Reactive Power Compensation in Grid Connected PV System Using STATCOM and Fixed Capacitor
Reactive Power Compensation in Grid Connected PV System Using STATCOM and Fixed Capacitor
𝐈𝐧𝐭𝐫𝐨𝐝𝐮𝐜𝐭𝐢𝐨𝐧
Grid-connected solar PV systems mainly inject 𝐚𝐜𝐭𝐢𝐯𝐞 𝐩𝐨𝐰𝐞𝐫 into the electrical network. However, many practical loads also require 𝐫𝐞𝐚𝐜𝐭𝐢𝐯𝐞 𝐩𝐨𝐰𝐞𝐫, especially inductive loads such as motors, transformers, and industrial equipment.
Reactive Power Compensation in Grid Connected PV System Using STATCOM and Fixed Capacitor
If this reactive power is taken completely from the utility grid, it can:
Increase grid current.
Reduce the power factor.
Increase transmission and distribution losses.
Cause additional voltage drops.
Reduce the effective power-transfer capability of the system.
This model demonstrates reactive power compensation in a 𝐠𝐫𝐢𝐝-𝐜𝐨𝐧𝐧𝐞𝐜𝐭𝐞𝐝 𝐬𝐨𝐥𝐚𝐫 𝐏𝐕 𝐬𝐲𝐬𝐭𝐞𝐦 using two different approaches:
𝐅𝐢𝐱𝐞𝐝 𝐜𝐚𝐩𝐚𝐜𝐢𝐭𝐨𝐫 𝐛𝐚𝐧𝐤 compensation.
𝐒𝐓𝐀𝐓𝐂𝐎𝐌-based dynamic reactive power compensation.
The simulation also shows how PV active power changes with solar irradiance and how the grid automatically supplies the remaining active power required by the load.
𝐒𝐲𝐬𝐭𝐞𝐦 𝐎𝐯𝐞𝐫𝐯𝐢𝐞𝐰
The complete system contains the following major sections:
Solar PV array.
DC–DC boost converter.
MPPT controller.
DC-link.
Three-phase PV inverter.
Harmonic filter.
Point of Common Coupling (PCC).
Three-phase utility grid.
Active and reactive local load.
Fixed capacitor bank.
STATCOM.
STATCOM harmonic filter.
PV inverter controller.
STATCOM controller.
Voltage, current, active-power, and reactive-power measurement blocks.
The 𝐏𝐂𝐂 is the common electrical point where the PV inverter, grid, load, and reactive power compensating device interact.
𝐌𝐚𝐢𝐧 𝐒𝐲𝐬𝐭𝐞𝐦 𝐏𝐚𝐫𝐚𝐦𝐞𝐭𝐞𝐫𝐬
Parameter | Value |
Grid voltage | 400 V |
Grid frequency | 50 Hz |
Solar PV rating | Approximately 100 kW |
Initial irradiance | 1000 W/m² |
Reduced irradiance | 500 W/m² |
PV power at high irradiance | Approximately 96 kW |
PV power after irradiance reduction | Approximately 50 kW |
Load active power | 100 kW |
Initial load reactive power | 100 kVAr |
Increased load reactive power | 150 kVAr |
Fixed capacitor rating | 100 kVAr |
PV inverter DC-link reference | Approximately 700 V |
STATCOM DC-link reference | 800 V |
The simulation uses an irradiance change at approximately 𝐭 = 𝟎.𝟐 𝐬 to demonstrate the active-power sharing between the PV system and the grid.
𝐖𝐨𝐫𝐤𝐢𝐧𝐠 𝐏𝐫𝐨𝐜𝐞𝐬𝐬
1. Solar PV Power Generation
The solar PV array produces DC electrical power according to the available solar irradiance.
The PV voltage and current are continuously measured and supplied to the 𝐌𝐏𝐏𝐓 controller.
The MPPT control system:
Measures PV voltage.
Measures PV current.
Determines the required PV operating point.
Generates a reference voltage.
Compares the reference with the actual PV voltage.
