are found, for all conditions, to achieve minimum ripple in each inductor current separately, and both inductor currents simultaneously. The practical applications of the analysis are shown by giving examples. The ranges found are verified by simulation in MATLAB/Simulink and experiments on laboratory prototype.

Universal droop controller for DC–DC converter interfaces onto a modular multi‐tiered DC microgrid

Microgrids are usually based on single voltage levels, supporting a number of distributed generation sources and loads. This paper describes a multi-tier DC microgrid, with multiple voltage levels able to source and supply different power demands. A universal droop controller is developed for this multi-tier microgrid, able to connect uni- and bi-directional elements on to the grid. Simulations are used to demonstrate the functionality of the controller to allow autonomous load sharing based on decentralised control, with bi-directional power transfer between tiers to balance supply and demand at each level. Power can also be directly sent from one element of the microgrid to another, which is demonstrated through simulation, allowing for integration with future peer-to-peer energy trading systems.

Adopting Circuit Breakers for High-Voltage dc Networks: Appropriating the Vast Advantages of dc Transmission Grids

Since the late 19th century, ac power transmiss ion systems have been widely used for interconnecting multiple power-producing plants with load centers. Highly meshed ac transmission grids with high redundancy and operating flexibility now operate worldwide. These complex ac systems have proven reliable in securely providing high levels of power, while also accommodating multiple voltage levels to reduce loss.

A Data-Driven Verilog-A ReRAM Model

The translation of emerging application concepts that exploit resistive random access memory (ReRAM) into large-scale practical systems requires realistic yet computationally efficient device models. Here, we present a ReRAM model, where device current–voltage characteristics and resistive switching rate are expressed as a function of: 1) bias voltage and 2) initial resistive state (RS). The model versatility is validated on detailed characterization data, for both filamentary valence change memory and nonfilamentary ReRAM technologies, where device resistance is swept across its operating range using multiple input voltage levels. Furthermore, the proposed model embodies a window function which features a simple mathematical form analytically describing RS response under constant bias voltage as extracted from physical device response data. Its Verilog-A implementation captures the ReRAM memory effect without requiring integration of the model state variable, making it suitable for fast and/or large-scale simulations and overall interoperable with current design tools.

A new structure of single‐phase two‐stage hybrid transformerless multilevel PV inverter

SummaryTransformerless inverters are becoming popular for grid‐connected photovoltaic applications due to their simplicity, reduced size, weight, cost, and higher efficiency. In this paper, a two‐stage hybrid transformerless multilevel inverter (MLI) for single‐phase grid‐connected photovoltaic power generation system (PVPGS) is presented. The proposed topology comprises a multilevel boost converter (MLBC) and a symmetrical hybrid MLI. MLBC combines the boosting and switched capacitor voltage functions to produce self‐balanced multiple voltage levels. The proposed MLI is derived from a combination of bidirectional switches, a half bridge, and a diode‐clamped branch, which can produce only two variations in the total common mode voltage and is capable of suppressing leakage current as per DIN VDE 0126‐1‐1 grid standards. It offers the advantages of scalability, reactive power capability, reduced total harmonic distortion, and filter size. The proposed hybrid transformerless seven‐level inverter is simulated in MATLAB, and experimental setup is built to validate the effectiveness of the proposed configuration. Finally, a comprehensive comparison is made with other seven‐level inverter topologies.

Optimal substation-based joint allocation of PMUs and measuring channels considering network expansion planning

This paper proposes an integrated framework to design wide area measurement system (WAMS) addressing the challenges of expansion planning and unknown transformer taps. The proposed framework is formulated as a mixed-integer linear programming (MILP) problem. It minimizes the number of substations disrupted for phasor measurement unit (PMU) placement, PMU buses, and PMU measuring channels. Concepts of substations and buses are separately treated. Power system expansion planning is also considered in order to achieve an optimal solution with the least cost of disrupting existing and future substations. Observability constraints are defined to make both present and expanded grids observable since the time span of WAMS planning is usually shorter than network expansion planning. Moreover, special attention is paid to multiple voltage levels inside a substation; transformers with unknown tap settings are exempt from being treated as observability paths and locating vicious measurement channels. Furthermore, novel ideas are proposed to model branch outages using the concept of backup observability and to model PMU failure using a hybrid method which is a modified version of previous ones. Numerical results from testing the proposed framework on standard test systems verify its performance from perspectives of solution optimality and computational burden.

