Page 229 - Modern Control of DC-Based Power Systems

Control Approaches for Parallel Source Converter Systems 193

bandwidth, that is to achieve the desired low pass behavior for R. For the
design of the weighting functions, we adopt first-order filter design.
Higher-order filters are also possible, but it will result in a higher-order
controller.

s=M e 1 ω e
W e sðÞ 5
s 1 ω e E
s 1 ω T =M T
W T s ðÞ 5 (5.228)
Es 1 ω T

s 1 ω u =M u
W u sðÞ 5
Es 1 ω u
The parameters ω e , ω u , and ω T represent the bandwidth required and
the parameter E is a small positive number used to introduce a left-half
plane pole in the high pass filter (HPF) transfer function W e . The para-
meters M e , M u , and M T represent the peak sensitivity values. The design
of these weighting functions will be explained in the next section with a
practical example of an MVDC grid.

5.7.5 Application to MVDC System
In this section, we show the application of the H N weighted sensitivity
control strategy for the voltage stability of MVDC grid. The same system
as in previous chapters is considered and the control design is done. The
primary control consists of the H N control and the secondary control
consists of the virtual resistance droop controller for power sharing.
Firstly, we explain how the weighting functions are designed to compute
the H N controller and then time domain simulations of the MVDC sys-
tem show the validity and effectiveness of the control design. The over-
view of the H N control technique is represented in Fig. 5.55.

5.7.5.1 Design of Weighting Functions
The design of weighting function is explained in this section. As
explained earlier, it is desired to have S with high pass characteristics
and T with low pass characteristics. Hence the bandwidth of S must be
smaller than that of T. The bandwidth of S and T are chosen as 45 Hz
and 100 Hz respectively. The bandwidth of S is more crucial than T,
since it gives the actual sense of aggressiveness of the system. The higher
the bandwidth of S, the greater is the sensitivity to disturbance.