Load sharing in dc micro grids using current & voltage control loop

Contents
 Introduction
 Why Microgrids
 Modes of Operation
 Working of Microgrids
 Control of Micro grids
 Requirements For Parallel
Load Sharing
 Use of Boost Converters
In Microgrids
 Techniques For Parallel
Sharing
 Sliding Mode Control
 Voltage & Current Control
Loop
 Hardware Implementation
 Conclusion

What Exactly a Micro grid ?
A micro grid is a group of
interconnected loads and
distributed energy sources
within clearly defined
electrical boundaries that act
as a single controllable entity
with respect to the grid.
Introduction

Why Micro grids
As DC electronic loads dominate today, the unnecessary
AC-to-DC converters are not required in DC Microgrids. This
will directly affect system cost and efficiency.
Transmission losses gets highly reduced.
Provide high quality and reliable energy supply to critical
loads
Easily availability of renewable energy sources and high
price of fuel.

In this mode the micro grid works
in integration with macro grid.
The two grids are connected at
the PCC with the help of either a
circuit breaker or a static switch
or a power electronic interface.
Modes of Operation
1. Grid Connected Mode

In islanded mode, micro grid
is isolated from main grid.
Modes of Operation
2. Island Mode

Control Of DC Micro grids
1. Primary Level Control
2. Secondary Level Control
3. Tertiary Level Control (Energy Management System)

 Hierarchical control
of dc micro grid

Use Of boost converter in Microgrids
 The DC-DC boost converters are used
where the output voltage needed to be
higher than the source voltage.
Vo = K Vs
Duty cycle
0-1
Source Voltage
Output voltage

Parallel Load Sharing
Purpose
To upgrade power capacity
Condition
Sources power must be same

Advantage of parallel load
sharing

Circulating Current
When converters are connected in
parallel and if there is change in power
output, then this will cause mismatch
in converter output voltage which will
in turn cause circulating current.
Circulating current will increase the
flow current through the switches
which will increase the power
electronic switch ratings and loses and
cause converters to overloading and
overheating, which decreases the system
reliability and can eventually lead to the
failure of the overall system.

1. Droop control
Droop control in a dc micro grid is a control strategy in which we control the voltage level
of a dc micro grid for the parallel operation of generating stations so that we can make
our system more reliable and flexible.
Limitations
 With the consideration of line resistance in a droop-controlled dc micro grid, since the
output voltage of each converter cannot be exactly the same, the output current sharing
accuracy is degraded.
 Circulating current is also an important issue. it is extremely important that voltages
produced by the generating equipment are as closely matched as possible.
 Major drawback is its poor voltage regulation whereas in case of instantaneously
produced droop.
Techniques For Parallel load Sharing

Sliding Mode Control
 On a daily basis Load Sharing is an important
feature in which efficient and dynamic sharing of
load is preferred
 dc micro grids are being considered because of
their high demand and operating requirement for
dc systems.
 The dc micro grids include synchronization of
sharing and controlling of generated energy.

 Sliding mode control is one of the most efficient
non linear techniques of recent time.
It is well-known for
 Model reduction (By degree one)
 Performance design (self-designing)
 Robustness (parameter invariance)
 dc-dc converters control strategy.

Continued
• Sliding mode control has a variable structure and gives
guaranteed Stability through its reaching condition.
• The transient response is fast.
• Shows robustness whenever some variations appear in the
system.
• The degree of model (system) is reduced by order one making it
easier to handle.
• The performance designs are designed according to the required
or desired results making system more accurate and easy to
handle.

 Hierarchical control
of dc micro grid

Schematic diagrams of SMC boost converter

Mathematical Model

Voltage & Current control loop
 Practical
Implementation

What we have done in our project?
 The used SMC technique starts with fixed frequency and boost converters
along with current controlled loop for the system.
 Achieved a fast dynamic response.
 Due to extreme high switching speed of SMC in power converters the
frequency is kept fixed.
 The dynamics of non-linear system are modified for load sharing (in dc micro
grid)
 For controlling system performance the systems current control loop comprise
of two nested-if loops where the inner one is current (I) controlled and outer
loop is voltage (V) controlled.
 The sliding mode control generates on/off discontinuous signals that forces
system to slide across the desired point resulting in guaranteed stability
(robustness).
 Furthermore the design is presented through practical simulations and design
implementation along with block diagrams presenting slide mode control as a
competent technique.

Conclusion
 Future scope: In the near future when cost of micro grid will be
affordable they will be replacing the conventional grid hence becoming
more popular.
 Using multiple power outputs connected in parallel, designers can get
more output current, while also achieving idleness, improving efficiency
and enhancing overall system reliability.

Thank You For Your
Attention…

Load sharing in dc micro grids using current & voltage control loop

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