Abstract
This paper deals with the development and design of digitally controllable, three-phase current and voltage power sources. The main, digitally controlled parameters of the power source are frequency, phase-shift and amplitudes of two separate sine-wave systems. Possibilities and means of implementation are discussed and a verified solution is described. The reason why this development was done is the lack of power sources on the market. The three-phase voltage and the tree-phase current systems are isolated by power transformers. Among many possibilities of voltage and current control, the method based on direct digital synthesis was selected. Control circuits of the power sources are described in VHDL and implemented in an FPGA device.
1. INTRODUCTION
This work deals with the design of numerically controlled three-phase voltage and current sources. The main requirement is the independent controllability and mutual phase-shift adjustability of the two three-phase systems. At present there are several companies that produce similar devices. Still, it is very difficult to find a power source on the market that satisfies the requirements for technical parameters. Professionally produced power sources are very expensive, unique devices. There are many needs for AC sources usage, such as setting of power equipment parameters, testing of over-current protection relays, etc.. The motivation for our research was designing a controllable power source that can be used as a component of a real-time simulator of a synchronous generator behavior. The outputs of these power sources are three-phase signals representing the output voltage and output current of a synchronous generator. In order to connect the power sources in a feedback, the system also includes digital and analog inputs and outputs compatible with the excitation regulator input and output circuits.
5. CONCLUSIONS
The requirements specified in Chap. 1.1 were achieved. The first version of controllable current and voltage power sources was developed and verified. The control unit and the test application can be used as a laboratory current and voltage power source or as a component of a real time synchronous generator simulator. The measured level of voltage source efficiency is 87 %. The measurement was performed for 50 % input value and maximum load. The measured level of current source efficiency is 86 %. The measurement was performed for 50 % load value. The following development in this field should aim to increasing the power sources efficiency. The connection of the control unit to the control computer could be done via USB.
