Modified SPWM technique for improved harmonic performance of single PV array fed grid‐tied five‐level converter
2020; Institution of Engineering and Technology; Volume: 13; Issue: 19 Linguagem: Inglês
10.1049/iet-pel.2020.0438
ISSN1755-4543
AutoresShivam Kumar Yadav, Nidhi Mishra, Bhim Singh, Sanjeevikumar Padmanaban, Frede Blaabjerg,
Tópico(s)Advanced DC-DC Converters
ResumoIET Power ElectronicsVolume 13, Issue 19 p. 4498-4506 Research ArticleFree Access Modified SPWM technique for improved harmonic performance of single PV array fed grid-tied five-level converter Shivam Kumar Yadav, Corresponding Author Shivam Kumar Yadav shivamyadaviitdelhi@gmail.com Department of Electrical Engineering, IIT Delhi, New Delhi, 110016 IndiaSearch for more papers by this authorNidhi Mishra, Nidhi Mishra Department of Electrical Engineering, IIT Delhi, New Delhi, 110016 IndiaSearch for more papers by this authorBhim Singh, Bhim Singh Department of Electrical Engineering, IIT Delhi, New Delhi, 110016 IndiaSearch for more papers by this authorSanjeevikumar Padmanaban, Sanjeevikumar Padmanaban Department of Energy Technology, Faculty of Engineering and Science, Aalborg University, Aalborg, DenmarkSearch for more papers by this authorFrede Blaabjerg, Frede Blaabjerg orcid.org/0000-0001-8311-7412 Department of Energy Technology, Faculty of Engineering and Science, Aalborg University, Aalborg, DenmarkSearch for more papers by this author Shivam Kumar Yadav, Corresponding Author Shivam Kumar Yadav shivamyadaviitdelhi@gmail.com Department of Electrical Engineering, IIT Delhi, New Delhi, 110016 IndiaSearch for more papers by this authorNidhi Mishra, Nidhi Mishra Department of Electrical Engineering, IIT Delhi, New Delhi, 110016 IndiaSearch for more papers by this authorBhim Singh, Bhim Singh Department of Electrical Engineering, IIT Delhi, New Delhi, 110016 IndiaSearch for more papers by this authorSanjeevikumar Padmanaban, Sanjeevikumar Padmanaban Department of Energy Technology, Faculty of Engineering and Science, Aalborg University, Aalborg, DenmarkSearch for more papers by this authorFrede Blaabjerg, Frede Blaabjerg orcid.org/0000-0001-8311-7412 Department of Energy Technology, Faculty of Engineering and Science, Aalborg University, Aalborg, DenmarkSearch for more papers by this author First published: 17 February 2021 https://doi.org/10.1049/iet-pel.2020.0438Citations: 4AboutSectionsPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL Share a linkShare onFacebookTwitterLinkedInRedditWechat Abstract This study presents a performance assessment of a single photovoltaic (PV) array fed transformer-based five-level converter topology with optimal shift factor-based modified sinusoidal pulse width modulation (OSF-MSPWM) technique under a dynamic solar PV environment. The five-level converter output is generated using H bridge cells and single-phase transformers. A single PV array is fed to all cascaded H bridge cells and isolation is provided by cascading secondary windings of the transformers in the AC side. The separate DC sources requirement is eliminated and galvanic isolation is provided by single-phase transformers. The decoupled controller with modified in-phase disposition PWM technique is used for active power injection into the grid at unity power factor. This work uses a new carrier shape at the same input carrier frequency and modulation index mf for improving the harmonics performance of the five-level converter. Hence, shift the dominant harmonics to the higher side for developed topology and performing optimal shift factor-based modulation is compared with the conventional SPWM technique. The steady-state and dynamic responses of the PV multilevel converter are observed in MATLAB simulation and tested in a real-time platform. Nomenclature Ppv, Ipv, Vpv photovoltaic power, voltage and current Vocn, Iscn open-circuit voltage and short circuit current of a PV module vfill, ifill voltage and current fill factor of a PV module Nss, Npp number of series and parallel connected PV modules VHabc three-phase multilevel converter output voltages V H a b c U , V H a b c L Cell voltage of upper H bridge and lower H bridge of phases a, b and c vabc, iabc three-phase grid voltages and currents RT, LT parasitic resistance and leakage inductance of a transformer Td, Tq dq components of transformation matrix Tabc abc components of transformation matrix VHd, VHq dq components of three-phase multilevel converter output voltages vd, vq dq components of grid voltages Id, Iq dq components of grid currents I d ∗ , I q ∗ reference dq components of grid currents w fundamental angular frequency Ud, Uq output of inner current loop PI controllers V H d ∗ , V H q ∗ reference dq components