Uses a PI controller to generate the converter control command.
Produces the switching pulses for the boost converter.
The boost converter therefore helps the PV array operate close to its maximum power point.
2. DC–DC Boost Converter
The boost converter is placed between the solar PV array and the PV inverter.
Its main functions are:
Extract maximum available PV power.
Increase and regulate the PV-side DC voltage.
Supply a controlled DC-link voltage to the inverter.
Respond to changes in solar irradiance.
The converter switching pulse is generated by comparing the controller output with a high-frequency carrier waveform.
3. PV Inverter
The PV inverter converts the DC power from the solar system into three-phase AC power.
Its primary objective in this model is to:
Transfer 𝐫𝐞𝐚𝐥 𝐩𝐨𝐰𝐞𝐫 from the PV system.
Maintain the PV inverter DC-link voltage.
Keep the PV inverter reactive power close to zero.
Synchronize the inverter with the utility grid.
A harmonic filter is placed at the inverter output to improve the quality of the current injected into the PCC.
𝐏𝐕 𝐈𝐧𝐯𝐞𝐫𝐭𝐞𝐫 𝐂𝐨𝐧𝐭𝐫𝐨𝐥
The PV inverter uses synchronous-reference-frame control.
Grid Synchronization
The three-phase grid voltage is measured and converted into a rotating reference frame.
The control structure performs:
Three-phase voltage measurement.
Stationary-frame conversion.
Rotating-reference-frame conversion.
Grid phase-angle estimation.
Generation of the synchronization angle.
A 𝐏𝐡𝐚𝐬𝐞-𝐋𝐨𝐜𝐤𝐞𝐝 𝐋𝐨𝐨𝐩 (𝐏𝐋𝐋) is used to synchronize the inverter controller with the grid voltage.
Direct-Axis Current Control
The direct-axis current channel mainly controls 𝐚𝐜𝐭𝐢𝐯𝐞 𝐩𝐨𝐰𝐞𝐫.
The controller:
Measures the inverter DC-link voltage.
Compares it with its reference value.
Processes the voltage error using a PI controller.
Generates the required active-current reference.
Compares it with the measured inverter current.
Uses another PI controller for current regulation.
Produces the corresponding voltage control command.
This loop allows the PV inverter to transfer the available solar power to the load and grid.
Quadrature-Axis Current Control
The quadrature-axis current channel is associated with 𝐫𝐞𝐚𝐜𝐭𝐢𝐯𝐞 𝐩𝐨𝐰𝐞𝐫.
For the PV inverter, the reactive-current reference is maintained approximately at zero.
Therefore:
The PV inverter mainly supplies active power.
The PV inverter provides negligible reactive power.
Reactive power compensation is handled separately by the capacitor bank or STATCOM.
The final control signals are converted back into three-phase quantities and used to generate PWM switching pulses for the inverter.
𝐎𝐩𝐞𝐫𝐚𝐭𝐢𝐨𝐧 𝐖𝐢𝐭𝐡𝐨𝐮𝐭 𝐑𝐞𝐚𝐜𝐭𝐢𝐯𝐞 𝐏𝐨𝐰𝐞𝐫 𝐂𝐨𝐦𝐩𝐞𝐧𝐬𝐚𝐭𝐢𝐨𝐧
Consider the load condition:
Quantity | Value |
Load active power | 100 kW |
Load reactive power | 100 kVAr |
Compensation device | None |
When solar irradiance is 1000 W/m²:
PV generation is approximately 96 kW.
Most of the load active power is supplied by the PV system.
Grid active-power contribution remains very small.
PV inverter reactive power remains approximately zero.
The complete 100 kVAr reactive-power demand is supplied by the grid.
Therefore, without compensation, the utility grid must support the full inductive reactive-power demand.
