Overview of power quality analysis and control technology for the smart grid

Abstract

Issue Title: Special Issue on Power Quality

With the wide application of non-linear loads and the large-scale access of distributed energy generations based on power electronics equipments, power quality problems in the distribution network are increasingly serious with new characteristics. Further in-depth research is of great significance in theory and practice. This paper provides an overview of power quality analysis, compensators, and control technologies under the new situation of smart grid. It focuses on the topologies and control methods for power quality conditioners, especially new characteristics of power quality and applicable control technologies in microgrids and distributed power plants. Finally, trends and prospects of power quality control technology are introduced, which is important to achieve security and efficient operation of the smart grid.

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Web End = Overview of power quality analysis and control technology for the smart grid

An LUO1, Qianming XU1, Fujun MA1, Yandong CHEN1

Abstract With the wide application of non-linear loads and the large-scale access of distributed energy generations based on power electronics equipments, power quality problems in the distribution network are increasingly serious with new characteristics. Further in-depth research is of great signicance in theory and practice. This paper provides an overview of power quality analysis, compensators, and control technologies under the new situation of smart grid. It focuses on the topologies and control methods for power quality conditioners, especially new characteristics of power quality and applicable control technologies in microgrids and distributed power plants. Finally, trends and prospects of power quality control technology are introduced, which is important to achieve security and efcient operation of the smart grid.

Keywords Power quality, Smart grid, Active control, Passive control

1 Introduction

In the modern smart grid, the diversity of loads and the demands for highly efcient consumption, as well as the use of renewable energy (solar, wind, biomass energy, etc.) generation and grid connection technology through the power electronics interfaces, have brought great challenges to governing power quality [14]. Compared with the traditional power system, the microgrid or distributed power plant, which integrates a variety of energy inputs, multiple load characteristics, and varied energy conversion technologies, is a nonlinear and complex system with inter-coupling of chemical energy, thermodynamics and electrodynamics. Meanwhile, due to the limitation of natural resources, the distributed generations (DGs) appear the features of intermittency, complexity, diversity and instability. Accordingly, some new problems with novel features occur in maintaining power quality. Therefore, power quality control theory and technology will play an important role in ensuring the stable and secure operation of the power grid when microgrids or distributed power plants are connected to it. In the Chinese national program for long-and medium-term scientic and technological development (2006-2020), it is specically mentioned that the analysis, detection, and control technology for power quality should be a priority objective in the energy eld, and it is highly recommended to promote the application of high-power power electronics technology and to control the power quality actively.

Figure 1 illustrates the typical structure of the smart grid including power quality controls. It consists of power transmission part, power distribution part, and power consumption part. The transmission grid is responsible for the regional power electricity supply and large renewable energy generation absorption. Its primary objective is to

CrossCheck date: 14 November 2015

Received: 14 November 2015 / Accepted: 28 December 2015 / Published online: 19 January 2016 The Author(s) 2016. This article is published with open access at

Springerlink.com

& An LUO [email protected]

Qianming XU [email protected]

Fujun MA [email protected]

Yandong CHEN [email protected]

1 National Electric Power Conversion and Control Engineering Technology Research Center (Hunan University), Changsha, China

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110 kV-220 kV

Remote Wind Farm

HVDC

Remote

HVDC Wind Farm

PV Plant

AC DC

10 kV-35 kV

Energy-intensive industries

Distributed Generation

PV Farm

10 kV-35 kV 0.4 kV-1 kV

DC/AC

SST/ST

PV

Load

Load

DC AC

EV Charging Station

DVR or

UPQC

DC DC

Power quality compensator

PF or SVC, HAPF

STATCOM or APF

LOAD

LOAD

LOAD

AC Microgrid

Hydroelectric power

AC

DC

DC Microgrid

SVG

AC

DC

AC

DC

AC

DC

AC

DC

DC

DC

DC

DC

Nuclear power

Wind turbine

PV

BES

SMES

Fuel cell

PV

Fig. 1 Structure diagram of a typical distribution grid system containing microgrid

maintain the voltage stability of transmission lines by regulating appropriate reactive power provided by high voltage power quality compensators. The high- and medium-voltage distribution network works as the bridge that connects the transmission grid and power consumers. With the connection of large amounts of distributed energy, its power quality features appear high penetration and stochastic volatility. In consequence, multiple compensation devices are recommended to operate cooperatively for ensuring a friendly power quality. Power quality on the consumer side directly affects the power efciency and production safety, which makes the power quality problems more complex. As a result, active control and local compensation technology are two important means to suppress the circulating current or harmonic resonance, and to analyze the emission features between DGs and electrical loads in the distribution network.

This paper provides an overview of the power quality control technology in the smart grid. Power quality compensators and their classication based on power electronics technology are comprehensively introduced. A brief description is introduced for novel power quality compensators featuring modular multilevel technology, such as

solid-state transformers and high voltage DC converters. Then, the control methods of power quality compensators are discussed for high efciency operation. Special attention is paid to the new characteristics of power quality and control technology in the distribution system with DGs. Finally, the paper analyzes the trends and prospects of power quality control technology.

