Hyun-Sam Jung

Genetic association study of adiponectin polymorphisms with risk of Type 2 diabetes mellitus in Korean population

Aims  To investigate any association between Type 2 diabetes mellitus and two single nucleotide polymorphisms (SNPs) in the adiponectin gene, T45G and G276T, in the Korean population.

Genetic polymorphisms in peroxisome proliferator-activated receptor gamma are associated with Type 2 diabetes mellitus and obesity in the Korean population.

Aims  We examined whether the common polymorphisms of the peroxisome proliferator‐activated receptor‐γ (PPARγ) gene are associated with Type 2 diabetes or obesity in the Korean population.

Control of Three-Phase Inverter for AC Motor Drive With Small DC-Link Capacitor Fed by Single-Phase AC Source

If a small dc-link capacitor is used in the dc link fed by a single-phase ac source, then the dc-link voltage severely fluctuates at twice of the source frequency. To handle this fluctuation, the concept of “average voltage constraint” is proposed in this study. On the basis of this concept, a flux-weakening scheme, generating the d-axis current reference (idsr*) for the interior permanent-magnet synchronous machine, is devised. The q-axis current reference (iqsr*) is modified for the unity power factor operation in the viewpoint of an ac source without an additional sensor. The proposed scheme has been applied to the inverter-driven 1-kW compressor of an air conditioner. From the experimental results, it has been verified that the compressor operates well at the required operating condition, regardless of the severe fluctuation of dc-link voltage, because of the reduced dc-link capacitance. The frequency spectrum of the ac source current reveals that the harmonics of the source current meet the regulation of IEC 61000-3-2 Class A and that the overall power factor is above 96% without any additional circuit, such as an input filter and a power factor correction circuit.

Low Voltage Ride Through(LVRT) control strategy of grid-connected variable speed Wind Turbine Generator System

In this paper, a Low Voltage Ride Through (LVRT) control strategy for variable speed full scale Wind Turbine Generator System (WTGS) is proposed. Grid-connected wind power system should satisfy LVRT requirement when grid fault occur, and the variable speed full scale WTGS has advantage of satisfying LVRT compared with the fixed speed WTGS. The proposed LVRT control strategy satisfies not only LVRT requirement but also stabilizing a DC link voltage regardless of reduced DC link capacitance. During the grid faults, especially three phase to ground fault, the grid side converter cannot control the DC link voltage because it is impossible to control grid side power. In this situation, the DC link voltage can be controlled by the generator side inverter using the proposed DC link voltage control scheme. The proposed control scheme can keep the power balance between grid and generator side power in any case of grid fault condition for LVRT. The compliance to Grid Codes has been evaluated by computer simulations. Though the experimental results, it is verified that the proposed method has satisfied the LVRT requirements and DC link voltage control specification simultaneously.

DC link voltage control of single phase back-to-back converter for medium voltage motor drive

This paper describes DC link voltage control method of single phase back-to-back converter for medium voltage motor drive system. Cascaded H-Bridge (CHB) topology is widely used to achieve medium voltage operation and low harmonic distortion, simultaneously. Each power cell of CHB should have the isolated DC link voltage by using input transformer and rectifier. Instead of three phase Active Front-End (AFE) which is mostly used, using single phase AFE could make the structure of input transformer and power cell be simple. However, even in the same three phase windings of the input transformer, the DC link voltage of each single phase AFE might be different due to the power imbalance of each phase. In this paper, DC link voltage balancing control method that uses the negative sequence voltage of converter is described. The proposed method is verified with experimental results. The DC link voltage of each AFE has been controlled within 1% error of its reference value.

