AC/DC Microgrid Control

Presented By:

Pankaj D. Achlerkar

Supervisor:

Prof. B. K. Panigrahi

Dept. of EE, IIT Delhi

Theme-1: Overall Project Management

Theme-3: Energy Storage (Modelling, Optimizing and Management)

Theme-4: Microgrid and Active Distribution System

Theme-5: Cyber Security (Cyber Infrastructure and Security)

Theme-6: DSO Functions-Energy Management

Theme-7: DSO- Market and Regulatory Issues

Theme-8: Lab Testing and Validation

Theme-9: Field Demonstration Pilots

Theme-10: Impact Analysis and Policy Recommendations

Theme-11: Capacity Building & Workforce Development

Theme-2: Distribution System Modelling and Benchmark System Development

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Theme 4: Microgrid and Active Distribution System

Objectives

Development of enhanced primary and inner control

algorithms for converter based AC and DC microgrids

Key Issues:

Low X/R ratio

Unbalanced network and loads

Weak grid scenario

Analyze impact of control actions on performance for transient

disturbances such as faults, islanding

Key Issues:

Converter response during faults

Islanding detection methodologies

Conflicts of grid-code compliance and islanding detection

Theme-8: Lab Testing and Validation

Objectives

Development of Lab Testbed to study control and protection

challenges in AC and DC Microgrids

DC Power

Supplies

VSC-2

VSC-1

LC

filter

Power

Analyzer

Rectifying unit

for 300 V DC

Typhoon HIL

602+ for

Experimental Test Bed of Autonomous

Microgrid for Testing the performance of

the controller under unbalanced loading

condition of distribution network

DSO

Three

Phase Load

RTDS Novacor for testing

protection algorithm on DC

distribution system with mixed

renewable energy sources

OPAL-RT for implementing

local and supervisory controller

for DC microgrid

3 phase auto-transformer

DC Power

Supplies

Grid connected

VSC

VSC with each leg used

as DC-DC converter

Ferrite core

inductors

Experimental Test Bed for

Grid Integrated Distributed

Storage SystemBattery Energy Storage System

Lab Testbed at IIT Delhi

Ref.: T. Kaipia et al., ”Field test environment for LVDC distribution Implementation experiences,” CIRED

2012 Workshop: Integration of Renewables into the Distribution Grid, Lisbon, pp. 1-4, 2012

# P. D. Achlerkar, V. Nougain and B. K. Panigrahi, "Backstepping Technique based Customer-end Voltage Control Strategy of DC

Distribution Network," in IEEE Journal of Emerging and Selected Topics in Power Electronics. doi: 10.1109/JESTPE.2019.2959670

𝑥3 =−1

𝐶𝑥1 + 𝜔𝑥4 +

1

𝐶𝑥5

𝑥4 =−1

𝐶𝑥2 − 𝜔𝑥3 +

1

𝐶𝑥6

𝑥5 =−1

𝐿𝑓𝑥3 −

𝑟𝑓

𝐿𝑓𝑥5 + 𝜔𝑥6 +

1

𝐿𝑓𝑉𝑖𝑑

𝑥6 =−1

𝐿𝑓𝑥4 − 𝜔𝑥5 −

𝑟𝑓

𝐿𝑓𝑥6 +

1

𝐿𝑓𝑉𝑖𝑞

Dynamics of VSC-DG: 𝑥 ≜ 𝐼𝑜𝑑 , 𝐼𝑜𝑞 , 𝑉𝑜𝑑 , 𝑉𝑜𝑞 , 𝐼𝑖𝑑 , 𝐼𝑖𝑞𝑇

Need for Robust Backstepping:

Load current 𝑥12 can be measured, however its dynamics

𝑥12 are unknown. Thus, controller has to be robust

enough to handle load dynamics.

