Calculation Of Switching Angles Research Articles

A Current-Reference-Based Selective Harmonic Current Mitigation PWM Technique to Improve the Performance of Cascaded H-Bridge Multilevel Active Rectifiers

In this paper, a selective harmonic current mitigation pulsewidth modulation (SHCM-PWM) technique with low switching frequencies is proposed for grid-connected cascaded H-bridge multilevel rectifiers to fully meet harmonic requirements within extended harmonic spectrum. In the proposed technique, instead of using the voltage references to calculate switching angles for the rectifier as in conventional selective harmonic elimination-PWM (SHE-PWM) or selective harmonic mitigation-PWM (SHM-PWM), current references are used to compensate the current harmonics due to both grid voltage harmonics and rectifier input voltage harmonics so as to meet the current harmonic requirements and total demand distortion within the whole harmonic spectrum. Furthermore, the techniques to design the critical parameters including switching frequency, the highest harmonic order that can be mitigated using the proposed current-reference-based technique, and the coupling inductance that can attenuate the current harmonic orders above the highest order are investigated. With the same switching frequency, the proposed SHCM-PWM technique uses smaller coupling inductance to meet higher orders of current harmonic requirements than the conventional SHE-PWM technique. Finally, simulations and experiments were conducted to validate the proposed technique.

Real-Time Solution and Implementation of Selective Harmonic Elimination of Seven-Level Multilevel Inverter

This paper proposes a new method to calculate switching angles in selective harmonic elimination technique. It is introduced as a substitute for Newton-Raphson method and similar iteration methods. By utilizing classical control such as the proportional-integral (PI) control, the proposed method can perform a real-time calculation for multilevel inverter's (MLI) switching angles over a wide range of modulation indexes. Therefore, it is able to respond to system dynamics without the need to store precalculated large lookup tables. The proposed method is applied to seven levels cascaded full H-bridge to eliminate its third- and fifth-harmonic contents from the modulation index 0.1 to 1.04. The same procedure can be extended to the vast majority of MLI topologies. A Simulink model is built to simulate and validate the accuracy, dynamics, and continuity of the solution generated by the proposed method. An experimental prototype is also built and its results are discussed to confirm the theory and simulation of the proposed method.

SHE–PWM Cascaded Multilevel Inverter With Adjustable DC Voltage Levels Control for STATCOM Applications

This paper presents a new multilevel selective harmonic elimination pulse-width modulation (MSHE-PWM) technique for transformerless static synchronous compensator (STATCOM) system employing cascaded H-bridge inverter (CHI) configuration. The proposed MSHE-PWM method optimizes both the dc-voltage levels and the switching angles, enabling more harmonics to be eliminated without affecting the structure of the inverter circuit. The method provides constant switching angles and linear pattern of dc-voltage levels over the modulation index range. This in turns eliminates the tedious steps required for manipulating the offline calculated switching angles and therefore, easing the implementation of the MSHE-PWM for dynamic systems. Although the method relies on the availability of the variable dc-voltage levels which can be obtained by various topologies, however, the rapid growth and development in the field of power semiconductor devices led to produce high-efficiency dc-dc converters with a relatively high-voltage capacity and for simplicity, a buck dc-dc converter is considered in this paper. Current and voltage closed loop controllers are implemented for both the STATCOM and the buck converter to meet the reactive power demand at different loading conditions. The technique is further compared with an equivalent conventional carrier-based pulse-width modulation to illustrate its enhanced characteristics. The effectiveness and the theoretical analysis of the proposed approach are verified through both simulation and experimental studies.

A Modified Single Phase H-Bridge Inverter for High Power Applications with Power Quality Improvement

Various multilevel inverter topologies are widely being used for real power exchange, reactive power compensation, harmonic current mitigation on grid and industrial drive applications with fundamental frequency switching mode of gate control. Still so many topologies are being currently developed with reduced number of switches, improved waveform for power quality improvement with fundamental frequency switching and pwm switching gate control mode. This paper presents the performance analysis of modified H-bridge single phase inverter for high voltage and high power applications. The switching method has been selected to operate the inverter at fundamental frequency switching mode of gate control to be free from lower order harmonics. The inverter has the modulation technique with pre calculated switching angles to generate the required fundamental voltage with reduced Total Harmonic Distortion (THD). So, the switching losses have been reduced hence the efficiency is improved with Power Quality (PQ) improvement in voltage-current waveform. The DC input power is feed to the inverter from DC capacitor voltage divider source, contributed to give various dc voltage levels during fundamental frequency switching of different switching combinations for the generation of stepping output voltage. During dynamic load condition, the magnitude of input dc voltage level across each capacitor has not undergone through big swing to feed the power to the load without affecting generated output ac voltage. The performance of the proposed inverter has been analyzed for dynamic reactive load and induction motor. The MATLAB based simulations have been presented to validate the inverter operation for dynamic reactive load and industrial drive applications with pre calculated THD reduced switching conduction angles for PQ improvement in waveform.