Suppression of circulating current in paralleled inverters with isolated DC-link

In this paper, it is described how the circulating current flows between inverters which have isolated DC-link such as Cascaded H Bridge (CHB) topology, when they operating in parallel. In this case, Zero Sequence Circulating Current (ZSCC) flowing through shared DC-link cannot flow between inverters in parallel. However, circulating current is provoked by asynchronous switching instant of devices and difference of DC-link voltages of parallel inverters. The circulating current should be suppressed by sharing inductor which is inserted between inverters. Generally, all of the inverters should synthesize the same output voltage reference for load current control, to minimize the size of this sharing reactor. However, this conventional method cannot guarantee to diminish circulating current in the transient state and even in the steady state. In this paper, to reduce circulating current, after deriving circulating current model, circulating current control method is devised based on the model. This proposed algorithm is applied to Active Front End 5Level-CHB inverter system for medium voltage drive. Simulation and experimental results are provided to verify the effectiveness of the proposed control scheme.

Control strategy of single phase back-to-back converter for medium voltage drive under cell fault condition

Cascaded H-Bridge (CHB) inverter is the most widely used topology for Medium Voltage (MV) drive system due to the high degree of modularity, easier implementation of medium output voltage, and ability to continuous operation under the cell fault condition. Because each power cell of CHB should have isolated DC source, multi-winding input transformer and three phase Active Front-End (AFE) are generally used for regenerative applications. The whole system can be reduced by replacing the three phase AFE with single phase AFE. However, input power imbalance among three phases under the cell fault condition inevitably occurs, if control strategy of normal operation is employed in system. This paper proposes a control scheme for the cell fault condition of single phase AFE CHB. Not only DC-link voltages of each cell but also grid current are regulated well without imbalance by applying the proposed control scheme to the system, even in the cell fault condition. Simulation and experimental results are provided to verify the effectiveness of the proposed scheme.

A design of circulating current controller for paralleled inverter with non-isolated dc-link

In this paper, the suppression of the circulating current flowing between inverters in parallel with non-isolated dc-link is described. If the inverters are connected in parallel through sharing inductor, circulating current would follow between inverters. In early researches, the circulating current generally is considered as zero sequence component. However, circulating current is not confined as zero sequence component, because differential current can flow by non-ideal conditions such as unbalanced impedance, different propagation delay and etc. of each inverter. In order to separate the components of the circulating current, equivalent circuits are derived from n-paralleled inverters. Based on these equivalent circuits, it is found that circulating current consists of Zero Sequence Circulating Current(ZSCC) and Differential Circulating Current(DCC). To minimize the circulating current and improve performance of total output phase current, a control scheme to suppress the circulating current is proposed from equivalent circuit models. The proposed algorithm is applied to a system consisted of 3 paralleled 2 level inverters, whose DC-links are connected. And, synchronous Pulse Width Modulation is used for PWM of each inverter. Experimental results are provided to verify the effectiveness of the proposed control scheme.

A novel filter structure to suppress harmonic currents based on the sequence of sideband harmonics

In this paper, a novel filter structure is proposed based on the sequence of PWM voltage harmonics. At first, the phase of voltage harmonics is thoroughly analyzed. Based on the phase difference between three phases, it is shown that the sideband harmonics can be divided into positive-sequence, negative-sequence and zero-sequence components. Through 120° interleaving and three paralleled converters, the positive-sequence and negative-sequence voltage harmonics can be synchronized to have the same phase. With the synchronized phase, the voltage harmonics can be suppressed by the proposed filters, which have an identical structure to the three-phase common-mode choke. Furthermore, considering the phase difference, the proposed filters can be integrated as a three-limb core which gives an additional size reduction. The validity of the proposed filter is verified through the simulation and an experiment. Common-mode choke, coupled inductor, high-power converter, paralleled converters, sideband harmonics.

Discrete state-space voltage controller for voltage source inverters with LC filter based on direct pole-zero placement design

State-space control provides both high dynamic performance and sufficient stability margin to voltage source inverters with LC filter. In this paper, discrete state-space voltage controller is proposed by using direct pole-zero placement in rotating reference frame. Based on the discrete-time system model, the state feedback control with the reference feedforward path is designed in consideration of the digital delay. The output current decoupling is incorporated to suppress the effect of the output current disturbance. The controller gains are derived as the functions of the system parameters and design specifications. Additionally, the guideline about pole-zero assignment is presented to improve the performance and stability of the proposed controller. The effectiveness of the proposed controller is verified with experimental results.