1. business and industrial
2. energy
3. electricity

Role of HVDC Configurations
in Modelling of NZ National
Reserve Market
Vladimir Krichtal
SO Development, Transpower NZ
Contents
• Existing Real HVDC Operation
• Proposed Real HVDC Operation
• SPD Reserve Transfer Modelling Options
2
Existing Real HVDC Operation
• Real HVDC configuration depends on total HVDC power
flow and change via steps:
• Bipole (both poles forward)
• Monopole (one pole forward, second pole shutdown)
• Monopole (one pole backward, second pole shutdown)
• Bipole (both poles backward).
• Each pole in real operation HVDC has dead bands
35MW from both directions.
• HVDC is modelled in the SPD as bipole without dead
bands.
3
HVDC bipole operation (No round power)
PHVDC
PRef
Bipolar
Operation
Monopolar
Operation P3
Dead
Band
Bipole Power
Pole2 Power
Pole3 Power
PoleMin=35MWW
4
Monopolar
Operation P2
Bipolar
Operation
Proposed Real HVDC Operation
• Real HVDC configuration depends on total HVDC power
flow and change via steps:
• Bipole (both poles forward)
• Monopole (one pole forward, second pole shutdown)
• Round Power (one pole forward, second pole backward)
• Monopole (one pole backward, second pole shutdown)
• Bipole (both poles backward).
• If HVDC is offered in monopole only mode in real
operation HVDC has dead bands 30MW from both
directions.
5
HVDC bipole operation (Round power)
PHVDC
PRef
Bipolar
Operation
Monopolar
Operation P3
Round Power
Operation
Bipole Power
Pole2 Power
Pole3 Power
PoleMin=35MWW
6
Monopolar
Operation P2
Bipolar
Operation
HVDC Risk in Bipole operation with Round Power (MW)
Possible Lost Power (MW)
1000
Transition at -270MW
500
Risk exists for duration of
Block sequences- for
reducing power
700 (-overload
capability)
400
Northward Risk
-1000
Southward Risk
400
-666
700
1000
Bipole Power (MW)
-270
-334 (+overload
capability)
500
Transition at 400MW
1000
7
1400
SPD Reserve Transfer Modelling Options (1)
•
•
Cap Export Equation.
𝑅𝐸𝑆𝐸𝑅𝑉𝐸_𝐸𝑋𝑃𝑂𝑅𝑇𝐸𝐷𝑖,𝑟𝑐 ≤ 𝑀𝑜𝑑𝑢𝑙𝑎𝑡𝑖𝑜𝑛𝐿𝑖𝑚𝑖𝑡𝑖,𝑟𝑐 ,
•
•
Can Only Export What You Got.
𝑅𝐸𝑆𝐸𝑅𝑉𝐸_𝐸𝑋𝑃𝑂𝑅𝑇𝐸𝐷𝑖,𝑟𝑐 ≤ 𝑟𝑜∈𝑅𝑂𝐹𝐹
𝑟𝑏∈𝐼𝐿𝑅𝐵𝐼𝐷 𝑖 PURCHESEIL𝑟𝑏,𝑟𝑐 ,
+
(2)
•
•
Energy and Reserve Transfer Limit.
𝑅𝐸𝑆𝐸𝑅𝑉𝐸_𝐸𝑋𝑃𝑂𝑅𝑇𝐸𝐷𝑖,𝑟𝑐 + 𝐻𝑉𝐷𝐶_𝐹𝐿𝑂𝑊𝑖 ≤ 𝑇𝑜𝑡𝑎𝑙𝐻𝑉𝐷𝐶𝐶𝑎𝑝𝑎𝑐𝑖𝑡𝑦𝑖 ,
•
Constraint (3) effectively limits transfer of Forward Reserves. Reserve transfer
in opposite HVDC flow direction (Backward) is still limited by constraint (3). In
real operation at some transitional modes like Bipole-Monopole, it impossible to
reverse pole quickly, so in the operational RTD schedule we have to address
this and set more tight Backward Reserve constraint.
Deadband issue will not exist if round power mode is used.
•
8
𝑖 ,𝑟𝑡∈𝑃𝐿𝑆𝑅∪𝑇𝑊𝐷𝑅 𝑅𝐸𝑆𝐸𝑅𝑉𝐸𝑟𝑜,𝑟𝑐,𝑟𝑡
(1)
(3)
SPD Reserve Transfer Modelling Options (2)
• In operational RTD schedule we can introduce new constraint
• 𝑅𝐸𝑆𝐸𝑅𝑉𝐸𝑆_𝐸𝑋𝑃𝑂𝑅𝑇𝐸𝐷𝑖,𝑟𝑐 ≤ 𝐻𝑉𝐷𝐶_𝐹𝐿𝑂𝑊𝑖 ,
(4)
where reserve exported is limited by HVDC flow.
