Poloidal Field Converter Research Articles

Installation Design and Integration of Poloidal Field Converter Units for ITER

The poloidal field (PF) converter units (CUs) with the four-quadrant operation and circulating current capability is to supply power to International Thermonuclear Experimental Reactor (ITER) superconducting magnets. To ensure PF converter system safety and reliability for the operation, the safety distance of transformer installation calculated and studied. The electromagnetic field of the installed equipment is analyzed and discussed to determine the installation layout design of the equipment. When the converter power supply system operates at the steady-state rated current of 55 kA, the heat dissipation of the equipment is analyzed to determine the design of the cooling water system. The grounding of the system is calculated according to the application scenario. According to the equipment performance parameters and operation requirements of the PF converter system, the electrical, mechanical, and water system test and acceptance criteria test presented to ensure the state of system installation and integration and the safety and reliability of operation.

Seismic Analysis Under SL-1 of New Structure Support Frame for ITER PF Converter System

The support frame is an important part of International Thermonuclear Experimental Reactor (ITER) poloidal field (PF) converter system. It is mainly used for dc busbars and dc disconnector switch support. This article mainly introduces a seismic analysis of three types of support frame. In order to evaluate the seismic response of the structure under specific seismic excitation, a method based on response spectrum is adopted in this article. The design earthquake spectrum of seismic level one (SL-1) with a damping factor of 2% as well as 4% provided by ITER is applied as load. The analysis is to define the maximum reaction forces, deformations, and equivalent stress of the support frame under seismic loads.

System-Level Analysis on the Effects of Seismic on Reliability of Rectifier Transformer for ITER Poloidal Field Converter Unit

This article proposed a seismic analysis method for rectifier transformer of International Thermonuclear Experimental Reactor (ITER) poloidal field converter based on response spectrum. The seismic response of structure under specific seismic excitation is evaluated by using the earthquake spectrum of seismic level one (SL-1) with damping factor of 2% provided by ITER. The results show the maximum deformation and stress are 31.18 mm (control cubicle) and 181.62 MPa (support of oil tank), respectively, which are less than the allowable stress. In addition, the simulation analysis is introduced in detail and the results as the displacements, stresses, and reactive forces are also presented. The seismic analysis method proposed in this article provided a reference for the seismic design of rectifier transformer of ITER polar field converter, and also provides ideas for the seismic design of similar large electrical equipment.

Fault analysis and solution in current sharing test of ITER PF converter bridge

International thermonuclear experimental reactor (ITER) poloidal field (PF) power supply is composed of 14 sets of AC/DC converter units. Converter bridges are the key components of ITER PF converter unit, which is supplied by converter transformer and output the on-load voltage (±1.05 kV) and the rated DC current (±27.5 kA). There are 12 thyristor branches in parallel on each arm of the converter bridge. Therefore, the current sharing test is essential to verify the current sharing characteristics of the converter bridge arm under steady rated current. At present, the current sharing tests of Converter Bridge for 14 sets of converter units have been completed. During the test, there have been all kinds of faults. Accordingly, the fault reason should be analyzed firstly, and then corresponding effective measures should be taken for specific reasons. This paper mainly presents the fault analysis methods and the corresponding treatment measures aiming at all kinds of faults appearing in the test. The contents described in this paper can provide guidance and reference for current sharing test of high-current converter applied in other fields.

Circuit Controller for PF Converter System Based on CODAC Core System

The poloidal field converter system of the International Thermonuclear Experimental reactor, which is developed, assembled, and tested by the Institute of Plasma Physics of the Chinese Academy of Sciences, uses the CODAC core system provided by ITER organization to design its control system. This paper completes the design of the circuit control system as well as realizes the transmission, state transition, and real-time control of the operating status of the poloidal field converter system to meet specific requirements for the control cycle of the control system. This paper provides solutions to some key problems, such as the state transition, real-time transmission, and operating state display, and real-time control of the converter circuit control system. The system designed by this paper has been successfully tested in the ITER PF prototype and ITER PF test platform.

