The method of DPWM injected offset voltage for control of neutral point voltage using 3-level NPC inverter

2016 ◽  
Author(s):  
Seul-A Lee ◽  
Seung-Wook Hyun ◽  
Seok-Jin Hong ◽  
Chung-Yuen Won
Keyword(s):  
Neutral Point ◽  
Offset Voltage

scholarly journals A Harmonic Voltage Injection Based DC-Link Imbalance Compensation Technique for Single-Phase Three-Level Neutral-Point-Clamped (NPC) Inverters

Energies ◽  
2018 ◽  
Vol 11 (7) ◽  
pp. 1886 ◽  
Author(s):  
Kyoung-Pil Kang ◽  
Younghoon Cho ◽  
Myung-Hyo Ryu ◽  
Ju-Won Baek
Keyword(s):  
Second Order ◽  
Neutral Point ◽  
Voltage Difference ◽  
Imbalance Problem ◽  
Offset Voltage ◽  
Half Wave ◽  
Unbalanced Voltage ◽  
Compensation Technique ◽  
Harmonic Voltage ◽  
Harmonic Components

In three-level neutral-point-clamped (NPC) inverters, the voltage imbalance problem between the upper and lower dc-link capacitors is one of the major concerns. This paper proposed a dc-link capacitor voltage balancing method where a common offset voltage was injected. The offset voltage consists of harmonic components and a voltage difference between the upper and the lower capacitors. Here, both the second-order harmonics and the half-wave of the second-order component were injected to compensate for the unbalanced voltage between the capacitors. In order to show the effectiveness of the proposed voltage injection, the theoretical analyses, simulations, and experimental results are provided. Since the proposed method does not require any hardware modifications, it can be easily adapted. Both the simulations and the experiments validated that the voltage difference of the dc-link could be effectively reduced with the proposed method.

scholarly journals DC-Link Capacitor Voltage Imbalance Compensation Method Based Injecting Harmonic Voltage for Cascaded Multi-Module Neutral Point Clamped Inverter

Electronics ◽  
2019 ◽  
Vol 8 (2) ◽  
pp. 155 ◽  
Author(s):  
Kyoung-Pil Kang ◽  
Younghoon Cho ◽  
Ho-Sung Kim ◽  
Ju-won Baek
Keyword(s):  
Theoretical Analysis ◽  
Compensation Method ◽  
Neutral Point ◽  
Voltage Difference ◽  
Imbalance Problem ◽  
Offset Voltage ◽  
Capacitor Voltage ◽  
Harmonic Voltage

In a three-level (NPC) converter, the voltage imbalance problem in the DC-link capacitors is major issue. This paper proposes the DC-link capacitor voltage imbalance compensation method, where a common offset voltage is injected for a multi-module NPC inverter. The offset voltage consists of a harmonic voltage and a voltage difference between the upper and lower capacitors. The proposed method does not require any hardware modification, so that it is easily implemented. In order to show the effectiveness of the proposed balancing method, theoretical analysis is provided to balance the voltages, and both the simulations and the experiments were carried out to show that the voltage difference of the DC-link was decreased by the proposed method.

scholarly journals Analytical Modeling of Neutral Point Current in T-type Three-level PWM Converter

Energies ◽  
2020 ◽  
Vol 13 (6) ◽  
pp. 1324
Author(s):  
Kui-Jun Lee
Keyword(s):  
Analytical Model ◽  
Neutral Point ◽  
Control Loop ◽  
Pwm Converter ◽  
Voltage Balancing ◽  
Loop Design ◽  
Offset Voltage ◽  
Three Phase ◽  
Effective Voltage ◽  
Balancing Control

Since a T-type three-level PWM converter has several intrinsic advantages, it has been researched for various applications such as grid-connected converter systems. However, it necessarily requires an additional voltage control loop for balancing the upper and the lower DC-link voltage. To satisfy this requirement, an offset voltage is widely used to provide a neutral point current without affecting other variables such as total DC-link voltage and three-phase input current. However, these methods are mostly based on the averaged value between the applied offset voltage and the neutral point voltage or current, and there is no exact analytical model. Therefore, in this paper, the exact theoretical relationship between the offset voltage and the neutral point current is analyzed. This result can be expected to be useful for an effective voltage balancing control loop design as well as the better understanding of the whole system operation. The validity of the obtained analytical model is verified by simulation and experimental results.

