Seung-Wook Hyun

A Method to Compensate the Distorted Space Vectors in the Unbalanced Neutral Point Voltage of 3-level NPC PWM Inverters

This paper proposes a compensation method to improve the distorted space vectors when a 3-level Neutral Point Clamped (NPC) inverter has an unbalanced neutral point voltage. Since both the neutral point voltage of the DC link and the space vector of a 3-level NPC inverter are closely related depending on the output load connecting state, a distorted space vector can occur when the neutral point voltage of a 3-level NPC inverter is unbalanced. The proposed method can improve the distorted space vectors by adjusting the injection time of the small and medium vectors and by modulating the amplitude of the carrier waveforms. In this paper, the proposed method is verified by both simulation and experimental results based on a 3-level NPC inverter.

Convenient thermal modeling for loss distribution of 3-level Active NPC using newton's law

In this paper, a new thermal modeling method is proposed for loss control method of 3-level Active NPC inverter. In the drawback of conventional 3-level NPC, the generated thermal in each switch is unbalanced. And utilization of designed system has decreased. In order to compensate, 3-level Active NPC inverter can distribute switch loss in accordance with operation of active switch. Therefore thermal modeling is required for thermal calculation. This paper is simple proposed new thermal modeling method based on newtons law of cooling than conventional thermal modeling method. Thought loss of active NPC is controlled. Proposed thermal modeling is verified by simulation.

A compensation method to reduce sampling delay of zero dead-time PWM using 3-level NPC PWM inverter

This paper proposed a compensation method for reducing sampling delay through ADC(Analog-to-Digital Converter) module of MCU(Micro Controller Unit) using ZDPWM method. In case of conventional PWM method of 3-level NPC inverter, the switching devices which is composed of silicon compounds are conducted complementary operation by both reference and carrier waveform. And this operating method needs to contain dead time state to prevent short-circuit fault. However, the phase voltage distortion is caused by the dead time state in conventional method. As a results, THD of phase current is increased when inverter system is operating. ZDPWM method which is non-complementary operation is suggested to compensate the distortion through dead time in 3-level NPC inverter. The ZDPWM method has some advantages such as simple operation through carrier waveform as same as conventional method and low harmonic factor at phase current based on non-complementary operation. However, the unexpected distortion of phase current can occur by phase angle delay through sampling of ADC module when the ZDPWM is used in experiment by MCU. Therefore, this paper proposed simple method to compensate sampling delay based on the modeling of delayed phase angle. The proposed method is demonstrated by experiment, and the method compares with same conditions as both conventional PWM method and the ZDPWM due to uncompensated sampling delay.

The Voltage-doubler Rectifier type Full-bridge converter built in voltage-balancing circuit for bipolar LVDC distribution system

This paper proposes Voltage-doubler Rectifier type Full-bridge converter for bipolar LVDC distribution system. This converter is possible of bi-directional power flow and perform DC_link voltage balancing operation. System of bipolar structure has neutral-point unlike unipolar structure. But, this neutral point is incur DC_Link voltage unbalance between top and bottom capacitor. Thus, bipolar structure need voltage balancing-circuit for voltage unbalance compensation. In Voltage-doubler Rectifier type Full-bridge converter to proposes, secondary side diodes of transformer are replaced to power transistors. And perform voltage balancing control using secondary side circuit without additional balancing-circuit. Also, primary side circuit of Full-bridge type can perform ZVS by phase-shift. And last, step-up and step-down operation also can. Such validity of converter is verified by simulation and experimental results.

Zero dead-time PWM implementation method for reducing total harmonic distortion in 3-level NPC inverter

This paper propose Zero Dead-time PWM method in 3-Level NPC(Neutral Point Clamped) inverter. Each switch of conventional PWM method is performs to complementary switching and semiconductor switch devices have time difference between rising time and falling time. Therefore, dead-time is applied to rising edge of switching signal for prevent short circuit fault. But this dead-time cause distortion of output voltage and current due to signal difference between reference switching and real switching. These distortions are responsible for system instable and DC-Link voltage unbalance. Whereas proposed ZDPWM method does not shows output current distortion because dead time is not exist. The validity of proposed method is verified it through simulation.

