Capability of Totem Pole PFC on Renesas RX MCU
The RX Family RX-T series is mainly adopted in outdoor units of air conditioning equipment and industrial inverters. Nonetheless, with its features well-suited for power control, such as AC-DC converters, it's seeing growing adoption in power control applications like Uninterruptible Power Supplies (UPS), power converters, and Electric Vehicle (EV) chargers.
The Totem Pole Interleaved Power Factor Correction (PFC) we introduce today is a topology that realizes the AC-DC converter function, which is essential for various electronic devices to convert AC power into DC power. This topology can significantly boost efficiency (typically reducing losses by about 40%) compared to a typical PFC circuit that employs a conventional rectifier circuit + chopper circuit using a diode bridge.
While dedicated products could be used, the built-in features of the RX-T series, as shown in “Built-in Peripherals of RX-T Series for Totem Pole Interleaved PFC Control” below, like PWM timers and analog circuits, enable control of Totem Pole Interleaved PFC by a single MCU. These features are ideal not only for inverter control but also for converter control, including AC-DC conversions. The MCU-based control offers numerous benefits compared to a dedicated ICs-based one, including precise protection through software control, the flexibility of control, and communication with other ICs via SCI, etc. making it highly compatible with system control, one of its distinct features.
The MCU used to control the Totem Pole Interleaved PFC introduced this time is the RX family RX-T series RX66T Group, but it can also be implemented with the RX26T and others that have the following functions (common functions of the RX family).
Built-in Peripherals of RX-T Series for Totem Pole Interleaved PFC Control
PWM Output Timer (MTU3, GPT)
12-bit A/D Converter (S12AD)
Port Output Enable (for emergency stop of PWM output) (POE3)
Comparator (for overcurrent detection) (CMPC)
12-bit D/A Converter (for comparator reference voltage) (R12DA)
The Totem Pole Interleaved PFC is controlled by these functions as follows.
Configuration of Totem Pole Interleaved PFC Control
The PWM output timer controls switching devices Q1/Q2, Q3/Q4, and Q5/Q6 with complementary PWM. The 12-bit A/D converter is used for current/voltage detection in feedback control. Overcurrent, which is fail-safe control, is configured to instantly stop driving Q1 to Q6 using the port output enable (POE3). The input of POE3 is the comparator and 12-bit D/A converter.
As a result, it is possible to achieve a maximum power efficiency of over 95% and a power factor of over 99%, which exhibits the same performance as dedicated products. In addition, while we use common IGBT + diodes as power semiconductors to configure Q1 to Q6, further efficiency improvement can be expected by using high-speed switching SiC devices, etc.
With NTC Thermistors:
Without NTC Thermistors:
In the response test results (a test in which the load is changed from 0% to 100% and 50% to 100% by a DC breaker), the voltage is kept constant by feedback controlling the load fluctuation, meaning it functions properly as an AC-DC converter.
This time, I have introduced the feasibility of power control (Totem Pole Interleaved PFC) by MCU as an application of inverter control. In addition to dedicated products like AC-DC PFC ICs, our MCUs offering high compatibility with system control expand the options available, enabling our customers to select the most proper solution for their application. Renesas is committed to delivering high-quality products that meet our customer’s needs, thereby facilitating innovation in their products. Please stay tuned for further advancements in the Renesas RX family.
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