scispace - formally typeset
Search or ask a question

Showing papers on "Total harmonic distortion published in 2012"


Journal ArticleDOI
Bo Yang1, Wuhua Li1, Yunjie Gu1, Wenfeng Cui1, Xiangning He1 
TL;DR: In this article, an improved single-phase inverter topology is presented to eliminate the common-mode leakage current in the transformerless photovoltaic grid-connected system, and the high efficiency and convenient thermal design are achieved thanks to the decoupling of two additional switches connected to the dc side.
Abstract: To eliminate the common-mode leakage current in the transformerless photovoltaic grid-connected system, an improved single-phase inverter topology is presented. The improved transformerless inverter can sustain the same low input voltage as the full-bridge inverter and guarantee to completely meet the condition of eliminating common-mode leakage current. Both the unipolar sinusoidal pulsewidth modulation (SPWM) as well as the double-frequency SPWM control strategy can be applied to implement the three-level output in the presented inverter. The high efficiency and convenient thermal design are achieved thanks to the decoupling of two additional switches connected to the dc side. Moreover, the higher frequency and lower current ripples are obtained by adopting the double-frequency SPWM, and thus the total harmonic distortion of the grid-connected current are reduced greatly. Furthermore, the influence of the phase shift between the output voltage and current, and the influence of the junction capacitances of the power switches are analyzed in detail. Finally, a 1-kW prototype has been simulated and tested to verify the theoretical analysis of this paper.

507 citations


Journal ArticleDOI
TL;DR: A new topology with a reversing-voltage component is proposed to improve the multilevel performance by compensating the disadvantages mentioned and the overall cost and complexity are greatly reduced particularly for higher output voltage levels.
Abstract: Multilevel inverters have been widely accepted for high-power high-voltage applications. Their performance is highly superior to that of conventional two-level inverters due to reduced harmonic distortion, lower electromagnetic interference, and higher dc link voltages. However, it has some disadvantages such as increased number of components, complex pulsewidth modulation control method, and voltage-balancing problem. In this paper, a new topology with a reversing-voltage component is proposed to improve the multilevel performance by compensating the disadvantages mentioned. This topology requires fewer components compared to existing inverters (particularly in higher levels) and requires fewer carrier signals and gate drives. Therefore, the overall cost and complexity are greatly reduced particularly for higher output voltage levels. Finally, a prototype of the seven-level proposed topology is built and tested to show the performance of the inverter by experimental results.

397 citations


Journal ArticleDOI
03 Jul 2012
TL;DR: A hierarchical control scheme is proposed for enhancement of sensitive load bus (SLB) voltage quality in microgrids to manage the compensation of SLB voltage unbalance and harmonics by sending proper control signals to the primary level.
Abstract: In this paper, a hierarchical control scheme is proposed for enhancement of sensitive load bus (SLB) voltage quality in microgrids. The control structure consists of primary and secondary levels. The primary control level comprises distributed generators (DGs) local controllers. Each of these controllers includes a selective virtual impedance loop which is considered to improve sharing of fundamental and harmonic components of load current among the DG units. The sharing improvement is provided at the expense of increasing voltage unbalance and harmonic distortion. Thus, the secondary control level is applied to manage the compensation of SLB voltage unbalance and harmonics by sending proper control signals to the primary level. DGs compensation efforts are controlled locally at the primary level. The system design procedure for selecting proper control parameters is discussed. Simulation results are provided in order to demonstrate the effectiveness of the proposed control scheme.

302 citations


Journal ArticleDOI
TL;DR: In this article, a grid-connected boost-half-bridge photovoltaic (PV) microinverter system and its control implementations are presented, where a plug-in repetitive current controller based on a fourth-order linear-phase IIR filter is proposed to regulate the grid current.
Abstract: This paper presents a novel grid-connected boost-half-bridge photovoltaic (PV) microinverter system and its control implementations. In order to achieve low cost, easy control, high efficiency, and high reliability, a boost-half-bridge dc-dc converter using minimal devices is introduced to interface the low-voltage PV module. A full-bridge pulsewidth-modulated inverter is cascaded and injects synchronized sinusoidal current to the grid. Moreover, a plug-in repetitive current controller based on a fourth-order linear-phase IIR filter is proposed to regulate the grid current. High power factor and very low total harmonic distortions are guaranteed under both heavy load and light load conditions. Dynamic stiffness is achieved when load or solar irradiance is changing rapidly. In addition, the dynamic behavior of the boost-half-bridge dc-dc converter is analyzed; a customized maximum power point tracking (MPPT) method, which generates a ramp-changed PV voltage reference is developed accordingly. Variable step size is adopted such that fast tracking speed and high MPPT efficiency are both obtained. A 210 W prototype was fabricated and tested. Simulation and experimental results are provided to verify the validity and performance of the circuit operations, current control, and MPPT algorithm.

