Abstract
KY boost converter (KBC) finds wide application in photovoltaic (PV) and single-phase inverters. In this study, a novel KBC containing seven levels of a multilevel inverter (MLI) is presented. Here, KBC between the direct current (DC) source and the inverter is proposed. Moreover, the authors considered a closed-loop response of the KBC-MLI system with a proportional integral (PI) controller and a fractional-order PID (FOPID) Controller. The main purpose of this suggested technique is to match the output current, total harmonic distortion (THD), and dynamic response of closed-loop PI and FOPID-controlled KBC-MLI systems. The proposed model is simulated with the MATLAB software, and the attained outcome illustrated an enhanced dynamic performance by using the FOPID-controlled KBC-MLI system. The simulation results of the KBC-MLI technique have been evaluated against the theoretical models. Finally, extensive experiments were carried out to validate the theoretical results.
1. Introduction
KBC is a DC-DC boost converter that has been evidently modified form of a canonical switching converter (CSC) [1] or topology alterations being carried out over DC-DC-BC [2]. The modifications in CSC possessing yield inductors have resulted in KBC [3–7]. The yield and input flows possess substantial current ripples that are deemed to be an impediment to the CSC-converter. In the increase of inductance at the conversion stage, the resultant structure is a genuine switched mode (SM) topology. In order to lower inductance, the resonant switching mode was applied to this topology. These results in low-yield ripple current in the DC-connect. Considering the existing DC-DC converters, the inductor capacitor (LC) satisfies the ideal inverter which has the lowest number of components but has elevated input and yield current ripple execution of the framework compared to other converters like an ordinary buck-boost Converter (BBC). The proposed LC topology has a noteworthy feature in which the current ripples at the inputs and yields are decreased.
Induction motors (IMs) are most utilized in the industry since they are rough, reasonable, and without support. It is evaluated that over half of the world’s electric energy created is devoured by electric machines. Enhancing proficiency in electric drives is critical, predominantly for monetary sparing and decrease of natural contamination [8, 9]. IM has high effectiveness at evaluated speed and torque. In any case, at light loads, engine proficiency diminishes significantly because of the occurrences of irregularities among copper. Consequently, power reduction could be accomplished using an appropriate choice of engine transition levels [10, 11].
IM has been employed for carrying out several tasks, for example, warming, aeration, and refrigeration, electrical drives such as motion control, robotics, and automotive controls such as electric vehicles [12] [13]. The induction motor drive (IMD) can be controlled by various execution capacities, for example, input control, speed, torque, air-gap motion, power factor, stator flow, and stator voltage in general productivity [2].
For electrical household appliances such as mechanical siphons, motorized fans, and wind blowers, single-stage machines frequently get coupled to single-phase power systems [14]. Whenever the electrical source’s frequency is constant, induction motors (IMs) may be used for a stable performance. It is a variable speed in application machines with the progression of intensity gadgets by creating a three-phase-supply of adjustable recurrence as well as potential energy with pulse width modulation (PWM) [15] procedures connected to a solid-state inverter (SSI) [16].
Three-stage IM is generally utilized in boost and vehicle applications for a considerable length of time on account of its moderately basic structure, which supports free activity and capacity to begin specifically from the supply start-up. The deployment machine’s superior elements are accomplished by the field orientation control (FOC). The three-stage induction motor FOC (IMFOC) utilizes the perplexing exchange work idea to tune the PI controller by utilizing the recurrence reaction capacity of the closed-loop complex exchange capacity of the controlled IM.
2. Research Gap
The abovementioned research works do not concentrate more on the use of motors in AC loads. This research work proposes the motor for AC loads. The KBC-MLI system, AC loads utilizing PI control devices, or FOPID control systems have been excluded in the aforementioned research. In the present investigation, PI as well as FOPID controllers for the KBC-MLI system that manages AC loads is compared. Increased power output and less ripple voltages, along greater reaction times, are all possible using the KY boost converters. The KY boost converter is modeled and simulated in constant output, and better speed regulation is included in this paper. In this article, a modified phase shifted-level pulse width modulation (PWM) for a 7-level inverter is utilized.
3. System Description
3.1. PI Controller
This constitutes a composite controlling mechanism that is created by combining integral and proportional modes. The key advantage of this mode of operation is the fact that it achieves a direct link between the proportional and integral modes, eliminating the difference between them and allowing the outcome to be reverted to zero inaccuracies in the event of load fluctuation.
3.2. FOPID Controller
Fractional differentiation has been employed to create the FOPID model. In comparison to a similar PI control structure, the reaction utilizing FOPID is quicker. Figure 1 shows a block diagram that represents the FOPID control mechanism. A FOPID controller’s transfer function has a structure ofwhere λ corresponds to the integral part order and μ represents the derivative part order, whereas Kp, Ki, and Kd signify the controller similar to the traditional PID controller.
