Renewable energy with sources such as photovoltaic (PV) or fuel cells can be utilized for the generation of electrical power. But these sources generate fewer voltage values and therefore require high gain converters to match with DC bus voltage in microgrids. These high gain converters can be implemented with switched capacitors to meet the required DC bus voltage. Switched capacitors operate in a series and parallel combination during switching operation and produce high static gain, limits reverse voltage that appears across the components. A novel converter is proposed that satisfies all the features such as high voltage gain, only one switch, forces less potential stress cross the components, ripple current is less. These features of the proposed converter are verified through MATLAB/SIMULINK.

The climate is influenced by conventional energy sources and global warming. The alternative is to embrace renewable energy sources for electricity generation to minimize the effect of global warming and, at the same time, need to meet the rising energy requirement. Photovoltaic cells (PV) and fuel cells are the primary power generation sources for renewable energy solutions systems. DC bus voltage, i.e., input of inverter or output of high gain dc converter, should be at least 380 V to reach the required sinusoidal voltage at the output of the inverter. This DC voltage can be implemented in many applications like Electric vehicles, microgrids, communications etc. [

Isolated converters have issues such as pulsated input current and require more turns ratio in the transformer, resulting in a more reverse voltage across the switch. Ideally, a conventional boost converter, in non-isolated mode, could achieve high gain at a high duty ratio, but practically, the same gain is limited because of the parasitic effect [

Techniques like a switched inductor switched capacitor, switched inductor, and switched capacitor are added to a simple boost converter to achieve high gain [

In this paper, a new converter with increased voltage gain was implemented with switched capacitor cells and is depicted in

The circuit diagram of the proposed converter is shown in _{1} stores energy from the supply, and _{2} stores energy from the difference of voltage across the capacitor _{s} and _{M}. The series-connected switched capacitor cells _{1} and _{2} supplies energy to the load. When switch ‘Q’ is OFF, as shown in _{1}, _{2}, and _{M} are charged by both the inductors _{1} and _{2}. The available voltage at switched capacitors _{1} and _{2} are equal as they are connected in parallel. Let the voltage across the capacitor _{s}, _{M}, and _{1} be _{cs}, _{CM}, and _{ceq}, respectively, the voltage across the switch ‘Q’ be _{Q}, the current through the inductor _{1} be _{L1} and load current be _{o}. The waveforms of the proposed converter in continuous conduction mode (CCM) are depicted in

The steady-state analysis requires that the voltage across the inductor L_{1} during each switching cycle should be zero, hence:

Similarly, for inductor L_{2} net voltage across it during each switching cycle is zero, hence:

During the OFF state of the switch ‘Q’,

From

From the above equations,

From

where V_{D1}, V_{D2}, V_{DM}, V_{D0} are the voltages across the diodes D_{1}, D_{2}, D_{M,} and D_{0}. Similarly, the voltage gain by considering only three inductors L_{1}, L_{2}, and L_{3} is given in

Similarly, for the converter having ‘n’ number of voltage multiplier cells, as shown in

The design of circuit parameters for the proposed converter is as follows.

Allowing 9% of ripples in the input current, the inductor value can be designed based on the following expression.

For the same input and output power, i.e., and using

Considering ripple current to be symmetrical and triangular, the RMS value for a triangular wave DC offset is expressed as follows.

The expression for the value of inductor L_{2} is the same as that of inductor L_{1}. But, the current in inductor L_{1} represents the average input current, and the current through the inductor L_{2} represents the output current. The value of second inductor L_{2} is not equal to input inductor value L_{1}, but has a value half of the input inductor value as the current through the second inductor L_{2} is significantly less than the input current.

The switched capacitors C_{s}, C_{M}, C_{1}, and C_{2}, need to allow a change in the charge and, therefore, input voltages. So the value of these capacitors needs to be small to allow the variations. The load current flows through these capacitors during the ON position of the switch. With 1% of voltage ripple, their value capacitance C is expressed as:

where _{sw} = Switching frequency. The selection of output capacitors _{o} is made considering voltage ripple _{O} max to be 1%.

Simulation studies for the proposed converter have been carried out on the MATLAB/SIMULINK platform with an input voltage of 30 V, 100 W load at a switching frequency of 20 kHz. The performance of the converter is carried out with the average current controller. The average current control technique has two loops. One is the outer loop to control the output voltage, and the second one is the inner loop to control the input current. The error from the current controller is compared with the carrier signal and generates the required pulse to the switch.

The performance analysis of the proposed converter is carried out at

Steady-state simulation study and

Dynamic-state simulation study

The steady-state simulation study has been done based on the circuit parameters mentioned in _{L1}), output voltage (_{o}), and the voltage across the switch (_{Q}) are plotted.