225 citations


Journal ArticleDOI
TL;DR: In this article, three bridgeless single-phase ac-dc power factor correction (PFC) rectifiers based on Cuk topology are proposed, which achieve almost a unity power factor and low total harmonic distortion of the input current.
Abstract: Three new bridgeless single-phase ac-dc power factor correction (PFC) rectifiers based on Cuk topology are proposed. The absence of an input diode bridge and the presence of only two semiconductor switches in the current flowing path during each interval of the switching cycle result in less conduction losses and an improved thermal management compared to the conventional Cuk PFC rectifier. The proposed topologies are designed to work in discontinuous conduction mode (DCM) to achieve almost a unity power factor and low total harmonic distortion of the input current. The DCM operation gives additional advantages such as zero-current turn-ON in the power switches, zero-current turn-OFF in the output diode, and simple control circuitry. Performance comparisons between the proposed and conventional Cuk PFC rectifiers are performed based on circuit simulations. Experimental results for a 150 W/48 Vdc at 100 Vrms line voltage to evaluate the performance of the proposed bridgeless PFC rectifiers are provided.

210 citations


Journal ArticleDOI
TL;DR: In this article, an improved active frequency drift (AFD) anti-islanding method is presented based on a different current distortion injection waveform, which generates 30% less harmonic distortion compared to classic AFD, resulting in faster island detection and improved non-detection zone.
Abstract: As more distributed generators join the utility grid, the concern of possible undetected islanding operation increases. This concern is due to the safety hazards this phenomenon imposes on the personnel and equipment. Passive anti-islanding detection methods monitor grid parameters to detect islanding, whereas active methods inject a perturbation into the current waveform to drive these parameters out of limit when islanding occurs. The performance of active methods, such as conventional active frequency drift (AFD), is limited by the amount of total harmonic distortion (THD) they inject into the grid, which defines its nondetection zone. In this paper, an improved AFD anti-islanding method is presented based on a different current distortion injection waveform. The proposed method generates 30% less THD compared to classic AFD, resulting in faster island detection and improved nondetection zone. The performance of the proposed method is derived analytically, simulated using Matlab and verified experimentally using a prototype setup. A single-phase grid-tied photovoltaic distributed generation system is used for the simulation and experimental setup, and considered as potential application.

206 citations


Journal ArticleDOI
TL;DR: In this article, a stator current harmonic suppression method using a sixth-order resonant controller was proposed to eliminate negative sequence fifth-and positive sequence seventh-order current harmonics in a doubly fed induction generator (DFIG) wind turbine system.
Abstract: Voltage harmonics in the grid can introduce stator current harmonics in a doubly fed induction generator (DFIG) wind turbine system, which may potentially impact the generated power quality. Therefore, wind turbine current controllers need to be designed to eliminate the impact of grid voltage harmonics, especially low-order harmonics. This paper proposes a stator current harmonic suppression method using a sixth-order resonant controller to eliminate negative sequence fifth- and positive sequence seventh-order current harmonics. A stator current harmonic control loop is added to the conventional rotor current control loop for harmonic suppression. The overall control scheme is implemented in dq frame. Based on a mathematical model of the DFIG control system, the effects on system stability using the resonant controller, an analysis of the steady-state error, and the dynamic performance, are discussed in this paper. Taking these effects into account, the parameters of the resonant controller can be designed and effectively damp the influence from the grid voltage harmonics. As a result, the impacts of the negative sequence fifth- and positive sequence seventh-order voltage harmonics on the stator current as well as the electromagnetic torque are effectively removed. Simulations and experiments are presented to validate the theoretical analysis.

