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This paper introduces a new adaptive notch filtering approach to extract the harmonic and reactive current components for power quality purposes in grid-connected converters. The main function of this method is to provide synchronized harmonic and reactive current components for control purposes. The theoretical analysis is presented, and the performance of the method is experimentally evaluated. The methodology is applicable for a wide range of equipment such as uninterrupted power supplies, regenerative converters, active power filters, etc., as a basis for generating the reference signals. Index Terms--Active power filters, adaptive filters, harmonics and reactive power compensation.

This paper introduces an approach for the real-time extraction of the frequency, phase angle, and symmetrical components of the grid signal, which is of great importance for many applications in power systems such as power quality and protection. The proposed method is based on the concept of the adaptive notch filter that provides a fast and accurate estimation of the symmetrical components in the presence of frequency and amplitude variations. In addition, the system offers a high degree of immunity and insensitivity to power system disturbances, harmonics, and other types of pollutions that exist in the grid signal. The simplicity of the structure makes the method suitable for both software and hardware implementations. Moreover, this very simple and very powerful tool can be used as a synchronization technique, which further simplifies the control issues currently challenging the integration of distributed energy technologies into the electricity grid. Mathematical derivations are presented to describe the principles of operation, and experimental results confirm the validity of the analytical work. Index Terms--Adaptive filters, distributed generation (DG) systems, grid-connected converters, grid-synchronization techniques, renewable energy.

A simple and effective space vector pulsewidth-modulation technique for six-phase voltage-source-inverter-fed split-phase induction motors is presented in this paper. The approach employs dual three-phase space vector modulators equipped with overmodulation schemes that compensate for the voltage gain reduction due to the use of two independently controlled three-phase inverters. It secures full control of the voltage gain up to the maximum achievable gain with negligible low-order harmonics and utilizes a simple classification algorithm for the implementation of the space vector modulation (SVM) in both linear and overmodulation modes. Experimental results are provided to verify the validity of the proposed SVM split-phase approach. Index Terms--Multiphase induction machines, pulsewidth-modulation (PWM) techniques, six-phase drives, voltage-source inverters.

This paper presents a simple voltage balancing scheme for m-level diode-clamped multilevel converters (DCMC). This paper first introduces a novel and simple current flow model for general m-level DCMCs. The superiority of the proposed model is its independence from the modulation scheme and its simplicity. It also provides a new perspective for voltage sharing accessibility among the dc link capacitors. The proposed current flow model, a cost function, and a space vector modulation (SVM) switching strategy are then used to balance the capacitors' voltages of the DCMCs in a very simple and optimized manner. Such a voltage balancing scheme was not developed for converters of five levels or greater due to the complexity of the converter and its modeling approaches. To validate the feasibility of the proposed voltage balancing scheme, this paper presents analytical and simulation results obtained from a five-level DCMC. In particular, this paper introduces a stability region within which the voltage balancing strategy converges. The impact of the cost function on the stability margins and converter performance is examined and discussed by means of comparison with different cost functions, and it is shown that the proposed cost function will improve the stability margins. The performance of the strategy for unbalanced and polluted loads shows that, unexpectedly, in some specific cases output current harmonics will improve the stability margin. Index Terms--Diode-clamped, modeling space vector modulation (SVM), multilevel converter, voltage balancing.

This letter introduces a new adaptive notch filtering (ANF) approach as a powerful tool for synchronization of converter-interfaced distributed generation systems that can potentially stimulate much interest in the field and provide improvement solutions for both grid-connected and stand-alone (islanding operation) modes of micro-grids. The proposed technique is simple and offers a high degree of immunity and insensitivity to power system disturbances, harmonics and other types of pollution that exist in the grid signal. A modified structure of the ANF-based synchronization technique is capable of decomposing three-phase quantities into symmetrical components, extracting harmonics, tracking the frequency variations, and providing means for voltage regulation and reactive power control. A prominent advantage of the proposed scheme is that it does not require a phase-locked loop for the synchronization. In addition, this very simple and very powerful power signal processor will simplify the control issues currently challenging the integration of distributed energy technologies onto the electricity grid. All converter-interfaced equipment, such as flexible ac transmission systems, custom power controllers, and active power filters, will benefit from this technique. Theoretical analysis is presented and the performance of the method is evaluated through simulation. Index Terms--Adaptive filters, distributed power generation, grid-connected converters, grid synchronization.

