2013-01-01：【技術專題】Regulations and...

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電力電子系統與晶片實驗室Power Electronic Systems & Chips Lab.交通大學 • 電機與控制工程研究所

Power Electronic Systems & Chips Lab., NCTU, Taiwan

Regulations and Performance Measures of Grid Converters

鄒應嶼教授

國立交通大學電機與控制工程研究所

2013年1月1日

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Grid Requirements

Total Harmonic Distortion (THD) and individual harmonic current levels

Power factor (PF) Level of injected DC current Voltage and frequency range for normal operation Detection of islanding operation (islanding or non-islanding

functions) Automatic reconnection and synchronizing Grounding of the system

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International Standards for Grid Converters

IEC 60364-7-712:2005. Electrical Installations of Buildings. Part 7: requirements for special installations or locations. Section 712: Photovoltaic power supply systems. [1]

IEEE 1547.1-2005 IEEE Standard Conformance Test Procedures for Equipment Interconnecting Distributed Resources with Electric Power Systems. [2]

UL 1741. Standard for Safety Inverters, Converters, Controllers and Interconnection System Equipment for Use with Distributed Energy Resources. 7th May 1999, updated in 2005.

IEEE 929-2000. Recommended Practice for Utility Interface of Photovoltaic (PV) Systems. [3]

IEC 61727 (1995-06) Photovoltaic Systems – Characteristics of the Utility Interface. [4]

DS/EN 61000-3-2 (2001) EMC, Limits for harmonic emissions (equipment input current up to and including 16 A per phase) [5]

VDE0126-1-1 (2006) Selbsstattige Schaltschtelle zwischen einernetzparalellen Eigenerzeugungsanlage und dem offentlichenNiederspannungsnetz [6]

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International Standards for Grid Converters

[1] Danish Standard Association; "DS/HD 60364-7-712 Electrical installations of buildings – Part 7-712: Requirements for special installations or locations – Solar photovoltaic (PV) power supply systems"; 2005.

[2] IEEE Std 1547.1-2005. IEEE Standard Conformance Test Procedures for Equipment Interconnecting Distributed Resources with Electric Power Systems.

[3] IEEE 929-2000. Recommended Practice for Utility Interface of Photovoltaic (PV) Systems. [4] IEC 61727; "Characteristics of the utility interface for photovoltaic (PV) systems"; International Electrotechnical

Commission, IEC 61727, 2002. [5] BS EN 61000-3-2. (2001) Electromagnetic Compatibility - Part 3-2: Limits - Limits for harmonic current

emmisions (equipment input current up to and including 16A per phase). [6] DKE Deutsche Kommission Elektrotechnik Electronik Informationstechnik im DIN un VDE; "Selbsttatige

Freischaltstelle zwischen einer netzparallelen Eigenerzeugungsanlage und dem offentlichenNiederspannungsnetz"; DIN VDE 0126-1-1, 2006.

REF: David L. King, Sigifredo Gonzalez, Gary M. Galbraith, and William E. Boyson, Performance Model for Grid-Connected Photovoltaic Inverters, Sandia Report, Sept. 2007.

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Regulations on Inverters for Photovoltaic Applications

[1] Utility aspects of grid connected photovoltaic power systems, International energy agency – photovoltaic power systems programme, IEA PVPS T5-01: 1998, 1998, www.iea-pvps.org.

[2] IEEE Standard for interconnecting distributed resources with electric power systems, IEEE std. 1547, 2003. [3] Grid-connected photovoltaic power systems: Status of existing guidelines and regulations in selected IEA member

countries, International energy agency – photovoltaic power systems programme, IEA PVPS V-1-03, 1998, www.iea-pvps.org.

[4] E.D. Spooner and G. Harbidge, "Review of international standards for grid connected photovoltaic systems," Renewable Energy vol. 22, pp. 235-239, 2001.

