Inverter Switching Frequency Research Articles

An Overview on Power Quality Issues and Control Strategies for Distribution Networks With the Presence of Distributed Generation Resources

Power systems based on centralized production are facing two limitations: the lack of fossil fuels and the need to reduce pollution; Therefore, the importance of distributed generation resources (DGs) has increased by connecting renewable energy systems to the network. With the increasing penetration of renewable energies in the network, power quality challenges in low voltage and medium voltage distribution systems have become one of the main fields of studies. Since most of the renewable energy systems are connected to the network with the help of electronic power converters devices and the main purpose of these converters is to connect DGs to the network in compliance with power quality standards; Therefore, if the switching frequency of inverters is not implemented properly, major power quality problems will be created. On the other hand, the reduction in power quality causes acute problems in power networks, which include lack of proper performance, reduction in useful life and efficiency of electrical and electronic devices in the network, creation of series and parallel resonance in some harmonics due to the presence of inductors and the capacitor, and as a result, more distortion in the voltage of the distribution network. This paper actually provides a road-map for researchers to investigate power quality issues. In other words, the mentioned cases show the importance of research and providing the solutions to improving power quality in distribution networks.

Telephone Interference From Solar PV Switching

The emergence of solar Photovoltaic (PV) generation has been one of the biggest changes in the Power Grid in the past decade. Such generation plants are generally inverter based and these devices are known sources of harmonics of the fundamental frequency and ‘supraharmonics’ (distortion in the frequency range 2 to 150 kHz). It has long been theorized that due to factors such as the frequency response of service transformers that interface solar PV plants to the grid, impedance of the power system at the point of common coupling and the impedance of devices connected near solar inverters, supraharmonics frequencies are localized and generally do not couple to the grid. Exceptions to this general hypothesis have been reported in Europe, where supraharmonics from PV and wind power plants have been shown to couple to the local three-phase three wire Medium Voltage (MV) system. This paper shows that in three-phase four wire multi-point grounded MV systems, such as the ones used in the United States (U.S.), application of conventional grounding schemes to PV plants can lead to the unintended consequence of coupling of supraharmonics to the grid through the neutral conductor and ground circuit. It describes a case study in which supraharmonics due to inverter switching led to telephone interference for customers located around a solar PV plant. To determine the mechanism by which the supraharmonics frequencies were coupling to the grid, an investigation of the emission from the plant was performed using conducted as well as radiated measurements. The novel setup used for performing these radiated measurements, the unique underlying mechanism by which inverter switching frequencies coupled to the grid and the lessons learned in this process regarding solar PV grounding and installation practices are described in this paper.

Bond Graph Modeling, Simulation, and Control of Permanent Magnet Linear Synchronous Motor

The high-performance feature of the Permanent Magnet Linear Synchronous Motor (PMLSM) makes it a reliable and valuable motor for use in the automotive industry, especially for electric vehicle (EVs) applications. This research proposes a bond graph approach in modeling the PMLSM as a multi-domain dynamical system. However, A time-based simulation was performed using 20-sim software to simulate the dynamical behavior of the motor. An equivalent model of the motor was first obtained and then modeled and simulated using 20-sim software. The model of the PMLSM drive system was modeled separately and incorporated with PMLSM Motor equivalent model to form a global model. Moreover, the motor drive system response was studied based on the sensor resolutions and the inverter switching frequency. The block diagram and the transfer function methods validated the bond graph model obtained. Two classical PIs such as continuous and discrete were implemented on the motor response to control the velocity of the motor.

Analysis and Design of Zero-Voltage-Switching Multiphase AC/DC Converters

In this article, the generic analysis and design of zero-voltage-switching (ZVS) multiphase ac/dc converters are proposed. With the edge aligned pulsewidth modulation (PWM) (EA-PWM) scheme, all switches of ZVS multiphase ac/dc converters can realize ZVS operation. Besides, the switching frequency is fixed and the auxiliary switch only operates once in each switching period. Its operation stages in a switching cycle are analyzed and a generic ZVS condition is derived. Based on the proposed theory, a ZVS two-stage three-phase photovoltaic (PV) inverter is investigated, which is regarded as a five-phase converter. Its ZVS condition under different working conditions is discussed. Finally, a 10-kW prototype with 150 kHz switching frequency of the ZVS two-stage three-phase PV inverter is built and the experimental results are given to verify the analysis. In addition, the extension of the ZVS multiphase converter in different applications is introduced.