205 citations


Journal ArticleDOI
TL;DR: In this article, a fixed-switching frequency sliding mode controller is proposed for a single-phase unipolar inverter, and the smoothing procedure is based on limitation of pulsewidth modulator.
Abstract: Sliding mode control (SMC) is recognized as robust controller with a high stability in a wide range of operating conditions, although it suffers from chattering problem. In addition, it cannot be directly applied to multiswitches power converters. In this paper, a high performance and fixed switching frequency sliding mode controller is proposed for a single-phase unipolar inverter. The chattering problem of SMC is eliminated by smoothing the control law in a narrow boundary layer, and a pulsewidth modulator produces the fixed frequency switching law for the inverter. The smoothing procedure is based on limitation of pulsewidth modulator. Although the smoothed control law limits the performance of SMC, regulation and dynamic response of the inverter output voltage are in an acceptable superior range. The performance of the proposed controller is verified by both simulation and experiments on a prototype 6-kVA inverter. The experimental results show that the total harmonic distortion of the output voltage is less than 1.1% and 1.7% at maximum linear and nonlinear load, respectively. Furthermore, the output dynamic performance of the inverter strictly conforms the standard IEC62040-3. Moreover, the measured efficiency of the inverter in the worst condition is better than 95.5%.

205 citations


Journal ArticleDOI
TL;DR: The proposed method to the sliding-mode control of single-phase uninterruptible-power-supply inverters is capable of shortening the tracking and sliding times, resulting in a smaller total harmonic distortion in the output voltage.
Abstract: A new method to the sliding-mode control of single-phase uninterruptible-power-supply inverters is introduced. The main idea behind this new method is to utilize a time-varying slope in the sliding surface function. It is shown that the sliding line with the time-varying slope can be rotated in the phase plane in such a direction that the tracking time of the output voltage is improved during load variations. The adjustment of the time-varying slope is achieved dynamically by employing a simple function which involves the error variables of the system. This function is obtained from the input/output relationship of the single-input fuzzy logic controller operating on the error variables. When a newly computed slope value is applied to the system, the position of the representative point is changed so as to achieve the desired response. The performance of the proposed control method has been tested through computer simulations and experiments using a triac-controlled resistive load and a diode bridge rectifier load. The results of the proposed method are compared with a classical sliding mode controller and a standard controller. It has been shown that the proposed method is capable of shortening the tracking and sliding times, resulting in a smaller total harmonic distortion in the output voltage.

178 citations


Proceedings ArticleDOI
01 Dec 2012
TL;DR: In this article, the authors present the most important topologies of multilevel inverters, including diode-clamped inverter (neutral-point clamped), capacitor-capped, and cascaded multi-level with separate dc sources.
Abstract: Multilevel inverters have been attracting in favor of academia as well as industry in the recent decade for high-power and medium-voltage energy control. In addition, they can synthesize switched waveforms with lower levels of harmonic distortion than an equivalently rated two-level converter. The multilevel concept is used to decrease the harmonic distortion in the output waveform without decreasing the inverter power output. This paper presents the most important topologies like diode-clamped inverter (neutral- point clamped), capacitor-clamped (flying capacitor), and cascaded multilevel with separate dc sources. This paper also presents the most relevant modulation methods developed for this family of converters: multilevel sinusoidal pulse width modulation, multilevel selective harmonic elimination, and space-vector modulation. Authors strongly believe that this survey article will be very much useful to the researchers for finding out the relevant references in the field of topologies and modulation strategies of multilevel inverter.

175 citations


Journal ArticleDOI
TL;DR: In this paper, a synchronous-frame repetitive controller for three-phase UPS inverters is presented, which minimizes the repetitive control time delay to one-sixth of the fundamental period such that the dynamic response is significantly improved.
Abstract: This paper presents a novel synchronous-frame repetitive controller for three-phase UPS inverters. Distinguished from conventional repetitive control techniques, the proposed synchronous-frame approach minimizes the repetitive control time delay to one-sixth of the fundamental period such that the dynamic response is significantly improved. In order to overcome the harmonic distortions under severe load conditions (e.g., unbalanced and nonlinear), in this paper, three synchronous rotating frames are deliberately selected, in each of which the repetitive controller is incorporated. Resultantly, the (6n ±1)th harmonics as well as the triplen harmonics are compensated. Moreover, a high-performance fourth-order linear phase infinite-impulse-response filter is applied to further enhance the accuracy of steady-state tracking. The proposed controller is programmed on the 16-bit fixed-point digital signal processor (TI TMS320LF2407) and eliminates high-resolution current sensors for cost effectiveness. Simulations and experimental tests have been carried out based on an 18-kW three-phase UPS system. Low total harmonic distortion (<;0025;) has been achieved under heavily distorted nonlinear load and unbalanced load. Fast dynamic response has been demonstrated during step load transients.

