Control, implementation, and analysis of a dual two‐level photovoltaic inverter based on modified proportional–resonant controller
2018; Institution of Engineering and Technology; Volume: 12; Issue: 5 Linguagem: Inglês
10.1049/iet-rpg.2017.0635
ISSN1752-1424
AutoresNayan Kumar, Tapas Kumar Saha, Jayati Dey,
Tópico(s)Multilevel Inverters and Converters
ResumoIET Renewable Power GenerationVolume 12, Issue 5 p. 598-604 Research ArticleFree Access Control, implementation, and analysis of a dual two-level photovoltaic inverter based on modified proportional–resonant controller Nayan Kumar, Corresponding Author Nayan Kumar nayansays@gmail.com Department of Electrical Engineering, National Institute of Technology, Mahatma Gandhi Avenue, Durgapur, IndiaSearch for more papers by this authorTapas Kumar Saha, Tapas Kumar Saha Department of Electrical Engineering, National Institute of Technology, Mahatma Gandhi Avenue, Durgapur, IndiaSearch for more papers by this authorJayati Dey, Jayati Dey Department of Electrical Engineering, National Institute of Technology, Mahatma Gandhi Avenue, Durgapur, IndiaSearch for more papers by this author Nayan Kumar, Corresponding Author Nayan Kumar nayansays@gmail.com Department of Electrical Engineering, National Institute of Technology, Mahatma Gandhi Avenue, Durgapur, IndiaSearch for more papers by this authorTapas Kumar Saha, Tapas Kumar Saha Department of Electrical Engineering, National Institute of Technology, Mahatma Gandhi Avenue, Durgapur, IndiaSearch for more papers by this authorJayati Dey, Jayati Dey Department of Electrical Engineering, National Institute of Technology, Mahatma Gandhi Avenue, Durgapur, IndiaSearch for more papers by this author First published: 08 February 2018 https://doi.org/10.1049/iet-rpg.2017.0635Citations: 31AboutSectionsPDF 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 modified proportional–resonant (M-PR) control topology for single-stage photovoltaic (PV) system, operating both in grid-connected and stand-alone modes. Dual two-level voltage source inverter fed three-phase open-end winding transformer is used to supply the load in this scheme. The M-PR controller is developed for the inner current control loop of the system. The M-PR controller has the ability to track ac current with zero steady-state error. The outer dc-link voltage control loop is developed through the indirect vector control method at synchronously rotating reference frame. The control scheme ensures improved performance of the system at variable solar irradiance and load disturbances. The performance analysis of the dual two-level PV inverter is carried out for different operating conditions. The control scheme is implemented in MATLAB–SIMULINK environment. The theoretical results are verified through experiments in a laboratory prototype. The experimental results show close match with their theoretical counterparts. 1 Introduction The capability of providing sustainable and independent power by the photovoltaic (PV) system has drawn considerable attention in it during recent years. Different control topologies have been developed over the years and are available in the literature [1-3]. Proportional–integral (PI) controller and proportional–resonant (PR) controller are the mostly used controllers in current control applications [4-6]. The proposed control strategy for dual two-level inverter (DTLI)-based PV system includes two cascaded loops: (i) an inner current control loop that generates inverter voltage references, (ii) an outer dc-link voltage control loop to generate current reference. The current controller is responsible for the power quality (PQ), a very important issue for complying with the standards [7]. Many authors [7-10] have reported favourable disturbance rejection capability and good tracking of current reference by the PR controller. The PI controllers are successfully used in vector control, or dc current controls. However, unlike PI controllers, the PR controllers are used to track instantaneous sinusoidal currents successfully. The PR controller resonates with the input signal, as notch filter, in its natural frequency [9]. Nowadays, PR controller is used because of its several advantages, such as reduced total harmonic distortion (THD), fast dynamic response, fixed switching frequency, low steady-state error, and excellent robustness against input/output changes [11]. The attenuation of lower order harmonics using a larger filter inductance (L, LC, LCL etc.) is not a good option since it increases cost of the system. Therefore, design of a suitable current control structure to reduce the harmonics is essential. The PR controller find more attention for several control applications like, PV system [5, 12-15] uninterruptible ac power sources [11], permanent magnet synchronous motor [16], and active filters [8]. The stability problem arising from an infinite gain in PR controller around the natural frequency can be avoided by modifications in it. The modification will reduce the sensitivity towards slight frequency variation [12, 14]. A damping is preferred in its structure and called as damped PR control by Devassy and Singh [15]. Similar modifications are incorporated in [10]. A modified version of the ideal PR