High-performance three-phase variable frequency power supply based on SPMC752413A microcontroller

1 Introduction
Variable frequency power supply is a power conversion device, which has the advantages of pure output waveform, stable output voltage, adjustable output frequency and output voltage. Its good performance is widely used in sensing, instrumentation, industrial control and other fields. This article mainly introduces the development of high-performance three-phase variable frequency power supply using SPMC75F2413A and IPM (PS21865A).
2 Introduction to chip features
SPMC752413A is a new member of the μ'nSP™ series of products. It is a 16-bit microcontroller specially launched by Lingyang Technology for variable frequency drive. It has excellent performance timer and PWM signal generator group.
SPMC75F2413A has an operating speed range of 0~24MHz within the operating voltage range of 4.5V~5.5V, and has 2K words of SRAM and 32K words of flash ROM; up to 64 programmable multi-function I/O ports; 5 general-purpose 16-bit timers/counters (including two motor drive dedicated PWM waveform generators and two position detection interface timers), and each timer has a PWM event capture function; 2 dedicated timing programmable cycle timers; programmable watchdog; low voltage reset/monitoring function; 8-channel 10-bit analog-to-digital conversion. With the support of these hardware peripherals, SPMC75F2413A can easily realize various frequency conversion systems.
The characteristics of SPMC75F2413A are as follows:

1. High-performance 16-bit CPU core a) Sunplus 16-bit u'nSP processor (ISA 1.2) b) On-chip phase-locked loop-based clock generation module c) Maximum system frequency Fck: 24MHz 2. On-chip memory a) 32K Words (32K×16bit) Flash b) 2K Words (2K×16bit) SRAM 3. Operating temperature: -40 ℃～85 ℃ 4. 10-bit ADC module a) Programmable conversion rate, maximum conversion rate 100Ksps b) 8 external input channels c) Can be linked with timers such as PDC or MCP to achieve electrical parameter measurement in motor control 5. Serial communication interface a) Universal asynchronous serial communication interface (UART) b) Standard peripheral interface (SPI) 6. 64 (QFP80)/48 (QFP64) general-purpose input and output pins 7. Programmable watchdog timer 8. Embedded online emulation circuit ICE interface: can realize online emulation , debugging and downloading of general 16-bit timer/counter

1. PDC timer a) Two PDC timers: PDC0 and PDC1 b) Can process three capture inputs at the same time c) Can generate three PWM outputs (center symmetric or edge mode) d) Dedicated position detection interface for BLDC drive e) Two-phase incremental encoder interface, supports four working modes, and has a quadruple frequency circuit 2. MCP timer a) Two MCP timers: MCP3 and MCP4 b) Can generate three-phase six-channel programmable PWM waveforms, such as three- phase SPWM, SVPWM, etc. c) Provide PWM duty cycle value synchronous loading logic d) Can be synchronized with PDC position detection changes e) Programmable hardware dead zone insertion function, dead zone time can be set f) Programmable error and overload protection logic 3. TPM timer a) One TPM timer: TPM2 b) Can process two capture inputs at the same time c) Can generate two PWM outputs (center symmetric or edge mode) Two CMT timers

3 System Overall Solution Introduction
This high-performance three-phase variable frequency power supply system is mainly composed of Lingyang 16-bit single-chip microcomputer SPMC75F2413A and Sanling's IPM power module chip PS21865A. The system block diagram is shown in Figure 3-1.


