Ikuro Suga

Determining parameter sets for low-frequency-oscillation-free operation of Hall thruster

We performed a theoretical and experimental study of low-frequency oscillation in a Hall thruster. The oscillation phenomenon depends on various external control parameters. However, we found that such dependence can be observed very clearly using certain expressions, which are combinations of external control parameters. Using these expressions, one can observe the oscillation strength and oscillation mode for a given set of external control parameters. We considered that low-frequency oscillation can be essentially suppressed by a method of determining parameter sets. The method of determining the parameter sets is very important for Hall thruster design and control; in particular, it makes it easy to manage electromagnetic compatibility with the other equipments in a satellite, using a power supply control.

Low-loss rectifier by self-driven MOSFET with gate drive voltage control circuit

The low-loss self-driven rectifier we developed requires no external power supply and uses a novel CMOS control circuit that generates the power MOSFET drive signal by boosting the intrinsic body diode voltage drop. The rectifier significantly improved conduction loss — a 47% decrease from intrinsic-body-diode-based conduction loss — during half-wave rectification. It can replace with a common diode for a rectifier.

Low-loss rectification circuit with no external drive input

We have developed the new low-loss rectification circuit that needed neither external signals nor power supplies for driving. This circuit creates the control power supply for the circuit operation from reverse voltage. The direction of the current that flows in this circuit is detected from the voltage between the MOSFET drain and source. The current is rectified by driving MOSFETs according to this detection result. Also, the circuit has several types of MOSFET connected in parallel. Types and numbers of MOSFETs are automatically selected to minimize the loss according to the magnitude of the current detected from the voltage between the MOSFET drain and the source. To create the power supply and the signal for the rectification circuit, the circuit needs no inputs from outside like a diode. Therefore, this circuit can be easily substituted for a conventional diode. In operation tests, the minimum forward voltage drop was 0.04 [V] when the current was rectified. As a result, the forward voltage drop was less than 1/10 compared to conventional diodes, and the loss could be decreased extremely. Therefore, the miniaturization of the electric equipment that radiation fin and fan becomes possible, too. The low-loss rectification circuit can save energies by substituting diodes for prevention of global warming.