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传动通用逆变器中，也普遍使用10 kHz以上的开关频率。这个开关频率的范围可能足够高，以降低逆变器供电的电机的转矩脉动和噪声。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，仍然迫切需要更高的开关频率，以满足对功率转换器的苛刻要求，如尺寸缩小、重量减轻、更高的输出功率密度、更高的输出波形精度和更高的速度响应。作为一种实现更高开关频率的方法，采用碳化硅和氮化镓等新材料的下一代功率半导体开关器件正在积极发展。为了充分利用这些高速开关器件的能力，必须开发出适合更高开关频率的脉宽调制(PWM)方法。在数字PWM控制器中，由内部时钟信号驱动的数字计数器来控制脉宽。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，较高的开关频率会导致较低的PWM分辨率。PWM操作的低分辨率可能会在输出电流中引起不希望的低次谐波分量。在这种情况下，无法获得更高开关频率的好处。在本研究中，讨论了应用噪声整形器来降低由于高开关频率三相PWM电压型逆变器分辨率低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、高质量输出波形的逆变器的有效解决方案。

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.