2 Power quality compensators classication

It is important to improve the power supply quality on power consumer side by taking advantage of the power quality control technology and equipment. The core principle of power quality control is to control and convert the electric energy, so as to meet the requirement of quality conformance and optimal efciency. The key elements to accomplish above-mentioned control and conversion are diverse power electronics devices and associated control circuits. The classication of compensators in terms of different kinds of power quality problems is depicted in Fig. 2. Power quality control technology can be divided into active control technology and passive control technology.

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Overview of power quality analysis and control technology for the smart grid 3

Power Quality Control Device

Passive Control

Active Control

Harmonic Suppression

Reactive Compensation

Voltage Stable

Advanced Structures

PFC/PWM

PF

FC

SSTS

MMCAPF

Active Micro Grid

APF

SVC

UPS

SST

HAPF

STATCOM

DVR

MMCSTATCOM

UPQC

MMC

UPQC

MMCHVDC

Fig. 2 Classication diagram of power quality compensators

2.1 Passive control technology

The passive control technology is characterized by adding extra devices to eliminate or relieve the impact of existing power quality problems. At present, the harmonic suppression techniques mainly contain the passive power lter (PPF) [5], active power lter (APF) [6, 7], and hybrid active power lter (HAPF) [8]. As mentioned in [9], HAPF can be classied as single-resonance injection hybrid active power lter (S-IHAPF), double-resonance injection hybrid active power lter (D-IHAPF), and multi-branch injection hybrid active power lter (M-IHAPF). The HAPF combines the advantages of both PPF and APF, effectively reducing the rated capacity and voltage of the active part without making a compromise of satisfactory performance in the integral lter system. It has been an effective way to suppress harmonic currents and compensate reactive power in high voltage distribution network. The reactive power compensator is capable of suppressing the voltage uctuation and icker. Off-the-shelf var compensators in distribution network include xed capacitor (FC) [1, 2], static var compensator (SVC) [10], and static synchronous compensator (STATCOM) [11], etc. Among these devices, the STATCOM is widely used for its multiple functions, such as grid voltage uctuation suppression, and unbalanced load compensation. The tendency has been to develop modularized harmonic suppression and var compensation systems due to high stability, reliability and power density.

Among the transient power quality problems, voltage sag and short interruption are perceived as the most common and harmful forms. The solid-state transfer switch (SSTS) [12] can effectively reduce the depth and time of voltage sag. Uninterruptable power supply (UPS) [13] is the most effective tool to restrain the voltage uctuation for low-power devices in the distribution network. The

dynamic voltage regulator (DVR) [14] can directly and quickly compensate the instantaneous voltage sag and swell. The unied power quality controller (UPQC) [15], comprised of the series APF and shunt APF, can make comprehensive compensation of voltage and current for the grid.

In less than two decades, cascade power converters based on modular multilevel converter (MMC) have been widely studied in scientic researches and engineering applications. Due to the identical module structure, MMC greatly reduces the manufacturing difculty and cost of high- and medium-voltage converters. Compared with the traditional power quality compensators, MMC based compensators have special advantages in standardization, expansibility, redundancy, fault ride-through, voltage level and ltering requirement [16, 17]. On the one hand, the modular power quality compensator can effectively lessen the rated voltage of the power switch and energy storage element in the sub module, which allows the use of low-loss and low-cost switch devices. On the other hand, the cascaded structure directly expands the application of diversied power quality compensator in medium- and high-voltage transmission systems. Currently, the APF, STATCOM, UPQC based on MMC have been discussed at a preliminary level [1820]. Due to their novel topology, many new problems different from traditional power converters need to be addressed. More precisely, the multilevel structure inevitably requires a complex control system since large amounts of data must be processed within a short time. This limits the engineering application and development of MMC in the eld of power quality control. More intensive theoretical and practical studies should be investigated to determine how to coordinate the interior power control, modulation method, circulating current suppression, and voltage balancing with exterior voltage and current compensation requirements. Fortunately, with the development of digital processing technology, the realization of complex topology and control system will gradually become simplied.

2.2 Active control technology

Active control technology is used to improve the impedance characteristics of the electrical equipment so as to prevent most power quality problems.

With the transmission and distribution network being instrumented, interconnected and intelligent, power quality problems caused by the future electrical equipment, especially the power electronics converting system, will be signicantly mitigated. At present, the power factor correction (PFC) and pulse width modulation (PWM) technology have improved the power quality of rectier devices [21]. The distributed generation and microgrid

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inverter using the active control [22] not only improve the quality of output voltage and current in distributed system, but also provide some extra compensation capacity for the adjacent grid. Further on, the prospective solid-state transformer (SST) [23] will block the transmission and emission of power quality problems between the power consumer side and power distribution side. The power quality level of the entire power grid will be enhanced due to the MMC-based high voltage direct current (HVDC) transmission and multi-terminal HVDC technology [24].