of three-phase multilevel converter output voltages kp, ki proportional and integral controller gains Tctrloop inner control loop time constant Vdc, Idc DC link voltage and current V dc ∗ reference DC link voltage Pdc, Pac DC power and AC active power k ratio from power balance equation Amax, Amin maximum and minimum amplitude of carrier wave X difference between maximum and minimum amplitude of carrier wave P1, P4, P7 stationary points on carrier wave P2, P3, P5, P6 movable points on carrier wave shape d shift factor Ts, fs time period and input frequency of carrier wave V a b c ∗ three-phase modulating signals 1 Introduction Multilevel converters have become popular in recent years because of an increase in medium power-based clean energy generation [[1]]. Renewable energy sources such as wind and solar, play a major role in the generation of clean power. The photovoltaic (PV) power is abundant in nature and wind is limited to coastal areas. Solar power generation has immense potential and viable replacement for coal-based plants. The advent of high power has led to the demand for high power switches. The series-connected switches and cascading of H bridge cells have become a promising solution. The cascaded-H-bridge (CHB) cells are the most popular converter for multilevel voltage generation [[2]]. Such converter has wide applications in the industrial sector and power generation. Multilevel converters have been synthesised for voltage output with higher quality, the minimum rate of change of voltage across switches, less electromagnetic interference [[3]]. The switching losses are less, as compared to two-level converters. Apart from merits, the device count of MLCs increases with an increase in voltage and power level. The requirement of isolated DC sources increases with an increase in CHB cells. The higher number of isolated DC sources leads to an increase in capacitor count. Due to separate DC sources, a large number of PV arrays and DC link capacitors are required. Moreover, voltage controllers and MPPT controllers are also increased. The requirement of more number of gate drivers and protection circuits is also a financial burden. The transformer-based MLCs solve the above-addressed problem, which uses a single DC source [[4]]. Each H bridge cell is connected to the primary winding of the low-frequency transformer, whereas secondary winding has provided a cascaded arrangement of five-level topology [[5]]. It achieves the whole power injection from a single PV source. The multilevel converters, which use transformers for multiple level generation in output voltage, are found in [[6]]. Implemented a Scott connection-based transformer for attaining multilevel converter output [[7]]. Research on three-phase transformer-based multilevel using nine H bridge cells is presented in [[8]]. In [[9]], modular multilevel converters (MMCs) are used for PV plants and require capacitor balancing control for each cell. It requires independent voltage control for each PV array and capacitor voltage balancing in PV fed multilevel diode clamped converters [[10]]. A single-phase grid-connected CHB cell with multiple PV arrays and DC link capacitors discussed in [[11]]. It achieves an enhanced active power balancing for three-phase CHB configuration with multiple PV fed CHBs in [[12]]. However, performance analysis of PV fed transformer-based MLCs under dynamic solar irradiations is needed to be explored for the demand for clean energy and low-cost power transmission. The harmonics performance and switching losses of MLI depend on the pulse width modulation implemented to generate switching signals [[13]]. The triangular carrier-based sine wave PWM (SPWM) is implemented for the five-level converter [[14]]. A phase-shifted PWM technique is implemented for CHB multilevel converter in [[15]]. Various schemes such as phase disposition (PD) PWM, alternative phase opposition disposition (APOD) PWM, phase opposition disposition (POD) PWM are used for asymmetric reduced switch converter [[16]]. Space vector modulation (SVM) based PWM is incorporated for a multilevel converter [[17]]. Presented the selective harmonic elimination and particle swarm optimisation-based PWM technique in [[18]]. The motivation to new modified PWM [[19]] techniques is given as follows: Poor harmonic performance and higher switching. Complex logic circuit design in SVM [[17]] and tough implementation. Offline calculations and initial guess are important for optimisation based SHE PWM techniques [[18]]. In this paper, got an optimal shift factor with optimal shift factor-based modified sinusoidal pulse width modulation (OSF-MSPWM) technique. The performance of a three-phase transformer-based