Sine-triangle Pulse Width Modulation Research Articles

LVRT Enhancement of DFIG-based WECS using SVPWM-based Inverter Control

Abstract: Across many countries, wind turbine generation systems (WTGS) have been established over the past few decades. In this paper, we augment the low voltage ride-through (LVRT) enrichment facility of driving a DFIG-based wind energy conversion system (WECS) using space vector pulse width modulation (SVPWM)-based inverter control. The proposed technique employs an SVPWM-based control algorithm to regulate the voltage and frequency of the output power during grid faults, thereby enhancing the WECS's ability to remain connected to the grid and provide power. The study focuses on decreasing transient current throughout the instant of fault. Modeling and control approaches were also discussed in this study. The performance of the proposed technique is evaluated using MATLAB/Simulink simulations, and the results demonstrate that the technique effectively improves the LVRT capability of the DFIG-based WECS. Background: Due to the variation in wind speed, the power generated by wind turbines is inconsistent. The power generated and the losses in wind turbines change correspondingly with changes in wind speed. The only type of machine that can generate power at speeds below the fixed speed is the doubly-fed induction generator (DFIG). But DFIG is oversensitive to network faults, which makes the bidirectional converters and DC link capacitor fail due to high inrush current and over-voltage. Methods: The converters connected to DFIG consist of an AC-to-DC converter, a boost converter, and a space vector pulse width modulation (SVPWM)-based DC-AC converter. The performance of the SVPWM controller is analyzed during symmetrical and unsymmetrical fault conditions. Results: The anticipated control provides adequate reactive power support to the network through the time of the fault and improves voltage and current waveform. The reactive power flow is also analyzed, and the effectiveness of the proposed controller is verified using MATLAB and Simulink. Conclusion: SVPWM (Space Vector Pulse Width Modulation)-based inverter control is an effective technique for wind energy conversion systems (WECS). The use of SVPWM can provide accurate and precise control of the AC voltage generated from the DC voltage source, resulting in improved system efficiency and reduced harmonic distortion in the output waveform. : The comparative analysis of THD suggests that SVPWM is a superior technique compared to other inverter control techniques such as sine-triangle pulse width modulation (SPWM) and carrier-based pulse width modulation (CPWM). SVPWM can help to reduce the distortion in the output waveform, leading to improved system efficiency, reduced wear on the system components, and overall better performance of the WECS. Furthermore, SVPWM offers several advantages over other inverter control techniques, including better utilization of DC voltage, improved voltage control, and better utilization of switching devices. These advantages make SVPWM a valuable tool for optimizing the operation of WECS and improving the reliability and performance of renewable energy systems. The value of THD for SVPWM inverter control in WECS is 1.53 under symmetrical fault and 1.34 for unsymmetrical fault, respectively. In summary, the use of SVPWM-based inverter control for WECS is an effective way to improve the efficiency and performance of the system while reducing the distortion in the output waveform and providing adequate reactive power support. The advantages of SVPWM over other inverter control techniques make it a valuable tool for the development and optimization of renewable energy systems.

Buck Boost Transformer Less in PV System with Grid Connected

For single-phase grid-connected solar PV applications, a novel single-stage buck boost trans formerless inverter (BBTI) topology is presented in this paper. Leakage currents are eliminated since the input PV source and grid neutral share a common ground in this topology. In addition, the buck-boost capability of the proposed topology ensures that the maximum power point is maintained throughout a wide range of input PV voltage variations. The fact that only one energy storage inductor is used in the proposed topology makes it symmetrical during both grid half cycles. Additionally, the proposed topology's two out of five switches operate at a line frequency, resulting in low switching losses, while the remaining three switches operate in any mode with low losses. To control the proposed inverter topology, a straightforward sine-triangle pulse width modulation strategy is outlined and analyzed across all operating modes. The 300W laboratory prototype is the subject of experiments, and all of the major findings are presented in the paper. These findings demonstrate that the proposed system offers higher efficiency with lower THD in output current.