Real-Time Validation of a Novel IAOA Technique-Based Offset Hysteresis Band Current Controller for Grid-Tied Photovoltaic System

Renewable energy sources have power quality and stability issues despite having vast benefits when integrated with the utility grid. High currents and voltages are introduced during the disconnection or injection from or into the power system. Due to excessive inverter switching frequencies, distorted voltage waveforms and high distortions in the output current may be observed. Hence, advancing intelligent and robust optimization techniques along with advanced controllers is the need of the hour. Therefore, this article presents an improved arithmetic optimization algorithm and an offset hysteresis band current controller. Conventional hysteresis band current controllers (CHCCs) offer substantial advantages such as fast dynamic response, over-current, and robustness in response to impedance variations, but they suffer from variable switching frequency. The offset hysteresis band current controller utilizes the zero-crossing time of the current error for calculating the lower/upper hysteresis bands after the measurement of half of the error current period. The duty cycle and hysteresis bands are considered as design variables and are optimally designed by minimizing the current error and the switching frequency. It is observed that the proposed controller yields a minimum average switching frequency of 2.33 kHz and minimum average switching losses of 9.07 W in comparison to other suggested controllers. Results are validated using MATLAB/Simulink environment followed by real-time simulator OPAL-RT 4510.

Field experimental tests and analyses of suspension frame vibration of low-medium speed maglev train

Pushed by social demands, China has continuously developed its low-medium speed maglev transportation systems in recent decades. However, with the increase of the running mileage of the train, high frequency vibration of suspension frame gradually appears. In this paper, a method to analyze the high frequency vibration of suspension frame by detecting the current of traction motor is proposed. Field measurements of suspension frame vibration and traction motor current of low-medium maglev train were conducted on a maglev line that has been commercially put into operation. The test results show that the speed of the measured maglev train was closely correlated with vibration accelerations of the suspension frame in three directions, but as the speed increased, the influence it imposed on the suspension frame vibration waned. The dominant frequency of traction motor resultant current was consistent with the dominant frequency of the suspension frame vibration acceleration. The switching frequency of traction inverter was the main cause of high frequency vibration of suspension frame.

PMSM Torque Ripple Minimization Based on Novel Low Carrier Ratio PWM Technique

Harmonic injection is commonly used in permanent magnet synchronous motor torque ripple minimization (TRM) of electric vehicle. Traditional inverter switching frequency limits TRM application at high speed due to harmonic modulation accuracy and inverter loss. To achieve TRM in the whole speed range and reduce inverter loss, a novel online calculated low carrier ratio pulsewidth modulation (LCRPWM) is proposed in this article. The carrier ratio determining regular according to the injected harmonics is established first. The relationship between injected harmonics and LCRPWM switching angle is revealed and a set of nonlinear equations is established. Thus, the problem is transformed from solving nonlinear equations into optimization by establishing a cost function. The analytical solutions of nonlinear equations are obtained, which avoids iterative operation and plunging into local minimum. Therefore, the switch angle solution method is suitable for online calculation. The LCRPWM is verified in simulation compared with the traditional regularly sampled space vector PWM, which achieves better results in voltage harmonic injection and flux tracking at a much lower switching frequency. At last, the LCRPWM is used in a test bench experiment that shows good TRM effects. The influence of sideband harmonics on torque ripple is analyzed.

An Improved Sliding Mode Control Method to Increase the Speed Stability of Permanent Magnet Synchronous Motors

A permanent magnet synchronous motor (PMSM) plays an important role in the operation performance of an electric vehicle. In order to increase the speed stability of PMSMs, an improved sliding mode control (SMC) method is proposed in this paper. Firstly, the control process of a PMSM is divided into parts, which are the torque closed-loop control and speed closed-loop control. Secondly, an integrated control method with proportional integral (PI) and inverter switching frequency is adopted in order to increase the torque performance of the PMSM. Lastly, compared with the traditional SMC method, an improved SMC method with saturation function is proposed in order to decrease the speed fluctuation of the PMSM from 7.7% to 5.9%, thereby increasing the speed stability of the PMSM. The results of the experimental test indicate that both the speed stability and starting performance of the PMSM are increased by the improved SMC method.

