Current Harmonic Content Research Articles

Design and Implementation of Bridgeless Power Factor Corrector with Low Static Losses

Research and development of power factor corrector (PFC) for AC/DC converters of single-phase AC power supply network are discussed within this article. Two-channel bridgeless PFC is proposed in this paper. The proposed converter allows us to lower current DC component generation in the power network and to reduce static and dynamic losses of semiconductor devices. The suggested solution characteristic features are the absence of a diode bridge while using two identical converters operating in different power network voltage half periods. Due to cumulative chokes in each converter, the function setting the consumption current sinusoidal form is realized with the ability of wide-range output voltage regulation. A number of Simulink-models have been developed in order to study operating modes and to test control algorithms of the proposed bridgeless PFC. The input current harmonic content, efficiency coefficient, passive elements’ electrical parameters, and output voltage pulsation coefficient of the proposed bridgeless PFC were researched by Simulink-models. The results obtained show the efficiency of the proposed solutions regarding PFC. The THD value does not exceed 1.3% in steady state mode and is not over 4% during the voltage stabilization process; the minimal value of the output voltage pulsation coefficient is 3.1%. The suggested solutions can be applied in accumulator batteries’ charging sets and DC motors’ reduced-current start.

THREE-LEVEL DIRECT TORQUE CONTROL BASED ON COMMON MODE VOLTAGE REDUCTION STRATEGY FED TWO PARALLEL CONNECTED FIVE-PHASE INDUCTION MACHINE

This survey proposes a mitigation approach for common mode voltage produced in a three-level five-phase inverter fed two parallel-connected five-phase induction machines controlled by direct torque control. The switching frequencies used in the inverter fed these types of drives are characterized by a large amplitude of the produced common mode voltage waveforms (), leading to prominent issues, especially with the near introduction of wide-gap semiconductor technologies. In this context, the introduced approach is an extension to a multi-motor drive of the TATTE method, exploiting the concept of virtual voltage vectors to mitigate the resulting common mode voltage. The collected results critically evaluate the reported approach by improving the drive’s generated common mode voltage status to () compared to () in the conventional method, in addition to a significant reduction in the flux and torque ripples by 22 % and 39 %, respectively, at the cost of an insignificant increase in the current harmonic content by 6 %.

Predictive power control strategy without grid voltage sensors of the Vienna rectifier

AbstractThis paper proposes a predictive power control strategy for the three‐phase, six‐switch Vienna rectifier without grid voltage sensors to reduce the hardware cost and complexity of a high‐power PWM rectifier system. Firstly, an algorithm for calculating the AC‐side voltage in the αβ coordinate system is derived according to the operating principle of the Vienna rectifier, and a voltage observer is constructed by combining a second‐order low‐pass filter to estimate the grid voltage. Secondly, a soft start method is designed to solve the problem that the rectifier is prone to inrush current when it is started. Furthermore, the control method of grid voltage sensorless is combined with predictive power control with good dynamic characteristics and simple parameter settings to form the control strategy proposed in this paper. Finally, simulation analysis and experimental verification are carried out on the proposed control strategy. Simulation and experimental results show that the grid voltage estimation has high accuracy, a good surge current suppression effect, unit power factor operation, low input current harmonic content, and good dynamic and steady‐state performance. Therefore, the correctness and effectiveness of the strategy proposed in this paper are verified.

A capacitor voltage ripple suppression method employing bidirectional‐switching channel for the MMC driven pumped storage system operating at low‐speed stage

SummaryThe Modular Multilevel Converter (MMC) has gained the widespread application in the DC power transmission, owing to the advantages such as modularity and low output current harmonic content. However, its adoption in variable‐speed pumped storage systems remains limited due to the significant voltage fluctuations in its sub‐module capacitors during the low‐speed operation. In this paper, a capacitor voltage ripple suppression method employing bidirectional‐switching channel is proposed. It aims to improve the driving performance of MMC when the variable‐speed pumped storage motor operates at low speed. The proposed method creates bidirectional‐switching channels between the sub‐modules of the upper and lower bridge arms and moves the sub‐module capacitors that originally fixed to the upper and lower bridge arms into the channels. By controlling the bidirectional‐switching channel, the same capacitor can be put into the sub‐modules of different bridge arms. At the same time, a threshold switching control method is proposed to reduce the switching loss. Without introducing the common mode voltage, the capacitor voltage fluctuation can be substantially suppressed when the pumped storage motor operates at low speed. Experimental and simulation results verify the effectiveness of the proposed method.

Discrete-Time Adaptive Control for Three-Phase PWM Rectifier.

