# Efficiency and Power Loss Distribution in a High-Frequency, Seven-Level Diode-Clamped Inverter

^{1}

^{2}

^{*}

## Abstract

**:**

## 1. Introduction

## 2. Four-Level Diode-Clamped Bridge Inverter Configuration and Modulation Concepts

#### 2.1. Inverter Configuration

- Efficiency analysis in a high-frequency circuit based on MOSFETs and Schottky diodes;
- Studies of the influence of the switching frequency on the efficiency of the system in the range of 100–300 kHz;
- Studies of the influence of the applied modulation on the efficiency of the system and the uniformity of the distribution of energy losses in its components;
- Simulation studies of energy losses and converter efficiency with the use of physical elements implemented in the Matlab/Simulink environment with the Simscape library;
- Hardware implementation of the modulation algorithm for research with the use of the Imperix RCP system, developed in MATLAB/Simulink R2022b Software.

#### 2.2. Modulation Concepts

_{2}is used most often, which is disadvantageous, except in cases where this capacitor is sipped from an energy source, as shown in [3] in a circuit with an active voltage balancer on the DC-link.

_{1}, C

_{2}, and C

_{3}at each modulation level. The pulse width can be realized using the classic carrier-based method. Next, the state machine-based (SM-based) algorithm selects the implementation of the appropriate order of states of modulation and DC-link capacitors (Table 1) according to the algorithm presented in Table 3.

_{2}. DC-link capacitor use by SM-based M2 modulation is such that the use of DC-link capacitors by the inverter is uniform and within the period of fundamental frequency. Reference [4] also proposes a switching pattern modifying SM-based M2, so states 1a, 1b, and 1c are implemented in the concordant and opposite order, which may affect the number of commutations during the pulsing period. This algorithm can be written as follows:

M3 states order for levels 1–2: {1a, 2a, 1c, 2b, …},

M3 states order for levels: 1–3: {3, 1a, 3, 1b, 3, 1c, 3, 1c, 3, 1b, 3, 1a, 1a, …}

## 3. Simulation Research

_{oss}junction losses in MOSFETs. A comparison of the results from Figure 3 and Figure 4 shows the significant influence of the output capacitance of the transistor on the power losses in the tested system.

## 4. Experimental Tests

#### 4.1. Experimental Setup

#### 4.2. Experimental Results

_{s}= 200 kHz and the output power P

_{out}= 550 W. The results presented in Figure 14 and Figure 15 characterize the operation of the system with M1 modulation, while the results presented in Figure 16 are a comparison of the temperature of the system when controlled with M1 and M2 modulation. The temperature measurement points are shown in Figure 14 (Sp1–Sp10). All results shown in Figure 14, Figure 15 and Figure 16 are on the same color-related temperature scale that is located to the right of each thermal image.

_{out}= 550 W. From these results, it is clear that the M2 modulation results in a more even distribution of energy losses in the elements. This is in line with the assumptions of this modulation method, according to which DC-link capacitors and active components are used symmetrically at each level.

## 5. Conclusions

_{DS(on)}devices, reducing conduction losses, which leads to increased converter efficiency. C

_{oss}losses are reduced significantly as well since the energy dissipated from the transistors’ output capacitance is reduced. Reduction of voltage across diodes to values much below 200 V allows the use of Schottky diodes of very low forward voltage V

_{F}, which gives an important reduction in conduction losses in diodes.

_{DS(on)}of MOSFETs or V

_{F}of diodes. In the analyzed case, the inverter operating at a DC voltage of 400 V was configured with the use of MOSFETs and Schottky diodes with a voltage of 200 V. The test was carried out for a switching frequency of up to 300 kHz, and the increase in frequency from 100 to 200 kHz did not cause a significant decrease in inverter efficiency. The practical significance of the analyzed modulation method with selective selection of DC-link capacitors (SM-based) is also important, as it simplifies the thermal design for the inverter and the selection of system components and protects DC-link from imbalance.

## Author Contributions

## Funding

## Data Availability Statement

## Acknowledgments

## Conflicts of Interest

## References

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**Figure 1.**General concept of a seven-level diode-clamped bridge (7LDCB) inverter with four-level branches.

**Figure 2.**M1 carrier-based modulation for 7LDCB [5].

**Figure 3.**Simulation results of the loss distribution in the A-phase elements of an inverter using carrier-based M1 modulation (

**a**) and SM-based M2 modulation (

**b**). P. u. results are related to total losses in semiconductor devices. R

_{ds(on)}= 30 mΩ, C

_{oss}= 395 pF.

**Figure 4.**Simulation results of the loss distribution in the A-phase elements of an inverter using carrier-based M1 modulation (

**a**) and SM-based M2 modulation (

**b**). P. u. results are related to total losses in semiconductor devices. R

_{ds(on)}= 12 mΩ, C

_{oss}= 900 pF.

**Figure 5.**Imbalance reduction by using the SM-based M2 strategy with implemented overloading of the DC-link with the highest voltage.

**Figure 10.**Steady state of operation with the output power at levels of 100 W (

**a**) and 1000 W (

**b**) and modulation type carrier-based M1. Load current (CH1) and unfiltered output voltage of the proposed inverter (CH2).

**Figure 11.**Steady state of operation with the output power on the level of 100 W (

**a**) and 1000 W (

**b**) and modulation type SM-based M2. Load current (CH1) and unfiltered output voltage of the proposed inverter (CH2).

**Figure 12.**Efficiency curves of the proposed inverter at three different switching frequencies for carrier-based M1 modulation strategy in the range of output power 50–1000 W.

**Figure 13.**Efficiency curves of the 7LDCB inverter performed with two different modulation types (type 1: carrier-based M1, type 2: SM-based M2) at a switching frequency of 200 kHz. Efficiency is calculated as the ratio of the output to the input power of the inverter from all three power supply units.

