Design of RPFC for Power Quality Improvement in Railway Power System using Fuzzy logic Controller

This paper is to create Power Quality in electric Railway systems with the assistance of Fuzzy Logic controller. Concentrating on the cargo prepare prevailing electrical railroad power system (ERPS) blended with air conditioning dc and air conditioning dc-air conditioning trains (its power factorε[0.70,0.84]), this paper proposes a power factor situated railroad power flow controller (RPFC) for the power quality improvement of ERPS. In this paper the thorough relationship of the primary power factor, converter limit, and the two phase load currents are introduced. By this technique we can likewise control the power flow trade between the grid and the load, with the goal that instantaneous active and reactive power is maintain constant. Moreover, as the main commitment of this paper, the ideal remunerating procedure suited the irregular varied two phase loads is broke down and planned based on a genuine footing substation, for the reasons for fulfilling the power quality standard, improving RPFC's control adaptability, and diminishing converter's ability. Here we are utilizing the fuzzy controller contrasted with different controllers i.e. The fuzzy controller is the most reasonable for the human basic leadership component, giving the operation of an electronic system with choices of specialists. What's more, utilizing the fuzzy controller for a nonlinear system takes into account a decrease of indeterminate impacts in the system control and enhances the effectiveness. By utilizing simulation results we can examine the improvement of the power quality in electric railroad systems utilizing fuzzy logic controller.

performance of traction units and imposes a capacity limit on the system. Harmonic distortion can cause damage to traction units, particularly motors [2]. Rail systems can cause harmonic distortion and voltage unbalance on the local distribution network. The harmonic distortion is caused by the non linear currents drawn by the railway system and in DC systems by rectifying substations. Voltage unbalance is present in AC systems, where the rail system draws large currents from a single phase of the supply. To additionally enhance RPFC's ability usage capacity and control adaptability in both outlining and working stages in cargo prepare overwhelming ERPS, in this paper, we will center around the arrangement of the accompanying perspectives: 1) Establishing the connection between the primary PF with RPFC's remunerating limit; the converter's ability can be adaptably composed by modifying the primary PF. 2) In the commence of limiting RPFC's ability for a given PF, considering an ideal control system to diminishing NSC and NSV in a satisfactory level.
3) The proposed control procedure ought not exclusively be connected in the basic single phase ERPS, yet in addition in the vital regular utilized two phase system (see Fig.1). This paper is sorted out as takes after, the mathematical model of the RPFC coordinated two phase ERPS is displayed in Section II. In the introduce of relief NSC, as the main commitment of this paper, Section III gives the PF situated ideal pay system for RPFC. Simulation are given in Section IV and V. Segment VI is the conclusion.

