Jong-Hyoung Park

Grid-connected PV System Using a Quasi-Z-source Inverter

This paper presents the MPPT (Maximum Power Point Tracking) and PCC (Point of Common Coupling) current control strategy for photovoltaic (PV) grid-connected generating system using the quasi-Z-source inverter (QZSI). At first, in order to explain the above controllers, the characteristic of QZSI is analyzed. And then, the MPPT control technique with a modified P&O method, the PCC current control one for the regulation of dc-link capacitor voltage, and the PWM methods for the proposed system are explained. The feasibility of the propose algorithm is verified through the simulation and experiment with 3kW system.

Power Conditioning System for a Grid Connected PV Power Generation Using a Quasi-Z-Source Inverter

This paper presents a grid connected photo-voltaic system using a quasi-Z-source inverter (QZSI) for power stage reduction. The power stage can be reduced because of an additional shoot-through stage which is a characteristic of QZSI. Therefore, by utilizing a QZSI the system’s efficiency can be increased. In this paper, for applying a QZSI to a PV system, control methods such as maximum power point tracking (MPPT), point of common coupling (PCC) current control and PWM are studied and verified through simulation and experiment. In order to explain the above controllers, the characteristics of a QZSI are first analyzed. Then the MPPT control technique with a modified P&O method, the PCC current control for the regulation of the dc-link capacitor voltage and the PWM methods for the proposed system are explained. The feasibility of the proposed algorithm is verified through simulation and experiment with a 3kW system.

LCL-filter design for grid-connected PCS using total harmonic distortion and ripple attenuation factor

This paper deals with a design method of LCL filter for grid-connected three-phase PWM voltage source inverters (VSI). By analyzing the total harmonic distortion of the current (THD i ) in the inverter-side inductor and the ripple attenuation factor of the current (RAF) injected to the grid through the LCL network, the parameter of LCL can be clearly designed. The described LCL filter design method is verified by showing a good agreement between the target current THD and the actual one through simulation and experiment.

Novel H-bridge multi-level inverter with DC-link switches

This paper proposed a new multi-level inverter topology based on a H-bridge with two switches and two diodes connected to the DC-link. The output voltage of the proposed topology is quite closer to a sinusoidal waveform compared with a typical single phase inverter. The proposed multi-level inverter is applicable to a power conditioning system for renewable energy sources, and it can be also used as a building block of a cascaded multi-level inverter for a high voltage application. In case of conventional H-bridge type or NPC type multi-level inverter, 8 controllable switches are used to obtain a 5 level output voltage, but the proposed multi-level inverter requires only 6 controllable switches. Thus the circuit configuration is quite simple, reliable and cost-effective implementation is possible. The efficiency can be improved owing to the reduction of the switching loss. A new PWM method based on POD modulation is suggested which requires only one carrier signal. The switching sequence to make the capacitor voltage balanced is also considered. The feasibility is studied through simulation and experiment.

Dead time compensation for grid-connected PWM inverter

This paper proposes a new dead time compensation method for a PWM inverter. Recently, PWM inverters are widely used for industrial applications, such as ac motor drives, distributed grid-connected systems and a static synchronous compensator (STATCOM). The nonlinear characteristics of the switch and the dead time cause a current distortion and a deterioration of the power quality. The dominant harmonics is the 5th and 7th harmonics in the stationary reference frame, and the 6th harmonics in the synchronously rotating frame. In this paper, a resonant controller which compensates the 6th harmonics in the synchronously rotating frame is proposed. This method does not require any off-line experimental measurements, additional hardware and complicated mathematical calculations. Furthermore it is easy to implement and does not cause any stability problem.

LCL Filter Design for Grid-connected PCS Using Total Harmonic Distortion and Ripple Attenuation Factor

This paper deals with a design method of LCL filter for grid-connected three-phase PWM voltage source inverters (VSI). By analyzing the total harmonic distortion of the current (THDi) in the inverter-side inductor and the ripple attenuation factor of the current (RAF) injected to the grid through the LCL network, the parameter of LCL can be clearly designed. The described LCL filter design method is verified by showing a good agreement between the target current THD and the actual one through simulation and experiment.

Capacitor voltage control for MPPT range expansion and efficiency improvement of grid-connected Quasi Z-Source Inverter

In a grid-connected PV system using a QZSI(Quasi Z-Source Inverter), the capacitor voltage of an impedance network is controlled to be constant to track the MPP(Maximum Power Point) of a PV array and generate the reference output current. For higher efficiency of the system, if possible, the reference voltage of the capacitor should be set at a lower value. On the other hand, the reference voltage of capacitor has to be set at a higher value to have margin for a shoot-through reference and to inject a current into the grid. Although the capacitor voltage of an impedance network is controlled to be constant, the output voltage of an impedance network varies according to the shoot-through time ratio. This may result in an unstable operation. To overcome these matters, in this paper, a method to keep the output voltage of an impedance network constant is proposed. This results in an expansion of MPPT range and a higher efficiency of QZSI

A control strategy for the grid-connected PV system using a Z-source inverter

This paper presents the MPPT (maximum power point tracking) and PCC (point of common coupling) current control strategy for grid-connected PV system using the ZSI (Z-source inverter). Several requirements of an inverter for PV-system and the shoot-through effect of the ZSI are analyzed. And then, the MPPT algorithm and PWM method for the ZSI are suggested. The feasibility is studied through the simulation and experiment with 3 kW system.

Resonance damping of LCL filter based grid-connected inverter

Three-phase PWM inverters are connected to the grid by an LC or an LCL filter. Although an LCL filter is more effective since it more efficiently attenuates the switching harmonics, but it causes stability problems. To enable a stable operation, either a damping resistor or an active damping algorithm has to be used. However, while a damping resistor causes additional losses, to avoid these disadvantages, this paper shows simulation results of a simple active damping solution which is suitable for industrial applications.

Dead Time Compensation of Grid-connected Inverter Using Resonant Controller

This paper proposes a new dead time compensation method for a PWM inverter. Recently, PWM inverters are extensively used for industry applications, such as ac motor drives, distributed grid-connected systems and a static synchronous compensator (STATCOM). Nonlinear characteristics of the switch and the inverter dead time cause a current distortion and deterioration of power quality. The dominant harmonics in the output current are the and harmonics in the stationary frame, and the harmonics in the synchronous rotating frame. In this paper, a resonant controller which compensates the harmonics in the synchronous rotating frame is proposed. This method does not require any off-line experimental measurements, additional hardware and complicated mathematical computations. Furthermore, the proposed method is easy to implement and does not cause any stability problem.