Advanced Power Electronics in Inverter Applications

Leo Casey, Milan IlicSatcon

2010 IEEE Conference on Advanced Energy, NY November 8th and 9th

Faster, Smarter, Controllable, Greener, Distributed, Grid

the Key is?-Power Electronics-

Outline

Greener – Renewables (solar emphasis)Grid – overview of challengesVision – Faster, Smarter interfacesOvercoming Technical Obstacles –

Controllable, Distributed, Renewables **Storage – The holy grail, but, how essential

and on what time scales? *

World Energy Consumption 500 (495) Quads•Today we get 18% from renewables•Incident radiation is 0.17 exawatts (~2.1017W)•Every 6 seconds get 1 exaJoule•3000 seconds get 500 EJ = 500 Quads

•So plenty of energy, BUT,Need to harness it, move it, and store it efficiently and cost effectively (what role electronics?) 

The Real Primary Energy Source is (or was) Radiation

United States used 94.5 quads in 2009 down from peakof 101.7 quads out of 495.2 quads in 2007 (International 

Energy Outlook 2010, EIA‐DOE)• Exajoule (EJ): 1 EJ = 1018 J• Quadrillion Btu(quad): 1 quad = 1015 Btu = 1.055 EJ• Terawatt‐year (TWyr): 1 TWyr = 8.76 x 1012 kWh = 31.54 EJ = 

29.89 quad

Electricity ~ 40% of Energy Economy1 km x 1 km = 106m2, 109W, 2,000+hrs0.2 (20% efficiency)=1.44+ 1015J 

100km by 100km would yield the 14 quadswe use today.

100 miles by 100 miles would yield 35 quads,which in an all electric world would be equal to 100 quads we use today  *

Electrical Energy

Modern Grid IssuesUtility Concerns About The Impact Of High Penetration DG on MV Feeders

• Fluctuating real power output from renewable sources– Increased switching operations for line regulators, tap changers, capacitors– Flicker due to fluctuating voltage– Transient voltage on sudden trip of DG station

• Effect of new generation and reversible power flow– Protective relay settings and operation– Conductor and equipment loading– Islanding of DG with residual load connected– Auto‐reclosing feeder breaker onto energized DG

Generation Connected thru Electronics can be Transformative – BUT different Paradigm

• Readily Controllable (remotely)• Supply Real Power, P, Dynamically• Reactive power, Q, (|P + jQ| < SINV), Dynamically• Active Damping (stabilizing)• Controllable or Synthetic Inertia• Fault Clearing• Rapid Dynamics• Unbalanced• Non‐linear sourcing• Active Filtering• Harmonic cancellation

• Also, high speed series devices would Limit faults and enable robust interactive microgrids

Southern Control AreaGenerator UF coordination curve

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Time (Cycles)

Freq

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z)

Trip Point per IEEE 1547

Trip Point of Turbines

A Future Grid Vision•Faster Protection & Control

•More robust•More renewable

•More efficient•More DC systems

•More ElectronicsIN ALL LAYERS

•Higher PQ•More Grids

•Improved CF•More distributed

•Reconfigurable•Faster Recovery

Power Electronics are  Grid Ready

1. Cost (30% drop in Utility scale solar PV in last 18 months)– Panels– Inverters, BOS– O&M

2. Controllability3. Intermittency (Variability/Capacity Factor/Capacity Value)4. Utility Industry Acceptance/Adoption

– Scale– Performance– Standards– Familiarity (interconnect studies, protection studies)

Barriers to High Penetration of Renewables

PV Module costs are expected to continue down experience curve

• Continued reductions from $1.60/W today to less than $1.30/W, are projected due to:

– Improved economies of scale

– Improved efficiency– Manufacturing yield– Operational 

excellence as manufacturing volume increases 

Weapons against local effects of Intermittency•Maintain real power with storage•Forecasting•Measurement coupled with ramping and regulation (auto)•Ramp rates (ramp rate control using storage)•Fast VARS (*)•Hybrid power plants•Curtailment of renewable (or other)

Averaging‐in space‐in timeWorks.  Transmission connected renewables utilize this.  But what of local effects?  Voltage change due to sudden power change on distribution feeder

Intermittency (storage?)

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Irradiance vs. Time (Boston, MA) July 20, 2010

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Simulated PV and Inverter Outputwith moderate storage (20%)

• PV input estimated power rate‐of‐change (light line)– assuming fast MPPT

• Inverter estimated power rate‐of‐change (heavy line)– Less than 5% of PV rate‐of‐change

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Modern Grid IssuesPV Inverter Simulation Shows Fast VARs* Step response And Effect On Local Bus Voltage

Increasing Penetration of Renewables - examplesDenmark•18% of Electrical Energy•New Control Regs.•European Grid•Curtailment

New Zealand•76% + renewables•Hydro, geothermal, wind

Lanai•20% PV in diesel grid•no storage but heavily curtailed•30% of peak with storage (coming)

Studies, NREL east and west, 10-30%, no storage, ramp CoalEU15, DisPower Study, 15-35%

Micro or Mini Grids – Stable Island & SDS Enable UPS-PQUtility Grid Connection optional – Tactical Micro Grid

•Renewables plus back-up generation plus storage plus SDS•UPS quality power•Dynamic balance of load and generation (plus storage)

