Development of High Speed Digital PWM Controller for High Performance Next Generation Power Devices

近年来，即使在低成本的交流驱动通用逆变器中，也普遍采用10kHz或以上的开关频率。这个开关频率的范围可能足够高，以减少转矩脉动和逆变器供电电机的噪声。从这些角度来看，不再需要进一步提高开关频率。然而，在一些先进的应用中，为了满足对功率变换器的小型化、轻量化、更高的输出功率密度、更高的输出波形精度和更快的响应速度等苛刻的要求，仍然需要更高的开关频率。作为实现更高开关频率的一种方法，使用SiC和GaN等新材料的下一代功率半导体开关器件正在积极开发中。为了充分利用这些高速开关器件的能力，必须开发适用于更高开关频率的脉宽调制（PWM）方法。在数字PWM控制器中，脉冲宽度由内部时钟信号驱动的数字计数器控制。因此，对于给定的内部时钟频率，计数器的分辨率与逆变器的开关频率成反比。因此，较高的开关频率导致较低的PWM分辨率。PWM操作的分辨率差可能会导致输出电流中出现不良的低阶谐波分量。在这种情况下，无法获得更高开关频率的好处。在本研究中，讨论了噪声整形器的应用，以减少高开关频率三相PWM电压源逆变器由于分辨率差而导致的输出波形失真。实验研究表明，噪声整形器是实现高开关频率PWM逆变器高质量输出波形的有效解决方案。

In recent years, switching frequency of 10kHz or above is commonly used even in low cost general-purpose inverters for AC drive. This range of the switching frequency may be enough high for the reduction of the torque ripple and acoustic noise in inverter-fed motors. From these points of view, the further increase of the switching frequency is not needed any more. However, the higher switching frequency is still strongly needed in some advanced applications to meet the severe requirements to the power converters such as size reduction, weight reduction, higher output power density, higher precision output waveforms, and higher speed response. As a method to realize higher switching frequency, power semiconductor switching devices in the next generation using new materials such as SiC and GaN are actively being developed. To utilize the ability of these high-speed switching devices fully, methods for pulse width modulation (PWM) suitable for the higher switching frequency must be developed.In digital PWM controller, the pulse width is controlled using a digital counter driven by the internal clock signal. Thus, for a given internal clock frequency, the resolution of the counter is inversely proportional to the switching frequency of the inverter. Consequently, a higher switching frequency results in lower PWM resolution. The poor resolution of the PWM operation may cause undesirable lower order harmonic components in the output current. In this case, the benefit of the higher switching frequency can not be obtained.In this research, the application of the noise shaper to reduce output waveform distortion due to the poor resolution of the high switching frequency three phase PWM voltage source inverters is discussed. From the experimental investigation, the noise shaper can be effective solution to realize the high switching frequency PWM inverter with high quality output waveforms.