controller is discussed in the present work as M-PR controller. Recently, multilevel voltage source inverters (VSIs) are finding more attention in new generation PV system for medium voltage (MV) and high-power delivery. Such inverter topologies can produce voltage and current waveforms of high quality, while in operation at a low switching frequency [17-19]. Furthermore, multilevel inverters (MLIs) feature multiple dc-links, which enables the voltages to be controlled independently, and also to track the maximum power point (MPP) in each string. The efficiency of the PV system can thus be increased by using these characteristics, even in the case of (i) unequal rating of the strings, (ii) different types of the cells used in the strings, (iii) accumulation of dust on the surface of the PV arrays, (iv) unequal solar irradiation, and (v) ageing of the PV panels. Among the available MLI topologies, the DTLI is one of the popular topologies because of its modular circuit layout [20]. Several authors use grid-tied and stand-alone mode inverters for PV-based system. The common practice is to keep the THD for the grid current within 5%, which lowers the adverse effects on other equipment, connected to the grid [4, 21]. Simultaneously, the cascaded inverter topology has been successfully introduced into an MV to high-voltage level applications, such as the control of static reactive power compensation (STATCOM) [20], open winding induction motor [22], grid-connected PV systems [23, 24], and open-end load [25]. The stand-alone PV system is popular for rural electrification because it provides a more affordable and reliable source of electricity [26]. These systems are developed using battery [27], without battery [28], three-phase inverter connected ac load [29], MLI with a transformer, and full-bridge inverter to realise MPP tracking (MPPT) operation [26]. The circuit model of PV cell array, proposed in [30-32], is developed in simulation environment. It is found that the circuit model of single-diode topology offers a reasonable trade-off between simplicity and accuracy. The simplicity of the single-diode model with the method for adjusting the parameters is preferred for the simulation of PV devices with power converters. Accordingly, the single-diode model of the PV cell is considered in this work. The DTLI-based power supply topology, used in this work, is shown in Fig. 1a. Fig. 1Open in figure viewerPowerPoint DTLI-based PV system (a) Circuit configuration, (b) Control block diagram of the M-PR control implementation, (c) Frequency response of M-PR, Ideal-PR and PI controller One modified proportional–resonant (M-PR) controller for DTLI-driven PV system, for both grid-tied and stand-alone operation, is proposed in this work. The vector control is designed for control of the dc-link capacitor voltage of the inverter. The total dc-link voltage is maintained at desired voltage to supply rated power at rated Indian solar irradiance from the PV modules. The PV panels are feeding the dc-link capacitor of the DTLI. The efficiency of the controller is tested with deviation in solar irradiance and perturbation in load. A comprehensive design of the M-PR controller is accomplished by the current loop. The implemented scheme can be effectively utilised for solar heaters, water pumps, electric vehicles, home, agricultural irrigations etc. This study covers a single-stage three-phase DTLI-based PV system, operating both in grid-connected and stand-alone modes for active power delivery to the load, with the following contributions. An M-PR current controller is developed and applied to control the DTLI-based PV system for the first time in available literature. The controller can achieve zero steady-state error at the selected oscillation frequency with relatively small gain. The performance of the proposed control for the considered system has been improved through necessary modification of the ideal PR control strategy. The stand-alone system with the proposed control scheme is successfully implemented through a laboratory prototype and demonstrated the performance of the control in real time. The structure of the paper is given below. The system modelling, grid-connected PV system has been derived in Section 2. Section 3 describes a control scheme for the overall topology. Section 4 provides the proposed real-time system. Section 5 presents the experimental and simulation results. Finally, a conclusion is drawn in Section 6. 2 Mathematical modelling of the DTLI-based PV system 2.1 DTLI-based PV system By considering the power scheme, as illustrated in Fig. 1a, the transformer input voltage is expressed as a function of the two-inverter pole voltages. The pole voltages for the isolated dc sources are measured with respect to the inverter negative terminals, respectively. The three-phase transformer primary winding's voltages are expressed as: (1) where and are the pole voltage of first inverter and second inverter, respectively. They depend on dc-link voltage and . In this proposed work, the total inverter dc-link voltage is kept at . are three-phase load/grid voltages. are the loss representing resistances, and are the leakage inductances of transformer windings. The unit signals and are considered for transformation to synchronous reference farm. With the use of Clarke's transformation, three-phase voltage is transferred to the reference frame. Again, the reference frame is transformed into rotating reference frame quantities using Park's transformation. Considering ‘n’ as the turns ratio of the transformer and considering to be equal to R and are equal to L, one obtains (2) The above equation can be represented in synchronously rotating reference frame by the suitable transformation, as stated above. The active and reactive currents can be decoupled in this frame and can be independently controlled. Equation (2) can then be represented as: (3) where and are d–q-axis components of the transformer output current. 