3 3

UTILITY GRID

FACILITY LOADS1000 kW MAX

CRITICAL LOADS

21 kV, 60 Hz

21 kV, 60 Hz

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480 V, 60 Hz

480

210003

3

3

1000 kWmax

500 kWmax

500 kWmax

EXISTING FUEL CELL

EXISTING PV ARRAY

NEW ENERGY STORAGE

FACILITY LOADS1000 KW MAX

CRITICAL LOADS

UTILITYGRID

STATIC DISCONNECT SWITCH (SDS)

ISLAND GRID

ENERGY STORAGE UNITCONTROLS VOLTAGE AND

FREQUENCY IN ISLAND MODE

3 3

UTILITY GRID

FACILITY LOADS1000 kW MAX

CRITICAL LOADS

21 kV, 60 Hz

21 kV, 60 Hz

3

480 V, 60 Hz

480

210003

3

3

1000 kWmax

500 kWmax

500 kWmax

EXISTING FUEL CELL

EXISTING PV ARRAY

NEW ENERGY STORAGE

FACILITY LOADS1000 KW MAX

CRITICAL LOADS

UTILITYGRID

STATIC DISCONNECT SWITCH (SDS)

ISLAND GRID

ENERGY STORAGE UNITCONTROLS VOLTAGE AND

FREQUENCY IN ISLAND MODE

3 3

UTILITY GRID

FACILITY LOADS1000 kW MAX

CRITICAL LOADS

480 , 60 Hz

480 , 60 Hz

3

480 V, 60 Hz

480

21000

3

3

RENEWABLE

DIESEL GENSETS (TQGs)

NEW ENERGY STORAGE

MICROGRID LOADS

UTILITYGRID IF

PRESENT

STATIC DISCONNECT

SWITCH (SDS)

TACTICAL MICROGRID

ENERGY STORAGE UNITCONTROLS VOLTAGE AND

FREQUENCY IN MICROGRID

G D

3 3

UTILITY GRID

3 3

UTILITY GRID

FACILITY LOADS1000 kW MAX

CRITICAL LOADS

480 , 60 Hz

480 , 60 Hz

FACILITY LOADS1000 kW MAX

CRITICAL LOADS

480 , 60 Hz

480 , 60 Hz

3

480 V, 60 Hz

480

21000

33

33

RENEWABLE

DIESEL GENSETS (TQGs)

NEW ENERGY STORAGE

MICROGRID LOADS

UTILITYGRID IF

PRESENT

STATIC DISCONNECT

SWITCH (SDS)

TACTICAL MICROGRID

ENERGY STORAGE UNITCONTROLS VOLTAGE AND

FREQUENCY IN MICROGRID

G DENERGY STORAGE CONVERTER OUTPUT CURRENT

FUEL CELL CONVERTER OUTPUT CURRENT

ISLAND GRID VOLTAGE

ISLANDVOLTAGE

MAINTAINED

GRID CURRENTS THROUGH INTER-TIE

UTILITY GRID (480 V) VOLTAGES (L-N)

FUEL CELLOUTPUT

MAINTAINED

LOAD SUDDENLY INCREASED

CHARGINGDISCHARGING

ENERGY STORAGE CONVERTER OUTPUT CURRENT

FUEL CELL CONVERTER OUTPUT CURRENT

ISLAND GRID VOLTAGE

ISLANDVOLTAGE

MAINTAINED

GRID CURRENTS THROUGH INTER-TIE

UTILITY GRID (480 V) VOLTAGES (L-N)

FUEL CELLOUTPUT

MAINTAINED

LOAD SUDDENLY INCREASED

CHARGINGDISCHARGING

ENERGY STORAGE CONVERTER OUTPUT CURRENT

FUEL CELL CONVERTER OUTPUT CURRENT

ISLAND GRID VOLTAGE

ISLANDVOLTAGE

MAINTAINED

GRID CURRENTS THROUGH INTER-TIE

UTILITY GRID (480 V) VOLTAGES (L-N)

FAULT

SDS CLOSED

SDS OPENED

DISCHARGINGCHARGING

CHARGING

FUEL CELLOUTPUT

MAINTAINED

ENERGY STORAGE CONVERTER OUTPUT CURRENT

FUEL CELL CONVERTER OUTPUT CURRENT

ISLAND GRID VOLTAGE

ISLANDVOLTAGE

MAINTAINED

GRID CURRENTS THROUGH INTER-TIE

UTILITY GRID (480 V) VOLTAGES (L-N)

FAULT

SDS CLOSED

SDS OPENED

DISCHARGINGCHARGING

CHARGING

FUEL CELLOUTPUT

MAINTAINED

Grid –”Load Following”

Controllability -- Lessons from Lana’i

• Nominal 4MW load• “Diesel” grid• 1.5MW Solar Farm• 12 SatCon, 135kW Inverters, 12 

SunPower tracking arrays• 10% of Lana’i annual power demand• 30% Supply during peak solar hours 

(4MW)

• CONCERNS: potentially destabilizing AND limits of Lana’i grid are extremely wide so non‐UL1741 non IEEE1547 inverter required, and under Utility Control1. Remote control of Real Power, also 

termed curtailment2. Remote control of Power Factor3. Grid disturbance ride‐thru capability4. Ramp rate limits and control (dP/dt)

Summary• Faster, Smarter, Controllable, Greener, Distributed Grid

• the real Key to enhanced power quality and enhanced control is -Power Electronics- (moderate bandwidthrequired)

• Power Electronics are the natural interface for renewables and provided many of the tools to mitigate the problems/challenges of renewables

• No one single solution. There are many components to the grid of the future, BUT, the technical challenges are tractable.