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

近年来，即使在用于AC驱动的低成本通用逆变器中，也通常使用10kHz或更高的开关频率。开关频率的该范围对于减小逆变器馈电电机中的转矩涟漪和声学噪声来说可能足够高。从这些观点来看，不再需要进一步增加开关频率。然而，在一些先进的应用中，仍然强烈地需要更高的开关频率以满足对功率转换器的苛刻要求，诸如减小尺寸、减轻重量、更高的输出功率密度、更高精度的输出波形以及更高的速度响应。作为实现更高开关频率的方法，正在积极开发使用诸如SiC和GaN的新材料的下一代功率半导体开关器件。为了充分利用这些高速开关器件的能力，必须开发出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，脉宽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，计数器的分辨率与反相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操作的低分辨率可能导致输出电流中的不期望的低阶谐波分量。在本研究中，探讨了应用噪声整形器来减少由于高开关频率三相PWM电压源逆变器分辨率差而导致的输出波形失真。实验结果表明，噪声整形器是实现高开关频率、高输出波形质量的PWM逆变器的有效方法。

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.