A grid-connected photovoltaic power conversion system with single-phase multilevel inverter

This paper presents a grid-connected photovoltaic (PV) power conversion system based on a single-phase multilevel inverter. The proposed system fundamentally consists of PV arrays and a single-phase multilevel inverter structure. First, configuration and structural parts of the PV assisted inverter system are introduced in detail. To produce reference output voltage waves, a simple switching strategy based on calculating switching angles is improved. By calculated switching angles, the reference signal is produced as a multilevel shaped output voltage wave. The control algorithm and operational principles of the proposed system are explained. Operating PV arrays in the same load condition is a considerable point; therefore a simulation study is performed to arrange the PV arrays. After determining the number and connection types of the PV arrays, the system is configured through the arrangement of the PV arrays. The validity of the proposed system is verified through simulations and experimental study. The results demonstrate that the system can achieve lower total harmonic distortion (THD) on the output voltage and load current, and it is capable of operating synchronous and transferring power values having different characteristic to the grid. Hence, it is suitable to use the proposed configuration as a PV power conversion system in various applications.

Design and Application of a Single Phase Multilevel Inverter Suitable for using as a Voltage Harmonic Source

This paper presents a single phase multilevel inverter for using as a voltage harmonic source. First, a single phase multilevel inverter system is presented and the structural parts of the inverter are described. In order to obtain multilevel output voltage waveforms, a switching strategy based on calculating switching angles is explained and an improved formula for determining switching angles is given. Simulation and experimental results of multilevel voltage waveforms are given for 15, 31 and 127 levels. The proposed topology does not only produce output voltages with low THD values. It also produces the required harmonic components on the output voltage. For this purpose, equations for switching angles are constituted and the switching functions are obtained. These angles control the output voltage as well as provide the required specific harmonics. The proposed inverter structure is simulated for various functions with the required harmonic components. The THD values of the output voltage waves are calculated. The simulated functions are also realized by the proposed inverter structure. By using a harmonic analyzer, the harmonic spectrums, which belong to the output voltage forms, are found and the THD values are measured. Simulation and experimental results are given for the specific functions. The proposed topology produces perfectly suitable results for obtaining the specific harmonic components. Therefore, it is possible to use the structure as a voltage harmonic source in various applications.

Real-Time Calculation of Switching Angles Minimizing THD for Multilevel Inverters With Step Modulation

Multilevel inverters have been widely applied in industries. A family of optimal pulsewidth modulation (PWM) methods for multilevel inverters, such as step modulation, can generate output voltage with less harmonic distortion than popular modulation strategies, such as the carrier-based sinusoidal PWM or the space vector PWM. However, some drawbacks limit the application of optimal PWM. One of such crucial drawback is that the optimal switching angles could not be calculated in real-time and one has to rely on lookup tables with precalculated angles. We propose a novel real-time algorithm for calculating switching angles that minimizes total harmonic distortion (THD) for step modulation. We give a mathematical proof that the output voltage has the minimum THD. We implemented the algorithm on a digital signal processor and provide experimental results that verify the performance of the proposed algorithm.

An application of SHEPWM technique in a cascade multilevel inverter

PurposeIn this paper, a new application of the Selected Harmonic Elimination Pulse Width Modulation (SHEPWM) technique used in the cascade multilevel inverter topology which is formed by series connections of one‐phase bridge type inverters (H‐bridge) is introduced. The advantage of the SHEPWM technique is its ability to operate in low switching frequency that makes it suitable for high power applications.Design/methodology/approachFirst, the switching angles are calculated using constrained optimization technique. By using these switching angles, the fundamental harmonic can be controlled and the selected harmonics can be eliminated. Then, using these calculated switching angles, a set of equation is formed which calculate the switching angles with respect to the modulation index. The switching angles at any modulation index can be easily obtained by solving the equation set. In this study, this equation set has been solved online using dSPACE DS1103 controller board. Using this technique, three‐phase voltages have been obtained from a five‐level cascade inverter. These voltages are applied to an induction motor.FindingsThe simulation results are verified by the experimental results. The results show that selected harmonics can be eliminated and an ac voltage with variable amplitude and frequency can be obtained using the proposed technique.Originality/valueThis paper presents a new application of the (SHEPWM) technique for multilevel inverters.

Simulation of three-phase loaded matrix converter

The theory of the three-phase to three-phase matrix converter is dealt with and its switching angles equations are presented. Matrix converter operation is based on the calculated switching angles. Modelling and numerical simulations of converter loaded with passive (R, L) and active (induction motor) loads are performed. Simulation results are presented.