photovoltaic inverter under dynamic isolation change is analysed. Tested a 57-kW transformer topology in real-time controller hardware in the loop using OPAL-RT. The steady-state and dynamic responses are analysed for active power injection to the grid. Performed the harmonics analysis with OSF-MSPWM technique. A single PV source three-phase multilevel inverter (STMLI) offers remarkable merits given as follows: It provides galvanic isolation between the grid and the converter side. The selection of different transformer ratios increases the number of levels [[6]]. Reduces leakage current in PV applications. Such topologies are helpful for flexible AC transmission applications. Transformers used in such topologies take responsibility for line transformers [[8]]. The elimination of multiple PV sources reduces component count and controlled complexity. The above advantages motivate for this work on transformers-based MLCs with a single DC source and improved modulation techniques for power quality improvement of solar photovoltaic systems. This paper integrates the merits of the modified PWM technique with a single PV source transformer-based five-level topology. It provides an insight into a new performance assessment when the benefits of both topology and new modulation are taken together under the dynamic solar photovoltaic environment. This work provides a better understanding of implementing the OSF-MSPWM technique with in-PD patterns and simple mathematical explanation with minute details on the point allocations of new carrier shape for solar photovoltaic applications. 2 Single PV array fed five-level MLC Shown the STMLI topology in Fig. 1, which has three phases with two H bridge cells per leg. Implements a 57-kW system topology for grid-tied PV fed application. Feed a single PV array to H bridge cell of three-phases. The switches (S3abc, S4abc) of cells of three phases are complementary of switches (S1abc and S2abc). Eliminates the requirement of separate DC sources from the DC side and feed a common DC to all H bridge cells. The single-phase transformer is connected as the interfacing component between cascaded cells and a three-phase AC grid. The five-level output voltage generation is achieved from a single PV array. The N level CHB converter requires (n − 1)/2 cells per leg. Employed the transformers T1 and T2 with turn ration 1:1 between primary and secondary winding. Got the benefit of galvanic isolation with transformer-based converter configurations. The secondary winding of both transformers is cascaded for each phase and connected to the AC grid. Feed the cell voltage of the upper H bridge and lower H bridge to the primary winding of the transformer. The leakage inductance of the transformer replaces the interfacing inductors. Takes the line voltage of 415 V for this three-phase topology. The PV array is formed by series and parallel connected modules from the equation given as follows: P pv = V oc n × v fill × N ss × I sc n × i fill × N pp . (1) Expression of the KVL equation of STMLI is as follows: V H a b c − v a b c = R T i a b c + L T d i a b c d t . (2) The converter voltage equation is a sum of cell voltages of individual H bridges of each phase given as V H a b c = V H a b c U + V H a b c L . (3) The five-level output is obtained on the secondary winding of the transformer. The three-phase voltages and currents are transformed into dq frame using transformation matrices given as follows: T d T q = 2 3 cos w t − sin w t cos w t − 120 ° − sin w t − 120 ° cos w t + 120 ° − sin w t + 120 ° T ∗ T a T b T c . (4) Applying (4) in (3) one obtains d I d d t = V H d − V d L T − R T L T I d + w I q (5) d I q d t = V H q − V q L T − R T L T I q − w I d . (6) Fig. 1Open in figure viewerPowerPoint Single PV array fed five level converters 3 Grid-tied PV fed control strategy Fig. 2 shows the control strategy for solar photovoltaic system to enable active power transfer into the AC grid. Compared the sensed DC link voltage of the multilevel converter with reference PV voltage signal. Obtain this reference voltage signal from the MPPT controller block, which provides maximum power extraction from the PV array. The three-phase phase-locked loop (PLL) generates the angular position of the instantaneous voltage signals. Moreover, abc to dq conversion is adopted to convert voltage and current quantities in the stationary frame. The unity power factor action is attained by setting the magnitude of I q ∗ to zero. The cross-coupling voltage drops are added for effective power control. The leakage inductance of the transformer provides better harmonic performance for grid current. Let U d , U q be the output of PI current controllers expressed as