Journal ArticleDOI
TL;DR: Using the genetic algorithm, a total harmonic distortion minimization process is directly applied to the line-to-line voltage of the inverter, indicating superiority of this approach over the commonly used phase-voltage THD minimization approach.
Abstract: In this paper, total harmonic distortion (THD) minimization of the output voltage of multilevel inverters is discussed. An efficient approach in reducing the harmonic contents of the inverter's output voltage is THD minimization. In multilevel inverters with a fundamental frequency switching strategy (each switch turning on and off once per output cycle), the switching angles can be selected so that the output THD is minimized (such as the so-called optimal-minimization-of-THD strategy). To obtain the optimum switching angles, an optimization algorithm is applied to the output-voltage THD. In three-phase multilevel inverters, the optimization algorithm is commonly applied to the phase voltage of the inverter. This results in the minimum THD in phase voltage but not necessarily in the line-to-line minimum THD, whereas in three-phase applications, the line-voltage harmonics are of the main concern from the load point of view. In this paper, using the genetic algorithm, a THD minimization process is directly applied to the line-to-line voltage of the inverter. This paper is based on a seven-level inverter. To verify the simulation results, a seven-level-cascaded-H-bridge-inverter-based hardware prototype, including an ATMEGA32 AVR microcontroller, has been implemented. Both simulation and experimental results indicate superiority of this approach over the commonly used phase-voltage THD minimization approach.

Journal ArticleDOI
TL;DR: Experimental results are shown to demonstrate that the proposed control method can generate good tracking of the output-current references, achieve unity input displacement power factor, and reduce the input-current distortion caused by the input filter resonance.
Abstract: A predictive control scheme for the indirect matrix converter including a method to mitigate the resonance effect of the input filter is presented. A discrete-time model of the converter, the input filter, and the load is used to predict the behavior of the instantaneous input reactive power and the output currents for each valid switching state. The control scheme selects the state that minimizes the value of a cost function in order to generate input currents with unity power factor and output currents with a low error with respect to a reference. The active damping method is based on a virtual harmonic resistor which damps the filter resonance. This paper shows experimental results to demonstrate that the proposed control method can generate good tracking of the output-current references, achieve unity input displacement power factor, and reduce the input-current distortion caused by the input filter resonance.

Journal ArticleDOI
TL;DR: In this paper, an improved software PLL is designed, which is capable of accurately and rapidly tracking the frequency and phase angle of the fundamental grid voltage under distorted grid conditions, and a proportional integral plus resonant (PI-R) current controller in the synchronously rotating reference frame is employed to simultaneously regulate the fundamental and harmonic components of rotor currents without any sequential component decomposition.
Abstract: This paper presents enhanced control strategies for doubly fed induction generator (DFIG)-based wind power generation systems under distorted grid voltage conditions. The mathematical model of DFIG, in view of the fifth- and seventh-order components of grid voltage harmonics, is proposed and analyzed in detail. Based on the analytical model, further studies are conducted on the distortions of stator/rotor currents and the oscillations in the stator active/reactive powers as well as the electromagnetic torque, where the impact of DFIG's load conditions is considered. Meanwhile, alternative rotor current references are calculated to enhance the uninterruptable operation capability of the wind-turbine-driven DFIG systems under distorted grid conditions. An improved software PLL is designed, which is capable of accurately and rapidly tracking the frequency and phase angle of the fundamental grid voltage under distorted grid conditions. A proportional integral plus resonant (PI-R) current controller in the synchronously rotating (dq) reference frame is employed to simultaneously regulate the fundamental and harmonic components of rotor currents without any sequential component decomposition. Experiment results on a 3-kW DFIG prototype demonstrate the correctness of the analytical results and the effectiveness of the software PLL and PI-R current controller when the grid voltage is distorted.

