Inverter Lifetime Research Articles

Economic Consequences Based on Reversible and Irreversible Degradation of PV Park in the Harsh Climate Conditions of Iraq

Photovoltaic (PV) system reliability and durability investigations are essential for industrial maturity and economic success. Recently, PV systems received much interest in Iraq due to many reasons—for instance, power shortage, global warming and pollution. Despite this interest, the precise economic implications of PV system reliability in harsh climates like Iraq remain uncertain. This work assesses the economic implications of PV system component reliability and soiling in Iraq using field experience and historical data. This study identifies the most common failure modes of PV systems installed in Iraq and similar climatic regions, and also ranks their severity. Simulations explore scenarios of PV module degradation rates, inverter lifetimes, soiling rates, and cleaning intervals, revealing that soiling has the most detrimental effect, with cleaning frequency leading to Levelized Cost of Electricity (LCOE) losses of over 30%, depending on the location. Inverter lifetime contributes to LCOE losses between 4 and 6%, depending on the PV system’s location. This study also evaluates the impact of tilt angle as a mitigation strategy for reducing soiling loss and its economic implications, finding that installing PV modules at higher tilt angles could reduce the economic impact of soiling by approximately 4.4%. Additionally, the optimal cleaning strategy identified is fully automated dry cleaning with robots, outperforming other strategies economically. Overall, the findings highlight that the LCOE in Iraq is relatively high compared to the global weighted average for utility-scale PV systems, primarily due to high soiling and degradation rates. The LCOE varies within the country, influenced by different degradation rates. This study aims to assist PV stakeholders in Iraq and the Middle East and North Africa (MENA) region in accurately estimating solar bankability; moreover, increasing reliability by minimizing the technical and financial risks by considering key parameters specific to these regions.

Multi-Objective and Multi-Agent Deep Reinforcement Learning for Real-Time Decentralized Volt/VAR Control of Distribution Networks Considering PV Inverter Lifetime

Multi-Objective and Multi-Agent Deep Reinforcement Learning for Real-Time Decentralized Volt/VAR Control of Distribution Networks Considering PV Inverter Lifetime

Lifetime Extension Method for Three-Phase Voltage Source Converters Using Discontinuous PWM Scheme with Hybrid Offset Voltage

This paper proposes a lifespan extension technique for three-phase voltage inverters using hybrid offset voltage. The proposed method lengthens the inverter lifetime by independently adjusting the switching frequency of the three phases in accordance with the aging degree. To reduce the switching operation of the phase with the shortest lifetime, the proposed technique injects the offset voltage for generalized discontinuous pulse-width modulation PWM (GDPWM) into the reference voltage in the region where the switching operation of the shortest lifespan phase can be stopped. When the switching operation does not need to be stopped, the offset voltage for space vector PWM (SVPWM) is injected into the reference voltage for high inverter load current quality. An offset voltage that varies according to the need to stop the switching operation is the proposed hybrid offset voltage. Using the proposed hybrid offset voltage, the switching frequencies of the three phases are independently controllable. In addition, since only the switching operation of the phase having the shortest lifespan is reduced, the load current quality in accordance with the switching operation reduction is good compared to the conventional method to simultaneously diminish all phase switching frequencies. The proposed method significantly increases the reliability of the three-phase voltage inverter, where the thermal stress of the phase having the shortest lifespan is decreased up to 55%, whereas the inverter lifetime can be increased by 10 times. The proposed technique was verified by simulations and experiments.

Lifetime model adjustments for GaN cascodes as a base for inverter lifetime estimation

Lifetime model adjustments for GaN cascodes as a base for inverter lifetime estimation

Impact of smart photovoltaic inverter control modes on medium‐voltage grid voltage and inverter lifetime: An experimental approach

AbstractThis study relies on an experimental approach, utilising real data from multiple photovoltaic (PV) sites located in the US Northeaster region, to inspect how different inverter reactive and active power settings impact gird voltage regulation and inverter life expectancy. These voltage regulation schemes come at a cost for the operator. Data from different solar sites with inverters running at different reactive and active power settings were analysed to compare operational trade‐offs. These trade‐offs range from production losses to shortening the lifetime of the inverters. Voltage versus reactive power plots were analysed to show production losses, while the thermal analysis was used to correlate with the inverter life expectancy.

