Control Schemes for Distribution Grids with Mass Distributed Generation AUTHOR: UMAIR SHAHZAD

AIMS AND OBJECTIVES To study the control schemes for distribution grids with large wind energy penetration Grid + Synchronous generator + Loads Two Synchronous generators + Loads Active & Reactive Power Sharing Droop Control Introducing Wind (Constant + Variable)

DISTRIBUTED GENERATION Distributed generation is the generation of electrical power using a small source which is not part of the large central power system and which is located in close vicinity of the load. Also known as decentralized, embedded or dispersed generation. Types Reciprocating Engines Micro turbines Fuel Cells Photovoltaics Wind Power

Reciprocating Engines Oldest technologies Fuel source: diesel/natural gas Engine design is vital for increased efficiency

Micro turbines Small turbine + compressor + generator Low emissions, less maintenance High cost, reduced efficiency Solution: recuperators Common types: simple cycle, combined cycle

Fuel Cells Fuel source: propane/natural gas Low emissions Less maintenance (no rotating parts) High cost Types include PAFC, PEMFC, AFC

Photovoltaics Modular Low emission rates, less maintenance High cost of purchase and installation Remote locations

Wind Power Low CO2 emissions, low pollution effects Maintenance of gearbox & rotor Birds and bats Unpredictable wind Solution: battery storage systems

Why to use Distributed Generation? Environmentally Friendly Power to local load Opportunities for players in energy market

MICROGRID A group of interconnected loads and distributed energy resources within clearly defined electrical boundaries that acts as a single controllable entity with respect to the grid (and can) connect and disconnect from the grid to enable it to operate in both grid-connected or island-mode. The basic function of micro-grid is to maintain stable operation under various faults and factors which can disturb the network stability.

MODES Grid Disconnected Grid Connected

Differences between main grid and microgrid Modular. There are many unconventional generators in a microgrid like wind power, photovoltaic or fuel cells. Besides power, microgrid has the ability to supply heat. It can utilize waste heat using CHPs, hence, giving a rise to the overall efficiency of the network.

Advantages of using microgrids CHP Modular Large variety Continuity of supply Environmentally friendly Jobs Minimum losses

Simulation Work Grid+SG+ Resistive Load

Behaviour of Active Powers Active power of synchronous generator= 0.5 MW

Behaviour of Active Powers Active power of main grid= 0.5 MW

Calculation of Load Active Power Load RMS Current= 52.5 A

Load RMS Voltage= 6353 Volts

Load Active Power Calculation Load Power= 3*Vrms*Irms*cos (phi) P= 3*6353*52.5*1= 1 MW Active Powers of the System: GRID+SG= LOAD

Behaviour of Reactive Powers Reactive power of grid= -36 KVARs

Reactive Power of synchronous generator= 36 KVARs

Investigation of Load angle Synchronous Generator + Resistive Load

Simulation Results As resistance increases, current decreases and load angle decreases. Load Resistance (Ohms) Load Current (Amps) Load Angle (Degrees) 40 20 1.16 50 16.2 0.96 70 11.6 0.73 15 52.96 2.815 5 135 8.214

Phasor Diagram Phasor diagram E jIXs V LOAD ANGLE

Investigation of Load angle Grid + SG + RL Load

Simulation Results As resistance increases, current decreases and load angle decreases. Load Resistance (Ohms) Load Current (Amps) Load Angle (Degrees) 40 66 1.4 50 57 1.2 70 43 1.1 5 94 4.34

Parallel operated synchronous generators Why operated in parallel? Reliability Flexibility Supply a much bigger load than a single machine Conditions for paralleling Same RMS line voltages, phase angles, phase sequences and frequency

Simulations for 2 synchronous generators 2 SGs + Resistive Load

Active Power of SG 1 (1 MW)

Simulations for 2 synchronous generators 2 SGs + Resistive Load

Simulation Results Active Power of SG 1 (0.5 MW)

