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

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enforces the slope whenever it lays inside the window, otherwise the bound of the window becomes the characteristic itself. When on this vertical portion, the frequency could assume any value demanded by the remaining sources, shown in Figure 3.27 with the arrows on the characteristic. As the window moves because of changing loading conditions, a different portion of the slope would be enforced, while the vertical parts of the characteristic would have rigidly translated. This enforces the maximum and minimum power limits. The fact that this approach uses a fixed slope (Eq. 3.3) ensures that the frequency will not exceed limits as long as power stays within limits (Figure 3.15). Figure 3.28 shows the full control diagram, where it is possible to see that the blocks on the upper part belong to the original control structure (as shown in Figure 3.11). The blocks that generate the frequency offsets are in the lower part and represent the change needed to enforce power limits. ω o P max F o F + _ -m 0 + + + ω 1 δ V (t) s + errP max Ki s Δ ω max P + P = 0 min errP min 0 Ki s Δ ω min Figure 3.28 Control Diagram to Enforce Limits with Feeder Flow Control. The equation that governs this control has been formally changed from Eq. 3.4 to an equation that keeps into account of changes made in Eq. 3.5 and Eq. 3.6 when respectively dealing with maximum and minimum power limits. The final equation is: ω ( F − F ) + Δω max+ Δ min i = ωo + o, i i ω m Eq. 3.12 The quantities Δωmax and Δωmin are added to the frequency as calculated in Eq. 3.8. Both quantities are zero when the unit operates within power limits. When Pmax is exceeded, Δωmax becomes negative (never positive) to enforce the limit. When Pmin = 0 is exceeded, then Δωmin becomes positive (never negative) to enforce the limit. 46
This control has been implemented in simulation and hardware and the results obtained prove the effectiveness of the control design. The control is tested with all known events that can cause either limit to be exceeded: the hardware results can be all found in Chapter 7. 3.2.3 Mixed System This Section describes the steady state characteristics for a mixed system consisting of some units that regulate their output power and some other units that control the feeder power flow. Figure 3.29 shows the steady state characteristics of the controlled power versus frequency. Notice that the controlled power could be output power, P, or feeder flow, F. They are both active powers and have dimensions of kW: that is why it is possible to plot them on the same horizontal axis, “P and F”. On this plane, the sign of the slope is a giveaway of the control being used: negative slope implies unit output control, while positive slope implies feeder flow control. ωo + Δω ω ω o F 01 P 02 ω 1 ωo − Δω F, P Pmax Figure 3.29 Characteristics on the ”Regulated Power vs. ω” Plane for a Mixed System. During grid connection the setpoints Po1 and Fo2 are tracked because the frequency is locked to the nominal value, ωo, by the utility. In island the solution will depend on the geometrical configuration of the units on the feeders. This is because when regulating feeder flow the location of the units determines the solution in island, as seen in Figure 3.23 and Figure 3.24. Then, as soon as there is at least one unit regulating feeder flow in the system, the solution in island will depend on the location of the units. Figure 3.30 shows a possible configuration. The combinations of different configurations could swell to a large number even with few units. For instance, with two only units (one controlling P, other F to have mixed system) there are three independent configurations. The first is with both units on the same feeder, unit controlling F nearest to the utility (as in Figure 3.30), the other 47
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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 and 46: ω Unit 2 Max Unit 2 ω o Unit 1 ω
Page 47 and 48: Unit 1 Min Unit 2 ω Unit 1 ΔPmin
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: ω ω ω o Fo ω o Fo F F Unit Powe
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
Page 97 and 98: works with an internal voltage leve
Page 99 and 100: terminals to achieve each of the th
Page 101 and 102: Table 6.5 Lookup Table for Switchin
Page 103 and 104: Chapter 7. Microgrid Tests There ar
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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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