Switching Harmonics Research Articles

Design and Implementation of a High-Efficiency Seven-Level Inverter for Solar Power Generation Systems

This paper presents a novel solar power generation system that integrates a DC/DC power converter with a new seven-level inverter, offering enhanced efficiency and simplified design. The DC/DC power converter combines a boost converter and a transformer to produce two independent voltage sources. These are processed by a capacitor selection circuit and a full- bridge power converter in cascade to generate a seven-level AC voltage. The proposed inverter topology uses only six power electronic switches, with only one switch operating at high frequency at any given time, thereby minimizing switching losses and improving overall power conversion efficiency. The reduced switching harmonics also decrease filter inductor requirements, contributing to a compact and cost-effective design. A prototype system was developed and tested, demonstrating its ability to deliver sinusoidal output current synchronized with utility voltage, confirming its suitability for residential solar power applications. This system represents a significant advancement in the field of solar energy conversion, addressing key challenges of efficiency, cost, and reliability. Keywords Seven-level inverter, DC/DC power converter, solar power generation, multilevel inverter, high-efficiency inverter, renewable energy, grid-connected inverter, switching loss reduction, photovoltaic systems.

Ground Fault Detection of Photovoltaic and Energy Storage DC Converter Load on User Side

With the rapid development of DC power supply technology, the operation, maintenance, and fault detection of DC power supply equipment and devices on the user side have become important tasks in power load management. DC/DC converters, as core components of photovoltaic and energy storage DC systems, have issues with detecting ground faults on the positive and negative input/output buses, leading to difficulties in troubleshooting device malfunctions and potentially endangering user safety. To address these issues, a method for detecting ground faults on the positive and negative buses of a synchronous buck photovoltaic and energy storage DC/DC converter is proposed, which involves the comprehensive measurement of multi-point common-mode voltages. This method collects the input positive bus voltage, output positive bus voltage, switch voltage, and the common-mode voltage at the midpoint of the bridge arm, then sums these after removing the switching harmonics. By analyzing the characteristic differences of the summed voltage under the ground fault modes of the positive and negative input/output buses, characteristic parameters are extracted to establish a ground fault identification method, thereby achieving effective detection of ground faults in the photovoltaic and energy storage DC/DC converter. Finally, the effectiveness of the method proposed in this paper was validated through simulations and experiments.

An enhanced algorithm for detection of HIAF in active distribution networks and real-time analysis

Identifying a downed conductor in distribution is challenging due to the insignificant variations in the current signal. Most of the distribution system faults are identified using overcurrent and earth fault protection. Fault path resistance decides the current magnitude while high resistance path may create timely issues in identifying a fault. Downed conductor and high resistance faults create arc in between the ground and conductor. Due to this the fault at the location is highly nonlinear with reduced magnitude. These faults are known as high impedance arcing fault (HIAF). Such faults can be identified effectively by conducting harmonic analysis of the signals. But in a modern distribution system apart from other renewable sources, the integration of electric vehicle (EV) may create HIAF detection challenges due to the inclusion of inverters and switching harmonics associated with EV. Considering the available advanced architecture of modern microgrid system, an effective solution is proposed in this work to securely detect HIAFs. The method is robust and highly reliable for HIAFs. The system stability and continuity can be unaffected with the help of the proposed method in case of various non-fault or transient/switching conditions. Comparison with other profound techniques is done to show the superiority of the proposed method.

High-frequency harmonics suppression in high-speed railway through magnetic integrated LLCL filter.

The traction converter modulation generates switching-frequencies current harmonics. The trapped filters can eliminate these switching harmonics, reducing total inductance and filter size. Nonetheless, in comparison with the typical inductor-capacitor-inductor (LCL) filter, the trap inductor needs a larger magnetic core. Moreover, the trapped filter has not been analyzed in the traction systems. This paper proposes a magnetic integrated inductor-trap-inductor (LLCL) filter to decrease the filter's size and investigate its application in traction converters. In fact, the application range of this filter is quite broad, and it can be used in various electrical power systems, including industrial power systems, renewable energy systems, transportation systems, and building power systems. The LC-trap may be formed by connecting the equivalent trap inductor, introduced through the magnetic coupling between inverter-side and grid-side inductors, in series with the filter capacitor. Furthermore, for H-bridge unipolar pulse width modulation (PWM) traction converters, the prominent switching harmonics are concentrated at the double switching frequencies. Therefore, the stability zone is expanded by moving the resonance above the Nyquist frequency. The presented filter's features and design are thoroughly analyzed. The proposed method is finally validated by the MATLAB/Simulink simulation and hardware-in-the-loop (HIL) experimental results. Compared to the discrete windings, the integrated ones can save two magnetic cores. Furthermore, the proposed filter can meet IEEE criteria with 0.3% for all the harmonics and total harmonic distortion (THD) of 2.15% of the grid-side current.

