Topology and control design of a sinusoidal very low frequency high voltage generator

To reduce the volume and the structural complexity of a very low frequency (VLF) high voltage (HV) generator, this paper introduces a novel sinusoidal VLF HV generator with 2 high frequency HV (HFHV) transformers and 2 metal-oxide semiconductor field-effect transistor cascaded HV bridge arms. Series-parallel resonant converter technology is applied to reduce the impact of the distributed parameters, decreasing the power loss and the volume of the transformer. Both the switching frequency and the duty cycle are utilized as actuating variables to cope with the large ranges of output. Simultaneously, the principle of segmental data processing is proposed to obtain different steady-state operating points, greatly reducing the calculation of the microcontroller unit (MCU), improving the accuracy of the control strategy, and the system response time. As a result, the control strategy is successfully achieved by the MCU dsPIC33FJ128MC706. The test of the 35 kV/0.1 Hz VLF HV power supply is taken on a capacitor (1.5 mu F), which is equivalent to the cross-linked polyethylene cable in the electrical characteristics. When the input voltage varies between 180 V and 250 V, the accuracy of the sinusoidal VLF HV is 2%. The step change response time is less than 120 mu s when the output changes from no-load to full-load. The total harmonic distortion is less than 1%, which meets the IEEE400.2 standard well. The total weight of the generator is less than 20 kg. The results of the experiment verify the accuracy and feasibility of the control theory and the topology.