Jinyong Lei ; Chaoyang J

As load and renewable penetration continues to grow, optimal placement and sizing of substations is becoming increasingly important in distribution system planning. This paper presents an improved methodology to solve the substation siting and sizing problem based on geographic information and supervised learning. The proposed approach can optimize the locations, capacities, and power supply ranges of substations with minimum investment and annual operation costs. Capital cost of land adds complexity and difficulty to the substation placement problem, especially for highly developed urban areas. This paper presents a theoretical framework to determine the optimal location of substations considering the cost of land. The state-of-the-art parallel computing techniques are employed so that co-optimization for substations of multiple voltage levels can be directly conducted in a computational efficient way. Case studies are presented to demonstrate the effectiveness of the proposed approach.

Hybrid Cascaded Multilevel Inverter (HCMLI) With Improved Symmetrical 4-Level Submodule

This letter proposes an improved symmetrical 4-level submodule as a basic cell for generating multiple dc voltage levels. A hybrid cascaded multilevel inverter (HCMLI) topology is formed by the combination of n submodules and a full-bridge. A comparative analysis against the recent multilevel inverters reveals that the proposed topology requires less number of switches and dc sources. In addition, the proposed submodule reduces the number of conducting switch and gate driver requirements compared to the widely used half-bridge submodule. To validate the operation of the proposed HCMLI topology, experimental results of a 9-level single-phase inverter controlled by selective harmonic elimination pulse-width-modulation is presented.

Design and Control of a Buck–Boost Charger-Discharger for DC-Bus Regulation in Microgrids

In DC and hybrid microgrids (MG), the DC-bus regulation using Energy Storage Devices (ESD) is important for the stable operation of both the generators and loads. There are multiple commercial voltage levels for both ESD and DC-bus; therefore, the ESD voltage may be higher, equal or lower than the DC-bus voltage depending on the application. Moreover, most of the ESD converter controllers are linear-based, hence they ensure stability in a limited operation range. This paper proposes a system to regulate the DC-bus voltage of an MG accounting for any voltage relation between the ESD and the DC-bus voltage. The proposed system is formed by an ESD connected to a DC-bus through a bidirectional Buck–Boost converter, which is regulated by a Sliding-Mode Controller (SMC) to ensure the system stability in the entire operation range. The SMC drives the Buck–Boost charger–discharger to regulate the DC-bus voltage, at the desired reference value, by charging or discharging the ESD. This paper also provides detailed procedures to design the parameters of both the SMC and the charger–dischager. Finally, simulation and experimental results validate the proposed solution and illustrate its performance.

A Pole-to-Pole Short-Circuit Fault Current Calculation Method for DC Grids

This paper proposes a generic pole-to-pole short-circuit fault current calculation method for dc grids. The calculation procedure begins from the simplified RLC equivalent model of a single modular multilevel converter, and then the prefault matrices and faulted matrices are established and modified to calculate the dc fault currents of all the branches. The proposed approaches are validated by comparing with the electromagnetic transient (EMT) simulation results on PSCAD/EMTDC. Besides, two case studies showed that the calculation method can be easily used to evaluate the severity of a dc fault. Moreover, the calculation can be applied to select the parameters of a fault current limiter (to match the circuit breaker capacity. The main contributions of the proposed numerical calculation method are: 1) The proposed method is accurate and much more time efficient than the EMT simulations; 2) the proposed method can handle all kinds of dc grid networks including the ring, radial, and meshed topologies; and 3) the proposed method is applicable to dc grid with multiple dc voltage level areas connected with dc/dc converters.

