Closed Loop Voltage Control (CLVC)
Closed Loop Voltage Control (CLVC) is the algorithm used to model how zone substations regulate voltage in response to load and generation changes. The CLVC settings affect voltage levels across the network and therefore influence both overvoltage constraint results (generation-driven) and undervoltage constraint results (load-driven).
How It Works
Zone substation transformers have discrete tap positions that adjust the output voltage in small increments. CLVC uses measurements at a sensing point to determine whether a tap change is needed. The sensing point is the MV-side node of the furthest three-phase distribution transformer from the zone substation, measured by cumulative upstream MV line length (resetting at any intermediate voltage regulators). On three-phase feeders, phase B is specifically monitored at this node.
Because the sensing point is on the MV network, CLVC is regulating voltage at the far end of the MV feeder - LV customer voltages are affected indirectly through the distribution transformer ratios downstream.
The algorithm continuously compares the sensed voltage against a target setpoint expressed in per-unit (p.u.), where 1.0 p.u. equals nominal voltage. If the voltage drifts outside a configured tolerance band (the deadband) and remains there for longer than the configured time delay, the algorithm commands a tap change to bring voltage back within range. A hard voltage ceiling prevents voltage from exceeding a defined limit regardless of other settings.
The p.u. setpoint, voltage limit, and deadband percentage are all converted to absolute volt values internally, using the nominal voltage at the sensing bus as defined in the CIM network model. If nominal voltage data is missing or incorrect for that location in the network model, CLVC behaviour may be unexpected. This is worth checking if a feeder with CLVC enabled is producing unusual voltage results.
Configuration Parameters
Voltage Setpoint (closed_loop_v_reg_set_point)
The setpoint is the target voltage at the sensing point, expressed in per-unit (1.0 p.u. = nominal voltage at that location). Most utilities operate below 1.0 p.u. to provide headroom for voltage rise caused by distributed generation, particularly solar PV. The gap between the setpoint and the voltage limit defines the effective overvoltage headroom window.
However, the setpoint also affects the other direction: on long feeders under heavy load, voltage naturally drops toward the far end, and a lower setpoint means the regulator is less aggressive in compensating for that drop. A setpoint that improves overvoltage headroom for DER may therefore worsen undervoltage outcomes under high load, and vice versa. Small differences in setpoint can materially affect voltage constraint results in both directions, so this value should reflect realistic operating practice for your network. Typical values range from 0.94 to 1.02 p.u., with 0.98-0.99 representing standard utility practice.
Voltage Deadband (closed_loop_v_band)
The deadband defines a tolerance band (in %) around the setpoint within which the regulator remains idle. Without a deadband, the regulator would continuously hunt for the exact setpoint in response to minor fluctuations - a condition known as tap hunting, which causes equipment wear and customer voltage flicker. For example, a setpoint of 0.985 with a deadband of 2% means the regulator won't act unless voltage falls outside the range 0.965-1.005 p.u.
A tighter deadband preserves more overvoltage headroom but increases tap operations. A wider deadband reduces tap operations but allows more voltage drift, consuming voltage margin in both directions. The deadband also interacts with the time delay: a very tight deadband will cause more tap operations unless paired with a suitably long delay to avoid hunting. Typical values are 1-5%.
Time Delay (closed_loop_time_delay)
The time delay (in seconds) controls how long voltage must remain outside the deadband before a tap change is triggered.
Description:
The time delay (in seconds) controls how long a voltage violation must persist at a regulator's sensing point before that regulator initiates a tap change command.
In single-regulator systems, this parameter has minimal effect due to the 30-minute time resolution of the simulation (the violation window between time steps far exceeds the delay threshold).
In multi-regulator systems, this parameter determines regulator priority (regulators with SHORTER delays act FIRST, regulators with LONGER delays act LATER). This allows coordinated control where upstream regulators (shorter delay) attempt voltage correction before downstream regulators (longer delay) respond, reducing unnecessary tap operations and 'hunting' behaviour.
The specific values used should reflect the network topology and desired control hierarchy based on exisitng downstream regulators.
Voltage Limit (closed_loop_v_limit)
The voltage limit is a hard ceiling in per-unit, set to protect equipment and comply with regulatory requirements - in most Australian frameworks, voltage must stay within +/-10% of nominal (0.90-1.10 p.u.).