• Reserves exported are bigger than reserves imported when
reserves and HVDC power flow are in the same direction and
reserve exported is smaller than reserves imported when reserve
and HVDC power flow are in different directions in bipole and
monopole configuration. We use lossless power flow for reserves
transfer.
9
SPD Reserve Transfer Modelling Options (3)
• HVDC losses. During real operation a total HVDC losses becomes
non-smooth, non-convex function, see solid curve in Figure 1.
Estimated HVDC losses for above HVDC configurations are in the
Table 1.
Losses(MW)
Monopole HVDC
Convex approximation
of HVDC losses
Bipole HVDC
losses
Round power HVDC
losses
losses
30
165
Figure 1. Losses for different HVDC modes (pole configurations).
10
HVDC Flow (MW)
SPD Reserve Transfer Modelling Options (4)
•
•
•
•
•
HVDC losses. Loss difference is very small at HVDC flow level of 165 MW.
Inconsistencies between modelling HVDC as Bipole and real configurations
can be resolved with the following options:
Approximate total HVDC losses at Figure 1 by piece-wise convex loss
function, see dashed curve in Figure 1. This will allow LP modelling.
Use Bipole losses (existing model). Inconsistencies are resolved via
constrained on/off payments. LP model is used.
Create a detailed HVDC model which reflects operational consequence and
configuration. It can be used in operational RTD schedule to model
precisely transition bipole-monopole, monopole – round power modes.
HVDC flow(MW)
Bipole losses (MW)
Monopole losses (MW)
Round Power losses (MW)
Table1
11
30
0.08
0.43
165
1.29
2.59
SPD Reserve Transfer Modelling Options (5)
• HVDC CE risk. In the SPD model HVDCCE risk is calculated as
max(0, 𝐻𝑉𝐷𝐶𝑅𝐸𝑆𝑖 − 𝑃𝑜𝑙𝑒𝐶𝑎𝑝𝑎𝑐𝑖𝑡𝑦𝑖 ) in Bipole mode and should be
𝑃𝑜𝑙𝑒𝑅𝑒𝑐𝑒𝑖𝑣𝑒𝑑𝑖 in Monopole mode. In real operation Monopole
mode, the second blocked pole can be available to be de-blocked
within 3 seconds.
• CE Risk in Round Power mode can be estimated at 35+25*5=160MW
as maximum of poles flow at Round Power to Monopole transition
point because 5 minute time waiting for the second pole reversal with
25(MW/min) ramping. In the North Island it always smaller than the
minimal generation risk. In the South Island it can be larger than
120MW manual risk. This situation lasts only 5 min, so real SI HVDC
risk should be modelled in this transitional RTD run. Reserve HVDC
transfer capacity in Forward direction is not affected.
12
SPD Reserve Transfer Modelling Options (6)
HVDC Instantaneous Reserves Transfer
• Bipole, Monopole modes. Reserve transfer into Forward direction is limited by
constraints (1,3). Real operation in Monopole mode does not affect HVDC ability to
ramp-up in Forward direction because second pole can be de-blocked in less than 3
seconds. Reserve transfer in Forward direction in Monopole mode can be modelled like
it is in Bipole mode.
• Backward Reserve transfer is limited by constraint (1). In real operation Backward
reserve transfer is possible by ramping down monopole or Bipole poles. In this case
backward reserve transfer will be restricted by constraint (4). This is a conservative
level of Backward reserves transfer. To make Backward reserve transfer effectively
unrestricted in case of island risk event we can change the pole direction. The pole has
to be blocked and then wait 5 minutes to be de-blocked in the opposite direction in the
bipole-monopole transition.
• The 5 minute waiting time is six times less than most market schedules 30 minutes
trading period. So we do not apply constraint (4) in 30 min. schedules. We will apply
constraint (4) in RTD run during transition Bipole-Monopole.
• Round Power mode. Reserves transfer into forward or backward directions is limited
by constraints (1). Constraint (3) does not affect a solution.
13
SPD Reserve Transfer Modelling Options (7)
• HVDC National Frequency Keeping Market.
• The same HVDC control system is used for
moving power from one island to another when
there is a difference in frequency between the
islands. In the future FK National Market we
need to limit the sum of FK reserve transfer and
Instantaneous reserve transferred by constraints
(1,2,3).
14
Summary and Recommendation
• Use Option 1 to model aggregated HVDC losses and use reserve
transfer constraints (1,2,3) for pre-dispatch and final pricing (30
minutes) schedules.
• Use Option 3 with more detailed HVDC losses can for all RTD (5
minutes) schedules.
– Use reserve transfer constraints (1,2,3) for all RTD runs except
transitional runs between bipole-monopole and monopole – round
power.
– In RTD schedule add constraint (4) and a new developed constraint for
round power – monopole transition with a separate algorithm to
address the Pole reversal 5 minutes waiting time issue.
– Reserve exported can only be used to cover AC type risks: Manual,
ACCE and ACECE. It cannot cover any DC risks: DCCE, DCECE.
15
Thank you