Patent
16 Aug 2012
TL;DR: In this article, an adaptive joint linear and non-linear digital filter that can adaptively estimate and reconstruct cascaded effects of self-jamming distortions introduced by nonlinearities in the transmit and/or receive chains is proposed.
Abstract: Certain aspects of the present disclosure propose an adaptive joint linear and non-linear digital filter that can adaptively estimate and reconstruct cascaded effects of linear and non-linear self-jamming distortions introduced by non-linearities in the transmit and/or receive chains. The proposed digital filter may be used to cancel second-order inter-modulation distortion (IM2) generated in the receive chain and/or harmonic distortion generated in the transmit chain, as well as other distortions introduced by the transmit/and or receive chains.

Journal ArticleDOI
TL;DR: This paper proposes and investigates alternative switching sequences, which use the pivot vector only once but employ one of the other two vectors twice within the subcycle of a continuous pulsewidth-modulation scheme.
Abstract: A three-level inverter produces six active vectors, each of normalized magnitudes 1, 0.866, and 0.5, besides a zero vector. The vectors of relative length 0.5 are termed pivot vectors. The three nearest voltage vectors are usually used to synthesize the reference vector. In most continuous pulsewidth-modulation (PWM) schemes, the switching sequence begins from a pivot vector and ends with the same pivot vector. Thus, the pivot vector is applied twice in a subcycle or half-carrier cycle. This paper proposes and investigates alternative switching sequences, which use the pivot vector only once but employ one of the other two vectors twice within the subcycle. The total harmonic distortion (THD) in the fundamental line current pertaining to these novel sequences is studied theoretically as well as experimentally over the whole range of modulation. Compared with centered space vector PWM, two of the proposed sequences lead to reduced THD at high modulation indices at a given average switching frequency.

Journal ArticleDOI
14 Aug 2012
TL;DR: In this paper, the authors proposed a bottom-up, probabilistic harmonic assessment technique for residential feeders, which is performed by determining the switching-on probability of a residential load based on the load research results.
Abstract: The proliferation of power-electronic-based residential loads has resulted in significant harmonic distortion in the voltages and currents of residential distribution systems. There is an urgent need for techniques that can determine the collective harmonic impact of these modern residential loads. These techniques can be used, for example, to predict the harmonic effects of mass adoption of compact fluorescent lights. In response to the need, this paper proposes a bottom-up, probabilistic harmonic assessment technique for residential feeders. The method models the random harmonic injections of residential loads by simulating their random operating states. This is performed by determining the switching-on probability of a residential load based on the load research results. The result is a randomly varying harmonic equivalent circuit representing a residential house. By combining multiple residential houses supplied with a service transformer, a probabilistic model for service transformers is also derived. Measurement results have confirmed the validity of the proposed technique. The proposed model is ideally suited for studying the consequences of consumer behavior or regulatory policy changes.

Journal ArticleDOI
TL;DR: An application of FORTRAN feasible sequential quadratic programming is presented to find the optimal sizing of parameters of C-type passive filters for minimizing the total voltage harmonic distortion of nonlinear loads, where maintaining a given power factor at a specified range is desired.
Abstract: In its broadest sense, passive filters have been a very potent technique for power system harmonic suppression because of their possible different frequency response characteristics that can achieve a certain required harmonic filtering target, also due to their simplicity and economical cost. This paper presents an application of FORTRAN feasible sequential quadratic programming to find the optimal sizing of parameters of C-type passive filters for minimizing the total voltage harmonic distortion of nonlinear loads, where maintaining a given power factor at a specified range is desired. The optimal design of the C-type passive filter as an alternative to the conventional passive filtering techniques is introduced, and a detailed comparison of the results between an uncompensated system and a C-type filter are discussed by means of different numerical examples, considering source and load nonlinearities, while taking into account compliance with the IEEE standards 519-1992 and 18-2002.