scholarly journals Output Voltage Imbalance Compensation Using dc Offset Voltage for Split dc-Link Capacitor 3-Leg Inverter

Electronics ◽  
2021 ◽  
Vol 10 (9) ◽  
pp. 1029
Author(s):  
Sun-Pil Kim ◽  
Sung-Geun Song ◽  
Sung-Jun Park ◽  
Feel-soon Kang
Keyword(s):  
Output Voltage ◽  
Harmonic Distortion ◽  
Neutral Point ◽  
Total Harmonic Distortion ◽  
Phase 3 ◽  
Dc Offset ◽  
Phase Current ◽  
Compensation Algorithm ◽  
Offset Voltage ◽  
Circuit Structure

In this paper, we analyzed the output voltage imbalance and the cause of the offset voltage in 3-phase 3-leg inverters by using Millman’s theory. Based on this result, we proposed a voltage imbalance compensation algorithm using the dc offset voltage that appeared at the neutral point voltage of the load. To apply the proposed imbalance compensation algorithm, it needs a circuit structure of 3-phase 4-wire such as split dc-link capacitor 3-leg inverter and 4-leg inverter. Therefore, the total harmonic distortion (THD) of the load phase current according to the imbalance rate of the load was analyzed for the two inverters. Then, PSIM simulation and experiments based on a 10 kW-prototype of split dc-link capacitor 3-leg inverter were implemented to verify the validity of the proposed imbalance compensation algorithm.

scholarly journals Three-Phase Three-Level Neutral Point Clamped Rectifier with Predictive Control Method without Employing Weighting Factor

2020 ◽  
Vol 10 (15) ◽  
pp. 5149 ◽  
Author(s):  
Eun-Su Jun ◽  
Minh Hoang Nguyen ◽  
Sangshin Kwak
Keyword(s):  
Predictive Control ◽  
Control Method ◽  
Weighting Factor ◽  
Neutral Point ◽  
Control Methods ◽  
Offset Voltage ◽  
Three Phase ◽  
Sinusoidal Input ◽  
Capacitor Voltage ◽  
Voltage Balance

A predictive control method using injected offset voltage to achieve neutral point (NP) voltage balance of three-phase three-level neutral point clamped (NP) rectifiers, without employing a weighting factor, is proposed in this study. One of the biggest problems with the three-level NP rectifiers is the dc link capacitor voltage imbalance. Therefore, it is necessary to maintain the balance of the NP voltage in addition to synthesize the three-phase sinusoidal input current by control methods. Conventional predictive control methods for the NP rectifiers have used a weighting factor in a cost function that determines the control ratio of the input currents and the capacitor voltage balance. As a result, it is burdensome to empirically redesign the weighting factor when the rectifiers’ parameter values and control conditions change. Unlike the conventional methods, the proposed approach without the weighting factor can significantly eliminate differences between two DC capacitor voltages by utilizing an offset voltage, which is generated by using the difference between the upper and lower capacitor voltages. Consequently, the proposed approach using the offset voltage injection can control the input currents and retain the balance of NP voltage. Simulation and experiments are presented to verify the correctness of the NP voltage balancing of the proposed control method.

scholarly journals Analysis of Allowable Unbalanced Load Conditions for T-type Three-Level PWM Converter

Energies ◽  
2021 ◽  
Vol 14 (18) ◽  
pp. 5969
Author(s):  
Kui-Jun Lee
Keyword(s):  
Low Voltage ◽  
Experimental Tests ◽  
Neutral Point ◽  
Stable System ◽  
System Operation ◽  
Pwm Converter ◽  
Conduction Loss ◽  
Offset Voltage ◽  
Unbalanced Load ◽  
Load Conditions

Since a T-type three-level PWM converter has several advantages in terms of harmonics and conduction loss, it has been widely adopted for various low voltage applications. However, a neutral point voltage control is necessarily required for stable system operation, and an offset voltage can effectively provide the required neutral point current under unbalanced load conditions. Nevertheless, all types of unbalanced loads cannot be accommodated; in other words, there is a limitation on how much unbalanced load conditions can be allowed. Therefore, this paper analyzed the maximum allowable unbalanced load conditions in the T-type three-level PWM converter. This result can be properly utilized for an effective design verification considering unbalanced load conditions as well as a comprehensive approach for the stable system operation. The feasibility of the analytical result is verified through simulation and experimental tests.

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