3 Control method of power quality compensator

Nowadays, power quality control equipment generally employs the voltage source converter or current source converter. The output of converters can be regulated to control the power quality according to the voltage or current reference. The control method of the converter has a signicant impact on the effect on power quality control. There are a lot of literatures describing the control methods, which are hysteresis control, dead-beat control, model predictive control, proportional integral control, proportional resonant control, repetitive control, and nonlinear robust control.

Hysteresis control (HC) is simple to realize and has a fast response speed, but its control accuracy depends on the hysteresis bandwidth and the switch frequency is unxed [25, 26]. Dead-beat control (DBC) is based on state equations of the converter and has a good dynamic performance with convenient parametric design, but its control performance is easily affected by circuit parameters and control delay. Compensating the control delay and adding state observation can strengthen the anti-jamming ability of the system [2729]. Based on the nite control set of the converter, model predictive control (MPC) selects the output switch state to optimize the cost function. It features good dynamic performance, but it is also a challenge to the control system because of a large computation requirement [3032]. However, developments in digital signal processing will contribute to the scale of application of MPC. In a synchronous reference coordinate system, proportional integral (PI) control [33, 34] has been widely used due to its tracking ability without error. Nevertheless, when applied to APF, it cannot realize zero error tracking over a broad frequency range. In order to improve the performance of alternating current control, proportional resonant (PR) control has been developed to achieve innite gain and zero error tracking at the tuned frequency [35, 36]. Repetitive control, derived from the internal model principle, makes it possible to accurately track the periodic signal and enhance the steady-state performance [37, 38], but its dynamic response still needs to be improved.

Making use of the nonlinear characteristics of the converter, sliding mode control based on feedback linearization is proposed in [3941], where it can improve the dynamic performance as well as the robustness of the system. In [42, 43], the articial neural network controller and the linear quadratic Gaussian controller are designed to optimize the performance of APF.

It is noteworthy that a lot of literatures promote methods to improve the compensation performance. [44] presents a multi-PR current controller based on the circuit model, which simplies the harmonic extraction unit. [45] describes a control method with decoupled fundamental component and harmonic component, resulting in dispensable unit for the harmonic voltage and current detection. Dividing frequency control proposed in [8] and [46] reduces the compensation error of the harmonic currents amplitude and phase, which is suitable for multi-structure active power lters.

4 Analysis and control of power quality for large scale distributed power plants

With the increasing penetration rate of large-scale distributed power plants by year, the cross-coupling of harmonic resonance between the distributed system and multi-inverter system has become increasingly complicated. The distributed power plant generates a lot of high-frequency and broadband harmonic components [47]. Moreover, there are series and parallel resonances depending on the transmission line conguration and harmonic frequencies. In cases where the background harmonic voltage matches the transmission line parameters, there will be series resonance, resulting in serious amplication of harmonic voltage. Harmonic currents generated by distributed power plants will also result in parallel resonance, causing serious current distortion, further increasing the total harmonic content in the system. Seriesparallel resonances are mainly responsible for voltage and current distortions, which disturb the efcient and stable operation of distributed power plants [48, 49]. Therefore, analyzing series and parallel resonance mechanisms of distributed power plant has become a hot topic in power system research.

The inuence of transmission line distributed capacitance on harmonic series and parallel resonance is analyzed in [50]. Then, a preliminary resonance suppression method is proposed in [51]. Quantitative analyses of the resonance caused by transformer magnetizing branch, parallel capacitors and other devices are presented in [52]. In [53], the step-up transformer, the reactive power compensation device, distributed capacitance of the transmission line and loads are considered to establish the multiport passive network model. This allows the transmission mechanism of

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Overview of power quality analysis and control technology for the smart grid 5

Curve 1

Curve 2

Amplification factor

150

75

Transmission distance(km)

0

10 20 30 40 0

100

200

300

Harmonic order

(a) Harmonic current amplification factor

200

150

Amplification factor

100

50

0 300

200

Transmission distance (km)

50

Harmonic order

100

0 10

20 30

40 50

(b) Harmonic voltage amplification factor

Fig. 3 The relationship between the resonance amplication factor and harmonic order, transmission distance

harmonics to be analyzed using the denition of resonance amplication factors. As shown in Fig 3a, double resonance curves are discovered, which means that transmission lines of different distances may amplify a harmonic current twice, or a transmission line of a xed distance may amplify the harmonic current of different frequencies. For transmission line distance within 100 km in resonance curve 1, the harmonics resonance frequency is between the 11th and 27th, and the amplication factor for the 17th and 19th harmonics may reach 20. In resonance curve 2, the dominant resonance frequency within 200300 km transmission line is the 9th harmonic, and its amplication factor can reach 10 at the resonance point. As depicted in Fig 3b, apparently, in the case of long-distance transmission (100300 km), the most dominant resonance frequency is between the 5th and 15th harmonics; the 7th harmonic voltage is magnied about 20 times. Whereas in the case of short-distance transmission (0100 km), the dominant

series resonance frequency is between the 17th and 50th harmonics. At the resonance points, the 17th and 19th harmonic voltages may magnify more than 20 times, and more than 100 times for the 23rd, 27th, 37th and 49th harmonic voltages.

