Increasing Efficiency of Electric Vehicle Powertrain using IGBT inverters
Summary
Ultimately, one of the key to being able to optimize the hardware design and the control software of inverters acting as motor controllers is having an in depth knowledge of the design of electric motors. It is one thing to ensure that electric motors and inverters not only have the highest possible efficiency as standalone products, but to design a truly efficient powertrain system, the challenge is keeping the combined efficiency of these components at the highest level possible.
With an history of more than 25 years in the vehicle electrification market, TM4 has long being known for its advanced expertise in the field of power electronics, which has allowed the company to implement breakthrough technologies in its inverters. One of these technologies is the patented ReflexTM gate drive technology that increases current output of IGBT modules by up to 100% in certain operating conditions, making TM4’s inverters some of the most power dense off-the-shelf products on the market.
TM4 is also known for taking a multiphase approach for its high power inverters used in commercial vehicle and bus powertrains, offering 6 phase and even 9 phase inverters along with similarly designed motors. You can learn more on the advantages related to this design here.
Ultimately, one of the key to being able to optimize the hardware design and the control software of inverters acting as motor controllers is having an in depth knowledge of the design of electric motors, because they will both influence each other’s behavior during operation. In fact, it is one thing to ensure that electric motors and inverters not only have the highest possible efficiency as standalone products, but to design a truly efficient powertrain system the challenge is keeping the combined efficiency of these components at the highest level possible. TM4 has achieved this is by working on two axis that can be used to optimize the pulse width modulation (PWM) signal: the carrier wave form and the carrier frequency.
For instance, TM4 uses a variable switching frequency method, allowing it to increase along with the electrical frequency of the motor, which is dictated by its rotational speed. Varying the switching frequency allows to reduce motor harmonics at high speed, without having to increase the switching losses of the inverter at low speed. However, faster switching time will leads to larger switching overvoltage. This is where the Reflex technology becomes most important, because it uses the parasitic inductance in the IGBT module as an overvoltage feedback and injects it into the gate driver as negative feedback to control and prevent an overvoltage. This technique permits a better usage of the IGBT, resulting in performance gains.
Over the operating range, space-vector PWM is used for highest frequencies since this technique leads to reductions of up to 30% in motor harmonics compared to another type of modulation, generalized discontinuous PWM (GDPWM). However, GDPWM is also used in some conditions, such as low frequency / RPM operation. This modulation technique permit stopping one IGBT during switching, when current is at its highest rating, hence where switching losses are also potentially the biggest. This process can result in up to 50% switching losses reduction compared to SVPWM over this operating range.
Clearly, at TM4 the proximity and capabilities of electromagnetic and power electronics teams working together under one roof has lead to the development of a wide range of highly efficient electric and hybrid powertrains optimized for their targeted markets and applications. Contact-us for more information, or visit our product’s section.