2009，V ol. 3，No. 3 SOUTHERN POWER SYSTEM TECHNOLOGY Featured
Articles 文章编号：1674-0629(2009)03-0007-08 中图分类号：TM934.5 文献标志码：A 法国电网电能质量承诺和电能质量评估 杨显军
（法国电力公司研究与开发部，92141 卡拉马特，法国）
摘要：介绍法国电网的电能质量承诺，包括输电运营商（TSO）的质量承诺和配电运营商（DSO）的质量承诺。TSO
和DSO在作出电能质量承诺的同时，还利用入网规则以协议的方式来考虑和限制每个客户的负荷和分布式电源对电能
质量的影响。这些协议的实施表明，只有遵守承诺，加上电网运营商与用户双方共同作出努力，才能获得全面良好的电
能质量。对于电网干扰评估，建议使用基波潮流计算与多相谐波注入相结合的方法。这个方法利用很短的计算时间就能
对非线性负荷建模情形给出可接受的结果。所提议的频域方法的要点在于，将每个谐波源逐一地同时作为扰动源和受扰
者来考察，以便计及扰动源之间的相互作用。研发了一个即插即用的HVDC组件并将其用在文章最后部分实例研究中。
关键词：电能质量承诺；频域建模；谐波；电力电子设备；高压直流输电
Grid Power Quality Commitments and Grid Power Quality Assessment
in France
YANG Xian-jun (Xavier X. YANG)
痔疮仪(R&D, Electricité de France, 92141 Clamart, France)
Abstract: Grid Power Quality Commitments in France are introduced, including the Power Quality Commitments of Transmission
System Operator (TSO) and the Power Quality Commitments of Distribution System Operator (DSO). Undertaking the commitments,
TSO and DSO are using connection rules to take into account and minimize the impact on power quality of each customer (load or
distributed generation) in the way of contracts. The practice of these contracts shows that a good overall power quality can only be
achieved by respecting commitments and doing effort from both of grid and customer sides. For grid disturbance assessment, it is
suggested to use multi-phase harmonic injection method with fundamental power flow. This method can give an acceptable results
with very short computing time for non-linear load modelling. The key point of proposed frequency domain method is that each
harmonic source is individually considered as both disturbance source and disturbance receiver in order to take into account
interactions between sources. A plug & play HVDC component has been developed and used in one of two case-studies in the end of
this article.
Key words: power quality commitment; frequency domain modelling; harmonic; power electronic device; HVDC
1 Power Quality Commitments
1.1 Power Quality Contracts and Commitments
Standard EN 50160 gives the main voltage pa-rameters and their permissible deviation ranges at the point of common coupling (PCC) in public low volt-age (LV) and medium voltage (MV) electricity distri-bution systems, under normal operating conditions.
Based on EN 50160 and the former French power quality contract Emeraude, two new grid access con-tracts have been put into service in France between system operators (utilities) and customers: called CART for transmission customers and CARD for dis-tribution customers, see Fig. 1. These contracts not only set the power quality commitments for the grid operators but also for the customer
disturbance emis-sion level.
Fig. 1 Power Quality Commitments in CARD and CART
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南方电网技术 第3卷
The power quality that is handled in grid access contracts includes harmonic, unbalance, flicker, inter-ruption, voltage dip disturbances. Among these dis-turbances, the number of interruption is considered as commitment and others are given as indicative values. 1.2 Power Quality Commitments of Transmis-sion System Operator (TSO)
French TSO has the standard and personalized contractual commitments with the customers concern-ing:
1） long interruptions (1 per year, 2 per 3 years, 1 per 3 years)；
水位水温传感器2） short interruptions (1 to 5 per year, 1 to 2 per 3 years)；
3） voltage dips (optional from 3 to 5 per year)； 4） RMS voltage magnitude (± 8 %)； 5） frequency (± 1 %)； 6） voltage unbalance (< 2 %)； 7） harmonics ；
8） rapid voltage fluctuations, flicker (P lt < 1). For transmission power supply voltage, harmonic limits have been set (Tab. 1). These limits are meas-ured by 10 min mean value at each harmonic voltage (h ≤ 25, the order of harmonics) and total harmonic distortion (THD , h ≤ 40) during 100% of time. For transmission customer, current harmonic emissions are also limited in % compared to contracted rated current
h HRU lim /%
h HRU lim /%
h HRU lim /%
5, 7 2.0 3 2.0 2 1.5 6.0 11, 13 1.5 9 1.0 4 1.0 6.0 17
1.0
15, 21
0.5
> 4
0.5
6.0
19 1.0 6.0 23, 25 0.7
6.0
1.3 Power Quality Commitments of Distribution
System Operator (DSO)
The Tab. 3 shows the contracted voltage interrup-tion values for the four geographical zones.
With personalized contracts signed jointly by system operators and customers, it is possible to in-clude some voltage dips in guaranteed power supply quality by network operators.
Tab. 2 Transmission Customer Current Harmonic Commitments Odd Order h
HRI lim /% Even Oder h HRI lim /%
3 4.0 2 2 5, 7 5.0
4 1.0 9 2.0 > 4 0.
