However, this technique doesn't allow controlling of the desired harmonic order, total harmonic distortion (THD) and modulation index. Another technique is Selective Harmonic Elimination (SHE).

For the purpose of avoiding malfunction on the PI controllers, the one used to determine the electrical frequency, [[omega].sub.e], must operate with lower dynamics than that of the other one used for generating the modulation index m, which corresponds to the normalized amplitude of the AC output voltages.

The frequency modulation index ([m.sub.f]) is as follows

where [v.sub.R], [v.sub.Y], and [v.sub.B] are the three phases, M is the modulation index, and [m.sub.cm] is the common mode signal.

Parameters Value DC voltage 6.6 kV Output frequency 60 Hz Output inductor 5mH Output resistor 7.5 [OMEGA] Flying capacitor 2200 [micro]F Modulation index 0.95

Parameters Unit Value Base module Tx power dBm 17.6 Tx frequency GHz 10.5 Rx frequency GHz 8.5 AM modulation index % 20 AM conversion gain dB 3.5 FM bandwidth MHz 420 FM sweep frequency kHz 2.5 FM conversion gain dB 61.5 Tag module Rx frequency GHz 8.5 Tx frequency GHz 10.5 Conversion gain dB 32 Antenna (horn) Gain dBi 24 Beam width [degrees] 20 TABLE 3: Comparison of high-accuracy radar systems.

The output voltage ([V.sub.o]), output current ([I.sub.o]) of the inverter at the pulse masking modulation index of 50 and 10% are shown in Figure 9 (a, b, c and d), respectively.