DC inverter range hood solution based on Renesas 8-bit MCU

With the continuous change of the consumption concept of household appliances, consumers have higher and higher requirements for range hoods. Usually, the speed of range hoods is manually adjusted, so in order to achieve the best oil exhaust effect and energy saving, users often need to intervene manually many times. Therefore, in order to enable the range hood to achieve automatic speed regulation, reduce noise, free up manpower and maximize energy saving, Renesas Electronics (the products involved in this article are mainly the former NEC part of Renesas Electronics) has launched a series of 8-bit MCUs dedicated to frequency conversion control. This article mainly introduces the main features of the 8-bit MCU-uPD78F0712 and the frequency conversion range hood solution based on this product.

Features of variable frequency range hood

The purpose of frequency conversion of range hood is to adjust the speed of oil fume extraction according to the amount of oil fume by adjusting the motor speed of the fan on the range hood. Excellent speed regulation and energy saving effect make frequency conversion range hood significantly superior to traditional range hood in performance. Frequency conversion range hood has different classifications and performance characteristics according to the specific frequency conversion technology, as shown in Table 1.

Table 1: Relationship and characteristics of various variable frequency range hoods

Nowadays, there are variable frequency range hoods on the market, but most of them are variable frequency range hoods with gears, generally divided into three gears: weak, medium and strong; only a few well-known brand manufacturers have launched variable frequency range hoods without gears. As can be seen from Table 1, 180° variable frequency range hoods of the same cost have better performance than other types.

The 180° variable frequency range hood has the following features in actual applications: a. It can identify the presence of oil smoke based on the sensor, and intelligently start and stop the range hood's suction without manual operation; b. It can automatically adjust the air volume according to the amount of oil smoke when stir-frying, frying, and deep-frying; c. When stewing, boiling, steaming, and boiling, it automatically reduces the suction speed to reduce power consumption; e. The silent feature allows users to not feel the noise of the motor; f. The smaller motor makes the range hood smaller and reduces costs at the same time.

180° frequency conversion requirements for MCU

Since 180° frequency conversion range hoods use vector control to achieve frequency conversion, they have high requirements for MCU. If the range hood needs to implement functions such as LCD display and delay control, the MCU also needs dedicated peripherals such as serial communication and timers. Renesas Electronics has developed a series of 8-bit MCUs for motor frequency conversion control, including 78K0/IY2, 78K0/IA2, 78K0/IB2, uPD78F0712, uPD78F0714, uPD789842 and uPD780988. Like 16-bit MCUs, they integrate internal hardware multipliers, powerful timers, multiple general registers, fast instruction running systems, programmable pulse generators, and independent frequency conversion control modules. Proprietary hardware functions make these 8-bit MCUs more suitable for small and medium-power 180° frequency conversion range hoods.

Since various mathematical transformations are used in the control of 180° variable frequency range hoods, and there are many multiplication operations in the transformations, the MCU is required to have fast multiplication operations. The hardware multiplier of Renesas Electronics' 8-bit MCU can execute various transformation algorithms of motor vector control faster, making the range hood respond faster. If the motor control of a 180° variable frequency range hood involves decoupling control and PID calculation, the MCU is required to have strong computing power and instruction running speed, which is difficult for a general 8-bit MCU to meet.

180° variable frequency range hoods require the MCU to receive information from the fan speed sensor for motor control. These 8-bit MCUs from Renesas Electronics have up to 6 external interrupt inputs, eliminating the need for a hardware capture unit to analyze the range hood fan speed sensor signal, reducing the cost of the range hood's internal motor control solution. The unique bank structure of 32 8-bit (16 16-bit) general-purpose registers makes the 180-degree vector control program of the range hood's brushless DC motor run more efficiently.

180° variable frequency range hoods are mid- to high-end kitchen appliances that require MCUs to provide customized personalized functions. Renesas Electronics' 8-bit MCU's programmable pulse generator (PPG) can specify pulse width and pulse period, which can be used to display the fan speed or air volume of the range hood and simplify software programming. It also provides an online self-programming function to store range hood setting parameters without the need for an external EEPROM, saving costs and space, and is particularly suitable for low-cost 180° variable frequency range hood control.

In addition, these MCUs also have a dedicated variable frequency control module with 2 free interrupts to generate interrupts at any time in the PWM cycle and sample the current at any time required by the user; an independent external signal input dedicated to controlling the PWM high-impedance output, which can quickly stop the fan under abnormal conditions; and 8-bit programmable dead zone control (dead zone time range: 0.1 s to 25.6 s), etc. Figure 2 shows the main features of the 8-bit variable frequency control MCU, and Table 2 gives a detailed description of these functions.

Figure 2: Features of Renesas Electronics (formerly NEC Electronics) MCU

Table 2: Features of 8-bit MCU for frequency conversion control

180° frequency conversion range hood system design

Renesas Electronics has developed a low-cost 180° variable frequency range hood solution HS/DC-8 based on the 8-bit MCU uPD78F071x, which includes the power supply and motor control parts (see Figure 3).

Figure 3: HS/DC-8 system composition

HS/DC-8 uses the unique hardware functions of 8-bit MCU to realize 180° frequency conversion of range hoods. HS/DC-8 is suitable for BLDC motors with rated capacity of 20W~1kW, electrical angular frequency of 6~120Hz and permanent magnet flux below 0.5Wb.

Compared with 180° variable frequency range hood solutions from other semiconductor manufacturers’ MCUs, HS/DC-8 has the following advantages:

Low loss: The dedicated frequency conversion control timer in the MCU can realize the two-phase modulation low-loss PWM mode, which can reduce the power switch tube loss of the motor control part in the range hood by about 30%, thereby extending the life of the range hood fan control;

High efficiency and low noise: Since the MCU's hardware multiplier can quickly implement the 180° vector control algorithm, automatic phase control is added to the solution to ensure that the range hood consumes minimal energy when running;

Rich protection and customization functions: relying on the powerful timer function, rich IO function and AD function in MCU, such as dead zone protection, Hall type selection, frequency feedback pulse number selection, PWM initialization abnormality detection, overvoltage protection. These rich functions can customize unique personalized functions for the range hood;

Low cost: 8-bit MCU saves external EEPROM and internal hardware capture unit, which reduces the cost of MCU.

Figure 4: 180° variable frequency range hood solution

Figure 4 is a physical picture of the 180° variable frequency range hood solution. It can be seen that in the 180° variable frequency range hood solution, the hardware circuit board can be installed in the side end cover of the motor to reduce the total volume of the range hood.

Professional technical support

In addition to the low cost and high performance of Renesas Electronics' 8-bit MCUs, users can also receive the following technical support services from Renesas Electronics' authorized distributor, Shiqiang Telecom, during the product development process of 180° inverter range hoods:

a) Application consultation: When applying the solution, Shiqiang Telecom can provide suggestions on motor usage based on the customer's specific range hood design requirements, such as what kind of motor can achieve energy saving and lowest cost.

b) Solution design: The 180° inverter range hood solution needs to be customized with different functions according to the specific product market and user targets. Shiqiang Telecom can help customers tailor the inverter range hood in product design and modify the HS/DC-8 solution.

c) Hardware reference design: HS/DC-8 can provide hardware reference design and prepare a rich external hardware interface for users. When users actually use the product, they need to design their own hardware interface so that they can control HS/DC-8 externally. For example, communication hardware functions and human-machine interface hardware functions can be added.

d) Software design: HS/DC-8 has provided a wealth of protection and customization functions to adapt to a variety of 180° variable frequency range hood products. Shiqiang Telecom can help users set parameters, product software debugging, etc.