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This paper proposes an ultra-low inductance half-bridge switching cell with substrate integrated 650V GaN bare dies. A vertical parallel-plate waveguide structure with 100 μm layer thickness results in a commutation loop inductance of 0.5 nH resulting in a negligible drain-source voltage overshoot in the inductive load standard pulse test. On the other hand reliable circuit operation requires an assessment of the isolation strength of the thin dielectric layer in the main commutation loop, because critical high local electric fields might occur between the pads. Measurements of the dielectric breakdown voltage followed by a statistical failure analysis provide a characteristic life of 14.7 kV and a 10% quantile of 13.5kV in the Weibull fitted data. This characteristic life depends strongly on the ambient temperature and drops to 4.1kV at 125°C. Additionally, ageing tests show an increasing in dielectric breakdown voltage after 500h, 1000h and 2000h at 125°C high-temperature storage due to resin densification processes.
A discrete-time design method for a robust current controller of a servo drive has been developed. It takes the sampling time, the processing dead time and the dynamic behavior of the A/D converter into account. The theoretical calculations are verified using a test stand for high dynamics. The test stand includes a voice coil motor and power electronics with Gallium Nitride (GaN) power semiconductors for switching frequencies of more than 100 kHz. The bandwidth of the current control loop can be improved from typically 1 kHz to 1.5 kHz with insulated-gate bipolar transistor (IGBT) power semiconductors in state-of-the-art motion control systems to 10 kHz and more.
A calculation method for a robust servo controller design depending on the sampling time and the processing dead time was developed for mechanically stiff drives. With a test stand for high dynamic and high positioning accuracy, the theoretical calculations for the high bandwidth improvements are verified. The test stand includes a voice coil motor and a power electronic with Gallium Nitride (GaN) power semiconductors for switching frequencies of more than 100kHz.
Design of a Low Multi-Loop Inductance Three Level Neutral Point Clamped Converter with GaN HEMTs
(2020)
This work shows a numerical and experimental analysis of a Neutral-Point-Clamp (NPC) three level inverter featuring an ultra low inductance printed circuit board (PCB) design in consideration of the mutual inductive and capacitive couplings. The commutation loops in this design are found to be strongly dependent on the vertical thickness of the used prepregs and the core. For vertical thicknesses ≤ 100 μm capacitive coupling must be taken into account in the switching cell design. Experimental measurements of a test set-up with a total PCB thickness of 400 μm results in commutation loop inductances from 1.4 nH up to 3.1 nH. In this set-up, switching tests without external gate resistor showed only a maximum voltage overshoot of 7% at 800 V. Based on a numerical analysis of the NPC cell we propose a further switching performance improvement with significant smaller parasitic inductance due to the application of novel printed circuit technologies such as the integration of bare dies into the printed circuit board or polyimide as an interlayer dielectric material.
Increased productivity in industrial processes can be achieved by dynamic and accurate positioning of servo drives. Therefore, improvement of servo drive dynamics using latest technologies in the key components such as inverter, control system and position measuring device are investigated. Using Gallium Nitride (GaN) or Silicon Carbide (SiC) semiconductors for motor inverters enables energy efficient operation up to pulse width modulation (PWM) frequencies of 500 kHz. This allows motor filters with small component sizes. As a result, high motor efficiency, low torque ripple, high control bandwidth and almost ideal sinusoidal output voltages are achieved. Experiments on a 200 kHz Gallium Nitride inverter with sine wave motor filter show a current control loop bandwidth of 3.2 kHz and almost ideal sinusoidal phase voltages. The achieved bandwidths of the speed and position control loops are 318 Hz and 106 Hz, respectively.
A hybrid current and acceleration control is presented and shown to improve the load disturbance behavior of servo drives significantly without additional sensor effort. The feedback signal of the acceleration control loop is calculated from the position data of the motor encoder. Hence, position measuring errors influence this control loop and lead to speed ripple. Therefore, the presented design of the acceleration control loop considers both load sensitivity and position measuring errors.
Position measuring devices with sinusoidal measuring signals are widely used in position-controlled servo drives in industrial automation, e.g., for machine tools or semiconductor production machines. Usually, the feedback signal for the speed or velocity controller is calculated from the measured position. Therefore, position measuring errors affect these control loops. This study presents an analytic error model that considers non-ideal sinusoidal measuring signals with basic deviations (amplitude differences, offset errors, and phase shift) as well as signal harmonics. The model was used to systematically investigate the influence of signal quality and the number of signal periods from position measuring devices on speed ripple, across a wide range of speeds. A test stand with a high-resolution reference angle measuring device was used to confirm the results.
The dynamic behavior and position stability of servo drives are influenced by many parameters. One major influencing parameter is the pulse width modulation (PWM) frequency. With inverters based on wide bandgap semiconductors, the PWM frequency can be increased. This enables a substantial increase in the current control bandwidth. The paper focuses on the influence of the PWM frequency on the dynamics of control loops and position stability, which are derived from theoretical correlations. The theory is verified using a test bench for high dynamic and position stability. The test bench is equipped with a voice coil motor and power electronic with gallium nitride (GaN) power semiconductors for switching frequencies of 100kHz and over. The achieved position stability, measured with a laser-based comparator at the tool center point, is lower than "+-1nm" with a standard deviation of "0.16nm" at a PWM frequency of "f_PWM=100kHz".