| A "regenerative load system" is proposed, replacing the conventional load for the long-term testing of power equipment and motor-generator set. This system consists of two parts: (1) impedance emulator and (2) inverter with power filtering function.; The proposed system has three significant merits: economic, safety and power quality. The first merit involves the recycling of the electrical energy, resulting in the energy consumption less than 20% of the conventional load. If the soft-switching technique is employed for the converter, the total energy dissipation can be even lower than 10%. Second, safety is a consideration. Due to the low energy dissipation, no appreciable Joule heating is observed. The third, power quality, is equally important. Since the current from the ac line is shaped into a pure sinusoidal waveform with power factor equal to one, problems such as harmonic currents and EMI will be greatly reduced. Hence the power quality of the utility source can be improved.; In order to accomplish the analysis and design of the system, the following contributions have been made. For the active power filter design, a new control method, using an integrator and sampling technique, is proposed to simplify the calculation algorithm for the real fundamental component of load current. In addition, a new simple control scheme, based on the energy balance concept, is proposed to control the voltage of an energy-storage capacitor.; Secondly, in the design of the system, a memory circuit is used to calculate and memorize the utility source current. This design provides an alternative method to the design of APF control circuits. Third, we have found that the utility source inductance may cause the APF system to become unstable. After the addition of the damping circuit, the system can be stable. However, even with the addition of the damping circuit, the APF or regenerative load system, will still be unstable if the gain of the current controller is greater than one. Therefore, for the stability of the system with utility source inductance, the following conditions must be met: (1) addition of a damping circuit and (2) the current controller gain must be kept smaller than one. This phenomenon has been verified by Matlab control analysis and PSpice simulation and has never been noted in the literature.; Fourth, employment of the equivalent impedance concept separates the regenerative load system into two equivalent subsystems and establishes the "input impedance specification" of the DUT (Device Under Test) for the stability of the "regenerative load system." Fifth, for the improvement of stability margin of the system, a new "two-damping-circuits" concept is proposed. The addition of a second high frequency damping circuit can further improve the stability margin of system. This "two-damping-circuits" concept can be applied also to other circuit design.; Sixth, and lastly, when using the active damping circuit to replace the conventional passive damping circuit, the overall system efficiency is improved. Also, a new "reactive-current-compensation" concept is developed to compensate the reactive component absorbed by the damping circuits. Hence the power factor of the utility source current can be increased to nearly one, even in the presence of the damping circuits. (Abstract shortened by UMI.)... |
