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The use of LCL-filter for reducing current harmonics has been commonly used for converters connected to the power grid. However, under non-ideal power grid condition, a converter using an LCL-filter may interact with other converters connecting to the grid. In this paper, a three-phase voltage source converter using an LCL-filter is studied. Simulations show that resonant oscillation occurs in the...
The resonance problem in multi-paralleled grid-connected inverters in microgrid is more complex than single one. The Norton's equivalent circuit associated with grid-connected inverter with LCL filter is figured out in this paper. And in terms of different reasons of causing resonance, resonance problems associated with multi-paralleled grid-connected inverters are categorized into three types: individual...
PR controller in stationary frame which is equivalent to PI controller in synchronous frame has been widely used in the application of PV inverters. While little attention has been devoted to VR(vector-resonant) controller in the application of PV inverters. VR controller in stationary frame is equivalent to VPI(vector PI) controller in synchronous frame, which takes decoupling into consideration...
This paper aims to analyze the applied hybrid controlled three-phase grid-connected inverter for marine current power generation system used in distributed generation. As inverter is a key part of the grid-based system, grid-connected technology plays an important role in the distributed generation to meet the stricter grid interconnection standards. In order to improve the power quality and strengthen...
An improved grid-connected photovoltaic (PV) power generation system is proposed to solve the problem that the total harmonic distortion (THD) of grid-connected current generally exceeds 5% under the condition of low output power of PV array in this paper. The system includes a larger capacity master inverter with an LCL filter and a smaller capacity slave inverter with an L filter. Two inverters...
Nowadays, electromagnetic interference (EMI) seems to be one of the major constraints of photovoltaic inverters. Unfortunately, it is too often regarded as the last phase of the development of the system since it represents the last step of its marketing. This paper discusses DC side EMI filter design methodology for photovoltaic inverter System. An analysis of noise source and propagation path impedances...
Due to the presence of the low-order background voltage harmonics in the grid, it will cause higher current harmonics in the AC side of the grid inverter with Selective Harmonic Elimination PWM (SHEPWM). Therefore the grid inverter with traditional SHEPWM has not prevailed since it is unable to overcome the background harmonics of the utility and satisfy the power quality requirement. In this paper,...
Software Phase-Locked-Loop (SPLL) is a kind of servo mechanism to adjust system's output synchronized with one reference signal. The polluted grid voltage is not only unbalanced, but also contains large quantities of low order harmonics. In this case, SPLL still can obtain fundamental positive sequence component (FPSC) effectively and realize synchronization with grid rapidly and accurately, that...
This paper presents a technique to be used for the cellular phone charger. The proposed technique identifies system conditions to control the output voltage, measuring only the primary side voltage and current. The method estimates the load and the coupling coefficient of the circuit by perturbing the operating frequency. The control method, designed in Primary-Series-Secondary-Series (SS) topology...
The Aalborg Inverter is a new type of high efficient DC/AC grid-tied inverter, where the input DC voltage can vary in a wide range. Compared with the LCL-filter, the LLCL-filter can save the total inductance for the conventional voltage source inverter. In this paper, an LLCL-filter based Aalborg Inverter is proposed and its character is illustrated through the small signal analysis in both “Buck”...
This paper presents a power density/efficiency evaluation in single phase power factor correction (PFC) applications operating in continuous conduction mode (CCM). The comparison is based on semiconductor dynamic characterization and a mathematical model for prediction of the conducted electromagnetic interference (EMI). The dynamic characterization is based on a low inductive double pulse tester...
This paper proposes a novel robust method for three-phase rectifier system with high quality for higher power applications. The system consists of two stages: The front stage combines the unique features of a low-kilovoltampere 12-pulse rectifier scheme along with a single-phase pwm rectifier scheme to shape the input current to a sinusoidal waveshape. The single-phase pwm rectifier stage is rated...
The accurate and rapid detection of voltage and current in non-sinusoidal and unbalanced voltage condition is the prerequisite for grid power quality management and stable operation. Based on analyzing the vectors of the grid voltage and current, the rotating vector detection is carried out which can detect the voltage and current specified harmonic component and reactive and active current in non-sinusoidal...
In order to reduce the harmonics in input currents effectively, this paper presents a double star rectifier with an auxiliary PWM rectifier at DC side. The volt-ampere rating of auxiliary PWM rectifier is only 10% of output power of the double star rectifier. The auxiliary PWM rectifier injects a particular triangular wave current into the secondary winding of inter-phase transformer to reduce the...
This paper investigates the dynamic interactions of current controllers for multi-paralleled, grid-connected inverters. The consequent harmonics instability phenomena, which features with oscillations above the fundamental frequency, are evaluated by the impedance-based stability criterion. The frequency range of effective impedance-based stability analysis is first identified. The effect of each...
Multiple resonances may result in instability of a LCL filter based multiple grid connected converter (MGCC) system. This paper investigates the critical factors of multiple resonances in MGCC system. It is found that, closed-loop output admittance of the grid connected converter can be configured to meet the requirements of resonances suppression, by properly designing control method and parameters...
Micro grid(MG) consists of a number of parallel operating inverters. The droop control strategy is commonly used in parallel-connected inverters. The conventional PI regulator for the voltage control has little effect on restraining the voltage harmonic content under the nonlinear load conditions. So an effective and reasonable control strategy for inverters must be adopted to ensure the output power...
Harmonics generated from Large-scale Grid-connected photovoltaic plant (GCPV) has the characteristics of high frequency and wide range. So the impact of distributed parameter of high-voltage cables becomes more significant. Based on an actual GCPV, harmonic output particularities were discussed according to its operating mechanism. Step-up transformer, reactive power compensation device, distributed...
A three-phase voltage source PWM rectifier(VSR) has some shortcomings that can lead to resonance, resulting in system instability problems. A novel multi-loop control strategy and a design of the control structure in synchronous coordinate system for LCL-VSR is proposed in this paper to solve the problem. The strategy belongs to active damping control, which introduces the filter capacitor current-loop...
Multiwinding transformer + H-bridge converters is a typical topology in high-voltage and high-capacity power electronic applications. Based on the analysis about the high frequency characteristics of a PWM controlled H-bridge and the high frequency equivalent model of the topology, the theoretical foundation of how carrier phase-shift control suppresses high frequency harmonics is derived, and a broader...
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