Magnetic integrated double-trap filter utilizing the mutual inductance for reducing current harmonics in high-speed railway traction inverters

Current harmonics are generated at the switching frequency and its multiples when the traction converters are modulated. To address this, multi-trap filters are introduced, which are capable of selectively eliminating these specific harmonics to the limits set by IEEE 519-2014. This targeted removal significantly reduces the need for high total inductance, thereby allowing for a more compact filter design. Comparatively, to traditional inductor-capacitor-inductor (LCL) filters, more magnetic cores are needed for trap inductors. Furthermore, the traction systems have not been examined in conjunction with multi-trap filters. To reduce the filter size and investigate its application in traction converters, this paper presents an integrated double-trap LCL (DTLCL) filter. A tiny capacitor is connected in parallel with the grid-side inductor to form one LC-trap. In addition, another LC-trap is formed by connecting the equivalent trap inductor, introduced through the magnetic coupling between inverter-side and grid-side inductors, in series with the filter capacitor. The presented filters' features are thoroughly analyzed, and the design method has been developed. Finally, the simulation and hardware-in-the-loop (HIL) experiment results validate the proposed method's viability and efficacy. Compared to the discrete windings, the integrated ones enable a size decrease of two cores. Furthermore, the proposed filters can meet IEEE 519-2014 criteria with 0.3% for all the current switching harmonics and total harmonic distortion (THD) of 2.36% of the grid‐side current.

Aliasing Suppression Method for a Three-Phase Grid-Connected Photovoltaic Inverter Based on Multi-Sampling and Mean Filtering

In order to reduce the sampling delay and improve bandwidth, sability margin, and the robustness of the active damping in LCL-filtered grid-connected inverters, real-time sampling provides a convenient method. However, aliasing is easily introduced in the control loop because of high-frequency switching harmonics, resulting in a rise in low-order harmonics. To address the challenge of aliasing under real-time sampling, a new method based on multisampling and mean filtering is proposed by combining the proposed harmonic detection and control methods in this paper. This method works by sampling and controlling the fundamental current and selective subharmonic currents separately. The fundamental current control loop without any additional filters maintains real-time sampling, while multisampling and mean filters are applied to the harmonic current control loop. The proposed control method can not only improve the dynamic response performance and control stability of the system but also effectively suppress the selective low-order current harmonics and the aliasing of sampling. Finally, the correctness of the proposed sampling scheme and control strategy is verified by the simulation based on R2018b, MathWorks, Natick, MA, USA and an experimental prototype of a three-phase grid-connected photovoltaic inverter rated at 230 V/50 Hz/40 kW.

A high step-up multiphase interleaved boost converter for fuel cells power system

The fuel cells need the high step-up DC/DC converter with low current ripples to interface to the high voltage DC grid. A novel zero voltage switching high step-up multiphase interleaved boost converter (ZVS HSMIBC) is proposed in this paper. This new converter employs advantages of low input current ripples, high voltage step-up ratio, soft-switching operation, and low switching harmonics and noise. In this paper, the two-phase interleaved structure of the proposed ZVS HSMIBC is analyzed and researched in detail as a representative topology. The relevant conclusions also can apply to multiphase (3 and above) interleaved structure of the HSMIBC. Finally, an experimental prototype is built and test, the experimental results show that the proposed converter can operated under ZVS conditions with low input current ripples and low switching noise and harmonics. In addition, this converter can obtain high voltage step-up ratio up to 45 (mn = 8, d = 0.8) with high efficiency, and proportion of the experimental ratios to theoretical ratios is also high (not less than 0.8).