МОДЕЛИРОВАНИЕ ЭЛЕКТРОПРИВОДА ПЕРЕМЕННОГО ТОКА С АЛГОРИТМАМИ ПРОСТРАНСТВЕННО-ВЕКТОРНОЙ МОДУЛЯЦИИ

The relevance of investigation of induction motor electric drives with frequency converters having voltage source inverter with space-vector modulation is shown. The brief survey of researches of such matter is carried out. The aim of this article is to develop mathematical and computer model of frequency converter with space-vector modulation algorithms by means of Matlab Simulink, this model has to be implemented into the Matlab models of AC electric drives with induction and synchronous motors. To achieve such an aim, it needs to introduce techniques of electric drive theory, numerical techniques, techniques of algebraic equations system solution, techniques of computer simulation. The still two-phase framework is applied to describe the converter model. The two-level voltage source inverter is chosen for the investigation of modulation algorithms. To verify the mathematical model of space-vector modulation, the model of 5.5 kW induction motor is used. Induction motor and power switches are modelled by means of Matlab SimPowerSystems units. The results of simulation show the adequacy of the developed model in both steady state and transient modes. One can conclude the dependence of total harmonic distortion of the induction motor stator current from load torque, switching frequency of voltage source inverter’s power switches and stator current frequency for the electric drive with scalar control system.

A modified power decoupling control strategy for a grid-connected inverter with a low switching frequency under unbalanced grid voltages

In the photovoltaic grid-connected power generation system, when proportional resonant (PR) control is adopted for the grid-side inverter in the two-phase stationary coordinate (αβ), there is a coupling problem between active power (P) and reactive power (Q). Under unbalanced grid conditions, especially in high-power applications where the switching frequency of the grid inverter needs to be reduced, the power coupling problem will be exacerbated. Based on the instantaneous power response characteristics of the grid inverter, expressions of the power coupling coefficient under unbalanced power grids are derived in this paper, and the influence of the unbalanced grid voltage on the power coupling is revealed. Moreover, a decoupled grid-side model of the grid inverter is established, and a modified controller based on positive and negative sequence (P–N sequence) decoupling is proposed to solve the power coupling problem. The closed-loop transfer function of the system with the modified current controller is studied, and the stability of the modified controller is analyzed according to the bilateral frequency response diagram. Based on analysis of the coupling coefficient, the degree of coupling between P and Q can be reduced significantly by applying the proposed control method. Furthermore, in order to solve the influence of the delay on the power coupling caused by the low switching frequency, the decoupling compensation link for the delay is introduced, which can eliminate the influence of delay on power coupling. Finally, experiments are performed on a grid-connected inverter prototype. The experimental results show that when the grid voltage is unbalanced, the proposed control method can reduce the coupling degree of the P and Q, which also improves the dynamic performance of the grid-connected inverter with a low switching frequency.

Iron Loss Analysis in Axial Flux Permanent Magnet Synchronous Motors With Soft Magnetic Composite Core Material

Accurate calculation of iron losses in electric machines are essential for optimal machine design. This is especially important for axial flux permanent magnet motors with solid stator and rotor cores. This paper investigates iron losses in axial flux motor with soft magnetic composite material for the stator and the rotor. First, an analytical model is proposed to estimate iron losses under different operating conditions. The model is based on combining the Quasi 3-D computation approach and the magnetic equivalent circuit. The proposed model can be modified to account for different motor topologies and different stator and magnet designs. Then, The effect of torque ripple, on iron losses, is studied by comparing two motors: an optimized motor, with dummy pocket added to the stator tooth, and a non-optimized motor. Finally, the effect of the motor control scheme and the inverter switching frequency is studied by implementing two controllers: the Field Oriented Control and the Trapezoidal control. Simulations using 3-D finite element analysis and experimental tests are conducted, under different operating conditions, on two <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$\text{12}\,V$</tex-math></inline-formula> , 6 slots, 8 poles single stator single rotor fractional horsepower axial flux permanent magnet synchronous motor prototypes. Test results shows that motor optimization, the choice of the motor control scheme, and the selected switching frequency can significantly affect iron losses in the motor. Using an optimized motor with a smooth control scheme, such as Field Oriented Control, and a high switching frequency, can cause a variation in iron losses by around 14% compared to a non optimized motor with the Trapezoidal control and a low switching frequency.

