NOVEL GATE DRIVERS FOR MV APPLICATIONS

The need of managing high power applications with acceptable efficiency level has boosted the development of medium voltage power electronic converters. One of the most important challenges for these converters is the voltage insulation capability, which must be guaranteed to operate medium voltage levels. Traditionally, galvanic isolation is achieved with dry transformers. These transformers present small air leaks, like cavities and delaminations that could lead to partial discharge and damage the insulation over time.

Medium-Voltage (MV) Silicon Carbide (SiC) devices with high blocking voltages (10-15 kV) have been developed in recent years, which allow to reduce the number of power switches and gate drivers connected in medium voltage applications compared to the use of devices with lower blocking voltages. These devices are still in their initial stage of development, but with the development of power electronics, they will expect to satisfy such application with lower costs. In any case, even with the perspective of the new developments of power semiconductors, the need to place devices in serial connection maintain the requirement of isolated gate drivers, which is the main objective of this work.

Some applications where MV SiC MOSFETs or IGBTs are used, are high-power electric vehicle battery charging facilities, Solid-State Transformers (SSTs) for medium voltage distribution system, traction systems, future all-electric aircraft or naval distribution electric systems.All of these applications handle large amounts of power at medium or high voltage, which implies that both the semiconductors used and the elements of the circuit need to have special characteristics, one of the most significant being the high blocking voltage. The current technological limitations in terms of blocking voltage is an actual problem for semiconductors. All these semiconductors are connected in special arrangements to distribute the controlled voltage.

Using semiconductors in medium voltage networks also brings a series of additional challenges for the gate driver circuit, like to ensure sufficient isolation between the control and power stages, feeding the semiconductors with floating signals and ensuring the correct synchronization between them. In medium voltage systems, standard methods of isolation still have some problems. New gate driver topologies for medium voltage have been developed to match the previously mentioned insulating specifications [11] keeping in mind to be reliable with respect to gating signal information and power transfer insulation, as well as to be an attractive solution in terms cost and complexity.

The transmission of the control and power supply signals through an insulation barrier is a technical challenge in many applications. Different solutions to control semiconductors in high voltage applications have been proposed. A Combination of opto-coupler and galvanic insulation as an insulation barrier is used to control the power semiconductors in a solid-state transformer. The opto-coupler circuit is also used to transmit control signal to command the MV semiconductor. Power signal is transmitted employing a special insulation transformer providing a supply required referred to medium voltage side. A different solution was proposed in which, employing galvanic insulation for power and control signals, allowing data and power transfer independently using a special isolation transformer.The driver concept uses a single E-core to transfer the needed power and the control signals between the primary and the secondary sharing the same core. A fiber optic to transmit the control signal and galvanic isolation for power is proposed in a separated reference. The required energy for the driver is transmitted through dielectric barrier; in the primary side a DC voltage converter to DC current converter is used, whereas in the secondary side, a DC current to DC voltage converter is used. A fiber optic to transmit the isolated control signal from primary to secondary side is used.

Wireless gate driver solutions are an attractive option to work in medium voltage applications. These types of gate drivers use air as a dielectric barrier. Air has great advantages over other dielectrics like the non-presence of partial discharges, which is the main cause of rupture in insulating materials. Another advantage of the air as a dielectric is a “practically zero cost” solution.

In wireless gate drivers, both control and power signals are transmitted through the air using antennas or magnetic couplings. The primary side transmits power and gate signal using an especial circuit. Receiving side obtains both signals (control and power) and are used to control the power switching devices.