6.1.2.1. PV monitoring

6.1.2.2. Wind power monitoring

6.1.2.3. Microturbine monitoring

6.1.2.4. Monitoring of other power sources

6.1.2.5. ES monitoring

6.1.2.6. Load monitoring

6.1.2.7. Overall monitoring

6.2.3.2. Frequency response characteristics of loads

$P_{\text{L}}=P_{\text{LN}}(a_0+a_1{f}_{*}+a_2{f}_{*}^2+\cdot \cdot \cdot +a_i{f}_{*}^i+\cdot \cdot \cdot +a_n{f}_{*}^n)$

(6.1)

where $f_{*}=f/f_{\text{N}}$, N refers to the rated condition, * is the per unit value, P_LN is the active power of load at the rated frequency, and a_i is the scaling factor.

$K_{{\text{L}}_{*}}=a_{1_{*}}=\frac{∆P_{\text{L}*}}{∆f_{*}}$

(6.2)

$\left\{\begin{array}{l}∆P_{{\text{L}}_{*}}=\frac{∆P}{P_{\text{L}\sum }}=\frac{∆P}{\sum P_{\text{L}i}}\\ ∆f_{*}=\frac{∆f}{f_{\text{N}}}=\frac{f^{(1)}-f^{(0)}}{f^{(0)}}\end{array}\right.$

(6.3)

$K_{\text{L}*}=\frac{∆P_{\text{L}*}}{∆f_{*}}=\frac{\left(\frac{P_{\text{qe}}-P_{\text{jh}}}{P_{\text{L}\Sigma }-P_{\text{jh}}}\right)}{\left(\frac{f^{(1)}-f^{(0)}}{f^{(0)}}\right)}$

(6.4)

$P_{\text{jh}}=P_{\text{qe}}-\frac{K_{{\text{L}}_{*}}(f^{(1)}-f^{(0)})(P_{\text{L}\sum }-P_{\text{qe}})}{f^{(0)}-K_{{\text{L}}_{*}}(f^{(1)}-f^{(0)})}$

(6.5)

$K_{\text{L}*}=\frac{\left(\frac{P_{\text{yy}}-P_{\text{qj}}}{P_{\text{L}\sum }-P_{\text{yy}}}\right)}{\left(\frac{f^{(1)}-f^{(0)}}{f^{(0)}}\right)}$

(6.6)

$P_{\text{qj}}=P_{\text{yy}}-\frac{K_{{\text{L}}_{*}}(f^{(1)}-f^{(0)})}{f^{(0)}}(P_{\text{L}\sum }-P_{\text{yy}})$

(6.7)

6.2.4.1. Power balance in grid-connected operation

$∆P^{(t)}=P_{\text{PCC}}^{(t)}-P_{\text{plan}}^{(t)}$

(6.8)

where $P_{\text{plan}}^{(t)}$ means the active power exchange setting value sent from the grid to the microgrid at the time of t, and $P_{\text{PCC}}^{(t)}$ the active power flowing through the PCC at the time of t.

6.2.4.2. Power balance during transition from grid-connected mode to islanded mode

$P_{\text{qe}}=P_{\text{PCC}}$

(6.9)

6.2.4.3. Power balance in islanded operation

Supposing that the power deficiency at a moment during islanded operation is P_qe, then $∆P_{\text{L}}\ast =P_{\text{qe}}/P_{\text{L}\Sigma }$. It can be inferred from Eq. (6.2) that

$P_{\text{qe}}=\frac{f^{(0)}-f^{(1)}}{f^{(0)}}\times K_{\text{L}*}{P}_{\text{L}\sum }$

(6.10)

$\left.\begin{array}{l}{P}_{\text{S}\Sigma }=\sum P_{\text{S}i}\\ P_{\text{SM}}=\sum P_{\text{Smax}–i}\end{array}\right\}$

(6.11)

b. If P_qe + P_S∑ ≤ 0, it indicates the ES is being charged, and if the charging power is greater than the power deficiency, reduce the charging power until $P_{\text{S}\Sigma }^{\text{'}}=P_{\text{S}\Sigma }^{}+P_{\text{qe}}^{}$, and stop the control. Otherwise, set the active output of the ES to 0 and recalculate the power deficiency $P^{\text{'}}$.