A Branch-&-Bound Test-Access-Mechanism Optimization Method for Multi- $V_{\mathrm{ dd}}$ SoCs

The use of multiple voltage levels introduces new challenges for testing multi- ${V_{\mathrm{ dd}}}$ systems-on-chip (SoCs). Time-division-multiplexing (TDM) tackles many of these challenges and offers very effective test-schedules. However, the effectiveness of TDM for minimizing test time depends on the test-access-mechanism (TAM) in the SoC. Single- $ {V_{\mathrm{ dd}}}$ TAM optimization techniques consider neither the highly constrained test environment of multi- $ {V_{\mathrm{ dd}}}$ SoCs nor the benefits provided by TDM, therefore they are not suitable for multi- $ {V_{\mathrm{ dd}}}$ SoCs. In this paper, we propose the first TAM optimization technique for multi- $ {V_{\mathrm{ dd}}}$ SoCs. The proposed method exploits unique scheduling opportunities and flexibility offered by TDM, and by the means of a branch-&-bound approach, it quickly identifies the most effective TAM configurations. Experiments using large benchmark SoCs as well as SoCs from industry highlight the benefits of the proposed technique on multi- $ {V_{\mathrm{ dd}}}$ designs, for both single-site and multisite test applications.

Allocation of annual electricity consumption and power generation capacities across multiple voltage levels in a high spatial resolution

The electrical energy system is in transition. There is continuing expansion of renewable generation, which causes a spatial and temporal shift of energy flows at different voltage levels of the power grid. On the consumption side, demand patterns are expected to change. The limited availability of data with high spatial resolution hinders independent and transparent assessments. In view of this, the research project open_eGo is developing methods focusing on electricity networks and open-science principles. In this work, electricity demand and power generation are allocated to their corresponding voltage levels and network nodes. By combining data on municipal boundaries with Voronoi cells we created catchment areas for each substation. On the demand side, OpenStreetMap data is used for mapping different demand sectors. We show that a consistent data set can be produced in a high spatial resolution using geographical data processing. Our results apply to Germany but the methodology can be adopted to other countries or regions where sufficient open data is available.

A Double-ended Converter System with Two Different DC-buses Using Open Winding Permanent Magnet Machine for Traction Applications

In hybrid electric vehicles (HEVs), there are usually several different DC-buses of different voltage levels to handle different loads. DC–DC converters are used to transfer energy between different DC-buses. This paper proposed a double-ended converter for two different DC-buses with large voltage ratio. The high-voltage DC-bus is 600 V for the traction motor drive, while the low-voltage DC-bus is 48 V for the electronic devices on the vehicle. By using the proposed system configuration, energy could be transferred freely between the generator and the two loads, forming a very flexible powertrain. In addition, the weight, volume, and cost of power electronics components could be reduced. This paper introduced the operation principal and control algorithm of the proposed system. Simulations verified the functionality of the proposed system. The proposed system configuration is not only suitable for automotive applications, but can also be implemented in other applications, such as aerospace, marine, and industrial, where multiple DC-bus voltage levels are required.

An Induction Generator-Based AC/DC Hybrid Electric Power Generation System for More Electric Aircraft

In more electric aircraft (MEA) system, both ac and dc electric power with multiple voltage levels are required for various aircraft loads. This paper presents an induction generator-based ac/dc hybrid electric power generation system for MEA. In the proposed system architecure, a high-speed induction starter/generator and a low-speed induction generator are installed on the high pressure (HP) and low pressure (LP) spools of the engine, respectively. In generating mode of operation, all of the constant voltage variable frequency ac power is generated by the HP generator while the dc power demand is shared by both HP and LP generators. A control scheme is developed to regulate the ac load voltage and coordinate dc power generation between the two generators. The proposed induction generator based ac/dc hybrid generation system results in reduced hardware requirement compared with both ac and dc primary generation systems.

Dual-DC-Port Asymmetrical Multilevel Inverters With Reduced Conversion Stages and Enhanced Conversion Efficiency

A new concept of dual-dc-port asymmetrical multilevel inverter (DP-AMI), which is able to interface a low-voltage dc port, a high-voltage dc port, and an ac port simultaneously using only one topology, is presented in this paper. A systematic method to derive the DP-AMI is proposed. With the proposed DP-AMI, a low-voltage dc source, e.g., photovoltaic (PV) modules or battery, can directly supply power to the ac load within single-stage power conversion. Therefore, in comparison with a traditional two-stage dc/ac power conversion system, the power conversion stages are reduced and the voltage/current stress of the front-end dc/dc converter can be significantly alleviated, which can improve the overall conversion efficiency dramatically. Furthermore, by using the low-voltage dc source as a new voltage level, asymmetrical multiple voltage levels are generated by the proposed DP-AMI, which is beneficial for the reducing switching losses and the size/volume of the output filter. The topology derivation method of the DP-AMIs is presented. The operation principles, modulation schemes, and characteristics of one of the proposed DP-AMIs are analyzed in detail. A 1-kW prototype is built and tested to verify the effectiveness and advantages of the proposed method.

