Below we described steps needed to understand how the solution has been programmed to create the RPWM three-phase inverter. However, if you just want to get the result of programming, download GreenPAK™ Designer software to view the already completed GreenPAK Design File. Plug the GreenPAK Development Kit to your computer and hit the program to design the device.
In power electronics, several Pulse Width Modulation (PWM) schemes have been successfully employed depending on the particular application. Most of the conventional PWM schemes, being deterministic in nature, produce a predetermined harmonic content. This can create a number of issues in real-world applications like the production of acoustic noise, radio interference, and mechanical vibration. In applications where interference with the environment and other equipment need to be mitigated, for example in industrial motor drives, traction drives, electric vehicles, the conventional PWM schemes inherently do not perform efficiently and additional equipment like electromagnetic interference (EMI) filters need to be added [Bhattacharya, Subhadeep, et al. “A discrete random PWM technique for acoustic noise reduction in electric traction drives.” Energy Conversion Congress and Exposition (ECCE), 2015 IEEE. IEEE, 2015]. One available option to cope with issues resulting in these applications is to increase the switching frequency of the conventional PWM schemes i.e.>18kHz [Capitaneanu, Stefan Laurentiu, et al. “On the acoustic noise radiated by PWM AC motor drives.” Automatika 44.3-4 (2003): 137-145]. However, this causes the switching losses to increase significantly. In such applications random pulse width modulation (RPWM) has been found to be effective to mitigate the cited issues without the need of considerably increasing the switching frequency.
In RPWM the width of each switching pulse varies stochastically. This causes the harmonics cluster to spread over a large range thus reducing the size of separate filters or entirely avoiding the use of filters in certain applications. RPWM technique has successfully been utilized in many power electronics applications e.g. in industrial motor control drives where the acoustic noise needs to be checked.
Usually, high-frequency PWM and RPWM signals for commercial sophisticated systems are implemented using Digital Signal Processors (DSP) and Field Programmable Gate Arrays (FPGA). However, these devices are more generic, powerful, and flexible which makes them quite expensive. Similar precision and high-frequency timing requirements needed for RPWM generation can be met with a low-cost Dialog GreenPAK IC. Many suitable RPWM schemes, especially for open-loop applications, can be implemented using Dialog ICs. Thus, the explicit programming or coding of embedded DSPs, MCUs or FPGAs is replaced by a simple interface provided in the GreenPAK designer. In addition, the size of the overall control circuit is considerably reduced.
There are several ways of producing the RPWM for three-phase inverter applications. In this project, a suitable RPWM technique is presented that can be implemented using the available GreenPAK IC’s resources. The RPWM technique is implemented using the dual matrix SLG46620 IC. Appropriate theoretical proposals and experimental results are also presented including the output voltage waveforms and their harmonic content that would justify the proposed strategy.
Proposed RPWM Scheme
The block diagram of the RPWM scheme driving a three-phase inverter is shown in Figure 1.
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