Voltage Optimization in PV-Rich Distribution Networks—A Review

Probably not a substantial claim: may not pass S3 (load-bearing). May combine two claims.

To solve such complex optimization problems, some authors use analytical methods and some use computational ones.

“To solve such complex optimization problems, some authors use analytical methods and some use computational ones.”

Probably not a substantial claim: may not pass S3 (load-bearing), S4 (based).

Almost all IEEE test network models have radial topology.

“Almost all have radial topology.”

Probably not a substantial claim: may not pass S3 (load-bearing).

The standard test model [70] is modified according to balance.

“For instance, the standard test model [70] is modified according to balance.”

• cites [70]Not matched

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Transformations into a linear form such as linear programming or mixed-integer linear programming are very rare due to the quadratic function of voltage deviation and poor performance of DC power flows in distribution networks, where the R/X ratio is not as small as in transmission networks.

“Transformations into a linear form (LP or MILP) are very rare due to the nature of the problem, i.e., the quadratic function of voltage deviation and poor performance of DC power flows in the environment of the DN (ratio R/X is not as small as in the TN).”

• AssumptionRests on an assumption: The R/X ratio is high in distribution networks and low in transmission networks.

Probably not a substantial claim: may not pass S3 (load-bearing).

Besides AC power flow, the reviewed authors use two other formulation approaches: decoupled AC power flow and DC power flow.

“Besides AC power flow, the authors use two other formulation approaches: decoupled AC power flow [49] and DC power flow [50].”

• cites [49]Not matched

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The quote only partly states this claim.

The most commonly used computational intelligence methods are genetic algorithms and particle swarm optimization.

“The most commonly used methods are GA [37,57,62,83] and PSO [64,82,85,88].”

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• AssumptionRests on an assumption: The selected bibliographic databases, IEEE Xplore, ScienceDirect, and MDPI, cover the relevant scientific literature on optimal power flow for voltage optimization in photovoltaic-rich distribution networks.

Probably not a substantial claim: may not pass S3 (load-bearing). May combine two claims.

The most commonly used analytical methods for linear optimal power flow are simplex methods, sequential linear programming, and interior point methods.

“The most commonly used analytical methods for linear OPF are the well-developed simplex methods [93], sequential linear programming (SLP) [94], and interior point methods (IPMs) [95].”

• cites [93]Not matched

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• AssumptionRests on an assumption: The selected bibliographic databases, IEEE Xplore, ScienceDirect, and MDPI, cover the relevant scientific literature on optimal power flow for voltage optimization in photovoltaic-rich distribution networks.

Probably not a substantial claim: may not pass S3 (load-bearing).

The most common test network models used in literature are IEEE test network models, including IEEE-13, IEEE-15, IEEE-33, IEEE-34, IEEE-37, IEEE-69, IEEE-123, and IEEE-8500 bus models.

“The most common test network models used in literature represent IEEE test network models which, depending on the number of buses, can be IEEE-13 bus, IEEE-15 bus, IEEE-33 bus, IEEE-34 bus, IEEE-37 bus, IEEE-69 bus, IEEE-123 bus, and IEEE-8500 bus.”

Probably not a substantial claim: may not pass S3 (load-bearing).

Some authors modify standard test models according to the processed problem.

“According to the processed problem, some authors modify standard test models.”

Probably not a substantial claim: may not pass S3 (load-bearing), S4 (based). May combine two claims.

Unbalanced networks are mostly low voltage and belong to real-life models.

“Unbalanced networks are mostly low voltage and belong to real-life models.”

Probably not a substantial claim: may not pass S3 (load-bearing).

A decision about which solution method would be used depends on the objective and mathematical formulation.

“According to Figure 10, a decision about which solution method would be used depends on the objective and mathematical formulation.”

• AssumptionRests on an assumption: The selected bibliographic databases, IEEE Xplore, ScienceDirect, and MDPI, cover the relevant scientific literature on optimal power flow for voltage optimization in photovoltaic-rich distribution networks.

Probably not a substantial claim: may not pass S3 (load-bearing).

The authors in [72] reduce an unbalanced system to a balanced assuming that voltage magnitudes between phases are analogous and phase angles on nodes are not drastic.

“For instance, the authors in [72] reduce an unbalanced system to a balanced assuming that voltage magnitudes between phases are analogous and phase angles on nodes are not drastic.”