Pareto Front Analysis Method for Optimization of PV Inverter Based Volt/Var Control Considering Inverter Lifetime

Pareto Front Analysis Method for Optimization of PV Inverter Based Volt/Var Control Considering Inverter Lifetime

Lifetime evaluation method of PV inverter considering the influence of fundamental frequency and low frequency junction temperature

As an important part of photovoltaic (PV) system, the reliability of PV inverter is the key to ensure the safe and reliable operation of PV power generation system. The existing lifetime evaluation methods of PV inverter are restricted by the extraction accuracy of junction temperature profile, and it is impossible to accurately evaluate the service lifetime of PV inverter. This paper, thus, divides the junction temperature profile according to the time scales, defines the concepts of fundamental frequency junction temperature and low frequency junction temperature. Then, this paper reveals the influence mechanism of fundamental frequency and low frequency junction temperature on PV inverter lifetime evaluation, and proposes a PV inverter lifetime evaluation method considering the influence of fundamental frequency and low frequency junction temperature. Finally, based on this method, the lifetime damage of PV inverter under different mission profiles and different sampling periods is studied, and the influence of fundamental frequency and low frequency junction temperature on lifetime evaluation is analyzed, which improves the accuracy of lifetime evaluation of PV inverter. It is helpful to guide the regular maintenance of PV inverter and reduce economic losses.

Broad Comparison of Multilevel Inverter Topologies Operating in Hostile Environments: DC Transmission Applicability and Feasibility

Especially in the mining industry, pulsewidth modulation voltage source converters driving induction motors located far away are often present. In this case, due to the long cable used for the converter-to-motor connection, several unwanted high-frequency phenomena are generated. In this context, a new configuration for motor drive systems was proposed, in which the rectifier is kept in its original position and the inverter bridge is installed close to the motor terminals, being the long cable used as a dc transmission line. Since this environment is always more hostile and can compromise the inverter lifetime, new concerns regarding the system reliability arise, despite the various technical-economic advantages of this new configuration. In this way, this article presents a comprehensive comparison of commercially widely accepted multilevel inverter topologies, searching for the best technical features for the aforementioned dc transmission applicability/feasibility. Simulations were performed assessing several essential quantities/indexes, with a major focus on reliability. Then, a discussion was made seeking those sets that could minimize the implementation costs and improve the system reliability, concerning the insulated gate bipolar transistor (IGBTs) and the metalized film and aluminum electrolytic capacitors of the dc link.

Analysis and Development of a Modular Fault‐Tolerant Multistring Power Converter for Solar Photovoltaic Applications

The increasing solar photovoltaic (PV) generation highlights the importance of PV systems’ scalability, reliability, and cost reduction. Herein, a modular fault‐tolerant PV multistring inverter to address this challenge is proposed. The proposed inverter features a modular dc‐dc conversion stage and a dc–ac conversion stage. This configuration allows scaling the inverter power rating by simply increasing the number of PV strings, associated dc‐dc modules, and dc–ac‐stage heatsink size and output‐filter inductances’ current rating. The fault‐tolerant capability allows for tolerating a first‐switch open‐circuit fault on either stage and continuing operation. This property allows increasing by half the inverter lifetime compared with nonfault‐tolerant solutions (dismissing inverter reparation and degraded mode of operation), with a low impact on the cost increase (3–7%) and an efficiency reduction after a fault occurs of only 0.33–1%, depending on the module count and fault localization. A generalized reliability assessment demonstrates that lifetime increase is achieved regardless of the number of modules. Additionally, it allows reducing the operation and maintenance costs and revenue losses due to unscheduled system shutdowns. To validate the proposed inverter, a lab–scale prototype with two modules is tested under emulated faults, validating the feasibility of the proposed inverter.