Pulsewidth-modulated (PWM) techniques equip power converters with unique features such as input-output linearity and control flexibility. Nevertheless, frequent switching of semiconductor switching devices causes considerable switching loss, and therefore makes traditional two-level PWM converters inappropriate for high-power applications. Two alternatives for building modular structures, namely multipulse and multimodule PWM converters were introduced to provide not only voltage and current sharing among the semiconductor switching devices, but also a high-quality output voltage at a much lower switching frequency. While multipulse converters offer minimal switching losses, low-order harmonic neutralization, and the best utilization of the inverter, multimodule PWM converters give control flexibility and power structure simplicity. This paper combines these two, and preserves the advantages of both multipulse and multimodule PWM converters. This not only provides an additional degree of freedom for voltage control, but also enables the converter to operate in PWM mode during transient and in single-pulse mode during the steady state. For the PWM switching mode, a special space vector strategy of 3 p.u. switching frequency is presented to maximize the voltage utilization and maintain a linear transfer characteristic. The power structure and control methods are analyzed, and validated by simulation and experimentally. Index Terms--Flexible AC transmission systems (FACTS), grid-connected converters, modulation techniques, multipulse converters, space-vector modulation (SVM).

This paper presents the application of a space vector modulation (SVM) strategy for a multimodule converter system that 1) enables low switching frequency, 2) eliminates/minimizes ac-side voltage harmonics, particularly low-order harmonics, and 3) provides maximum ac-side fundamental voltage component. The SVM strategy is based on a sequential sampling technique. The SVM provides harmonic cancellation/minimization by introducing appropriate phase shift for the corresponding voltage harmonics of the converter modules, while maintaining the fundamental voltage components of modules in-phase to obtain maximum ac-side voltage. The SVM eliminates the need for complicated transformer arrangement for harmonic reduction, and thus provides high degree of modularity by utilization of identical transformers for converter modules. The proposed SVM strategy is developed for a back-to-back HVDC converter station in which each converter system is composed of four identical modules. Based on a dynamic model of the system, converter controls are designed and performance of the SVM strategy in terms of converter harmonics and dynamic performance are presented. The studies are performed in time-domain, using the PSCAD/EMTDC software tool. Index Terms--Dynamic model, harmonics, HVDC, multimodule converter, space vector modulation (SVM).

Three-level neutral point clamped (NPC) voltage source converters have recently emerged as important alternatives to conventional two-level converter topologies in high-power medium-voltage energy conversion applications, particularly in high performance ac motor drive systems. An all-inclusive modulation strategy for NPC converters should have the capability of extending the operating range of the converter into the overmodulation region with a smooth and linear transition characteristic. An overmodulation switching strategy based on the space vector classification technique for three-level NPC converters is introduced in this paper. The proposed overmodulation modes, make possible continuous control of the output voltage up to the maximum possible with a smooth linear transition characteristic, and minimum distortions. A theoretical basis for the vector classification space vector modulation technique in the overmodulation region is presented, and the proposed overmodulation schemes are validated by analysis, simulation and experimentation on a 2-KVA three-level NPC converter laboratory prototype. Index Terms--Classification Algorithm, overmodulation, space vector modulation (SVM), three-level converter.

An adaptive notch filter (ANF) is presented to achieve noise reduction and signal decomposition. It verifies the validity of the presented algorithm and confirms its desirable transient and steady-state performances as well as its desirable noise characteristics.

Force-commutated multiconverter systems have been proposed and recently implemented for high power applications, particularly high-voltage direct current (HVDC) transmission and flexible ac transmission systems (FACTS) devices, including STAtic var COMpensators (STATCOM). This paper demonstrates that pulse-width modulation (PWM) based on space vector modulation (SVM), and using low switching frequencies (a few hundred Hertz) can be implemented in multimodule power converter systems. The proposed scheme is based on a delayed sampling technique and allows output voltage control and minimization of harmonic components. Pattern generation options are analyzed and system waveforms are presented for different switching frequencies and number of modules. Results are validated by simulation and confirmed by experiments on a 5-kVA prototype unit. Index Terms--Delayed sampling technique, multimodule converters, space vector modulation (SVM).

This paper provides an adaptive filter for synchronous detection and extraction of harmonics. The filter can he used as integral part of the control system of a power electronic apparatus (e.g., STATCOM, APF, and UPFC) to generate the desired control signals. Stability and convergence analyses of the adaptive filter are presented based on dynamical systems theory. Performance of the filter is verified as a means for reference signal generation in a shunt active power filter. Index Terms--Active power filter, adaptive filter, averaging theorem, synchronous harmonic detection.