[5] PV System Installation and Grid-Interconnection Guidelines in Selected IEA countries, Task 5, November 2001.

Line Current Harmonics: EN61000-3-2, IEEE std. 1547 Power Factor: >0.85 (Japan) Islanding Protection: Both active and passive methods should be installed

according to the guideline (Japan). AC voltage operating range: 100V +20/-20%(Maximum) in case of 100V system, 200V +20/-

20%(Maximum) in case of 200V system (Japan)

AC frequency operating range: 50Hz +1,5/-1,5Hz(Maximum), 60Hz +1,8/-1.8Hz(Maximum), Reaction time: 0,5 to 2 seconds (Japan)

Reaction Time: AC frequency operating range:

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Regulations for Grid-Connected PV Inverters

EN 60950SafetyLV 73/23/EECLV guidelineEN 50082-2ImmunityEN 61000-3-2Harmonisation

EN 50081-1EmissionEMC 89/336/EEGEMC guidelineyesCE

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Testing the Inverter

European Efficiency Line Current THD and Power Factor Islanding Protection MPPT Response Time & Efficiency HF Capacitive Leakage Currents

PV SMPSDC

DC

DC

ACGrid

Microcontroller with PWM and ADCiPV uPV iPV,ref uDC igrid

ugrid

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Current Harmonics

Most countries have agreed upon the EN61000-3-2-A standard for current harmonics. However, Japan and the US demands a current Total Harmonic Distortion (THD) below 5 %, and any harmonics below 2 % of the fundamental current.

EN 61000-3-2-A harmonic current limits

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Line Current THD of Several PV Inverters

Dpto. de Fisica Aplicada II, Universidad de Ma’laga, and Campus de Teatinos, “Analysis of the current total harmonic distortion for different single-phase inverters for grid-connected pv-systems," Solar Energy Materials & Solar Cells 87, pp. 529–540, 2005.

Enertron2500300-250Max: 94

< 3 withP0=1

Solete 2500

Ingeteam2500125-450Max: 94

< 4.0

IngeconSun 2500

Sun Power1700252-45090-94With P0> 0.153.0

Sun Profi 2400

Atersa190042-66Max: 9389 with P0=0.8< 3.5 withP0=0.6 and THDv < 2%

Tauro PRM3

SMA1500150-300≧93

< 4 withP0 > 0.5 and THDv < 2%

Sunnuy boy2400

ManufacturerNominal Power (W)Voltage range (VDC)Efficiency (%)

THD1(%)

%100)()()(

1

223

22

hhhh

THD n

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Power Factor

The Power Factor (PF) should be close to unity in order not to generate or consume reactive power. Denmark requires a PF better than 0.95 for 50% of nominal power.

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Inrush Current

During fault situations on the medium or high voltage overhead lines, these lines may be switched out in order to clear the fault. This causes a sudden voltage drop at the grid and hence the inverter. The inverter must cease to energize the grid if this happens. Disabling the semiconductors in the output circuit is sufficient. When the voltage restores or the inverter is connected to the grid for the first time, the current into the inverter must not reach damaging values.

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Efficiency of Grid Converters

PV inverters usually have two efficiencies reported by the manufacturer: the highest DC-AC conversion efficiency, also called as “Maximum Efficiency”, and a weighted efficiency dependent on efficiencies at different irradiation levels, called “European efficiency”, based on the formula below [1]:

[1] H. Haberlin, Ch. Liebi, and Ch. Beutler; "Inverters for grid connected PV-Systems: Test results of some new inverters and latest reliability data of the most popular inverters in Switzerland"; in 14th European Photovoltaic Solar Energy Conference, 30 Jun. - 4 Jul. 1997.

[2] H. Haberlin, L. Borgna, M. Kaempfer, and U. Zwahlen; "New tests at grid connected PV inverters: Overview over test results and measured values of total efficiency"; in 21st European Photovoltaic Solar Energy Conference, 4-8 Sep. 2006

[3] M. Meinhardt; "Improvement of Photovoltaic Inverter Efficiency – Targets, Methods, Limits"; SMA Technologie AG, 2005.

