Line Current Total Harmonic Distortion Research Articles

Single-stage sine-wave inverter for an autonomous operation of solar photovoltaic energy conversion system

This paper proposes a high performance single-stage inverter topology for the autonomous operation of a solar photovoltaic system. The proposed configuration which can boost the low voltage of photovoltaic (PV) array, can also convert the solar dc power into high quality ac power for driving autonomous loads without any filter. An MPPT circuit with parallel connection is implemented so that the part of the energy generated is processed by the dc–dc converter to supply dc loads. The line current total harmonic distortion (THD) obtained using this configuration is quite reasonable. The proposed topology has several desirable features such as low cost and compact size as number of switches used, are limited to four as against six switches used in classical two-stage inverters. In this paper analysis, simulation and experimental results are presented.

Implementation of a New Linear Control Technique Based on Experimentally Validated Small-Signal Model of Three-Phase Three-Level Boost-Type Vienna Rectifier

In this paper, the design and implementation of a new multiple-input-multiple-output linear control technique based on a theoretically established and experimentally validated small- signal model for the three-phase three-level boost-type ac/dc Vienna converter are presented. Averaging and local linearization techniques are used to derive the dynamic model expressed in the dqo reference frame. The resulted transfer functions are discretized for the sake of a digital controller design. Multiple-loop control strategy is adopted and consists of inner current feedback loops, which are based on the straightforward looping technique that neglects interactions between the dq components of control inputs and currents, respectively, and of an outer voltage loop, which is designed to ensure dc voltage regulation by adjusting the magnitude of the references for the inner current loops. The output dc voltage unbalance is also controlled in the inner loops. The proposed modeling and control approaches are first simulated and then validated on a 1.5-kW laboratory prototype supported by the DS 1104 digital real-time controller board of dSPACE. The obtained results prove the accuracy of the proposed new small-signal model and, therefore, its reliability for dynamic analysis and control design purposes. It is also proved that a judicious choice of controller parameters, as well as an adequate rating of boost inductors, allows one to meet the IEEE standard requirements in terms of ac line-current total harmonic distortion and power factor. The efficiency of the proposed control technique is maintained in case of disturbances occurring on both source and load sides.

Space Vector Sequence Investigation and Synchronization Methods for Active Front-End Rectifiers in High-Power Current-Source Drives

Space vector pulsewidth modulation (PWM) schemes for the active front end of a high-power drive normally produce low-order and suborder harmonics due to the low switching frequency and the drifting of synchronization between the PWM waveform and the rectifier input frequency. To provide a synchronized PWM and achieve the best harmonic performance, different space vector sequences suitable for a current-source converter are investigated in this paper. Details on how to achieve the waveform symmetries with a minimum switching frequency for each sequence are discussed. A thorough comparison of the harmonic performance of different space vector sequences is carried out. An optimum space vector modulation method by switching between two best sequences is proposed to achieve the best line-current total harmonic distortion with reduced switching losses. In addition, two synchronization methods, namely a PWM frame regulation method and a direct digital phase-locked loop synchronization method, are proposed. Both methods are equally effective in providing tight synchronization of the PWM waveform with the rectifier input frequency. The work has been verified in simulation and experiment.

A Modified Valley Fill Electronic Ballast Having a Current Source Resonant Inverter With Improved Line-Current Total Harmonic Distortion (THD), High Power Factor, and Low Lamp Crest Factor

In this paper, a modified valley fill (VF) circuit is employed to combine with a current-fed resonant inverter as a passive high power factor (PF) electronic ballast. A conventional VF circuit limits the line current to conduct when the conduction angles are: 30deg les omegat les 150deg and 210deg les omegat les 330deg during the line period, which results in high total harmonic distortion (THD). The modified VF circuit has the following advantage: When the capacitors are connected in parallel, the voltage across the capacitors is one-third of the peak voltage, which allows the conduction angle of the line current to be further extended to 19.5deg les omegat les 160.5deg and 199.5deg les omegat les 340.5deg, so that a lower THD can be achieved. The high lamp crest factor (CF) problem generated by the high ripple voltage from the modified VF circuit is improved in the proposed ballast as variable frequency control is employed to continuously regulate the lamp current. An experimental prototype is then built in the laboratory to verify the feasibility of the proposed work for a 26-W compact fluorescent lamp. The final results confirm that a PF of 0.986 and a lamp CF of 1.49 are achieved with the proposed circuit, whereas a PF of 0.96 is achieved with the conventional VF ballast.

