# Implementation of Non-Isolated Zeta-KY Triple Port Converter for Renewable Energy Applications

^{1}

^{2}

^{3}

^{4}

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## Abstract

**:**

## 1. Introduction

## 2. Proposed Non-Isolated Zeta-KY Converter

#### 2.1. Structure of Zeta-KY Converter

_{1}, S

_{2}and S

_{3}, three diodes D

_{1}, D

_{2}and D

_{3,}three inductors L

_{1}, L

_{2}and L

_{3}and three capacitors C

_{1}, C

_{2}and C

_{3}. L

_{1}and L

_{2}are individual coupled inductors and L

_{3}is a filter inductor. The converter is designed to be operated in continuous conduction mode.

#### 2.2. Modes of Operation of the Zeta-KY Converter

#### 2.2.1. Topology 1: Unidirectional Converter

_{1}and L

_{2}, capacitor C

_{1}along with the switch S

_{1}belonged to the Zeta part of the circuit. The switches S

_{2}and S

_{3}, capacitor C

_{2}and diodes D

_{2}and D

_{3}belonged to the KY part of the circuit. The diodes D

_{2}and D

_{3}were provided to avoid reversal of current towards the source V

_{2}. The diode D

_{1}was provided for the purpose of freewheeling. The inductor L

_{0}and capacitor C

_{0}were filtering elements common for both the Zeta and KY converters. Both converters shared a common load. The operation of the converter has been explained through different modes.

- (i)
- Mode 1 (S
_{1}is ON and S_{2}, S_{3}are OFF): In this mode, the switch S_{1}is turned on and switches S_{2}and S_{3}were turned off. Both the sources V_{1}and V_{2}were supplying the multiport converter. The inductors L_{1}and L_{2}were charged to the value of input voltage V_{1}. The current through L_{1}increased linearly to a value V_{1}/L_{1}. The capacitor C_{1}was charged equal to V_{o}, which was the output voltage of the converter. Diode D_{1}was reverse biased and diodes D_{2}and D_{3}were forward biased.

- (ii)
- Mode 2 (S
_{2}is ON and S_{1}, S_{3}are OFF): In Mode 2, the switch S_{2}was turned on and switches S_{1}and S_{3}were turned off. V_{1}was therefore not supplying the circuit. The source V_{2}supplied the load through D_{2}and D_{3}. The inductor L_{1}discharged its magnetic energy and reduced the voltage across it. The positive voltage of V_{2}turned on switch S_{2}and the input current flowed through S_{2}, capacitor C_{2}and to load through L_{0}. Capacitor C_{2}discharged. In addition, L_{2}then discharged to a value equal to the output voltage.$${\mathrm{V}}_{\mathrm{L}2}={\mathrm{V}}_{2}-{\mathrm{V}}_{\mathrm{C}2}-{\mathrm{V}}_{\mathrm{LO}}+{\mathrm{V}}_{\mathrm{C}1}+{\mathrm{V}}_{\mathrm{L}1}$$$${\mathrm{V}}_{\mathrm{LO}}=-{\mathrm{V}}_{2}-{\mathrm{V}}_{\mathrm{CO}}-{\mathrm{V}}_{\mathrm{C}2}$$$${\mathrm{i}}_{\mathrm{LO}}={\mathrm{i}}_{\mathrm{L}2}+{\mathrm{i}}_{\mathrm{CO}}+{\mathrm{i}}_{\mathrm{O}}$$

- (iii)
- Mode 3 (S
_{3}is ON and S_{1}, S_{2}are OFF): The switches S_{1}and S_{2}were turned off in this mode. Switch S_{3}was turned on. C_{2}started charging and the voltage across it was equal to V_{2}. The source V_{2}supplied the load through C_{2}and L_{O}.$${\mathrm{V}}_{\mathrm{L}2}={\mathrm{V}}_{2}-{\mathrm{V}}_{\mathrm{LO}}+{\mathrm{V}}_{\mathrm{C}1}+{\mathrm{V}}_{\mathrm{L}1}$$$${\mathrm{V}}_{\mathrm{LO}}={\mathrm{V}}_{\mathrm{C}2}-{\mathrm{V}}_{\mathrm{CO}}$$$${\mathrm{i}}_{\mathrm{C}2}={\mathrm{i}}_{2}-{\mathrm{i}}_{\mathrm{LO}}$$