The DC output has been measured and assessed against standard output voltage providing the error signal which is discharged by the PID for withstanding the motor speed outcome as constant as well as reducing the steady-state error. The set current is compared with the actual current. The FOPID parameters, proportional gain (Kp), and double integral times (Ti) have been evaluated utilizing the Zeigler–Nichols tuning process. The schematic articulation of the closed-loop KBC-MLI system with a PI controller is shown in Figure 2.
The elementary expression for the KY boost voltage ratio is represented aswhere = output voltage in volt, = input voltage in volt, = on time in seconds, and = total time in seconds.
The representation of FOPID is derived from the fractional differential equations. The output of FOPID is quicker when compared with the equivalent PI control technique. FOPID control system transfer function shall be expressed aswhere λ corresponds to the integral part order and μ represents the derivative part order, whereas Kp, Ki, and Kd signify the controller similar to the traditional PID controller.
The DC yield voltages are sensed and assessed against reference yield voltage that offers error signals. Output motor speed is controlled by this error signal, and steady-state error gets reduced. The set speed is compared with the actual speed. The FOPID parameters, proportional gain (Kp), and double integral times (Tis) have been calculated utilizing the Zeigler–Nichols tuning technique. The schematic representation signifying the FOPID control system has been shown in Figure 3.
The DC yield voltage has been sensed and assessed against the standard yield motor speed providing the error signals. These error signals are processed using the FOPID for sustaining the resultant motor speed constants as well as diminishing the steady-state errors. The schematic representation of the closed-loop KBC-MLI system of a DC-AC converter with a motor is shown in Figure 4.
While achieving a reduced current THD [17–20], voltage with increased motor speed regulations for satisfying the appropriate standards is attained. The speed, as well as current regulators, was utilized for regulating the output current sequence for PI and FOPID-controlled validation of KBC as well as MLI systems. This research work focuses on the reduced output current THD and speed regulation of the KBC-CMLI system concerning an AC-DC converter with a motor load network.
In this study, two H-bridge systems were used. 1 : 2 voltage ratios are used to get the seven-level output in this system. The resulting voltage from the CHB inverter regulated employing MSF PWM via the equivalent dc-link voltage ratio (1/2 Vdc: 1/2 Vdc) has the fewest low-order harmonics, whereas the resultant voltage from the CHB inverter regulated utilizing PWM with a disproportionate dc-link voltage ratio (2/3 Vdc: 1/3 Vdc) possesses seven levels. The quantity of accessible values for the resultant voltage continues to increase, which is in accordance with the overall level of the voltage that is produced. In this case, a 2-cell H-bridge inverter with 8 switches is all that is required to provide a voltage output with 7 levels.
The main contribution of this paper is to reduce output current THD and motor speed dynamic response of closed-loop PI and FOPID-controlled KBC-MLI systems. The better response of the FOPID controlled system can be seen in Tables 1 and 2.
4. Results and Discussion
4.1. Open-Loop KBC-MLI
The open-loop source disturbances of the KBC-MLI structure have been represented in Figure 5. The input voltage of the open-loop KBC-MLI structure has been displayed in Figure 6, and the voltage across PV is increased from 48V to 54V. The output voltage of KBC-MLI is shown in Figure 7, and the output voltage is 165V. The output voltage across the motor load of the KBC-MLI structure has been displayed in Figure 8, and the inverter output voltage is 165V. The output current of the KBC-MLI system is depicted in Figure 9, and the output current of the KBC-MLI system is 10A. In lower load resistance, a high load current is achieved. The output current THD of the motor load is described in Figure 10 with the value being 12.27%. For higher order harmonics, THD gets reduced. The motor speed of the KBC-MLI system is displayed in Figure 11, and the value of motor speed in the KBC-MLI system is 1150 rpm from completing 1 second onwards. The motor torque of the KBC-MLI structure has been shown in Figure 12, and the value of motor torque in the KBC-MLI system is 5.3 N-m. Motor torque starts to settle from 1.1 seconds onwards. The motor’s generated torque rises quickly towards the highest possible level before leveling out at its level of stability.
4.2. KBC-MLI System with a Closed-Loop PI Controller
Figure 13 displays the schematic representation of closed-loop KBC-CMLI utilizing a PI controller. Input voltage across the PV has been represented in Figure 14; the voltage across the PV is increased from 48V to 54V. The output voltage of the KBC-MLI structure is represented in Figure 15; the output voltage value is 150V. The motor load voltage is displayed in Figure 16; the motor load voltage is 150V. The motor load current has been articulated in Figure 17; the value of current through the motor load is 16A. The output current THD of the motor load is described in Figure 18 with 8.42%. Motor speed and zoom-out are delineated in Figures 19 and 20, respectively; the motor speed is 1050 rpm. Motor torque is shown in Figure 21; 5.1 N-m is the motor torque value.
