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This paper focuses on the comparative study of analog and digital control techniques for Negative Output Superlift Luo converter (NOSLC). NOSLC is a high gain converter in which the positive source voltage is converted into a negative load voltage. Though the negative load voltage is produced effectively, there is lot of non-linearities that affects the voltage level. To overcome this, analog controllers like Proportional-integral (PI), fuzzy PI and a sliding mode controller (SMC) were proposed for NOSLC. However PI controller does not respond to changes in operating point, fuzzy PI is based on the systematic approach and proved to be a trial and error oriented method and SMC brings an oscillation in the duty cycle. Therefore, to overcome these drawbacks, a digital control technique using PIC microcontroller is proposed in this paper which provides high versatility and programmability approach. Simulation studies are carried out in MATLAB and the performances of these controllers have been investigated for the proposed DC-DC converter. A prototype of the NOSLC converter is built by employing digital control and the results are verified experimentally.

The rapid development in DC-DC conversion finds applications in various industries. This has led to the production of DC voltage from various converters and here the significance is on the negative voltage. NOSLC is a type of DC-DC converter in which the output negative voltage increase is shown as a progressive rise. It also possesses a fast response with a low voltage overshoot and a minimum ripple.

To have a good regulation in the output voltage, various controllers were designed and implemented. This paper focuses on PI, fuzzy PI, sliding mode and digital controllers. These controllers provide a good response thereby bringing the output to a steady state value.

Initially, PI controller is designed and implemented for NOSLC. The values of Kp and Ti are tuned using Ziegler-Nichols tuning and applied in the transfer function of the controller and simulated using Matlab. Though the controller proves to be a better linear controller it may not respond well to changes in the operating point. To overcome this, a non-linear controller namely fuzzy PI controller is designed by fuzzyfying the Kp and Ti values with the expert knowledge. Here, it works only for systematic approach and prefers the trial and error method in the absence of expert understanding. So a robust method of control is implemented using SMC for uncertainties and other disturbances. However this control is also a time delayed one and brings oscillation in the output voltage with the duty cycle variations. Finally a digital control using peripheral interface controller is implemented which highly helps in reducing the usage of passive components and with an ease to integrate with digital systems. It also provides an inherent programmability approach.

The following sections will reveal the operation of NOSLC with its complete performance analysis of controllers. Section 2 deals with the modes of operation of NOSLC and Section 3 depicts the simulation results of NOSLC and Section 4 deals with the design of various controllers for NOSLC and Section 5 portrays the PI controller design and Section 6 deals with fuzzy PI controller. The SMC technique has been dealt in Section 7 and Section 8 portrays the digital control technique followed by conclusion in Section 9.

The NOSLC is a DC-DC converter which has a high gain, high efficiency and a low value of ripple. Here the NOSLC elementary circuit is considered which is operated with two modes as mosfet switch on and off.

Circuit diagram of NOSLC is shown in

Based on the design equations, [

The simulation of NOSLC is carried out using Matlab. The output voltage rise to −34 V for an input of 12 V is shown in Figures 2-4 depicts the switching pulse of 67% duty ratio.

To provide a regulation in the output voltage, controllers have to be designed and implemented for NOSLC. In

Sl. No | Parameter | Symbol | Value |
---|---|---|---|

1 | Input voltage | Vin | 12 V |

2 | Output voltage | Vo | 36 V |

3 | Inductors | L1 | 10 mH |

4 | Capacitors | C1,C2 | 50 μF |

5 | switching frequency | fs | 100 kHz |

6 | Load resistance | R | 50 Ω |

7 | duty cycle | k | 67% |

this regard, various controllers have been taken for study and designed and implemented and its performance comparison is also carried out. The following sections will reveal the merits of each and every controller taken for NOSLC. It also deals with the various analog and digital controllers of NOSLC. The linear analog controller namely PI controller, the non-linear fuzzy PI controller, is designed and implemented. Further SMC control and digital control is implemented for NOSLC to have an enhanced regulation.

This section deals with design of PI controller. These types of controllers modify the error signal and produce a proper output [

The PI controller proves to be a good linear controller but may not respond well to non-linear conditions. Hence fuzzyfying the values of Kp and Ti [

e/de | NB | NM | NS | ZR | PS | PM | PB |
---|---|---|---|---|---|---|---|

NB | NB | NB | NB | NB | NS | ZR | PS |

NM | NB | NB | NB | NM | NS | ZR | PS |

NS | NB | NB | NM | NS | ZR | PS | PM |

ZR | NB | NM | NS | ZR | PS | PM | PB |

PS | NM | NS | ZR | PS | PM | PB | PB |

PM | NS | ZR | PS | PM | PB | PB | PB |

PB | ZR | PS | PM | PB | PB | PB | PB |

e/de | NB | NM | NS | ZR | PS | PM | PB |
---|---|---|---|---|---|---|---|

NB | NB | NB | NB | NB | NB | NB | PS |

NM | NB | NB | NB | NB | NB | NB | PS |

NS | NB | NB | NB | NS | ZR | PS | PM |

ZR | NB | NM | NS | ZR | NS | PM | PS |

PS | NM | NS | NS | PS | PM | PB | PB |

PM | NS | ZR | PS | PM | PB | PB | PB |

PB | ZR | PS | PB | PB | PB | PB | PB |

The PI controller and fuzzy PI controller has been explained. Though fuzzy PI controller proves to be a non-linear controller, it is predicted only by the expert knowledge which proves to be a trial and error oriented. To overcome this, sliding mode controller [

The sliding mode control of NOSLC [_{1} as 17 V.

The switch pulse produced with a duty ratio of 67% is shown in

The relay is energized based on the summer output. Thus the relay output is considered as input to the switch and a closed loop will be achieved. Based on the variation parameter of load, input voltage, and change in component values the gain parameter is chosen and converter in closed loop control is executed. Various SMC techniques have been discussed in [

where

This section deals with the control of NOSLC using PIC 16F877A microcontroller. The closed loop control is depicted in

Controller | Rise time t_{r(s)} | Settling time t_{s(s)} | Peak overshoot (%Mp) |
---|---|---|---|

PI | 0.2 | 0.1 | 0.8 |

Fuzzy PI | 0.002 | 0.04 | 0.005 |

Sliding mode controller | 0.080 | 0.088 | 0.097 |

The control algorithm is implemented in PIC 16F877A microcontroller. The PWM signal with a duty ratio of 70% is generated for the initial load conditions by the PIC. Again when the load change is sensed, it generates a duty ratio of 20% and thus stabilizes the output which is shown in the experimental results.

Thus the digital technique with a good versatility approach has been clearly explained in the above section [

of −36.5 V for an load of 300 Ω and the generated duty ratio for that ohmic value is shown to be 70% (

Various controllers for NOSLC have been investigated in this paper. The PI controller makes the response of NOSLC to reach its steady state value after a long interval of time and hence proved to be a slow response controller. To compensate for non-linearities, and to reduce the settling time, fuzzy PI controller is implemented whose dynamic response is better compared to PI controller. SMC technique is implemented as fuzzy control is based on trial and error approach but, it is observed that SMC brings an oscillation in the duty cycle. Therefore, a digital controller is implemented and the performance of the converter is improved as it provided a better load regulation compared to the analog controllers, Therefore, digital control seems to be a better control technique for the negative output super lift Luo converter.

Chamundeeswari Vinayagam,Seyezhai Ramalingam, (2016) Comparative Analysis of Analog and Digital Controllers for Negative Output Superlift Luo Converter (NOSLC). Circuits and Systems,07,1689-1700. doi: 10.4236/cs.2016.78146