Discussion on “Mitigation of Fault Induced Delayed Voltage Recovery (FIDVR) by PV-STATCOM”

The authors of [1] presented a novel controller for PV-STATCOM. The theory posits dynamic modulation of PV inverters’ active/reactive power through non-unitary power factor operation. The proposed approach is applied to mitigate the effects of fault-induced delayed voltage recovery (FIDVR) experienced in power systems with high penetration of solar PVs and induction motor loads. The structure of the proposed control algorithm is based on 4 modes: 1) normal operation, 2) active power control, 3) reactive power control, and 4) ramp-up active power process. The methodology is tested and comprehensively validated on a radial distribution network (RDN) for numerous scenarios of LLL-G faults, X/R ratios, and night-time operation. For clarity, the authors’ insights on the following technical points are appreciated: 1)The authors meticulously adhered to many standards (IEEE std. 1547-2018, German grid code - BDEW and NERC) to formulate the PV-STATCOM and RDNs’ operational constraints. As per the IEEE std. 1547-2018, the PV inverter design is recommended to be oversized by 11% to address numerous operational challenges [2]. Did the authors consider this standard for the solar farm placed at Bus 3 of the RDN as depicted in Fig. 1? 2)In [Section IV-A (3 and 4)], the authors introduced the values of variables “$k_2$” and “$k_1$” as 1.1 and 0.96 that were used in Mode 2 and Mode 3 for active and reactive power control of the PV-STATCOM respectively as depicted in Fig. 2. What is the selection criteria and/or the range(s) of these variables? Will these values be the same under different RDN scenarios or different RDN networks (for instance, IEEE 34 feeder test system)? 3)In [Section VII], the authors comprehensively presented in-depth analytical case studies for the proposed PV-STATCOM. Most of these studies considered only a single solar farm. Practically, the active-reactive power coordination strategies through PV inverters mostly consider high PV penetration (at each bus) in RDNs [3]. Therefore, how will the proposed PV-STATCOM framework coordinate with more than one solar farm? 4)In [Section VII-E], the author validated the economical dominance of the proposed PV-STATCOM over conventional STATCOM in terms of equivalent size. Nevertheless, the operation of PV inverters as STATCOM negatively affects the inverter lifetime and hence impacts their economical significance [4]. In this respect, is the inverter of the PV-STATCOM economically dominant for long-term operation as well? 5)In [Section VII-G], the authors presented 5 cases to study the voltage recovery rate of the proposed PV-STATCOM based on different fault locations. These faults are LLL-G (for 100 ms) induced at various distances from the substation and the PV solar farm, high voltage side, and low voltage side of the 138/12.6 kV transformer. Considering these 5 cases, will the obtained recovery time be different if the PV-STATCOM was placed at different bus of the study system considered. In other words, is the placement of PV-STATCOM optimal? 6)Finally, the authors proposed a novel application of PV-STATCOM in the field of PV-integrated power network. Voltage stability requirement is one of the key parameters that affects the permissibility of integrating high-scale, inertia-less, and unpredictable PVs in a power network [5]. Therefore, with the proposed PV-STATCOM configuration, what is the maximum achievable hosting capacity of the RDN under consideration?

Minimization of leakage current in a maximum boost control impedance source transformer-less inverter

The solar energy is utilized the most for a decade and the grid connected inverter is necessary for the distribution systems as the grid connected inverter will performances as in interface between the renewable solar energy source and the distribution end. However, due to the existence of magnetizing current in the transformer, the lower order harmonics in the grid current is high in PV systems. In addition, the efficiency of the system and inverter lifetime is reduced due to the usage of high volume capacitance. To overcome this issue, the transformer-less inverter is used in grid-tied PV system where the size and weight is reduced which results in reduction of cost and improve the efficiency of system. However, the leakage current is a major issue needs to be addressed which is minimized by Galvanic isolation methods in the transformer less photovoltaic (PV) inverters. In this project, the performance of the boosting H5 topology is proposed theoretically and analysed with validated simulation and experimental results. It helps in choosing and providing the best design principles.

Reliability-based trade-off analysis of reactive power capability in PV inverters under different sizing ratio

Due to the intermittent characteristic of solar irradiance, photovoltaic (PV) inverters usually operate below rated power conditions. In this scenario, commercial PV inverters can be used to provide ancillary services, such as reactive power compensation. On the other hand, over-sizing PV inverters by increasing the number of installed PV panels can increase the generated energy during low irradiance conditions. Despite the advantages, both approaches can increase the PV inverter wear-out, leading to early failures. The trade-off between reactive power compensation and lifetime consumption under different inverter sizing ratios (ISR) was not previously addressed in the literature. Hence, this paper proposes to evaluate the system-level reliability of a single-phase two-stage PV inverter performing reactive power compensation. The analysis is carried out from three different mission profiles (Aalborg, Goiânia, and Izaña). The thermal loading on the inverter components is translated to lifetime prediction. The results from Goiânia show that the PV inverter lifetime is reduced from 22.6 to 6.2 years when compensating reactive power. In addition, this reduction is observed in all three regions, going from 40.8 to 12.4 years and 10 to 4.4 years, for Aalborg and Izaña, respectively. To improve the lifetime, a reactive power capability factor QR is applied to the maximum reactive power condition. The unreliability map is presented as a tool to match the inverter sizing ratio with reactive power capability in agreement with lifetime requirements. An economic analysis based on Levelized Cost of Electricity (LCOE) showed that the reactive power compensation increases the costs of the system installed in Goiânia with ISR = 100 % by 46.6 % in comparison with the conventional operation. These additional costs can be reduced if the reactive power is partially compensated.

