Control and Design of Microgrid Components - Power Systems ...

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The only way to make sure that the frequency would be readjusted is to add a term to this equation and modify it as follows: ω ( P − P ) + Δ max i = ωo − o, i i ω m Eq. 3.5 If Δωmax = 0 when the output power is within limits then Eq.3.5 is effectively identical to Eq. 3.4. And if Δωmax is calculated so that it generates an appropriate amount of frequency change (in this example Δωmax= ω2-ω1, negative value), when limits are exceeded, then max power can be enforced. Eq. 3.4 is represented in Figure 3.16 by the “Unit 2” characteristic, while Eq. 3.5 is represented by the “Unit 2 Max” characteristic. This second characteristic is obtained from the first by adding a frequency offset Δωmax that translates down on the P-ω plane the original characteristic. Notice that since unit 1 does not reach maximum, then its offset will be calculated as zero and the original characteristic (Eq.3.4) is enforced at all times. Next section gives the details on how to generate this appropriate value of frequency offset to achieve maximum power limiting. Now the attention is to find the changes that need to be done when zero power limit is exceeded. It will be shown that this problem is the mirror image of the max power problem. Figure 3.17 shows the units operating in island at the frequency ω1, circles, with unit 1 injecting negative power. The output power of the units at this frequency is: P1(at ω1) = Pmin – Δpmin (Pmin = 0) P2(at ω1) = P2_1 ΔPmin is the excess power over the minimum limit that unit 1 is injecting. The ideal solution would be to operate at the frequency ω2, squares, where unit 1 is held at the zero power level while unit 2 injects the power it had before minus the amount of power that unit 1 is no longer adsorbing (ΔPmin). The output from the units at this new frequency are: P1(at ω2) = Pmin (Pmin = 0) P2(at ω2) = P2_1 - Δpmin Notice that the sum of the power injections is the same at either frequencies because the sum of all the loads has been assumed constant. The problem is that at frequency ω2, unit 1 is operating at a point that does not belong to the characteristic labeled “Unit 1”, but rather to the characteristic labeled “Unit 1 Min”. Respectively, the first one is generated by Eq. 3.4, while the second one is generated by the following equation: ω ( P − P ) + Δ min i = ωo − o, i i ω m Eq. 3.6 34
Unit 1 Min Unit 2 ω Unit 1 ΔPmin ω 2 Δωmin ΔPmin ω 1 ω o P P = Output Power Within Limits Pmax Figure 3.17 Effectively Limiting Pmin=0 on Output Power Control. Where in this case Δωmin=(ω2-ω1), positive number, in steady state. Δωmin=0 each time the power output is larger than zero to ensure that the behavior of the unit follows the desired characteristic of Eq. 3.4. Notice that Δωmin translates upwards the original characteristic enforced when no limit is exceeded. Next paragraphs deal on how to generate the offsets for maximum and minimum power excursions. It is possible to take advantage of two assumptions: 1) the prime mover will never give a fraction of extra power over P_max, but because of the storage interface, there is some extra power available transiently. Furthermore, the inverter is rated to be able to inject over P_max as stated in Section 3.4. Therefore it is assumed that there is enough stored energy available and silicon ratings to deliver it so that the inverter can transiently sustain overshoots of the value P_max for short periods of time. 2) as soon as the inverter is absorbing power, (P
Page 1 and 2: PSERC Control and Design of Microgr
Page 3 and 4: Information about this project For
Page 5 and 6: Executive Summary Economic, technol
Page 7 and 8: Table of Contents Chapter 1. Introd
Page 9 and 10: List of Figures Figure 1.1 Microgri
Page 11 and 12: List of Figures (continued) Figure
Page 13 and 14: Chapter 1. Introduction Distributed
Page 15 and 16: 1.2.2 Operation and Investment The
Page 17 and 18: Figure 1.1 Microgrid Architecture D
Page 19 and 20: Chapter 2. Static Switch The static
Page 21 and 22: ω ωo ω1 Preq Pgrid P Pload Figur
Page 23 and 24: 2.3 Synchronization Conditions The
Page 25 and 26: droop. The issue is that it is poss
Page 27 and 28: This synchronizing behavior is unac
Page 29 and 30: Figure 2.12 shows on the upper plot
Page 31 and 32: Chapter 3. Microsource Details This
Page 33 and 34: with different size. This control i
Page 35 and 36: u + _ K F ω o + _ ω o s P u ω o
Page 37 and 38: Q versus E Droop E req Q m Q _ + E
Page 39 and 40: currents from the microsources incr
Page 41 and 42: inverter ratings limits (in kVA) ca
Page 43 and 44: A 16 DG B 22 DG Static Switch C 8 D
Page 45: ω Unit 2 Max Unit 2 ω o Unit 1 ω
Page 49 and 50: positive value. When this value has
Page 51 and 52: needs of power. This solution would
Page 53 and 54: This expression is very similar to
Page 55 and 56: Li-Pmax < Fi < Li for unit ‘i’
Page 57 and 58: ω ω ω o Fo ω o Fo F F Unit Powe
Page 59 and 60: This control has been implemented i
Page 61 and 62: characteristic will coincide with t
Page 63 and 64: ating on the voltage output, establ
Page 65 and 66: Prime Mover DC Storage Voltage Sour
Page 67 and 68: linearity. A value of 30 degrees pr
Page 69 and 70: Figure 4.8 P and Q Plane Capability
Page 71 and 72: 4.4 System Ratings The inverter per
Page 73 and 74: Switching Sequence 145 146 136 236
Page 75 and 76: generated by the inverter: the VA r
Page 77 and 78: % of voltage unbalance = 100 maximu
Page 79 and 80: Figure 5.2 shows the plots for P,Q
Page 81 and 82: Figure 5.5 shows the measures of P
Page 83 and 84: Figure 5.7 One Unit Connected to th
Page 85 and 86: Microsources are connected to the l
Page 87 and 88: The transformer impedance can be se
Page 89 and 90: o r 1 = 0.3277 Ω = 0.0547 Ω x x 1
Page 91 and 92: Table 6.3 Load Data Summary. Rated
Page 93 and 94: The worse case scenario is represen
Page 95 and 96: The filtering is achieved by a low
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works with an internal voltage leve
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terminals to achieve each of the th
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Table 6.5 Lookup Table for Switchin
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Chapter 7. Microgrid Tests There ar
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Table 7.1 Summary of Experiments fo
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Table 7.2 Series Configuration Cont
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Figure 7.6 Control of F1 and F2, Fe
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Figure 7.10 Control of P1 and F2, F
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pu, but when it is fed from a remot
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Unit 1: P, Q, F, Frequency, Voltage
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7.4.1 Unit 1 (F), Unit 2 (F), Impor
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Import From Grid, Setpoints are 10%
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Island, Setpoints are 10% and 90% o
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7.4.2 Unit 1 (F), Unit 2 (F), Expor
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Export to Grid, Setpoints are 10% a
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7.4.3 Unit 1 (F), Unit 2 (P), Impor
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7.4.4 Unit 1 (F), Unit 2 (P), Expor
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Chapter 8. Conclusions This work sh
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[14] Lasseter, R.,” Microgrids,
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