A new approach for three-phase loads compensation based on the instantaneous reactive power theory

The original instantaneous reactive power theory or p–q theory has been systematically used in the control of active power filters (APFs). When the APF is connected in parallel to a non-linear and unbalanced load, the p–q theory application has allowed a compensation strategy named constant power to be obtained. This means that, after the APF connection, the instantaneous power supplied by the source is constant and it has the same value as the average power consumed by the load. Nevertheless, the use of other compensation strategies is possible: unity power factor or sinusoidal and balanced supply currents, among others. This paper shows that any compensation strategy may be developed into the p–q theory frame. Besides, the paper presents a p–q theory reformulation without using mapping matrices, which makes easier the obtention of the compensation currents. Finally, an exhaustive analysis of practical cases has been carried out at simulation and experimental level through a laboratory prototype which has allowed the proposed approach to be verified.     

A new approach for voltage harmonic distortion minimization

The problem of harmonic reduction is alternatively approached as an energy user’s problem. The user’s objective is to eliminate his voltage harmonic distortion problem locally without considering the effects of voltage distortion at neighboring buses. The remedy is insertion of a reactor in series with the local compensating capacitor. A method is presented for finding the optimum fixed LC combination to minimize voltage harmonic distortion at a load bus while holding the power factor at a desired value and constraining the compensator values which would create resonant conditions and the manufacturer’s standard values for power shunt capacitors.     

One approach for reactive power control of capacitor banks in distribution and industrial networks

This paper presents an efficient solution for reactive power control of capacitor bank using changes in reactance of connected reactor. This solution ensures smooth control of reactive power of capacitor banks as important operational characteristic for maintaining the quality of supply. The proposed method works for a wide-range of reactive power variations in the system and is capable of injecting or absorbing reactive power when necessary. This control method can be successfully used in distribution and industrial networks where many loads vary their demand for reactive power. Other applications of this method are voltage regulation, power-factor correction and reactive power compensation. The effectiveness of the proposed method is demonstrated through the case studies in order to prove its feasibility for improvement of voltage profile and reduction of power losses.     

A new approach to frequency domain power measurement based on distortion responsibility

This paper takes us a step forward with respect to previous definitions for the measurement of electric power quantities under non-sinusoidal conditions.A new decomposition of voltage, current and power is presented in order to determine the extent to which the distribution company and the electrical energy consumer are each responsible for the harmonic distortion measured at the point of common coupling, PCC.This gives us three different quantities: fundamental frequency, frequencies associated with the distribution system distortion and frequencies associated with consumer distortion. These magnitudes can also be measured in relation to power factor compensation and harmonic elimination problems in power distribution systems.In addition to this, the power factors resulting from the new decomposition are also analyzed and the decomposition algorithm implemented on a measurement platform based on a digital signal processor, DSP.Finally, the general structure of the system, focusing on both hardware and software, is also discussed.     

网络化谐波与无功参数在线监测分析与治理仿真系统

本文设计了一种网络化谐波与无功参数在线监测与治理仿真系统,运用基12的快速傅立叶算法对谐波与无功参数进行快速准确的检测和分析,将web服务用于谐波与无功监测,实现网络化在线监测,同时,本文以某电站为例,建立了电能质量仿真模型,给出了注入式混合有源滤波器谐波抑制和无功补偿方案,并采用参数模糊自整定PI控制电流的方法进行控...     

Fuzzy logic controller for three-level shunt active filter compensating harmonics and reactive power

In this paper, the three-level inverter is used as a shunt active power filter, making use of the multilevel inverter advantages of low harmonic distortion, and reduced switching losses. This PWM inverter is employed as shunt APF compensating reactive power and suppresses harmonics drawn from a nonlinear load. Most previously reported three-phase active power filters are based on two-level inverters with conventional controllers requiring a complex and a complicated mathematical model. In order to overcome this problem a fuzzy logic controller applied and extended to a three level shunt APF is proposed.     