Impact of Grid-Connected Inverter Parameters on the Supraharmonic Emissions in Distributed Power Generation Systems

In this paper, a mathematical analysis is presented to show the effect of grid-connected inverter (GCI) parameters on its emissions in the supraharmonic range. This analysis is extended to explain the effect of asymmetry on the emissions of parallel-connected GCIs on distributed power generation systems. The switching harmonics of a GCI appear as bands around the switching frequency and its multiples. A MATLAB/Simulink model is built to perform two studies. In the first study, we use one GCI to examine the effect of the parameters on the emissions, while in the second study, we examine the effect of the asymmetry of two parallel-connected GCIs on the total emission toward the grid. An actual setup is built to verify the results of the mathematical analysis and the simulation study. It is found that the SHs of single-phase GCI amplitude are strongly dependent on the DC-link voltage and the coupling inductor, while the phases of the sideband harmonics only change with changing the injected power. The variation of the injected power does not have any tangible effect on the carrier harmonics.

PWM harmonics reduction for dual-branch three-phase PMSMs using interleaving topology

High-frequency pulse width modulation (PWM) acoustic noise is generated by PWM switching harmonics in the dual-branch three-phase permanent magnet synchronous motor (PMSM) systems during the switching process of the drivers. Because of the special winding structure of the double branch motor, the sum of the current of the two branches reflects the high frequency vibration of the motor. This paper proposes a method using four voltage source inverters and coupled inductors with a special connection method to eliminate the carrier frequency as well as its twice, triple noise for dual-branch three-phase PMSMs. Carrier-phase-shift technique is used to change the direction of the current harmonics. Compared with the conventional method, four paralleled VSIs can be saved. The simulation results verify the effectiveness of the method.

Discontinuous PWM Technique With Reduced Low-Order Harmonic Distortion for High-Power Applications

The modulation techniques used in high power applications have to generate high quality waveforms with reduced switching losses. As an attractive alternative, Discontinuous PWM (DPWM) techniques present lower device switching frequencies than conventional continuous PWM methods lowering the converter switching loss. Considering the same cooling system, this allows to increase the carrier frequency of DPWM methods displacing the main switching harmonics to higher frequencies. As a main drawback, when low carrier to fundamental ratios are used, DPWM methods present some undesired low-order harmonics that are required to be filtered. This paper presents a low-order harmonic minimization method for synchronous DPWM methods by modifying the conventional modulating reference to limit low order harmonics amplitude, while keeping the same effective switching frequency and thus limited switching losses.

Carrier Phase Shift Method of SPWM for Concurrent Wired and Wireless Power Transfer Systems

This paper presents an approach for concurrent power transfer to wired and wireless systems using just a single inverter. The approach utilizes a novel carrier phase-shift (CPS) method that independently controls the inverter output voltages at the fundamental and switching frequencies. This proposed method can be a cost-effective solution to wireless power transfer (WPT) systems used in contactless slip rings (CSR), which transfer power to auxiliary loads such as sensors, radars, and IoT devices. There are two separate converters in conventional CSR systems: one is for the motor drive, and the other is for the WPT system. It is proposed that the switching harmonics of the motor drive can also be utilized to excite the WPT system while the low-frequency component can still be used to drive the motor. In order to control these independently, the CPS method is introduced. The proposed method is investigated analytically for sinusoidal-PWM (SPWM). Then, an experimental setup consisting of a 3-phase 3-wire GaN-based inverter and a 3-phase motor is built. Experimental results show that the WPT and motor systems are operated concurrently, and their powers are controlled independently by the proposed method.

A New Active Front-End Control for Regenerative Cascaded H-Bridge Motor Drives With Filter- Less Interfacing Capability

This paper proposes a new active-front-end (AFE) control method for regenerative Cascaded H-bridge (CHB) motor drives. Conventional CHB converters have dominated the market for the medium-voltage industrial motor drives. However, conventional CHB converters cannot provide regenerative capability. To enable regeneration; diode-front-ends (DFEs) in power cells are replaced with IGBT-based PWM AFEs. Despite the appealing dynamic performance of PWM AFEs, their integration to the CHB converters is not optimal. First, they introduce more semiconductor losses due to the high frequency switching. Second, they introduce switching harmonics that are not cancelled by phase-shifting transformers. Therefore, they require additional harmonic filtering solutions to comply with grid harmonic standards. To resolve these challenges, this paper proposes a new AFE control for regenerative CHB converters based on fundamental frequency switching (FFE) to reduce switching frequency and thus power losses. The operation of FFEs at nominal and sag voltage conditions is presented, in addition to the capability of filter-less interfacing to the transformer. Finally, the performance of the proposed control is validated experimentally on a seven-level regenerative CHB drive.