Parameters | Values |
---|---|

Input voltage | 30 V |

Output voltage (Vo) | 380 V |

Output power (Po) | 100 W |

Capacitor Cs, Cm, C_{1}, C_{2} |
3.3 μF |

Capacitor Co | 220 μF |

Inductor L1, L2 | 1.95 & 1 mH |

Switching frequency | 20 kHz |

Duty cycle | 0.781 |

_{L1}) with respect to time on the x-axis. The input power drawn from the 30 V source is 100 W. It can be pointed out that the inductor current (_{L1}) waveform has an average value of 3.33 A. The peak-peak value of the inductor current (_{L1}) is 0.6 A based on the design values. It is observed that the input current is continuous in nature, which is essential, particularly in solar applications. _{L2}). The second inductor current has a peak value of 0.6 A, and its average current is equal to the load current. The peak current of 0.6 A of the second inductor is due to considering half of the input inductor value. Its value is half of the input inductor because the average current that passes through this inductor is equal to load current, which is a very small value, i.e., 0.263 A. In _{s}, C_{m,} and C_{f} are shown. The value of voltage across the capacitor C_{M} (V_{cm}) is around 136.69 V and across capacitor C_{s} (V_{cs}) is approximately 106.72 V. The desired output voltage is 380 V. Based on _{cm} and _{cs} and is satisfied. _{1}, D_{M,} and D_{0} during their OFF state. The voltage that appears across these diodes is 136.69 V satisfying the _{o}) and switch voltage (_{Q}). The voltage across the switch is 136.69 V satisfying

The dynamic state simulation studies were performed on MATLAB/SIMULINK in the following lines.

Case 1: By considering the variation in the load from 100% to 50%.

Case 2: By considering the variation in the load from 50% to 100%.

The dynamic state simulation study of the proposed converter has been done by varying the load from 100% to 50% at a simulation time of 1.2 s. The closed-loop operation of the proposed converter with the average current method is implemented in the dynamic state study. The MATLAB/SIMULINK results are shown in _{in}). The input voltage is constant during the dynamic change in the load from 100% to 50%. It means that the input voltage to the converter is not affected during its dynamic state. _{L1}). The value of the inductor current is 3.33 A at 100 W output power. Its value is 1.67 A at 50 W output power. As the load is varied from 100% to 50%, the inductor current (_{L1}) is changed from the average value of 3.33 to 1.67 A. The inductor current (_{L1}) is settled to 1.67 A at 1.55 s. The inductor current is well controlled by the inner loop current controller in the average current control method. _{o}). The value of load current (_{o}) at 100 W load is 0.263 A. During the dynamic change in the load from 100% to 50%, the load current (_{o}) is changed from 0.263 to 0.132 A. The load current (_{o}) is settled to 0.132 A at 1.55 s. _{o}) has a surge, and its value is about 385 V. The output voltage is settled to 380 V at 1.55 s. The control of output voltage is well regulated by the outer loop voltage controller in the average current control method.

_{in}). The input voltage is constant during the dynamic change in the load from 50% to 100%. It means that the operation of the converter is not affecting the input voltage applied. _{L1}). As the load is varied from 50% to 100%, the inductor current (_{L1}) is changed from the average value of 1.67 to 3.33 A. The inductor current (_{L1}) is settled to 3.33 A at 1.55 s. The input inductor current is controlled by the current controller in the inner loop of the average current controller. _{o}). The value of load current (_{o}) at 50 W load is 0.132 A. During the dynamic change in the load from 50% to 100%, the load current (_{o}) is changed from 0.132 to 0.263 A. The load current (_{o}) is settled to 0.263 A at 1.55 s. _{o}). During the dynamic change in the load from 50% to 100%, the output voltage (_{o}) has a sag, and its value is about 375 V. The output voltage is settled to 380 V at 1.55 s. The desired output voltage 380 V is achieved with the voltage controller in the outer loop of the average current controller.

The dynamic state simulation study of the proposed converter has been done by varying the load from 50% to 100% at a simulation time of 1.2 s. The MATLAB/SIMULINK results are shown in

Name | Ref. 9 | Ref. 17 | Ref. 19 | Proposed |
---|---|---|---|---|

Volt.gain | 3D/1−D | 3-D/1−D | 2/1−D | 2+D/1−D |

Volt.stress across |
(1/1−D)Vo | (1/3−D)Vo | (1/2)Vo | Vo/(2+D) |

Power level | 200 W | 200 W | 75 W | 100 W |

Count of inductors | 3 | 1 | 1 | 2 |

Count of switches | 1 | 1 | 1 | 1 |

Count of diodes | 3 | 4 | 3 | 4 |

Count of capacitors | 5 | 4 | 3 | 5 |

Value of duty ratio | 0.809 | 0.829 | 0.842 | 0.780 |

The high voltage needed in DC bus for inverter input can be accomplished with proposed high-gain DC converters utilizing the photovoltaic (PV) or fuel cell as a source. The design of switched-capacitor cells performs the boosting operation. The switched capacitor produces significant static gains while simultaneously limiting the voltage stress of the various components. This converter can be able to

It has continuous input current from the source with reduced ripples in the input current.

It has a single switch with reduced voltage devices, resulting in a low cost to build the converter.

The closed-loop operation proves that the output voltage can be well regulated.

The operation of the proposed converter with steady-state and dynamic state analysis was discussed. This new topology with a switched capacitor is implemented to accomplish all the features such as one switch, high gain with continuous current from the source, and, therefore, can be implemented in renewable energy applications. All these features are validated through MATLAB/SIMULINK.