U d = V H d − V d + ω L T I q (7) U q = V H q − V q − ω L T I d . (8) Now (9), (10) are utilised to have reference converter voltages as V H d ∗ = U d + V d − ω L T I q (9) V H q ∗ = U q + V q + ω L T I d . (10) Equations (7) and (8) represent decoupled control as shown in Fig. 2. The reference voltages are fed to inverse Park transformation to get the desired reference modulating signals for PWM generation. Here, U d and U q are the output signals of the PI controllers, which reduces the error between actual and reference values of the dq currents. Fig. 2Open in figure viewerPowerPoint Decoupled controller for STMLI configuration 3.1 Inner current control loop Shown the inner current control loop in Fig. 3, express the direct axis component equation of current as d I d d t = − R T L T I d + 1 L T U d . (11) Taking Laplace transform, it is expressed as U d ( s ) = s L T I d ( s ) + R T I d ( s ) (12) U d ( s ) I d ( s ) = s L T + R T . (13) From Fig. 3, one has I d ∗ ( s ) − I d ( s ) k p + k i s = U d ( s ) . (14) Substituting the value of U d I d ∗ ( s ) − I d ( s ) k p + k i s = I d ( s ) ( s L T + R T ) . (15) Rearranging terms I d ∗ ( s ) I d ( s ) − 1 = ( s L T + R T ) k p + ( k i / s ) . (16) The inner controller time constant is kept faster than the switching time constant for better performance of the grid-tied control system. The inner current controller parameters are designed such that the transfer function becomes the first-order system as desired and (16) is rewritten as I d ∗ ( s ) I d ( s ) = 1 + s T ctrloop . (17) Fig. 3Open in figure viewerPowerPoint Design of inner current loop 3.2 Outer voltage control loop The outer voltage control loop becomes a second-order system with first-order inner control loop as shown in Fig. 4. Fig. 4Open in figure viewerPowerPoint Design of outer voltage loop Obtained capacitor current as the difference between PV array and DC link capacitor current. It can be formulated as the equation of DC voltage as follows: V dc ( s ) = i pv ( s ) − i dc ( s ) s C . (18) The ratio k is obtained from the power balance equation as follows: P dc = P ac (19) V dc I dc = 3 2 V d I d (20) I dc = k I d (21) k = 3 V d 2 V dc . (22) The uncompensated open-loop transfer function is given as follows: G u ( s ) = k s C ( 1 + s T ctrloop ) . (23) The Bode plot is obtained with positive gain and phase margin as shown in Fig. 5. Fig. 5Open in figure viewerPowerPoint Bode diagram 4 Modified SPWM strategy Conventional SPWM techniques need to have high carrier frequencies to reduce lower order harmonics. Converter experiences EMI (electromagnetic interference) issues at higher switching frequencies. It must improve the harmonics performance with a little increase in switching losses by introducing new modulation techniques in multilevel converters. To have such solutions, the shape of the triangular carrier is modified with considerations of four points on a carrier wave and has been first introduced in [[19]] with phase opposition pattern. In this section, shift factor 'd' based OSF-MSPWM with in-PD pattern and simple mathematical formulation are discussed for easier implementation in STMLI configuration. Divides the total time period Ts into six equal parts and increase the position of point placement to seven for better analysis as shown in Fig. 6. The OSF-MSPWM is evolved from a conventional SPWM scheme as shown in a generalised carrier wave in Fig. 6a. Among the seven points, red-marked points are stationary points numbered as (P1, P4, P7) and green points (P2, P3, P5, P6) are movable points. Obtained the simple formulation equations from a geometrical analysis of carrier waveform shown in Fig. 6a. Furthermore, give the difference between the maximum and minimum amplitude of carrier wave that decides to level formation as X = A max − A min . (24) Gives the initial locations of stationary points as P 1 = A min , P 4 = A max , P 7 = A min . (25) The movement of movable points depends on the value of shift factor 'd' given as P 2 ∧ = P 2 + d . (26) Also P 2 ∧ = P 6 ∧ = A min + X 3 + d . (27) Similarly P 3 ∧ = P 3 − d (28) P 3 ∧ = A min + 2 X 3 − d = P 5 ∧ . (29) Fig. 6b shows modified SPWM where movable points are shifted by a factor of X/3. The new placement of point P 2 ∧ corresponding to the y-axis intercept at triangular carrier waveform is given as P 2 ∧ = A min + X 3 + X 3 = P 3 (30) P 3 ∧ = A min + 2 X 3 − X 3 = P 2 . (31) Similarly, P 5 ∧ and P 6 ∧ are positioned for modified carrier wave generation. Fig. 6c shows carrier wave with a shift of 2X/3 with the change in the frequency modulation index after the intersection of movable points on the time axis. Formulates the equations in the same manner and fs carrier wave