𝐄𝐟𝐟𝐞𝐜𝐭 𝐨𝐟 𝐈𝐫𝐫𝐚𝐝𝐢𝐚𝐧𝐜𝐞 𝐂𝐡𝐚𝐧𝐠𝐞
The irradiance is reduced from:
Operating condition | Irradiance | Approx. PV Power |
Initial condition | 1000 W/m² | 96 kW |
Reduced solar condition | 500 W/m² | 50 kW |
When irradiance decreases:
PV output falls from approximately 96 kW to about 50 kW.
The load continues to require approximately 100 kW.
The grid supplies the remaining active-power deficit.
The PV inverter continues to operate with almost zero reactive-power output.
Without compensation, grid reactive power remains determined by the load requirement.
This demonstrates automatic active-power balancing between the 𝐏𝐕 𝐬𝐲𝐬𝐭𝐞𝐦 and the 𝐠𝐫𝐢𝐝.
𝐑𝐞𝐚𝐜𝐭𝐢𝐯𝐞 𝐏𝐨𝐰𝐞𝐫 𝐂𝐨𝐦𝐩𝐞𝐧𝐬𝐚𝐭𝐢𝐨𝐧 𝐔𝐬𝐢𝐧𝐠 𝐚 𝐅𝐢𝐱𝐞𝐝 𝐂𝐚𝐩𝐚𝐜𝐢𝐭𝐨𝐫
A fixed capacitor bank can locally supply capacitive reactive power and reduce the reactive power taken from the grid.
Consider:
Parameter | Rating |
Inductive load reactive power | 100 kVAr |
Fixed capacitor bank | 100 kVAr |
Under this condition:
Load demands approximately 100 kVAr.
Capacitor supplies approximately 100 kVAr.
The inductive and capacitive reactive powers compensate each other.
Grid reactive-power requirement becomes approximately zero.
The capacitor has almost no contribution to the real-power requirement of the load.
𝐖𝐡𝐚𝐭 𝐇𝐚𝐩𝐩𝐞𝐧𝐬 𝐖𝐡𝐞𝐧 𝐭𝐡𝐞 𝐋𝐨𝐚𝐝 𝐂𝐡𝐚𝐧𝐠𝐞𝐬?
The limitation of fixed compensation becomes clear when the reactive load is increased.
Consider:
Parameter | Value |
Load reactive power | 150 kVAr |
Capacitor compensation | 100 kVAr |
Remaining reactive demand | Approximately 50 kVAr |
The capacitor continues to supply only its designed compensation level.
Therefore:
Capacitor supplies approximately 100 kVAr.
Load requires approximately 150 kVAr.
The remaining approximately 50 kVAr must be supplied by the grid.
This demonstrates one of the major limitations of a 𝐟𝐢𝐱𝐞𝐝 𝐜𝐚𝐩𝐚𝐜𝐢𝐭𝐨𝐫 𝐛𝐚𝐧𝐤: its reactive power support does not automatically follow varying load demand.
𝐒𝐓𝐀𝐓𝐂𝐎𝐌-𝐁𝐚𝐬𝐞𝐝 𝐑𝐞𝐚𝐜𝐭𝐢𝐯𝐞 𝐏𝐨𝐰𝐞𝐫 𝐂𝐨𝐦𝐩𝐞𝐧𝐬𝐚𝐭𝐢𝐨𝐧
A 𝐒𝐓𝐀𝐓𝐂𝐎𝐌 is connected at the PCC through a coupling filter.
Unlike a fixed capacitor, the STATCOM can dynamically modify its reactive-power output according to the load requirement.
The STATCOM section contains:
Voltage-source converter.
DC-link capacitor.
Harmonic filter.
Current measurement.
Load-current measurement.
Synchronous-reference-frame controller.
PI current controllers.
PWM pulse generator.
The STATCOM DC-link voltage is regulated at approximately 𝐑𝟖𝟎𝟎 𝐕.
𝐒𝐓𝐀𝐓𝐂𝐎𝐌 𝐂𝐨𝐧𝐭𝐫𝐨𝐥 𝐒𝐭𝐫𝐚𝐭𝐞𝐠𝐲
DC-Link Voltage Control
The STATCOM capacitor voltage is continuously measured.
