1 Introduction
A frequency converter is a power conversion device that offers advantages such as pure output waveform, stable output voltage, and adjustable output frequency and voltage. Its superior performance makes it widely used in sensing, instrumentation, and industrial control. This article mainly introduces the development of a high-performance three-phase frequency converter using the SPMC75F2413A and IPM (PS21865A).
2. Chip Features Overview The SPMC752413A is a new member of the μ'nSP™ series, a newly launched 16-bit microcontroller from Sunplus Technology specifically designed for frequency converter drives. It features high-performance timers and PWM signal generators.
The SPMC75F2413A operates within a 4.5V to 5.5V voltage range and has a speed range of 0 to 24MHz. It features 2K words of SRAM and 32K words of Flash ROM; up to 64 programmable multi-function I/O ports; five general-purpose 16-bit timers/counters (including two dedicated PWM waveform generators for motor drives and two position detection interface timers), each with PWM event capture functionality; two dedicated programmable periodic timers; a programmable watchdog timer; low-voltage reset/monitoring functionality; and an 8-channel 10-bit analog-to-digital converter. With these hardware peripherals, the SPMC75F2413A can easily implement various frequency conversion systems.
The features of the SPMC75F2413A are as follows:
3. System Overall Scheme Introduction
This high-performance three-phase frequency converter power supply system is mainly composed of Sunplus 16-bit microcontroller SPMC75F2413A and Mitsubishi IPM power module chip PS21865A. The system block diagram is shown in Figure 3-1.
Figure 3-1 System Block Diagram
The functions of this system are:
The system operating parameters are adjustable to adapt to the needs of different applications by adjusting the system's output frequency and output voltage;
It features real-time information and status display, primarily used for displaying the current system's status information and as part of the human-machine interface;
It has a keyboard for setting and controlling system parameters;
Comprehensive system protection functions protect the system from damage in the event of system malfunction;
System workflow:
The SPMC75F2413A receives control information from the keyboard or communication interface and generates corresponding SPWM drive signals. These signals are then converted by a PS21865A power converter, filtered, and transformed by an output transformer before being output. Simultaneously, the SPMC75F2413A continuously monitors the system's operation to ensure normal output. In case of any abnormality, it will immediately activate protection and sound an alarm to alert the user.
4 System Hardware Design
The core circuit of the entire system is the waveform synthesis circuit, whose structure and performance determine the overall system performance. This system's waveform synthesis circuit consists of several parts: an SPMC75F2413A, a PS21865A power module, an output transformer, and an output filter circuit. The PS21865A internally contains a three-phase power bridge and corresponding driver circuitry, used to amplify the SVPWM signal. The output transformer and output filter circuit are mainly used to convert the PS21865A's output 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. To generate the SVPWM signal required to drive the frequency converter. 2. To enable human-machine interaction, facilitating user control of the system. 3. To handle relevant abnormal information, ensuring the system's safety and reliability.
The three complementary SVPWM signals generated by the SPMC75F2413A are output through IOB0-5 of the chip to control the three-phase full-bridge circuit of the PS21865A. The signals are then output to the load after power combining, low-pass filtering, and a three-phase output transformer. Simultaneously, the system's operating current and output voltage are fed back to the SPMC75F2413A for system control. IOB6 and IOB7 of the SPMC75F2413A are error detection and overload protection inputs. By detecting the signals returned from these inputs, if the PS21865A experiences an operational abnormality (such as overvoltage, undervoltage, overcurrent, or overheating) or a system overload, the driver hardware will immediately disable the PS21865A and request an interrupt for CPU processing.
Since the other modules are common modules, they will not be described in detail here. Please refer to Figure 3-1 for the overall system structure.
5 System Software Design
The entire system software is divided into three parts: 1. The core waveform generator, which mainly consists of the SVPWM signal generator and some related driver service programs; 2. The system control program; 3. The human-machine interface program.
The core waveform generator of this system is shown in Figure 5-1. A simplified SVPWM signal generator structure is used here to suit the characteristics of this system. This part of the structure (excluding the PWM generation module) will be implemented in software during 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 waveform synthesis. Its process is shown in the figure. The program will execute in the following order: phase accumulation and lookup calculation of the sine and cosine coefficients of the current phase, vector coefficient calculation, space vector transformation and duty cycle update, and then return after completion.
Figure 5-2 Flowchart of PWM interrupt service subroutine
The system control unit is the heart of the entire system, coordinating its operations. The entire system functions smoothly under its control. This unit primarily provides corresponding control information based on system settings and the current system status to ensure reliable system operation.
The human-machine interface (HMI) program primarily provides users with a simple and easy-to-use interactive interface to facilitate reliable control of the frequency converter. This includes starting and stopping the frequency converter and setting various operating parameters.
6. Conclusion Typically, the development of variable frequency drives (VFDs) requires writing code that demands real-time performance and high readability, necessitating hybrid programming. Sunplus's m'nSP™ IDE provides an excellent programming environment, enabling easy and straightforward hybrid programming (calling assemblers from C programs and vice versa). This system utilizes two timers and approximately 30 I/O ports from the SPMC75F2413A, which offers a wealth of resources. Its professional VFD hardware support simplifies VFD system development. Furthermore, the SPMC75F2413A demonstrates outstanding performance in VFD control. Therefore, VFD systems based on the SPMC75F2413A have broad application prospects in general-purpose VFDs, VFD home appliances, and other VFD-related fields.
7 References
[1] Lei Sixiao, Li Bocheng, Lei Xiangli, et al., Microcontroller Principles and Practical Technology—Sunplus 16-bit Microcontroller 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 Datasheet [M]