- (iv)
- Mode 4 (S
_{1}, S_{2}, S_{3}are OFF): This is the mode in which all the switches were open. The current i_{2}flowed through the inductor L_{0}. The diode D_{1}freewheels through the inductor L_{2}when there is no source voltage. The energy stored in the inductors dissipated when all switches are turned off. Thus, in turn diode D_{1}was forward biases_{.}$${\mathrm{V}}_{\mathrm{L}2}={\mathrm{V}}_{2}-{\mathrm{V}}_{\mathrm{LO}}+{\mathrm{V}}_{\mathrm{C}1}+{\mathrm{V}}_{\mathrm{L}1}$$$${\mathrm{V}}_{\mathrm{LO}}={\mathrm{V}}_{2}-{\mathrm{V}}_{\mathrm{CO}}$$$${\mathrm{i}}_{2}={\mathrm{i}}_{\mathrm{LO}}$$

#### 2.2.2. Topology 2: Bidirectional Mode

_{2}and D

_{3}connected in the circuit of Topology 1 (unidirectional) were eliminated in the circuit of Topology 2 (bidirectional). This was implemented to provide a bidirectional power flow i.e., the power flow from the battery source to the load and from the load to the battery for charging the battery. The bidirectional power flow was implemented in this topology to charge the battery through the KY converter itself. Switch S

_{4}was connected in such a way that it was suitably turned on to allow power flow from the load to the source. CCM of operation was also performed in this topology. The operation of the MPC is explained in Figure 7 through variations in the power of PV panel (P

_{PV}), battery (P

_{battery}) and load (P

_{LOAD}).

- (i)
- Case 1—presence of high irradiation (P
_{PV}> P_{LOAD})_{:}The PV panel fed the load through the Zeta converter. Switch S_{1}was turned on. In this case, the converter operated as single input single output (SISO) converter. The excess power that was not consumed by the load was utilized for charging the battery through turning on switch S_{4}from the load bus. The converter acts in bidirectional mode as shown in Figure 7a. Hence, energy conservation is carried out in this case.

- (ii)
- Case 2—presence of moderate irradiation (P
_{PV}< P_{LOAD}): When the PV was not able to completely meet the load demand, the battery energy storage system supported it through the KY converter. Now, switches S_{1}, S_{2}, S_{3}were turned on sequentially. In this case, the converter operated as dual input single output (DISO) converter as shown in Figure 7b.

- (iii)
- Case 3—absence of irradiation (P
_{PV}= 0): The battery fed the load through the KY converter. Switches S_{2}and S_{3}were turned on as in Figure 7c and the converter operated as single input, single output (SISO) converter.

**Figure 7.**(

**a**) Case 1: P

_{PV}> P

_{LOAD;}(

**b**) Case 2: P

_{PV}< P

_{LOAD;}(

**c**) Case 3: P

_{PV}= 0 (when there is no irradiation).

_{1}, S

_{2}, S

_{3}and S

_{4}are operated with a switching frequency of 25 kHz. The actual output voltage of the converter is fed to the controller and is actuated in the PI controller. Thus, a closed loop controller is implemented in the converter. The operating mode of the converter is decided according to the load. The transfer function of the converter plant is determined for PV mode and battery mode.