5 11, 13
3.0
>13 2.0
Tab. 3 DSO Commitments of Voltage Interruptions per Year Interruption Duration
Zone 1 Zone 2 Zone 3Zone 4
≥ 3 min
6 3 3 2 > 1 s and < 3 min
30
10
3
2
As grid commitments (Tab. 4), harmonic limits have been set for distribution power supply voltage. These limits are measured by 10 min mean value at
each harmonic voltage (h ≤ 25) and total harmonic distortion (THD , h ≤ 40) during 100% of time. For distribution customer, current harmonic emissions are also limited in % compared to contracted rated current (Tab. 5).
Tab. 4 Distribution Voltage Harmonic Commitments Odd Harmonic Order
Not-Triplet Triplet Even Harmonic
Order
THD lim /13 3.0 8.0 17 2.0 8.0 19, 23, 25
1.5 8.0
Tab. 5 Distribution Customer Current Harmonic Commitments Odd Order h
饮料瓶提手
HRI lim /% Even Oder h HRI lim /%
3 4.0 2 2.0 5, 7 5.0
4 1.0 9 2.0 > 4 0.
5 11, 13
3.0
>13 2.0
第3期杨显军：法国电网电能质量承诺和电能质量评估 9
For more detail of the power qualify commit-ments of TSO and DSO, please see the following web site: /.
四巧板1.4 Customer Load Connection
In order to meet their power quality commitments, TSO and DSO are using connection rules to take into account and minimize the impact on power quality of each customer (load or distributed generation). DSO has set up a number of technical referential documents and studying tools for load connection. Before per-forming a load or a DG connection, DSO undertakes three level’s studies which are based on standards and site measurements. The aim is to anticipate the possi-ble disturbances which may be provoked by the equipment to be connected and to determine the most adaptive Point of Common Coupling (PCC). Follow-ing these steps, DSO can ensure the optimal perform-ance of the network for all users.
The first level study includes identifying the main characteristics of the installation to be connected and effectuating a global analysis. The second level con-sists of evaluating particularly the disturbances. The third level is composed of a detailed study on the iden-tified disturbances. In wind mill connection, this study is based on the standard IEC 61400-21 which evalu-ates the impact in terms of power quality [1].
1.5 Power Quality Indices and Evolution of
Commitments
In order to measure the evolution of power qual-ity, DSO calculates a number of criterions based on network parameters. These indicators make it possible to evaluate the needs of power supply infrastructure improvement. The following values have been defined as power quality indicators:中央空调通风管道
1）SAIDI or B-Criterion in France, index of mean duration of interruption for LV customers;
2）SAIDI for MV customers weighted by the supplied power;
3）SAIFI, indices of mean number of interrup-tion of the network, for the long interruption (t id > 3 min), the short interruption (1 s≤ t id≤ 3 min) and the very short interruption (t id < 1 s) . 2 Harmonic Source Modelling and Grid
Disturbance Assessment
2.1 Simulation Method
Frequency domain analysis uses an admittance matrix system model developed from individual com-ponent level models connected according to system topology. The development of admittance matrix mod-els is based on multi-port network theory. Linear grid components are similarly developed from multi-port admittance parameters.
In frequency domain simulation, harmonic gener-ating devices are usually modelled by current sources and the whole system admittance matrix is resolved from a start frequency to an end frequency with a fixed or variable frequency step. The deficiencies in the current source method can be partially overcome using a technique that has come to be known as “harmonic power flow”. More often, a fundamental frequency power flow solution is executed using a linear model for all power delivery equipment and loads, and the resultant fundamental frequency load terminal volt-ages are used to “adjust” non-linear load harmonic current vectors automatically without additional user action. However, in frequency approach, initial har-monic current patterns are still required to be known for each nonlinear load.
2.2 Harmonic Source Modelling
Harmonic model based on a constant current source, see Fig. 2(a), can’t represent real harmonic currents generated by a power electronic device con-nected to an actual network.
Fig. 2 General Structure of Three Phase Harmonic Source Model
The method (a) is too simplified because actual harmonic current of an electric device is always con-
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trolled by network configuration. In order to overcome this drawback, we have developed multiphase har-monic model with a voltage vector controlled current source and a frequency-variable impedance to repre-sent an actual harmonic source, see Fig. 2(b). In pro-posed method (b), J (f ) is a current source controlled by the fundamental voltage crossing frequency-variable impedance Z (f ). Z (f ) represents the behaviour of the power electronic device towards harmonic distur-bances coming from power supply side.
The method (b) is detailed in the following para-graphs.
Equivalent harmonic current source of a nonlin-ear load is generated by two main steps: the initial cur-rent J 0(f ) and the corrected current source J (f ) by load-flow. In parameter setting before simulation, the initial J 0(f ) is defined by pre-designed waveform pat-tern, rated power and rated volt
age of the load. In fre-quency domain, J 0(f ) is represented by the following
formula:
00()()cos()k k
J f J k k t ωφ=⋅+.
