Control and Design of Microgrid Components - Power Systems ...

The filtering is achieved by a low pass LC circuit. The capacitors are connected at delta. The
values for the components are:
L = 1.2 mH
C = 30 μF
Table 6.4 summarizes all the data relevant to the microsources.
Table 6.4 Summary of Microsource Data.
V
rated
[V]
S rated
[kVA]
P rated
[kW]
Q rated
[kVar]
MS 1 480 18.75 15.0 11.25
MS 2 480 18.75 15.0 11.25
m
[rad/kW]
π
15.0
π
15.0
m
Q
[V/kVar]
X
[Ω]
L
[mH]
C
[μF]
0.2578 1.88 1.2 30
0.2978 1.88 1.2 30
6.3 Control Implementation
Microsource control can be implemented with a limited number of measurements passed to a
hardware block that creates the pulses for the gates of the power electronic devices inside the
inverter. The hardware block consists of three distinct boards. The first board is responsible for
conditioning the values of the measured quantities to voltage levels that allow the interface with
the second board, the DSP. The DSP implements the control block, constantly comparing desired
and measured quantities to generate the gate pulses. These pulses are then passed to the third
board, that amplifies the low voltage pulse signals coming out from the DSP to the voltage level
needed to operate the actual power electronic devices.
The control blocks are encoded in Assembly language and compiled with Metrowerks
CodeWarrior software. The executable code is then passed to the program memory of the DSP
board.
The Digital Signal Processor (DSP) is a versatile hardware device that uploads an executable
code with the information on how to manipulate inputs to generate outputs. The DSP is the ideal
environment to code the control of the microsource. The input of this board are the signals
coming from the sensing devices and the outputs are the firing pulses that are sent to the gates of
the power electronics inside the inverter.
The code is uploaded in the DSP memory through a connection with a computer, where the
program is compiled to an executable format. It is possible to debug the code by executing it on
the DSP and sending some of the internal variables to dedicated pins where it is possible to
connect with oscilloscope probes. The sensing signals reach the board as analog signals and are
converted into digital form to be processed inside the integrated circuit. It is also possible to
debug the code by means of a special application called PCMaster, a program written by
Motorola to support the code builders for their DSP products.
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