This paper proposes a dual-loop discrete-time adaptive control (DDAC) method for three-phase PWM rectifiers, which considers inductance-parameter-mismatched and DC load disturbances. A discrete-time model of the three-phase PWM rectifier is established using the forward Euler discretization method, and a dual-loop discrete-time feedback linearization control (DDFLC) is given. Based on the DDFLC, the DDAC is designed. Firstly, an adaptive inductance disturbance observer (AIDO) based on the gradient descent method is proposed in the current control loop. The AIDO is used to estimate lump disturbances caused by mismatched inductance parameters and then compensate for these disturbances in the current controller, ensuring its strong robustness to inductance parameters. Secondly, a load parameter adaptive law (LPAL) based on the discrete-time Lyapunov theory is proposed for the voltage control loop. The LPAL estimates the DC load parameter in real time and subsequently adjusts it in the voltage controller, achieving DC load adaptability. Finally, simulation and experimental results show that the DDAC exhibits better steady and dynamic performances, less current harmonic content than the DDFLC and the dual-loop discrete-time PI control (DDPIC), and a stronger robustness to inductance parameters and DC load disturbances.

Grid Quality Services from Smart Boilers: Experimental Verification on Realistic Scenarios for Micro-Grids with Demand-Side Management Oriented to Self-Consumption

The deeper penetration of renewables in the energy mix is an intense requirement in order to reduce global carbon dioxide emissions. In addition, new technologies are being developed, such as electric mobility and Distributed Generation (DG) in urban areas. However, the unpredictable fluctuations in energy generation from roof-installed PVs and the switching operation of their inverters greatly aggravate the already-present grid quality problems. In this paper, the Smart Boiler (SB) concept for grid quality improvement is presented. Furthermore, its experimental verification is implemented on a flexible testbed that accurately emulates several realistic scenarios for the low voltage distribution grid, under complex operating conditions. The proposed low-cost electronic kit, which contains a converter of fairly simple topology and requires connection to the internet, is used to upgrade conventional domestic boilers to smart devices. The SB automatically regulate the local reactive power flow, helping to stabilize the voltage level and suppress the grid current harmonic content, with both services provided in a matter of seconds. The higher the active power consumed and the denser the SB cluster, the wider the beneficial impact on the affected network area. While this service is provided, excess energy generated by PVs is temporarily stored as heat in the boiler tanks, given the users’ hot water consumption habits. The whole application, as a powerful demand-side management tool, proves beneficial for both the network operator and the end-user, especially when self-consumption is desirable in order to achieve a Nearly Zero Energy Building.

Characteristics and Parameters of a Three-Phase, Three-Wire Balanced Circuit with Non-Linear Load

The existing non-linear load in a three-phase circuit limits the possibilities of using the symmetrical components method to analyse it. This paper presents a method for analysing such a circuit when only the zero and positive components are present. Nonlinear loading in a circuit limits the applicability of the symmetrical components method in the analysis of a three-phase circuit. When there is only a zero component and a positive component, it is possible to carry out the analysis as presented in this article. The analysed circuit is balanced. An equal nonlinear load with a voltage described by a signum function of the current is considered in three phases. This load, through equal series RL elements, is supplied from a symmetrical three-phase voltage source. For a steady state with unbroken current flows, the equations of the circuit are solved symbolically. In the broader scope of the equation, solutions obtained using MATLAB-Simulink R2021b were used. The matching of the symbolic and simulation solutions was obtained. The current and voltage harmonic content coefficients of the receiver, the equivalent resistance and inductance of the nonlinear load, and the distribution of active and reactive power in the circuit were determined. The reactive power analysis shows that the considered load nonlinearity when generating higher harmonics, increases the reactive power of the circuit and the inductance of the circuit, which is seen from the terminals of the power source.

Harmonic suppression control strategy of distribution networks based on the distributed power flow controller

New energy and multiple loads, such as distributed wind–solar storage and charging, are connected to the distribution network through power electronic converters, which increases the harmonic content in the distribution network and causes operational safety risks. In this paper, the mathematical model of harmonic current and harmonic power content in a distribution network is constructed by an equivalent circuit and vector diagram. The distributed power flow controller is proposed for harmonic control of the distribution network. The mathematical expressions of the harmonic current and harmonic power based on a distributed power flow controller are constructed, and the control strategy of the distributed power flow controller for harmonic control is proposed. The simulation results show that the proposed method can effectively suppress the fifth and seventh harmonics of the distribution network.