becomes 3fs. The shift factor d, provides an extra degree-of-freedom for both device switching frequency and change in a carrier wave shape. Fig. 6Open in figure viewerPowerPoint Modified carrier waveforms (a) Generalised carrier schematic (OSF-MSPWM), (b) OSF-MSPWM carrier construction at d = X/3, (c) OSF-MSPWM carrier construction at d = 2X/3 4.1 Implementation in five-level topology A five-level converter output is achieved, which has two cascaded stages of the H bridge cells. The five-level output is obtained at the secondary winding ends with a single PV source-based topology. The levels attained in this five-level topology are +2Vdc, +Vdc, 0, −Vdc, and −2Vdc. The modulation strategy used is OSF-MSPWM, which has the in-PD in the arrangement of the carriers. The carrier-based strategies are a viable choice for five-level converters. Here, four carriers are required to be compared with the modulating signal to provide necessary switching pulses to the multilevel converter. Employed the input carrier frequency of 1 kHz with period Ts for low switching loss in the multilevel converter. In Figs. 6a and b, shift factor d controls the device switching frequency and carrier shape together. The carrier shape does not cut the time axis in these figures, and the frequency modulation index remains the same. However, the carrier frequency is 3 times in Fig. 6c with a change in the frequency modulation index of 3 times that of wave shapes in Figs. 6a and b. Table 1 show values of seven points with different shift factors (0, X/3) for all levels of five-level converter voltage. The four carriers are level shifted with X = 0.5 for each carrier. Figs. 7a–c show carrier wave construction with four carriers for a five-level converter in the MATLAB/Simulink at the shift factors of d = 0, d = X/3 and d = X/2. Table 1. Points allocation for carrier shape generation Voltage levels d = 0 (Conventional SPWM) d = X/3 = 0.166 (OSF-MSPWM) P1 P2 P3 P4 P5 P6 P7 P1 P2 P3 P4 P5 P6 P7 + 2 V dc 0.5 0.66 0.83 1 0.83 0.66 0 0.5 0.88 0.66 1 0.66 0.83 0.5 + V dc 0 0.16 0.33 0.5 0.33 0.16 0 0 0.33 0.16 0.5 0.16 0.33 0 − V dc −0.5 −0.33 −0.17 0 −0.17 −0.33 −0.5 −0.5 −0.16 −0.33 0 −0.33 −0.16 −0.5 − 2 V dc −1 −0.83 −0.67 −0.5 −0.67 −0.83 −1 −1 −0.66 −0.83 0 −0.83 −0.66 −1 Fig. 7Open in figure viewerPowerPoint Five level OSF-MSPWM carrier and modulating wave (a) d = 0, (b) d = X/3, (c) d = X/2 5 Numerical simulation results The OSF-MSPWM technique is executed for STMLI configuration. Figs. 8 and 9 show the extensive harmonics analysis with variation in shift factors and comparative graphs on the entities such as dominant harmonics, total harmonic distortion (THD) and fundamental output. Fig. 10 shows the performance of the STMLI under the dynamic profile of the solar irradiance. Fig. 8Open in figure viewerPowerPoint Harmonic spectrum of five level converter voltage (a) d = 0, (b) d = X/3, (c) d = X/2 Fig. 9Open in figure viewerPowerPoint Harmonic spectrum (a) d = 2X/3, (b) Dominant harmonic comparison, (c) THD and fundamental voltage comparison Fig. 10Open in figure viewerPowerPoint Dynamic Performance of STMLI (a) Internal control signals, (b) PV fed grid-tied five level converter 5.1 Dominant harmonics analysis The input carrier frequency is 1 kHz with a frequency modulation index of 20 for a 50 Hz reference signal. The dominant harmonics reside around sidebands of mf. In Fig. 8a, the shift factor is taken zero and has 19th and 21th dominant with THD of 26.99%. Fig. 8b shows a shift factor of X/3 leads to higher fundamental output with 21th and 61th dominant harmonics with a frequency modulation index of 20. In Fig. 8c, the value of mf remains 20, with better fundamental output, same carrier frequency, and improved harmonic performance as compared to Fig. 8b. Fig. 9a shows an increase in mf to the value of 60 at the same carrier frequency and is not a viable solution for multilevel converters. Hence, it can be seen that shift factor d = X/2 is the most optimal shift factor and provides optimal point placement with a new carrier shape. This new optimal carrier shape leads to better fundamental output and improved harmonic performance at the same input carrier frequency fs. However, device switching is increased marginally with a change in shape due to higher chopping in the carrier pattern. The OSF-MSPWM technique is implemented in STMLI configuration with a dynamic change in irradiance. Figs. 9b and c show comparative graphs of OSF-MSPWM and conventional SPWM with improved performance. Fig. 9b shows the leftmost and rightmost dominant harmonic trajectory with variations in shift factor. The encircled points represent the harmonic performance of the conventional SPWM and OSF-MSPWM. The