Figure 3-1 System Block Diagram

Functions of this system:
The system operating parameters can be adjusted to meet the needs of different applications to adjust the system's output frequency and output voltage;
it has real-time information and status display, which is mainly used for the current system status information display and part of the human-machine interface;
it has a keyboard for system parameter setting and control;
it has a complete system protection function to protect the system from damage when the system is abnormal;
system workflow:
SPMC75F2413A receives the control information from the keyboard or communication interface according to the settings and generates the corresponding SPWM drive signal. The signal is output after the PS21865A power conversion, output filtering and output transformer. At the same time, SPMC75F2413A will monitor the operation of the system at any time to ensure that the output is normal. Once an abnormality occurs, it will immediately protect and alarm to remind the user to handle it.
4 System hardware design
The core circuit of the entire system is the waveform synthesis circuit, and its structure and performance determine the performance of the entire system. The waveform synthesis circuit of this system is composed of SPMC75F2413A, power module PS21865A, output transformer and output filter circuit. The PS21865A contains a three-phase power bridge and a corresponding drive circuit to realize the power amplification function of the SVPWM signal. The output transformer and output filter circuit are mainly used to convert the PS21865A output power SVPWM signal into a sinusoidal output and filter out its high-order harmonics to ensure the purity of the output waveform. The main functions of the SPMC75F2413A microcontroller are: 1. Generate the SVPWM signal required to drive the variable frequency power supply. 2. Complete human-computer interaction to facilitate user control of the system. 3. Process related abnormal information to ensure the safety and reliability of the system.
The three-phase complementary SVPWM signal generated by the SPMC75F2413A is output through the chip's IOB0~5 to control the three-phase full-bridge circuit of the PS21865A. The signal is output to the load after power synthesis, low-pass filtering and a three-phase output transformer. At the same time, the system's operating current and output voltage will be fed back to the SPMC75F2413A for system control. IOB6 and IOB7 of SPMC75F2413A are error detection and overload protection input terminals. By detecting the signals sent back, once PS21865A has abnormal working conditions (such as overvoltage, undervoltage, overcurrent, overheating) and system overload, the driver hardware will immediately prohibit PS21865A from working, and apply for interrupts to request CPU processing.
Since other modules are common modules, they are not described in detail here. Please refer to Figure 3-1 for the structure of the entire system.
5 System software design
The entire system software is divided into three parts: 1. The core waveform generator, which is mainly the SVPWM signal generator and some related driver service programs; 2. System control program; 3. Human-machine interface program;
The structure of the core waveform generator part of the system is shown in Figure 5-1. Here, a simplified SVPWM signal generator structure is used according to the characteristics of this system. This part of the structure (except the PWM generation module) will be implemented by software in the PWM periodic interrupt. The modulation coefficient calculation and multiplier here are mainly used to achieve waveform amplitude control and power supply fluctuation compensation.



Figure

5-1 Drive Structure
The PWM periodic interrupt service subroutine is the core of the whole waveform synthesis. Its flow is shown in the figure. The program will execute in the order of phase accumulation and the table calculation of the sine and cosine coefficients of the current phase, vector coefficient calculation, space vector transformation and duty cycle update, and return after completion.


Figure 5-2 PWM interrupt service subroutine flow chart

The system control part is the heart of the whole system coordination. The whole system works in an orderly manner under its coordination. This part mainly gives corresponding control information according to the system settings and the current system status to ensure the reliable operation of the system.
The human-machine interface program mainly provides users with a simple and easy-to-use interactive interface to facilitate users to reliably control the inverter. Including the start and stop of the inverter and the setting of various operating parameters are all executed at this level.

6 Conclusion
Usually, in the process of developing frequency conversion equipment, it is necessary to write real-time and highly readable code, and then hybrid programming is needed. Lingyang's m'nSP™ IDE has a good programming environment, which can easily and easily perform hybrid programming (calling the assembly program in the C program, and calling the C program in the assembly program). The system uses two timers and about 30 IO port resources of SPMC75F2413A. In fact, the resources of SPMC75F2413A are quite rich. Because it has professional frequency conversion hardware support, the development of the frequency conversion system becomes relatively simple. At the same time, SPMC75F2413A has a very outstanding performance in frequency conversion control. Therefore, the frequency conversion system based on SPMC75F2413A has broad application prospects in the frequency conversion fields such as general frequency conversion and frequency conversion home appliances.

7 References
[1] Lei Sixiao, Li Bocheng, Lei Xiangli, etc., MCU Principles and Practical Technology - Lingyang 16-bit MCU Principles and Applications [M] Xi'an: Xi'an University of Electronic Science and Technology Press
[2] SUNPLUS, SPMC75F2413A Programming Guide V1.1 [M] Beijing: SUNNORTH
[3] Mitsubishi, PS21865A Data Sheet [M]