## 3. Analysis and Design of the Proposed Zeta-Ky Converter

#### 3.1. Output Voltage of the MPC

_{2}used in the multiport converter. Combining Equations (1), (4), (7), and (10), the average voltage across the inductor ${\mathrm{L}}_{2}$ is:

_{1}and V

_{2}are the input voltage sources. V

_{C1}and V

_{C2}are the voltages at C

_{1}and C

_{2,}respectively.V

_{L1}, V

_{L2}and V

_{LO}are the voltages across inductors L

_{1}, L

_{2}and L

_{O,}respectively.

#### 3.2. Power Devices Voltage

#### 3.3. Inductor Currents

#### 3.4. Voltage and Current Ripples

#### 3.5. Passive Components Selection

_{s}is the switching frequency of the proposed converter. To calculate inductors size, $\Delta {\mathrm{i}}_{\mathrm{Lx}}$ is generally assumed to be in the range of 10% to 20% of full load. Similarly, the capacitors size is chosen according to the maximum ripple voltage allowed at the capacitors. Size calculation for each capacitor is expressed as:

_{1}, C

_{2}and C

_{3}and i

_{1}, i

_{2}and i

_{0}denote the currents related with the PV power source, energy storage battery and load consumption, respectively. The calculated values for inductors L

_{1}, L

_{2}and L

_{O}are 0.62836 mH, 0.72361 mH and 0.517122 mH, respectively. The calculated values of capacitors C

_{1}, C

_{2}and C

_{O}are 0.12860 mF, 0.381944 mF and 0.10706 mF, respectively.

## 4. Results and Discussions

#### 4.1. Simulation Results

_{1}and V

_{2}were varied and the output voltage was estimated by maintaining constant duty cycles for the switches. These estimated output voltages were compared with the actual output voltages as shown in Table 3. In both tables, the actual voltages obtained from simulation were approximately closer to the estimated output voltages. Thus, the operation of the unidirectional modified triple port Zeta-KY MPC was elucidated, and the calculated and actual output voltages are compared.

_{1}, S

_{2}, S

_{3}and S

_{4}. The pulses are generated by the controller that is continuously tracking the output voltage, comparing it with the reference voltage and thereby generate pulses according to the operating mode. The proportional gain for the PI controller, K

_{P}= 100 and integral gain, K

_{I}= 0.1 have been considered. These values have been obtained by tuning the PI controller in MATLAB.

_{1}. Figure 9 shows the output voltage and current fed from the PV at a constant irradiance. At a particular irradiance, the output current of PV will be constant only. This current will change only when the irradiance will change.

_{4}. Figure 10 shows battery state of charge (SOC), with a battery voltage of 45 V and a current of −2 A in bidirectional mode. It should be noted that since the SOC of battery changes, the battery current falls immediately and again increases within a very shorter time.

_{1}is initially charged to a value equal to the input voltage of the PV with 40 V. Later it discharged to −40 V. With the MPC working in continuous conduction mode, the current through the inductor L

_{1}is continuous as shown in Figure 11.

_{2}, L

_{0}and C

_{2.}The CCM mode was demonstrated from the waveform shown by the current through the inductor L

_{0}.

#### 4.2. Experimental Results

_{1}, S

_{2,}S

_{3,}S

_{4.}The generated pulses from the controller were observed through the digital storage oscilloscope (DSO). The pulses generated for all MOSFETs shown in Figure 15 are similar to the simulated waveforms of the converter.

_{1}and L

_{2}are shown in Figure 16a,b, in which the plot is obtained for a scale of 25 V/div. The inductor L

_{1}charged and discharged to its input voltage from the PV source of 40 V. The voltage across the capacitor C

_{1}initially charged to a value equal to the input voltage and discharged to maintain a constant output voltage, thus maintaining at −70 V as shown in Figure 16c. Figure 16d shows that capacitor C

_{2}charged to a voltage equal to the battery voltage of 40 V, since C

_{2}was connected to the KY part of the MPC in which battery acted as the input source.