3 Description of control strategy 3.1 Controller structure Fig. 1a presents the complete proposed topology. The voltage controller maintains the inverter dc-link voltage at its reference level by controlling the real power flow. The power output of the inverter has ensured to be same as the power, obtained from the PV modules. Through the conversion, real and reactive currents are decoupled and can be controlled independently. In the synchronously rotating reference frame, d-axis voltage aligns with the load voltage vector and q-axis voltage is found to be zero. The transformer output voltages can be expressed in synchronously rotating reference frame as: (4) (5) where and are output of the transformer d–q-axes voltages and currents, respectively. The proposed control strategy is divided into two cascaded control loops: (i) outer dc-link voltage control loop, and (ii) inner M-PR current control loop. 3.2 Voltage controller Fig. 1a illustrates that the current reference, , is generated by the dc-link voltage controller through processing of the error between the actual dc-link voltage and its corresponding reference value. The control law adopted for is (6) where and represent the actual dc-link capacitor voltages of the inverters. With the PI controller, the voltage loop has the transfer function as: (7a) where are the leakage resistances of dc-link capacitors of the DTLI PV system. The controller gains are designed to be of and . Equation (7a) is found out to be same for both of the inverters, and the numeric values are used to produce (7b) 3.3 Current controller The current control is implemented through M-PR controller. The M-PR controller is adopted due to its fast and robust dynamic response to external perturbations. The gate signals for DTLI are generated by sinusoidal pulse-width modulation (PWM) topology, where the switching frequency is considered as . The inverter-1 and inverter-2 modulating signals are phase shifted by . The proposed M-PR controller for the transformer output currents are developed in stationary reference frame using the conversion. The ideal-PR controller is represented by (8) where , , and are the proportional gain, the resonant frequency, and resonant gain, respectively. The design of PR controller includes the tuning of four parameters, namely , , and . The ideal-PR controller is challenged for implementation in reality since it operates as a network with infinite quality factor, which cannot be achieved in either analogue or digital system. Accordingly, for the realisation of PR controller, the transfer function of the M-PR controller, used in general by the authors in [12, 14] and [13, 33] is (9) In the design procedure of the M-PR controller, there are four main parameters to be considered; Since is the fundamental frequency of the system, it can be selected as . The control model of the inner current loop can be shown in Fig. 1b, where is the first-order inertia link that represents the delay caused by the sampling; programme calculation and PWM control links, and is the sampling time. When the feedforward compensation term of grid voltages is not considered, the open-loop transfer function of the inner loop can be obtained as (10) Then, the closed-loop transfer function is (11) For , the following relationship can be obtained (12) Thus, it is known that, when the resonant frequency of M-PR controller is equal to the angular frequency of controlled object, the input currents can track reference values without steady-state errors. Implementation of M-PR: The is chosen to eliminate the phase and magnitude steady-state errors at low and high frequencies. The cut-off frequency is chosen to provide a permitted bandwidth around the resonant frequency. The PQ standard of Macau and Hong Kong states that, the limit of frequency deviation is ±2%, where can be calculated from the expression [12]. Accordingly, can be found as 6.28 rad/s for . However, the stability margin will be reduced with the increment in . The main objective of employing the M-PR controller is to generate by processing the load current error at its input. It is well known that, while affects the dynamics of this process, the significantly reduces the steady-state error in and , and determines the bandwidth centred at the fundamental frequency (50 Hz) [13] (13) Steady-state error can be minimised by adjusting the value of . The frequency response of the ideal-PR, M-PR, and PI controller are depicted in Fig. 1c. To achieve high gain around , the gain cross-over