Alireza Mojab

15-kV single-bias all-optical ETO thyristor

A new all-optical emitter-turn-off (ETO) configuration is proposed in this paper which is operated under 15 kV single bias and a current of 10 A. This ETO is completely controlled by two optical signals, one for the 15 kV SiC gate-turn-off (GTO) thyristor and the other one for a triggering low-voltage optically controlled Si switch. The latter, called optically-triggered power transistor (OTPT), is used in series with the anode contact of the SiC GTO thyristor in order to handle the current switching between anode and gate path of the SiC GTO thyristor. This OTPT is triggered with a 5-W laser of 808-nm wavelength and the main SiC GTO thyristor is triggered with a laser having a low wavelength of 266 nm. The voltage drop on the OTPT during the on-state is controlled by the power of the laser. For an optical power of 5 W, the structure is optimized to have an on-state voltage of 0.2 V at the junction temperature of 200 °C. This is less than 0.002% of the total bias of 15 kV.

Evaluation of first 10-kv optical ETO thyristor operating without any low-voltage control bias

In this paper a new single-biased all-optically triggered ETO configuration is proposed. For this purpose, an optically triggered power transistor with vertical structure is used as a power switch to help the main thyristor achieving a unity gain turn-off. In order to handle all-optical control, two different laser sources with a wavelength of 808 nm for the high power optical switch and a wavelength of 250 nm for the integrated thyristor are used to trigger them. Our simulation results show a good transition between on and off states with a rise and fall times of 26 ns and 362 ns. The total on-state voltage across the ETO is 4.4 V which is about 0.04% of the total supply voltage. The effect of parasitic inductances and the temperature on the output characteristics of the ETO is investigated separately.

Closed-loop control of switching transition of SiC MOSFETs

This paper presents a novel closed-loop active-gatecontrol (AGC) circuit for high-voltage SiC MOSFETs, used in the high-voltage, high-frequency and high-power-density applications. The proposed controller independently adjusts the switching di/dt and dv/dt by closed-loop control of the gate current and enables one to reach optimal performance in terms of loss, device stress, and EMI. The di/dt is adjusted to control the overvoltage stress and peak reverse recovery current while the dv/dt is adjusted to control the common mode (CM) noise and switching loss. The dv/dt is the primary source of the common mode noise in power electronics converters. Dynamic control of switching dv/dt has been somewhat overlooked in the state-of-the art works based on Si based power semiconductor devices (PSDs), and maximum achievable dv/dt is used to decrease the switching loss. However, the magnitude of generated dv/dt in the high-voltage SiC-based applications is appreciable because of the exceptionally higher switching speed of the SiC MOSFETs as compared to Si IGBTs. In contrast to other works, the proposed controller dynamically and independently controls the turn-off di/dt and dv/dt of a SiC MOSFET using closed-loop control of the gate current. Independent control of turn-off di/dt and dv/dt is achieved using a delay compensation circuit. This circuit compensates the total delay in the feedback loop and predicts the onset of transition between dv/dt and di/dt control regions. The proposed control circuit operation and advantages are presented and verified by experimental results.

Low ON-State Voltage Optically Triggered Power Transistor for SiC Emitter Turn-OFF Thyristor

In this letter, a new optically triggered power transistor (OTPT) rated for 100-A load current is proposed. Moreover, some modifications in the base epitaxial layer are made to reduce both the ON-state voltage drop and the required optical power for the driving laser. This new structure benefits the fact that increasing the leakage current yields to a lower ON-state voltage in power semiconductor devices (PSDs). Although the proposed structure has a higher leakage current during the OFF-state, the high leakage current is blocked by a high-power low-leakage SiC thyristor that is connected in series with the proposed OTPT. Therefore, one can use the advantage of a rather leaky OTPT to further decrease the ON-state voltage. ON-state voltage drop of 0.8 V is achieved across the proposed OTPT in operating condition of 100 A and 100 °C while it is illuminated by optical power of 5 W. The proposed OTPT, respectively, features 22% and 92% improvement in the textscon-state voltage drop at optical powers of 5 and 2 W, as compared with the conventional low-leakage OTPT.

A discontinuous PWM strategy optimized for high-frequency pulsating-dc link inverters

This paper presents a discontinuous pulse width modulation (PWM) scheme optimized for three-phase high-frequency pulsating-dc link (HFPDCL) inverters. HFPDCL inverters consist of a high-frequency dc/ac converter, high-frequency (HF) transformers, a rectifier, and an output three-phase inverter. HF transformers provide galvanic isolation and reduce the transformer volume in the inverter. HFPDCL inverters do not require bulky DC-link capacitors; therefore, eliminating them from the power stage of the converter increases the power density and reliability of the HFPDCL inverters. The proposed discontinuous PWM scheme is optimized based on the HF pulsating-dc waveform of the dc link of the HFPDCL inverters. It decreases the switching requirement and generates high-quality output waveforms. It clamps one predetermined phase of the output inverter to the dc bus which decreases the switching requirement of the inverter. A 2 kW prototype HFPDCL inverter is implemented to verify the performance of the proposed discontinuous PWM scheme. Using the proposed DPWM scheme for the HFPDCL inverters improves the performance of the inverter.

