This study presents a new control strategy for three-level neutral point-clamped pulse-width modulated (PWM) rectifier. The relationship between instantaneous power and voltage vectors is derived mathematically from the model of three-phase three-level voltage source PWM rectifier, and a direct power control (DPC) scheme for three-level PWM rectifier is presented. An optimal switching table is established, from which appropriate voltage vectors can be selected to control active and reactive power directly. Principle for vector switching to avoid excessive ΔV in phase and line-to-line voltages and balance strategy for the neutral point potential are also discussed. A digital-signal-processor-based experimental system is developed to implement a series of experiments. The obtained results have verified the theoretical approach, and the three-level PWM rectifier with proposed DPC exhibits advantages of simple algorithm and good dynamic performance, compared with conventional voltage-oriented control.

TABLE-BASED direct power control for three-level neutral point-clamped pulse-width modulated rectifier

In this paper analysis results of a cooperation of the Unified Power Quality Conditioner (UPQC) with the photovoltaic system are presented. The proposed system consists of a series inverter, a shunt inverter, and some photovoltaic arrays connected in the dc link through the Multi-Input Single-Output (MISO) DC-DC converter. A numerical formulation of the proposed control schemes, which are based on the instantaneous power theory, is presented. The proposed system can improve the power quality at the Point of Common Coupling (PCC) on power distribution systems. The performance of the proposed system was analyzed using simulations with Power System Computer Aided Design/ElectroMagnetic Transients DC (PSCAD/EMTDC) analysis program.

Modeling the combination of UPQC and photovoltaic arrays with Multi-Input Single-Output DC-DC converter

This paper presents the performance evaluation and comparisons of three typical control strategies for three-level neutral point clamped (NPC) rectifier with pulse width modulation (PWM). These are voltage oriented control (VOC), direct power control (DPC) and direct power control based on space vector modulation (DPC-SVM). The theoretical background is described, and the advantages and disadvantages of each scheme are studied through analyses and a series of experiments. A comprehensive comparison and evaluation are implemented for the three methods from several aspects such as algorithm complexity, steady state and dynamic performances, current THD with unbalanced power source voltage, and startup current which is important for the high power applications. The results show that all the three schemes can provide good abilities; and VOC and DPC-SVM possess better steady state performance while DPC is provided with best dynamic performance.

Performance evaluation of three control strategies for three-level neutral point clamped PWM rectifier

With the dawn of the competitive environment, electric power system restructuring is becoming a great concern for both electric utilities and customers. In this paper, the effect of power system deregulation on the power quality problems is investigated. Identifying the high priority research areas related to electric power quality in deregulated power systems and investigating the advances made in this area over the last decade constitutes the main goal of this paper. The paper addresses the definition of deregulated environment, and the different mitigation techniques implemented to improve the system power quality. Moreover, the advances in research on using modem signal processing techniques like a wavelet transform in developing automated recognition of power system disturbances is pointed out.

https://ieeexplore.ieee.org/iel5/7665/20941/00971294.pdf

Effect of new deregulation policy on power quality monitoring and mitigation techniques

A novel direct power control (DPC) strategy for three-level neutral-point-clamped (NPC) pulse-width-modulation (PWM) rectifier, based on fixed synthesizing vectors, is proposed in this paper. The strategy breaks through the restrictions of vector switching with a simple switching table, improves the excellent dynamic performance of DPC, avoids the neutral-point voltage unbalance and the excessive voltage jumps in phase and line-to-line voltages of the rectifier, and guarantees the proper minimum pulse width and switching intervals between switches in different phases simultaneously. Experimental results verify the validity and feasibility of the proposed scheme.

http://ieeexplore.ieee.org/iel5/4753968/4770630/04770891.pdf

A novel direct power control strategy for three-level PWM rectifier based on fixed synthesizing vectors

In this paper, a general powerful circuit of a universal custom power conditioner (UCPC), which is used to improve power reliability and quality applied to distribution networks, is presented in detail. The UCPC is based on series and shunt tri-level PWM converters with a battery energy storage system (BESS) for multi-function operations such as harmonic elimination, reactive power control, voltage sags compensation and uninterruptible power supply (UPS). The basic algorithm of system is deadbeat control with a repetitive compensation strategy based on the voltage space vector PWM method. Some simulation results are use to verify that UCPC can synthetically fulfill different compensation functions.

Universal custom power conditioner (UCPC) in distribution networks

Based on the concept of switching function (SF) and space vector (SV), and cited the coordinate transformation matrix on space reference frame in the unified theory of an AC motor, a new mathematical model of the tri-level PWM reversible rectifier was presented in detail. The synchronous reference frame model was used to achieve the dq decoupling control of the converter. All control algorithms were implemented in dual digital-signal processors (DSP). The validity of the system model was verified by the results of computer-aided simulation and experiment.

Mathematical model and dual-DSP control of tri-level PWM reversible rectifier

This paper gives a short description of the state-of-art of FACTS and DFACTS study in China. Based on the experience in the development of China's first 20 MVAr STATCOM, the authors lay the stress on the performance differences between the FACTS and DFACTS inverter and that of the conventional industrial ones due to the diverse operating conditions. This gives an engineering insight into the operation of FACTS and DFACTS devices.

Study of FACTS and DFACTS in China

In this paper, a novel voltage space vector (NVSV) method used for 3-phase pulse width modulation voltage source reversible rectifier (PWM VSR) is described in detail. Based on the conventional voltage space vector (CVSV) method and its geometry topology, the actual switching time has a very simple form. With the /spl alpha//spl beta/-coordinate transformation, the NVSV can be easily realized. Its effect is exactly the same as the CVSV method. Thus, the NVSV method can be simply implemented by using a common microprocessor. It has the attractive features such as short execution time and little memory size compared with the method. Furthermore, every phase of the converter can have its switching stopped for 120/spl deg/ in one period, so the switching loss of the power device can be minimized by about 33%. The proposed method is implemented by an 80c196KC and its performance has been proved by a 15 kW IGBT laboratory prototype.

The 3 phase PWM voltage source reversible rectifier based on a novel space vector control method

This paper establishes a mathematical model of three-phase four-wire center-split single-turned hybrid active power filters(HAPF) in d-q-0 coordinate.Based on this mathematical model,the filtering characteristics of the passive part of the single-tuned HAPF with and without neutral inductor are analyzed and discussed.According to the HAPF active part capacity analysis and the filtering characteristics of its passive part,the structure of the three-phase four-wire single-turned HAPF can be optimized and its minimum DC-link voltage expression can be deduced based on the general harmonic current contents of the loading.Therefore,the cost of the HAPF can be lowered by reducing its active part capacity.Finally,the correctness of the minimum DC-link voltage theory and the effectiveness of this optimized structure are verified by simulation.

Wong Manchung

Papers

Universal custom power conditioner (UCPC) in distribution networks

Mathematical model and dual-DSP control of tri-level PWM reversible rectifier

Study of FACTS and DFACTS in China

The 3 phase PWM voltage source reversible rectifier based on a novel space vector control method

Active Part Minimum Capacity Analysis of Three-phase Four-wire Hybrid Active Power Filters