#### 4.3. Comparative Analysis

## 5. Conclusions

## Author Contributions

## Funding

## Data Availability Statement

## Acknowledgments

## Conflicts of Interest

## Appendix A

#### Appendix A.1. Calculation of Power Loss

#### Appendix A.1.1. Power Loss in the MOSFET Switches $\left({\mathrm{S}}_{1},{\mathrm{S}}_{2},{\mathrm{S}}_{3}\right),\left({\mathrm{P}}_{\mathrm{S}}\right)$

_{rise}and t

_{fall}is the rise time and fall time taken by MOSFET respectively.

#### Appendix A.1.2. Power Loss in the Diodes $\left({\mathrm{D}}_{1},{\mathrm{D}}_{2},{\mathrm{D}}_{3}\right),\left({\mathrm{P}}_{\mathrm{D}}\right)$

#### Appendix A.1.3. Power Loss in the Inductors $\left({\mathrm{P}}_{\mathrm{L}}\right)$

- (i)
- Core loss: the core loss is defined by:$${\mathrm{P}}_{\mathrm{fe}}={\mathrm{P}}_{\mathrm{fe}1}+{\mathrm{P}}_{\mathrm{fe}2}+{\mathrm{P}}_{\mathrm{fe}3}$$$${\mathrm{P}}_{\mathrm{fe}}={\mathrm{a}}_{1}{\mathrm{B}}_{1}^{\mathrm{b}}{\mathrm{f}}_{1}^{\mathrm{C}}{\mathrm{I}}_{\mathrm{m}1}{\mathrm{A}}_{\mathrm{C}1}+{\mathrm{a}}_{2}{\mathrm{B}}_{2}^{\mathrm{b}}{\mathrm{f}}_{2}^{\mathrm{C}}{\mathrm{I}}_{\mathrm{m}2}{\mathrm{A}}_{\mathrm{C}2}+{\mathrm{a}}_{3}{\mathrm{B}}_{3}^{\mathrm{b}}{\mathrm{f}}_{3}^{\mathrm{C}}{\mathrm{I}}_{\mathrm{m}3}{\mathrm{A}}_{\mathrm{C}3}$$
_{fe1,}P_{fe2,}P_{fe3}represent the core losses in the inductors L_{1}, L_{2}and L_{3}respectively, B is half of ac flux, f—frequency, ${\mathrm{A}}_{\mathrm{C}}$—area of core and ${\mathrm{I}}_{\mathrm{m}}$—magnetic path length of the core.

- (ii)
- Copper loss: the inductor copper loss is dependent on the RMS of currents in the inductors and is given by$${\mathrm{I}}_{\mathrm{L}1\mathrm{rms}}=\frac{-{\mathrm{i}}_{1}}{\frac{1}{{\mathsf{\delta}}_{1}}-2};{\mathrm{I}}_{\mathrm{L}2\mathrm{rms}}={\mathrm{i}}_{\mathrm{L}0}+\frac{{\mathrm{i}}_{0}}{2{\mathsf{\delta}}_{1}-1};{\mathrm{I}}_{\mathrm{L}0}={\mathrm{i}}_{\mathrm{L}2}-\frac{-{\mathrm{i}}_{0}}{2{\mathsf{\delta}}_{1}-1}$$$${\mathrm{P}}_{\mathrm{Cu}}={\mathrm{r}}_{\mathrm{L}1}{\mathrm{I}}_{\mathrm{L}1\mathrm{rms}}^{2}+{\mathrm{r}}_{\mathrm{L}2}{\mathrm{I}}_{\mathrm{L}2\mathrm{rms}}^{2}+{\mathrm{r}}_{\mathrm{L}3}{\mathrm{I}}_{\mathrm{L}3\mathrm{rms}}^{2}$$

#### Appendix A.2. Calculation of Efficiency

#### Appendix A.3. Converter System Stability

#### Appendix A.4. Control Algorithm Fed in the Controller

SL. NO | Irradiance (W/sq.m) | V_{PV} (V) | I _{PV} (A) | P_{PV} (W) |
---|---|---|---|---|