frequency of the controller is chosen at ten times of . This leads (9) to satisfy the following condition: (14) where Further, following the Routh stability criteria, one can obtain the condition (15) Satisfying (14) and (15), one can obtain and . The frequency response of the system with this controller is found to be satisfactory. The steady-state current tracking error is reduced by M-PR controller according to the magnitude and phase response in Fig. 1c. Thus, the M-PR controller is a more suitable one than PI controller for the DTLI-based PV system. The efficiency of the system is calculated as (16) The output power in (16) has been calculated from the measured values, and thus can be considered to be available after the losses happening in the DTLI (switching and conduction losses in the devices) and the losses in the transformer (copper loss and core loss). 4 Laboratory prototype description The two independent PV panels are connected to the capacitors of DTLI, following the scheme is illustrated in Fig. 1a. The total dc-link voltage is controlled to maintain the level at 96 V to ensure real power delivery corresponding to the rated Indian solar irradiance level. The output terminals of DTLI are directly connected to the primary side of the open winding three-phase step-up transformer (48 V/230 V, 5 kVA). The transformer secondary side is connected to the load/grid. The experimental prototype is prepared for verification of the stand-alone operation of the system, and has been illustrated in Figs. 2a–c. The equipment used to prepare the prototype is mentioned in Table 1. The implementation scheme of the proposed system is developed using digital control board dSPACE1104. Table 1. Parameters of implemented DTLI-based PV system Parameter Quantity Value solar module two SYNERGY SOLAR Synergy Electric Pvt. Ltd (SPEL100) open-circuit voltage — 80 V inverter two SEMIKRON- MDB6U220/300-30F + MDB6CI400/220-27F loss representing resistance per phase, R — 13% leakage inductance per phase, L — 9% load box one 3-phase, 240 V/phase, 10 A Fig. 2Open in figure viewerPowerPoint Laboratory prototype for DTLI-based stand-alone PV system (a) Isolated PV panels for inverter-1 and inverter-2, (b) DTLI-based stand-alone system, (c) Three-phase loading arrangements 5 Simulation and real-time verification The PV systems are operated in the simulation environment at different working conditions. The control is started at a chosen instant, and the inverters total dc-link voltage is found to be controlled to reach the desired voltage level, 96 V. The implementation of the topology has been simulated in the MATLAB/SIMULINK environment. The different transient behaviour of the variables, in response to the deviation of solar irradiance and load disturbances, are presented and analysed. The controller is also switched at a chosen instant in real time for the experimental prototype, as it was happening in the simulation environment. 5.1 Operation of grid-connected PV system The system is considered to be connected with grid, following the scheme shown in Fig. 1a. The transient behaviours of the different variables are portrayed in Fig. 3. Fig. 3Open in figure viewerPowerPoint DTLI-based grid-connected PV system (a) DTLI output phase voltage with THD, (b) Transformer output current phase a with THD, (c) Simulated d-axis and q-axis transformer output current component, (d) dc-link voltage with solar deviation THD for the inverter output voltage and transformer output current are found to be 28.93 and 4.94%, as shown in Figs. 3a and b, respectively. For similar power circuit, in [25], the THD is found to be 33.4%. Here, the load is chosen as to be of more value than the power available from the PV source. Accordingly, a part of the load is supported by the grid. The load increment is performed to check the performance of the system, at 2 s, in the simulation. The connected load is increased, in a step; by 40%. Load is reduced back to the initial level at 2.3 s. The grid supports the load increment of the system, and the change in d-axis component of transformer output current is negligible here. The variation of solar irradiation is considered to be ±30%. The change in d-axis and q-axis component of transformer output current, in response to the load and solar irradiance variations, are portrayed in Fig. 3c. The solar irradiance decreases at 2.6 s. The direct axis component of the transformer output current, has decreased to 0.2 A from the initial value of 1 A to reduce the power delivery from the system at this point. Similarly, the current returns back to 1 A, with increment in the solar irradiance at 2.9 s. The increases to 1.86 A at 3.2 s, and then gets back to 3.5 s in response to further increment and decrement in solar irradiance. The total dc-link voltage has deviated by ±5 V from the initial value of 96 V during these solar variations. The total dc-link voltage of the two converters is found to be tracking its reference value (96 V), successfully during these changes, and portrayed in Fig. 3d. 5.2 Operation of stand-alone PV system Case study 1: Turn on transient: The total dc-link voltage of the inverters is brought to the desired level of 96 V after the switch is on. The transient behaviour of