Core Loss Estimation for an Inverter-Fed Induction Motor With More Accurate Realisation of Material Non-Linearity and Impact of Hysteresis Minor Loops

The work presents a fast and accurate core loss evaluation method for inverter-fed induction machines. The proposed method takes into account the influence of time variation of magnetic permeability on the eddy current loss. Furthermore, the proposed method presents an accurate approach to precisely evaluate the hysteresis loss. The results obtained from the proposed method are compared with the existing methods for a 1.5kW inverter-driven induction motor. The method shows sufficiently high accuracy with reduced complexity and implementation-time for a wide range of inverter switching frequency and motor's loading.

Adaptive Neuro Fuzzy Inference System Based controller for Electric Vehicle's hybrid ABS braking

To improve braking safety, modern electric vehicles are equipped with both friction and regenerative braking systems. The combined use of these two modes is mainly carried out in ABS operation. This paper deals with the problem of electric braking torque control in ABS mode. The EV considered is equipped with a traction motor of the interior permanent magnet synchronous machine type (IPMSM). Using field-oriented control (FOC) strategy, two torque regulators, namely adaptive fuzzy PID (AFPID) and adaptive neuro-fuzzy inference system (ANFIS) are developed and their control performances are analyzed and compared. In order to perform a realistic evaluation of the two aforementioned regulators, the hybrid ABS system, consisting of a slip controller, a braking torque references distribution law (electrical/friction), a friction brake, and an electric brake (IPMSM) is considered. Based on several performance indices, e.g. torque ripple, flux ripple, inverter switching frequency, control accuracy, dynamic response, and algorithm complexity, a comparison is made by simulation using Matlab /Simulink.

Optimisation of switching frequency of three-phase four-wire inverter under different dead time

Optimisation of switching frequency of three-phase four-wire inverter under different dead time

Optimisation of switching frequency of three-phase four-wire inverter under different dead time

Optimisation of switching frequency of three-phase four-wire inverter under different dead time

Variable Switching Frequency Control-Based Six-Step Operation Method of a Traction Inverter for Driving an Interior Permanent Magnet Synchronous Motor for a Railroad Car

Most railroad cars employ a natural ventilation cooling method. For this reason, severe problems occur in the control devices for the railroad cars due to the heat generated by the high-power switching loss. Therefore, the traction inverter for the railroad car requires a control method that can reduce the switching loss. In this paper, we propose a control method for an interior permanent magnet synchronous motor in consideration of the driving conditions of the railroad cars. The proposed method combines a variable switching frequency-based synchronous pulse width modulation control method, a flux-weakening control method that considers the maximum voltage modulation index, and an optimized over-modulation method. Through the proposed method, the utilization rate of the DC-link voltage can be maximized while lowering the switching frequency of the traction inverter as much as possible, and the high-performance current control can be performed in the entire speed region of the railroad car. The validity and effectiveness of the proposed method are verified by the simulation results and the experimental results.

