High Switching Frequency Research Articles

Efficiency of Series APF based on Nine-level NPC Inverter Compared to Seven-level Configuration

This article presents the performance comparison of Series Active Power Filter (Series APF) based on seven and nine multi-level Neutral Point Clamped (NPC) inverters using the same control scheme. The Series APF is one of the most efficient and effective modern custom power devices used in power distribution networks to compensate voltage harmonic and all voltage disturbances. The conventional configuration based on voltage source inverter (VSI) operated at very high switching frequency presents several drawbacks and limited for low power applications. To overcome these problems and improve the output voltage different multi-level are used in various power application in particular Flying Capacitor (FC), Cascade H-Bridge (CHB) and multi-level (NPC) inverters. In this study seven and nine-level (NPC) inverters are proposed for active power filtering system; these inverters present diverse advantages include the capability to reduce the harmonic content, decrease the voltage or current ratings of the semiconductors and mainly they can work at low switching frequency. To generate switching pulses Multi-Carrier Level-Shifted Pulse Width Modulation (MC-LSPWM) control technique is adopted with modified P-Q control strategies. To verify the accuracy and the performance of the proposed Series APF models, simulation is performed using MATLAB-Simulink platform and SimPowerSystem Toolbox. The obtained results show the superiority of series APF based on nine-level in term of THDv reduction compared to the systems with seven-level inverter topology.

Analysis and Design of Bidirectional Parallel-Series DAB-Based Converter

Unprecedented expansion of renewable, energy storage and fast charger system applications has diversified the bidirectional converter designs over the past decade. This paper presents a new dual-active bridge (DAB) converter topology which employs parallel and series switches arrangements for low-voltage (LV) bridge configurations. The additional switch inclusion provides high dc conversion gain, which enables attractive fast charger applications. The performance of the proposed DAB-based converter with wide dc range has been investigated through several design techniques and comparisons. The use of use of silicon carbide devices (SiC) in higher power conversion significantly improves switching losses. However, unsupervised design will result in significant switching losses and increased electromagnetic emissions. Since the DAB-based converter's high switching frequency allows operation with smaller magnetics, the system stray capacitance plays a critical role. The common-mode current (CMC) propagated through the system's stray capacitance generates undesired electromagnetic interferences (EMI) and impacts the soft-switching achievable range. To overcome the common-mode current circulation issue, design solutions have been employed to reduce the emergence of system stray capacitance. A harmonic analysis is further discussed along with evaluation of transformer design comparisons. The experimental results show the performance of the DAB-based converter in bidirectional operation and improved common mode current generation with respect to EMI emissions. The simulation and experimental results have been performed using a 5kW rated power DAB-based converter with SiC power semiconductors.

Circulating Current Suppression Scheme for Interleaved Active Neutral Point Clamped Nine-Level Inverter

The interleaved active neutral point clamped nine-level (ANPC-9L) inverter can be used in 1500V photovoltaic power generation because of its advantages of low voltage stress, high equivalent switching frequency and small filter size. Circulating current between sub modules is a key problem for ANPC-9L. A simple scheme to realize circulating current suppression for ANPC-9L inverter is presented in this paper. The operation of the ANPC-9L is briefly discussed, and the model of coupled inductor is given. Analysis shows that the redundant working states of the inverter with same output voltage can be used to suppress the circulating current. Another objective is to analyze circulating current imbalance at the band transition when using phase disposition pulse width modulation (PD SPWM) strategy. A solution is proposed to cancel current imbalance. Simulation and experiment verify the effectiveness of the proposed strategy.