1 | 1000 | 37.42 | 7.3 | 273.17 |

2 | 800 | 36.86 | 6.6 | 243.28 |

3 | 600 | 36.80 | 5.3 | 195.04 |

4 | 400 | 36.7 | 4.3 | 154.14 |

5 | 200 | 36.7 | 2.3 | 84.41 |

6 | 100 | 36.7 | 1.8 | 66.06 |

7 | 0 | 36.7 | 0 | 0 |

#### Appendix A.5. Example of Calculated Efficiencies at Different Operating Modes

- (i)
- PV to load

^{2}irradiance, PV is supplying the load. At 10 Ω and 15 Ω load, both PV and battery are supplying the load to provide a calculated efficiency of 94.02% and 94.37% respectively. In this circumstance, the converter was operating in a dual input single output mode (DISO).

- (ii)
- Battery to load

- (iii)
- PV to battery

^{2}irradiance, PV was charging the battery at 35 Ω and 40 Ω load and at the same time supplying the load to provide a calculated efficiency of 92.35% and 91.73% respectively. Here, the converter is operating in a single input single output (SISO) and bidirectional mode.

SL. NO | Irradiance (W/m^{2}) | PV Panel | Battery | Total Input Power (W) | Load (Ohm) | Converter Output | Calculated Efficiency (%) | ||||||
---|---|---|---|---|---|---|---|---|---|---|---|---|---|

V_{pv}(V) | I_{pv}(A) | P _{pv}(W) | V_{b} (V) | I_{b} (A) | P_{b} (W) | V_{o} (V) | I_{o} (A) | P_{o} (W) | |||||

1 | 1000 | 37.42 | 7.30 | 273.17 | 40 | 6.20 | 248.00 | 521.17 | 10 | 70.00 | 7.00 | 490.00 | 94.02 |

2 | 1000 | 37.42 | 7.30 | 273.17 | 40 | 1.80 | 72.00 | 345.17 | 15 | 69.90 | 4.66 | 325.73 | 94.37 |

3 | 1000 | 37.42 | 7.30 | 273.17 | 40 | −3.05 | −122.00 | 151.17 | 35 | 69.90 | 2.00 | 139.60 | 92.35 |

4 | 1000 | 37.42 | 7.30 | 273.17 | 40 | −3.50 | −140.00 | 133.17 | 40 | 69.90 | 1.75 | 122.15 | 91.73 |

5 | 0 | 36.70 | 0.00 | 0.00 | 40 | 8.90 | 356.00 | 356.00 | 15 | 69.90 | 4.65 | 324.76 | 91.22 |

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**Figure 1.**Block diagram of (

**a**) conventional multi input multiple converter system and (

**b**) multiport converter.

**Figure 5.**Equivalent circuits of the proposed multiport converter with current directions: (

**a**) Mode 1; (

**b**) Mode 2; (

**c**) Mode 3; and (

**d**) Mode 4.

**Figure 14.**(

**a**) PV panel of 250 W; (

**b**) experimental set-up of the proposed converter with dSPACE controller; and (

**c**) closer view of the converter.

**Figure 15.**Pulse generated for (

**a**) Switch S

_{1}; (

**b**) Switch S

_{2}; (

**c**) Switch S

_{3}; and (

**d**) Switch S

_{4}.

**Figure 16.**(

**a**) Voltage across L

_{1}; (

**b**) voltage across L

_{2}; (

**c**) voltage across C

_{1}; (

**d**) voltage across C

_{2}.

**Figure 17.**Constant output voltage of the MPC (

**a**) with constant resistive load of 20 Ω; (

**b**) with dynamic loads (varied from 20 Ω to 30 Ω).

**Figure 19.**Comparison of conventional multiport converters with the proposed modified triple port converter on the basis of components employed.

**Figure 20.**Scatter plot between calculated efficiency and rated load for comparing the proposed and conventional MPCs.