• cites [72]Not matched

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May combine two claims.

In volt-VAR control mode, the voltage values are lower than at unit power factor and are in the narrower range of 0.992 p.u. to 1.005 p.u.

“In the volt-VAR control mode, the voltage values are lower than the unit power factor and are in the narrower range of 0.992 p.u. to 1.005 p.u.”

Probably not a substantial claim: may not pass S3 (load-bearing).

According to the reviewed literature, more authors utilize standard test network models IEEE-33 bus, IEEE-69 bus, and IEEE-123 bus node due to their flexibility and robustness.

“According to the reviewed literature, more authors utilize standard test network models IEEE-33 bus, IEEE-69 bus, and IEEE-123 bus node due to their flexibility and robustness.”

May combine two claims.

Besides photovoltaic inverter reactive power, other optimization variables include photovoltaic active power, on-load tap changer, capacitor bank, static compensator, reactive power from the substation, voltage regulators, charge/discharge rate of energy storage systems, electric vehicle active power, and shunt capacitor.

“Besides PV inverter reactive power, other variables include: (i) PV active power, (ii) OLTC, (iii) CB, (iv) static compensator, (v) reactive power from the substation, (vi) VRs, (vii) charge/discharge rate of ESS, (viii) EV active power, and (ix) SC.”

• AssumptionRests on an assumption: The selected bibliographic databases, IEEE Xplore, ScienceDirect, and MDPI, cover the relevant scientific literature on optimal power flow for voltage optimization in photovoltaic-rich distribution networks.

Probably not a substantial claim: may not pass S3 (load-bearing).

Real-life-based test network models represent urban residential feeders located in the US, China, Italy, Egypt, Australia, Ireland, and the UK.

“Real-life-based models represent urban residential feeders located in the US, China, Italy, Egypt, Australia, Ireland, and the UK.”

Probably not a substantial claim: may not pass S3 (load-bearing).

In some papers, hybrid methods are applied.

“In some papers, hybrid methods are applied.”

Probably not a substantial claim: may not pass S3 (load-bearing).

The voltage optimization problem is mostly described as the objective of voltage deviation minimization, that is, maintaining voltages within boundaries determined by grid codes.

“Furthermore, the voltage optimization problem is mostly described as the objective of voltage deviation (VD) minimization, i.e., maintaining voltages within boundaries determined by grid codes.”

Probably not a substantial claim: may not pass S3 (load-bearing). May combine two claims.

Other computational intelligence methods that appear in the literature are the sine-cosine algorithm, feasibility pump method, sparrow search algorithm, pattern search algorithm, and grey wolf optimization.

“Other computational intelligence methods that appear in the literature are the sine-cosine algorithm (SCA) [66], feasibility pump (FP) method [67], sparrow search algorithm (SSA) [74], pattern search algorithm [80], and grey wolf optimization (GWO) [81].”

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• AssumptionRests on an assumption: The selected bibliographic databases, IEEE Xplore, ScienceDirect, and MDPI, cover the relevant scientific literature on optimal power flow for voltage optimization in photovoltaic-rich distribution networks.

Probably not a substantial claim: may not pass S3 (load-bearing).

Recently, computational intelligence methods have been applied to solving optimal power flow problems.

“Recently, computational intelligence methods have been applied to solving OPF problems.”

• AssumptionRests on an assumption: The selected bibliographic databases, IEEE Xplore, ScienceDirect, and MDPI, cover the relevant scientific literature on optimal power flow for voltage optimization in photovoltaic-rich distribution networks.

Probably not a substantial claim: may not pass S3 (load-bearing).

Some authors propose a mixed-integer nonlinear formulation due to integer variables such as the OLTC tap setting.

“Additionally, some authors propose a mixed-integer nonlinear formulation due to integer variables such as the OLTC tap setting.”

May combine two claims.

Other objectives are rare and are used only in a few papers.

“Other objectives are rare and they are used only in a few papers.”

• Also stated in: § 5. Conclusions · plain

  “Other objectives are rare and they are used only in a few papers.”

May combine two claims.

DSO tries to reach the optimal operation point regarding several objectives, and the most commonly used ones are loss minimization together with voltage deviation minimization.

