US 2024/0204531 A1 · SINGLE-CONTROLLABLE LOW VOLTAGE MICROGRID, CONTROL PROCESS AND USE

Abstract

This technology refers to a control process for single-controllable low-voltage microgrids (Mgs) (SCM) having centralized communication. The process is based on the “Power-Based Control” (PBC) technique by adapting it to the context of SCMs through a modified PBC process (MPBC). The technology includes a process that provides the following technical effects: (1) sharing of active power and reactive power proportionately to the capacity of distributed energy resources (DERs or DGs) in the MG, for example, rendering the use of batteries based on different technologies (lead-acid, ion-lithium, etc.) compatible; (2) compensation for the current unbalance at the point of common coupling (PAC); (3) allows exploration of battery banks by balancing the charging status of storage elements; (4) allows implementation of the control process without knowing the electrical grid's parameters and topology; (5) is able to deal with the arbitrary connection of inverters into the MG, in addition to other advantages. The technology is applied in the technical field of equipment and infrastructure for the development of MGs.

A control process for a single-controllable low voltage microgrid characterized in that it comprises the following steps:

a) temporally delimiting a control cycle k;
b) measuring for control cycle k found in step “a” the status of each DERmn, where index mn represents the connections between phases in the three-phase system a, b and c (mn=ab,bc,ca) and j is a numeric identifier for each DER in the MG, wherein such status is represented by:
(i) PDERjmn(k), QDERjmn(k), output active and reactive power, respectively;
(ii) actual maximum capacity to provide active power PDERjmnmax(k), actual maximum capacity to absorb active power PDERjmnmin(k), expressed as a negative value;
(iii) maximum capacity of processing reactive power QDERjmnmax as calculated by expression (1), where ADERjmn(k) is the DER apparent power:
Q
DERj
mn
max
(
k
)
=
A
DERj
mn
(
k
)
2
-
P
DERj
mn
(
k
)
2
;
(
1
)
c) once the CC located at the secondary level has gathered all the required data packets from each DER in the MG, calculating the status of the MG in terms of power quantities, with the first step calculating the total power and energy EDERjmn(k) quantities stored in DER battery banks connected between the mn phases using expression (2):
[
P
DERt
mn
,
Q
DERt
mn
,
P
DERt
mn
max
,
Q
DERt
mn
max
,
E
DERt
mn
]
=
∑
j
=
1
J
[
P
DERj
mn
,
Q
DERj
mn
,
P
DERj
mn
max
,
Q
DERj
mn
max
,
E
DERj
mn
]
;
(
2
)
d) converting the power computed per phase in the PCC (PPCCa, PPCCb and PPCCc) by the central controller due to power star measurement between phases (PPCCab, PPCCbc and PPCCca) using conversion matrix (A) using expression (3) and analogously converting the reactive powers using expression (4), where PPCCm and QPCCm are the active and reactive powers, respectively, as measured in m phase on the grid side at the PCC:
[
P
PCC
ab
P
PCC
bc
P
PCC
ca
]
=
[
1
1
-
1
-
1
1
1
1
-
1
1
]
︸
A
·
[
P
PCC
a
P
PCC
b
P
PCC
c
]
(
3
)
[
Q
PCC
ab
Q
PCC
bc
Q
PCC
ca
]
=
[
1
1
-
1
-
1
1
1
1
-
1
1
]
︸
A
·
[
Q
PCC
a
Q
PCC
b
Q
PCC
c
]
;
(
4
)
e) determining for control cycle k the active (PLtmn(k)) to reactive (QLtmn(k)) power balance between MG phases i.e., the sum of charges plus losses equals generation, expressions 5 to 10:
P
Lt
ab
(
k
)
=
P
PCC
a
(
k
)
+
P
PCC
b
(
k
)
-
P
PCC
c
(
k
)
+
P
DERt
ab
(
k
)
(
5
)
P
Lt
bc
(
k
)
=
-
P
PCC
a
(
k
)
+
P
PCC
b
(
k
)
+
P
PCC
c
(
k
)
+
P
DERt
bc
(
k
)
(
6
)
P
Lt
ca
(
k
)
=
P
PCC
a
(
k
)
-
P
PCC
b
(
k
)
+
P
PCC
c
(
k
)
+
P
DERt
ca
(
k
)
(
7
)
Q
Lt
ab
(
k
)
=
Q
PCC
a
(
k
)
+
Q
PCC
b
(
k
)
-
Q
PCC
c
(
k
)
+
Q
DERt
ab
(
k
)
(
8
)
Q
Lt
bc
(
k
)
=
-
Q
PCC
a
(
k
)
+
Q
PCC
b
(
k
)
+
Q
PCC
c
(
k
)
+
Q
DERt
bc
(
k
)
(
9
)
Q
Lt
ca
(
k
)
=
Q
PCC
a
(
k
)
-
Q
PCC
b
(
k
)
+
Q
PCC
c
(
k
)
+
Q
DERt
ca
(
k
)
;
(
10
)