Mathematical model of RPFC
The frame-ABC by the V/v transformer's primary three phase voltage VA, VB, and VC (1) where Vp is the root mean square (RMS) value of VA, VB, and VC. From Fig. 2, we define the PF in phase-A, B, and C, i.e., PFA~PFC as: Where , φk>0 means that the present slacks the voltage, generally, the present leads the voltage (k=a, b, c). It can be seen from Figs. 1 and 2 that, the output currents Iα and I β of the V/v transformer in outline pα qα and outline pβ qβ (see Fig.2) can be Where, subscript "p" and "q" speaks to the active and reactive component of the relating variable in outline pαqα or outline pβ qβ, separately. Furthermore, Fig. 2 additionally demonstrates that the relationship of the p, q components of Iα and Iβ in outline pα qα and pβ qβ fulfill: I αq =I αp tan δ α =(I Lαp -I Cαp ) tan δ α I βq =I βp tan δ β =(I Lβp -I Cβp ) tan δ β (4) Note: for V/v transformer, Δα=30° , Δβ=90°. Disregarding the converter's losses, and accepting Vα=Vβ, the active power adjust of the consecutive converter can lead the consequence of: Then again, Fig. 2 shows that Iγ's phase point Θγ in outline ABC fulfil θ γ = 120°-∅ c or tan θ γ =tan( 120°-∅ c ).
Based on kirchhoff's law , I α , I β , I γ in frame ABC I α ABC ,  (7), the genuine and nonexistent piece of -Iγ, Term-I and Term-II, can be computed as I αp cos ∆ α + I αq sin ∆ α + I βp cos ∆ β + I βq sin ∆ β -I αp sin ∆ α + I αq cos ∆ α -I βp sin ∆ β + I βq cos ∆ β (9) Substituting (9) into (6), and considering the expressions of Iα p, Iαq, Iβp, and Iβq in (3)-(5), the relationship of Icαp with the two phase load active currents ILαp and ILβp can be calculated as Re-substituting (10) into (3)-(5), the remunerating currents of RPFC can be acquired as Increasing the feeder voltage Vα or Vβ in the two sides of (11), RPFC's remunerating power in phase α and β, i.e., Pcα, Qcα and Pcβ, Qcβ, can be ascertained as P Cα =µ -µ Where, PLα and PLβ are the load's active power in phase α and β. It can be seen from (12), in light of the fact that Δα, Δβ can be pre-acquired for a specific sort of a transformer (e.g., the V/v transformer and other sort of the adjust transformers [35], [36]), μα and μβ are just dictated by PFA~PFC or φa~φc [see (10) and (2)]. Henceforth, the active and reactive power of the RPFC can be adaptably balanced by controlling the primary three phase power factors, if the PFs of the two phase loads are pre-ascertained [see φLα and φLβ in (12)], which will be talked about later on.
Where PF* is the primary reference power factor. It can be observed from Fig. 2 that Iα, Iβ, and Iγ (or IA, IB, and IC) may leads or slacks VA, VB, and VC, individually, which means eight (i.e., 8=23) conceivable combination models with positive or negative esteem are existed in φa, φb, and φc. In addition, Fig. 2 additionally demonstrates the reactive power of converter-α is bigger than the one created by converter-β (i.e., Icαq>Icβq), to lessen the VAlimit of converter-α, Iα must be confined slacking than VA (i.e., φa>0), so the over eight conceivable combination models of φa~φc will decline into four profitable hopefuls, which are recorded in Table I (i.e., Model-2 to -5).

B. Compensating Capacity Analysis:
The VA-capacity SRPFC of the RPFC is: Substituting (12) into (14), the RPFC's VAlimit in the five repaying model recorded in Table I

C.The NSC Mitigation Ability Analysis
But of remunerating reactive power, alleviation of the NSC is another motivation behind RPFC. In other words, a satisfactory repaying technique ought to limit SRPFC, as well as has the obligation to diminish NSC inside a satisfactory level. iThe iNSC iMitigation iAbility iAnalysis i iFig i4.4: iThe icurves iof iIunb ivs iPF* iof iModel-1~5 Combing (7)-(8), the primary positive and negative sequence currents, I+ and I-, can be deduced by where ξ=∠120°, N=VsN/VfN is the turn's ratio of the main transformer (VsN and VfN are the grid and feeder normal line voltage respectively; as shown in Fig. 1).
i iFig i4.5: iThe ioptimal icompensating istrategy iof iconsidering ithe iNSC isuppressing iability. i i ( (17( From (13), (17), and Table I, the relationship of Iunb and PF* of Model-1~ 5 are shown in Fig. 4 and Fig. 3 (a), we can observe that,however the limit surfaces of Model-3 and 5 are close[ Fig. 3 (a)], the NSC stifling capacity of Model-3 issuperior to that of Model-5 (Fig. 4). It demonstratesthat, if Model-5 is substituted by Model-3, RPFC canshow signs of improvement NSC stifling capacitywith nearly has a similar VA limit of Model-5. In other words, the remunerating procedure joined of Model-2, 4, and 3 has higher exhaustive execution than the one consolidated by Model-2, 4, and 5. So the certified OCS ought to be adjusted from Fig. 3