trajectory shows that there occurs a shift in dominant harmonics with an increase in the shift factor. Here, d = 0.25, where X = 5 provides similar performance as that of 3 kHz carrier wave without a change in frequency modulation index and input carrier frequency. Fig. 9c shows THD and fundamental output with variations in shift factors. Here, at d = 0.33, i.e. 2X/3, one has the best performance but at the cost of increased device switching frequency (up to 3 kHz). At d = 0.25, THD of converter voltage is 25.63% with a fundamental output of 555.8 V, with less device switching frequency and the same frequency modulation index. This new optimal carrier shape of d = X/2, leads to optimal shape and better performance between two conventional SPWM triangular shapes, which are observed as d = 0 (at 1 kHz device switching) and d = 0.33 (at 3 kHz device switching frequency). Therefore, with little higher device switching, an optimal location is searched which gives better results. This search can also be further refined with extensive optimisation approaches, but observed the most promising results at d = 0.25. The tolerance to the shift factor can be 0.02, but a higher tolerance below d = 0.25 creates a poor performance in terms of dominant harmonics. The higher tolerance above d = 0.25 improves performance as well, but at the cost of higher device switching. Hence a trade-off is maintained, where device switching does not increase much with improvement in the harmonic's performance. This OSF-MSPWM technique is further implemented for performance assessment of STMLI configuration with dynamic change in solar irradiance. 5.2 Dynamic performance Fig. 10a shows dynamic performance of the control signals with a fall in solar irradiance at 0.65s. Achieved the three-phase modulating signals for multilevel switching of the cascaded cells. It balances the modulating signals with the variation in the solar irradiance. I d ∗ , which changes with input irradiance magnitude is reduced with the fall in solar irradiance. Achieve the proper tracking of actual signals towards the reference dq signals and also, the zero reactive power with smooth tracking of the actual reactive current signal. Also achieves controlled dynamic performance for reference PV voltage. The proper tuning of the outer layer voltage control loop makes DC link voltage stable under the dynamic operation. Fig. 10b shows STMLI operation with balanced three-phase grid current and voltages. The grid currents maintained the balanced operation even after the sudden change in PV array profile. It shows that system maintains the stability and feeds the active power constantly at the unity power factor. Fig. 10b shows system performance in which PV current and PV array power are reduced to half with a decrease in irradiation. The STMLI five-level operation is also tracked, can see it that attain five-levels back after step change point at time instant of 0.65s. The active power injection depends on the PV power input, which is maintained with a fall in irradiance. The improved modulation based closed-loop control is investigated and simulation results shows excellent performance of the STMLI. 6 Real-time test results Figs. 11-13 show real-time test results of STMLI, which are executed through OPAL-RT simulator. The real-time testing becomes important because it makes the system to run at physical clock time as a real-life system would perform in the practical installation. Fig. 11a shows internal control signals, which remain stable in steady-state conditions. Figs. 11b and c show the results for Vpv and Ipv, which attains maximum power point operation and constant five-level operation is achieved. The grid voltage and current remain sinusoidal at constant solar power input. Achieved unity power factor, which is visible from the AC waveforms. Fig. 12 shows real-time dynamic results for the SPV system with solar irradiance change from 1000 to 500 W/m2. Fig. 12a shows that control signal performance is validated successfully with simulation results in a real-time environment. The encircled area shows the instant of dynamic change for the test results. In Fig. 12a, the performance in real-time is for control signals is observed. Similarly, Figs. 12b and c show that real-time response to a change in irradiance is channelised excellently. Maintain the power transfer to the grid with five-level converter output. The real-time dynamic operation is validated successfully with transformer integrated SPV system. Furthermore, improves harmonic performance in real-time with modified OSF-MSPWM. Figs. 13a–c depict the real-time harmonic assessment of the STMLI configuration. The OSF-MSPWM technique improved the THD to 