Journal ArticleDOI
TL;DR: In this article, an adaptive control strategy was proposed to improve the behavior of both, the conventional SRF-PLL and the conventional PR controller, when they are used in a polluted grid with a time varying frequency.
Abstract: The proportional + resonant (PR) controller has been proposed in the past as a suitable method to control the current generated by the grid-connected photovoltaic voltage source inverters. Due to the fact that information regarding the frequency of the grid is needed to use this control technique, the synchronous reference frame phase-locked loop (SRF-PLL) is commonly used. To assure that the total harmonic distortion of the injected current (THDi) meets the appropriate standards, even if the grid voltage is polluted and its frequency varies, an adaptive control strategy is presented in this paper. This control strategy can improve the behavior of both, the conventional SRF-PLL and the conventional PR controller, when they are used in a polluted grid with a time varying frequency. The experimental results obtained by means of a digitally controlled 10-kVA inverter, show up that the THDi of the injected current is improved when the proposed adaptive control strategy replaces the conventional one.

Journal ArticleDOI
TL;DR: The proposed method is capable of estimating the accurate values of frequency, amplitude, and phase angle of the distorted current or voltage signals for a wide range of sampling frequency and measurement noise.
Abstract: Harmonic, which is becoming more and more important day by day in the emerging power system, is one of the most critical power quality parameters. In this paper, the estimation of signal parameters via rotational invariance technique (ESPRIT)-based method is proposed with an accurate model order (the number of frequency components) estimate for power system harmonic and interharmonics detection. It is demonstrated that, even for high noise signal, the proposed algorithm is able to accurately estimate the number of frequency components present in the signal. The proposed method is capable of estimating the accurate values of frequency, amplitude, and phase angle of the distorted current or voltage signals for a wide range of sampling frequency and measurement noise. The robustness of the proposed method has been tested on several simulated synthetic signals and measured experimental signals for different nonlinear loads.

Journal ArticleDOI
Xuxuan Chen1, Baichao Chen1, Cuihua Tian1, Jiaxin Yuan1, Yaozhong Liu1 
TL;DR: The structure and the mathematical model of a two-stage saturable MCR (TSMCR) are proposed and it is shown that the maximum current harmonics of the novel MCR can be limited to 3.61% of the rated output current.
Abstract: Magnetically controlled reactors (MCRs) are usually used as three-phase shunt reactors. They have low harmonic distortion independent of the third harmonic current because most three-phase MCRs are delta connected. However, as arc suppression coils, MCRs are operated in the single-phase mode, and the harmonics can be much higher than those of three-phase MCRs. In this paper, the structure and the mathematical model of a two-stage saturable MCR (TSMCR) are proposed. There are two stages with different lengths and areas in the iron cores. The stages saturate at different times when the TSMCR outputs reactive current. The current harmonics of the first saturated stage can be compensated for when the second stage begins to saturate, to reduce the total harmonics of the output current. The mathematical model that reveals the distribution characteristics of the current harmonics for the TSMCR is also presented. A study of the mathematical model indicates that there are two key factors that affect the total current harmonics of the TSMCR. One is the parameter k, which represents the area ratio of the second stage to the first stage. The other one is the parameter m, which represents the ratio of the length of the first stage to the total length of the magnetic valve in the iron core. The simulations and experiments show that the maximum current harmonics of the novel MCR can be limited to 3.61% of the rated output current when k and m are chosen according to the theoretical mathematical model.

Journal ArticleDOI
TL;DR: The proposed dc link APF, which is composed of two series-connected bidirectional boost converters, intends to eliminate the input current harmonics and exhibits better total harmonic distortion of the ac line current when compared with the traditional ac side shunt APF.
Abstract: In this paper, a dc link active power filter (APF) for three-phase diode rectifier is proposed. The proposed dc link APF, which is composed of two series-connected bidirectional boost converters, intends to eliminate the input current harmonics. It is paralleled at the dc link of the diode rectifier and is coupled to the ac input with three line-frequency switches. Compared with the full power processed power factor correction (PFC) solution, the dc link APF is partially power processed in that it only compensates for the harmonic current component at the dc link. Thus, it features with lower power processing. Moreover, it exhibits better total harmonic distortion of the ac line current when compared with the traditional ac side shunt APF. Voltage and current loop models are developed for average current control, and the selection of the current loop bandwidth is presented. Switching stresses of the ac APF, the dc link APF, and the six-switch PFC are also calculated and analyzed. Experimental and simulation results demonstrate the effectiveness of this dc link APF.