“DSO tries to reach the optimal operation point regarding several objectives and the most commonly used ones are loss minimization together with voltage deviation minimization.”

Probably not a substantial claim: may not pass S3 (load-bearing), S4 (based).

One trend in applying computational intelligence methods is using well-known power flow calculation tools to feed the computational intelligence method with multiple power flow solutions.

“One of the trends in applying computational intelligence methods is using well-known power flow calculation tools in order to feed the computational intelligence method with multiple power flow solutions.”

May combine two claims.

In multi-objective problems, VD is most combined with losses, but many other objectives also appear.

“In multi-objective problems, VD is most combined with losses, however, many other objectives also appear.”

May combine two claims.

Computational intelligence methods can solve complex optimization problems without transformation of the original formulation, but they require higher computational performance and more computational time.

“On the other hand, computational intelligence methods can solve complex optimization problems without the transformation of the original formulation but they required higher computational performance as well as more computational time.”

Probably not a substantial claim: may not pass S3 (load-bearing).

To apply an analytical method, the original problem must be transformed to a level it can solve.

“To apply the analytical method, it is necessary to perform a transformation of the original problem to a level that it can solve.”

May combine two claims.

The linear programming formulation uses the DC power flow approach, so both the objectives and the constraints are linear.

“The LP formulation uses the DC power flow approach, i.e., both the objectives and the constraints are linear.”

May combine two claims.

Some optimization variables are continuous and some are discrete, such as on-load tap changer tap settings, which affects the formulation of the optimal power flow problem and largely the choice of solution method.

“Some of the variables are continuous but some are discrete (such as OLTC tap settings), which will affect the formulation of the OPF problem (the appearance of integer variables) and largely the choice of the solution method.”

May combine two claims.

If multiple local optima exist, global optima cannot be guaranteed and the analytical method can get stuck in local optima.

“If multiple local optima exist, global optima cannot be guaranteed and the analytical method can stuck in local optima.”

May combine two claims.

Analytical methods can straightforwardly find an optimal solution, but there is no guarantee that the optimum is global.

“Analytical methods are able to straightforwardly find an optimal solution but there is no guarantee that the optimum is global.”

Probably not a substantial claim: may not pass S3 (load-bearing).

Computational intelligence methods have been developed to overcome the weak capabilities of analytical methods for solving global optimization.

“Computational intelligence methods have been developed to overcome the weak capabilities of analytical methods for solving global optimization [102].”

• cites [102]Not matched

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May combine two claims.

The imbalance in distribution networks is because the distribution network supplies unequal single-phase loads and contains unequal conductor interspace of three-phase segments.

“The reason for the imbalance is that the DN supplies unequal single-phase loads and contains unequal conductor interspace of threephase segments [49,50].”

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May combine two claims.

Due to modeling assumptions, linear programming is not adequate for problems such as minimizing power losses, and a global optimum cannot be guaranteed.

“However, due to the modeling assumptions, LP is not adequate for problems such as minimizing power losses, and a global optimum cannot be guaranteed.”

May combine two claims.

Distributed generation can both cause voltage violation in distribution networks and help solve voltage violation by managing active or reactive power, especially through reactive power management.

“While DG can cause voltage violation in the DN, the same DG can help solve the problem of voltage violation, for example by managing active or reactive power.This problem/solution principle is especially interesting in the case of reactive power management [7].”

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Probably not a substantial claim: may not pass S3 (load-bearing).

The optimal power flow concept was proposed in the early 1960s as an enhancement of economic dispatch to find the optimal solution for controlling variable settings under different constraints.

“The OPF concept was proposed in the early 1960s [43] as an enhancement of economic dispatch to find the optimal solution for controlling variable settings under different constraints.”

• cites [43]Not matched

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Probably not a substantial claim: may not pass S3 (load-bearing).

Photovoltaic systems are the main representative of renewable energy sources in distribution networks.

“When it comes to RESs in DNs, the main representative is a photovoltaic (PV) system [8,9].”

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Probably not a substantial claim: may not pass S3 (load-bearing).

One possible problem that can appear is the OPF application for unbalanced DNs.

“One possible problem that can appear is the OPF application for unbalanced DNs.”

May combine two claims.

Voltage rise is a major issue caused by prosumers and impacts distribution networks.