Multi-source data driven harmonic spectrum estimation of substation feeder current

With the proliferation of non-linear loads and distributed power resources that connect through power electronic equipment, decentralized harmonic pollution in three-phase symmetric power system becomes increasingly serious. Despite this, monitoring the current harmonic of all substation feeders regardless of cost is unrealistic. To this end, a multi-source data driven method is proposed in this paper, utilizing data from the power quality monitoring system, dispatching system, and market business system, to estimate the harmonic spectrum of substation feeder currents and estimate the harmonic current components of each feeder with monitoring data of bus voltage harmonics and line harmonic currents. The objective function of the harmonic spectrum estimation model is constructed based on the analysis of current harmonic phasor and power relationship on the feeders. An improved particle swarm optimization (PSO) algorithm is proposed to solve the proposed estimation model thereby obtaining the current harmonic content of each feeder and the phase angle difference between the current harmonics of the feeders. The performance of the proposed model and algorithm is validated by numerical simulation with a test system and an actual system.

Maximum Efficiency Point Tracking Algorithm for Resonant Full-Bridge Converter in Charging Applications

In this paper, a novel maximum efficiency point tracking algorithm is proposed for a resonant DC-DC power converter in charging applications. Based on a total harmonic analysis (THA), a method for minimizing the harmonic content of the input AC current is investigated. An online algorithm is proposed for achieving the maximum efficiency at the whole charging spectrum, by controlling the angle under which zero-voltage switching occurs. The suggested control algorithm is simple to implement with very low computational complexity. Additionally, an effective winding method is proposed for increasing the leakage inductance without greatly increasing the air gap, thus eliminating the need for additional resonant inductors. A prototype converter of 2kW|20A is implemented for verifying the proposed method and 98% maximum efficiency is achieved.

Improved calculation of core losses of high-speed motors with two different permanent magnets considering higher order current harmonics

In high-speed permanent magnet synchronous motor drives, time harmonics in the current occur owing to the carrier frequency of the inverter, which affects the core losses among the electromagnetic losses. According to Steinmetz’s equation, the core loss depends on the frequency and magnetic flux density, with each term influenced by harmonic currents. Therefore, to accurately predict core loss, it is necessary to consider harmonic currents. This study presents the effects of differences in the resistance, inductance, switching frequency, and harmonic current on the core loss for two models with different PMs at the same output power. Core losses are significantly affected by harmonic current content and magnetic field behavior, making the analysis of harmonic components and magnetic field behavior essential. To achieve this, the stator core was divided into segments to examine the magnetic field behavior owing to harmonic currents in each region, thus facilitating a comprehensive analysis of the core losses. When the results were compared with the experimental data, it was observed that the analysis of harmonic currents significantly improved the accuracy compared to the analysis based solely on sinusoidal currents; in particular, the error rate reduced from 37.8% to 4.1%. Furthermore, it was confirmed that ferrite PMs resulted in smaller core losses owing to harmonic currents than rare-earth PMs. This finding suggests that ferrite PMs are a suitable alternative to high-speed permanent-magnet synchronous motors.

Evaluation of Harmonic Currents and Network Impedance using Norton Model in an Unidentified Network Configuration

This paper presents a study that focuses on the evaluation of the analysis of harmonic currents emitted by loads and the harmonic impedance of a real electrical network using the Norton model. The primary advantage of employing this model lies in its ability to address scenarios where the complete network configuration, particularly from the distribution side, is not known. By calculating currents and voltages at the supply-side for two different operating conditions, the harmonic current content and the network impedance can be evaluated. To induce variations in operating conditions, a switching shunt capacitor is utilized. The results show that the fifth and the seventh harmonics clearly appear with values of 189.382 A and 135.073 A, respectively, while the other harmonics have values close to zero. The harmonic impedance also shows the presence of the fifth and the seventh harmonics with values of 1865.681 Ω and 4289.3 Ω, respectively. The main contribution of this paper focuses on converting the real electrical network into numerical data that can be accepted by the software. The components of the network model have to be carefully selected to understand the harmonic analysis and to success the simulation, which is conducted using the EMTP-ATPDraw program. The results of this investigation can be used as a database for electrical transmission and distribution companies in case of making any changes in the network, such as installation of new loads or cables, or in case of making measurements.

Fault Location and Phase Selection Method of Distribution Network Containing IIDG Based on Online Active Detection

This paper proposes a fault location and phase selection method for the distribution network containing IIDG based on online active detection, utilizing online active detection. In this method, the characteristic harmonic current injection control strategy based on d- and q-axis control is obtained by analyzing the structure, control strategy, and short-circuit current of IIDG. During a fault, the distributed power supply injects characteristic harmonic current into line, adapting its magnitude with the short-circuit current’s size. By detecting the difference in harmonic current content rate for both ends of the fault point, the method achieves online location and line selection of fault points. A 10 kV IIDG distribution network model is simulated by using PSCAD to validate the feasibility and accuracy of the proposed fault location and phase selection method.