The controller:
Compares the measured DC-link voltage with the 800 V reference.
Processes the error through a PI controller.
Generates the required direct-axis current component.
Maintains the STATCOM internal energy balance.
This ensures stable STATCOM operation.
Load Current Measurement
The three-phase load current is transformed into direct-axis and quadrature-axis components.
These components allow the controller to distinguish between:
Active-current demand.
Reactive-current demand.
The STATCOM current is also transformed into the same rotating reference frame for closed-loop control.
Reactive Current Compensation
The quadrature-axis control loop determines the reactive current required by the load.
The STATCOM controller then:
Detects the load reactive-current requirement.
Generates the required compensating current.
Regulates the actual STATCOM current.
Produces the corresponding converter voltage reference.
Generates PWM pulses.
Injects the necessary reactive power at the PCC.
As a result, the grid reactive-power requirement can be maintained very close to zero.
𝐒𝐢𝐦𝐮𝐥𝐚𝐭𝐢𝐨𝐧 𝐑𝐞𝐬𝐮𝐥𝐭𝐬
Case 1 – 100 kVAr Load Without Compensation
Parameter | Observed Behavior |
PV active power | Approximately 96 kW initially |
PV reactive power | Approximately 0 kVAr |
Load active power | 100 kW |
Load reactive power | 100 kVAr |
Grid reactive power | Approximately 100 kVAr |
The grid supplies practically all the reactive-power requirement.
Case 2 – 100 kVAr Load With 100 kVAr Fixed Capacitor
Parameter | Observed Behavior |
Load reactive power | 100 kVAr |
Capacitor reactive power | Approximately 100 kVAr |
Grid reactive power | Approximately 0 kVAr |
Capacitor real power | Approximately zero |
For a matched load condition, fixed-capacitor compensation performs effectively.
Case 3 – 150 kVAr Load With 100 kVAr Fixed Capacitor
Parameter | Approximate Value |
Load reactive power | 150 kVAr |
Capacitor support | 100 kVAr |
Grid reactive power | 50 kVAr |
The fixed capacitor cannot automatically increase its output, so the grid supplies the remaining reactive power.
Case 4 – 100 kVAr Load With STATCOM
The STATCOM automatically supplies approximately the reactive power required by the load.
Observed behavior:
Load reactive power ≈ 100 kVAr.
STATCOM reactive power ≈ 100 kVAr.
Grid reactive power ≈ 0 kVAr.
STATCOM real power remains close to zero under steady-state operation.
Case 5 – Reactive Load Increased to 150 kVAr With STATCOM
When reactive load demand increases:
STATCOM reactive output automatically increases.
STATCOM supplies approximately 150 kVAr.
Grid reactive-power contribution remains close to zero.
No manual capacitor resizing is required.
This clearly demonstrates the dynamic compensation capability of STATCOM.
𝐅𝐢𝐱𝐞𝐝 𝐂𝐚𝐩𝐚𝐜𝐢𝐭𝐨𝐫 𝐯𝐬. 𝐒𝐓𝐀𝐓𝐂𝐎𝐌
Feature | Fixed Capacitor | STATCOM |
Reactive power compensation | Fixed | Dynamic |
Response to changing load | Limited | Automatic |
Control system | Simple | Advanced |
Power-electronic converter | Not required | Required |
DC-link control | Not required | Required |
Compensation accuracy | Depends on capacitor sizing | High |
Variable reactive load support | Limited | Excellent |
Grid reactive-power reduction | Good at designed operating point | Good over varying operating conditions |
Initial complexity | Low | Higher |
Suitability for rapidly changing loads | Limited | High |
The comparison shows why fixed capacitors are suitable for relatively constant reactive loads, whereas STATCOM is more effective for systems with 𝐝𝐲𝐧𝐚𝐦𝐢𝐜 𝐫𝐞𝐚𝐜𝐭𝐢𝐯𝐞-𝐩𝐨𝐰𝐞𝐫 𝐝𝐞𝐦𝐚𝐧𝐝.