In high-DER scenarios, the voltage limit is frequently the binding constraint. Once approached, additional generation cannot be accommodated without causing a violation - this is what ultimately caps hosting capacity. The voltage limit is often more influential than any other parameter: reducing it from 1.10 to 1.05 p.u. can significantly reduce predicted hosting capacity on solar-heavy feeders. Typical values are 1.05-1.10 p.u.
Deployment Flags
closed_loop_v_reg_enabled controls whether CLVC regulators are deployed at zone substations at all. When set to false, existing regulators are modelled as-is using their existing Line Drop Compensation (LDC) settings from the network model. If a zone substation has no existing regulator and enabled is false, that substation will have no active voltage control in the model at all.
closed_loop_v_reg_replace_all controls whether all existing regulators are replaced with the configured CLVC settings, or whether CLVC is only added where no regulator exists. Setting both to true gives consistent, reproducible behaviour across the network and is generally recommended for planning studies. Setting replace_all to false is appropriate when modelling heterogeneous configurations, for example where some substations have CLVC and others use LDC or have fixed taps.
Scope and Limitations
CLVC is a network-wide modelling assumption. When closed_loop_v_reg_replace_all is set to true, the same control scheme and parameters apply uniformly to every zone substation in the work package. This makes it straightforward to configure, but means it cannot reflect the reality that different substations may have different regulator settings or that only some feeders have active voltage control.
Because CLVC affects every feeder, changes to the configuration affect results across the entire network - there is no way to apply different CLVC settings to individual feeders or substations within a single work package. If your network has significantly different regulator configurations at different zone substations, consider running separate work packages, or using replace_all = false to preserve the existing diversity in the network model.
Comparison with Other Voltage Control Options
The HCM also includes several intervention types that address voltage through different mechanisms. Understanding the distinction helps when choosing the right tool for a given analysis.
DVMS (Dynamic Voltage Management System) is the most direct analogue to CLVC - both control zone substation taps. The key difference is that DVMS is a targeted intervention applied after a base work package, using a more sophisticated dual-loop control algorithm that responds to actual customer voltage distributions rather than a single sensing-point measurement. DVMS is considerably more computationally intensive as it re-solves the network at each time step. CLVC, by contrast, is the baseline voltage control assumption applied uniformly across the network and is far less expensive to compute.
DISTRIBUTION_TAP_OPTIMIZATION adjusts distribution transformer taps, not zone substation taps. It makes static, once-per-year tap changes based on historical voltage patterns from the base work package - there is no real-time feedback. It is best suited to addressing persistent, predictable voltage bias on LV circuits where a fixed tap adjustment would improve annual compliance.
DISTRIBUTION_TX_OLTC retrofits distribution transformers with on-load tap changers, enabling dynamic voltage regulation at the LV level. This operates downstream of where CLVC acts and complements rather than replaces zone substation regulation.
Choosing Settings
The voltage limit and setpoint are typically the most influential parameters. Note that because the HCM captures both overvoltage and undervoltage constraints, the "best" settings depend on the nature of your network - a low setpoint helps generation-heavy networks but may worsen results on load-heavy feeders with long runs.
For a generation-heavy network, use a lower setpoint and tighter deadband to maximise overvoltage headroom. This gives the best conditions for DER but may understate undervoltage risk under high load.
For a realistic or baseline analysis, use settings that reflect your network's actual zone substation operating practice, or the defaults. This is the most appropriate starting point for general network constraint analysis.
For a load-heavy or long-feeder network, a higher setpoint may reduce undervoltage constraints under high demand, at the cost of less overvoltage headroom.
Time delay has no practical effect at 30-minute resolution unless set above 1800 seconds.
Example Configurations
High DER penetration - aggressive regulation
closed_loop_v_reg_set_point = 0.96
closed_loop_v_band = 1.5
closed_loop_time_delay = 100
closed_loop_v_limit = 1.05
Low setpoint and limit with a tight, responsive deadband. Maximises overvoltage headroom for generation-heavy networks. May worsen undervoltage outcomes on load-heavy feeders.
Standard distribution feeder - defaults
closed_loop_v_reg_set_point = 0.985
closed_loop_v_band = 2.0
closed_loop_time_delay = 100
closed_loop_v_limit = 1.1
Reflects ANSI voltage standards and typical utility practice. A reasonable baseline for most analyses.
Conservative planning estimate
closed_loop_v_reg_set_point = 0.99
closed_loop_v_band = 2.5
closed_loop_time_delay = 100
closed_loop_v_limit = 1.1
Higher setpoint and wider deadband. Reduces overvoltage headroom but may improve undervoltage outcomes on load-heavy or long-feeder networks.