“A voltage rise is addressed as a major issue caused by prosumers and impacts DNs [2].”

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May combine two claims.

The volt-VAR control mode voltage values are more acceptable for distribution network operation because voltage deviation is smaller.

“These values are more acceptable for the operation of DN, i.e., voltage deviation is smaller.”

May combine two claims.

Compared to analytical methods, computational intelligence methods require hard computational effort and there is no guarantee of finding an optimal solution, so some expert knowledge of the system is needed.

“Compared to analytical methods, a hard computational effort is required and there is no guarantee of finding an optimal solution thus some expert knowledge of the system is needed.”

Probably not a substantial claim: may not pass S3 (load-bearing). May combine two claims.

Therefore, an unbalance between phases is low, and almost balanced.

“Therefore, an unbalance between phases is low, and almost balanced.”

May combine two claims.

Voltage control mechanisms that were once applicable in passive distribution networks become less valid, and new mechanisms are required.

“However, voltage control mechanisms that were once applicable in passive DNs become less valid and new mechanisms are required [4][5][6].”

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Probably not a substantial claim: may not pass S3 (load-bearing).

Analytical methods are well-developed and applicable in systems where the requirements of modeling accuracy are low.

“Analytical methods are well-developed and applicable in systems where the requirements of modeling accuracy are low.”

May combine two claims.

When analytical methods are used, the compromise regarding the transformation of the original problem into a standard one is present, but the analytical approach enables the straightforward method to find the optimum of a well-defined optimization problem, although special attention is required to determine whether a calculated optimum is local or global.

“When analytical methods are used, the compromise regarding the transformation of the original problem into a standard one is present but the analytical approach enables the straightforward method to find the optimum of a well-defined optimization problem (although special attention is required in order to determine whether a calculated optimum is local or global).”

Classified as probably not a substantial claim. May combine two claims.

Determining the optimal operating point of photovoltaic inverters imposes using optimization algorithms, with optimal power flow as a logical solution.

“Determining the optimal operating point of the PV inverters imposes using optimization algorithms from which the OPF are imposed as a logical solution.”

May combine two claims.

Inclusion of discrete variables in nonlinear programming results in mixed-integer nonlinear programming being the most realistic and accurate optimal power flow formulation, but also the most complex and difficult to solve.

“The inclusion of discrete variables (transformer tap settings, shunt capacitor settings, etc.) in NLP results in MINLP being the most realistic and accurate formulation of OPF, but also the most complex and difficult to solve.”

May combine two claims.

Unlike transmission networks, distribution networks are inherently unbalanced and more complex.

“Unlike TNs, DNs are inherently unbalanced and more complex [48].”

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Classified as probably not a substantial claim.

The distribution system operator is responsible for maintaining voltage within allowable limits for secure operation of distribution networks.

“The distribution system operator (DSO) is responsible for maintaining voltage within the allowable limits for the secure operation of DNs [3].”

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Probably not a substantial claim: may not pass S3 (load-bearing). May combine two claims.

Analytical methods require that a multi-objective problem transforms or scalarizes into a single-objective using weighting coefficients, which is not a straightforward procedure.

“Analytical methods require that a multi-objective (usually known as Pareto optimization) problem transforms (scalarizes) into a single-objective using weighting coefficients, which is not a straightforward procedure.”

Probably not a substantial claim: may not pass S4 (based). May combine two claims.

Some probabilistic OPF solutions are already created for the transmission system environment, but their replication in the distribution network (or microgrid) is not straightforward.

“Some probabilistic OPF solutions are already created for the transmission system environment but their replication in the distribution network (or microgrid) is not straightforward.”

May combine two claims.

Some optimization variables are continuous but some are discrete (such as OLTC tap settings), which will affect the formulation of the OPF problem (the appearance of integer variables) and largely the choice of the solution method.

“Some of the variables are continuous but some are discrete (such as OLTC tap settings), which will affect the formulation of the OPF problem (the appearance of integer variables) and largely the choice of the solution method.”

Probably not a substantial claim: may not pass S2 (checkable), S3 (load-bearing).

If OPF is regarded as part of the distribution energy management system (DEMS), the dominance of the multi-objective formulation of OPFs is logical.

“If OPF is regarded as a part of the distribution energy management system (DEMS), the dominance of the multi-objective formulation of OPFs is logical.”