Performance Improvement of Isolated High Voltage Full Bridge Converter Using Voltage Doubler

The performance of an isolated high voltage full bridge converter is improved using a voltage doubler. In a conventional high voltage full bridge converter, the diode of the transformer secondary voltage undergoes a voltage spike due to the leakage inductance of the transformer and the resonance occurring with the parasitic capacitance of the diode. In addition, in the phase shift control, conduction loss largely increases from the freewheeling mode because of the circulating current. The efficiency of the converter is thus reduced. However, in the proposed converter, the high voltage dual converter consists of a voltage doubler because the circulating current of the converter is reduced to increase efficiency. On the other hand, in the proposed converter, an input current is distributed when using parallel input / serial output and the output voltage can be doubled. However, the voltages in the 2 serial DC links might be unbalanced due to line impedance, passive and active components impedance, and sensor error. Considering these problems, DC injection is performed due to the complementary operations of half bridge inverters as well as the disadvantage of the unbalance in the DC link. Therefore, the serial output of the converter needs to control the balance of the algorithm. In this paper, the performance of the conventional converter is improved and a balance control algorithm is proposed for the proposed converter. Also, the system of the 1.5[kW] PCS is verified through an experiment examining the operation and stability.

Advanced control method of 3-phase AC/DC PWM converter for DC distribution using the SOGI-FLL

In this paper, control method which detects positive-sequence voltage and phase angle is proposed for dc distribution system. Apart from positive-sequence voltage extraction using phase delay of APF, conventional control method needs phase angle detection using the PLL. On the other hand, control method applied in proposed system is able to perform phase angle detection, positive-sequence voltage extraction and harmonic filtering only using SOGI-FLL. Validity of control method using SOGI-FLL is verified by PSIM simulation and experimental results.

Feedforward compensation method to reduce startup inrush current of Three-phase PWM converter

In this paper, a fast voltage strategy of three-phase AC/DC pulse width modulation (PWM) converter applying a feedforward compensation method is proposed. Conventional PI regulator control method and soft staring method are easy to generate inrush current from startup period. It leads to influence devices parts life, system reliability and increase the stresses on the switches. The paper analyzed Three-phase PWM converter and researched cause of inrush current during startup. Also, it solved the small signal modeling with output current. Based on contents, this paper determines feedforward compensation value and prevents saturating PI controller by applying feedforward compensation. The proposed feed forward compensation method is illustrated with PSIM simulation.

A study on the improvement of transient response during torque control of IPMSM

IPMSM has advantage of high efficiency than other types of motors because of its high generating output per unit volume. However, when torque controlled in certain transient state, the transient response difference occurs due to difference of magnetic resistance. It means that difference of response on q-axis and d-axis currents, thus causing the motor control performance is reduced in transient. Therefore, control measure, considering the rated parameter and driving speed of IPMSM and compensation technique for efficient motor drive are needed. In this paper, we will analyze the problem of the IPMSM drive systems. We will also propose algorithm that improves the transient response and will confirm it by simulations and experiments.

A new voltage balancing control for dual full-bridge converter and single-phase half-bridge inverter

In this paper, the proposed algorithm for output voltage balancing control of the dual full bridge converter with parallel input / series output. The proposed system is composed of using two voltage doubler full-bridge converters and half-bridge inverter. The proposed system is used for input voltage of half-bridge inverter. In this case, the fluctuation on the input capacitor voltage may be occurred by an operation of half-bridge inverter, and that can cause DC injection in output voltage of inverter. Also, when converter modules are connected in series, the DC link voltage unbalanced may be occurred because of differences of impedance which include line, passive and active components, and the difference of sensor sensitivity. So in this paper, to control dual converters which have different transient response, the new control algorithm is proposed. The improved performance by proposed algorithm is verified with experimental results on applying 1.5kW power system.