Tang Guangfu

A study on MMC model and its current control strategies

Modular multilevel is a new type of topological structure. The voltage source converter that adopts this type is named as Modular Multilevel Converter-MMC. In this paper, the operating principle of MMC is analysed and the mathematical model based on switching function is presented, and then average value model of MMC in DQ coordinates is deduced in order to meet the requirements of MMC control system design. The non-linear current decoupling control strategy is proposed. Computer simulation is performed to verify the MMC model and the efficiency of current control strategy. In addition, the simulation results show good performance and the quick response ability of the proposed controller.

Research of AC/DC Parallel Wind Farm Integration Based On VSC-HVDC

With wind power taking up an increasingly important share of the total power generation in the system, the larger proportion of wind power have led to problems such as voltage instability, inappropriate power flows etc. The great demand of wind power requires enhanced system capacity, while securing the power quality and AC stabilization. The capacity of VSC-HVDC for fast independent active and reactive power control provides important benefits regarding power quality and successful and reliable system operation. In this paper the parallel AC-DC system for wind power generation is presented. To verify the basic operation principles of operating wind farm and advanced control strategies of VSC- HVDC transmission, the wind farm consisted of five wind turbines with pitch control systems and the VSC-HVDC transmission with relative control systems are modeled by PSCAD\EMTDC to test control algorithms, to identify problems, to investigate different modes of operation of the system and to demonstrate the unique capability of integrating large wind farm to network by VSC-HVDC. Simulation results show that VSC-HVDC transmission is an excellent tool to transmit power from wind farm to a network and at the same time it will contribute to AC stabilization and power quality.

Interaction Analysis and Coordination Control between SSSC and SVC

With the wide application of flexible AC transmission system (FACTS) controllers in power system, the researches have been interested in on interaction among FACTS controllers, on interaction between FACTS controller and power system. This interaction can bring negative influence on the reliability of system. With technical development, power electronics devices, such as GTO, IGCT and IGBT, have been applied widely in power system. A typical application is the static synchronous series compensator (SSSC) , a series reactive power compensation device. In this paper, the relative gain array (RGA) theory is proposed to analyze the interaction between SSSC and static var compensator (SVC); And the negative interaction is solved through direct feedback linearization (DFL) based nonlinear control. Finally, the effect of the proposed methods are confirmed on a single machine infinite bus system with a SSSC and a SVC, and the simulation results agree with that from RGA theory described in this paper.

Research of Main Circuit on the Series Resonance Fault Current Limiter

Fault current limiter can limit short circuit current of the bulk load centre. The series resonant fault current limiter (SRFCL) has more advantages than others applied on the EHV. It increases the system stability and has flexible ways to adapt the system operation mode. Bypass breaker is the key technology of SRFCL. The multi-bypass breaker design for protecting the capacitor is introduced in this paper. Based on the main circuit, the resonance parameters are analyzed in the background of one machine-infinity bus system. The results of simulation experiments show that the parameters are optimized and SFRCL gets good response to the fault.

A New Overcurrent Test Equipment for TSC Valve

Rough test must be done before the TSC (Thyristor switched capacitor) is put into service, to demonstrate the proper design of the valve during over-current conditions, caused by valve firing at instants with non-zero voltage between its terminals. However, modern TSC thyristor valves have a high power rating and are difficult to test directly. The core to design TSC over-current test equipment is to correctly reproduce the stresses on the thyristor under fault conditions. The overcurrent fault conditions of TSC and the corresponding current, voltage and heating stresses on the thyristor valves during over-current are studied. The existing test equipments are appraised. New overcurrent test equipment for TSC valve is proposed. The heating current of the new test equipment is supplied by large current source; the over-current and corresponding reapplied voltage are produced by LC resonant circuit. The schematic diagram of the test equipment is given. The working principles are introduced, and the real test waveforms are analyzed. It is proved that the proposed new over-current test equipment is more flexible, whose test ability is also improved evidently, and the most important is that the new equipment can fully meet the IEC standard so is more equivalence to the real fault, which make it override all the existing TSC over-current test equipment.

Upgrade Study of High Power Electronics Laboratory for ±800kV UHVDC Valves

The paper mainly described the upgrade study of High Power Electronics Laboratory (HPEL) in China Electric Power Research Institute (CEPRI), which will meet all the test requirements of plusmn 800 kV UHVDC valves. Based on the valves electrical parameters of plusmn 800 kV UHVDC demonstration project in China, the paper studied the UHVDC valve type test technology, gave the valve test parameters, the main equipments topologies, rated parameters and the basic waveshapes of the UHVDC valve insulation and operational tests.