An Improved Frequency Measurement Method from the Digital PLL Structure for Single-Phase Grid-Connected PV Applications

The Phase Locked Loop (PLL) technique has been studied to obtain the phase and frequency information in grid-connected distributed generations for the sake of synchronizing the grid voltage and the inverter output current. In particular, the line frequency information, such as the anti-islanding function, is very important for the grid connection requirement. This paper presents a novel frequency measurement method from the digital PLL control structure for single-phase grid-connected PV applications. The conventional PLL controller uses the phase information to calculate the frequency of PV inverter output voltage after every line cycle and has shown a relatively low accuracy. This paper uses the angular frequency to directly measure the frequency after every line cycle. To verify the validity of the proposed method compared with the conventional method, a simulation was conducted. According to the simulation results, the measurement error of the proposed method is 80 times lower than the conventional one.

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Direct Usage of Photovoltaic Solar Panels to Supply a Freezer Motor with Variable DC Input Voltage

Electronics ◽

10.3390/electronics9010167 ◽

2020 ◽

Vol 9 (1) ◽

pp. 167

Author(s):

Ali Farzan Moghaddam ◽

Alex Van den Bossche

Keyword(s):

Leakage Current ◽

Single Phase ◽

Pulse Width Modulation ◽

High Efficiency ◽

Input Voltage ◽

Boost Converter ◽

Solar Panels ◽

Pv Inverter ◽

Pv Panel ◽

Grid Connection

In this paper, a single-phase photovoltaic (PV) inverter fed by a boost converter to supply a freezer motor with variable DC input is investigated. The proposed circuit has two stages. Firstly, the DC output of the PV panel that varies between 150 and 300 V will be applied to the boost converter. The boost converter will boost the input voltage to a fixed 300 V DC. Next, this voltage is supplied to the single-phase full bridge inverter to obtain 230 V AC. In the end, The output of the inverter will feed a freezer motor. The PV panels can be stand-alone or grid-connected. The grid-connected PV is divided into two categories, such as with a transformer and without a transformer, a transformer type has galvanic isolation resulting in increasing the security and also provides no further DC current toward the grid, but it is expensive, heavy and bulky. The transformerless type holds high efficiency and it is cheaper, but it suffers from leakage current between PV and the grid. This paper proposes a stand-alone direct use of PV to supply a freezer; therefore, no grid connection will result in no leakage current between the PV and Grid. The proposed circuit has some features such as no filtering circuit at the output of the inverter, no battery in the system, DC-link instead of AC link that reduces no-loads, having a higher efficiency, and holding enough energy in the DC-link capacitor to get the motor started. The circuit uses no transformers, thus, it is cheaper and has a smaller size. In addition, the system does not require a complex pulse width modulation (PWM) technique, because the motor can operate with a pulsed waveform. The control strategy uses the PWM signal with the desired timing. With this type of square wave, the harmonics (5th and 7th) of the voltage are reduced. The experimental and simulation results are presented to verify the feasibility of the proposed strategy.

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Synchronous Reference Frame Repetitive Control of a Single-Phase Three-Level Dual-Buck Photovoltaic Inverter

Electronics ◽

10.3390/electronics7100226 ◽

2018 ◽

Vol 7 (10) ◽

pp. 226 ◽

Cited By ~ 1

Author(s):

Jung-Yong Lee ◽

Younghoon Cho

Keyword(s):

Reference Frame ◽

Control Strategy ◽

Single Phase ◽

Harmonic Distortion ◽

Current Control ◽

Output Current ◽

Pv Inverter ◽

Synchronous Reference Frame ◽

Conduction Mode ◽

Repetitive Controller

This paper proposes a synchronous reference frame (SRF) control strategy for a single-phase, three-level, dual-buck photovoltaic (PV) inverter. The concept of virtual d-q transformation is adapted to the current control of the inverter, and the repetitive controller is implemented in the SRF. With the proposed control strategy, the memory allocation quantity for the repetitive controller is decreased and the capability of the current reference tracking is maximized. Thus, the proposed method significantly reduces the total harmonic distortion (THD) of the output current in both the continuous conduction mode (CCM) and the discontinuous conduction mode (DCM). In addition, the distortion of the output current is mostly composed of odd harmonics. Odd harmonic expressed to the even harmonic in SRF can be calculated using Park’s transformation. Therefore, a repetitive controller can improve dynamics by considering only even harmonic components in SRF rather than including all harmonics. The simulation and the experimental results verify the effectiveness of the proposed control strategy. The proposed method not only reduces the THD of the output current in both the CCM operation and the DCM operation, but also improves the dynamics of the current controller.

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