A Novel Three-Phase Transformerless Cascaded Multilevel Inverter Topology for Grid-Connected Solar PV Applications

Nowadays, multilevel inverters (MLIs) are gaining huge popularity for high power transformerless PV applications. Among the traditional MLIs, the cascaded H-bridge (CHB) MLI accommodates lower voltage rated input dc sources, which reduce the voltage stress across the devices. However, the CHB MLI requires multiple PV sources as separate dc-link voltage sources, which create more paths for leakage currents. Therefore, it is a challenging task to deal with the leakage currents in the case of CHB MLIs. In this article, a novel three-phase transformerless inverter topology for grid-connected solar PV application is introduced. This proposed that the inverter topology has six switches per phase, and it has the combined advantages of dc-bypass and ac-bypass circuit configurations. A new modulation strategy is developed for the proposed topology; it is based on a sine triangle pulsewidth modulation technique combined with the dedicated logic functions. The gate pulses for all switches are provided by using these dedicated logic functions. The switching pulses obtained from the dedicated logic functions control all the inverter switches so that the variation of common-mode voltage (CMV) is constant during the inverter operation. This results in reduced leakage current throughout the operation of the inverter. The theoretical analysis, simulations, and experimental results are presented to validate the proposed topology concept for a 3-kVA grid-connected system. Both the simulation and experimental results show that the proposed solution can well attenuate the leakage current; all the results are presented in the article.

Offline Recursive Identification of Electrical Parameters of VSI-Fed Induction Motor Drives

Accurate estimation of electrical parameters of voltage-source-inverter-fed induction machine (IM) drives is very important while employing high-dynamic-performance control schemes, such as vector control. Parameter estimation schemes reported in the literature can estimate only four parameters ( $R_s$ , $L_{ss}$ , $\sigma$ , and $\tau _r$ ) independently out of five electrical parameters ( $R_s$ , $R_r$ , $L_{\sigma s}$ , $L_{\sigma r}$ , and $L_m$ ), when the core loss resistance is neglected. All the five parameters are not independently identified. This article proposes a parameter estimation method that independently identifies all the six electrical parameters ( $R_s$ , $R_r$ , $R_c$ , $L_{\sigma s}$ , $L_{\sigma r}$ , and $L_m$ ) of the IM, including the core loss resistance. Besides, the variation of core loss resistance with frequency is also discussed in this article. The Kalman filter algorithm is used to estimate machine parameters in the proposed method. In the proposed method, a sine-triangle pulsewidth modulation signal is used as input excitation, instead of pseudorandom binary sequence signals. The proposed estimation method is validated using both simulation and experimental results.

An Improved Sensorless DTC Technique for Two/Three-Level Inverter Fed Asynchronous Motor

The Direct Torque Control (DTC) technique was designed to provide high performance for a three-phase asynchronous motor’s behavior by accurately controlling the flux and torque of the latter. However, this conventional DTC generates strong ripples at the level of flux and torque and a variation of the switching frequency since it uses hysteresis comparators, for this reason, the sine-triangle pulse width modulation (SPWM) has been proposed to improve it. The use of Integral Proportional Regulators (PI) allows the generation of the voltage direct and quadrature components that serve as inputs for the SPWM. The technique thus presented provides a fixed switching frequency and lower undulations at the torque and the stator flux. The objective of this work is to apply the improved DTC technique for the control of a cage asynchronous motor that will be powered by two inverters of different topologies; the first is the two-level and the second is the three-level of Neutral point clamped NPC structure. In addition, the control strategy uses a speed estimator that allows the elimination of the mechanical sensor, which greatly increases the reliability of the system. To evaluate the performance and efficiency of the proposed method, a simulation using the MATLAB / SIMULINK software and a fair comparison between the results of the two inverters will be made.

