
Energies 2019, 12, 1918 2 of 23
to participate in the power grid operation as a whole, which is conducive to the rational allocation and
utilization of resources [8–11].
In general, a VPP framework promotes the aggregation of various resources by simultaneously
participating in multiple markets, such as the day-ahead energy market (DAM) and real-time energy
market (RTM), which can improve the flexibility of scheduling [
12
]. Existing studies have mostly only
considered VPP participation in the DAM, and participation has been rarely extended to multiple
markets. For example, a VPP model that considers only DAM participation has been established,
where the overall demand response (DR) was divided into incentive-based DR and price-based DR
mechanisms [
13
–
15
]. A DR was also applied in a multi-market model, where a VPP participates in
both the DAM and RTM simultaneously [
12
,
16
]. However, the DR in the above studies was regarded
strictly as an interruptible/transferable load, and no specific modeling analysis was applied.
Meanwhile, VPP operations are impacted by uncertain factors such as RES outputs in the
scheduling process, resulting in economic and security issues. Therefore, addressing uncertain factors
in VPP operations has become a topic of increasing interest [
17
,
18
]. Numerous approaches have been
applied toward addressing uncertainty in VPP operations, such as stochastic programming [
19
–
21
],
robust optimization [
22
], chance-constrained programming [
23
], and point estimation [
24
]. In contrast,
the application of adaptive robust optimization has been relatively rare in this case. However, this
approach is more flexible than robust optimization because the decision making process is conducted
in stages, which to some extent can alleviate the conservativeness of robust optimization solutions.
Adaptive robust optimization considers the optimal solution under the worst-case conditions of
uncertain factors and is generally divided into two stages for decision making [
25
,
26
]. The first stage
employs what are denoted as here-and-now variables to make decisions before the level of uncertainty
is known. The second stage employs what are denoted as wait-and-see variables to make decisions
after the level of uncertainty is known. For example, an adaptive robust unit commitment model was
established to account for uncertainties in wind power output by the active regulation of pumped
storage power stations [
27
], and an adaptive robust reactive power optimization model was proposed
to address the uncertainties in wind power output under conditions of high wind power penetration
integrated into active distribution networks [28].
At present, numerous methods have been applied for solving adaptive robust models, such as
the affine policy, Benders decomposition, the column and constraint generation (CCG) algorithm,
and scenario-based algorithm. The affine policy method uses the linear decision rule to establish the
affine relationship between decision variables and uncertain parameters and transforms the two-stage
problem into a single-stage problem [
29
]. However, the results are conservative. A Benders/CCG
algorithm has been adopted for decomposing an original stochastic adaptive robust model problem
into a master problem and a sub-problem, but the Karush–Kuhn–Tucker (KKT) or duality method was
needed to transform the sub-problem into a single-level model, and a large number of integer terms
were introduced in the linearization process, leading to high model solution complexity in large-scale
problems [
30
,
31
]. The scenario-based algorithm was employed to transform a three-level adaptive
robust model into a single-level model by enumerating the uncertainty set based on the scenarios [
32
].
However, the computational efficiency of the scenario-based algorithm decreases as the scale of the
problem increases compared with the binding scenario identification approach. This is particularly the
case for large-scale scenario sets, where the number of scenarios required for solving the problem is
quite large, resulting in a very large computational burden [33,34].
Based on the above analysis, the present study considers a VPP that aggregates a photovoltaic
(PV) power plant, a gas turbine, an ESS, a central air-conditioning system (CACS), and interruptible
load, and simultaneously participates in multiple market transactions in the DAM, RTM, and carbon
trading market (CTM). The contributions of this paper can be briefly summarized as follows:
1.
This paper establishes a stochastic adaptive robust model for VPP dispatch that considers CACS
and multiple markets. The stochastic programming approach is used to address the uncertainty of
market electricity price owing to the high accuracy of market price forecasting, and the adaptive
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