Therefore, the value of grid impedance [Z.sub.g] can be estimated according to the impedance

voltage ratio of the transformer.

Figure 4(a) shows the efficiency in the circular study area under a fixed

voltage ratio and load, [V.sub.1] : [V.sub.2] = 1 : 5 and [R.sub.L] = 10 [ohm].

Next, using [S.sub.11] and [S.sub.21] measured with the network analyzer, it was possible to determine the

voltage ratio [V.sub.p1]/[V.sub.p2] using the following Equation.

The DCC1000 is a DC motor controller that comes equipped with a heatsink and fan, as well as an encoder and

voltage ratio input for motors with position feedback capabilities.

"High

voltage ratio DC-DC converter for fuel-cell applications," IEEE Trans.

The dc-dc converter operation is optimum only when the

voltage ratio of the HVS and LVS is equal to the turn ratio of the transformer.

High

voltage ratio, low voltage stress on the diodes and capacitors, compactness, and high efficiency are the main reasons for this choice [3, 5, 6].

Many topologies have been proposed such as fly-back, boost converter, buck-boost converter, Zeta converter, SPEIC converter, forward topology, push-pull topology, half bridge topology, full bridge topology converter can adjust

voltage ratio. A boost converter consists on some inductor, capacitor and switches which convert DC voltage from one level to another level [9][17].

In general, crosstalk (dB) = 20 [log.sub.10] (

voltage ratio).

In applications where the output voltage to input

voltage ratio is large, the Schottky diode is reversed-biased for the majority of the time.

VSC, Local load and grid parameters Parameter Value [R.sub.l] 30 [ohm] [L.sub.l] 50 mH [R.sub.s] 1 [ohm] [L.sub.s] 10 mH [R.sub.t] 1.5 m[ohm] [L.sub.t] 300 [micro]H VSC rated power 1 MW PWM carrier frequency 3,960 HZ [F.sub.0] 60 HZ VSC terminal voltage 600 V DC voltage 1500 V C 9625 [micro]F Nominal grid Line-Line voltage 13.8 kV (rms) Transformer

voltage ratio 0.6/13.8 kV Transformer rated power 1 MW

Alesina and Venturini (1981) theoretically proved that the maximum

voltage ratio, [q.sub.max], is equal to 0.866 for the three-phase MC when using balanced input voltage [7].