The PWM approach has been employed in the present investigation to regulate the acceleration of a single-phase induction motor utilizing FOPID. Using an optimized inductive motor type, the PWM-generated output serves as the basis for a voltage source inverter having a desirable duty cycle. The development of a method of control for producing controlled PWM signals. The motor speed response created the system’s steady-state error as well as settling time found to be within the prescribed speed control limits, according to the findings. The motor speed responses of PI and FOPID-controlled system results are included in Figures19 and 22.
4.3. KBC-MLI System with a Closed-Loop FOPID Controller
Closed-loop KBC-MLI using the FOPID controller has been illustrated in Figure 23. Figure 24 illustrates the input voltage across the solar PV, and the value of solar PV voltage is increased from 48 V to 54 V.
The voltage across the motor load is delineated in Figure 25; the value is 150 V. Figure 26 shows the current through the motor load, and the value is 16A. Output current THD of the motor load is described in Figure 27 with 5.21%. Motor speed and zoom-out are depicted in Figures 28 and 22, respectively; the motor speed is 1050 rpm. Motor torque is shown in Figure 29 with 5.1 N-m.
Table 1 compares the time domain with PI and FOPID controller parameters. By using FOPID, the rise time has been seen to be lowered from 1.12 to 1.09 secs; the settling time has been seen to be lowered from 1.15 to 1.10 secs; similarly, the peak time has been seen to be lowered from 3.80 to 3.10 secs; the steady-state error has been lowered from 6.3 to 5.2 rpm. The graphical illustration of time-domain responses is presented in Figure 30. Table 2 represents the assessment of the output current THD without a controller, with PI, and FOPID controller, and the bar chart for THD response is shown in Figure 31. Hence, closed-loop KBC-MLI with a FOPID controller is superior to closed-loop KBC-MLI with a PI controller system.
In the present study, a multilayer inverter has been developed utilizing 8 switches as well as dual 1 : 2 dc-link voltages. The suggested architecture is also capable of producing voltages across seven stages with the right gate inputs. In cascaded 7-level inverter structures, the imbalanced operating time, as well as distribution of power, was recently addressed by employing phase-shifted PWM pulse-switching techniques.
5. Experimental Results
The single-phase KBC-MLI-based PV inverter system hardware snapshot is displayed in Figure 32. The voltage through PV has been illustrated in Figure 33. The switching pulse of KBC M1 and M2 is shown in Figure 34. These switching pulses are used to drive the controller circuit. The voltage across KBC has been displayed in Figure 35. The switching pulse of MLI S1 and S3 is shown in Figure 36. The output voltage across MLI and output current through the motor load are displayed in Figures 37 and 38, respectively. Table 3 summarizes the list of components used for simulation and hardware of the KBC-MLI system.
Figure 39 displays the output voltage spectra for every H-bridge preceding the net outputs on a comparable scale.
Power sharing in the cascaded 7-level inverter system in H-bridge-1 and H-bridge-2 output power is shown in Figure 40.
6. Conclusions
For real-time machine tool applications using PI and FOPID controllers, simulation investigations involving open-loop source disturbance as well as closed-loop KBC-MLI systems were conducted. Simulink-based modeling for KBC-MLI structures has been utilized to conduct this investigation. The results showed that in comparison with the PI-controlled KBC-CMLI method utilized for machine tool uses, the closed-loop FOPID-controlled method delivered a decreased output current THD of 12.27% to 5.21% and enhanced time response for motor speed. Lower rising time and lowered settling time, as well as lower steady-state error voltage, are the advantages of the suggested KBC-CMLI method. The adoption of a closed-loop FOPID controller design has improved dynamic responsiveness. The hardware analysis coincides with the KBC-CML inverter systems’ simulated outcomes. The main disadvantage of the KBC-CMLI method is the increase in device blocks incurred during the cascade. The analysis of PI and FOPID-controlled closed-loop KBC-MLI structures is the main focus of the current research. In the future, studies will analyze KBC-MLI structures with fuzzy logic controllers.
Abbreviations
| BC: | Boost converter |
| BBC: | Buck-boost converter |
| CSC: | Canonical switching converter |
| FOPID: | Fractional order PID |
| FOC: | Field orientation control |
| IM: | Induction motors |
| IMD: | Induction motor drive |
| IMFOC: | Induction motor field orientation control |
| KP, KI, and KD: | Controller |
| KBC: | KY boost converter |
| LC: | Inductor capacitor |
| MLI: | Multilevel inverter |
| PV: | Photovoltaic |
| PWM: | Pulse width modulation |
| SM: | Switched mode |
| SSI: | Solid-state inverter |
| THD: | Total harmonic distortion |
| : | Output voltage |
| : | On time |
| : | Total time |
| : | Order of the integral part |
| : | Order of the derivative part. |
Data Availability
The data used to support the findings of this study are available from the corresponding author upon request.
Conflicts of Interest
The authors declare that there are no conflicts of interest regarding the publication of this article.
Acknowledgments
All the expenses of this work are fully carried out at the author’s own expense.