Inverter Harmonic Suppression for Permanent Magnet Synchronous Machine Drives Based on Discontinuous SVPWM With Variable Switching Frequency

Since one phase of discontinuous space vector pulse-width modulation (DSVPWM) is always clamped, the inverter nonlinearity induces obvious 3rd and 6th harmonics in <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">dq</i> -axis currents and voltages. Besides, there are non-negligible spiky switching harmonics in permanent magnet synchronous machine (PMSM) drives of PWM-controlled with fixed switching frequency. To solve these issues, an inverter harmonic suppression strategy for DSVPWM with variable switching frequency is proposed in this paper. Firstly, an inverter nonlinearity model including dead time, switching delay, and device voltage drops under DSVPWM is proposed, and a standstill test is presented for the estimation of distorted voltage terms due to inverter nonlinearity. Then the spiky switching harmonics are dispersed by the proposed chaotic-DSVPWM based on Tent map. Finally, the effectiveness of the proposed method is demonstrated on a PMSM platform, which shows quite good performance in the suppression of both low- and high-frequency harmonics. The paper reveals that the inverter harmonics under DSVPWM can be easily reduced by distorted voltage compensation and variable switching frequency.

An Evolutionary Annealing–Simplex Method for Inductance Value Selection for LCL Filters

Grid-connected voltage-source inverters (VSIs) have evolved over the past years for the interconnection of renewable energy sources with the grid to satisfy the increased electrical load demand and utilize clean carbon-free energy. However, VSIs suffer a significant drawback of switching harmonics caused by the inverter switches. To reduce the amount of current distortion injected into the utility grid and meet harmonic constraints as defined by power quality standards, an LCL filter is often used. Although extensive literature describes assorted design procedures for an LCL filter, all these methods cannot guarantee an optimal solution, because no direct mathematical function between the LCL filter parameters and the total harmonic distortion (THD) exists. Presented in this paper is the application of an evolutionary annealing–simplex method to select the inductance values in the LCL filter. This method is compared to other methods previously presented in the literature: a systematic method and an inductance grid-search method based on a calculated distribution of total harmonic distortion for various inductance values. The goal is to select the smallest overall inductance values to ensure lower manufacturing costs while maintaining the filter performance. Simulation and experimental results verify that at least a 40% reduction in overall inductance can be achieved with the proposed method while simultaneously guaranteeing the filtering performance.

2DOF-based current controller for single-phase grid-connected voltage source inverter applications

This paper presents the design of a discrete-time control scheme for the current injected into the grid by a single-phase voltage source inverter (VSI). The VSI is connected to the grid by means of an LCL filter that attenuates the switching harmonics present in the output waveform of the inverter. The current control is based on a resonant regulator implemented in a Two-Degrees-Of-Freedom (2DOF) scheme that allows the location of all the poles to be defined in the closed loop of the system without the need for observers and measuring only the current injected into the grid. This control scheme, therefore, allows the attenuation of the resonance frequency of the LCL filter and requires no additional damping methods with which to mitigate the resonance phenomenon. The design parameters can be obtained using a fairly straightforward mathematical approach that involves only operations with real numbers. The simulation and experimental results obtained show that the control scheme performs correctly even considering changes in the grid inductance.

Fault detection and localization method for modular multilevel converters in offshore DC wind turbines

The offshore DC wind turbine, consisting of direct-drive permanent magnet synchronous generator (PMSG) and modular multilevel converter (MMC), has become a promising candidate for the large-capacity wind energy conversion system. Submodule (SM) failure detection and localization are crucial for reliable operation of the MMC. However, existing techniques mainly focus on the rated operation condition, which may not be suitable for the MMC in wind turbine due to varying wind speed. Moreover, proper injection of second-order harmonic circulating current (SHCC) is desirable to reduce capacitor voltage ripple and power loss, which may also affect the accuracy of fault detection. This paper proposes a fault-tolerant strategy immune to variable operation conditions, as well as SHCC injection, for the MMC with phase-shifted carrier modulation. Firstly, the inherent switching harmonics of circulating current with SM failure are analyzed, based on which the fault detection method is developed. Then, the localization approach is presented by measuring the difference of SM capacitor voltages. Compared with existing techniques, the proposed strategy requires neither estimator nor additional sensor, which is robust, simple, and economical. Finally, both simulation and experimental results demonstrate the effectiveness of the proposed method, which is not influenced by SHCC and varying wind speed.