A Passive 36-Pulse AC–DC Converter With Inherent Load Balancing Using Combined Harmonic Voltage And Current Injection

A combination of two, simple, passive injection circuits is used to eliminate virtually all the low-order harmonics from the line currents of a standard 12-pulse rectifier, transforming its performance into that of a 36-pulse system. A line current total harmonic distortion of 1.51% is achieved in a 15-kW, 400-Hz prototype. The basic 12-pulse rectifier comprises two 6-pulse bridges that are series connected on both the ac and dc sides along with a 50%-rated, delta-star, phase-shifting transformer, while each injection circuit principally consists of a small transformer that operates at six times the supply frequency and carries around 1% of the total power throughput. The injection techniques are also valid for a fully isolated transformer arrangement. Full details of the circuit operation and design are reported

Active Damping Control of a High-Power PWM Current-Source Rectifier for Line-Current THD Reduction

The use of active damping to reduce the total harmonic distortion (THD) of the line current for medium-voltage (2.3-7.2 kV) high-power pulsewidth-modulation (PWM) current-source rectifiers is investigated. The rectifier requires an LC filter connected at its input terminals, which constitutes an LC resonant mode. The lightly damped LC filter is prone to series and parallel resonances when tuned to a system harmonic either from the utility or from the PWM rectifier. These issues are traditionally addressed at the design stage by properly choosing the filter resonant frequency. This approach may result in a limited performance since the LC resonant frequency is a function of the power system impedance, which usually varies with power system operating conditions. In this paper, an active damping control method is proposed for the reduction in line current THD of high-power current-source rectifiers operating at a switching frequency of only 540 Hz. Two types of LC resonances are investigated: the parallel resonance excited by harmonic currents drawn by the rectifier and the series resonance caused by harmonic pollution in the source voltage. It is demonstrated through simulation and experiments that the proposed active damping control can effectively reduce the line-current THD caused by both parallel and series resonances.

Fuzzy Logic Control of an Active Power Line Conditioner

Fuzzy logic and active power line conditioners (APLC) are two tools that are being increasingly applied to power quality problems. In this paper, a switch-mode APLC that uses fuzzy logic to control the semiconductor switches is described. Frequency-domain analysis is used to determine the desired compensation current, and a rule-based piecewise-linear fuzzy proportional-integral controller (FPIC) provides the appropriate switching pattern of the APLC to generate the actual compensation current. MATLAB simulations and experimental measurements on a low-power (700 VA), digital signal processor-based, hardware prototype show that the APLC produces excellent results despite the use of a relatively low switching frequency, which is necessary to minimize semiconductor switching losses. The simulations and measurements are in good agreement and show that the APLC/FPIC system can significantly improve line current total harmonic distortion and power factor during both steady-state and transient operating conditions.

Characteristics of fixed-frequency hybrid resonant converter operating on the utility line

A single-phase single-stage AC-to-DC controlled rectifier using a high-frequency transformer isolated hybrid parallel series resonant converter bridge, operating on the utility line, is described. A fixed-frequency phase-shift control scheme is used to achieve high line power factor with reduced line current harmonic distortion. Based on both approximate AC and state-space analysis, design curves are obtained. A design example for a 150 W converter is presented. The converter performance is evaluated with SPICE simulation (without active control) and by measurements on the 150 W broadband model. The line power factor is greater than 0.95 with harmonic distortion of 16.5% (at full load), even without active control. A simple active line current control technique has been used for waveshaping the line current waveform close to sinusoid, and to reduce the line current total harmonic distortion.

Characteristics of a fixed-frequency series-parallel resonant converter operating on the utility line with and without active control

A single-phase high-frequency transformer-isolated ac-to-dc controlled rectifier using a fixed-frequency series-parallel (or LCC-type) resonant converter (SPRC) is presented. A simple analysis and design procedure is used for designing the converter for low line-current harmonic distortion and high power-factor (PF) operation. The converter performance characteristics have been verified with SPICE simulations and an experimental prototype SPRC, without using active control. These results show that, although no active control is used, the converter operates with a line-current total harmonic distortion (THD) of 13.5% at full load and 23.6% at half load, with line PF > 0.97. Active control has also been implemented in the experimental prototype to achieve a line PF > 0.99 with a THD of < 16%, for variation in supply voltage and load (full load to half load).

High power factor operation of resonant converters on the utility line

Operation and characteristics of resonant converters on the utility line are presented. Series-parallel (LCC-type) resonant converter operating with discontinuous current mode and continuous current mode (variable frequency control as well as fixed-frequency) are considered. Design examples are presented. SPICE simulation and experimental results obtained for the designed converters (rated at 150 W) are presented to verify the theory. It is shown that high line power factor (>0.95) and line current total harmonic distortion (THD) of <25% are obtained for the LCC-type converter for a wide load range (from full load to 10% rated load) without any active control, and the switch peak current decreases with the load current. With active line current control, low distortion and zero voltage switching for the entire cycle are realized.

Operation of high-frequency resonant converters on the utility line with improved characteristics

Operation and characteristics of Class-D-type resonant converters on the utility line are presented. Two types of resonant converters (LCC- and LCL-type) operating with variable frequency control as well as variable pulse width (fixed frequency) are considered. Analysis and simple design procedures (with design examples) are given. SPICE simulation and experimental results obtained for the designed converters (rated at 250 W) are presented to verify the theory. It is shown that high-line power factor (PF) (>0.95) and line-current total harmonic distortion (THD) of <25% are obtained for the LCC-type converter (with a capacitor ratio of one) for a wide-load range (from full load to 10% rated load) without any active control, and the switch-peak current decreases with the load current. Although the LCL-type converter gives about 20% THD at full load, it increases to about 29% at lighter loads. However, the LCL-type resonant converter can operate in lagging PF mode for the entire line cycle and for a wide-load variation.