The line voltage sinking ratio d can be set to any value. Fig. 7 shows the characteristics of THD vs. d for three values of system output P_out. It is seen that since THD is almost proportional to d, THD can be adjusted with d to some extent.

　

Fig. 8 V_d and V_sc0 vs. P_out

Fig 9 u vs. _out.

Fig. 10 THD vs. _out.

Fig. 11 V_d and V_sc0 vs. P_out.

　

5. STEADY-STATE CHARACTERISTICS

　

Let us discuss here the steady-state characteristics of the proposed system with duplex reactor on the basis of the theory derived so far.

Fig. 8 shows the characteristics of dc link voltage V_d and synchronous compensator terminal voltage V_sc0 versus output power P_out for the case of constant output voltage and constant power factor of the load. The characteristics for the conventional system with AC reactor are also shown for the sake of comparison. From the figure, it is shown that V_d and V_sc0 increase greatly with output power for the case of proposed system. In this case, when output terminal voltage is kept constant, since the voltage at the imaginary terminal u in Fig. 4 (V_μ) should increase because of voltage drop in L_γ V_d and V_sc0 increase with P_out accordingly. The measured and calculated results are in good agreement, supporting the appropriateness of the theory.

In Fig. 9 the characteristics of the angle of overlap of inverter output currents u , with which operation limit is determined, versus output power P_out for the tested system are shown. It is shown from the figure that the increase in u is suppressed greatly for the case with duplex reactor. This is because V_μ becomes larger for the proposed system. Hence, we can say that when the proposed system is used the operation limit of the system can be enlarged with the increases in system voltages.

Fig. 10 gives the characteristics of THD of the output voltage versus P_out for the tested system. It is shown that THD increases with d as mentioned in Fig, 7. The measured THD for the system with duplex reactor was below 5% for all cases, showing usefulness of the proposed system.

　

6. SUPPRESSION OF VOLTAGE INCREASE WITH CAPACITORS

　

The voltage increases for the system with duplex reactor should be suppressed to lessen the voltage ratings of the system. We propose here a simple method of suppressing the voltage increases in the system. The insertion of a set of capacitors in series with the output terminals makes it possible to reduce the voltages.

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