CVCF inverter based on nonlinear control of instantaneous active and reactive power and its operation characteristics

This paper describes a direct‐power‐controlled CVCF inverter and presents its experimentally examined operation characteristics. The most important feature of this strategy is the direct selection of the switching states of the CVCF inverter to restrict errors between the feedback and command values of active and reactive power. In addition, this paper presents a theoretical analysis of the relationship between the instantaneous power and the switching state, which is essential for deriving a switching‐state table for the controller. The feasibility of the proposed method was verified through several computer simulations and experimental tests using a 2.0‐kVA prototype setup. The output voltages were confirmed to be stable sinusoidal waveforms with a total harmonic distortion of 1.13% under nonlinear load conditions. Excellent voltage balance was achieved by the proposed strategy even under unbalanced load conditions. © 2010 Wiley Periodicals, Inc. Electr Eng Jpn, 174(3): 62–69, 2011; Published online in Wiley Online Library ( wileyonlinelibrary.com ). DOI 10.1002/eej.21023     

单片机无功补偿控制器的设计

详细介绍了单片机无功补偿控制器的硬件和软件设计。单片机的外围扩展采用SPI接口芯片,简化了电路结构,可降低成本和提高可靠性。软件设计中详细讨论了CT极性的自动识别、功率因数测量方法以及简化编程和控制算法和抗干扰措施等问题。     

Electronic reactive energy meters’ performance evaluation in environment contaminated with power quality disturbances

This paper evaluates and interprets the performance of electronic reactive energy meters that are currently used in electric power systems and operate in an environment contaminated with harmonics due to nonlinear loading and power quality disturbances that could result due to modern load operation in the context of smart grid. The operating principle of each type of meter is provided, the performance of each type is evaluated, and an interpretation relating performance in a non-distorted environment and performance in a distorted environment is given. To improve the next-generation of smart meters, a time-frequency modified version of these operating principles is developed using discrete wavelet transform which is a powerful tool in handling time-varying power quality disturbances. The wavelet-based approach is tested on simulated and real case studies under harmonics and different power quality disturbances. Results of test cases included in this study are presented, and the outcomes are analyzed.     

考虑运行方式转移过程的无功优化控制

电力系统的运行方式是一个连续转移过程。将单点的无功优化控制扩展到考虑运行方式转移过程,从而使电压控制的可操作性和效率更符合实际需求。构建了包括变压器档位在内的非线性约束条件下的无功最优化目标函数,提出了优化和潮流计算相互迭代算法,两个实例分析说明了考虑转移过程的无功优化控制具有更好的鲁棒性和效率。     

Joint bus voltage/reactive generation control in multimachine power plants: a multivariable approach

This paper presents a design procedure for a centralized regulator, armed for the joint bus voltage/reactive generation control in multimachine power plants, by using the modern multivariable systems and optimal regulator theories. The regulator is of output feedback, proportional-plus-integral type. It is based on the concept of optimal linear regulators, using a reduced number of local measurements, and acting through reference inputs of individual unit's automatic voltage regulators. The proposed control is of two-level type, with separate features that enable the common plant-bus voltage control and desired distribution of reactive generation to individual units in operation.

The paper presents the procedure for the regulator system design and gives the simulation results performed on a 17th order, two-unit hydropower plant model and considers the practical feasibility of the regulator system.     

10 kV配电线路远距离无功补偿

分析了配电线路采用并联高压电容器实现无功补偿的传统方法中,因电容器不能随负荷的变化自动投切而引起的一系列问题。针对存在的问题,提出了一种尤其适合于远距离配电线路的新型无功补偿系统。介绍了该系统的结构和功能,以应用实例说明效果良好。     

A heuristic technique to determine corrective control actions for reactive power flows

This paper presents a sensitivity-based heuristic tool designed to help the system operator in the reactive power flow control problem. The objective of the proposed technique is to determine control actions to ensure that reactive power flows in transmission-subtransmission boundary transformers remain within specified limits, satisfying the new regulatory constraints imposed in most of deregulated markets. With this new constraint the utilities want to guarantee that the utility is able to satisfy its own reactive power requirements, avoiding reactive power flows through long distances in order to reduce the well known disadvantages that reactive power circulation has in the system.A 5-bus tutorial system is used to present the proposed algorithm. The results of the application of the proposed technique to the IEEE 118 buses system and to a regional subtransmission network of the South of Spain are reported and analyzed. In this last actual case, the aim is to maintain reactive power flows in transmission/distribution transformers between those limits set by the Spanish Regulation. A comparison between the proposed tool and a conventional OPF is discussed.     