European Efficiency is defined as:

100503020105 2.048.01.013.006.003.0 EU

CEC (California Energy Commission) Efficiency is defined as:

10075503020105 05.053.021.012.005.004.000.0 EU

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Efficiency

v(t)i(t)p(t)=Power ousInstantane

AVGAVG

Tt

tAVGivp(t)dt

T1=P=Power Average 0

0

Tt

t ss

Tt

t oo

s(AVG)

o(AVG)

0

0

0

0

(t)dt(t)ivT1

(t)dt(t)ivT1

=PP

= )( Efficiency

Power Supply LOADvo(t)

io(t)

vs(t)

is(t)

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European Efficiency – A Weighted Efficiency

European Efficiency is defined as:100503020105 2.048.01.013.006.003.0 EU

Output Power [%]

Effic

ienc

y [%

]

0 20 40 60 80 10060

63

66

69

72

75

78

81

84VIN = 85V

VIN = 140V

VIN = 110V

105

CEC (California Energy Commission) Efficiency is defined as:10075503020105 05.053.021.012.005.004.000.0 EU

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Efficiency Measurement of PV Inverters

Inverter performance measurements conducted by a nationally recognized testing laboratory and documented by the CEC (California Energy Commission).

10%0% 20% 30% 40% 50% 60% 70% 80% 90% 100%70

75

80

85

90

95

100

% of Rated Output Power

Effic

iency

,%

300 Vdc

345 Vdc480 Vdc

Measured Performance 2.5-kW Inverter, 13-Day Period

“Field test” results for a 2.5-kW Solectria PVI2500 inverter recorded during system operation at Sandia, showing both inverter efficiency and relationship between ac-power and dc-power over an extended 13-day test period, including both clear and cloudy days.

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Galvanic Isolation Requirement for PV Inverters

Germany: Not required for low-voltage grid applications [1]. Spain and Great Britain: Required for all applications [2]. Italy: Required for Power > 20 kW [3] US: Required Grounding of one of the panel outputs [4] ,

which leaves few alternatives for the use of transformerless topologies, aside from a few specially developed circuits [5], [6].

[1] Eigenerzeugungsanlagen am Niederspannungsnetz—Richtlinie für An-schluß und Parallelbetrieb von Eigenerzeugungsanlagen am Niederspan-nungsnetz (Energy Generation Equipment Connected to the Low Voltage Grid—Guideline for the Connection and Parallel Operation of Energy Generation Equipment on Low Voltage Grid), 4th ed. Berlin, Germany: Verband derElektrizitätswirtschaft VDEW e. V., 2001.

[2] M. Haag, “Auswirkungen neuer modultechniken und marktbeson-derheiten auf die technik von PV-Wechselrichtern,” in Proc. ETG-Fachtagung Leistungselektronische Systeme für die dezentrale Stromerzeugung. Berlin, Germany: VDE Press, 2008.

[3] DK-5940 Criteri di Allacciamento di Impianti di Produzione alla rete BT di ENEL Distribuzione (Criteria for the Connection of Generating Appliances on the Low Voltage Grid of the ENEL Distributor), Jun. 2006.

[4] M. W. Earley, J. S. Sargent, J. V. Sheehan, and J. M. Caloggero, National Electrical Code Handbook, 10th ed. Long Beach, CA: Nat. Fire Protection Assoc., 2005, pp. 1031–1032.

[5] D. Karschny, “Wechselrichter,” German Patent DE19 642 522 C1, Apr. 1998.[6] D. Schekulin, “Transformerless ac inverter circuit for coupling photovoltaic systems or wind generator systems, especially in the low

power range, to current networks,” German Patent DE19 732 218 C1, Mar. 1999.