The voltage response test of ITER PF converter bridge

As the key component of international thermonuclear experimental reactor (ITER) poloidal field (PF) converter units, converter bridges are supplied by converter transformer with two primary and two secondary three-phase windings, and output the on-load voltage (±1.05 kV) and the rated DC current (±27.5 kA). Moreover, the converter bridge should provide the symmetrical voltage response not more than 2 electrical cycles (40 ms) for full scale change (-1.05 kV to 1.05 kV) when the AC power is in the rage of 62 kV–72 kV. The voltage response test is essential to verify the voltage response performance of PF converter bridge meet ITER requirements or not. The double closed-loop control mode of inner current loop and outer voltage loop is usually adopted in the dynamic response test of low-power converter in other fields. ITER PF converter is a special high-power converter used in nuclear fusion field. According to its operation characteristics, the voltage step response of the converter only needs to be detected in the case of open-loop voltage, and the output current of the converter must reach the rated value in the process of voltage response. Therefore, the double closed-loop control method is not suitable for the voltage response test of ITER PF converter, and a new and reasonable test scheme need to be designed. This paper mainly presents the analysis and design of the voltage response test scheme, and the feasibility of test scheme is confirmed by the simulation results and test results, which will provide the method and reference for the voltage response test of high-power converter in nuclear fusion field.

Seismic design of external bypass for ITER poloidal field converter

The main purpose of this research is to survey seismic performance of equipment. It discusses and provides a theoretical seismic model through the response spectrum method. With this seismic model, maximum equivalent stress, directional deformation and reaction force of fixed supports under seismic excitation are calculated by simulation. The results indicate that the maximum equivalent stress is no more than 8.3 MPa, and the maximum directional deformation is no more than 2.6 mm. From these results we can also see that the structure of external bypass can meet anti-seismic requirements. The research has resulted in a solution for seismic analysis and design of large electrical equipment.

Final Design and Analysis of Control Strategies on ITER PF Converter

The ITER poloidal field (PF) coil power supply system consists of 14 basic converter units that feed six superconducting coils. The converter unit is the complicated, challenging, and unique system to realize four-quadrant operation compatible with the superconductive load and the demand for plasma control. This paper describes the final design of the control strategies, which are implemented in the local controller of the PF converter system. They are zero crossing current control strategy in circulating operation mode, current balance control strategy in parallel operation mode, and hysteresis band control strategy in mode transition. In addition, the performance of the control system is demonstrated by the analysis, and the control strategies are validated by the simulations and corresponding tests.

Fuzzy Controller Using Circulating Mode for ITER Poloidal Field AC/DC Converter System

This paper proposes a novel technique using fuzzy logic controller (FLC) in circulating mode to improve the performance of the International Thermonuclear Experimental Reactor (ITER) poloidal field (PF) converter systems. The accurate mathematical modeling of the complex system is challenging using conventional proportional integral and derivative (PID) controller. The novel approach using FLC overcomes the complexity of the modeling by human expert’s knowledge and experience. The FLC is considered for ITER PF converter system and compared with a conventional PI controller. The dynamic behavior and transient response of the PF converter system in the circulating mode are verified by analysis and simulation. The analysis results determine that the FLC can achieve better operation performance.

System Realization of CASHIPS DC High Power Test Facility

Aims to complete the test of the International Thermonuclear Experimental Reactor (ITER) poloidal field (PF) converter system, and to meet future continuous upgrading needs of a modern industrial power system and scientific research, direct current (DC) high-power test facility of Hefei Institutes from Physics science, Chinese Academy of Sciences (CASHIPS) is built in 2011. As the largest DC high-power test facility in China, the rated steady state DC current is 120 kA and the pulse peak current is 500 kA. Four thyristor-based AC/DC converter modules are paralleled to handle this huge current. In May 2017, 15 testing items are accredited by the China National Accreditation Service (CNAS) for Conformity Assessment . Tip to now, the test for 17 devices of 16 companies and manufacturers in the world have been completed. In this paper, the topology and the control of DC High-Power test facility are presented. In addition, the testing capability and the completed tests of DC high-power test facility are illustrated.