24.94%, which is less than the conventional SPWM scheme. Injected grid current meets the 5% limit of IEEE 519 standard. It found to be the THD of grid current around 2% with the modified modulation strategy. Overall, achieve power quality enhancement for STMLI under the dynamic environment with the execution of OSF-MSWPM strategy. Fig. 11Open in figure viewerPowerPoint Recorded results at constant irradiance (a)–(c) Steady state STMLI performance in real time Fig. 12Open in figure viewerPowerPoint Recorded results at variable irradiance (a)–(c) Dynamic state STMLI performance in real time Fig. 13Open in figure viewerPowerPoint Harmonic Analysis in real-time at 1000 W/m2 (a) OSF-MSPWM (at d = 0) or Conventional SPWM, (b) OSF-MSPWM with shift factor at (d = X/2), (c) grid current THD with OSF-PWM 7 Comparative analysis Table 2 shows a comparative chart of different modulation techniques. Discussed various PWM techniques in [[1]-[3], [7]]. It covers the performance of such techniques under dynamic solar PV environment. However, harmonic performance is fair with a lack of dominant harmonics shift capability. The technique in [[11]], provides a phase-shifted PWM approach, but performance under the dynamic irradiance is missing. However, as it increases levels, the vector diagram size increases and trigonometric calculations are more in such techniques. Carrier-based techniques are simple to understand and implement over tedious SVM-based approaches. The topology presented in [[19]], require only a single source with the modified SPWM technique. This topology reduces the demand for a separate PV array for each H bridge cell. The modified technique provides good harmonic performance with the ability to shift dominant harmonics. Discussed the performance with phase-opposition PWM in [[19]]. However, this modified technique for the solar PV environment is not covered in multilevel literature. The proposed work integrates most of the benefits from single PV source topology to OSF-MSPWM (in-PD), which results in a new power quality solution towards multilevel-based solar photovoltaic systems. Table 2. Comparative analysis References Modulation schemes Lower order harmonic elimination Dominant harmonics shift capability Harmonic performance Dynamic solar PV environment Single source topology [[1]] clamping PWM no no fair yes no [[2]] phase-shifted PWM no no fair yes no [[3]] PD-PWM no no fair yes no [[7]] LS-PWM no no fair yes no [[11]] phase-shifted PWM no no fair no no [[14]] LS-PWM no no fair — no [[17]] SVM no no good — no [[18]] PSO-SHEPWM yes no good — no [[19]] MSPWM no yes good no yes proposed OSF-MSPWM no yes good yes yes 8 Conclusion Performance of a 57 kW three-phase single PV source solar photovoltaic system with reduced components, galvanic isolation, utility workable system has been validated. This work presented the decoupled controller modelling with the ability to control active power injected into the grid at the unity power factor. Also, presented the active power transfer to the grid under sudden irradiance changes with improved power quality. Unlike conventional SPWM, the OSF-MSPWM technique has provided an extra degree-of-freedom for carrier wave shape at an optimal shift factor of d = X/2 without an increase in frequency modulation index mf. The optimal shift factor formulation is predicted, which has led to a shift of dominant harmonics to the higher-order side with an increase in the fundamental component. This paper assessed the performance under the dynamic change in irradiance. Conducted the comparative analysis, which shows the merits of this work to provide new insight towards power quality enhancement of the solar PV system. Real-time test results validated the harmonic performance and numerically simulated results. 9 Acknowledgments The authors acknowledge DST, GOI, for granting fund and research facilities to the Electrical Department, IIT Delhi, in FIST scheme under RP31095. Appendix 11 Ppv = 57,000 W, C = 7 mF, Iscpv = 9.37 A, Vmpv = 30.3 V, Impv = 7.97 A, ns = 10, np = 24, Vpv = 300.3 V, Ipv = 190.4 A, fs = 1 kHz, Vocpv = 35.64 V, TR = 60,000 VA, LT = 0.0067 H, RT = 0.05 Ω. Kp1 = 0.05 and Ki1 = 10, Kp2 = 0.67 and Ki2 = 5.2, Kp3 = 0.67 and Ki3 = 5.2. 10 References [1]Lingom, P.M., Song-Manguelle, J., Mon-Nzongo, D.L., et al.: 'Analysis and control of PV cascaded H-bridge multilevel inverter with failed cells and changing meteorological conditions', IEEE Trans. Power. Electron., 2021, 36, (2), pp. 1777– 1789 [2]Kumar, A., Verma, V.: 'Performance enhancement of single-phase grid-connected PV system under partial shading using cascaded multilevel converter', IEEE Trans. Ind. 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