High proportion and large value harmonic current influence on the magnetic field, loss and temperature distribution for ultrahigh voltage converter transformer

AbstractThe temperature distribution of ultrahigh voltage (UHV) converter transformer is the key to its service life, allowable load and safe operation. The influence of a high‐proportion and large‐value harmonic current on the magnetic field, loss and temperature distribution of a UHV converter transformer is studied. A new calculation method is proposed to determine the winding temperature under the combined actions of multiple key factors. First, the skin effect of UHV converter transformer winding under high proportion and high current harmonics is analysed extensively. It is found that the increase of harmonic current frequency leads to exponential increase of winding loss and temperature by changing skin depth. Second, based on the superposition principle, a calculation method for winding loss considering harmonic current and different load rates is developed. The temperature distribution under different harmonic current frequencies and contents is obtained. The winding losses and temperature under different harmonic currents are quantified. Finally, a new calculation method is proposed for the converter transformer winding temperature, considering the combined actions of factors such as load rate, cooling oil inlet rate and temperature, harmonic current frequency and content. Experimental verification showed an error of only 0.58 K in the actual transformer hotspot temperature, confirming the effectiveness of this method. This method is of great significance for temperature control and safe operation of UHV converter transformers.

Research on the control strategy of LCL grid-connected inverters based on improved auto disturbance rejection.

The grid-connected inverter is the key to ensure stable, reliable, safe, and efficient operation of the power generation system; the quality of the grid-connected output current waveform directly affects the performance of the entire power generation system. To improve the anti-interference performance and reduce the output current harmonic content of the grid-connected inverter, an improved control strategy that combined repetitive control (RC) and auto disturbance rejection control (ADRC) is designed in this paper. Firstly, decoupled the ADRC to realize the individual adaptation between tracking performance parameters and anti-interference performance parameters of the controller, through which the difficulty of adjusting parameters is reduced. Secondly, the control approach is devised by adding RC to ADRC. To demonstrate the effectiveness of the proposed method in this paper, detailed experimental studies are conducted using proportional integral control, traditional ADRC, and the proposed method under normal power grids, weak power grids, and periodic disturbances. And dynamic performance simulation experiment is done to verify the dynamic performance of the self-disturbance rejection controller before and after the addition of RC links. The results indicated the effectiveness and feasibility of the proposed method. Finally, after simulation, the steady state and dynamic performance are conducted on a hardware testing platform. The impacts of the obtained results indicate the effectiveness and feasibility of the control algorithm proposed, the ability to suppress intermediate frequency disturbances is improved, the bandwidth of the auto disturbance rejection controller is expanded, and the harmonic content of the output current is depressed.

Analysis of Inter-Turn Short Circuit Faults in Dual Three-Phase PMSM for Electromechanical Actuator

Dual three-phase permanent magnet synchronous machine (DTPM) is an attractive choice for electromechanical actuator owing to its advantages of double redundancy, high power density and high reliability. However, the winding insulation is susceptible to the high thermal and mechanical stress, which will lead to the inter-turn short circuit faults (ITSCF) and poses threat to the safety of the machine system. Moreover, the ITSCF of DTPM is not only limited to single-phase, but also occurs between adjacent phases. Therefore, in this paper, the characteristics of single-phase and phase-to-phase ITSCFs are investigated and compared while the short-circuit contact resistance is considered. Firstly, a general mathematical model for single-phase and phase-to-phase ITSCFs are established, and the expressions of short circuit current (SCC) and output torque are derived. Then, the characteristics of flux density, back-EMF, SCC, fault phase current and output torque of the different fault models are compared by finite element analysis. It is demonstrated that when the contact resistance is not zero ( <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">R_f</i> ≠0), the amplitude of SCC and the third harmonic content of fault phase current are inversely proportional to the contact resistance and proportional to the number of short-circuit turns. In addition, the amplitude of SCC, torque ripple and braking torque caused by a phase-to-phase ITSCF will be larger than those of the single-phase ITSCF under the same fault conditions, especially when the contact resistance is small. Finally, an experimental prototype is made and tested to validate these analyses.