The pre-designed waveform patterns include cur-rent waveforms generated by the most usual distur-bance sources such as 6-pulse and 12-pulse rectifiers, dimmers, arc furnaces, etc. The following procedure summarizes the proposed source modelling method:
1） Choosing a pre-designed waveform (database, analytical formulas, wave form generated by Excel data sheet, empirical data table, on-site measurements) which represents the current harmonic distortion to be used;
2） Refining the waveform by particular working state of the device. For example, by switching angle of rectifier and by short-circuit power of upstream net-work;
镜面银油墨
3） Spectrum calculation of the refined wave-form by means of Fast Fourier Transform;
4） Calculation of the designed fundamental current and phase angle between voltage and current from rated electric values of the device: voltage, pow-ers P and Q ;
5） Pre-design of the harmonic spectrum at rated current and creation of a voltage controlled current source model for frequency domain simulation J 0(f ), see example in Fig. 3 for the used current pattern of a 12-pulse rectifier.
Fig. 3 Current Waveform and Harmonic Spectrum
of a 12-Pulse Rectifier
Define the source impedance Z (f ) as a function of frequency. Z (f ) reflects the device behaviour to the disturbances coming from power supply side.
For particular case, it is very important to define Z (f ) values within the studied frequencies. For instance, a static converter’s impedance was set an infinite value in the past in performing inter-harmonic studies. This is not true for a number of static converters. Some in-dustrial cases show the ripple control signal at 175 Hz can be partially absorbed by a rectifier with a capacitor filter as in a va
riable-speed drive [2].
The proposed harmonic source model behaviours as follows: when the source J (f ) is activated, imped-ance Z (f ) is naturally set to an infinite value because the device behaviours as a current source. When the source J (f ) is not activated, Z (f ) has to be added into the system admittance matrix. In this case, the device behaviours as a passive component. Value of Z (f ) is defined case by case in accordance with studied phe-nomena:
At fundamental frequency, Z (f ) is calculated from rated voltage and powers P , Q of the simulated device.
第3期杨显军：法国电网电能质量承诺和电能质量评估 11
At studied harmonic or inter harmonic frequen-cies whose source comes from the power supply side, Z(f) can be defined from the real response of the de-vice at these frequencies. Z(f) is depending on device structure, it can be modelled by series (or parallel) RL, RC circuits, by mixed model of CIGRE 36.05[3] or by a data table for irregular cases.
If it is difficult to define a general analytical for-mula representing Z(f) for all studied frequencies. For
studying a specific frequency, a simple solution is to perform a time domain simulation on the power elec-tronic device in order to obtain the impedance re-sponse. For example, at ripple control frequency of 175 Hz, the equivalent impedance at input of a recti-fier changes with the type of the rectifier structure, DC bus filter, AC filter and rectifier control techniques. A time domain simulation shows that for a 400 V, 250 kV A diode rectifier used in a variable-speed drive, the impedance at 175 Hz (Z175) is mainly determined by the DC bus type: Z175 = (0.1 ~ 0.9) × Z50 for a capaci-tive DC filter, and Z175 = (0.8 ~ 3) × Z50 for an induc-tive DC filter (Z50 is the rated fundament equivalent impedance) [2].
2.3 HVDC Link Frequency Domain Model
An High V oltage DC link (HVDC) model has been studied in frequency domain and a plug & play HVDC component has been created by using studied harmonic source models. A general HVDC link is composed of two power electronic devices (converter stations): one works as rectifier and another as inverter (or generator), see Fig. 4.
Fig. 4 HVDC Link Structure between Two Grids
The studied HVDC component is decomposed in Fig. 5. Each side of HVDC is composed of a three-
phase controlled harmonic current source with 74 harmonic number, an impedance and a regulator for power regulation. Two current sources are independent and each current source is synchronized with con-nected fundamental voltage after fundamental fre-quency load flow. This model can simulate independ-ently power quality and electromechanical transient phenomena of each side of HVDC link such as har-monic, reactive power, voltage fluctuation, etc. One case study below will show the application of pro-posed model.
Fig. 5 Structure of Frequency Domain HVDC Model
2.4 Power Quality Meter Modelling
For a power quality software, PQ meter algorithm is also a key component to think about. A general power quality software that gives just the harmonic spectrum is not enough for a site engineer to perform grid disturbance assessment in a short delay. In fact, the software needs to spend a lot of time in post-data processing in order to get necessary PQ values such as inter-harmonic, harmonic grouping, flicker, unbalance, voltage sag, etc. In most commercialised time domain software, there is no integrated power quality meter. Users have to create tool box in post data processing in order to perform grid PQ assessment. Generally, this step is time-consuming.
Simulation tools for grid power quality assess-ment should include at least a build-in total harmonic distortion and individual harmonic computation unit. An advanced power quality simulation tool has to in-tegrate other disturbance metering such as in-ter-harmonic, harmonic grouping, IEC flicker meter, etc [4−5]. Tab. 6 gives some electric measurements to be integrated into power quality simulation tools.
An advanced power quality meter algorithm has been studied and implanted in our power quality
