An Ultra Compact GaN 3x3 Matrix Converter

Due to the direct AC to AC power conversion only by bi-directional switches, a matrix converter has been expected to be an ultimate system, which can eliminate limited-lifetime capacitors and achieves a high efficiency power conversion even without Power Factor Control circuits. However, it has not been practically used because the matrix converter consists of discrete components and results in its complicated and its large-scale system.

We describe an ultra-compact GaN 3x3 matrix converter, which are composed of a GaN/Si integrated bidirectional power switching chip, a novel isolated dividing coupler in printed circuit board (P.C.B.) to reduce the complicated gate lines, and an one-chip and low consumption GaN/Si Drive-by-Microwave (DBM) driver for 9 bi-directional power switch control. The proposed GaN 3x3 matrix converter is overwhelmingly compact than the conventional one because of a GaN power device integration and the DBM technology, which provides isolated gate signals by microwave wireless power transmission without photo-couplers and isolated power supply.

On contrast to the conventional bi-directional switch with two power switches and two power diodes, a GaN bidirectional switch is very attractive because it achieves low loss with one device. For a 3x3 matrix convertor, the proposed GaN/Si integrated bi-directional switching chip has 9 GaN normally-off bi-directional switches. The GaN device with a high junction temperature can well cope with the issues related to the high heat density that comes from the beneficial compactness of the power device integration. Since each GaN bidirectional switch has co-integrated RF rectifier circuits with a single shunt diode at their gate ports, it behaves switching operation when the RF signal from the DBM driver are input through isolated couplers. The fabricated GaN/Si bi-directional switch successfully demonstrated bi-directional switching operation by 5.0 GHz RF signal inputs.

Since a bi-directional power switch need two identical isolated gate signals against each source ports, the electromagnetic resonance based isolated dividing coupler that create two isolated gate signals with separated references from an original signal is newly developed, in which three of a quarter wavelength resonator with open and short edges are stacked vertically. The fabricated isolated dividing coupler in a low-cost P.C.B. has a 1.1 dB insertion loss at 5.0 GHz with 5.0 kV DC-isolation by the 0.28 mm layer thickness.

The DBM gate driver chip with 9 signals output for 9 power switches control is designed using GaN HFETs (HFET: Hetero junction Field-Effect Transistors) with the gate length of 700 nm on a Si substrate. The DBM gate driver chip is implemented with 3 sets of a 5.0 GHz oscillator and a 3-way switching mixer. By taking advantage of the algorism of a 3x3 matrix converter, this gate driver outputs 3 signals from the shared 5.0 GHz oscillator by switching among three output ports. Then, its power consumption is very low as a 1.95 W (13V, 150mA) in comparison with the conventional system with individual 18 drivers that constantly operate. The fabricated DBM gate driver chip successfully outputs the PWM modulated 5.0 GHz signal from 3 output ports in sequence.

Figure shows the photo of the fabricated GaN integrated bidirectional switching chip (1.74 mm x 3.5 mm) and the fabricated DBM gate driver chip (4.5 mm x 2.0 mm) mounded on the PCB that includes 9 sets of the isolated dividing coupler. The fabricated GaN 3x3 matrix converter has the capability to drive 5.0 kV motor, since the GaN-GIT switches can switch 10 A under 600 V. The switching operation by the ultra-compact (25 mm x 18 mm) fabricated matrix converter was demonstrated.