Post on 25-Dec-2021
Grid Stability – Large Scale Solar
Mark Parker16 May 2018
1 CONSEQUENCE OF RENEWABLES – TECHNOLOGY INHERENT LIMITATIONS
2 SYSTEM STRENGTH
3 SHORT CIRCUIT CONTRIBUTION
4 INERTIA, FREQUENCY AND ACTIVE POWER
5 CONTROL SYSTEM INSTABILITY
Grid Stability –Solar Challenges
6 MODEL ADEQUACY
CONSEQUENCE OF RENEWABLES- Weakening System -> Reduced Short Circuit Power (Low SCR)- Reduced Inertia -> Displacement of Rotating Machines- Higher Reliance on Control Systems- Reduced Power Quality
- Synchronous Machines- Inherent Response (Inertia, Short Circuit)- Create own speed reference (Grid Leader)
- Asynchronous (e.g. Solar Inverter)- Delayed Response (Control System)- Rely on healthy grid sine wave (Grid Follower)
No technology can retire synchronous machines from the existing grid
1 CONSEQUENCE OF RENEWABLES – TECHNOLOGY INHERENT LIMITATIONS
2 SYSTEM STRENGTH
3 SHORT CIRCUIT CONTRIBUTION
4 INERTIA, FREQUENCY AND ACTIVE POWER
5 CONTROL SYSTEM INSTABILITY
Grid Stability –Solar Challenges
6 MODEL ADEQUACY
SYSTEM STRENGTH
2019 2029 2039
Strong
Weak
1 CONSEQUENCE OF RENEWABLES – TECHNOLOGY INHERENT LIMITATIONS
2 SYSTEM STRENGTH
3 SHORT CIRCUIT CONTRIBUTION
4 INERTIA, FREQUENCY AND ACTIVE POWER
5 CONTROL SYSTEM INSTABILITY
Grid Stability –Solar Challenges
6 MODEL ADEQUACY
SHORT CIRCUIT CONTRIBUTIONSynchronous Machine
- Initial response is electro-mechanically coupled
Asynchronous Machine
- Initial response requires control detection
SCC Typical:Asynchronous :
- Solar Inverter - 1pu
- Statcom - 3 pu
Synchronous:
- Generator - 2.5 pu
- Condenser - ≥ 5 pu
Voltage (kV) Clearance Time (ms)
400kV 80
250kV 100
100kV 120
Asynchronous response too slow at higher voltages for meaningful SCC
NER Fault Clearing Times
SCC – STABILITY EXAMPLES
Loss of Protection Grading
dI
dT
Longer faults -> controller instability
SCC – SOLAR INVERTER RESPONSESNot OK for Transmission1. IQ settling time >70ms
2. Gate Blocking
OK for Transmission1. IQ settling time <70ms
Gate Blocking Delay
V
P
Q
I
V
P
Q
I
Slow P Rise
Delay & Slow Q Rise
1 CONSEQUENCE OF RENEWABLES – TECHNOLOGY INHERENT LIMITATIONS
2 SYSTEM STRENGTH
3 SHORT CIRCUIT CONTRIBUTION
4 INERTIA, FREQUENCY AND ACTIVE POWER
5 CONTROL SYSTEM INSTABILITY
Grid Stability –Solar Challenges
6 MODEL ADEQUACY
INERTIA AND FREQUENCYA
ctiv
e P
ow
er
0
100%
~0.12s ->0.4s(Response Time)
Asynchronous Controller Initiated Response
300s
Inertia
Frequency Response – Synchronous Vs Asynchronous
≥ 3s(Rise Time)
Response Time: ~ 120ms to 400ms depending on technology> Meter processing time 1-2 cycles (~20-40ms)> Frequency filter delay 3-5 cycles (~60ms->100ms)> PLC or Power Plant Controller (PPC) delay (~40ms->200ms)
Rise Time: Will depend on controller response (e.g. PI control, ramp rate, etc...)
Inherent Responsefollowed byPrimary Frequency Response (e.g. Governor, Bypass Valve)
Synchronous Asynchronous
INERTIA & FREQUENCY – EXAMPLE QLDQLD OVER FREQUENCY - LOSS OF QNI
LARGE SCALE SOLAR PLANT REQUIREMENTS:- New GPS to include active power reduction within 3s - Demonstrate frequency response during commissioning (NOT ENABLED)- Run-back schemes
HIGH GENERATOR (Δf) RESPONSE
LOW GENERATOR (Δf) RESPONSE
INERTIA & FREQUENCY – EXAMPLE QLDCONTINGENCY ANALYSIS
System Normal Pre-Event Contingency – N-1
- Lack of frequency response for modelled generation
- Controller instability
SOLAR - ACTIVE POWER VOLATILITY & DIVERSITY
https://anero.id/energy/solar-energy
Curtailment Unconstrained
NEM Solar Average - Diversity Reduced Volatility Unconstrained Average - Diversity Reduced Volatility
INTERCONNECTED NEM REDUCES OVERALL SOLAR VOLATILITY
1 CONSEQUENCE OF RENEWABLES – TECHNOLOGY INHERENT LIMITATIONS
2 SYSTEM STRENGTH
3 SHORT CIRCUIT CONTRIBUTION
4 INERTIA, FREQUENCY AND ACTIVE POWER
5 CONTROL SYSTEM INSTABILITY
Grid Stability –Solar Challenges
6 MODEL ADEQUACY
CONTROL SYSTEM INSTABILITY
Solar Inverter Essentials:
1. Stable Phase Locked Loop (PLL)
2. Operate Plant within Design Capability
CONTROL SYSTEM INSTABILITY - EXAMPLESolar Inverter & Statcom Interaction:- Inverter PLL Instability = Bad response
- Inverter Inductive Q (adverse impact)
- Inverter slow IQ - 300ms (70ms target)
- Inverter Q windup/overshoot on recovery
Inductive Q – Adverse fault impact
Q Overshoot on fault clearance
PLL instability = slow correction
Statcom - Good response
CONTROL SYSTEM INSTABILITY - EXAMPLEPLANT OSCILLATORY INSTABILITY - PPC dispatch greater than MVA capability- Interaction between separate control functions
(ID control & IQ control)
Step in-out of limiter
Command inside MVA capability
Command outside MVA capability
1 CONSEQUENCE OF RENEWABLES – TECHNOLOGY INHERENT LIMITATIONS
2 SYSTEM STRENGTH
3 SHORT CIRCUIT CONTRIBUTION
4 INERTIA, FREQUENCY AND ACTIVE POWER
5 CONTROL SYSTEM INSTABILITY
Grid Stability –Solar Challenges
6 MODEL ADEQUACY
MODEL ADEQUACY
PSS/E Numerical Inaccuracies
- Future grid planning requires model improvement
- PSS/E (RMS) numerical inaccuracies (AEMO PSS/E Model)
- PSCAD (EMTD) more accurate, but also has limitations:- Non-existent PSCAD models of existing NEM Generators
- Significant investment required & lack of maturity (Cost & Delay)
- AEMO rules do not enable sharing of models to new intending participants
- NSP tasked with PSCAD studies -> Biased outcomes (lack of independence)
PSS/E SCR 3 PSCAD SCR 3
PSCAD oscillations
not captured in PSS/E
PSCAD BENCHMARKING CONNECTION STUDY (AEMO PSS/E MODEL)