Independent Speed Control of Two Parallel Connected Split-Phase IM With a Common DC Link and Inverter

A novel pulsewidth modulation (PWM) scheme for the decoupled and coordinated control of two parallel connected split-phase induction machines is discussed in this paper for the first time. Both the motors are operated from a single six-phase voltage source inverter which acts as a power source, and two switched capacitor-fed auxiliary inverters to limit the flow of nontorque producing currents in each motor. Both the motors can be operated at its full rated power with low switching frequency, and decoupled control for full power range can be achieved with the proposed topology. This is possible because the individual machines do not carry the load/harmonic currents of other machine (unlike the conventional series or parallel connected systems). The converters can be modulated using sine-triangle PWM or space vector pulsewidth modulation (SVPWM). Furthermore, two different schemes of SVPWM techniques are proposed and compared in this paper. Exhaustive experimental results for all the modulation schemes are provided for steady state and transient operating conditions including start-up to validate the proposed topology and modulation schemes.

Analytical Evaluation and Reduction of Torque Harmonics in Induction Motor Drives Operated at Low Pulse Numbers

Induction motor drives operated with a low ratio of the switching frequency to the fundamental frequency (i.e., pulse number) are prone to have high magnitudes of low-order torque harmonics. This paper proposes a method to analytically evaluate the harmonic torque spectrum based on the pulsewidth-modulated voltage waveforms for low pulse number operation. The predicted torque harmonic spectra for different pulsewidth-modulated waveforms are validated through simulations and experiments. This paper also reports optimal switching angles to minimize the total rms value of torque harmonics of order 6, 12, 18 $,\dots,$ $6(N-1)$ , considering the number of switching angles per quarter ( $N$ ) to be 4 and 5. Compared to sine triangle pulsewidth modulation and selective harmonic elimination pulsewidth modulation with the same pulse number, the proposed optimal switching angles significantly reduce the total rms value of all harmonic torques of order lower than $6N$ . Extensive simulation and experimental results on a 3.7-kW induction motor drive are presented to demonstrate the superior performance of the proposed optimal pulsewidth modulation.

A New Family of 1- Five-Level Transformerless Inverters for Solar PV Applications

This article presents a family of 1-φ transformerless switched-capacitor based five-level inverter (TSC5LI) topologies for photovoltaic (PV) applications. The proposed family comprises four inverter topologies: H8, H8-UPF, H10, and H10-UPF capable of mitigating the leakage current by having continuous grid frequency voltage at PV parasitic capacitor in spite of considering switch terminal capacitances. A distinctive attribute of the TSC5LI is that 100% dc-bus utilization, symmetrical operation, and constant total common-mode voltage (TCMV) are achieved together. H8 variant of the proposed inverter family is studied extensively. The control strategy used is a simple level-shifted sine-triangle pulsewidth modulation followed by the synthesis of the gate pulses utilizing logical functions. Switching function based TCMV analysis, switched capacitor design, and loss analysis are presented. Simulation and experimental results of H8 variant are presented to validate the theoretical claims. Proposed topology is also compared with the existing five-level transformerless inverters to prove its various advantages.

Digital Adaptive Hysteresis Current Control for Multi-Functional Inverters

This paper proposes a digital adaptive hysteresis current control method for multi-functional inverters in a power-flow control device called digital grid router. Each inverter can be controlled in master, grid-connected, or stand-alone modes, which can be specified by the controller. While the popular linear sine-triangle pulse width modulation (SPWM) control technique requires complicated proportional-integral (PI) regulators with an unavoidable time delay, hysteresis current control has a simple structure, fast responses, and robustness due to its independent system of parameters. Since the hysteresis current control method controls the output current stay around the reference current directly, in the multi-functional inverter, the reference output is not given by a current directly. Thus, the reference current used to implement the hysteresis current control in this study is calculated from the given reference voltage or power in each control mode. The controller uses high-speed sampled data at MHz level and is implemented by using a field-programmable gate array (FPGA). Experimental results show good performances of the proposed controller in controlling power exchanges in the digital grid router.