Thermal design of external bypass for ITER poloidal field converter

The main objective of our investigation has been to survey thermal condition of equipment working in high power state work. A theoretical thermal model has been developed for the thermal design of external bypass. The junction temperature of thyristor, thermal stability and heat distributions of arms have been numerically studied. The peak junction temperature decreases with the parallel number of thyristor increases, while the parallel number is limited to the current sharing distribution. The calculated results indicate that the external bypass has excellent potential power performance and reliability. It has also been found that the temperature of stainless steel arms is highest and the bypass can work again after its first work in 390 s when all units return initial temperature. The test results show that thermal condition of the prototype is consistent with the analysis data. The research has resulted in a solution of high-power equipment.

Current sharing design of ITER poloidal field converter bridges

Due to high rated current and special Fault Suppression Capacity (FSC) criterion, 12 thyristors connected in parallel are applied in one bridge arm of ITER Poloidal Field (PF) converter. A large amount of parallel thyristors will give rise to significant difficulties in the current sharing design due to the electromagnetic coupling between different parts of the bridge arm. This paper presents a new method to analyze the influence of the electromagnetic coupling on current sharing performance and guide the bridge arm structure design. At first, the bridge arm is decomposed to many segments and the stray inductances are extracted. Then, an equivalent circuit of the decomposed model is built and a mathematical model is established to analyze the circuit. It will result in the current waveforms of parallel thyristors and thus provide the current sharing information. Based on the mathematical model, the optimization design of PF converter is conducted along with conventional methods. Experimental tests are also performed, and the results fit well with the analyzed ones. The current sharing coefficient of the 12-parallel thyristors is over 0.8, which is far beyond the value required by ITER Organization. In a word, the method presented in this paper provides an effective tool for the current sharing structure design for high-current fusion power supplies.

Operation Analysis and Improvement of Impulse Current Test on High-Power DC Test Platform With SVC System

The international thermonuclear experimental reactor poloidal field converter unit is comprised of four converter bridges, dc reactors, dc switches, etc., and most are nonstandard. To evaluate the performance of these equipments, a high-power dc test platform has been built to carry out the steady-state current test and impulse current test. The latter is significant to verify the fault suppression capability of products. The dc test platform can output the rated 400-kA impulse current. The principle design and structure of the dc test platform is introduced in this paper. The transient large current in impulse current test could cause huge impact reactive power and grid voltage sag. The impact is analyzed by theoretical calculation and simulation. A static var compensator system is added to suppress the transient effects of the reactive power. A predictive reactive power control strategy is proposed to improve the dynamic response. The comparisons with the traditional control demonstrate that the proposed control is effective in compensating impact reactive power and it also performs well on inhibiting the grid voltage sag.

Design a Suitable Test Scheme for Triggering Bypass Protection Test of ITER PF Converter Unit

The external bypass, as an important component of the international thermonuclear experimental reactor (ITER) poloidal field converter unit (PFCU), will provide a freewheeling loop for the load current to protect the magnets and PF converter modules from being damaged by overcurrent and overvoltage under fault conditions. The triggering bypass protection test is used to verify that the designed bypass is triggered normally and endure the rated load current. In this paper, a suitable test scheme is designed for triggering bypass protection test of ITER PFCU based on the PF converter integrated test platform at the Institute of Plasma Physics, Chinese Academy of Sciences. This test scheme includes the triggering bypass method, calculating the trigger angle of the converter in inverter and a method of reducing the bypass current to zero in the absence of ITER mechanical switch. The feasibility of the test scheme is successfully verified by the simulation results and test results, both of which prove that the external bypass of ITER PFCU is triggered normally and withstands the load current for 100 ms. Due to the integrated inductance of the actual dc output circuit, the actual transfer time of bypass current in the test is more than the simulation results.

The sequential control of ITER PF in series converters

The international thermonuclear experimental reactor (ITER) poloidal field (PF) converter system leads to fluctuation of reactive power flow in AC grid, which has become a major concern in PF converter system. A static var compensator (SVC) will be installed for reactive power compensation thereby improving the voltage stability of AC grid. The ITER PF in series converters, which consisted by three converter units connecting in series, provide an additional method to decrease the reactive power. In this paper, the detailed theoretical analysis is carried out to investigate an optimal sequential control algorithm of ITER PF in series converters with the consideration of commutation angle. Moreover, representative simulation and experimental results of the proposed optimal sequential control are presented to show its effectiveness in comparison with the symmetrical control.

