Distorted Mains Voltages Research Articles

Novel SWISS Rectifier Modulation Scheme Preventing Input Current Distortions at Sector Boundaries

This paper describes a new modulation concept for the uni- and bidirectional SWISS rectifier, which mitigates ac input current distortions at the mains voltage sector boundaries. An analytical model is derived and compared to simulations, which allows an estimation of the distortion's magnitude from design parameters, showing that these distortions increase the input current total harmonic distortion (THD) significantly. A modification of the original circuit topology is proposed, which decouples the operation of SWISS Rectifier's active third-harmonic current injection network and its dc–dc converter switches. An algorithm is presented which allows the calculation of a temporary pulse width modulation for the SWISS Rectifier's current injection network to mitigating the distortions. The concept is verified for both power flow directions and for operation with unsymmetrical and distorted mains voltages by measurement results taken on a bidirectional 7.5-kW SWISS Rectifier prototype. An ac input current THD of 1.3% results for symmetric sinusoidal mains voltages and 1.4% and 1.6% for operation with distorted and unsymmetrical mains voltages.

Two-phase Three-wire Shunt Active Power Filter Control by Using the Single-phase P-Q Theory

This paper presents a study of a shunt active power filter (APF) to be applied to two-phase three-wire electric networks. The application of this new APF is presented and possible topologies are discussed. The control algorithm of the APF is based on the single-phase p-q theory, which is briefly reviewed. Then, alternative–αβ transformations for voltages and currents are proposed to implement the single-phase p-q calculations. These adaptations are followed by the description of the proposed current reference calculation algorithm. Digital simulation and experimental results validate the effectiveness of the proposed shunt APF and control algorithm in compensating current harmonics, reactive power and imbalances of two-phase three-wire loads, even under distorted mains voltage condition.

A novel digital control strategy of three-phase shunt active power filter under non-ideal mains voltages

A novel control strategy for three-phase shunt active power filter (SAPF) was proposed to improve its performance under non-ideal mains voltages. The approach was inspired by our finding that the classic instantaneous reactive power theory based algorithm was unsatisfactory in terms of isolating positive sequence fundamental active components exactly under non-ideal mains voltages. So, a modified ip-iq reference current calculation method was presented. With usage of the new method, not only the positive sequence but also the fundamental active current components can be accurately isolated from load current. A deadbeat closed-loop control model is built in order to eliminate both delay error and tracking error between reference voltages and compensation voltages under unbalanced and distorted mains voltages. Computer simulation results show that the proposed strategy is effective with better tracking ability and lower total harmonic distortion (THD). The strategy is also applied to a 10 kV substation with a local electrolysis manganese plant injecting a large amount of harmonics into the power system, and is proved to be more practical and efficient.

DSP-based implementation of capacitor voltage balancing strategy for a three-phase three-level bidirectional rectifier

Digital signal processing (DSP)-based implementation of a modified space-vector modulation strategy for balancing the DC-bus capacitor voltages of a three-phase neutral-point clamped bidirectional converter is presented. The proposed modulation strategy is simple in nature. It first identifies the switching states responsible for the unbalancing of capacitor voltages and then, based on the knowledge of polarity of capacitor voltage difference and direction of power flow, uses the appropriate redundant switching vectors to achieve the balancing of capacitor voltages. The analysis and control of the converter is described. The proposed control algorithm is validated through experimental results obtained on a laboratory prototype of the converter. The performance of the converter is found excellent in terms of the line-side and load-side power quality. A perfect balancing of the DC-bus capacitor voltages is achieved under balanced as well as unbalanced load conditions. The performance of converter is also investigated with distorted mains voltages and found satisfactory. DSP of dSPACE has been used for real-time simulation and implementation of the proposed control algorithm.

A Control Algorithm for Compensation of Customer-Generated Harmonics and Reactive Power

This paper presents a new control algorithm for a shunt active power filter to compensate harmonics and reactive power required by nonlinear loads. If the utility voltage is distorted, active power filter (APF) allows similar level of distortion in the compensated source current. Therefore, the resultant source currents have the same waveform as that of the supply voltage, thereby attributing the responsibility of utility and customer at the point of common coupling (PCC). Due to similar shape of the source voltage and currents, reactive power is compensated completely. The proposed scheme provides an additional feature of compensation of either only harmonics, or both harmonics and reactive power simultaneously, based on the desired capacity of the APF. Various simulation results are presented with ideal and distorted mains voltage and compared with other algorithms. Proposed algorithm is implemented as a prototype to verify the simulation results.

An instantaneous active and reactive current component method for active filters

A shunt active filter based on the instantaneous active and reactive current component i/sub d/-i/sub q/ method is proposed. This new control method aims to compensate harmonics and first harmonic unbalance. To evaluate its relative performance, it is compared with the instantaneous active and reactive power p-q method under various mains voltage conditions and for different harmonic injection high-pass filters. Both methods are completely frequency-independent, however under distorted mains voltages the proposed method presents a better harmonic compensation performance. The system synthesis and implementation are performed. Simulation and experimental results are presented.

A study of three-phase active power filters under nonideal mains voltages

The performance of three-phase active power filters under nonideal voltage scenarios is investigated in this paper. It begins with the analysis of an instantaneous reactive power algorithm applied for the three-phase active power filter design, which was found to present poor performance under nonideal test scenarios. This motivates our proposed design of a new active power filter for solving such problems. In the proposed scheme, the circuit not only shows its effectiveness in the tests, but also implements with a simpler control circuit when compared with the other algorithm. The method has been implemented as a prototype and tested through various simulation cases, including ideal mains voltage, unbalanced three-phase mains voltage, and distorted mains voltage. Test results have demonstrated the feasibility and practicality of the proposed method approach for the applications.

Performance comparison of single-phase active power line conditioners for harmonic suppression and reactive power compensation

Use of an active power line conditioner is a new solution for power system harmonic and reactive power compensation. In this paper, the performance of a proposed single-phase and four typical single-phase power line conditioners is simulated and compared under arc furnace, half-wave rectifier, and full-wave rectifier loads. Their performance under a distorted mains voltage is also discussed. The simulation results show that the performance of the proposed active power line conditioner is superior to that of the conventional ones. A prototype of the proposed active power line conditioner is implemented and tested to verify its performance.

A Static Synchronous Compensator for Displacement Power Factor Correction under Distorted Mains Voltage Conditions

A STATCOM system is presented in this paper applied for compensation of displacement power factor under distorted mains voltage conditions. The developed STATCOM control system consists of two regulating loops - DC link voltage control loop with anti-windup PI controller and the current control loop with a feed-forward PI controller. The simulation results indicate that the developed control system performs well, ensuring displacement power factor compensation with good transient and steady state performance even under significantly distorted grid voltage conditions. Ill. 15, bibl. 8 (in English; abstracts in English and Lithuanian).http://dx.doi.org/10.5755/j01.eee.110.4.291