A Forward-Type Single-Stage Multi-Input Inverter With Series-Time-Overlapping Power Supply

A Forward type single-stage multi-input inverter with series-time-overlapping power supply is proposed. The circuit structure and topological family, energy management control strategy (EMCS), high frequency (HF) switching process analysis, the relationship between multiple duty cycles and power decoupling, common mode interference suppression between multiple inputs are fully studied. The circuit structure is composed of multi-input selection switches in series and an isolated bidirectional Forward type single input single output inverter. This topological family includes 6 circuits such as full-bridge type. A master-slave energy management SPWM compound control strategy with independent control of input source power based on input voltage feedforward and output voltage feedback is proposed. It realizes the energy management of the input source by controlling the instantaneous value of the output voltage and the output power ratio of the multiple inputs and achieves the smooth switching between the two power supply modes. The designed and developed 3kVA inverter prototype has excellent performances such as single-stage power conversion, HF electrical isolation, high conversion efficiency, small size and weight, wide duty cycle adjustment range, high output waveform quality, and strong load adaptability.

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.

An improvement of direct torque controlled PMSM drive using PWM technique and kalman filter

The paper describes pulse-width-modulation (PWM) technique and Kalman filter (KF) process to improve performance of direct torque controlled permanent magnet synchronous motor (DTC-PMSM) drive. Performance of DTC methods are strongly affected by high stator current ripple. For lowering the ripple, high switching frequency space vector PWM and KF are utilized in the paper. Mathematical model of PMSM and calculations of important quantities of DTC applied to PMSM drive are presented in the first part. The second part shows computation process of space vector PWM and KF. Performance indices are utilized to evaluate the drive structures. Theorectical assumptions are validated via simulations with Gaussian noised stator current measurement.

An improvement of direct torque controlled PMSM drive using PWM technique and kalman filter

The paper describes pulse-width-modulation (PWM) technique and Kalman filter (KF) process to improve performance of direct torque controlled permanent magnet synchronous motor (DTC-PMSM) drive. Performance of DTC methods are strongly affected by high stator current ripple. For lowering the ripple, high switching frequency space vector PWM and KF are utilized in the paper. Mathematical model of PMSM and calculations of important quantities of DTC applied to PMSM drive are presented in the first part. The second part shows computation process of space vector PWM and KF. Performance indices are utilized to evaluate the drive structures. Theorectical assumptions are validated via simulations with Gaussian noised stator current measurement.

Grid Harmonics Suppression for Three Phase Dual-Frequency Grid-Connected Inverter Based on Feedforward Compensation

Using a low pulse ratio, the electromagnetic interference and switching loss of an inverter can be effectively reduced, particularly in high-power applications. However, due to variations in grid impedance, it is a challenging task to achieve stable operation of an LCL-type grid-connected inverter (GCI) using the active damping method with low pulse ratio. Thus, a novel three-phase dual-frequency GCI is presented to ensure the symmetry of the output power and the stable operation of the system address stability issues. The proposed inverter topology in this article is composed of two inverters in parallel, which are, respectively, a power inverter unit (PIU) and an auxiliary harmonic elimination unit (AHEU). To reduce the switching loss and improve the inverter efficiency, the switching frequency of the PIU is relatively low, injecting current into the grid. Moreover, the feedforward compensation method is used in AHEU. AHEU operates at high switching frequency to generate a current component that is symmetrical with the ripple com-ponent, improving the power quality, without extracting the current harmonic as the current reference. The operating principle of feedforward compensation is explained, and a proper parameter design procedure is presented in this paper. Since L filters are used for the proposed inverter, the system can operate stably where the ratio of switching frequency to fundamental frequency is low. A 10 kW laboratory prototype was built. The experimental results showed that the grid current ripple could be effectively eliminated and the THD of the grid current was 3.01%. The proposed inverter has good stability in a weak grid, and the efficiency of the proposed inverter is 95.98% at rated current, which is 0.81% higher than the traditional GCI, effectively increasing the efficiency of the system.