Experimental study on physical characteristics of dielectric-boosted gliding arc discharge

To augment the plasma processing capability, and obtain an enhanced plasma area, a dielectric-boosted gliding arc discharge (DBGAD) reactor was developed. The electrical, gliding arc motion and energy injection characteristics of the DBGAD reactor were investigated. The process of AC DBGAD includes breakdown gliding mode (B-G) and steady arc gliding mode (A-G), with peak currents on the order of amperes in B-G mode and on the order of milliamps in A-G mode. Situating a 50 mm quartz dielectric underneath the plasma area at a distance of 10 mm from the base of the blade electrodes, enhanced discharge power is obtained, and sustained arc gliding time is extended efficiently. At an input voltage of 9.2 kV, the DBGAD demonstrates a 27% increase in arc stabilization gliding time compared to the gliding arc discharge (GAD) and delivers an average discharge power 1.12 times superior to that of the GAD. In the DBGAD reactor, the plasma column twists following the minor vortex of the reflow and has a more pleated shape. The energy injection characteristics are analyzed using the fast Fourier transform system, and the results show that the current harmonic content of DBGAD is reduced and the discharge fluctuation is mitigated, which is favorable for stable discharge. The primary benefit of incorporating quartz dielectric is that it provides the mobile arc with a supportive force, leading to a more substantial and intensely focused plasma field. This in turn facilitates greater system stability and yields measurable enhancements in power output.

A coordinated control hybrid MPPT algorithm for a grid-tied PV system considering a VDCIQ control structure

In this paper, a new coordinated maximum power point tracking (MPPT) algorithm has been developed for a grid-tied PV system, whose inverter follows a VDCIQ control scheme. The control objectives of this system are shared between 2 converters: a DC boost converter which performs MPPT of the PV plant, and an inverter which is responsible for DC voltage setpoint control, specific reactive current injection under request and reduced harmonic content of AC grid currents. The proposed algorithm operates upon a proper switching amongst conventional MPPT algorithms, namely perturb and observe (P&O) and incremental conductance (IC) algorithms, to take advantage of the best characteristics of each MPPT method with a different step size and considering the influence of the inverter control constants. Two coordination schemes are proposed for this algorithm to prioritise the improvement of different performance aspects over others. The impact of the proposed algorithm according to the 2 coordination schemes is evaluated and compared with the impact of conventional MPPT algorithms according to the trackability of power, the impact on DC voltage and on the AC grid side. The results are analysed by simulations conducted in MATLAB-Simulink.

Robust cascade controller for the power factor of the three-phase supply and the induction motor velocity

It is well known that induction motors consume active and reactive energy from the utility grid to operate; additionally, when a power converter drives the motor, a high content of current harmonics is produced, and both circumstances decrease the utility grid power factor, which later requires to be improved. To this end, this paper presents a novel complete solution through a robust control system employed in a back-to-back topology power converter to deliver, instead of consuming, regulated reactive power toward the main grid, which comes from a capacitor bank in a DC-bus. This salient feature of delivering reactive power, and simultaneously, regulating the speed for an induction motor, becomes one of the contributions of this work to enhance the power factor. The robust converter controller is synthesized in a cascade form, by applying the linearization block control and state-feedback techniques. These techniques are combined with the super-twisting strategy for canceling the nonlinearities and the effect of the external disturbances. The complete system consists of a back-to-back converter, an LCL filter coupled to the main grid for mitigating the current harmonic content, and an induction motor under variable load conditions. Experimental tests expose the performance and robustness of the proposed controller, where a robust control for the reactive power acts under sudden changes in the active power produced through abrupt variations in the motor load.

Research on Harmonic Overvoltage of Cable Sheath on 220kV Side of Electric Railway Traction Station

Abstract The special operation mode of high-speed railway will generate a large amount of harmonics. The harmonics will be transmitted to the 220kV side high-voltage cables through the traction transformer, and harmonic voltages will be generated on the cable sheath, threatening the safe operation of the cables. In this paper, on the basis of the measured harmonic data of the traction substation, a harmonic source model based on the measured data is established, which solves the complex problem of harmonic source modeling and can accurately reflect the actual operating conditions of high-speed trains. On this basis, the harmonic voltage characteristics of the cable sheath on the 220kV side of the high-speed railway under the three working conditions of traction, regenerative braking and inertia are simulated and calculated, and the effects of cable length, cable grounding method, and harmonic current parameters on the harmonic voltage are explored. Affect the law. The results show that under different operation modes of high-speed rail, the harmonic voltage of the sheath far exceeds the normal operation of the power frequency, and the maximum value of the harmonic voltage of the cable sheath can reach 454V under the traction condition; Under working conditions, the overvoltage of the metal sheath is greatly affected by the grounding method of the cable, the length of the cable and the harmonic current content. The above research results have important reference significance for the safe operation of electrified railways.