­IGBT Gate Driver Board Offers 2,300V Isolation for Renewable Generation

Energy generation from renewable energy sources usually provide a DC signal, which then has to be manipulated into a form that we can easily use. This conversion could be performed by an inverter to change it into an AC signal to be fed into the grid, or it could be a DC-DC conversion for battery storage. Because of the power levels, IGBTs and SiC MOSFETs are the only realistic options for this type of high efficiency conversion. In terms of performance, SiC MOSFETs are the better option as they have lower switching losses and they more rugged. However, SiC solutions are expensive, at up to 5 times the cost of a similar IGBT design. Since renewable applications can be very cost sensitive, IGBTs are therefore still the preferable solution for a majority of installations. To help with the design of IGBT solutions for renewable applications, some companies have introduced packaged solutions that include almost all of the components required for the conversion. These solutions include Mitsubishi’s LV100, Infineon’s XHP 2 and Fuji’s HpnC ranges.

The only main function that is not included in these modules is the gate driver circuit, which gives designers the flexibility to design one that suits the application. However, as renewable sources are now moving towards standardized designs and voltage outputs, and the inputs to the grid and batteries are known, plug-and-play type drivers can make the designers life even easier.

Although IGBTs don’t specifically require bespoke gate driver circuits, they are able to offer advantages in both terms of isolation and thermal management. Isolation is necessary in the design to protect the sensitive control components that supply the gate from the large currents that flow between source and drain. Thermal management is of major importance for IGBT designs, as one of their main disadvantages is that they are prone to thermal runaway, which can easily destroy the IGBT and other components. To prevent thermal runaway, normally one of two techniques is used. The first one is to restrict circuits to only operate in safe zones. This buffer may protect the circuit, but it also means that it can be running below its potential maximum capacity. The second method of tackling thermal runaway is to use temperature sensing to control the IGBT and ensure that it doesn’t overheat. The sensing option allows IGBTs to operate more effectively, but requires additional space for the discrete design on a separate board. The sensing solution also has another advantage, in that the data can be used to predict the lifetime of the IGBT for preventative maintenance.

Thorsten Schmidt, product marketing manager at Power Integrations expands further by saying, “In a sensorless design, system simulation and testing are used to calculate the maximum allowable junction temperature for the IGBT, which includes a safety margin of up to 50^oC. This thermal design factor can reduce the performance of the IGBT by up to 25%. The alternative is to implement a sensing solution that requires a cable connection and a dedicated board, which adds more components to the system, as there needs to be at least a second isolation barrier, another microcontroller and a cable. Additional components lead to lower reliability”.

Schmidt was speaking at the launch of Power Integrations’ SCALE-iFlex XLT Dual-Channel Gate Driver family. The new gate driver design integrates a negative temperature coefficient (NTC) temperature sensor circuit directly on the gate driver board. The temperature signal is routed through the isolation barrier that already exists in the system and then converted to a PWM signal on the primary side to help control the IGBT switching speed. This solution gets rid of the need for a separate temperature board and components.

The SCALE-iFlex XLT board is also compact enough at 98 x 65.5 x 31.3 mm to fit within the IGBT module outline. For isolation, the gate drivers provide up to 2300 V blocking voltage, a claimed first for this type of design. The device is suitable for both 2-level and 3-level ANPC topologies and meets IEC 61800-5-1 with reinforced isolation at 2-level for 1,200V and 1,500V and basic isolation at 2,300V. It also offers basic isolation at 1200V for 3-level ANPC topology. The board protects the power switches in the event of a short-circuit.

The solution uses Power Integrations’ SCALE-2 technology, which allows optimized dynamic switching performance and accuracy for IGBT module applications. It also provides features including a secondary-side Intelligent Gate Driver (IGD) and a primary-side dual channel Logic-to-Driver Interface (LDI).

www.power.com/scale-iflex-xlt