Page 144 - Decision Making Applications in Modern Power Systems

Power quality issues of smart microgrids Chapter | 4 109

added to the equation, since there is no fundamental frequency resonant con-
troller involved, and the gain is small, tracking of line current harmonic
would not affect fundamental voltage control of HCM. Finally, a propor-
tional term is added to actively damp the fundamental voltage and harmonic
current control oscillations. The previous PQI objectives could be satisfied
easily by applying HCM to MFDGs interfacing converters. To have a
h should be set to zero; in
harmonic-free line current, similar to CCM, I ref
this case, fundamental power flow is controlled through the first term and
harmonic current tracking is done by the setting the second term of (4.7) to
zero. It is worth mentioning that HCM could be used instead of CCM; in the
case of fundamental current control, the first term of (4.7) should be replaced
by a fundamental current control loop, and the harmonic current is being
tracked using the second term of (4.7). In this case, fundamental and har-
monic current elements are controlled in a decoupled way without affecting
each other. If the mentioned method is used instead of traditional CCM, it
has the advantages of HCM, such as no need for harmonic extraction block
for local load harmonic compensation, since the small gain of the harmonic
control loop would not affect the fundamental frequency current, local load
current could be used as harmonic current reference without any harmonic
extraction block.
To compensate local load harmonic current, in a similar way to CCM,
but with a slight difference of not using the harmonic extractor, the local
load harmonic current could be fed into the closed-loop harmonic current
controller, without the need for a harmonic extractor block since it does not
have any fundamental frequency controller elements to affect the fundamen-
tal frequency current, so that MFDG interfacing converter would provide
most of the harmonic components produced by nonlinear load, leading to an
improved PCC current, this advantage of HCM to previously introduced con-
trol methods would make it an appropriate, cost-effective option for low-
power MFDG units with lower computing capabilities. To compensate the
PCC voltage harmonics, similar to what has been done in CCM, the har-
monic reference should be calculated based on PCC voltage harmonics as
(4.4), which would be fed to the harmonic current loop controller; as a result,
MFDG at selected harmonic frequencies will operate as a small virtual resis-
tive impedance to improve the PCC voltage similar to what was done in
CCM [14,43].

4.3.4.4.2 Model-based predictive control (MPC)
The other popular control method in PQI area is model predictive control or
direct control that could be utilized in harmonic compensation, PQI, and
APF applications because of its fast dynamic response and simplicity of the
controller. The model-based predictive control (MPC) is a direct control
method that uses the discrete model of a system to forecast behavior of