Active Power of SG 2 (0.5 MW)

Reactive Power of SG 1 (-21KVARs)

Reactive Power of SG 2 (21 KVARs)

Summary of Results SG1 Active Power= 0.5 MW SG2 Active Power= 0.5MW Load Active Power= 1 MW SG2 can be made to run at 0.7 MW , SG1 will then give out 0.3 MW. SG1 Reactive Power= -21 KVARs SG2 Reactive Power= 21 KVARs Load Reactive Power = ZERO

Load Transients Resistive Load Transient

Graphical Representation of Resistive Load Transient

Resistive-Inductive Load Transient

Graphical Representation of Resistive-Inductive Load Transient

Droop Control of Synchronous Generators Typical Droop Graphs (P-F and Q-V)

Simulations for Droop Control 2 SGs + RL Load

Q-V Droop SIMULATION RESULTS. Load Q= 210 KVARs K1 K2 Q1 (VARs) 0.01 1.05e5 0.05 3.02e4 1.51e5 0.001 2.5e5 2.5e4

P-F Droop SIMULATION RESULTS. Load P= 0.96 MW K1 K2 P1 (W) P2 (W) 0.01 0.05 4.7e5 5e5 0.001 4.95e5 4.75e5

Variations in Inductive Load Load inductance is varied. Reactive power sharing is observed. Load Inductance (H) Q1 (VARs) Q2 (VARs) Qload (VARs) 0.001 1555 3110 0.1 0.1e6 0.2e6 0.5 0.16e6 0.32e6

Simulations involving Wind Power Wind Active and Reactive Power introduced through Id and Iq

Simulations and Results Constant Id (20A) and zero Iq Behaviour of Active Powers was observed. Active Power of SG 1 (0.13 MW)

Active Power of SG 2 (0.5 MW)

Load RMS Phase Voltage

Load RMS Phase Current

Calculation of Wind Active Power RMS Phase Voltage (6350 V)

RMS Phase Current (19.39 A)

Wind Active Power is 3*6350*19.39=0.37 MW In short, Active Powers of the system: SG 1= 0.13 MW SG 2= 0.5 MW WIND= 0.37MW LOAD= 1 MW SG1+SG2+WIND= LOAD

Relationship between Iq and Reactive Power Consider the network:

Reactive Power of SG 1 (150 KVARS to 300 KVARs) Step Iq (15 A to 30A at 3s) is applied instead of constant. As Iq is doubled, reactive powers of SGs doubled. Reactive Power of SG 1 (150 KVARS to 300 KVARs)

Reactive Power of SG 2 (125 KVARS to 250 KVARs)

Variable Wind Id was input as variable data Iq was set at zero Time (seconds) Wind Speed (m/s) 0.0 13.2 0.1 13.9 0.2 14.2 0.3 14.8 0.4 16.5 0.5 16.7 0.6 18.4 0.7 20.1 0.8 0.9 11.9 1.0 11.2

Trend of Active Powers Active power of SG 1 decreases up to 0.7 s, then increases After 1s, SG 1 = 0.29 MW, SG 2=0.5 MW, Wind= 0.21 MW (3*6300*10.76)

Active Power of SG 2 (0.5 MW)

Summary of Results Active Powers: SG 1= 0.29 MW SG 2= 0.5 MW WIND= 0.21 MW LOAD= 1MW SG1 + SG2+ WIND= LOAD

Future Work In-depth investigation and evaluation of various frequency and voltage control techniques under grid-connected and grid-disconnected modes. Observing the transition phenomenon closely from grid-connected mode to grid-disconnected mode and vice versa. Observing the same under high penetration of wind power. Researching, designing and implementing protection schemes for microgrids. Operation of microgrids under unbalanced and non-linear loads.

Conclusions Theoretical Background and development projects discussed Active & Reactive Power sharing, Droop control and load transients were investigated Wind introduced and behaviour of the system observed