Diagnosis of Interturn Short-Circuits in SRMs by High-Frequency Switching of Phases Amid Low-Torque Unaligned Rotor Positions

The inherent problems of torque ripple, noise and vibrations associated with switched reluctance motors (SRMs) are escalated when the machine is subjected to inter-turn short-circuits (ITSCs). Also, leaving it unchecked can ultimately lead to a complete winding short-circuit due to the insulation failure owing to the heat produced by locally generated hotspots. To avoid such ruinous damage, the diagnosis of ITSCs is very critical. This article proposes a method of diagnosing ITSCs by injecting high-frequency signals in the phases in their low torque regions around unaligned rotor positions. The proposed method utilizes the drive power converter to inject and diagnose the ITSCs and thus requires no additional hardware. It has a higher sensitivity even toward minor fault conditions, i.e., as low as ITSC of 4 turns ( <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$ \approx$</tex-math></inline-formula> 4% ITSC over a phase). The devised fault indicator is immune to load or speed variation and, hence, better detection reliability. Also, the method can diagnose the fault under load and speed transients proving it to be more robust. Experiments are performed on a test rig of customized 8/6 SRM emulating the ITSCs to verify the potency of the proposed scheme.

Structure and the Thermal Management of a 3-D Silicon Carbide MOSFET Module

Silicon carbide (SiC) device has higher switching frequency, higher breakdown voltage, and lower on-state voltage drop, which makes it subversive potential in the high power density applications. However, the traditional packaging structure cannot cope with the high power density of SiC devices, so the existing commercial SiC power module can only be used in derating applications. This paper proposed a 3-D packaging design method for high power density MOSFET power module, in which the cooling system is integrated inside the module to reduce the thermal resistance and the temperature difference of the SiC MOSFET chips. At the same time, the heat dissipation process of the new structure is modeled and analyzed, and the accuracy of the model is proved by experiment and simulation.

A Novel DC Electronic Load Topology Incorporated with Model Predictive Control Approach

This paper presents a novel topology of a modified isolated single-ended-primary-inductance converter (SEPIC) with a model predictive control (MPC) approach applied to direct current (DC) electronic loads. The proposed converter uses an actual transformer rather than a coupled inductor for isolation between the source and the load. The transformer allows the proposed converter to operate at a higher switching frequency, ultimately reducing the passive components’ size. A low-power hardware prototype is developed and tested with a model predictive control algorithm under variable input voltages and load conditions. The performance of the proposed converter is demonstrated to be satisfactory under steady state, as well as sudden input voltage transients. The proposed converter utilizes a switched capacitor technique to generate alternating current in both windings of the transformer. As the coupled inductor is eliminated from the circuit, the problem of high voltage spikes occurring due to leakage inductances is also eliminated for the proposed converter. Therefore, the proposed converter can be used for isolated medium power applications. The experimental results show that the efficiency of the proposed converter reached 96%. The MPC allows this converter’s DC voltage level to remain stable even as the input voltage and output terminal load change. Lastly, this converter with an MPC approach can be applied to different DC electronic loads, improving DC power quality and DC electronic load life.

Simple Discrete Control of a Single-Phase Voltage Source Inverter in a UPS System for Low Switching Frequency

Previous research has shown that the inverter output voltage distortions are higher for low switching frequencies, and it is impossible to increase the controller gains because it will cause oscillations of the output voltage. The main reason is the real frequency domain characteristic of the PWM modulator and measuring traces, which can be modelled as switching periods delays. The thesis of this paper is that by using the control system that takes care of these delays, it is possible to decrease output voltage distortions for the standard loads for relatively low switching frequencies (e.g., 12,800 Hz). The Luenberger observer was implemented in the multi-input-multi-output passivity-based control of the system with the delay, in order to predict the state variables of the inverter. It is shown that state variable prediction is unnecessary for high switching frequencies (e.g., 51,200 Hz). The theory, simulations and breadboard verification, using the inverter model controlled with the real-time interface MicroLabBox, are presented.

