Renewable Energy Grid Integration Jian Sun Professor and Director
Grid Integration Issues Cost, Reliability & Efficiency of Grid Interface Grid Congestion, Weak Grids Variability of Renewable Production Bidirectional Power Flow in Distribution Networks, Localized Voltage Stability Problems Possible Solutions Enhance Transmission Lines, Active Grid Control Energy Storage: Large Scale (e.g. Pumped Hydro) for Balance of Power; Fast Acting Storage for Stability Load Management and Demand Response 2
Power Electronics as an Enabler Renewable Generation Energy Storage Load Manag. Power Grid 3
AC Generation Synchronous Generator PWM VSC Converter B() v(t) t 4
Generator Control Traditional Generator Prime Mover Control Excitation Control Limited Controllability at Low Frequencies Complex Control at High Frequencies Large Wind Generator Turbine Speed Control DC-Link Control Grid Q & V Control Grid Synchronization Current Semiconductor Control Switching 0.0 0. 0 00 000 0000 Frequency (Hertz) 5
Research Areas and Projects Overall Theme: Operation and Control of Power Grids with Pervasive Power Electronics Fundamental Research Small-Scale System Demonstration Wind Turbines Integration with Weak Grids (GE) High-Voltage DC Transmission for Offshore Wind (Stanford) DC Micro Grid for Integration of Renewable Energy and Energy Storage (Ultralife, NYSERDA) Smart Grid Voltage Stability and Control (NSF) Multi-Terminal HVDC for Offshore Wind Farms and Bulk Power Transmission (ARPA-E, GE, CURENT ERC) 6
Voltage Instability 7
Impedance-Based Method Im + V s s Source + V l l Load Gain Margin Re Vl V s l l s s l c Phase Margin Partition System into a Source and a Load Subsystem Determine Source Subsystem Output Impedance ( s ) and Load Subsystem Input Impedance ( l ) System is Stability if s / l Meets Nyquist Stability Criterion 8
Distributed Generation Test-Bed 3 208 V Utility-Grid Passive Impedance Bank Reactors Invert. Invert. Solar Fuel Cell ~ / / Filter Invert. Rect. Wind Active Grid Simulator 3 208 V Simulated Grid Load A Simulated Distribution Grid with Programmable Voltage, Frequency Variation, Harmonics Programmable Grid Impedance Various Distributed Generation Sources & Loads 9
Grid-Connected Inverter Modeling i a v a i b i c v b v c Filter Grid PWM abc dq PLL abc dq K d i d H PLL (s) v q v d v qm abc dq v dm K d H i (s) H i (s) i q i dr i qr p s p0 p0 n0 s dc s sl H ( s j2πf ) V sl 2 V 2 2 dc VH V H PLL H ( s ( s j2πf) VdcI ( s j2πf ) V p i i j2πf ) Hi s n n0 2 VH V H PLL ( s j2πf) VdcI ( s j2πf ) V p H i 0
Harmonic Resonance High Inductive Grid Impedance Causes Resonance with Capacitive Inverter Output Impedance Phase (deg.) Magnitude (db) 50 40 30 20 0 50 00 50 0-50 -00-50 p g 00 Hz khz 0 khz Hz =75 n 00 Hz khz 0 khz
Mitigating Harmonic Resonance Increase Inverter Impedance to Avoid Intersection with Grid Impedance Reshape Inverter Output Impedance to Ensure Sufficient Stability Margin Current Compensator PLL Design Online Grid Impedance Identification, Adaptive Control Inverter Currents with Reduced PLL Bandwidth 2
HVDC for Offshore Wind Farms 690 V Stability & Control of AC Collection Bus Speed Source ω mech PM 600 rpm Direct-Drive Technology Speed Source ω mech PM 600 rpm Speed Source ω mech PM 600 rpm 690 V 690 V 7 km 7 km 7 km 33kV AC Bus HVDC Rectifier (VSC or LCC) 300 MVA STATCOM HVDC Speed Source ω mech PM 600 rpm Speed Source 400*2.5MW Turbines ω mech PM 600 rpm 690 V 690 V 7 km 7 km 7km Cable AC Bus Filters 3
DC Micro Grid Supervisory Control Ultra Caps = = DC Bus ~ = Hardware Embedded Control Subsystem-Level Autonomous Control Supervisory Control & Com Switching Protection Function, Stability Power Quality Loading/Unloading Weather Change Hourly, Daily & Seasonal Variation Second 0-6 0-4 0-2 0 2 0 4 0 6 0 8 4
Summary Research Focus on Future Grid with Pervasive Power Electronics Renewable Energy Energy Storage, Dynamic Load Management Active Grid Control AC, DC & Hybrid AC-DC Networks Stability & Compatibility Over a Wide Frequency Range Local Control with Predictable Global Effects Impedance-Based Analytical Approach Test-Bed as a Platform for System Demonstration 5