Analysis of Low Frequency Oscillations in Autonomous Microgrid in Staic and Dynamic Loac
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This document presents an analysis of low frequency oscillations in autonomous microgrids driven by dynamic loads, emphasizing the importance of effective control strategies to stabilize system performance. It introduces a two degree of freedom active damping controller designed to mitigate oscillatory dynamics while enhancing power quality and reliability. The findings highlight the significant impact of induction motor loads on microgrid stability and the proposed strategies improve operational efficiency across varying conditions.
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Analysis of Low Frequency Oscillations in Autonomous Microgrid in Staic and Dynamic Loac
- 1. ANALYSIS OF LOW FREQUENCY OSCILLATION IN AUTONOMOUS MICROGRID WITH STATIC AND DYNAMIC LOAD Presented by-Godwin Lobo
- 2. INTRODUCTION The concept of microgrid is gaining high momentum as enabling structure to integrate renewable and distributed energy resources in power networks. Moreover, the distinctive autonomous operational capability of microgrids has brought in higher reliability measures in supplying power demands when the utility grid is not available. The majority of distributed/renewable generation (DG) units are interfaced to the network by voltage source converter (VSCs). One well established approach for autonomous microgrid operation is droop control.
- 3. MOTIVATION OF MICROGRID 1. Accurate current control performance with a strong ability of rejecting the grid distortion and voltage disturbances caused by interfacing parameters mismatch and compensating for inverter system delays. 2. Insensitivity to distribution system and ac side filter parameters. 3. Grid voltage sensorless operation with function fusion to reduce system cost and increase the accuracy and reliability. 4. Fast voltage control performance with strong ability of mitigating fast and dynamic voltage disturbances. 5. Stable and high power quality microgrid operation along the whole loading trajectories of microgrid generators.
- 4. OBJECTIVES MICROGRID 1. To stabilize the microgrid system in the presence of IM loads, a two degree of freedom active damping controller is proposed to stabilize the newly introduced oscillatory dynamics 2. Development of an interface monitoring unit along with a grid voltage sensorless interfacing scheme for inverter based DG units. 3. Development of a voltage control system for the DG interface featuring fast load voltage regulation and effective mitigation of fast and dynamic voltage disturbances. 4. Development of an autonomous control strategy of a microgrid system with effective damping of low frequency modes. 5. Integration of the developed control algorithms to realize a robust DG interface for gird connected and microgrid systems. 6. Improve reliability for mission-critical loads by connecting generators on a microgrid using existing distribution networks. 7. Reduce reliance on fuel for diesel power by using renewable energy sources during outages.
- 5. NECESSITY OF MICROGRID 1. Utilization of Microgrid can help utilities defer investments in generation and transmission capacity 2. Microgrid have the potential to offer increased total energy efficiency when used with combined heat and power (CHP) or combined cooling heat and power, and can therefore reduce energy costs 3. Appropriately integrated Microgrid can improve power availability and quality 4. Distributed systems offer potential security advantages over centralized systems 5. Microgrid promote fuel diversity (e.g., biomass, landfill gas, flare gas, wind, solar) and therefore reduce overall energy price volatility 6. Renewable DG such as wind and solar photovoltaics provide emissions-free energy 7. Microgrid offer a quicker solution with regards to installation, lead time and siting relative to centralized generation.
- 6. ORGANIZATION
- 7. PROBLEM STATEMENT 1. Electromechanical rotor oscillations in large IMs couple the rotor speed oscillations, which are directly coupled to the supply frequency, and the rotor flux dynamics 2. Unlike the idealized operation of an IM under an infinite-bus condition, in a typical micro-grid system with IMs, active and reactive power oscillations will be coupled. 3. The droop gains in a micro-grid system can vary over a considerable range to optimize the cost and operation aspects of micro-grid via a higher-level management controller. Therefore, system stability should be guaranteed over a wide range of droop gain variation. 4.System stability should be also preserved under uncertainty in motor and system parameters.