Methodology for bondwire lifetime evaluation of multifunctional PV inverter during harmonic current compensation

Multifunctional photovoltaic (PV) inverters have been described as a suitable power quality solution in modern power systems based on distributed generation. The basic idea is to use the PV inverter to perform ancillary services, such as harmonic current compensation (HCC). Nevertheless, this extra functionality may affect the lifetime consumption of the PV inverter. Indeed, only few works in literature discuss this topic, since the lifetime evaluation procedure during HCC is not straightforward. In addition, the traditional methodology currently available in the literature cannot be easily extended to HCC operation. Therefore, this work proposes a new lifetime prediction methodology which considers the effects of both fundamental and harmonic currents injected by the PV inverter. The proposed methodology can take into account all the additional power cycling due to any harmonic current combination. Furthermore, the lifetime evaluation is carried out considering the mission profiles of solar irradiance, ambient temperature, harmonic current amplitude and phase angle. The obtained results indicate that HCC increases the number of temperature cycles and may significantly affect the PV inverter lifetime. When the ratio between the harmonic and fundamental current amplitudes increases, the PV inverter lifetime consumption also increases. In addition, a strong dependence between lifetime consumption and the harmonic phase angle is observed for low order harmonics, such as 3rd and 5th harmonics.

Current-source 1-Ph inverter design for aircraft applications

PurposeThis paper aims to present an inverter with a current-source input for 400 Hz avionic systems to have a system which removes DC-link capacitors and presents a high efficiency.Design/methodology/approachA battery-powered DC link inductor generates a constant-current source. A single high-frequency switch is used to provide a sinusoidally modulated current before the inverter. The output of the switch is “unfolded” by a thyristor-based H-bridge inverter to generate an AC output current. The system uses a CL low-pass filter to obtain a 400 Hz pure sine wave by removing pulse width modulation components.FindingsSimulations and Typhoon HIL real-time experiments were performed with closed-loop control to validate the proposed inverter concept while meeting the critical standards of MIL-STD-704F.Originality/valueThis current source inverter topology is suitable for avionic systems that require 400 Hz output frequency. The topology uses small DC-link inductor and eliminates bulky capacitor which determines the inverter lifetime.

The Impact of PV Panel Positioning and Degradation on the PV Inverter Lifetime and Reliability

The photovoltaic (PV) inverter lifetime is affected by mission profiles, which include the solar irradiance and ambient temperature of the installation site. In previous research, the design for reliability approach has been used to evaluate the reliability of the PV inverter, where the solar irradiances have been measured on a fixed tilt and orientation angle. In most cases, the tilt is chosen to be the latitude angle and the orientation is facing south for maximum energy production throughout the year. However, the impact of the tilt and orientation of the PV array on the inverter lifetime has not been considered so far. The tradeoff between the PV energy yield and the inverter lifetime can be analyzed for different PV array positioning. This article thus evaluates the lifetime of the PV inverter with varying the tilt and orientation angle of PV panels, where the PV panel degradation rate is also taken into account. The evaluation is based on the mission profiles of Algiers, Algeria. The results reveal that orientation has a strong impact on the PV inverter loading and certain orientations result in high PV energy production and long lifetime of the PV inverter. It is also shown that the PV panel aging in Algeria has a significant impact on the lifetime estimation of the PV inverter for different orientations.