D. Negative Sequence Standard Consideration
From (16), the primary NSC I-can be calculated as: The negative sequence capacity S-in the primary side is Considering the Chinese national standard of the negative sequence component is Where V -and V+ are the primary negative and positive voltages, Sd is the short out limit of the footing substation.
The negative sequence prerequisite of the proposed system can be figured by joining (20) and (21), i.e., Fig. 7 gives the two phase loads' distribution graph of a genuine V/v transformer based footing substation (see Table II). The measurement results of Fig. 7 demonstrate that right around 95.2% of the loadpoints are situated in the rectangle zone of CEDO, where the likelihood of the points distributed in ΔACO and ΔABO (or ΔAB1O, or ΔAB2O) is around 85%. Besides, we can likewise locate that, surpassing half of the load points are situated at stake OC and OD (take note of: a few points are covered on these two lines), which means the V/v transformer's ability usage ratio can be additionally improved in a vast potential. Based on the above measurement results, our consideration ought to be centered around the loads situated in CEDO and its limits. The surface of S -versus PLα and PLβ (inside rectangle region of CEDO appeared in Fig. 7) can be gotten based on (20) and the Sd given in TableII, which is appeared in Fig.   8. From the state of thesurfaces appeared in Fig. 8, it can be reasoned that the maximum S -of Model-3, 2, and 4 happens on the point A, B, and E for any given PF*, individually. The surface of S -vs. PLα and PLβ (within rectangle area of CEDO shown in Fig. 7) can be obtained based on (20) and the Sd given in Table II, which is shown in Fig. 8. From the shape of the surfaces shown in Fig. 8, it can be concluded that the maximum S -of Model-3, 2, and 4 occurs on the point A, B, and E for any given PF*, respectively (note: PF*=0.95) Fig. 9 gives the relationship of the S-in A, B, and E, i.e., the maximum S -, S-max, with PF* for this footing substation in Model-2~4. Clearly, the Sblocking capacity of Model-4 is greatly improved than that of Model-3 and 2, however the last's S-max diminishes when PF* turns out to be extensive. Fig. 9 additionally demonstrates that the maximum negative sequence powers controlled by OSC are not as much as the authorization esteem 9.72MVA (i.e., 486MVA×2%), which means the Chinese national standard can be fulfilled when PF* is set inside 0.9 to 0.99. It ought to be commented here is that, if the authorization line of Scrosses with other maximum Sline of Model-2 or 3 appeared in Fig. 9, the correct hand abscissa of that intersection point ought to be chosen as the important PF*, on the grounds that the left one will lead Vunb out of the utmost. The capacity utilization capability of RPFC should also be included in our concerning scope. From Fig. 10, the maximum SRPFC's (i.e., SRPFCmax) reducing ratio decreases heavily when PF*>0.95 [note: the maximum SRPFC point in PLα-PLβ panel (i.e., Fig. 7) is labeled in Fig. 10]. Besides, RPFC's designing capacity SRPFCdesign's decreasing ratio also shows relatively large value (>23.43%) when PF*ϵ[0.9,0.95], it increases when PF*→0.9 [note: ① SRPFCdesign=2×max{Sconveter-α, Sconveter-β}, this is because IGBT is a voltage sensitive device and the dc-link voltages of converter-α and β are the same; ② Eα in Fig.10 means the maximum converter capacity belongs to converter-α located in point E]. Considering cost-efficiency, PF* can be selected from 0.9 to 0.95 for this traction substation.

E.Control Strategy Realization
The control system of the RPFC is plotted in Fig. 11. A few particulars ought to be made for it: The FFT strategy or the instantaneous reactive power theory [37] can be utilized for the estimation of the load's active and reactive power in the "PQ block", while the relative resounding controller (PS) is received as the present controller for its great following capacity in sing phase system. For the adjustment of vdc in the back-to -back system, rather than the figured Pcα, the genuine Pcα is produced by the dc-link voltage PI controller in converter-α. Furthermore, more consideration must be paid on the acknowledgment of the "repaying power figuring" block, and the accompanying four steps can help us to get the objective: 1) According the deliberate two phase loads (e.g., Fig. 7), Sd, and the exhibited slops of OA and OB appeared in Fig. 6, the PF*'s directing extent can be resolved for the motivations behind fulfilling the negative sequence's standard (e.g., Fig. 9) and having generally little limit (e.g., Fig. 10). 2) Based on the pre-set PF* (e.g., PF*ϵ[0.9,0.95]), the inclines of OA and OB can be resolved from Fig. 6. The remunerating model of OCS can be controlled by the load point's area in the load distribution panel appeared in Fig. 5 or 7, which can be reasoned by distinguishing 4) If the repaying model is gotten from step 3, φa, φb, and φc can be figured from Table I and (13), so as μα and μβ [see (10)]. Consequently, the repaying active and reactive power of RPFC can be at long last gotten from (12), [note: in (12), φLα=arctan(QLα/PLα), φLβ=arctan(QLβ/PLβ)].