Harmonics generated by large-scale distributed power plants have the characteristics of high frequency and wide frequency range. Therefore, the adverse impact of distributed parameters of high-voltage cables becomes more signicant [54].

The methods to eliminate the series-parallel harmonic resonance can be summarized in two categories:

1) By changing the parameters of the transmission network, the harmonic resonance can be restrained [55]. Existing measures set the shunt reactors at both ends of transmission lines to weaken the effect of distributed capacitances. But this approach shows some drawbacks when it is applied to distributed power plants. On the one hand, the shunt reactors reduce the power factor at the export side of distributed power plants. On the other hand, the variation of the output active and reactive power of distributed power plants may cause large voltage uctuations at the point of common coupling (PCC).

2) Adding lter device can markedly reduce the harmonic content owing into the grid [56]. Most conventional lter devices are available for lower order harmonic currents compensation, but incapable of eliminating harmonic frequencies more than 25th.

Hence, new lter topologies that can effectively accomplish broadband harmonic detection and elimination will undoubtedly be paid critical attention in the near future.

It is worthy of note that the hybrid active power lter with the grid current detection function [57] can be equivalent to a harmonic impedance in series with the grid impedance. It can ameliorate the grid equivalent impedance to suppress the resonance. Concurrently, harmonic currents will be ltered at low cost. Hence, it is useful for the harmonic management of distributed power plants.

5 Analysis and control of power qualityfor microgrids and power distribution systems containing microgrids

The DG units, energy storage system (ESS) and loads are connected to the microgrid through power electronics converters. This structure is the main form of the DGs for renewable energy at present. The power quality problems of the microgrid exist in a wide-band frequency domain along with an increasing penetration of the microgrid.

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Determining how to effectively tackle the problem of the harmonic currents in the wide-band frequency domain caused by the distributed and clustered inverters has been gained much attention in the ied of the power quality of the microgrid operating in both islanded and grid-connected mode [58]. The most signicant problems in the islanded mode are how to effectively realize power sharing among parallel inverters, also reduce the fundamental and harmonic circulating currents among them. The prominent problems in grid-connected mode are how to solve the coupling resonant among parallel inverters as well as between the inverters and the distribution network. This section will focus on the new characteristics of the power quality and its control technologies in the microgrid.

5.1 Suppression methods of internal circulating current in microgrids

The equivalent output impedances of the parallel inverters are different from each other at PCC [59] in an AC or hybrid microgrid since the control strategies, lter parameters and length of transmission lines [60], are not the same. Consequently, it will cause the fundamental and harmonic circulating currents, and also the uctuations of the amplitude and frequency of the PCC voltage of the islanded microgrid [61, 62]. There have three types of circulating currents in the islanded mode, i.e., active circulating current, reactive circulating current and harmonic circulating current. The active circulating current is caused by the frequency and phase deviations of inverter output voltages. The reactive circulating current results from the magnitude deviations of inverter output voltages. The harmonic circulating current is the result of harmonic components of inverter output voltages. The slight deviations of the frequency, phase and magnitude of the inverter output voltages will lead to large fundamental or harmonic circulating currents [63]. Moreover, the circulating currents will reduce the output capacities of the DG units, and increase the line losses, also endanger the safe operation of the microgrid [64, 65].

The virtual impedance technology can effectively reduce the circulating currents by changing the equivalent output impedance of the parallel inverters. The resistive (R-type) inverter, inductive (L-type) inverter, resistive-inductive (RL-type) inverter, and resistive-capacitive (RC-type) inverter can be easily designed by using the virtual impedance technology to meet the different operating requirements of the microgrid [6669]. In general, the output impedance of the inverters in the middle-voltage-level microgrid is designed to be inductive; on the contrary, the output impedance is often designed to be resistive-inductive in the low-voltage-level microgrid.

5.2 Harmonic analysis and suppressionin the microgrids operating in grid-connected mode

The nonlinear action and dead time effect of distributed inverter bring plenty of high-order harmonic currents in the microgrids. Thus, the output lter devices for inverters are indispensable. There have two main types of output lter for inverters in grid-connected mode, i.e., L-type and LCL-type lter. Besides, the LC-type lter is mainly used in the islanded mode [70]. The equivalent output impedance of each inverter will easily be changed due to the deviation of lter parameters. Impedance coupling exists among the equivalent impedances of the parallel inverters, as well as between the equivalent output impedance of the inverter and the equivalent impedance of the distribution network. Therefore, it can provide a low-impedance channel for specic harmonic, resulting in the amplication of the harmonic current with specic orders. The active damping loop can provide solutions to this problem in terms of the inverter control. Cascade control method [71, 72], splitting capacitance method [73], zero-pole compensation method [74], and lter-capacitor-voltage feedback method [75] are the effective active damping schemes.

