Research And Design On0.1Hz VLF Cosine Square Wave System

Cross-linked polyethylene cable with its easy installation, good thermal performance, large transmission capacity, high reliability, simple operation and maintenance, economic advantages to replace the traditional paper insulated cable, became the main body of the urban distribution network. Conventional DC voltage test is not suitable for XLPE cables,0.1Hz VLF cosine square wave voltage test as a new cable pressure test equipment has small in size, low power needs, easy to carry, power frequency equivalence well, no hidden damage characteristics, which is widely used by the German, European power systems. Traditional foreign0.1Hz VLF cosine wave equipment uses the system structure of HVDC source regulation voltage and polarity switching circuit one-way booster. One-way booster easily lead to space charge accumulation, which is going ill with cable stable operation. Mechanical rotating rectifier control is relatively cumbersome, due to its low frequency, the system needs additional resistance discharge circuit.In this paper, the system structure is the HVDC source stabilize voltage and the polarity switching circuit regulate voltage and frequency. Due to the HVDC source is only responsible for stabilizing voltage, using only an analog IC-IR1150achieved stability and PFC, simplified the control circuit and improved power efficiency. The polarity switching circuit with reverse feeding circuit realized bidirectional voltage consistent, reduced the space charge accumulation, improved power frequency equivalence. Using high voltage relay and low silicon rectifier stack instead of rotating rectifier simplified the control circuit and canceled additional resistance discharge circuit which is replaced by LC oscillatory discharge circuit, improved discharge effectiveness.The first part of this paper describes the research background, analyses XLPE cable voltage test, discusses the mechanism of the One-way booster leads to space charge accumulation. By contrastive analyzed the HVDC source and polarity switching circuit with traditional circuit, provided topological diagram of the system.The second part describes in detail the hardware design of HVDC source, including: Boost-APFC DC chopper circuit, half-bridge inverter circuit of constant frequency control,4times bidirectional voltage doubling rectifying circuit.First, the third section elaborates on the topology and principle of the polarity switching circuit, then describes the tuning of its hardware parameters, finally, introduces the ways of digital control based on MCU, included drive circuit, breakdown protection and program design diagram. At last, it builds the model via the Platform of Matlab/Simulink, and the simulation results verifies the correctness of theoretical analysis and design.