MPPT and SPPT Control for PV-Connected Inverters Using Digital Adaptive Hysteresis Current Control

Most PV systems are usually controlled by a Maximum Power Point Tracking (MPPT) algorithm to maximize the generated electrical power. However, the maximum power is often unstable and depends on the solar irradiance and temperature. This makes it difficult to control the power grid supply-demand balance due to fluctuations caused by the increase of renewable and variable PV systems. This paper proposes a new control algorithm for a PV-connected inverter called Specified Power Point Tracking (SPPT) control in addition to the conventional Maximum Power Point Tracking (MPPT) control. The PV system is controlled to generate the maximum power or a specified power depending on the electricity transactions comes from the electricity trading system. A high-speed FPGA-based digital adaptive hysteresis current control method, which has fast and stable response and simple structure comparing with the popular Sine-triangle Pulse Width Modulation (SPWM) method, is proposed to implement the MPPT and SPPT control. The adaptive hysteresis current band is calculated adaptively to improve a disadvantage of the classical fixed band hysteresis current control on the varying switching frequency. A reference current used in the adaptive hysteresis current control is calculated such that the output power of the PV-connected inverter is maximized in the MPPT control or is maintained at a given value in the SPPT control. The experimental and simulation results show that the PV-connected inverter under the proposed control algorithm generates the desired power almost exactly and yields stable and fast response despite the varying irradiance.

Torque Ripple Minimization in Neutral-Point-Clamped Three-Level Inverter Fed Induction Motor Drives Operated at Low-Switching-Frequency

Neutral-point-clamped (NPC) multilevel inverter fed high power drives operating at low switching frequency are prone to low-order torque pulsations. For a case of $N$ switching angles per quarter, apart from maintaining the fundamental component, $(N-1)$ voltage harmonics can be eliminated. Consequently, ${\frac{N-1}{2}}$ or lower number of torque harmonics could be eliminated. This paper proposes an optimal pulse-width modulation (PWM), which minimizes the combined root mean square (RMS) value ( $\tau _{{\rm RMS}}$ ) of torque harmonics of order lower than $6N$ at any modulation index ( $M$ ) for an induction motor drive fed from an NPC three-level inverter. This paper considers cases of two, three, and four switching angles per quarter cycle of the pole voltage. Compared with synchronized sine-triangle PWM and selective harmonic elimination (SHE) PWM, the proposed PWM reduces the first ( $N-1$ ) torque harmonics (i.e., $\tau _6$ , $\tau _{12}, \ldots, \tau _{6(N-1)}$ ) over a wide speed range. Simulation and experimental results are presented on a 3.7-kW open-loop constant volts-per-Hertz induction motor drive.

Dynamic Behavior Study of a VSC-HVDC System with SPWM Command Subjected to an Important Variation of Load

To interconnect sources of production, it is necessary to watch that the technical parameters as tension, frequency and phase shift of the sources of production are equal. In Benin, it is difficult for the company in charge of the production and of the transport of the electricity to interconnect the production coming from Nigeria and that coming from Ghana because all the parameters are not equal. It is thus necessary to find a way to interconnect the sources of productions to satisfy not only the request in electrical energy but also to insure the continuity of the service and the stability of the electricity network [1,2]. In this work, we studied the dynamic behavior of the Voltage Source Converter based High Voltage Direct Current (VSC-HVDC) system subjected to an important variation of load and commanded by the Sine-triangle Pulse Width Modulation ( SPWM) to improve the quality of the electrical energy. We developed thus first of all the electric model of all the constituents of the system. These models allowed designing easily the control systems of the static converters VSC (the rectifier and the inverter). The simulation of the inverter showed that the rate of distortion of harmonious varied considerably according to the load for important variations of load. The solution brought by this work is the elaboration of a control system to vectorial PWM who improves the rate of distortion of harmonious.