- 9. The above figure shows the complete control system of a typical VSC based DG unit, which consists of: 1) Power sharing control which sets the voltage phase and magnitude for the inverter output voltage according to the droop settings 2) Voltage control loop to yield close control characteristics of the output voltage 3) Inner current loop to control the filter inductor current, limiting the converter current during up normal conditions
- 11. STATE SPACE MODEL OF A VSC BASED DG UNIT:
- 12. MATLAB SIMULINK MODEL Three phase Breaker Continuous powergui dynamic Freq2 g A B C + - g A B C + - A B C UTILITY GRID 1000 MVA, 69 KV, X/R=22 A B C a b c A B C a b c A B C a b c Vabc Iabc A B C a b c Vabc Iabc A B C a b c Vabc Iabc A B C a b c Vabc Iabc A B C a b c Vabc Iabc A B C a b c Vabc Iabc A B C a b c Vabc Iabc A B C a b c A B C A B C A B C A B C A B C A B C Tm m A B C THREE PHASE INDUCTION MOTOR T9 T8 T7 T6 T5 T4 T3 T2 T13 T12 Step1 Static Freq1 A B C STATIC LOAD RPM static load voltage static load current static real power static reactive power static Freq RL LOAD RESULT Vabc_inv Iabc_inv Id_ref Iq_ref POWER REGULATOR2 Vabc_inv Iabc_inv Id_ref Iq_ref POWER REGULATOR1 A B C A B C LC Filter1 A B C A B C LC Filter Istatic Vstatic PULSES1 IM PULSES2 Iinv2 Vinv2 Iinv1 Idg2 Vdg2 Idg1 Vdg1 Idynamic Igrid Vgrid Vdynamic Vinv1 Iinv2 Iinv1 IM Vinv2 PULSES2 PULSES1 Vinv1 DC+ DC - DG2 SYSTEM DC+ DC - DG1 SYSTEM Id_ref Iq_ref Iabc_inv CURRENT REGULATOR2 Id_ref Iq_ref Iabc_inv CURRENT REGULATOR1 dynamic load voltage dynamic load current dynamic real power dynamic reactive power Dynamic Freq 3 Ph IM RESULTS A B C a b c 25 kV - 2.4 kV 6 MVA A B C 2 MW A B C a b c 10 MVA 69 kV/13.8 kV 1 30/pi ->RPM A B C a b c 2.5 MVA 0.68 KV/ 13.8 KV1 A B C a b c 2.5 MVA 0.68 KV/ 13.8 KV A B C a b c 1.25 MVA 13.8 KV/0.48 KV <Rotor speed (wm)>
- 14. POWER REGULATOR 2 Iq_ref 1 Id_ref Vabc Iabc P & Q Subsystem3 1 1 Vstatic In RMS Discrete RMS value3 PI PI -1 1/Base3 -K- 1/Base2 2 Iabc_inv 1 Vabc_inv
- 16. DG OUTPUT WITH AND WITHOUT FILTERS OF INVERTERS (a) (b)
- 17. THE RESPONSE OF MICRO-GRID SYSTEM UNDER UNCONTROLLED PULSE OPERATE WITH STATIC LOAD (A) VOLTAGE (B) CURRENT (C) REAL POWER (D) REACTIVE POWER. (a) (b) (c) (d)
- 18. THE RESPONSE OF MICRO-GRID SYSTEM UNDER UNCONTROLLED PULSE OPERATE WITH DYNAMIC LOAD (A) VOLTAGE (B) CURRENT (C) REAL POWER (D) REACTIVE POWER.. (a) (b) (c) (d)
- 19. THE FREQUENCY AND SPEED OF MICRO-GRID SYSTEM OPERATE WITH UNCONTROLLED GATE PULSE (A) DG1 FREQUENCY (B) DG2 FREQUENCY (C) NOLOAD SPEED (D)FL SPEED. (a) (b) (c) (d)
- 20. MICROGRID OPERATE AT TRANSIENT CONDITION(UNCONTROLLLED GATE PULSE) Loads PARAMETERS VOLTAGE(KV) CURRENT (KA) FREQUENCY(Hz ) SPEED (RPM) P(MW) Q(MVAR) Static load magnitude 0.48 1.13 49.89 --- 1.5 0.85 Time in sec to settle waveform at standstill 0.01 0.01 1 ---- 0.3 0.27 Dynamic load Load at(J=1 kgm2) 2.4 0.39 49 1500 2.9 1.9 Full load(J=10 kgm2) 2.35 0.7 49.89 1491 3 2 Time(s) to settle waveform at standstill 0.2 0.2 Not standstill Noload 0.8 & Full load 1 variation variation
- 21. AUTONOMOUS MODE MICROGRID OPERATE WITH CONTROLLED GATE PULSE THE RESPONSE OF MICROGRID SYSTEM UNDER STATIC LOAD (A) VOLTAGE (B) CURRENT (C) REAL POWER (D) REACTIVE POWER. (a) (b) (c) (d)
- 22. THE RESPONSE OF NOLOAD SPEED AND FREQUENCY OF MICROGRID (A)DG1 FREQUENCY(B) DG2 FREQUENCY (C) NOLOAD SPEED. (a) (b) (c)
- 23. THE RESPONSE OF MICROGRID SYSTEM UNDER DYNAMIC LOAD (LOAD AT J=1KGM2) (A) VOLTAGE (B) CURRENT (C) REAL POWER (D) REACTIVE POWER. (a) (b) (c) (d)
- 24. FIGURE-5.8: THE RESPONSE OF MICRO-GRID SYSTEM WITH FULL LOAD IM (LOAD AT J=10KGM2) (A) CURRENT (B) REAL POWER (C) REACTIVE POWER. (a) (b) (c)
- 25. THE RESPONSE MICROGRID UNDER FULL LOAD SPEED AND FREQUENCY (A)DG1 FREQUENCY(B) DG2 FREQUENCY (C) NO LOAD SPEED OF IM (D) FULL LOAD SPEED OF IM (a) (b) (c) (d)