Development of a Digitally Controlled Inductive Power Transfer System with Post-Regulation for Variable Load Demand

Inductive Power Transfer (IPT) is an emerging technology enabling a contactless charging process in manifold applications such as electric vehicles, wearable and portable devices, or biomedical applications. Such technology can be profitably used to develop enhanced electronic solutions in the framework of smart cities, homes and smart workplaces. This paper presents the development and realization of a series–series compensated IPT System (IPTS) followed by a post-regulator implemented by means of a DC–DC converter. Such a system is modeled through a first harmonic approximation method, and a sensitivity analysis of the IPTS performance is carried out with respect to the variations of the primary inverter switching frequency and phase-shift angle. As an element of novelty of this work, the bias points are determined which allow the efficiency maximization while ensuring system controllability. An enhanced dynamic modeling of the system is then performed by means of a coupled mode theory, including the inverter phase-shift modulation and extending its validity to whatever operating frequency. A digital control of the post-regulator is implemented by means of a commercial low-cost microcontroller enabling the output voltage regulation under both fixed and variable load conditions through a voltage mode control technique. An IPTS prototype is eventually realized, which is able to correctly perform the output voltage regulation at the desired nominal value of 12 V for static resistive loads in the range [5, 24] Ω, yielding the output power in the range [6, 28.8] W and the experimental efficiencies going from 72.1% (for 24 Ω) to 91.7% (for 5 Ω). The developed system can also be effectively used to deliver up to 35 W output power to variable loads, as demonstrated during the battery charging test. Finally, an excellent output voltage regulation is ascertained for load transients between 5 Ω and 24 Ω, with limited over- and undershoot amplitudes (less than 3% of the nominal output voltage), thus enabling the use of the proposed system for both fixed and variable loads in the framework of smart homes and workplaces applications.

Analysis and Verification of Traction Motor Iron Loss for Hybrid Electric Vehicles Based on Current Source Analysis Considering Inverter Switching Carrier Frequency

In this study, a current source analysis method considering the inverter switching frequency is proposed to improve the precision of loss analysis of a traction motor for a hybrid electric vehicle. Because the iron loss of the traction motor is sensitively influenced by input current fluctuations, the current source analysis using the actual current obtained from an inverter is the ideal method for accurate analysis. However, as the traction motor and inverter should be manufactured to obtain the real current, the traction motor is generally designed based on an ideal current source analysis. Our proposed method is an analytic technique that fits the loss of a traction motor similar to the actual loss by injecting harmonics of the same order of the inverter switching frequency into the ideal input current. Our method is compared with the analysis of the ideal current source to assess the difference in loss. In addition, a test motor was manufactured, and an efficiency test was conducted to compare the efficiency and verify the effectiveness of our method.

A dual fuzzy logic controller‐based active thermal control strategy of SiC power inverter for electric vehicles

Thermal stress is one of the most important factors leading to power module failure. Under the load condition of high current with low fundamental frequency or largely changed load current, it would cause high junction temperature swing amplitude (JTSA) of chips, which could accelerate the failure of power module. To address this issue, this paper proposes a dual fuzzy logic controller-based active thermal control (ATC) strategy to reduce the JTSA of chips in cases of variable power profiles. Two fuzzy logic controllers are designed to reduce the JTSA of chips by adjusting the switching frequency and pulse width modulation (PWM) strategy, respectively. One fuzzy logic controller is designed to reduce the transient JTSA of chips, which is done by changing the switching frequency according to the fundamental frequency and transient JTSA. The other one is to reduce the mean JTSA of chips, which is implemented by regulating the switching frequency and PWM modes according to the mean junction temperature and its variation. The minimum one is selected as the switching frequency of power inverter. Finally, the effectiveness of the proposed ATC strategy is verified by simulation and experimental results.

Reduction of total harmonic distortion of three-phase inverter using alternate switching strategy

Alternating current (AC) electrical drives mainly require smaller current (or torque) ripples and lower total harmonic distortion (THD) of voltage for excellent drive performances. Normally, in practice, to achieve these requirements, the inverter needs to be operated at high switching frequency. By operating at high switching frequency, the size of filter can be reduced. However, the inverter which oftenly employs insulated gate bipolar transistor (IGBT) for high power applications cannot be operated at high switching frequency. This is because, the IGBT switching frequency cannot be operated above 50 kHz due to its thermal restrictions. This paper proposes an alternate switching strategy to enable the use of IGBT for operating the inverter at high switching frequency to improve THD performances. In this strategy, each IGBT in a group of switches in the modified inverter circuit will operate the switching frequency at one-fourth of the inverter switching frequency. The alternate switching is implemented using simple analog and digital integrated circuits.