Pursuing computationally efficient wear-out prediction of PV inverters: The role of the mission profile resolution

Over the last decades, the connection of photovoltaic (PV) plants into the grid has increased. In this context, the analysis of the PV inverter reliability became a target of study for many researchers in the area. The solar irradiance and ambient temperature mission profiles are highly used in the literature to perform the PV inverter lifetime evaluation. However, the choice of the mission profile resolution is not straightforward. The increasing of the mission profile sampling time can reduce the consumed simulation time during the lifetime evaluation process. Nevertheless, the evaluation accuracy decreases. Therefore, this work analyzes the effect of the mission profile resolution for the semiconductor devices and the electrolytic capacitors, separately. A maximum allowed error equals 10% in the obtained lifetime consumption is assumed. For the case study analyzed in this work, the total processing time was reduced in 27.91% for a lifetime evaluation error lower than 9%.

Adaptive dc-link voltage control strategy to increase PV inverter lifetime

This work proposes an adaptive dc-link voltage strategy applied to a double-stage three-phase grid-connected PV inverter, in order to decrease the power devices and capacitors thermal stress, and increase the system-level reliability as a consequence. The objective is to reduce the dc-link voltage to the minimum value required to inject power into the grid. A system reliability analysis is made based on mission profiles from Brazil. The results show that the proposed technique has a positive impact on the system reliability, increasing the estimated lifetime by 75% when compared to the traditional fixed dc-link voltage strategy.

Lifetime evaluation of three-phase multifunctional PV inverters with reactive power compensation

The multifunctional operation of photovoltaic inverters consists in providing ancillary services to the grid, such as reactive power injection, harmonic current compensation, frequency regulation and others. These extra activities can cause higher electro-thermo-mechanical stress in the inverter components, affecting their reliability. Hence, this work aims to analyze the multifunctional inverters reliability when the injection of a real industry reactive power profile is performed. The evaluation has been carried out on a grid-connected three phase photovoltaic system, considering a mission profile from Denmark. An equivalent thermal model is used to estimate the power devices junction temperature. Furthermore, a lifetime model applied to the Palmgren-Miner's rule is used to evaluate the inverter lifetime consumption. Afterward, a statistical analysis simulates several power devices operation scenarios, for the cases with and without reactive power injection. Finally, the results show that the reactive power injection has a considerable impact on the inverter reliability, reducing by 3 and 1.5 times the lifetime estimation when this service is performed without power restrictions and considering the dynamic power saturation, respectively.

Reactive Power Cost From PV Inverters Considering Inverter Lifetime Assessment

Photovoltaic (PV) system inverters have been frequently utilized for reactive power support in the literature. Although the benefits of PV reactive power for the grid have been quantified, the costs incurred by the PV owner have largely been ignored. This paper combines the findings from power electronics research and power system economics to formulate the cost of reactive power from PV inverters, considering the inverter degradation due to the reactive power provision. One-year simulations with real weather and load data for the case of Singapore for different levels of PV penetration have been conducted. Subsequently, the benefits of local reactive power provision to the system and its effect on the lifetime of PV inverters were analyzed. It was found that the cost of inverter lifetime reduction is a significant part of the reactive power cost (more than 50% at lower PV penetration), but decreases at higher PV penetration when the reactive power support is distributed over more PV systems. Through comprehensive analysis, the feasible range for monetary incentives for PV reactive power support has been identified. The results from this paper can, therefore, be used as a foundation for future research, formulating regulations, and for market analysis.

How Adding a Battery to a Grid-Connected Photovoltaic System Can Increase its Economic Performance: A Comparison of Different Scenarios

The current work investigates how adding a battery of optimal capacity to a grid-connected photovoltaic (PV) system can improve its economic feasibility. Also, the effect of different parameters on the feasibility of the PV system was evaluated. The optimal battery capacity (OBC) was determined for different saving targets of the annual electricity consumption of the chosen building. For this aim, real electricity consumption data of a residential building in Landskrona, Sweden, was used as energy consumption profile. A Solar World SW325XL, which is a monocrystalline solar panel, was selected as PV panel. The calculations were performed under the metrological and economic conditions of southern Sweden. Different working parameters (WPs) were considered (prices of the battery, feed-in tariffs, and saving targets). The performed calculations show that the optimal battery capacity (OBC), in which the payback time (PBT) of the system is maximized, strongly depends on the WP. The proper selection of the battery can considerably increase the economic feasibility of the PV system in southern Sweden. However, in some cases, using battery can have a negative impact on the PBT of the system. The results show that the electricity price, the module price, the inverter price, and the inverter lifetime have the highest effect on the PBT.