Output Current Harmonics Research Articles

Online Dead Time Effect Compensation Algorithm of PWM Inverter for Motor Drive Using PR Controller

This paper proposes the dead time effect compensation algorithm using proportional resonant controller in pulse width modulation inverter of motor drive. To avoid a short circuit in the dc link, the dead time of the switch device is surely required. However, the dead time effect causes the phase current distortions, torque pulsations, and degradations of control performance. To solve these problems, the output current including ripple components on the synchronous reference frame and stationary reference frame are analyzed in detail. As a results, the distorted synchronous d-and q-axis currents contain the 6th, 12th, and the higher harmonic components due to the influence of dead time effect. In this paper, a new dead time effect compensation algorithm using proportional resonant controller is also proposed to reduce the output current harmonics due to the dead time and nonlinear characteristics of the switching devices. The proposed compensation algorithm does not require any additional hardware and the offline experimental measurements. The experimental results are presented to demonstrate the effectiveness of the proposed dead time effect compensation algorithm.

H∞ Repetitive Control Based on Active Damping with Reduced Computation Delay for LCL-Type Grid-Connected Inverters

In the paper, the H∞ repetitive current control scheme based on active damping along with the design method is proposed for three-phase grid-connected inverters with inductor-capacitor-inductor (LCL) filters. The control scheme aims to reduce the harmonic distortion of the output currents and achieve better efficiency. The design method introduces capacitor-current-feedback active damping into the H∞ controller design process by proposing an equivalent controlled plant. Additionally, based on the discrete model of the controlled plant with variable computation delay, the algebraic expression of the stable region for the feedback coefficient and the computation delay is obtained to avoid system instability caused by the digital control delay. Finally, the stability criterion is proposed to evaluate the stability of the discrete control system with the H∞ repetitive current control scheme. The theoretical analysis and experimental results prove that the control scheme presented in this paper not only can reject the harmonics of output currents, but is robust under the variation of the grid-impedance.

Reduction in Current THD of Grid Parallel Inverters Using Randomized PR Control

In grid connected system, unity power factor current injection into the grid is vital. This can be achieved by choosing the right inverter topology, passive filter components, current controllers, and PWM switching scheme. This paper compares the output current harmonics profile between when using the conventional proportional resonant (PR) current controller and when using the modified PR current controller. By applying the latter technique, via experimental validation using TMS320F2812, the THD of the injected grid current in a parallel connected inverters system is improved.

Switching State Vector Selection Strategies for Paralleled Multilevel Current-Fed Inverter Under Unequal DC-Link Currents Condition

A paralleled multilevel inverter topology consists of n three-phase three-level current-fed inverters (CFIs) connected in parallel on ac side. AC currents with (2n+1) levels can be generated utilizing redundant switching states when all three-level inverters have equal dc-link currents. However, the multilevel space vector diagram gets modified, redundancy in the switching states is lost and the multilevel current pattern changes when the dc-link current of all inverters is not the same. This introduces low-frequency harmonics in output current, thereby deteriorating total harmonic distortion (THD). The presence of low-frequency components in the output current could be avoided by selecting suitable switching state vectors and ensuring proper time sharing among these vectors. Two methods to select such switching state vectors are proposed in this paper. In the first method, a reference current space vector is realized using the nearest switching state vectors. However, this method results in low-frequency pulsation in dc-link voltage of each inverter. In the second method, the switching state vectors are chosen to eliminate this low-frequency pulsation. Effectiveness of these methods is experimentally validated for a five-level CFI. Further, performance of these methods is compared based on efficiency, THD, and dc-link voltage ripple for various inequality ratios in dc-link currents.

Closed-Form Solution of Time-Varying Model and Its Applications for Output Current Harmonics in Two-Stage PV Inverter

The single-phase photovoltaic (PV) inverter needs significant capacitance to buffer the double-line frequency power pulsation at ac port. The two-stage inverter allows the designer to choose the dc-link voltage and the capacitor size flexibly. With the reduced capacitance, the lifetime of the dc-link capacitor can be prolonged by replacing the electrolytic capacitors with film capacitors. However, the capacitance deduction results in high double-line frequency voltage ripple on dc-link, which increases a series of odd harmonics in the output current. This paper hence analyzes the harmonics caused by the voltage ripple in an inverter with feedback control. The inverter is modeled as a time-varying system by considering the dc-link voltage ripple. A closed-form solution is derived to calculate the amplitude of the ripple-caused harmonics. This analysis helps the designer to understand the effect of the dc-link voltage ripple on current harmonics, evaluate effectiveness of existing approaches, and stimulate new ideas and solutions. The study also derived the theoretical limit to select dc-link capacitance and sampling rate of current reference without violating the grid-tied regulations in power quality. The analysis is verified both by simulation and experimental evaluation.