The resonant problem of multi-parallel inverters is complex [76, 77], and there exists both a xed and an unxed resonant band. The xed resonant band is caused by inverter lter system, and its resonant frequencies will not migrate with the different number of parallel inverters. However, the unxed resonant band results from the coupling effect of the equivalent output impedance of the parallel inverter system and its resonant frequencies will migrate to the low-frequency range along with the increase in the number of the parallel inverters. In addition, the series resonance exists between the parallel inverter and the distribution network [78], and its resonance peak frequency will also migrate to the low-frequency range along with the increase in the number of parallel inverters. To restrain the series resonance, the Nyquist stability criterion can be extended to provide a feasible solution for reshaping the equivalent output impedance of the inverter. Besides, the active damping schemes should be taken to attenuate the coupling resonance among parallel inverters.

6 Trends and prospects of power quality control

With concern about the consumption of fossil fuels and the resulting greenhouse effect, a large number of sustainable energy sources are connected to the utility grid in the form of DGs. This will affect the power quality of power grid and bring new demands of the compensation devices. At the same time, the potential application of wide

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Overview of power quality analysis and control technology for the smart grid 7

Acknowledgment This work was supported by the General Program of National Natural Science Foundation of China (No. 51477045).

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References

[1] Miller TJE (1982) Reactive power control in electric system. Wiley, New York

[2] Wang ZA, Yang J, Liu JJ (2006) Harmonic suppression and reactive power compensation. Machinery Industry Press, Beijing (in Chinese)

[3] Green MA (2002) Third generation photovoltaics: comparative evaluation of advanced solar conversion options. In: Proceedings of the 29th IEEE photovoltaic specialists conference, New Orleans, 1924 May 2002, pp 13301334

[4] Zhao ZM, Liu JZ, Sun XY (2005) Solar photovoltaic power generation and its application. Science Press, Beijing (in Chinese)

[5] El-Saadany EF, Salama MMA, Chikhani AY (2000) Passive lter design for harmonic reactive power compensation in single-phase circuits supplying nonlinear loads. IEE P-Gener Transm Distrib 147(6):373380

[6] Akagi H (1994) Trend in active power line conditioners. IEEE Trans Power Electron 9(3):263268

[7] Khadkikar V, Chandra A (2008) A new control philosophy for a unied power quality conditioner (UPQC) to coordinate load-reactive power demand between shunt and series inverters. IEEE Trans Power Deliv 23(4):25222534

[8] Luo A, Zhao W, Deng X et al (2009) Dividing frequency control of hybrid active power lter with multi-injection branches using improved ip-iq algorithm. IEEE Trans Power Electron 24(10):23962405

[9] Zhao W (2010) Harmonic suppression and reactive power compensation theory and application research in high voltage distribution networks. Ph D Thesis, Hunan University, Changsha (in Chinese)

[10] Gyuyi L, Talor ER (1980) Characteristic of static, thyristor-controlled shunt compensators for power transmission system applications. IEEE Trans Power Appar Syst 99(5):17951804

[11] Ghosh A, Ledwich G (2003) Load compensating DSTATCOM in weak AC systems. IEEE Trans Power Deliv 18(4):13021309

[12] Chan K, Kara A, Kieboom G (1998) Power quality improvement with solid state transfer switches. In: Proceedings of the 8th international conference on harmonics and quality of power, vol 1, Athens, 1418 Oct 1998, pp 210215

[13] Bashi SM, Jasni J, Weng OY (2003) Voltage regulation of uninterrupted power supplies. In: Proceedings of the IEEE student conference on research and development (SCOReD03), Putrajaya, 2526 Aug 2003, pp 385389

[14] Liu JW, Choi SS, Chen S (2003) Design of step dynamic voltage regulator for power quality enhancement. IEEE Trans Power Deliv 18(4):14031409

[15] Fujita H, Akagi H (1998) The unied power quality conditioner: the integration of series and shunt-active lters. IEEE Trans Power Electron 13(2):315322

band semiconductors (SiC), and the development of new converter topologies will promote the development of advanced power quality compensators. In addition, solid state circuit breakers, SSTS and MMC-HVDC, which can cooperatively control active power and reactive power to achieve power quality active control, have been extensively studied. The continuous application of such technology will have a positive impact on power quality control.

Considering the issues and technologies presented in these papers, the following areas require further research:

1) The harmonics generated by power electronics converters have characteristics of high-frequency, wide frequency range, and multi-type coupling. How to detect and suppress the high-order harmonics and inter-harmonics still needs to be further investigated.

2) The emission level and superposition characteristic of the power quality problem as well as the interaction effect between the micro-grid and the utility grid are worth researching.

3) Power quality characteristics of large wind power farms, photovoltaic power plants, their interaction effect with public power grid and suitable power quality control methods merit intensive research.

4) The characteristics of the power quality in large scale distributed power plant as well as the power quality control method are prime candidates for in-depth study.

5) New designs for power quality compensators based on wide band semiconductors or modular multilevel technology need to be developed.

