power conversion systems for microgrids - e2rg
TRANSCRIPT
Power Conversion
Systems for
Microgrids
Burak Ozpineci
Yan Xu
Tom King
Tom Rizy
Oak Ridge National Laboratory
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Utility-Scale Power Electronics Needs
Devices
Modules Converters
System
Device Issues
● Reliability
● Low cost
● Higher efficiency
●Wide bandgap
materials
● Higher switching
frequency
●High temperature
operation
Module Issues
● Thermal
Management
● High Temperature
Packaging
● Low cost
Converter Issues
● Modularity
● Availability
● Low maintenance
● Low cost
● Higher Efficiency
System Issues
● Stability
● Reliability
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Distributed Energy and Storage (DE/DS)
Power Conversion Technologies
DCDC
DCDC
DCAC
ACDC
DCAC
For this discussion the inverter might or might not include the dc/dc
converter and/or the rectifier
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Objective of the Session
• Define specifications for inverters for microgrids
• Identify the technical and cost challenges for deploying inverter technology within microgrids
• Focus on three elements of the inverter (lowering the cost and advancing state-of-the-art)
– Hardware
– Control / Operations - Functionality
– Topologies
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Inverter Specifications for Microgrids
• Power levels (20kW, 50kW, 100kW, 250kW, higher?)
• Voltage levels (480V - 13.8kV)
– Today – Low voltage inverter with step-up transformer
– Future – Medium voltage rated/ distribution system grade inverter?
• Efficiency
– Today – 97%
– Future – 99% (67% reduction in losses)
• Switching frequency
– Today – 10-20kHz
– Future – 50kHz
• Thermal management
• Cost
• Difference between a microgrid inverter and grid-connected inverter
– Functionality and control
– Inverter topologies for medium voltage inverters
– Other differences?
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Inverter Hardware Components
• DC/DC converters
– Power switches (semiconductor switches and their packaging)
– Passive components (inductors, capacitors, high frequency transformers)
– Controllers and gate drivers
– Communication
• Inverters/Rectifiers (typically voltage source converters)
– Power switches (semiconductor switches and their packaging)
– Coupling inductor/transformer
– Controllers and gate drivers
– Communication
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Microgrid Inverter Control Functions
• Today – Fundamental functions
– On-grid: MPPT, droop control during high frequency, local voltage regulation to a pre-set level
– Islanding: P-f droop control, Q-V droop control
– Transition: mode change based on local voltage and current sensors
• Future – Advanced functions with communication and microgrid central controller
– On-grid: following the P, Q (or V) references dispatched from microgrid central controller or distribution operation center
– Islanding: frequency secondary control, optimized Q dispatch, source and load dynamics
– Transition: situation awareness, mode switch and power re-dispatch based on local and microgrid information
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Inverter Controllable Independent Variables
Active power related variables
Reactive power related variables
Active power
Active current
Power factor
Frequency
Reactive power Yes Yes Yes Yes
Reactive current Yes Yes Yes Yes
Power factor Yes Yes NA Yes
Local voltage Yes Yes Yes Yes
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Inverter and Microgrid Topologies
• Inverter
– More efficient inverter topologies needed to reduce the operational costs
– New inverter topologies
• Multilevel inverters
• Matrix converters
• High frequency link converters
• Microgrid
– AC microgrids
– DC microgrids
– DC-AC hybrid microgrids
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Factors Affecting Inverter Cost
• Capital costs
– Components
• Power device cost
• Number of devices – new topologies?
• Current/voltage sensors – sensor elimination?
• Communication – autonomy?
• Control
– Standardization of devices and converters
– Scalability and modularity
– Reliability
• Operational costs
– Added functionality (volt/var support, frequency regulation, etc)
– Efficiency
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“Sunshot”
Dollar-a-Watt PV Program
• What are the current
number for microgrid
converters?
• What should be the target
numbers for future
microgrid converters?
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Challenges/Opportunities
• Multiple inverter operation (grid-connected/stand alone)
– Collaborating inverters
– Plug and Play
– Hierarchy - autonomous and coordinated
• Reliability
– Warranties up to 20-30 years
– Reliable active and passive components
– Operating under harsh conditions
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Challenges/ Opportunities
• Standardization
– Microgrid specific standard inverter or
– Modified grid-connected inverters
• Scalability/Modularity
– Medium voltage inverter
– Determine cost benefit of medium voltage inverters
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Challenges/ Opportunities
• Compatibility/interoperability – Plug ‘n Play operation for cost reduction
– Inverter
– Communications
– Control
• Efficiency
– High efficiencies at high switching frequencies or elevated temperatures
• EMI
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Key R&D areas where DOE can make
an impact
• Medium voltage microgrid inverter
• Advanced inverter controls for microgrids
• Robust operation during fault conditions