Harmonics analysis of the ITER poloidal field converter based on a piecewise method

Poloidal field (PF) converters provide controlled DC voltage and current to PF coils. The many harmonics generated by the PF converter flow into the power grid and seriously affect power systems and electric equipment. Due to the complexity of the system, the traditional integral operation in Fourier analysis is complicated and inaccurate. This paper presents a piecewise method to calculate the harmonics of the ITER PF converter. The relationship between the grid input current and the DC output current of the ITER PF converter is deduced. The grid current is decomposed into the sum of some simple functions. By calculating simple function harmonics based on the piecewise method, the harmonics of the PF converter under different operation modes are obtained. In order to examine the validity of the method, a simulation model is established based on Matlab/Simulink and a relevant experiment is implemented in the ITER PF integration test platform. Comparative results are given. The calculated results are found to be consistent with simulation and experiment. The piecewise method is proved correct and valid for calculating the system harmonics.

Research on the test scheme of fault suppression capability for ITER PF converter

Fault suppression capability (FSC) test with DC short downstream DC reactor of international thermonuclear experimental reactor (ITER) poloidal field (PF) converter is performed to verify the thermal stability characteristics of the converter bridge arms. In this paper, firstly, DC short downstream DC reactor of ITER PF converter is analyzed to get the fault current. Then, the appropriate test scheme is designed and the feasibility of the test scheme is verified by simulation based on test platforms in Institute of Plasma Physics, Chinese Academy of Science (ASIPP). Finally, the effectiveness of the designed test scheme results are verified by the test platforms in ASIPP.

Feasibility analysis of fuzzy logic control for ITER Poloidal field (PF) AC/DC converter system

This paper describes the feasibility analysis of the fuzzy logic control to increase the performance of the ITER poloidal field (PF) converter systems. A fuzzy-logic-based controller is designed for ITER PF converter system, using the traditional PI controller and Fuzzy controller (FC), the dynamic behavior and transient response of the PF converter system are compared under normal operation by analysis and simulation. The analysis results show that the fuzzy logic control can achieve better operation performance than PI control.

Stray Magnetic Field Analysis of ITER Poloidal Field Converter Unit

Due to the space limitation and safety concerns, the non-same-phase anti-parallel connection structure is applied in the International Thermonuclear Experimental Reactor (ITER) Poloidal Field (PF) converter unit. Consequently, the electromagnetic interference caused by the strong stray magnetic field has been one of the main concerns in its design. And this paper mainly presents the stray magnetic field analysis of ITER PF converter unit. At first, an isolated phase bus (IPB) is designed for the shielding of the alternating magnetic field generated by the ac busbars to avoid overheating on ferromagnetic materials in the fire wall. The stray magnetic field on the fire wall is analyzed to verify the shielding effectiveness of the IPB. Then, the stray magnetic field generated by the converter bridges and dc reactors which is very hard to be shielded is analyzed separately. The results show that the stray magnetic field exceeds the limit value and will be a potential threat for the instrument and control (I&C) system. All the analysis presented in this paper will provide useful inputs for the electromagnetic compatibility design and test of the I&C system.

Seismic analysis under SL-1 of high-power DC reactor prototype for ITER poloidal field converter

This paper mainly introduces the seismic analysis of the high-power dc reactor prototype, whose functions are to limit the ripple current and the increasing rate of fault current in the ITER poloidal field (PF) converter. The stacked reactors with the assembly dimension (L×W×H) of 2955 mm×1639 mm×3296mm and weight about 5 tons are fixed to the steel base by five support components. In order to evaluate the seismic response of the structure under specific seismic excitation, a method based on response spectrum is adopted in this paper. The design earthquake spectrum of seismic level one (SL-1) with damping factor of 2% as well as 4% provided by ITER is applied as load. In addition, the simulation analysis is introduced in detail and the results as the displacements, stresses and reactive forces are also presented. This analysis could provide reference for the foundation design of dc reactor, as well as make a contribution to the similar seismic design work.