6) The functionality and widespread application of solid state circuit breakers, solid state transformers and MMC-HVDC, all of which can perform active power quality control, require in-depth research.

7 Conclusion

With the growth of extensive nonlinear loads and renewable power integration, power quality problems in distribution grids have become increasingly serious. Problems such as voltage uctuation, voltage sag, harmonic and reactive power, not only directly harm the normal operation of sensitive loads, but also decrease the power transmission efciency of the distribution system. This paper summarizes available and emerging control technologies to solve power quality problems in the strong smart grid. Particularly, it focuses on new power quality features, control technologies and trends and prospects, to form a valuable reference to assist the secure and economical operation of distribution grids.

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[16] Lesnicar A, Marquardt R (2003) An innovative modular multilevel converter topology suitable for a wide power range. In: Proceedings of the 2003 IEEE Bologna power technology conference, vol 3, Bologna, 2326 June 2003, 6 pp

[17] Kouro S, Malinowski M, Gopakumar K et al (2010) Recent advances and industrial applications of multilevel converters. IEEE Trans Ind Electron 57(8):25532580

[18] Ghetti FT, Ferreira AA, Brage HAC, et al. (2012) A study of shunt active power lter based on modular multilevel converter (MMC). In: Proceedings of the 10th IEEE/IAS international conference on industry applications (INDUSCON12), Fortaleza, 57 Nov 2012, 6 pp

[19] Nieves M, Maza JM, Mauricio JM, et al. (2014) Enhanced control strategy for MMC-based STATCOM for unbalanced load compensation. In: Proceedings of the 16th European conference on power electronics and applications (EPE14-ECCE Europe), Lappeenranta, 2628 Aug 2014, 10 pp

[20] Long YB, Xiao XN, Xu YH et al (2013) MMC-UPQC: application of modular multilevel converter on unied power quality conditioner. In: Proceedings of the 2013 IEEE Power and Energy Society general meeting (PES13), Vancouver, 2123 July 2013, 5 pp

[21] Yao K, Ruan XB, Zou C et al (2012) Three-phase single-switch boost PFC converters with high input power factor. Proc CSEE 32(6):97105 (in Chinese)

[22] Zeng Z, Zhao RX, Yang H et al (2012) A multi-functional grid-connected inverter and its application to customized power quality of microgrid. Power Syst Technol 36(5):5867 (in Chinese)

[23] Leung CK, Dutta S, Baek S et al (2010) Design considerations of high voltage and high frequency three phase transformer for solid state transformer application. In: Proceedings of the 2010 IEEE energy conversion congress and exposition (ECCE10), Atlanta, 1216 Sept 2010, pp 15511558

[24] Railing RD, Moreau G, Ronstrm L et al (2004) Cross sound cable project second generation VSC technology for HVDC. In: Proceedings of the 2004 CIGRE conference, Paris, 2123 July 2004, pp B4B102

[25] Lam CS, Wong MC, Han YD (2012) Hysteresis current control of hybrid active power lters. IET Power Electron 5(7):11751187

[26] Suresh Y, Panda AK, Suresh M (2012) Real-time implementation of adaptive fuzzy hysteresis-band current control technique for shunt active power lters. IET Power Electron 5(7):11881195

[27] Kamran F, Habetler TG (1998) Combined deadbeat control of a series-parallel converter combination used as a universal power lter. IEEE Trans Power Electron 13(1):160168

[28] Han Y, Xu L, Khan MM et al (2011) Robust deadbeat control scheme for a hybrid APF with resetting lter and ADELINE-based harmonic estimation algorithm. IEEE Trans Ind Electron 58(9):38933904

[29] Biagini V, Zanchetta P, Odavic M et al (2013) Control and modulation of a multilevel active ltering solution for variable-speed constant-frequency more-electric aircraft grids. IEEE Trans Ind Inform 9(2):600608

[30] Drobni K, Nemec M, Nedeljkovic D et al (2009) Predictive direct control applied to AC drives and active power lter. IEEE Trans Ind Electron 56(6):18841893

[31] Acua P, Morn L, Rivera M et al (2015) A single-objective predictive control method for a multivariable single-phase three-level NPC converter-based active power lter. IEEE Trans Ind Electron 62(7):45984607

[32] Panigrahi R, Subudhi B, Panda PC (2015) Model predictive-based shunt active power lter with a new reference current estimation strategy. IET Power Electron 8(2):221233

[33] Xu Y, Li FX (2014) Adaptive PI control of STATCOM for voltage regulation. IEEE Trans Power Deliv 29(3):10021011

[34] Rahmani S, Mendalek N, Al-Haddad K (2010) Experimental design of a nonlinear control technique for three-phase shunt active power lter. IEEE Trans Ind Electron 57(10):33643375

[35] Micallef A, Apap M, Spiteri-Staines C et al (2014) Reactive power sharing and voltage harmonic distortion compensation of droop controlled single phase islanded microgrids. IEEE Trans Smart Grid 5(3):11491158