15-kV 100-A single-bias all-optical SiC emitter turn-off thyristor

A new design of a very high-voltage, single-bias, and optically-controlled emitter turn-Off thyristor (ETO) is introduced. Both the thyristor and the controlling switch are triggered optically using two lasers. In the outlined structure, only a single power bias of 15 kV is required. The low-voltage control bias, typically used for triggering devices in an electrical ETO thyristor [1, 2], is eliminated due to all-optical control. This eliminates the problem of susceptibility to electromagnetic interference (EMI) and yields complete electrical isolation between the power and the control stages. It is found that this new optically-triggered ETO is capable of switching the thyristor to the conducting mode in less than 65 ns for a rated current of 100 A. In order to use high current levels, a Darlington structure is used in our silicon controlling switch which is called optically triggered power transistor (OTPT). The first stage of the Darlington OTPT is triggered with a 5 W laser of 808 nm wavelength and the current is then amplified through the second electrical stage of the Darlington OTPT. The main silicon carbide (4-HSiC) SGTO thyristor is triggered with a low wavelength laser of 266 nm. The current fall time is found to be 393 ns and the total on-state voltage drop across the ETO is 5.4 V at 100 A current. This is about 0.04 % of the total applied voltage. The designed optical switch is able to conduct the rated current of 100 A at a low on-state voltage of 0.8 V under a laser power of 5 W.

Introducing Optical Cascode GaN HEMT

A novel optically activated cascode gallium nitride (GaN) high-electron-mobility transistor (HEMT) is introduced and evaluated in this paper. Furthermore, optical triggering of GaN HEMT structures by cost-effective and high-power long-wavelength light sources is proposed for the first time. In electrical domain, GaN HEMTs suffer from being normally on devices, making it more complicated to design and implement gate drivers for these devices. In optical domain, GaN devices suffer from being triggered by low-power short-wavelength light sources, making them significantly more expensive and practically unprofitable. Therefore, a new optical cascode (OC) GaN HEMT is proposed in this paper to solve the problems of both electrical and optical domains. The structure of this OC GaN HEMT includes a high-power normally on (depletion mode) GaN HEMT in combination with a low-power optical switch in cascode configuration. This OC not only realizes an overall normally off (enhancementmode) structure, but also offers activationwith cost-effective long-wavelength optical sources. It also offers a single-biased configurationwithout the need for complicated electrical gate drivers. Unlike conventional electrically activated cascode GaN HEMT structures, which may be prone to electromagnetic interference noise due to the high-frequency switching operation, the optical link in this proposed scheme is immune to external noise. The results showa high-frequency switching capability of 1MHz for theOCGaN HEMT under a bias voltage of 600 V and a current of 10 A. Less voltage and current ringing are observed in the OC compared with the electrical alternative due to the elimination of gate controlling inductance introduced in the electrical cascode configuration.

Soft-switched discontinuous pulse-width pulse-density modulation scheme

This paper presents a soft-switched discontinuous pulse-width pulse-density modulation (PWPDM) scheme to decrease the switching losses of the capacitor-less high-frequency pulsating dc-link (HFPDCL) inverters. The proposed modulation scheme employs both pulse-width modulation (PWM) and pulse-density modulation (PDM) schemes to increase the overall efficiency of the inverter and generate high-quality output line-frequency (LF) Sine waveforms. In order to increase the efficiency of the converter, it decreases the switching requirement of the converter and it also provides soft-switching condition for the output inverter. The performance of the proposed PWPDM scheme is verified using am experimental 2 kW HFPDCL inverter.

Active Optical Modulation for Series-Connected Emitter Turn-Off Thyristors

Series connection of high-power thyristors is proposed in the literature for high-voltage applications. Due to the high dv/dt across series-connected thyristors during turn-off, charge equalization techniques have been pursued that increase the fall time to avoid overshoot voltage and device breakdown. Longer fall time for thyristors yields reduced switching frequency and increased losses. As such, a new method to control turn-off transition for the series connection of recently developed optical emitter turn-off (o-ETO) thyristor is outlined in this letter. The turn-off speed of series-connected o-ETOs and their voltage balance are controlled by modulating the optical intensity of the triggering (instead of the high-power) device of the o-ETO.

Experimental optical transistor for all-optical SiC ETO thyristor

A high-current and low on-state voltage optical transistor is provided in this paper for high-power applications. The structure of this device includes a twostage transistor in which the first stage is triggered optically using an infrared laser of 808-nm wavelength. The photogenerated current in the first stage drives the second stage of the optical transistor for current amplification.