Modified T-type topology of three-phase multi-level inverter for photovoltaic systems

In this article, a three-phase multilevel neutral-point-clamped inverter with a modified t-type structure of switches is proposed. A pulse width modulation (PWM) scheme of the proposed inverter is also developed. The proposed topology of the multilevel inverter has the advantage of being simple, on the one hand since it does contain only semiconductors in reduced number (corresponding to the number of required voltage levels), and no other components such as switching or flying capacitors, and on the other hand, the control scheme is much simpler and more suitable for variable frequency and voltage control. The performances of this inverter are analyzed through simulations carried out in the MATLAB/Simulink environment on a three-phase inverter with 9 levels. In all simulations, the proposed topology is connected with R-load or RL-load without any output filter.

Three-phase inverter with a variable control algorithm

The paper presents the construction of a three-phase frequency converter with the possibility of choosing the type of PWM modulation and a smooth change of the frequency of the modulated signal. In a practical way, various inverter control algorithms were implemented in the same hardware system using the STM ARM Cortex M3 processor. The use of THIPWM modulation allowed to reduce the harmonic content in the output signal and effectively use the possibilities of the power source. The system can choose one of two scalar control algorithms, with the option of compensation for the influence of the stator resistance on the motor shaft torque in the initial range of the linear control characteristic at a constant voltage to frequency ratio. The research confirmed that the most advantageous type of PWM in this system is unipolar double-edge modulation. The use of the THIPWM method resulted in a gain in the amplitude of the fundamental harmonic of the output voltage for the three-phase inverter operation mode compared to the SPWM method. The appropriate precision of the frequency control step was also obtained, and the test results confirmed the functionality of the converter.

Hybrid PWM Techniques for a DCM-232 Three-Phase Transformerless Inverter with Reduced Leakage Ground Current

Pulse Width Modulation (PWM) strategies are crucial for controlling DC–AC power converters. In particular, transformerless inverters require specific PWM techniques to improve efficiency and to deal with leakage ground current issues. In this paper, three hybrid PWM methods are proposed for a DCM-232 three-phase topology. These methods are based on the concepts of carrier-based PWM and space vector modulation. Calculations of time intervals for active and null vectors are performed in a conventional way, and the resulting waveforms are compared with a carrier signal. The digital signals obtained are processed using Boolean functions, generating ten signals to control the DCM-232 three-phase inverter. The performance of the three proposed PWM methods is evaluated considering the reduction in leakage ground current and efficiency. The proposed modulation techniques have relevant performances complying with international standards, which make them suitable for transformerless three-phase photovoltaic (PV) inverter markets. To validate the proposed hybrid PWM strategies, numerical simulations and experimental tests were performed.

A Precise Current Detection Method Using a Single Shunt and FET Rds(on) of a Low-Voltage Three-Phase Inverter

In this study, a low-voltage three-phase inverter was used alongside a shunt resistor to measure the current. However, it is known that this type of inverter and shunt resistor system has a region where the measurement of current is impossible due to structural limitations. As a result, many studies have focused on this region through the use of additional algorithms. Most studies measured current by forcibly adjusting the PWM duty in order to measure the current at the region where it could not be sensed. However, unfortunately, the total harmonic distortion (THD) increases in the current due to PWM adjustment. This causes an increase in torque ripple and inverter control instability. Therefore, in this paper, current was measured using the Rds(on) value between the drain source resistor when MOSFET was turned on and the Kalman filter in a low-voltage three-phase inverter with a single shunt. Additionally, the value was verified via comparison with the values achieved when a Hall-type current sensor and single shunt were used. As a result, this study confirmed that the inverter with a single shunt performs the same as a Hall-type sensor at the region where current cannot be detected.

PI CONTROLLER FOR CONTROLLING A THREE-PHASE INVERTER OF A PV SYSTEM CONNECTED TO THE ELECTRICAL NETWORK

In order to improve the efficiency of photovoltaic panels it is necessary to introduce the technique of Maximum Power Point (the technique of the MPPT). In the literature, several strategies are mentioned, among which the perturbation and observation (P&O) algorithm. The aim of this work is to a simulation study in MATLAB of a photovoltaic panel connected to the network using DC-DC and DC-AC converters. DC Boost converter is checked by the MPPT command to adjust the output voltage of the photovoltaic panel and maximize the power produced by the photovoltaic panel. The PI controller is used to control the inverter three-phase to make the connection of the photovoltaic panel to a three-phase electrical network.