Investigations on Optimal Pulse Width Modulation to Minimize Total Harmonic Distortion in the Line Current

High-power and high-speed motor drives have only a few switching transitions in each line cycle. Pulse width modulation (PWM) waveforms with positive voltage transition at the positive zero crossing of the fundamental voltage (type-A) are generally considered for PWM waveform with an even number of switching angles per quarter, whereas waveforms with negative voltage transition at the positive zero crossing (type-B) are considered for an odd number of switching angles per quarter. Optimal switching angles to minimize the total harmonic distortion (THD) in motor current are reported for both type-A and type-B waveforms of pulse numbers ( $P$ ) of 5, 7, 9, and 11. Based on simulation and experimental studies on a $3.7$ kW induction motor (IM) drive, optimal type-A and type-B PWM methods are shown to be better than each other in different modulation ranges for each pulse number. The space vector based analysis of optimal type-A and type-B waveforms brings out the optimal vector sequence at any modulation index for a given $P$ . Findings of the space vector based analysis lead to a new approach for determining optimal switching angles with much reduced computational effort. Compared to sine-triangle PWM, deployment of optimal vector sequences in an IM drive, having a maximum switching frequency of 250 Hz, leads to significant reduction in both THD of line current as well as motor losses over a wide range of speeds and load conditions.

Analysis of sine‐triangle and zero‐sequence injection modulation schemes for split‐phase induction motor drive

A split-phase induction motor is fed from two three-phase voltage source inverters for speed control. This study analyses carrier-comparison based pulse width modulation (PWM) schemes for a split-phase motor drive, from a space-vector perspective. Sine-triangle PWM, one zero-sequence injection PWM where the same zero-sequence signal is used for both the inverters, and another zero-sequence injection PWM where different zero-sequence signals are employed for the two inverters are considered. The set of voltage vectors applied, the sequence in which the voltage vectors are applied, and the resulting current ripple vector are analysed for all the PWM methods. Besides all the PWM methods are compared in terms of dc bus utilisation. For the same three-phase sine reference, the PWM method with different zero-sequence signals for the two inverters is found to employ a set of vectors different from the other methods. Both analysis and experimental results show that this method results in lower total harmonic distortion and higher dc bus utilisation than the other two PWM methods.

Thermal test method for high power three‐phase grid‐connected inverters

Semiconductor device junction temperatures are maintained within datasheet specified limits to avoid failure in power converters. Burn-in tests are used to ensure this. In inverters, thermal time constants can be large and burn-in tests are required to be performed over long durations of time. At higher power levels, besides increased production cost, the testing requires sources and loads that can handle high power. In this study, a novel method to test a high power three-phase grid-connected inverter is proposed. The method eliminates the need for high power sources and loads. Only energy corresponding to the losses is consumed. The test is done by circulating rated current within the three legs of the inverter. All the phase legs being loaded, the method can be used to test the inverter in both cases of a common or independent cooling arrangement for the inverter phase legs. Further, the method can be used with different inverter configurations - three- or four-wire and for different pulse width modulation (PWM) techniques. The method has been experimentally validated on a 24 kVA inverter for a four-wire configuration that uses sine-triangle PWM and a three-wire configuration that uses conventional space vector PWM.

Harmonic analysis of DC capacitor current in sinusoidal and space-vector modulated neutral-point-clamped inverters

The voltage ripple and power loss in the DC-capacitor of a voltage source inverter depend on the harmonic currents flowing through the capacitor. This paper presents a double Fourier series based analysis of the harmonic contents of the DC capacitor current in a three-level neutral-point clamped (NPC) inverter, modulated with sine-triangle pulse-width modulation (SPWM) or conventional space vector pulse-width modulation (CSVPWM) schemes. The analytical results are validated experimentally on a 3-kVA three-level inverter prototype. The capacitor current in an NPC inverter has a periodicity of 120∘ at the fundamental or modulation frequency. Hence, this current contains third-harmonic and triplen-frequency components, apart from switching frequency components. The harmonic components vary with modulation index and power factor for both PWM schemes. The third harmonic current decreases with increase in modulation index and also decreases with increase in power factor in case of both PWM methods. In general, the third harmonic content is higher with SPWM than with CSVPWM at a given operating condition. Also, power loss and voltage ripple in the DC capacitor are estimated for both the schemes using the current harmonic spectrum and equivalent series resistance (ESR) of the capacitor.