Journal ArticleDOI
TL;DR: Simulation results and mathematical analysis have achieved a reduced total harmonic distortion, increased power factor, inject maximum power of renewable energy resources via a multilevel converter as an interface to the AC grid.
Abstract: This paper presents a multiobjective control scheme based on the dynamic model of three-level, neutral-point-clamped voltage source inverter for integration of distributed generation (DG) resources based on renewable energy resources to the distribution grid. The proposed model has been derived from the abc/αβ and αβ/dq transformation of the AC system variables. The proposed control technique generates the compensation current references and by setting appropriate references of DG control loop, the DG link not only provides active and reactive currents in fundamental frequency, but also it can supply nonlinear load harmonic currents with a fast dynamic response. Simulation results and mathematical analysis have achieved a reduced total harmonic distortion, increased power factor, inject maximum power of renewable energy resources via a multilevel converter as an interface to the AC grid. It also compensated the active and reactive powers of linear and nonlinear loads. The analyses and simulation results show the high performance of proposed control scheme in the integration of renewable energy resources to the AC grid.

Journal ArticleDOI
TL;DR: In this article, a switching strategy based on minimisation of total harmonic distortion (MTHD) has been proposed to regulate this value on a predefined value, thus, desired value is employed for optimising THD value.
Abstract: Recently, a switching strategy based on minimisation of total harmonic distortion (MTHD) has been proposed. Normally, in multilevel flexible AC transmission systems, DC voltages of capacitors are changed. It is proposed to regulate this value on a predefined value. Thus, desired value is employed for optimising THD value. Results show effectiveness of the proposed method in minimising THD, when it is compared with the case of a multilevel inverter with constant DC sources. Genetic algorithm as a powerful tool is used to minimise THD as well as satisfy fundamental component. To verify theory and simulation results, a seven-level cascaded inverter-based hardware prototype is built.

Journal ArticleDOI
TL;DR: In this article, a new inverter topology based on mixture of cascaded basic units and one H-bridge unit is presented, where the basic unit includes one Z source, one DC voltage source and two switches generating two voltage levels.
Abstract: This study presents a new inverter topology based on mixture of cascaded basic units and one H-bridge unit. The basic unit includes one Z source, one DC voltage source and two switches generating two voltage levels. The cascaded basic units produce positive and zero-voltage levels and in the same time suggested inverter obtains positive, zero- and negative voltage levels, as a result the number of power semiconductor switches is reduced with respect to traditional multilevel inverters. In this topology, output voltage amplitude is not limited to DC sources voltage summation similar to traditional cascaded multilevel inverters and can be boosted with Z network shoot-through state control; therefore other DC/DC converters are not needed and it is more reliable against short circuit. Besides as compared with traditional Z -source inverter, total harmonic distortion of injected voltage is decreased in the suggested inverter topology. The performance of proposed topology and its controller are validated with simulation results using MATLAB/SIMULINK software and the validity of the proposed multilevel inverter-based Z source is verified by experimental results.

Journal ArticleDOI
TL;DR: In this article, it is shown how MPDTC can be adapted to the five-level active neutral-point-clamped converter topology, which offers low harmonic distortion and a high output voltage.
Abstract: The five-level active neutral-point-clamped converter is a recently introduced topology that offers low harmonic distortion and a high output voltage. In addition to a neutral point potential in the dc link, this topology features, in each phase, a flying phase capacitor. Balancing these four internal converter voltages around their references while providing fast torque and/or current control for the machine is an intrinsically challenging control problem. Model predictive direct torque control (DTC) (MPDTC) is an ideal control methodology to address this problem. It is shown, in this paper, how MPDTC, originally developed for three-level inverters, can be adapted to this new five-level topology. Compared to DTC, the performance results of MPDTC are very promising-for the same switching frequency, the harmonic distortions of the stator currents and the torque can be more than halved. At the same time, the very fast torque response of DTC is maintained.