IV. FUZZY LOGIC CONTROLLER:
In FLC, basic control action is determined by a set of linguistic rules. These rules are determined by the system. Since numerical variables are converted into linguistic variables, mathematical modeling of the system is not required in FC.
The FLC comprises of three parts: fuzzification, interference engine and defuzzification. The FC is characterized as i. seven fuzzy sets for each input and output. ii. Triangular membership functions for simplicity. iii. Fuzzification using continuous universe of discourse. iv. Implication using Mamdani's, 'min' operator. v. Defuzzification using the height method.   (24) Where α is self-adjustable factor which can regulate the whole operation. E is the error of the system, C is the change in error and u is the control variable. A large value of error E indicates that given system is not in the balanced state. If the system is unbalanced, the controller should enlarge its control variables to balance the system as early as possible. One the other hand, small value of the error E indicates that the system is near to balanced state.

V. SIMULATION RESULTS THE PARAMETERS OF THE ISOLATION TRANSFORMER AND RPFC
The VA-capacity of IT 5MVA Short circuit impendence of IT 21% IT's turn's ratio 27.5KV:27.5KV The dc-link voltage of RPFC 51.15KV

Case 1: PI CONTROLLER
The waveforms represents the primary three phase currents, power factor, voltage and current unbalance ratio, capacity of RPFC when it is driving a constant load with variable power factor.It demonstrates the three phase load changes such that the primary PF move along PF* with the satisfactory execution. Also, iA, iB, and iC have a tendency to be the adjusted three phase currents when PF* wound up bigger.The waveforms in the condition of variable PF* with constant load. Fig 5.3 represents the Primary three phase currents. b) The waveforms represents the primary three phase currents, power factor, voltage and current unbalance ratio, capacity of RPFC when it is driving variable load with constant power factor.It demonstrates the three phase load changes such that the primary PF move along PF* wth the satisfactory execution. Also, iA, iB, and iC have a tendency to be the adjusted three phase currents when PF* wound up bigger. The waveforms in the condition of variable PF* with constant load. Fig 5.7 represents the Primary three phase currents. Fig 5.8 represents the PF* and PF. Fig 5.9 represents the Voltage's and current's unbalanced ratio. Fig  5.10 represents the Capacity of RPFC

Case 2 : FUZZY CONTROLLER
a) The waveforms represents such that the primary three phase currents, power factor, voltage and current unbalance ratio, capacity of RPFC when it is driving a constant load with variable power factor of a FUZZY based controller .It demonstrates the three phase load changes such that the primary PF move along PF* with the satisfactory execution. Also, iA, iB, and iC have a tendency to be the adjusted three phase currents when PF* wound up bigger.
The waveforms in the condition of variable PF* with constant load. Fig 5.11 represents the Primary three phase currents. Fig 5.12 represents the PF* and PF. Fig 5.13 represents the Voltage's and current's unbalanced ratio. Fig  5.14 represents the Capacity of RPFC The waveforms represents such that the primary three phase currents, power factor, voltage and current unbalance ratio, capacity of RPFC when it is driving a variable load with constant power factor of a FUZZY based controller .It demonstrates the three phase load changes such that the primary PF move along PF* wth the satisfactory execution. Also, iA, iB, and iC have a tendency to be the adjusted three phase currents when PF* wound up bigger. The waveforms in the condition of variable PF* with constant load. Fig 5.15 represents the Primary three phase currents. Fig 5.16 represents the PF* and PF. Fig 5.17 represents the Voltage's and current's unbalanced ratio. Fig  5.18 represents the Capacity of RPFC In the start of fulfilling the norms of the reactive power and NSV, this paper gives an ideal control technique for the PQ improvement, control adaptability upgrade, and the lessening of RPFC's remunerating and planning limit in two or single phase RPFC incorporated ERPS. In other words, this control technique can influence the system to have an attractive high cost-effectiveness in two or single phase footing load conditions.