Harmonic Characteristic Analysis of Five-Phase Space Vector PWM

Pulse modulation width (PWM) of multi-phase inverter is the key technologies of ships electrical propulsion. In this paper, theories and realization of space vector PWM (SVPWM) for five-phase inverter is analyzed. The proposed SVPWM adopts two adjacent large voltage vectors to composite the reference voltage vector and this method have advantages of easy to realize. Theoretical waveform and harmonics of five-phase inverter output voltages under the proposed control method are deduced. The analysis shows that there are very large third harmonics in the inverter output voltages and currents. The total harmonic distortion (THD) is large also, and changes small with the modulation index. Simulation and experiments certify the conclusions.

Photovoltaic plant with reduced output current harmonics using generation‐side active power conditioner

This study presents a study on a scheme to reduce the current harmonics from a photovoltaic (PV) plant. The scheme uses a power conditioner unit, which is placed parallel with the plant and works in feed-forward mode, and behaves to compensate the PV plant's output current distortion, so that the total current flows to the grid is sinusoidal. In addition, this scheme includes an effective control structure, which combines a simple sine-wave generation for synchronisation, as well as a distortion current's components extraction, and a conditioner current control. In this study, the control system was implemented to a voltage source inverter with LCL output filter as conditioner power circuit. The workability of the scheme and the power quality improvement achieved were evaluated by using a TMS320F28335 DSP-based control conditioner proto-type; using real signal from PV plant operation. Then, the effect on the conditioner installation to the power quality improvement for different power operation of PV-inverter was analysed. Finally, the improvement on the utilisation factor of PV-inverter and plant was analysed and described.

Non-Linear 3D Impedance Spectroscopy

Non-linear Dielectric spectroscopy of Biological suspensions was first proposed by the Woodward and Kell group. The above mentioned arose as a technique able to monitor the enzymes state placed in the cell membrane of the biological tissue. This technique is limited to such enzymes because an external low frequency electrical field notably disturbs the membrane's electrical entourage. This kind of interactions can be monitor if the system generates current harmonics. This phenomenon was theorized by Astumian and Robertson. Treo, on his work suggests that the harmonics are originated at the interface and altered by the microorganism presence. Then Ruiz developed a fast method to detect the global non-linearity of a biological suspension. Nevertheless, on these works, the non-linearity interference due to the electrode-electrolyte interface was not controlled. The observed response is the result of the interface modulation because of the microorganism presence. On our work, we employed a tripolar measurement cell. The working electrode (WE) is a gold disc, the counter electrode (CE) is made of stainless steel and the reference electrode (RE) is a standard Ag/AgCl electrode. 1.74 g of lyophilized Saccharomyces cerevisiae was dissolved in 90 ml of saline medium. A frequency (0.1 - 1000 Hz) and tension AC (0- 600 mV) sweep was carried out without DC polarization. The first 5 output current harmonics were monitored. Results would indicate that it was successfully possible to measure the non-linearity due to only the yeasts cells, without the non-linear interference of the electrode - electrolyte interface.

Electromechanical Coupling Vibration of Rolling Mill Excited by Variable Frequency Harmonic

Using torque telemetry system to test the mechanical drive system of rolling mill,it is found that the torsional vibration and current signal in the electric drive system have the same obviously vibration frequency. The model of cycloconverter, synchronous motor and mechanical drive system of rolling mill are built and analysed by Matlab/Simulink and ANSYS.The simulation results show when the harmonic torque frequency and the torsional vibration natural frequency of for mechanical drive system are equal or close, the strong torsional vibration arouse It is proved that the convertor output current harmonics can induce the electromechanical coupling vibration of main mechanical drive system under the certain conditions.

Simplified implementation of optimised carrier‐based PWM in three‐level inverters

Carrier-based modulation has been widely adopted since it offers some benefits compared to space-vector modulation in both two-level and in multilevel three-phase inverters, such as inherent simplicity, flexibility, reduced computational times and easy implementation on industrial DSPs. Among the numerous types of pulse width modulation (PWM) techniques, the centred PWM (CPWM) is nearly optimal modulation since it minimises the RMS of the output current harmonics. Despite optimised CPWM being easy to implement in two-level inverters, the complexity increases in the case of three-level and multilevel inverters. A straightforward and simplified procedure to implement optimised CPWM in carried-based modulation for the three-level inverter is proposed and numerically verified.