Modeling geomagnetically induced currents

AbstractUnderstanding the geomagnetic hazard to power systems requires the ability to model the geomagnetically induced currents (GIC) produced in a power network. This paper presents the developments in GIC modeling starting with an examination of fundamental questions about where the driving force for GIC is located. Then we outline the two main network modeling approaches that are mathematically equivalent and show an example for a simple circuit. Accurate modeling of the GIC produced during real space weather events requires including the appropriate system characteristics, magnetic source fields, and Earth conductivity structure. It is shown how multiple voltage levels can be included in GIC modeling and how the network configuration affects the GIC values. Magnetic source fields can be included by using “plane wave” or line current models or by using geomagnetic observatory data with an appropriate interpolation scheme. Earth conductivity structure can be represented by 1‐D, 2‐D, or 3‐D models that are used to calculate the transfer function between electric and magnetic fields at the Earth's surface. For 2‐D and 3‐D structures this will involve a tensor impedance function and electric fields that are not necessarily orthogonal to the magnetic field variations. It is now technically possible to include all these features in the modeling of GIC, and various software implementations are being developed to make these features more accessible for use in risk studies.

A General Voltage-Behind-Reactance Formulation of a Multivoltage n × 3-Phase Hybrid-Excited Synchronous Machine

The paper describes a general model of a hybrid-excited synchronous machine with multiple voltage levels each generated by a 3 -phase stator system in a voltage-behind-reactance formulation. The different voltage level of each 3 -phase stator system is realized in the same machine design. The rotor is excited through an excitation winding and a permanent magnet. The model incorporates magnetic saturation of the main inductance, magnetic and electric coupling between all phases, and the field winding and a mechanical displacement angle. The cross coupling between q and d axes of the main inductances is included as a constant saliency factor $\alpha$ for all saturation levels. The turn ratio of each 3 -phase stator winding system to another 3 -phase system is also modeled as a constant value. Each 3 -phase system saturates the iron core with a different weighting represented by the number of turns relative to the reference stator system. The proposed model is included in a field-oriented control scheme. Simulations are carried out with requested $\boldsymbol{I_{q,d}}$ and field winding currents to demonstrate model's dynamics, and the results are verified with measurements on a test bench.

An Efficient Switched-Capacitor DC-DC Buck Converter for Self-Powered Wearable Electronics

This paper introduces an efficient reconfigurable, multiple voltage gain switched-capacitor dc-dc buck converter as part of a power management unit for wearable electronics. The proposed switched-capacitor converter has an input voltage of 0.6 V to 1.2 V generated from an energy harvesting source. The switched-capacitor converter utilizes pulse frequency modulation to generate multiple regulated output voltage levels, namely 1 V, 0.8 V, and 0.6 V based on two reconfigurable bits over a wide range of load currents from 10 $\mu\text{A}$ to 800 $\mu\text{A}$ . The switched-capacitor converter is designed and fabricated in 65-nm low-power CMOS technology and occupies an area of 0.493 mm2. The design utilizes a stack of MIM and MOS capacitances to optimize the circuit area and efficiency. The measured peak efficiency is 80% at a load current of 800 $\mu\text{A}$ and regulated load voltage of 1 V.

Differential Evolution based SHEPWM for Seven-Level Inverter with Non-Equal DC Sources

This paper presents the application of differential evolution algorithm to obtain optimal switching angles for a single-phase seven-level to improve AC voltage quality. The proposed inverter in this article is composed of two H-bridge cells with non-equal DC voltage sources in order to generate multiple voltage levels. Selective harmonic elimination pulse width modulation (SHPWM) strategy is used to improve the AC output voltage waveform generated by the proposed inverter. The differential evolution (DE) optimization algorithm is used to solve non-linear transcendental equations necessary for the (SHPWM). Computational results obtained from computer simulations presented a good agreement with the theoretical predictions. A laboratory prototype based on STM32F407 microcontroller was built in order to validate the simulation results. The experimental results show the effectiveness of the proposed modulation method.