The Evolution Of Insulated Gate Bipolar Transistors

Introduction

Since their proposal in the late ‘60s and early ‘70s and their development through the ‘70s and the ‘80s, the Insulated Gate Bipolar Transistor (IGBT) has represented the ideal device for a large number of applications. Initially proposed for replacing metal-oxide-semiconductor field-effect transistors (MOSFETs) in applications requiring lower reverse currents and lower ON resistance, today, IGBTs find their sweet spot in switching power electronics where high voltages and high currents are needed. A few examples featuring modern IGBTs can be found in a number of applications, including electric vehicles (EV), electrical motor drivers, variable speed drivers, unidirectional inverters for solar generation, and bidirectional inverters for battery applications. More recent and future market applications also include chargers for electric vehicles and rectifiers for hydrogen generation via water electrolysis.

Energy markets applications

Of particular interest for the electrification revolution, though, are the bidirectional inverters (or, better, four-quadrant inverters) used in energy (battery-based) storage applications.

Over the last few years, the key focus and demand for energy storage has quickly shifted from local energy storage and domestic applications to the need for large Battery Energy Storage Systems (BESS) for grid applications, effectively reaching the level of battery power plants. BESS is based on hundreds of thousands of lithium battery cells (approximately rated at 3.6V) organized in banks and are designed to absorb or release into the grid hundreds of MWs for durations that span from the sub-second domain to 2-4 hours.

The need for increasingly larger power and energy deployments has been pivotal to the augmentation of the battery bank voltage, historically around 24-48V for domestic and telecommunication applications and up to 120-480V for backup and UPS systems. Today’s BESS plants are based on 1500V battery banks, obtained by connecting in series lithium battery modules (for example, approximately 180V with 50 cells). The battery banks are connected to DC/AC power electronics, the necessary interface for the connection to the grid.

In this scenario, ‘IGBTs switching’ being capable of turning ON or OFF in hundreds of nanoseconds and able to withstand 1500V can be easily found on the electronics market and IGBT modules (with several IGBT connected in series and parallel) exceeding the 1500V voltage limit (up to 6500V) are quite common as well. When compared to MOSFETs, IGBTs can be parallelled more easily and have lower electromagnetic interference (EMI).

Further advantages of IGBTs over MOSFETs are: 1) the handling of large voltages and currents at the same time (reaching hundreds of kW), 2) no reverse current flow and 3) lower on-voltage drop at higher voltages due to the independence from the transported current. Given the latter, at lower voltages, though, power MOSFETs can become more suitable and have lower conduction losses. Moreover, due to slower ON and OFF times compared to the MOSFET, for high-frequency applications beyond the tens of kHz, the IGBTs might be inadequate, and the MOSFET, able to reach hundreds of kHz, could be preferred again for lower switching losses.

Today’s and future scenarios

Today, energy-application large-scale power electronics manufacturers like Power Electronics, SMA, Ingteam, ABB and others have their current products based on IGBT devices with applications targeting renewable energy technologies like solar generation, battery storage and hydrogen production. This has caused a number of IGBT shortages in the market and a general increase in pricing. Nevertheless, the market is expected to grow by 8-10% over the next 10 years projecting to more than double its current value. The growth is linked to a number of new applications, with the diffusion of EVs and the electrification revolution being two significant contributors. On the competition side, IGBTs are challenged by the rise of Silicon Carbide (SiC) MOSFET, which is available in the market. SiC MOSFETs have a higher voltage range than conventional MOSFETs and ensure better performance over IGBTs in some applications despite their higher cost.