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Grounding

Equipment ground is required in all countries. System ground is required in some countries for systems with voltages over 50 V (PV module open circuit voltage) [1]. Equipment ground involves that all metallic surfaces, etc., are grounded.

Grounding is necessary when considering maintenance safety, lightning protection, electromagnetic coupling (EMC) diminishment, and electromagnetic pulses (EMP) protection.

Above certain dc voltage level, e.g., 100 V, the DG resource is required earth-grounded.

A single-phase inverter with line-to-neutral grid interconnection also has one terminal to be grounded. In such a case, the DG inverter has to operate normally under the “dual-grounding” circumstance.

Dual Grounding: Both the DG resource and the grid converter must be grounded.

[1] Utility aspects of grid connected photovoltaic power systems, International energy agency – photovoltaic power systems programme, IEA PVPS T5-01: 1998, 1998, www.iea-pvps.org.

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Limit of Injected DC Current

REF: S. Kjaer, J. Pedersen, and F. Blaabjerg; "A review of single-phase grid connected inverters for photovoltaic modules"; IEEE Transactions on Industry Applications, vol. 41, no. 5, Sep. 2005, pp. 1292- 1306

Note: The VDE 0126-1-1 standard states, that in the case of a DC current injection greater than 1 A, disconnection is mandatory in 0.2 s. The other standards do not mention a requirement for disconnection time.

< 0.5% of rated output current

IEEE 929-2000

< 0.22A corresponds to

a 50W half-wave rectifier

EN61000-3-2

< 0.5% of rated output

current

IEEE1547

< 1A

VDE0126-1-1

< 1% of rated output current

IEC61727

DC currentinjection

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Limits for DC Injection into AC Grid

[1] IEEE Recomended Practice for Utility Interface of Photovoltaic (PV) Systems, IEEE Std. 929-2000, Apr. 2003.[2] Japan Ind. Standards Assoc., Technical Guideline for the Grid Interconnection of Dispersed Power Generating Systems, Japan,

2001.[3] Engineering Recommendation, United Kingdom ER G83/1 Recommendations for the Connection of Small-Scale Embedded

Generations (up to 16 A per phase) in Parallel With Public Low-Voltage Distribution Network, Sep. 2003. [4] DIN V VDE V 0126-1-1 Automatic Disconnection Device Between a Generator and the Public Low-Voltage Grid. Berlin, Germany:

VDE Press, 2006, 9 pp.

Leakage Currents to Ground

According to the German standard VDE 0126-1-1, there are three different currents that have to be monitored:

Ground Fault current, which happens in case of insulation failure when the current flows through the ground wire;

Fault current, which represents the sum of the instantaneous values of the main currents, that in normal conditions leads to zero;

Leakage Ground currents, which is the result of potential variations of capacitive coupled parasitic elements;

Vg

Photovoltaicarray

Inverter

EMC FILTER

AC

EMC FILTER

DC

A

B

GroundStray capacitance

icm

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Switching Noise of Inverter System

Differential-Mode Noise: reduced by LC-filter Common-Mode Noise: its effect depends on parasitic values

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Monitoring of Leakage Current (VDE 0126-1-1)

Leakage current jumps and their corresponding disconnection times for VDE 0126-1-1

The monitoring is typically done using a Residual Current Monitoring Unit (RCMU), which measures the fault and leakage current of the whole system. The standard states that disconnection from the grid is necessary within 0.3 s in case the leakage current is higher than 300 mA.

Furthermore, it recommends a table detailing the Root Mean Square (RMS) value of the fault/leakage current jumps and their respective disconnection times, as detailed in above Table.

