Sensorless Control of 3-Phase PWM Rectifier in Case of Grid Phase Disconnection

Standard drive systems are usually connected to the utility grid using six pulse diode rectifiers. This kind of the rectifiers has many disadvantages, for example non sinusoidal supply currents, non unity power factor, and the DC-link voltage cannot be controlled. To overcome these disadvantages the use of controlled PWM rectifiers seems to be appropriate. There are many control schemes proposed for active rectifiers. One of the most popular schemes is the voltage oriented control (VOC) method. It is easy to implement and simple to analyze especially because of its analogy to the well-known field oriented control (FOC) for the synchronous and asynchronous drives. One of the problems connected with this method is the need for grid voltage measurement. Voltage measurement systems are costly and each failure in the measurement device can lead to the destruction of the PWM rectifier. Due to these problems voltage estimation methods often are implemented. One of the many sensorless strategies, a phase tracking concept was presented on the PESC03 conference. The method proved to be robust to system parameter changes when being used for line current control. It was also successfully tested under the distorted voltage supply like over-voltage and under-voltage. After the presentation of the respective results on the PESC04 conference some questions arose from industry concerning the behavior of the sensorless PWM rectifier when one of the grid phase voltages disrupts. This paper shows the possible solution for this particular problem. The sensitivity of the phase tracking method to the voltage phase asymmetry is also presented. The control was performed on a rapid prototype system for power electronics control according to A. Linder (2001). Experimental results of the test are presented