- 26. MICROGRID OPERATE AT STEADY STATE CONDITION (WITH CONTROLLED GATE PULSE) Loads PARAMETERS VOLTAG E(KV) CURRENT (KA) FREQUEN CY(Hz) SPEED (RPM) P(MW) Q(MVA R) Static load magnitude 0.48 1.13 48.89 --- 1.5 0.85 Time in sec 0.09 0.09 0.13 ---- 0.3 0.27 Dynamic load Load at(J=1 kgm2) 2.4 0.4 50.15 1500 2.9 1.95 Full load(J=10 kgm2) 2.35 0.7 48.89 1491 3 2 Time in sec (improvement of waveform) 0.2 0.2 0.1 Noload 0.3 & Full load 0.6 0.3 0.3
- 27. IN GRID CONNECTED MODE MICROGRID OPERATE WITH CONTROLLED GATE PULSE THE RESPONSE OF GRID SYSTEM UNDER STATIC LOAD (A) VOLTAGE (B) CURRENT (C) REAL POWER (D) REACTIVE POWER (a) (b) (c) (d)
- 28. DYNAMIC LOAD POWER RESPONSES OF THE GRID SYSTEM AT LOAD J=5 KGM2 (A) VOLTAGE (B) CURRENT (C) REAL POWER (D) REACTIVE POWER (a) (b) (c) (d)
- 29. SPEED RESPONSE OF THE SYSTEM AT LOAD J=5 KGM2 (A) WHEN IM CONNECTED WITH GRID (B) WHEN IM CONNECTED WITH BOTH GRID WITH MICRO GRID (a)
- 30. CONNECTED WITH GRID (B) LOAD CONNECTED WITH BOTH GRID AND MICROGRID (a)
- 31. THE RESPONSE OF MICROGRID SYSTEM UNDER STATIC LOAD (A) VOLTAGE (B) CURRENT (C) REAL POWER (D) REACTIVE POWER. (c) (d) (a) (b)
- 32. THE RESPONSE OF MICROGRID SYSTEM UNDER DYNAMIC LOAD (A) VOLTAGE (B) CURRENT (C) REAL POWER (D) REACTIVE POWER. (a) (b) (c) (d)
- 33. MICROGRID CONNECTED WITH MAIN GRID Loads parameters Voltage (kv) current (ka) frequency (hz) speed (rpm) P (mw) Q (mvar) Static load magnitude 0.48 1.14 49.5 --- 1.45 0.87 Time of improvement 0.15 0.2 0.1 --- 0.4 0.4 Dynamic load Full load(J=5 kgm2) 2.35 0.63 49.2 1498 3 1.9 Time in sec(Improveme nt) 0.2 0.2 0.1 0.3 0.3 0.35
- 34. HARDWARE IMPLEMENTATION BLOCK DIAGRAM OF MICROGRID SYSTEM
- 35. SCHEMATIC DIAGRAM OF LABORATORY HARDWARE TEST SYSTEM
- 37. PIC CONTROLLER PIN DIAGRAM
- 38. DG’S INVERTER CIRCUIT USING MOSFET DEVICE
- 39. DRIVER CIRCUIT FOR INVERTER
- 40. HARDWARE RESULTS LOAD GRID VOLTAGE GRID WITH MICROGRID NO LOAD 220V 220V STATIC LOAD 201V 219V DYNAMIC LOAD 186V 202V SPEED OF MOTOR 1390 RPM 1402 RPM
- 41. CONCLUSION This project addressed low frequency oscillations in converter based microgrids with dynamic loads. A complete small-signal model of a typical MV microgrid with a typical dynamic load (IM load) has been developed. Small-signal stability analysis has revealed that the electromechanical rotor oscillations of large IM is source of lightly damped dynamics (low frequency modes) in MV microgrid systems yielding to and oscillatory frequency and voltage performance even under conservatively selected low droop gains. The large motor type loads, the dominant low frequency microgrid are highly sensitive to the motor dynamics and droop gains. It is shown that the active power drawn by the induction motor is highly participating in shaping the lightly damped system. This finding has been used to design a simple and effective two DOF active damping strategy which is based on remote compensation of the power swings. The proposed active damping controller introduces transient supplementary power angle and voltage magnitude signals to effectively damp microgrid frequency and voltage oscillations without affecting the steady state power sharing characteristics. The proposed active damping controller shows robust performance under large-signal microgrid dynamics, such as large variation in motor slip during motor starting, full load torque step disturbance, and large voltage dips associated with motor starting. Further, the proposed active damping controller facilitates the use of an extended range of the static droop gains, which is essential to optimize the economic and technical aspects of microgrid operation at different operating conditions. A theoretical analysis, simulation and experimental results have been presented to validate the effectiveness of the proposed scheme.