the simulated dc voltage is presented in Fig. 4a. The transformer output current's direct axis component, , is reaching the level of 1 A to maintain the voltage. The real power supplied by the inverters are calculated in the d–q-axis frame and found to be as: (17) Fig. 4Open in figure viewerPowerPoint Turn on transient of the proposed system (a) Simulated total dc-link voltage, (b) Experimental total dc-link voltage, (c) Simulated d-axis, q-axis transformer output current, (d) Experimental d-axis, q-axis transformer output current Considering in (17) is constant, it can be concluded that the power is proportional to the magnitude of. The magnitude of is controlled to maintain the dc-link voltage at the desired level. The is kept constant at zero throughout the operation. The transient behaviours of these currents in simulation environment are portrayed in Fig. 4c. The turn-on transient behaviours are studied in the experimental prototype. Here also the dc-link voltage controller is successfully bringing the voltage back to the desired level (96 V) after the switching. The transient behaviour of the dc-link voltage, direct, and quadrature axis components of transformer output currents are shown in Figs. 4b and d, respectively. The behaviour is found to be of similar pattern, as its simulated counterpart. However, the undershoot and the settling time of the dc-link voltage are greater in real time, because of unmodelled dynamics, inherent non-linearity and transportation lag, present in practical system. The efficacy of the M-PR, to keep the actual and reference currents within band, during turn on, is portrayed for transformer output current in Fig. 5. Fig. 5Open in figure viewerPowerPoint Current tracking waveforms during turn-on transient (a) Simulated current tracking characteristics of and , (b) Experimental tracking characteristics of and , (c) Simulated current tracking characteristics of and , (d) Experimental current tracking characteristics of and The simulated waveforms of Figs. 5a and c are closely followed by the real-time waveforms in Figs. 5b and d. The actual current reaches the reference level within 0.04 s in both simulation and experimental cases. The switching noise is reducing considerably after this interval, in real time also. Fig. 6a shows the line-to-line output voltage of the voltage source DTLI, in the simulation environment. The output voltage is found to be produced by the multilevel operation of the inverter, switched on at 1 s. The line voltage is having voltage levels of in the output of the DTLI in this topology. Fig. 6Open in figure viewerPowerPoint Turn-on transient of DTLI (a) Simulated line-to-line voltage, (b) Experimental line-to-line voltage, (c) Simulated line current, (d) Experimental line current Fig. 6c shows one of the three line currents of the DTLI output in simulation environment. The current is found to be having low harmonic contents even without use of any additional filter in this case. Star-connected three phase resistive–inductive load of same value is used in both simulation and real-time implementation. The developed system is then operated in real time. The five-level output voltage of the DTLI and the corresponding output current for the one line are portrayed in Figs. 6b and d, respectively. The real-time results are confirming the control implementation nicely. Case study 2: Change in load: The load increment is performed at 2 s, in the simulation. The connected load is increased, in a step; by 100%. The variation in the dc-link voltage is settled within 0.07 s. The nature of dc-link voltage is depicted in Fig. 7a. Fig. 7Open in figure viewerPowerPoint Load changes for DTLI-based stand-alone PV system (a) Simulated reference and total actual dc-link voltage, (b) Experimental reference and total actual dc-link voltage, (c) Simulated direct axis, quadrature axis components of transformer output current, (d) Experimental direct axis, quadrature axis components of transformer output current The change in following the action of the dc-link voltage control has been shown in Fig. 7c. The increment in has happened to supply the increased load. Similarly, an extra load has been introduced to the running system in real time, nearly at 6.2 s. Here, the dynamics of the variables are portrayed in Figs. 7b and d. The increased demand is found to be successfully supported by stand-alone PV system. The effect of increment in the load is reflected in the total dc-link voltage waveform. The d-axis current is found to be increasing, similarly as the simulated system in the experimental one. The direct axis current command is generated from the total dc-link voltage controller. The efficacies of the controller in both the environments are ensured with this operation, successfully. Case study 3: Deviation in solar irradiance: In simulation, the solar irradiance level is varied by , to check the active power variation of the system through proper control. Here, the solar irradiance decreases at 2.6 s, and increased back to the initial value after 0.3 s. The solar irradiance increases by 20% at 3.2 s, and then decreased back to the initial value after 0.3 s. The change in the total dc-link voltage and the change in the d–q-axis currents, in