(6.12)

$\left.\begin{array}{l}{P}_{\text{qe+}}=\frac{K_{{\text{L}}_{*}}(f_{\max }-f^{(0)})(P_{1\sum }-P_{\text{qe}})}{f^{(0)}-K_{{\text{L}}_{*}}(f_{\max }-f^{(0)})}\\ P_{\text{qe}-}=\frac{K_{{\text{L}}_{*}}(f^{(0)}-f_{\min })(P_{1\sum }-P_{\text{qe}})}{f^{(0)}+K_{{\text{L}}_{*}}(f^{(0)}-f_{\min })}\end{array}\right\}$

(6.13)

$\left.\begin{array}{l}{P}_{\text{jh}-\text{min}}^{(1)}=P_{\text{qe}}-P_{\text{qe}-}\\ P_{\text{jh}-\text{max}}^{(1)}=P_{\text{qe}}+P_{\text{qe+}}\end{array}\right\}$

(6.14)

d. Shed less important loads. Shed loads in an ascending order of importance. For loads of the same importance, shed them in a descending order of power. If P_Li (power of a load) > $P_{\text{jh}-\max }^{(1)}$, do not shed this load and proceed to check the next one; if P_Li < $P_{\text{jh}-\min }^{(1)}$, shed this load and proceed to check the next one. If $P_{\text{jh}-\min }^{(1)}\le P_{\text{L}i}\le P_{\text{jh}-\max }^{(1)}$, shed this load and stop checking other loads. After shedding the load i, recalculate the power deficiency based on Eq. (6.15), and the amount of less important loads needing to be shed based on Eq. (6.14), and then proceed to check the next load.

$P_{\text{qe}}^{\text{'}}=P_{\text{qe}}-P_{\text{Lqc}-i}$

(6.15)

$\left.\begin{array}{l}{P}_{\text{jh}-\text{min}}^{(2)}=P_{\text{qe}}-P_{\text{SM}}\\ P_{\text{jh}-\text{max}}^{(2)}=P_{\text{qe}}+P_{\text{SM}}\end{array}\right\}$

(6.16)

f. Shed important loads in a descending order of power. If P_Li (power of a load) >$P_{\text{jh}-\max }^{(2)}$, do not shed the load and proceed to check the next one; if P_Li < $P_{\text{jh}-\min }^{(2)}$, shed the load and proceed to check the next one; if $P_{\text{jh}-\min }^{(2)}\le P_{\text{L}i}\le P_{\text{jh}-\max }^{(2)}$, shed the load and stop checking other loads. After shedding the load i, recalculate the power deficiency based on Eq. (6.15) and the amount of important loads needing to be shed based on Eq. (6.16), and then proceed to check the next load.

b. If –P_SM ≤ P_yy – P_S∑ ≤ P_SM, adjust the output of the ESs to absorb the power surplus after a proper number of generators are tripped until $P_{\text{S}\Sigma }^{\text{'}}=P_{\text{yy}}-P_{\text{S}\Sigma }$, and then stop the control. Otherwise, proceed to the next step.

$\left.\begin{array}{l}{P}_{\text{yy+}}=\frac{K_{\text{L}*}(f^{(0)}-f_{\min })}{f^{(0)}}(P_{\text{L0}}-P_{\text{yy}})\\ P_{\text{yy}-}=\frac{K_{\text{L}*}(f_{\max }-f^{(0)})}{f^{(0)}}(P_{\text{L0}}-P_{\text{yy}})\end{array}\right\}$

(6.17)

$\left\{\begin{array}{l}{P}_{\text{yy}}=P_{\text{yy}}-P_{\text{S}\sum }\hfill \\ P_{\text{S}\sum }=0\hfill \end{array}\right.$

(6.18)

$\left.\begin{array}{l}{P}_{\text{qj}-\text{min}}=P_{\text{yy}}-P_{\text{SM}}-P_{\text{S}\sum }-P_{\text{yy}-}\\ P_{\text{qj}-\text{max}}=P_{\text{yy}}+P_{\text{SM}}-P_{\text{S}\sum }+P_{\text{yy+}}\end{array}\right\}$

(6.19)

${P^{\prime }}_{\text{yy}}=P_{\text{yy}}-P_{\text{Gqc}-i}$

(6.20)

6.2.3.4. Power balance

6.3.4.2. Energy balance control in islanded operation