The Design and Implementation of SCG H-bridge Unit Test System

Abstract

SVG in distribution power grid has completely entered into the practical phase, as Hbridge of the core part of SVG, which is low test efficiency, poor reliability, high cost and requires repeated manual testing in the process of production. This thesis firstly analyzes the test environment of H-bridge unit, put forward the indicators, the overall design of testing system, puts forward the solution, then describes in detail the realization of the system hardware and software solutions, and finally through the chain H-bridge unit test, test the applicability of the system and work stability, this paper designed and implemented the SVG link test system has a broad application prospect. During 2001 to 2003, the United States put the large capacity SVG into use, and proved it has advantages in improving circuit transmission capacity, damping power oscillation, and enhance the system stability is superior performance, which shows that SVG has completely entered the practical stage in transmissiondistribution power grid[1]. H-bridge unit, as the core module of SVG, its performance defines the overall performance of SVG system. To improve the quality of product and system safety in production, before the system put into use the performance test is deemed to undertake, the assemble can start once the test results satisfy the standard. A 35kv / 15mvar cascading SVG has 66 H-bridge unit need to be tested which require 66 times tests. As far as no H-bridge unit performance testing molding system exists, the test of H-bridge unit mainly rely on manual testing, which of low efficiency, poor reliability, high cost, difficulty in data storage, and waste of human resources. Therefore, to develop a set of reliable performance, flexible, easy to operate, suitable for a variety of voltage grade H-bridge unit test system is very meaningful [2]. 1 H-bridge Unit Test Environment 1.1 H-bridge Unit Test Platform H-bridge unit test platform is mainly responsible for DC side capacitor to H-bridge unit module provides a controlled dc power supply, its structure includes industrial power distribution cabinets, voltage regulator, transformer, three-phase rectifier bridge and its control and protection circuit, etc. After air switch closing, test platform getting power, by adjusting the voltage regulator changing the transformer three-phase AC output voltage to achieve the input DC voltage which can change the DC side of H-bridge unit. The structure of H-bridge unit test platform is shown in Figure 1. Figure 1. the circuit of test platform The main parameters of H-bridge unit test platform are as follows: 4th International Conference on Computer, Mechatronics, Control and Electronic Engineering (ICCMCEE 2015) © 2015. The authors Published by Atlantis Press 1235 Power supply:380V Air switch:380V/400A Voltage regulator: 40 kVA/ 50 Hz, self-coupled voltage-adjusting, input: 380 v, output: 0 ~ 430 V Transformer: 200 kVA / 50 Hz, DY11 wiring, Ratio 400:3000 Rectifier bridge, three-phase rectifier bridge (3200 V / 270 A) Test platform capacity: 200 kVA 1.2 H-bridge unit H-bridge unit mainly includes five parts: DC capacitance, H-bridge circuit, DC power supply, controller and drive circuit, its structure is shown in Figure 2. Figure 2. Internal structure of H-bridge unit 2 Design of H-bridge Unit Test System According to the control requirements of cascading SVG system, there is some design requirements of the system performance in this test as follows: (1)the SPWM modulation ratio must be set in the range of 5% ~ 95%. (2) the SPWM carrier frequency, according to the cascading SVG system and the differences of different types of IGBT close frequency characteristic, can be selected as follows: 500hz, 600hz, 800hz, 600hz, 1000hz, 1500hz, 2000hz and other alternatives. (3) the DC voltage in H-bridge unit has real-time acquisition and dynamic display, and display error is within 3%. (4) Faults Display To find the problems in the operation of the unit module, specific communication fault, such as DC over-voltage, IGBT overheat, SPWM wave fiber fault, + 24v power supply fault, H bridge driver fault, these faults must display the accurate positioning in real-time. And the communication failure, IGBT overheat fault, SPWM wave fiber fault, the failure of + 24v power supply, H bridge fault, required the test system to immediately stop SPWM wave sending, as to cancel the SPWM pulse for later transmit fault. (5) Communication Test system with H-bridge unit has two plastic optical fiber functioning as communication between modules, because the SVG system requirement for communication rate is 6.4K BPS, so the test system and communication between H-bridge unit must have a communication rate above 6.4 Kbps. The communication methods using in the test system is asynchronous serial communication. (6) Human-Computer Interaction Test system requirements has a real-time display H-bridge unit operation module, including Hbridge unit modulation, DC voltage, fault information, data, carrier frequency data and other information. Other information can also request by a peripheral module to change SPWM wave