Design Specification | Values | Design Specification | Values |
---|---|---|---|

PV Voltage, Vmp | 36 V | Duty Cycle | 0.67 |

PV Current, Imp | 7.64 A | Inductor Ripple Current | 0.76 A |

PV, Voc | 43.20 V | Minimum Inductor, L1 | 0.63 mH |

PV, Isc | 9.17 A | Minimum Inductor, L2 | 0.72 mH |

PV Power (Max) | 275 W | Ipeak of Filter Inductor | 7.71 A |

Battery Voltage | 40 V | Output Ripple Voltage | 0.07 V |

Battery Capacity | 550.50 Ah | Output Capacitor, Co | 0.11 mF |

Output Voltage | 72 V | Input Ripple Voltage | 0.72 V |

Output Current | 6.94 A | Input C1 Capacitor, C1 | 0.13 mF |

Output Power | 500 W | Ripple Voltage of C1 | 0.36 V |

Output inductor, Lo | 0.52 mH | ||

Switching Frequency | 25 kHz | C2 capacitor | 0.38 mF |

SL. NO | V_{1} = V_{2} (V) | D_{1}(%) | D_{2}(%) | D_{3}(%) | V_{OUT} (Est)(V) | V_{OUT} (Act)(V) |
---|---|---|---|---|---|---|

1 | 24 | 25 | 25 | 40 | 69 | 68.0 |

2 | 24 | 50 | 10 | 30 | 80 | 79.2 |

3 | 24 | 40 | 10 | 40 | 60 | 59.0 |

4 | 24 | 30 | 26 | 40 | 66 | 65.1 |

5 | 24 | 35 | 15 | 40 | 63 | 62.6 |

SL. NO | D_{1} = 25%D _{2} = 25%D _{3} = 40% | V_{OUT} (Est)(V) | V_{OUT} (Act)(V) | |
---|---|---|---|---|

V_{1} (V) | V_{2} (V) | |||

1 | 6 | 6 | 17.25 | 16.2 |

2 | 24 | 12 | 42.0 | 41.3 |

3 | 12 | 24 | 61.5 | 61.0 |

4 | 24 | 24 | 69.0 | 68.5 |

5 | 24 | 20 | 60.0 | 59.1 |

6 | 20 | 24 | 66.5 | 65.6 |

7 | 12 | 12 | 34.5 | 33.8 |

SL. NO | Parameters | Values |
---|---|---|

1 | IRF250-MOSFET Losses (Zeta) | 5.47W |

2 | TST20L200CW Diode Losses | 2.92 W |

3 | PT500R-2000 Inductor Losses | 3.53 W |

4 | IRF250-MOSFET Losses (KY) | 5.98 W |

5 | Overall Losses in the MPC due to MOSFETs, Diodes and Inductors | 32.30 W |

6 | Output Power of Converter | 500 W |

7 | Calculated Efficiency | 93.54% |

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## Share and Cite

**MDPI and ACS Style**

Chandran, I.R.; Ramasamy, S.; Ahsan, M.; Haider, J.; Rodrigues, E.M.G. Implementation of Non-Isolated Zeta-KY Triple Port Converter for Renewable Energy Applications. *Electronics* **2021**, *10*, 1681.
https://doi.org/10.3390/electronics10141681

**AMA Style**

Chandran IR, Ramasamy S, Ahsan M, Haider J, Rodrigues EMG. Implementation of Non-Isolated Zeta-KY Triple Port Converter for Renewable Energy Applications. *Electronics*. 2021; 10(14):1681.
https://doi.org/10.3390/electronics10141681

**Chicago/Turabian Style**

Chandran, Ilambirai Raghavan, Sridhar Ramasamy, Mominul Ahsan, Julfikar Haider, and Eduardo M. G. Rodrigues. 2021. "Implementation of Non-Isolated Zeta-KY Triple Port Converter for Renewable Energy Applications" *Electronics* 10, no. 14: 1681.
https://doi.org/10.3390/electronics10141681