While appearing to be revolutionary in design, the Hitachi L100 is in fact the result of an evolution of inverter construction. The real revolution occurred some years ago with the development of solid state electronics.

The introduction of isolated gate bipolar transistors (IGBTs) created what we now accept as the standard modern voltage/frequency inverter - the IGBTs bringing about quiet operation and superior performance.

The inverter drives of a decade or so ago consisted of a number of key elements. There was input rectification of the input voltage, inrush resistors, output transistors (the IGBTs), diodes associated with the IGBTs, protection circuits for the IGBTs, firing circuits for the IGBTs, a microprocessor for the pulse width modulation (PWM) function and a microprocessor for the control of the drive. Additionally there are the DC link capacitors, heatsink and interface (keypad/screen).

The development a few years ago of intelligent power modules (IPMs) consolidated the IGBTs, their diodes and their protection circuits into a single encapsulated module which improved reliability and reduced the number of discrete components.

Hitachi's latest inverter system power module (ISPM) takes this evolution on a generation by integrating all the inverter functions within a single encapsulated unit. This not only reduces the physical size of the inverter, but also improves reliability through the incorporation of greater numbers of surface mounted electronic components.

In some ways the most fundamental change has been the ability to manufacture these ISPM devices using methods more akin to those employed in the semiconductor industry - namely greater automation, the capacity to make vastly higher volumes of products and dramatically reduced manufacturing costs for the main part of the drive. Clearly, the potential to make the ISPM in huge numbers at low cost will expand the market for inverter control. The ISPM - which is effectively the first monobloc inverter - sits at the heart of the latest Hitachi L100 drive.