f) by knowing the power balance, the CC calculates the active and reactive power references (PDERtmn*(k+1), QDERtmn*(k+1)) to be provided by the MG DERs in the next control time cycle (k+1) using expressions 11 to 16, where PPCCm*(k+1) and QPCCm*(k+1) are, respectively, the active and reactive power references associated with the power flow per phase in the PCC, being defined by the tertiary controller layer:
(
11
)
P
DERt
ab
*
(
k
+
1
)
=
P
Lt
ab
(
k
)
-
P
PCC
a
*
(
k
+
1
)
-
P
PCC
b
*
(
k
+
1
)
+
P
PCC
c
*
(
k
+
1
)
(
12
)
P
DERt
bc
*
(
k
+
1
)
=
P
Lt
bc
(
k
)
+
P
PCC
a
*
(
k
+
1
)
-
P
PCC
b
*
(
k
+
1
)
-
P
PCC
c
*
(
k
+
1
)
(
13
)
P
DERt
ca
*
(
k
+
1
)
=
P
Lt
ca
(
k
)
-
P
PCC
a
*
(
k
+
1
)
+
P
PCC
b
*
(
k
+
1
)
-
P
PCC
c
*
(
k
+
1
)
(
14
)
Q
DERt
ab
*
(
k
+
1
)
=
Q
Lt
ab
(
k
)
-
Q
PCC
a
*
(
k
+
1
)
-
Q
PCC
b
*
(
k
+
1
)
+
Q
PCC
c
*
(
k
+
1
)
(
15
)
Q
DERt
bc
*
(
k
+
1
)
=
Q
Lt
bc
(
k
)
+
Q
PCC
a
*
(
k
+
1
)
-
Q
PCC
b
*
(
k
+
1
)
-
Q
PCC
c
*
(
k
+
1
)
(
16
)
Q
DERt
ca
*
(
k
+
1
)
=
Q
Lt
ca
(
k
)
-
Q
PCC
a
*
(
k
+
1
)
+
Q
PCC
b
*
(
k
+
1
)
-
Q
PCC
c
*
(
k
+
1
)
;
g) the CC calculates the scalar coefficients for the Jth DERs connected between the “mn” αPmn and αQmn phases (all varying withing the range of [−1, 1]), wherein the active power is controlled by coefficient αp, while the reactive power is controlled by coefficient αQ, o;
the scalar coefficients are calculated using expressions 17 to 20, being dependent on PDERt* and QDERt* as compared to the maximum (PDERtmax) and minimum (PDERtmin) values;
sign αPmn indicates active power injection when positive and or active power storage when negative, while sign aoindicates injection of capacitive reactive power (if negative) or absorption of inductive reactive power (if positive), and after calculating αPmn and αQmn, they are transmitted to all DERs:
If
⁢
P
DERt
mn
*
(
k
+
1
)
<
P
DERt
mn
min
(
k
)
⁢
then
⁢
α
P
mn
=
-
1
(
17
)
(
18
)
If
⁢
P
DERt
mn
min
(
k
)
≤
P
DERt
mn
*
(
k
+
1
)
≤
P
DERt
mn
max
(
k
)
⁢
then
⁢
α
P
mn
=
P
DERt
mn
*
(
k
+
1
)
P
DERt
mn
max
(
k
)
If
⁢
P
DERt
mn
*
>
P
DERt
mn
max
(
k
)
⁢
then
⁢
α
P
mn
=
1
(
19
)
If
⁢
P
DERt
mn
*
>
P
DERt
mn
max
(
k
)
⁢
then
⁢
α
P
mn
=
1
;
(
20
)
h) if the MG is provided with different battery banks in terms of aging and/or technology, then energy sharing cannot only be proportional to the energy capacity of the DERs, but must also consider the usable energy, thus, it is necessary maintain equalization of usable energy between all battery banks dispersed in the MG in order to reach their maximum and minimum SOC values at approximately the same instant of time, and thus the scalar coefficients are weighted in terms of usable energy to ensure maximum usage of the battery banks based on the usable capacity of each bank, the CC calculates the average energy using expression 21 and then applies expression 22 to weight the scalar coefficients to be sent to the respective DERs:
E
avg
(
k
)
=
E
DERt
ab
(
k
)
+
E
DERt
bc
(
k
)
+
E
DERt
ca
(
k
)
J
⁡
(
k
)
(
21
)
Se
⁢
P
DERt
mn
min
(
k
)
≤
P
DERt
mn
*
(
k
+
1
)
≤
P
DERt
mn
max
(
k
)
(
22
)
Then
⁢
α
P
mn
=
P
DERt
mn
*
(
k
+
1
)
P
DERt
mn
max
(
k
)
·
E
DERt
mn
(
k
)
E
avg
(
k
)
;
i) after the DERs receive the scalar coefficients sent by the CC, they calculate their individual active and reactive power references to be used in their internal control loops, i.e. The primary controller layer, according to their individual maximum power capacity, and Table 1 is used to obtain power references defined in DER local controller for different values of scalar coefficients:
TABLE 1
Power references implemented in the DER local controller
Scalar coefficients
Power reference for the DER
αPmn = −1
P*DERjmn = PDERjmnmin
−1 < αPmn ≤ 0
P*DERjmn = αPmn · PDERjmnmin
0 < αPmn < 1
P*DERjmn = αPmn · PDERjmnmax
αPmn = 1
P*DERjmn = PDERjmnmax
−1 ≤ αQmn ≤ 1
Q*DERjmn = αQmn · QDERjmnmax

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Single-controllable low voltage microgrid, control process and use

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Single-controllable low voltage microgrid, control process and use

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Abstract

Claims5