Journal ArticleDOI
TL;DR: This work proposes applying ring oscillator integrators (ROIs) in the design of high order analog filters to achieve infinite DC gain at low supply voltages independent of transistor non-idealities and imperfections such as finite output impedance.
Abstract: Integrators are key building blocks in many analog signal processing circuits and systems. The DC gain of conventional opamp-RC or Gm- C integrators is severely limited by the gain of operational transconductance amplifier (OTA) used to implement them. Process scaling reduces transistor output resistance, which further exacerbates this issue. We propose applying ring oscillator integrators (ROIs) in the design of high order analog filters. ROIs implemented with simple CMOS inverters achieve infinite DC gain at low supply voltages independent of transistor non-idealities and imperfections such as finite output impedance. Consequently, ROIs scale more effectively into newer processes. A prototype fourth order filter designed using the ROIs was fabricated in 90 nm CMOS and occupies an area of 0.29 mm2. Operating with a 0.55 V supply, the filter consumes 2.9 mW power and achieves bandwidth of 7 MHz, SNR of 61.4 dB, SFDR of 67.6 dB and THD of 60.1 dB. The measured IM3 obtained by feeding two tones at 1 MHz and 2 MHz is 63.4 dB.

Journal ArticleDOI
TL;DR: The proposed multiresolution control strategy for a digital signal processor (DSP)-controlled 400 Hz active power filter achieves the total harmonic distortion as low as 5.7%, which meets the avionic DO-160F standard, and also exhibits good dynamic performance.
Abstract: A multiresolution control strategy is proposed for a digital signal processor (DSP)-controlled 400 Hz active power filter (APF) to reduce the real-time computational requirements. By rearranging the computational elements into high- and low-frequency control groups, the proposed control strategy takes best advantages of the DSP computation resources to increase the control frequency for the high computational group, which mainly determines the APF performance. Based on bandwidth features of different control plants in APF, detailed analysis is given to determine the control and sampling frequencies for these plants. Anti-aliasing filters are designed to avoid aliasing when downsampling scheme is used to further reduce computation resource. A 20 kVA prototype is set up to verify the validity of the proposed strategy and analysis. Experimental results show that the proposed control strategy meets the computational requirements for the control system using a DSP. The proposed control strategy achieves the total harmonic distortion as low as 5.7%, which meets the avionic DO-160F standard, and also exhibits good dynamic performance.

Journal ArticleDOI
TL;DR: In this article, a smooth transition control strategy for voltage-source inverters between standalone (SA) and grid-connected (GC) modes of operation is proposed, where the amount of power exchanged with the utility grid is controlled by regulating the phase currents.
Abstract: This paper proposes a smooth transition control strategy for voltage-source inverters between standalone (SA) and grid-connected (GC) modes of operation. In the GC mode, the amount of power exchanged with the utility grid is controlled by regulating the phase currents. In the SA mode, the load voltage is regulated by the inverter with its phase dictated by the inverter control. The transition between SA and GC operations that will ensure continuous power delivery to the load requires continuation in the phase of the system voltage. The proportional-integral, trapezoidal, sinusoidal, and staircase frequency variation techniques have been analyzed to find the best approach for minimizing the total harmonic distortion (THD). A smooth frequency variation technique has been developed, which provides lower THD on the voltage waveforms compared with the other techniques. The new algorithm has been implemented on a 5-kW single-phase utility interactive inverter having the SA operation capability. The simulation and experimental results show that the proposed technique provides seamless transition between the inverter modes of operation with minimal distortion at the inverter output voltage.

Journal ArticleDOI
TL;DR: A new control method based on differential flatness control technique is presented, with the possibility to define the behavior of the state variable system in the steady state as well as in transients, and high dynamic properties of the system are obtained.
Abstract: Recently, hybrid electrical power sources composed of storage elements and renewable energy sources are known to have made great development. These energy sources are connected to a dc bus and need a dc-to-ac converter to transfer the produced energy to the grid. Three-leg voltage source inverters equipped with an output LC filter are often used. The main objective of this stage is to generate a three-phase sinusoidal voltage with defined amplitude and to ensure the smallest harmonic distortion rate of the output voltage for any load conditions. To satisfy the defined objectives, we present in this paper a new control method based on differential flatness control technique. The main interest of this control method is the possibility to define the behavior of the state variable system in the steady state as well as in transients. The use of only one control loop allows obtaining high dynamic properties of the system which ensure small harmonic distortion rate of the output voltage. Experimental results under balanced, unbalanced, and nonlinear load conditions are presented and validate the effectiveness of the proposed control methods.