**Figure 14.**Temperature measurement points on transistors and diodes housings of A-phase (f

_{s}= 200 kHz, P

_{out}= 550 W). Carrier-based M1 modulation method.

**Figure 15.**Results for carrier-based M1 modulation for various switching frequencies: 100 kHz (

**a**), 200 kHz (

**b**), and 300 kHz (

**c**) for P

_{out}= 550 W, Q = 0 Var, after 1 min from the start of the converter.

**Figure 16.**Results for carrier-based M1 (

**a**) and selective SM-based M2 (

**b**) modulation strategies. Temperature measurement on the transistor and A-phase diode housings for switching frequency 200 kHz, P

_{out}= 550 W, Q = 0 Var, after 1 min from the start of the converter.

**Figure 17.**Results based on thermal imaging registration for carrier-based M1 and selective SM-based M2. Temperature measurement on the housings of the transistor and A-phase diode components for switching frequency 200 kHz, P

_{out}= 550 W, Q = 0 Var, after 10 min from the start of the converter.

Level ^{1}and State Name | Used Switches and DC-Link Capacitors | ||
---|---|---|---|

{S_{1A}, S_{2A}, S_{3A}, S_{4A}, S_{5A}, S_{6A}} | {S_{1B}, S_{2B}, S_{3B}, S_{4B}, S_{5B}, S_{6B}} | DC-Link Capacitor | |

3 | {1, 1, 1, 0, 0, 0} | {0, 0, 0, 1, 1, 1} | C_{1}, C_{2}, C_{3} |

2 (2a) | {1, 1, 1, 0, 0, 0} | {0, 0, 1, 1, 1, 0} | C_{1}, C_{2} |

2 (2b) | {0, 1, 1, 1, 0, 0} | {0, 0, 0, 1, 1, 1} | C_{2}, C_{3} |

1 (1a) | {1, 1, 1, 0, 0, 0} | {0, 1, 1, 1, 0, 0} | C_{1} |

1 (1b) | {0, 1, 1, 1, 0, 0} | {0, 0, 1, 1, 1, 0} | C_{2} |

1 (1c) | {0, 0, 1, 1, 1, 0} | {0, 0, 0, 1, 1, 1} | C_{3} |

^{1}Voltage level is presented as p.u.: u

_{out}/(U

_{in}/3).

Modulation Step ^{1} (One or Two Repetition Periods),and DC-Link Capacitor Use | |||||||
---|---|---|---|---|---|---|---|

n | n + 1 | n + 2 | n + 3 | … | |||

Levels used for modulation | 0–1 | state: | 1b C _{2} | 0 none | 1b C _{2} | 0 none | … |

1–2 | state: | 1b C _{2} | 2a C _{1}, C_{2} | 1b C _{2} | 2b C _{2}, C_{3} | … | |

2–3 | state: | 2a C _{1}, C_{2} | 3 all | 2b C _{2}, C_{3} | 3 all | … |

^{1}n is an index of realization of the next modulation state.

Modulation Step ^{1} (One Repetition Periods),and DC-Link Capacitor Use | |||||||||
---|---|---|---|---|---|---|---|---|---|

n | n + 1 | n + 2 | n + 3 | n + 4 | n + 5 | … | |||

Levels used for modulation | 0–1 | State: | 1a C1 | 0 None | 1b C2 | 0 None | 1c C3 | 0 None | … |

1–2 | State: | 1a C1 | 2a C1, C2 | 1c C3 | 2b C2, C3 | … | |||

2–3 | State: | 1a C1 | 3 All | 1b C2 | 3 All | 1c C3 | 3 All | … |

^{1}n is an index of realization of the next modulation state.

Parameter | Value |
---|---|

All the MOSFETS R_{ds(on)} [mΩ] | 12–30 |

MOSFETS C_{OSS} [pF] | 395 and 900 |

Schottky clamping diodes V_{F} [V] | 0.72 |

Input voltage U_{in} [V] | 400 |

Switching frequency f_{S} [kHz] | 100 |

Parameter | Value |
---|---|

Transistors | IPB073N15N5 U _{DS} = 150 VI _{D} = 114 AR _{DS(on)} = 7.3 mΩ |

Diodes | VBT10202C-M3/4W I _{F(AV)} = 2 × 5 AU _{RRM} = 200 VU _{F} = 0.65 V at I_{F} = 5 A |

LC filter | 150 uH/2 × 4.7 uF |

Input voltage U_{in} | 400 (3 × 133) V |

Switching frequency f_{S} | 100–300 kHz |

Output voltage U_{out} | 150 V (RMS) |

Output power P_{out} | 50–1100 W |

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**MDPI and ACS Style**

Stala, R.; Folmer, S.; Penczek, A.; Hachlowski, J.; Mikoś, Z.
Efficiency and Power Loss Distribution in a High-Frequency, Seven-Level Diode-Clamped Inverter. *Energies* **2023**, *16*, 7866.
https://doi.org/10.3390/en16237866

**AMA Style**

Stala R, Folmer S, Penczek A, Hachlowski J, Mikoś Z.
Efficiency and Power Loss Distribution in a High-Frequency, Seven-Level Diode-Clamped Inverter. *Energies*. 2023; 16(23):7866.
https://doi.org/10.3390/en16237866

**Chicago/Turabian Style**

Stala, Robert, Szymon Folmer, Adam Penczek, Jakub Hachlowski, and Zbigniew Mikoś.
2023. "Efficiency and Power Loss Distribution in a High-Frequency, Seven-Level Diode-Clamped Inverter" *Energies* 16, no. 23: 7866.
https://doi.org/10.3390/en16237866