An Advanced Switching Harmonic Cancellation Method for a Dual-Generator Power System in More-Electric Aircraft

Dual-generator power systems have attracted increased attention in recent years as it can significantly reduce the fuel assumption of aircraft engines allowing power transfer between different engine shafts. In such a system, two generators supply a common dc bus together. A dc-bus capacitor is required to filter switching harmonics to ensure that the dc-bus voltage satisfies the MIL-STD-704F standard. Due to the high current rating, this capacitor is normally bulky and heavy. This article aims to introduce a switching harmonic cancellation method, which can effectively reduce harmonics at the dc bus. This, in return, will extend the lifetime and reduce the weight of the dc-bus capacitor. With the assumption that power converters connected to the dc bus are modulated with the commonly used space vector pulsewidth modulation (SVPWM) technique, a simplified mathematical model to estimate both first and second switching harmonics is developed. Based on the proposed models, an advanced method of switching harmonic cancellation scheme is proposed through an adaptive phase shift of carrier signals for different power outputs of converters. Both simulation and experimental results are used to validate the proposed model and the suppression method.

A New Type of Three-Phase Asymmetric-LCL Power Filter for Grid-Tied Voltage Source Inverter With Step-Up Transformer

Power filters have been widely used to suppress switching harmonics caused by the modulation of grid-connected inverters. In order to save the total inductance and cost and reduce the volume, different power filters were proposed for the three-phase three-wire grid-connected voltage source inverter. However, in industrial applications, due to the consideration of production cost, the difficulties caused by the deviation of actual parameters have to be addressed. In this article, we propose a new three-phase three-wire power filter with a simple structure, almost the smallest total inductance, and strong resistance to the adverse effects of parameter shifts. The parameters of the proposed filter and the design of the grid-connected system controller are introduced in detail. When studying the influence of parameter offset, a comparison between different types of notch power filters is also given. Simulation and experimental results on a 380 V/50 Hz/6 kW three-phase inverter prototype verify the performance of the proposed power filter.

Passivity-Based Multisampled Converter-Side Current Control of LCL-Filtered VSCs

With the gradually decreasing cost of high-performance digital processors, multisampling current control is a potential method to reduce the control delay and improve the stability in <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">LCL</i> -filtered grid-connected converters. In the practical implementation, an antialiasing filter is required to remove the sampled switching harmonics and suppress the low-order aliasing. However, due to the phase lag from the antialiasing filter, the dissipative region of converter output admittance still cannot be lifted to switching frequency, which leads to a risk of system instability under wide grid admittance variation. In order to tackle this challenge, a filter capacitor voltage feedforward scheme using multisampling is proposed in this article. Consequently, the dissipation below the switching frequency is harvested for a three-phase converter. Furthermore, by doubling the multisampling rate, the proposed method can extend the dissipative region to the apparent switching frequency for a single-phase converter using unipolar modulation. The experimental results validate the effectiveness of the proposed method on a down-scaled single/three-phase converter.

Decoupled Magnetic Integration of Symmetrical LCL Filter With a Common-Mode Inductor for Single-Phase Grid-Connected Converters

High-frequency power electronic devices in grid-connected converters excited vast switching harmonics and electromagnetic interference (EMI) noises. Conventional <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">LCL</i> -type harmonic filters can well attenuate switching harmonics, but have a poor EMI suppression capability, especially for common-mode (CM) noise. Symmetrical filter structure and an additional EMI filter are generally needed to effectively suppress EMI in power converters, but this will inevitably increase the size and cost of the output filter. In order to tackle this issue without sacrificing the filter performance, this article proposes a decoupled magnetic integration of symmetrical <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">LCL</i> filters with a CM inductor for single-phase grid-connected converters. The harmonic inductors of a symmetrical <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">LCL</i> filter and a CM inductor are integrated on the side-limbs and middle-limb of an EE-type magnetic core, respectively. Due to the decoupled magnetic structure and the reasonable assignment of the windings, the magnetic coupling between converter-side inductors and grid-side inductors can be greatly canceled to improve the performance of <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">LCL</i> filters on the basis of the integration of CM inductor to suppress CM EMI. The detailed design guidance of the proposed integration method is presented. A single-phase decoupled magnetic integration filter is fabricated and tested, and the experimental results verify the effectiveness and feasibility of the proposed method.