A Quad Two-Level Inverter Configuration for Four-Pole Induction-Motor Drive with Single DC Link

A multilevel inverter topology for a four-pole induction-motor drive is presented in this paper, which is constructed using the induction-motor stator winding arrangement. A single dc source with a less magnitude when compared with conventional five-level inverter topologies is used in this topology. Therefore, power balancing issues (which are major challenges in conventional multilevel inverters) are minimized. As this configuration uses a single dc source, it provides a path for zero-sequence currents because of the zero-sequence voltages present in the output, which will flow through the motor phase winding and power electronic switches. To minimize these zero-sequence currents, sine-triangle pulsewidth modulation (SPWM) is used, which will shift the lower order harmonics near to switching frequency in the linear modulation region. However, in the case of overmodulation, harmonic voltages will be introduced close to the fundamental frequency. In this regard, a modified SPWM technique is proposed in this paper to operate the drive in the overmodulation region up to the modulation index of 2/√3. The proposed quad two-level inverter topology is experimentally verified with a laboratory prototype on a four-pole 5-hp induction motor. Experimental results show the effectiveness of the proposed topology in the complete linear modulation region and the overmodulation region.

Evaluation and minimization of low-order harmonic torque in low-switching-frequency inverter fed induction motor drives

A low-order harmonic pulsating torque is a major concern in high-power drives, high-speed drives, and motor drives operating in an overmodulation region. This paper attempts to minimize the low-order harmonic torques in induction motor drives, operated at a low pulse number (i.e., a low ratio of switching frequency to fundamental frequency), through a frequency- domain (FD) approach as well as a synchronous reference frame (SRF) based approach. This paper first investigates FD-based approximate elimination of harmonic torque as suggested by classical works. This is then extended into a procedure for minimization of low-order pulsating torque components in the FD, which is independent of machine parameters and mechanical load. Furthermore, an SRF-based optimal pulsewidth modulation (PWM) method is proposed to minimize the low-order harmonic torques, considering the motor parameters and load torque. The two optimal methods are evaluated and compared with sine-triangle (ST) PWM and selective harmonic elimination (SHE) PWM through simulations and experimental studies on a 3.7-kW induction motor drive. The SRF-based optimal PWM results in marginally better performance than the FD-based one. However, the selection of optimal switching angle for any modulation index $(M)$ takes much longer in case of SRF than in case of the FD-based approach. The FD-based optimal solutions can be used as good starting solutions and/or to reasonably restrict the search space for optimal solutions in the SRF-based approach. Both of the FD-based and SRF-based optimal PWM methods reduce the low-order pulsating torque significantly, compared to ST PWM and SHE PWM, as shown by the simulation and experimental results.

Reduction of Torque Ripple in Induction Motor Drives Using an Advanced Hybrid PWM Technique

A voltage source inverter-fed induction motor produces a pulsating torque due to application of nonsinusoidal voltages. Torque pulsation is strongly influenced by the pulsewidth modulation (PWM) method employed. Conventional space vector PWM (CSVPWM) is known to result in less torque ripple than sine-triangle PWM. This paper aims at further reduction in the pulsating torque by employing advanced bus-clamping switching sequences, which apply an active vector twice in a subcycle. This paper proposes a hybrid PWM technique which employs such advanced bus-clamping sequences in conjunction with a conventional switching sequence. The proposed hybrid PWM technique is shown to reduce the torque ripple considerably over CSVPWM along with a marginal reduction in current ripple.

A Modified Reference Approach for Harmonic Elimination in Pulse-width Modulation Inverter Suitable for Distributed Generations

An online harmonic elimination technique of the output voltage for a pulse-width-modulation-based voltage source inverter is proposed. The sinusoidal reference waveform of sine-triangle pulse-width modulation is modified using a separate signal of proper phase, frequency, and amplitude to reduce the total harmonic distortion of the output. The proposed scheme is simulated using the MATLAB 7.0 and PSIM 6.0 environment and is, subsequently, compared with experimental results. The scheme is simple and can easily be implemented without attempting the rigorous solution of the coupled transcendental equations usually required for normal selected harmonic elimination technique.