Fractional fuzzy PI controller using particle swarm optimization to improve power factor by boost converter

The power circuit of AC voltage controller capable of operating at a leading, lagging, and unity power factor is studied by a lot of researchers in the literature. Circuits working with high switching frequency are known as power factor correctors (PFCs). The single-phase boost converter has become the most popular topology for power factor correction (PFC) in general purpose power supplies. Power factor correction circuit provides conventional benefits to electric power systems. The benefits are the reduction of power factor penalty and utility bill and power loss. Therefore, a boost converter power factor correction scheme is presented in this paper. A PI, fuzzy logic PI and fractional order PI (FOPI) controllers are used to fix an active shaping of input current of the circuit and to improve the power factor. The controller parameters (coefficients) are optimized using the Particle Swarm Optimization (PSO) algorithm. Average current mode control (ACMC) method is used in the circuit. The converter circuit consists of a single-phase bridge rectifier, boost converter, transformer and load. A mathematical model of the plant is required to design the PI controller. A model for power factor correction circuit is formed in MATLAB/Simulink toolbox and a filter is designed to reduce THD value. The proposed model is simulated using a combination of PI, fuzzy logic and FOPI controllers. The control scheme is applied to 600 Watt PFC boost converter to get 400 Volt DC output voltage and 0.99 power factor. The input voltage is 230 VRMS with 50 Hz. The combination of FOPI and PI controller has the best solution to control the power factor according to PI and fuzzy controllers.

A Book Review of Exporting Chinese Architecture: History, Issues and “One Belt One Road”

Power devices are used in various industrial applications, including energy transfer (grid, wind), industrial applications (rail, photovoltaic systems) and civil equipments (electric vehicles, battery charges, home appliance). Power switches reliability may be affected by their high switching frequency, causing strong thermal fluctuations. Therefore, an electro-thermal analysis is essential to improve their reliability and to ensure continuous operation. The device aging phenomenon is taken in consideration for lifetime estimation.

A Review on Modular Converter Topologies Based on WBG Semiconductor Devices in Wind Energy Conversion Systems

This paper presents a comprehensive review on the employment of wide bandgap (WBG) semiconductor power devices in wind energy conversion systems (WECSs). Silicon-carbide- (SiC) and gallium-nitride (GaN)-based power devices are highlighted and studied in this review, focusing on their application in the wind energy system. This is due to their premium characteristics such as the operation at high switching frequency, which can reduce the switching losses, and the capability to operate at high temperatures compared with silicon (Si)-based devices. These advantages promote the replacement of the conventional Si-based devices with the WBG semiconductor devices in the new modular converter topologies due to the persistent demand for a more-efficient power converter topology with lower losses and smaller sizes. The main objective of this paper was to provide a comprehensive overview of the WBG power devices commercially available on the market and employed in the modular converter topologies for renewable energy systems. The paper also provides a comparison between the WBG power technologies and the traditional ones based on the Si devices. The paper starts from the conventional modular power converter topology circuits, and then, it discusses the opportunities for integrating the SiC and WBG devices in the modular power converters to improve and enhance the system’s performance.

Electro-Thermal Modeling, Aging and Lifetime Estimation of Power Electronic MOSFETs

Power devices are used in various industrial applications, including energy transfer (grid, wind), industrial applications (rail, photovoltaic systems) and civil equipments (electric vehicles, battery charges, home appliance). Power switches reliability may be affected by their high switching frequency, causing strong thermal fluctuations. Therefore, an electro-thermal analysis is essential to improve their reliability and to ensure continuous operation. The device aging phenomenon is taken in consideration for lifetime estimation.