Backstepping Approach:

Design 𝑉𝑖𝑑𝑞 such that, 𝑥56 → 𝑥56∗,

where 𝑥56∗ are such designed that, 𝑥34 → 𝑥34

∗

𝑣𝑖𝑑 = 𝐾3𝐿𝑓𝐶𝑥1 − 𝐾3 𝑟𝑓 + 𝐾5 𝑥3 −𝐾3𝐿𝑓

𝐶+ 𝐾5 𝑥5

+ 1 − 𝜔2𝐿𝑓𝐶 + 𝐾3 𝑟𝑓 + 𝐾5 𝑥3∗

𝑣𝑖𝑞 = 𝐾3𝐿𝑓𝐶𝑥2 − 𝐾3 𝑟𝑓 + 𝐾5 𝑥4 −𝐾3𝐿𝑓

𝐶+ 𝐾5 𝑥6

+𝜔𝐾3𝐿𝑓𝑥3∗ + 𝜔𝐶 𝑟𝑓 + 𝐾5 𝑥3

∗

Key Features:

• Proposed backstepping controller implements a memoryless,

instantaneous state feedback

• Simple and intuitive design process, computationally efficient

implementation

• Enhanced transient profile and robustness towards parametric

variations, DC side voltage fluctuations, load switching etc.

• Load current sensor is not necessarily required for implementation

• Stable current and voltage controllers irrespective of type of load

(balanced/unbalanced, linear/non-linear/dynamic etc.)

Eigenvalue analysis

comparison:

(a) Conventional nested PI controller

(b) Proposed robust backstepping controller

Robustness Verification:

Different type of loads

Severe load variations

DC-link voltage variations

𝟏𝝋 Bridge Rectifier

𝐋𝐂 𝐅𝐢𝐥𝐭𝐞𝐫

Gate Driver

𝐒𝐞𝐦𝐢𝐤𝐫𝐨𝐧𝟑𝛗 𝐈𝐧𝐯𝐞𝐫𝐭𝐞𝐫

𝐑− 𝐋 𝐥𝐨𝐚𝐝

3𝝋Bridge

Rectifier

Nonlinear load

𝑣𝑜 𝑎𝑏,𝑏𝑐𝑖𝑖 𝑎,𝑏,𝑐𝑖𝑜 𝑎,𝑏,𝑐

𝐏𝐚𝐫𝐤′𝐬 𝐓𝐫𝐚𝐧𝐬𝐟𝐨𝐫𝐦𝐚𝐭𝐢𝐨𝐧

2𝜋501

𝑠𝛉

𝑣𝑜 𝑑𝑞𝑖𝑖 𝑑𝑞𝑖𝑜 𝑑𝑞

𝐀𝐧𝐚𝐥𝐨𝐠𝐭𝐨

𝐃𝐢𝐠𝐢𝐭𝐚𝐥𝐂𝐨𝐧𝐯𝐞𝐫𝐬𝐢𝐨𝐧𝐓𝐬 = 𝟐𝟎 𝛍𝐬.

𝐏𝐫𝐨𝐩𝐨𝐬𝐞𝐝Voltage/Current

𝐂𝐨𝐧𝐭𝐫𝐨𝐥𝐥𝐞𝐫

𝟐

𝐕𝐝𝐜

𝐯𝐢 𝐝,𝐪

𝐈𝐧𝐯𝐞𝐫𝐬𝐞𝐏𝐚𝐫𝐤′𝐬

𝐭𝐫𝐚𝐧𝐬𝐟𝐨𝐫𝐦

𝑷𝑾𝑴𝒇𝒔𝒘= 𝟏𝟎 𝒌𝑯𝒛

𝐓𝐲𝐩𝐡𝐨𝐨𝐧 𝐇𝐈𝐋 𝟔𝟎𝟐 + 𝐂𝐨𝐧𝐭𝐫𝐨𝐥𝐥𝐞𝐫

# P. D. Achlerkar, and B. K. Panigrahi, “A Robust Backstepping Output Voltage Controller for

Standalone Voltage Sourced Converters” (Under Review)

(a) Load current variation

(d) Nonlinear loading of DG

(b) DC link voltage variation

(c) Voltage set point variation

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Tentative Future Tasks

Study of harmonic and unbalanced loading of power electronic converter

interfaces in microgrid with conventionally used controllers, and improvement of

controllers if needed

Study of islanding phenomenon of inverter interfaced DGs with practical loads

Development of better primary control strategies for power sharing in microgrids

Addition of following to the laboratory setup of AC and DC microgrids:

Photovoltaic simulator

Electronically controlled AC and DC dynamic loads

Grid simulator to study weak grid scenarios, grid contingencies and faults