A Study of Novel Cuk Grid-Connected Inverter Based on Double-Loop Control

A kind of Cuk grid-connected inverter is proposed for renewable energy power generation. The grid-connected inverter using Cuk input series output parallel circuit, form a new type of non isolated single stage output parallel input series double Cuk inverter circuit. Firstly, On the basis of the topological structure and principle, the double-loop control strategy is researched to enhance its adaptability and robustness. Simulative results show that,the proposed inverter with double-loop control has better dynamic and static performances, with less output current harmonics and better waveform quality.

DC-Bus Design and Control for a Single-Phase Grid-Connected Renewable Converter With a Small Energy Storage Component

This paper presents a control design approach for optimum dynamic response in single-phase grid-connected renewable converters with minimum energy storage components. This is a crucial matter in realizing compact and robust converters without use of bulky and sensitive electrolytic capacitors. Nonoptimum dynamic response results in undesired interruptions of the maximum power point tracking and reduction of the overall efficiency of the system. Common practice is to select a large dc-bus size in order to reduce the double-frequency ripples that cause harmonics and to slow down the dynamic response to avoid large fluctuations on the bus caused by random input power jumps. This paper shows that both problems can be addressed to a great extent by improving the control system and without need to excessively increase the size of the bus component. This paper proposes a control system to achieve these goals and provides an analytical design method to optimize both dynamic response and output current harmonics. The proposed method succeeds to reduce the size of bus component several times without compromising the system performance. Details of the proposed method, mathematical modeling of the bus control and current control systems, simulations, and experimental results are presented and discussed.

A Systematic Approach to DC-Bus Control Design in Single-Phase Grid-Connected Renewable Converters

This paper presents a method for design and control of dc-bus capacitance and transients in a renewable single-phase grid-connected converter. Conventionally, a proportional (P) or proportional-integrating (PI) controller is commonly used and the design stage is performed using trial-error or using a simplified analysis that does not take the dynamics of the current control loop into consideration. This paper proposes 1) a systematic and efficient method for design of dc-bus PI controller gains; and 2) an accurate method for the design of the dc-bus controller gains without neglecting the dynamics of the current control loop. Two main objectives are to have control over the amount of output current harmonics and over the level of bus fluctuations caused by random input power swings. The proposed method is transparent and it provides a convenient and rigorous insight for the designer to properly select the size of dc-bus component and to determine the controller gains.

A SPACE VECTOR PWM SCHEME FOR NEUTRAL POINT CLAMPED MULTILEVEL INVERTERS

Multilevel inverters are increasingly being used in high power medium voltage applications when compared to two level inverter due to their merits, such as lower common mode voltage, lower dv/dt, lower harmonics in output voltage and current. Among various modulation techniques for a multilevel inverter, space vector pulse width modulation is poplar due to the merits like, it directly uses the control variable given by the control system and identifies each switching vector as a point in complex space. However the implementation of the SVPWM for a multilevel inverter is complicated. The complexity is due to the difficulty in determining the location of the reference vector, the calculations of on times and the determination and selection of switching states. The multilevel SVPWM method uses the concepts of two level modulations to calculate the on times of an n-level inverter. Use of multilevel inverters has become popular for motor drive applications. Various topologies and modulation strategies will be studied from the available literature. This work is devoted to the study and simulation of a new NPC multilevel inverter system typically suitable for high-performance high-power applications. Simulation of this work will be done in MATLAB/Simulink .

Harmonic reduction in wind turbine generators using a Shunt Active Filter based on the proposed modulation technique

The grid connected Wind Energy Conversion Systems (WECSs) have two practical topologies, the traditional fixed speed and the new variable speed. Variable speed systems have several advantages over the traditional ones, such as reduction of mechanical stress and increase in captured energy; however, the systems need a Power Electronic (PE) converter, in which the machine is connected to the grid via the PE converter. To improve the power quality and decrease electrical losses in the variable speed WECS, choosing a full control PE converter or a simple PE converter including an active filter is essential. In this paper, a new modulation technique is proposed to be used in a Shunt Active Filter (SAF) to improve the output current harmonics of a WECS, including a Permanent Magnet Synchronous Generator (PMSG) and the AC-to-DC converter. The filter contains three parts: the identification, modulation, and an inverter. Most identification methods are sensitive to non-sinusoidal sources, but in the proposed filter an algorithm is used to make it non-sensitive to some extent. The simulation results confirm the superior performance of the proposed SAF over the previous SAFs applied in wind energy conversion systems.