A PWM Method for Reducing dv/dt and Switching Losses in Two-Stage Power Converters

Today's semiconductor devices are accompanied by high switching frequencies (> kilo-hertz) and small transition times (< micro-seconds). Such fast transition times are accompanied by undesirable effects such as voltage overshoots at the load terminals, ground leakage currents, wide-band electromagnetic noise, etc. With the advent of wide band-gap devices, several applications are moving towards higher switching frequency operation with at-least an order of magnitude reduction in transition times. While these characteristics are considered necessary to break the next-generation barriers in power density, efficiency and applicability, the undesirable effects due to faster transitions are expected to present obstacles. This work proposes a PWM approach to modify the shape of the switching voltages to overcome the disadvantages of the fast transition times without any increase in switching losses. In fact, several of the switching transitions feature ZVS operation, resulting in reduced switching losses. The paper discusses the analytical details of the approach using a simple DC-DC boost-buck converter and extends it to a DC to three-phase AC converter using the principles of space vector modulation. The paper presents detailed simulation and comparative results in terms of voltage over-shoots over long cables, loss calculations and electromagnetic noise. Results from a laboratory-scale working prototype confirm the benefits of the proposed approach in terms of EMI and loss reduction.

Current Zero-Crossing Prediction-Based Critical Conduction Mode Control of Totem-Pole PFC Rectifiers

Critical conduction mode (CRM) is widely used in totem-pole Boost power factor correction converters due to its compatibility with soft-switching and high switching frequency. Conventionally, a current sensor or zero-current detector is required to realize CRM operation. The system performances highly rely on the behaviors of peripheral circuits. Additional power loss and delay are also introduced. Moreover, the inductor current contains obvious differential mode noise, which brings interferences to the sensing signals. To address this issue, a novel CRM realization method is proposed. It utilizes an inductor current estimator model to estimate the averaged current and to predict the current zero-crossings. The noisy sensing signal is replaced by estimated values. Therefore, the zero-current detection circuit is removed, which simplifies the peripheral circuit design. Valley-switching and zero-voltage switching can also be achieved. Operation principles, digital implementation, and error suppression of the proposed control are analyzed. The proposed concepts are validated on a <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$\rm{550}~W$</tex-math></inline-formula> , <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$150\mathrm{k}Hz-1.6\mathrm{M}Hz$</tex-math></inline-formula> , GaN-based prototype. Experimental results record 98.96% peak efficiency with a 0.9972 power factor.

I-V Characteristics Measuring System for PV Generator based on PDM Inverter

This paper presents a new method to characterize photovoltaic panels. The power electronic converter used is a Pulse Density Modulation (PDM) inverter. In this method, the inverter plays two roles: First, it is a DC inductor emulator. Second, it allows assembly between inductive and capacitive load methods. The PDM inverter is adapted to operate at very high switching frequency. In this application, it avoids the difficulties of making DC inductors with high DC current and its control remains very simple. This is an asset for increasing the power, power density and rapidity of tracers based on this method. The main disadvantage of this method, compared to methods based on DC-DC converter, is the use of twice as many semiconductor components. But this disadvantage can be compensated by a gain on reactive components. The simulations and experimental results of the proposed system are shown.

DC-Side Soft-Switching Inverter With Modified Space-Vector Modulation Scheme

Three-phase soft-switching inverters are promising in order to reduce the losses in the switching devices and to reduce the electromagnetic interference produced by severe di/dt and dv/dt, which enables the operation of the inverter at higher switching frequency. This work proposes a DC-side three-phase zero-voltage soft-switching inverter topology that can be sub-categorized under actively clamped resonant dc-link topologies. Moreover, a modified space-vector modulation scheme is proposed, such that all the devices operate under zero-voltage switching condition. Compared to other similar dc-link soft-switching topologies, the proposed topology does not require feedback from the inverter output currents to achieve soft-switching operation. Unlike conventional space-vector modulation techniques, the proposed modified space-vector modulation does not require to turn-on the top and/or the bottom three switches of the two-level inverter at the same time to implement the zero vectors, which allows a reduction of the effective commutating time of the two-level inverter switches by one-third, during a grid voltage cycle. The auxiliary capacitor is only charged to a fraction of the dc bus voltage. Simulation and experimental results on a 10-kW and 100-kHz switching frequency lab-scale prototype are presented to demonstrate the validity and effectiveness of the proposed zero-voltage switching topology and modulation scheme on reducing the switching losses and electromagnetic interference.