Application design of AC variable frequency air conditioner based on SPMC75F2413A single chip microcomputer

1 Introduction

With the development of China's national economy and the continuous improvement of people's material and cultural living standards, air conditioners have been widely used in various occasions in society. DC variable frequency air conditioners have the characteristics of energy saving, low noise, constant temperature control, all-weather operation, low frequency compensation at startup, and rapid reaching of set temperature, which greatly improves the comfort of air conditioning and will be more and more popular. The wide application of single-chip microcomputer technology, the successful application of DC variable frequency technology and fuzzy control technology in the field of embedded control of air conditioners, and the rapid development of semiconductor power devices provide technical guarantees for the promotion of DC variable frequency control.

The AC variable frequency air conditioner controller of this design scheme consists of two parts: indoor unit controller and outdoor unit controller. Based on the superior performance of SPMC75F2413A, it is easy to realize the modularization and intelligent characteristics of the product by designing the outdoor unit AC variable frequency controller. The control parameters adopt an open structure, which is easy to connect with various compressors, so that the product can be upgraded according to the requirements of different manufacturers in the shortest time. In this way, the product can be brought to market faster and gain a competitive advantage in time. This controller contains the following key technologies:

1. Fuzzy control technology: According to indoor ambient temperature, pipe temperature, outdoor ambient temperature, pipe temperature, compressor exhaust temperature, compressor overload protection temperature, compressor current and other parameters, fuzzy logic relationships are established to control the operating speed of the compressor, outdoor fan and other load operations;

2. Efficient third harmonic injection based on DDS SPWM generation technology, making full use of power supply voltage, precise frequency adjustment, and real-time voltage compensation function to make the compressor work more effectively;

3. Module control protection circuit: When the module has a protection signal output, the PWM module output control signal is disconnected through the hardware circuit to achieve the effect of protecting the module, and reliably provide the single-chip module with a protection signal;

4. EMC and reliability design technology: Under the premise of mastering the interference mechanism of the air conditioner, the hardware design focuses on the following points: power supply circuit design, filter circuit parameter design, printed circuit board ground and signal line design, and the software adopts fault-tolerant technology.

2 Introduction to the overall system plan

This AC variable frequency air conditioning system is divided into two parts: indoor unit system and outdoor unit system. The indoor unit system mainly processes some logical state information of the system, while the outdoor unit system is mainly the variable frequency drive part of the compressor. In this system solution, the indoor unit is implemented by SPCE061A, and SPMC75F2413A is mainly used in the variable frequency drive part. Therefore, the indoor unit system will not be described in detail here. The circuit structure block diagram of the outdoor unit is shown in Figure 2.1.

Figure 2.1 Block diagram of outdoor unit system The

basic working process of this system:

the main control MCU (SPMC75F2413A) of the outdoor unit receives the control and status information from the indoor unit at any time, so as to control the outdoor fan, four-way valve and compressor to complete the corresponding control functions. At the same time, some status of the outdoor unit and some outdoor temperature information will be transmitted back to the indoor unit. For the indoor unit to control.

3 System hardware design

The system circuit schematic diagram is shown in Figure 3.1. Among them, the PS21865A three-phase power full-bridge circuit module is used to realize the power synthesis of the PWM signal to drive the compressor. ULN2003A is a power inverter with open collector output, which is mainly used to drive the relay in the system to control the fan and solenoid valve. The main functions of the SPMC75F2413A microcontroller: 1. Control the entire system according to the command of the indoor unit. 2. Complete the generation and control function of the variable frequency drive signal of the AC variable frequency compressor.

The Power_Line in Figure 3.1 is a half-duplex current loop conversion circuit. It mainly uses power supply and a dedicated communication line to form a current loop between indoor and outdoor. The current loop is powered by the indoor unit. This circuit provides a communication loop for the indoor and outdoor units. The SPWM signal injected with the third harmonic synthesized by SPMC75F2413A is output through IOB0~5, input into PS21865A after buffering and optical isolation, and then output to control the motor. IOB6 of SPMC75F2413A is the error detection input terminal. By detecting the signal it returns, once the PS21865A has an abnormal operation (such as overvoltage, undervoltage, overcurrent, overheating), the driver hardware will immediately prohibit the PS21865A from working, and apply for interruption at the same time, requesting CPU processing. IOA0~3 are analog input ports, mainly temperature sensor interfaces and DC high-voltage measurement interfaces. IOC8~10 are for controlling the four-way valve and the outdoor fan.