[36] Herman L, Papic I, Blazic B (2014) A proportional-resonant current controller for selective harmonic compensation in a hybrid active power lter. IEEE Trans Power Deliv 29(5):20552065

[37] Zou ZX, Zou KL, Wang Z et al (2015) Frequency-adaptive fractional-order repetitive control of shunt active power lters. IEEE Trans Ind Electron 62(3):16591668

[38] Grino R, Cardoner R, Costa-Castell R et al (2007) Digital repetitive control of a three-phase four-wire shunt active lter. IEEE Trans Ind Electron 54(3):14951503

[39] Wu JY, Chen QC, Du MJ et al (2013) Sliding-mode variable structure controller for cascade static var compensator. IET Trans Power Electron 6(2):343352

[40] Matas J, de Vicua LG, Miret J et al (2008) Feedback linearization of a single-phase active power lter via sliding mode control. IEEE Trans Power Electron 23(1):116125

[41] Al Chaer T, Gaubert JP, Rambault L et al (2009) Linear feedback control of a parallel active harmonic conditioner in power systems. IEEE Trans Power Electron 24(3):641653

[42] Radzi MAM, Rahim NA (2009) Neural network and bandless hysteresis approach to control switched capacitor active power lter for reduction of harmonics. IEEE Trans Ind Electron 56(5):14771484

[43] Panigrahi R, Subudhi B, Panda PC (2016) A robust LQG servo control strategy of shunt- active power lter for power quality enhancement. IEEE Trans Power Electron 31(4):28602869

[44] He JW, Li YW, Blaabjerg F et al (2014) Active harmonic ltering using current-controlled, grid-connected DG units with closed-loop power control. IEEE Trans Power Electron 29(2):642653

[45] Zobaa AF (2014) Optimal multiobjective design of hybrid active power lters considering a distorted environment. IEEE Trans Ind Electron 61(1):107114

[46] Luo A, Shuai ZK, Zhu WJ et al (2012) Combined system for harmonic suppression and reactive power compensation. IEEE Trans Ind Electron 56(2):418428

[47] Agorreta JL, Borrega M, Lpez J et al (2011) Modeling and control of N-paralleled grid-connected inverters with LCL lter coupled due to grid impedance in PV plants. IEEE Trans Power Electron 26(3):770785

[48] Xu W, Huang ZY, Cui Y et al (2005) Harmonic resonance mode analysis. IEEE Trans Power Deliv 20(2):11821190

[49] Xu DZ, Wang F, Mao HL et al (2013) Modeling and analysis of harmonic interaction between multiple grid-connected inverters and the utility grid. Proc CSEE 33(12):6471 (in Chinese)

[50] Shuai ZK, Liu DG, Shen J et al (2014) Series and parallel resonance problem of wideband frequency harmonic and its elimination strategy. IEEE Trans Power Electron 29(4):19411952

[51] Shuai ZK, Xiao F, Tu CM et al (2013) Resonance degradation mechanism of wide-band frequency harmonics and elimination strategy. Trans China Electrotech Soc 28(12):1623 (in Chinese)

[52] Zhong HQ, Xu ZX, Zou YP et al (2005) Effects of parasitical capacitors on charging characteristic of series resonant CCPS. Proc CSEE 25(10):4044 (in Chinese)

[53] Luo A, Xie N, Shuai ZK (2015) Large-scale photovoltaic plant harmonic transmission model and analysis on resonance characteristics. IET Power Electron 8(4):565573

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Overview of power quality analysis and control technology for the smart grid 9

[54] Ineld DG, Onions P, Simmons AD et al (2004) Power quality from multiple grid-connected single-phase inverters. IEEE Trans Power Deliv 19(4):19831989

[55] Indulkar CS, Viswanathan B, Venkata SS (1989) Maximum power transfer limited by voltage stability in series and shunt compensated schemes for AC transmission systems. IEEE Trans Power Deliv 4(2):12461252

[56] Ma FJ, Luo A, Shuai ZK et al (2014) Voltage ripple analysis of simplied active power compensator for negative sequence and reactive power compensation. IET Power Electron 7(10):25822594

[57] Luo A, Peng SJ, Wu CP et al (2012) Power electronic hybrid system for load balancing compensation and frequency-selective harmonic suppression. IEEE Trans Ind Electron 59(2):723732

[58] Li YW, Nejabatkhah F (2014) Overview of control, integration and energy management of microgrids. J Mod Power Syst Clean Energy 2(3):212222. doi:http://dx.doi.org/10.1007/s40565-014-0063-1

Web End =10.1007/s40565-014-0063-1

[59] Guerrero JM, De Vicuna LG, Matas J et al (2005) Output impedance design of parallel-connected UPS inverters with wireless load-sharing control. IEEE Trans Ind Electron 52(4):11261135

[60] Tuladhar A, Jin H, Unger T et al (2000) Control of parallel inverters in distributed AC power systems with consideration of line impedance effect. IEEE Trans Ind Appl 36(1):131138

[61] Guerrero JM, De Vicuna LG, Matas J et al (2004) A wireless controller to enhance dynamic performance of parallel inverters in distributed generation systems. IEEE Trans Power Electron 19(5):12051213