response to these variations, are portrayed in Fig. 8. Fig. 8Open in figure viewerPowerPoint Response to the solar irradiance level deviation (a) Simulated dc-link voltage with solar deviation, (b) Simulated d-axis, q-axis transformer output current with solar deviation The total dc-link voltage of the DTLI exhibits undershoot at the time of decrement in the solar irradiance (at 2.6 s) and returns to 96 V within 0.015 s. On the other hand, the total dc-link voltage exhibits an overshoot at the time of increment in solar irradiance (at 3.2 s). In both the cases, the controller is successfully maintaining the voltage at 96 V with transients for 0.02 s only. The transient behaviour of the dc-link voltage is portrayed in Fig. 8a. The d-axis current component of the transformer output is found to accommodate these variations successfully. It reduces to 0.75 A from the initial value of 1 A, during the reduction in the input. On the other hand, the current increases to 1.15 A, during the increment in the input. This change in is describing the change in real power delivery of the system with response to the change in the available power from solar PV. The is kept constant at zero throughout the operation. The current responses are portrayed in Fig. 8b. The PV panel-2 is subjected to increment in solar irradiance level by 20% to check the efficacy of the controller with two different output powers from the PV panels. The total dc-link voltage is successfully controlled at 96 V in this case also. The different power output from the PV panels and the efficiencies for the considered situations are presented in Table 2. Table 2. Power output of DTLI-based PV system Equal solar for two PV panels Unequal solar for two PV panels solar irradiance (panel-1, panel-2), W/m2 1000, 1000 1000, 1200 power output (panel-1, panel-2), W 696, 696 668, 864 dc-link voltages (panel-1, panel-2), V 48, 48.02 40.03, 56 efficiency, % 95.42 95.5 Case study 4: Change in reference dc-link voltage level: The efficacy of the dc-link voltage controller is tested through variation in the reference dc voltage level. The transient behaviours of dc-link voltage, in a simulated system and in the experimental system, are portrayed in Fig. 9. Fig. 9Open in figure viewerPowerPoint Reference changes 96–80 V (a) Simulated dc-link voltage reference changes, (b) Experimental dc-link voltage reference changes The actual dc-link voltage reaches the reference level (reduced by 20%) within 0.017 s. The dc-link voltage reference is brought back to the actual value in both the simulation and experimental systems successfully. The efficacy of the M-PR, to keep the actual and reference current tracking within band during change in reference dc voltage level, is portrayed for transformer output current in Fig. 10. The simulated waveforms of Figs. 10a and c are closely followed by the real-time waveforms in Figs. 10b and d. Fig. 10Open in figure viewerPowerPoint Current tracking waveforms during change in reference dc voltage (a) Simulated current tracking characteristics, (b) Experimental tracking characteristics of and , (c) Simulated current tracking characteristics, (d) Experimental current tracking characteristics of and The M-PR control is compared with some of the existing schemes and presented in Table 3. Table 3. Comparison of the proposed schemes with some of the existing systems Paper Schemes dc-link voltage Control strategy Inverter type DC–DC converter Efficiency, % THD, % Pires et al. [23] grid-connected 40–50 V SMC three phase (VSC-CTLI) 2 # # Babu and Fernandes [20] grid-connected (STATCOM only) 659 and 241 V vector control three phase (VSC-CTLI) 0 # 11.82 Grandi et al. [24] grid-connected 30–40V Sigma-delta three phase (VSC-CTLI) # # # Debnath and Chatterjee [26] stand-alone 35V MPPT-based control full-bridge 1 93.9 # Das and Agarwal [27] stand-alone # vector control three phase 2 94 # Saxena et al. [4] grid-connected/stand-alone 350V MPPT-based control VSC 1 # 2.18 proposed M-PR PV system 48V M-PR DTLI 0 95.5 4.94 #, data inadequate. 6 Conclusion The paper presented an M-PR control structure for a single-stage, PV system. Here, the performance of the control is found to be satisfactory in all the considered operating conditions. The salient features of the proposed scheme include the following: (i) maintains the dc-link voltage at the desired level to extract power from the solar PV modules, (ii) isolated dual-inverter dc-link connected PV source is used to produce multilevel output voltages, and (iii) both the dc-link voltage controller, and the current controller are performing satisfactorily during the changes in: (a) load, (b) input solar irradiation, and (c) reference dc-link voltage levels. One laboratory prototype is developed for the real-time implementation of the control The effectiveness and feasibility of the proposed scheme are verified with a set of experiments. It is found that all of the experimental results closely match with the simulation results throughout the operation in stand-alone mode. The grid-connected mode of operation is also tested in simulation environment and is found to be capable of delivering power according to the availability in input. 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