Regulations and Performance Measures of Grid Converters

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

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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 einer netzparalellen Eigenerzeugungsanlage und dem offentlichen Niederspannungsnetz [6] 3/30

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 offentlichen Niederspannungsnetz"; 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  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: <0.2 sec (Austria)

 Limits for DC Injection into AC Grid: < 1% (Japan), 0.5% (USA), 5mA (UK)  Limits regarding high-frequency capacitive leakage currents [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 2001.5/30

Regulations for Grid-Connected PV Inverters CE

yes

EMC guideline

EMC 89/336/EEG

Emission

EN 50081-1

Harmonisation

EN 61000-3-2

Immunity

EN 50082-2

LV guideline

LV 73/23/EEC

Safety

EN 60950

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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

DC PV

DC DC

iPV

Grid

SMPS AC

uPV iPV,ref uDC Microcontroller with PWM and ADC

ugrid

igrid

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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 Sunnuy boy 2400

Tauro PRM3

Sun Profi 2400

Ingecon Sun 2500

Solete 2500

Manufacturer Nominal Power (W) Voltage range (VDC) Efficiency (%)

SMA 1500 150-300 ≧93

Enertron 2500 300-250 Max: 94

< 4 with P0 > 0.5 and THDv < 2%

Sun Power 1700 252-450 90-94 With P0> 0.15 3.0

Ingeteam 2500 125-450 Max: 94

THD1(%)

Atersa 1900 42-66 Max: 93 89 with P0=0.8 < 3.5 with P0=0.6 and THDv < 2%

< 4.0

< 3 with P0=1

(h2 ) 2  (h3 ) 2    ( hn ) 2 THD   100% h1

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.

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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 DCAC 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]: European Efficiency is defined as:  EU  0 .03 5  0 .0610  0 .13 20  0 . 1 30  0 .48 50  0 .2100

CEC (California Energy Commission) Efficiency is defined as:  EU  0 .00 5  0 .0410  0 .05 20  0 .12 30  0 .2150  0 .53 75  0 .05100

[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. 12/30

Efficiency is(t) vs(t)

io(t)

Power Supply

vo(t) LOAD

Instantaneous Power = p(t)  v(t)i(t) Average Power = PAVG

Efficiency ( ) =

1 t0  T =  p(t)dt  vAVGiAVG t T 0

Po(AVG) Ps(AVG)

1 =T 1 T



t0  T



t0  T

t0 t0

vo (t)io (t)dt vs (t)is (t)dt 13/30

European Efficiency – A Weighted Efficiency 84 VIN = 85V 81

Efficiency [%]

78

VIN = 110V

75 VIN = 140V 72 69 66 63 60 0

20

40

60

80

100 105

Output Power [%]

European Efficiency is defined as:  EU  0 .03 5  0 .0610  0 .13 20  0 . 1 30  0 .48 50  0 .2100 CEC (California Energy Commission) Efficiency is defined as:  EU  0 .00 5  0 .0410  0 .05 20  0 .12 30  0 .2150  0 .53 75  0 .05100

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Efficiency Measurement of PV Inverters 100

Efficiency, %

95 90 85 80 300 Vdc

75 70 0%

345 Vdc 480 Vdc

10%

20%

30%

40%

50%

60%

70%

80%

90%

100%

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

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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.

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 der Elektrizitätswirtschaft 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 17/30 power range, to current networks,” German Patent DE19 732 218 C1, Mar. 1999.

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. 18/30

Limit of Injected DC Current IEC61727

DC current injection

< 1% of rated output current

VDE0126-1-1

IEEE1547

EN61000-3-2

IEEE 929-2000

< 1A

< 0.5% of rated output current

< 0.22A corresponds to a 50W halfwave rectifier

< 0.5% of rated output current

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.

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 19/30

Limits for DC Injection into AC Grid    

<0.5% (USA) [1] < 1% (Japan) [2] 5mA (UK) [3] 1A (Germany) [4]

VPV PV Array

Idc may exist due to unbalance!

EMI

Igrid

Filter

[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: 20/30 VDE Press, 2006, 9 pp.

Leakage Currents to Ground Photovoltaic array

Inverter A

EMC FILTER DC

B

EMC FILTER AC

Vg

Stray capacitance Ground

icm

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;

Switching Noise of Inverter System

 Differential-Mode Noise: reduced by LC-filter  Common-Mode Noise: its effect depends on parasitic values 22/30

Monitoring of Leakage Current (VDE 0126-1-1) Leakage current jumps and their corresponding disconnection times for VDE 0126-1-1 Leakage current jump value

Disconnection time

(mA)

(s)

30

0.3

60

0.15

100

0.04

 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. 23/30

Earthing System for Electric Power Distribution TN Networks

TN-S Networks

TT Networks IT Networks

TN-C Networks

TN-C-S Networks

Input Voltage Levels

PV Array Levels for a Given Grid Voltage and Topology Ratio

(1000 W/m2 and 20ºC) Max. Grid Peak Voltage

Topology specific ratio

Min. MPP voltage

Max. MPP Voltage

Max. Array Voltage

Full-Bridge

358

1

376

537

751

Half-Bridge

358

2

751

1073

1503

Type

(100 W/m2 and 50ºC)

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 28/30

Define and Check of Specifications Interfaces and Parameters PV

Grid

Specified value

Obtained value

Observed?

Nominal PV module power

160 W

Min. 150 W

(Yes)

Maximal open circuit voltage

50 V

Min. 42 V

(Yes)

Maximum power point range

23 V to 38 V

20 V to 38 V

Yes

Ripple at normal power (LF-amplitude, and HF peak-peak)

4.1 V / 0.5 V

0.06V to 0.7 V

Yes / No

Maximum short circuit current

8A

Min. 6.4 V

(Yes)

MPP current range

0-7.2 A

Saturates at 5 A

No

Nominal grid voltage

230 V ± 10%

230V±10%

Yes

Nominal grid frequency

49.5 Hz to 50.5 Hz

Not tested for.

TBD

Non islanding operating range, voltage

195 V to 253 V

197 V to 255 V

Yes

Non islanding operating range, frequency

48 Hz to 52 Hz

Not tested for.

TBD

Standby losses

-

0.5 W

-

Current harmonics

EN61000-3-2A

-

Yes

82/308/CDV

-

No

Power factor at 50% of nominal power

0.95

0.98

Yes

Inrush current and voltage

< 13 A, <450 V

0.5 A / 350 V

Yes

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References: Distributed Power Generation [1] [2] [3] [4] [5] [6] [7]

[8] [9]

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. David L. King, Sigifredo Gonzalez, Gary M. Galbraith, and William E. Boyson, Performance Model for Grid-Connected Photovoltaic Inverters, Sandia Report, Sept. 2007. 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. Blaabjerg, F., Guerrero, J.M., "Smart grid and renewable energy systems", International Conference on Electrical Machines and Systems (ICEMS), pp. 1–10, 2011. 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. 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. 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. 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. 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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Smart Power Processing for Energy Saving

Thanks for your kind attention! Knowledge, Innovation, and Education

電力電子系統與晶片實驗室 Power Electronic Systems & Chips Lab.


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Any Questions ??? Questions inspire effective learning!

學習的關鍵

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電力電子系統與晶片實驗室 Power Electronic Systems & Chips Lab.


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Regulations and Performance Measures of Grid Converters

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