[62] Ding GQ, Gao F, Zhang S, Loh PC, Blaabjerg F (2014) Control of hybrid AC/DC microgrid under islanding operational conditions. J Mod Power Syst Clean Energy 2(3):223232. doi:http://dx.doi.org/10.1007/s40565-014-0065-z

Web End =10. http://dx.doi.org/10.1007/s40565-014-0065-z

Web End =1007/s40565-014-0065-z

[63] Vasquez JC, Mastromauro RA, Guerrero JM et al (2009) Voltage support provided by a droop-controlled multifunctional inverter. IEEE Trans Ind Electron 56(11):45104519

[64] De Brabandere KD, Bolsens B, Van den Keybus J et al (2007) A voltage and frequency droop method for parallel inverters. IEEE Trans Power Electron 22(4):11071115

[65] Zhong QC (2013) Robust droop controller for accurate proportional load sharing among inverters operated in parallel. IEEE Trans Ind Electron 60(4):12811290

[66] Yao W, Chen M, Matas J et al (2011) Design and analysis of the droop control method for parallel inverters considering the impact of the complex impedance on the power sharing. IEEE Trans Ind Electron 58(2):576588

[67] Guerrero JM, Vasquez JC, Matas J et al (2011) Hierarchical control of droop-controlled AC and DC microgrids: a general approach towards standardization. IEEE Trans Ind Electron 58(1):158172

[68] Zhong QC, Zeng Y (2014) Control of inverters via a virtual capacitor to achieve capacitive output impedance. IEEE Trans Power Electron 29(10):55685578

[69] Chen YD, Guerrero JM, Shuai ZK et al (2015) Fast reactive power sharing, circulating current and resonance suppression for parallel inverters using resistive-capacitive output impedance. IEEE Trans Power Electron. doi:http://dx.doi.org/10.1109/TPEL.2015.2493103

Web End =10.1109/TPEL.2015.2493103

[70] Wai RJ, Lin CY, Huang YC et al (2013) Design of high-performance stand-alone and grid-connected inverter for distributed

generation applications. IEEE Trans Ind Electron 60(4):15421555[71] Twining E, Holmes DG (2003) Grid current regulation of a three-phase voltage source inverter with an LCL input lter. IEEE Trans Power Electron 18(3):888895

[72] Dannehl J, Fuchs FW, Hansen S et al (2010) Investigation of active damping approaches for PI-based current control of grid-connected pulse width modulation converters with LCL lters. IEEE Trans Ind Appl 46(4):15091517

[73] Shen GQ, Xu DH, Cao LP et al (2008) An improved control strategy for grid-connected voltage source inverters with an LCL lter. IEEE Trans Power Electron 23(4):18991906

[74] Malinowski M, Bernet S (2008) A simple voltage sensorless active damping scheme for three-phase PWM converters with an LCL lter. IEEE Trans Ind Electron 55(4):18761880

[75] Dannehl J, Liserre M, Fuchs FW (2011) Filter-based active damping of voltage source converters with LCL lter. IEEE Trans Ind Electron 58(8):36233633

[76] Wang F, Duarte JL, Hendrix MAM et al (2011) Modeling and analysis of grid harmonic distortion impact of aggregated DG inverters. IEEE Trans Power Electron 26(3):786797

[77] Ghiani E, Pilo F (2015) Smart inverter operation in distribution networks with high penetration of photovoltaic systems. J Mod Power Syst Clean Energy 3(4):504511. doi:http://dx.doi.org/10.1007/s40565-015-0165-4

Web End =10.1007/s40565- http://dx.doi.org/10.1007/s40565-015-0165-4

Web End =015-0165-4

[78] Enslin JHR, Heskes PJM (2004) Harmonic interaction between a large number of distributed power inverters and the distribution network. IEEE Trans Power Electron 19(6):15861593

An LUO is a Professor with the College of Electrical and Information Engineering, Hunan University, where he also serves as the Chief of National Electric Power Conversion and Control Engineering Technology Research Center. He has published over 100 journal and conference articles. He is engaged in research on power conversion systems, harmonic suppression and reactive power compensation, and electric power saving.

Qianming XU received the B.S. degree from the College of Electrical and Information Engineering, Hunan University, in 2012. He has been working toward the Ph.D. degree in Hunan University since 2012. His research interests include multilevel converters, power quality control technique.

Fujun MA received the B.S. and Ph.D. degrees from Hunan University, Changsha, in 2008 and 2015, respectively. Since 2013, he has been an Assistant Professor with the College of Electrical and Information Engineering, Hunan University. His research interests include power quality managing technique of electried railway, electric power saving, reactive power compensation, and active power lters.

Yandong CHEN received the Ph.D. degrees from Hunan University, Changsha, in 2014. Since 2014, he has been an Assistant Researcher with the College of Electrical and Information Engineering, Hunan University. His research interests include power electronics for Microgrid, distributed generation, and power quality.

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