Investigation of the behavior of a three phase grid-connected photovoltaic system to control active and reactive power

In this paper, a photovoltaic (PV) system, with maximum power point tracking (MPPT), connected to a three phase grid is presented. The connection of photovoltaic system on the grid takes place in one stage using voltage source inverter (VSI). For a better utilization of the photovoltaic system, the control strategy applied is based on p-q theory. According to this strategy during sunlight the system sends active power to the grid and at the same time compensates the reactive power of the load. In case there is no sunlight (during the night for instance), the inverter only compensates the reactive power of the load. In this paper the use of p-q theory to supply the grid with active power and compensate the reactive power of the load is investigated. The advantage of this control strategy is that the photovoltaic system is operated the whole day. Furthermore, the p-q theory uses simple algebraic calculations without demanding the use of PLL to synchronize the inverter with the grid.     

电力系统无功功率控制与优化综述

电力系统无功优化是一个非线性混合优化问题,它的目标是在满足约束条件的前提下,使系统的某个指标或多个指标达到最优。本文综合分析了用于电力系统无功优化的各种优化方法,并特别地列出了一些新兴的方法,同时指出了各种方法的优势与弱点,分析了这个领域当前存在的问题。     

Instantaneous reactive power theory—A general approach to poly-phase systems

The systematic use of active power filters, APF, to compensate non-linear loads, has extended the use of the instantaneous reactive power theory. Originally, p–q theory appeared; it obtained constant instantaneous power in the source side after compensation. Later, other formulations have been developed. They have allowed different compensation objectives to be obtained. Nevertheless, all of them can only be applied to three-phase systems, i.e. those formulations frameworks cannot be used to establish versatile control strategies in multi-phase systems. This paper presents a new approach which can be applied to multi-phase power systems. Thus, a new tensorial product is introduced that allows an operative definition of the instantaneous reactive power tensor and the derived instantaneous reactive current component. According to these expressions, different compensation strategies can be defined in multi-phase systems. The powers and currents expressions derived from the formulations presented up now can be obtained applying this new approach. In this work, original p–q and modified p–q formulations expressions are derived in the new approach framework. In addition, a series of practical examples has been included to improve the understanding of the proposed formulation.     

基于模糊边界无功调节判据的电压无功综合控制

介绍电压无功综合控制的基本原理,为提高控制性能,引入了模糊边界的无功调节判据,在建立数学模型判据的基础上得出了基于模糊边界无功判据的控制策略。通过对九区细分图和模糊边界无功判据的比较,分析基于模糊边界无功判据的控制策略特点,并在实际电压无功控制系统的设计中验证。同时概述系统的基本结构、功能及实现。系统的实际运行表明,基于模糊边界无功判据的控制策略能减少分接头调节和电压波动的次数,与通常的九区图控制相比较,基于模糊边界无功判据的控制策略能提高变压器分接头使用寿命而不降低电压无功的控制效果。     

新型混合型滤波器设计

根据目前常见的几种混合有源滤波器,提出一种注入式混合有源滤波器,使有源滤波器不再承受基波电压,最大限度地减少了有源滤波器的容量。阐述混合有源滤波器和注入式有源滤波器的工作原理,通过样机实验验证结论正确性。     

采用改进下垂控制和双层无功优化的风电场无功均衡分配研究

计及风电场详细模型,按照双馈风电机组(DFIG)无功容量比例分配无功,难以实现风电场无功裕度均衡控制。根据DFIG无功裕度和并网点(PCC)允许电压偏差,提出可变下垂系数以改进无功-电压控制。结合每台DFIG无功裕度及其与PCC间电气距离,定义新的无功不均衡度。针对大规模风电场控制问题,建立双层无功优化模型,其中电网层以减小网损、电压偏差和风电场铜耗为目标,整定电网无功需求量;风电场层以场内线损、DFIG铜耗及无功不均衡度最小为目标,确定各台DFIG无功出力。采用有限记忆拟牛顿信赖域(LBFGS-TR)算法求解无功均衡分配方案。算例结果表明,所提算法可充分利用DFIG无功调控能力,实现风电场无功裕度均衡控制。     

浅谈电力系统中电压无功功率的控制

电力系统的负荷需要消耗大量的无功功率,而无功功率平衡要满足众多的结点电压,就需要分级分层就地平衡。地区电网的电压无功控制,主要是控制其管辖范围内的各级变电站,使电网的电压合格,并实现无功的就地平衡,降低网损。为此,通过分析变电站电压无功控制的主要设备：有载调压变压器、并联电容器以及并联电抗器,说明变电站电压无功控制的原则、要求、实现方式。