New Industry Products

Premo Introduces 99% Efficiency EV Charging Solution

July 08, 2023 by Jake Hertz

With an LLC topology and a new heat sink design, Premo’s product targets fast-charging EV solutions. This article will examine LLC converters, how they work, and the latest product from Premo.

In high-power electronic systems like EV chargers, thermal management is a major design concern. While thermal management is a multifaceted problem, two major ways it’s addressed include improving electrical efficiencies (to generate less heat) and improving cooling design (to remove heat more effectively). 


Premo’s transformer for high-efficiency LLC-based EV chargers

Premo’s transformer for high-efficiency LLC-based EV chargers. Image used courtesy of Premo

Premo has introduced a new high-performance transformer designed to enable high-efficiency LLC-based EV chargers. 


LLC Converters

In the world of high-efficiency power electronics, one of the most popular converter topologies is the LLC resonant converter.

LLC stands for Inductor-Inductor-Capacitor, which refers to the two inductors (Ls) and one capacitor (C) used to form a resonant tank circuit. In the circuit, the two inductors are magnetically coupled, with one inductor in series with the resonant capacitor and the other inductor in parallel with the resonant capacitor, forming an LCLC resonant tank.


Schematic diagram of an LLC resonant converter

Schematic diagram of an LLC resonant converter. Image used courtesy of Texas Instruments


When power is supplied to the primary side of the resonant converter (from an AC or DC source), it's fed into the resonant tank circuit through a series of specially-controlled switches (transistors). Generally, LLC resonant converters utilize a mechanism known as zero voltage switching (ZVS), where the switches change states when the input voltage or current is zero, respectively. The advantage of this is it reduces the so-called switching losses, which are energy losses that occur each time a switch changes state.

The switches are controlled in such a way (i.e., at the correct resonance frequency) to create oscillations in the resonant tank circuit. This oscillating circuit is then connected to a transformer which enables the transfer of power from the primary to the secondary side of the converter through magnetic coupling. At the secondary side, the transformed voltage (either stepped up or down) is rectified and used as a DC output for the load.


LLC Converter Benefits

A significant advantage of LLC resonant converters is their energy efficiency.

In general, switching losses are a major form of loss and heat generation in power converters and occur every time a semiconductor switch changes its state from ON to OFF or vice versa. However, LLC resonant converters can minimize these losses since the switches operate at zero voltage or zero current. This ability to perform Zero Voltage Switching (ZVS) or Zero Current Switching (ZCS) allows the converter to achieve higher efficiency rates.


Current and voltage waveforms of hard switching versus resonant switching circuits

Current and voltage waveforms of hard switching versus resonant switching circuits. Image used courtesy of Halim et al.

Additionally, LLC converters offer extremely high-efficiency thanks to their use of resonant behavior of the LLC topology. In contrast to traditional hard-switched converters, resonant converters use the natural resonant behavior of the LC circuit to transition the voltage and current waveforms more gradually. This reduces the magnitude of the instantaneous power contributing to the switching losses.

Furthermore, LLC converters also offer flexibility with load changes. Unlike traditional converters, which exhibit peak efficiency only at a specific load and input voltage, LLC converters demonstrate a broader efficiency curve. This means that even with load and input voltage changes, the converter can maintain high efficiency, making it particularly suitable for applications like EV chargers that may require a power supply under varying load conditions.


Premo’s Latest Innovation

Premo has unveiled a transformer module for LLC converter EV charging solutions.

The BCBM-50KW-001 Module is a 50 kW transformer enclosed in a whole aluminum housing filled with a thermal compound. With an 8:4 turn ratio, a primary inductance of 620 µH ± 10%, and a secondary inductance of 155 µH ± 10%, the product is said to offer power conversion efficiencies as high as 99%. Notably, the module also features an embedded resonant choke for LLC topology, allowing for efficient energy transfer. 


The airflow simulation of the BCBM-50KW-001

The airflow simulation of the BCBM-50KW-001. Image used courtesy of Premo


The module, encased in a sleek 300 x 174 x 100 mm aluminum casing, is complemented by Premo’s newly patented technology cooling design. Consisting of internal fins working in conjunction with Coolmag thermo-conductive resin, the BCBM module offers an efficient heat-dissipating mechanism designed to counter temperature-induced damage. The result is that the device supports a wide temperature range from -40 degrees C to 150 degrees C.