NPC 3-레벨 인버터를 적용한 차세대 고속전철 IPMSM의 구동

NPC 멀티레벨 인버터는 2-레벨 인버터 방식에 비해 전력용 반도체 소자의 정격 전압과 출력전류의 고조파를 감소시킬 수 있는 장점이 있어 고압 대용량 전동기 구동시스템에 적합하다. NPC 3-레벨 인버터를 이용한 IPMSM의 속도 제어에서 일정 토크 영역에서는 최대 토크 제어, 일정 출력 영역에서는 약계자 제어 방식을 적용하였다. 제안된 시스템은 MATLAB/Simulink를 이용한 시뮬레이터를 구현하여 모의 시험 결과 분석을 통해 그 타당성을 검증하였다. In this paper, speed control of IPMSM drives for the next generation domestic high speed railway system using NPC 3-level inverters is presented. The NPC multilevel inverter is suitable for the high-voltage and high-power motor drive system because it has advantages in that the voltage rating of the power semiconductor devices and output current harmonics are reduced. For the speed control of IPMSM using NPC 3-level inverters, maximum torque control is applied in the constant torque region, and filed weakening control is applied in the constant power region. Simulation programs based on MATLAB/Simulink are developed. Finally the designed system is verified and their characteristics are analyzed by the simulation results.

Evaluation effective parameters on the output current harmonics of SHE-PWM voltage source inverters

Many important parameters are effective on the output current of voltage source inverter (VSI) that among them load type, frequency, and load connection can be mentioned. In VSI, the current waveform is affected from mentioned parameters. Variation of these parameters can change the output current total harmonic distortion (THD). It is desired that the output current waveform to be close to sinusoidal. In this paper, by constructing a VSI, effect of load connection, frequency, and load type such as resistive, resistive-inductive, and inductive on VSI output current harmonics are investigated. For this purpose, different operational modes are defined for two structures of VSI, and effects of these parameters on output current are evaluated. Also, this voltage source inverter is simulated in PSpice that verify the experimental results.

The Design and Realization of Digital Controlled Frequency-Variable Speed-Adjustable System Based on DSP and SVPWM

The paper introduces voltage space vector pulse wide modulation (SVPWM) arithmetic and the field oriented control (FOC), develops a suit of Digital Controlled frequency-variable speed-adjustable system based on digital signal processor (DSP) TMS320LF2407 of TI company For motor control, and research and analyze design parts of the system, presents the instantiation application result. The experimental results indicate: the laboratorial setting has a simpler hardware construction, less output current harmonics distortion, higher control precision and stronger real-time sigal processing.

Analysis of a hybrid controlled three-phase grid-connected inverter with harmonics compensation in synchronous reference frame

The power quality of three-phase grid-connected inverters has drawn attention with the increasing numbers of distributed generation systems. In order to effectively eliminate the harmonics in output currents, a hybrid system based on proportional–integral (PI) control and repetitive control (RC) implemented in the synchronous reference frame (SRF) is presented. Based on the reference frame transformation, the use of a repetitive controller is not for achieving fundamental reference current tracking but attaining the harmonics compensation, which is different from the RC designed in a static reference frame. In addition, analyses of the SRF-based hybrid controlled converter system, including stability constraints, harmonics rejection principles and the relationship between the PI controller and repetitive controller, are further developed in frequency domain and time domain. Finally, experimental results are demonstrated to validate the steady-state and dynamic performance of the proposed hybrid controlled system.

Harmonic Mitigation, Maximum Power Point Tracking, and Dynamic Performance of Variable-speed Grid-connected Wind Turbine

This article presents a method for harmonic mitigation and maximum power point tracking for a variable-speed grid-connected 20-kW wind turbine. The wind energy conversion system consists of a permanent magnet synchronous generator driven by variable-speed 20-kW wind turbine. The output of the permanent magnet synchronous generator is connected to a single-switch three-phase boost rectifier to generate DC voltage, which feeds a current-controlled inverter to interface the system with the electric utility. The single-switch three-phase boost rectifier is an active power factor correction technique to maintain the power factor at the permanent magnet synchronous generator side to nearly unity and mitigate the permanent magnet synchronous generator current harmonics. To mitigate inverter output current and voltage harmonics, an LCL filter has been used. A complete analysis of the harmonic content has been done everywhere in the system. The results show that the proposed maximum power point tracking control strategy succeeded to track the maximum wind power irrespective of the wind speed. This strategy in presence of an LCL filter achieved harmonic mitigation at the permanent magnet synchronous generator and inverter output sides. The dynamic response of the wind energy conversion system is tested under a three-phase fault condition. For comparison purposes, an active power filter is designed and checked against the single-switch three-phase boost rectifier for harmonic mitigation at the permanent magnet synchronous generator side.