0.04

0.15

0.3

Disconnection time

(s)

100

60

30

Leakage current jump value

(mA)

Earthing System for Electric Power Distribution

TN Networks

TT Networks

IT Networks

TN-S Networks TN-C Networks TN-C-S Networks

Input Voltage Levels(1000 W/m2 and 20ºC)

(100 W/m2 and 50ºC)

PV Array Levels for a Given Grid Voltage and Topology Ratio

1503751

Max.ArrayVoltage

1073537

Max.MPP Voltage

751376

Min.MPP voltage

21

Topologyspecificratio

358358

Max. Grid PeakVoltage

Half-BridgeFull-Bridge

Type

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Islanding Protection

Islanding is the continued operation of the inverter when the grid has been removed by purpose, by accident, or by damage. In other words, the grid has been removed from the inverter, which then only supplies local loads. The inverter must be able to detect an islanding situation, and take appropriated measure in order to protect persons and equipment.

Limits for detection of islanding operation

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Islanding Protection Compliance

Collection of international standards, which the inverter must fulfill.

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Test Plan

Static Power Efficiency Power Factor Current Harmonics MPP Tracking Efficiency. Standby Losses Disconnections of AC Power Line Disconnections of DC Power Line AC Voltage Limits Frequency Limits Response to Abnormal Utility Conditions Field Test

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Define and Check of Specifications

NoSaturates at 5 A 0-7.2 AMPP current range

(Yes)Min. 6.4 V8 AMaximum short circuit current

Yes0.5 A / 350 V< 13 A,

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References: Distributed Power Generation

[1] A. Timbus, M. Liserre, R. Teodorescu, P. Rodriguez, and F. Blaabjerg, "Evaluation of Current Controllers for Distributed Power Generation Systems," IEEE Transactions on Power Electronics, vol. 24, no. 3, pp. 654-664, March 2009.

[2] David L. King, Sigifredo Gonzalez, Gary M. Galbraith, and William E. Boyson, Performance Model for Grid-Connected Photovoltaic Inverters, Sandia Report, Sept. 2007.

[3] A. F. Zobaa and C. Cecati, "A comprehensive review on distributed power generation," International Symposium on Power Electronics, Electrical Drives, Automation and Motion (SPEEDAM), pp.514-518, 23-26 May 2006.

[4] Blaabjerg, F., Guerrero, J.M., "Smart grid and renewable energy systems", International Conference on Electrical Machines and Systems (ICEMS), pp. 1–10, 2011.

[5] T. Suntio, J. Puukko, L. Nousiainen, T. Messo, and J. Huusari, "Change of paradigm in power electronic converters used in renewable energy applications", IEEE 33rd International Telecommunications Energy Conference (INTELEC), pp. 1-9, 2011.

[6] Mohamed, Y.A.-R.I., El-Saadany, E.F., "A Robust Natural-Frame-Based Interfacing Scheme for Grid-Connected Distributed Generation Inverters", Energy Conversion, IEEE Transactions on, On page(s): 728 - 736 Volume: 26, Issue: 3, Sept. 2011.

[7] Reyes, M., Rodriguez, P., Vazquez, S., Luna, A., Teodorescu, R., Carrasco, J.M., "Enhanced Decoupled Double Synchronous Reference Frame Current Controller for Unbalanced Grid-Voltage Conditions", IEEE Transactions on Power Electronics, pp. 3934-3943, vol. 27, no. 9, Sept. 2012.

[8] Qing-Chang Zhong, Hornik, T., "Cascaded Current–Voltage Control to Improve the Power Quality for a Grid-Connected Inverter With a Local Load", Industrial Electronics, IEEE Transactions on, On page(s): 1344 - 1355 Volume: 60, Issue: 4, April 2013.

[9] A. Kahrobaeian and Mohamed Y.A.-R.I. "Interactive Distributed Generation Interface for Flexible Micro-Grid Operation in Smart Distribution Systems", IEEE Transactions on Sustainable Energy, pp. 295 – 305, vol. 3, no. 2, April 2012.

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Knowledge, Innovation, and Education

Smart Power Processing for Energy Saving


Thanks for your kind attention!


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Questions inspire effective learning!

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2013-01-01：【技術專題】Regulations and...

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