𝐊𝐞𝐲 𝐅𝐞𝐚𝐭𝐮𝐫𝐞𝐬
100 kW class grid-connected solar PV system.
MPPT-controlled DC–DC boost converter.
Three-phase grid-connected PV inverter.
Synchronous-reference-frame current control.
PLL-based grid synchronization.
Separate active- and reactive-current control.
Fixed capacitor reactive-power compensation.
Dynamic STATCOM compensation.
800 V STATCOM DC-link control.
Compensation under changing reactive-load conditions.
PV operation under changing irradiance.
Active-power sharing between PV and utility grid.
Measurement of inverter, grid, load, capacitor, and STATCOM power.
Analysis of instantaneous three-phase voltages and currents.
𝐖𝐡𝐲 𝐒𝐓𝐀𝐓𝐂𝐎𝐌 𝐈𝐬 𝐌𝐨𝐫𝐞 𝐄𝐟𝐟𝐞𝐜𝐭𝐢𝐯𝐞 𝐟𝐨𝐫 𝐕𝐚𝐫𝐢𝐚𝐛𝐥𝐞 𝐋𝐨𝐚𝐝𝐬
A fixed capacitor is selected according to a particular reactive-power requirement.
For example:
100 kVAr capacitor + 100 kVAr inductive load → good compensation.
100 kVAr capacitor + 150 kVAr inductive load → approximately 50 kVAr still required from the grid.
STATCOM does not have this fixed-compensation limitation.
When load reactive power changes from 100 kVAr to 150 kVAr:
The controller detects the increased requirement.
STATCOM reactive current increases automatically.
Additional reactive power is supplied locally.
Grid reactive power remains close to zero.
This makes STATCOM especially useful where load conditions change continuously.
𝐏𝐨𝐰𝐞𝐫 𝐅𝐥𝐨𝐰 𝐒𝐮𝐦𝐦𝐚𝐫𝐲
Operating Condition | PV | Grid | Capacitor / STATCOM |
High solar irradiance | Supplies most active power | Very low active-power support | Supplies reactive compensation when connected |
Low solar irradiance | Reduced active power | Supplies active-power deficit | Continues reactive compensation |
No compensation | Supplies active power | Supplies load reactive power | Not available |
Fixed capacitor matched to load | Supplies active power | Reactive power near zero | Supplies fixed reactive power |
Reactive load above capacitor rating | Supplies active power | Supplies remaining reactive power | Limited to fixed rating |
STATCOM operation | Supplies active power | Reactive power maintained near zero | Dynamically supplies required reactive power |
𝐀𝐩𝐩𝐥𝐢𝐜𝐚𝐭𝐢𝐨𝐧𝐬
This type of reactive power compensation can be applied in:
Grid-connected photovoltaic plants.
Industrial distribution networks.
Renewable-energy-integrated distribution systems.
Commercial electrical networks.
Microgrids.
Smart grids.
Distribution feeders with varying inductive loads.
Motor-intensive electrical systems.
Power-factor improvement systems.
Voltage-support applications.
Renewable energy power-quality studies.
𝐁𝐞𝐧𝐞𝐟𝐢𝐭𝐬 𝐨𝐟 𝐑𝐞𝐚𝐜𝐭𝐢𝐯𝐞 𝐏𝐨𝐰𝐞𝐫 𝐂𝐨𝐦𝐩𝐞𝐧𝐬𝐚𝐭𝐢𝐨𝐧
Proper reactive power compensation helps to:
Improve grid power factor.
Reduce unnecessary reactive-current flow.
Reduce distribution losses.
Improve voltage regulation.
Reduce grid loading.
Improve utilization of electrical infrastructure.
Support renewable-energy integration.
Improve overall power quality.
Reduce dependency on utility-supplied reactive power.
𝐖𝐡𝐚𝐭 𝐂𝐚𝐧 𝐁𝐞 𝐀𝐧𝐚𝐥𝐲𝐳𝐞𝐝 𝐟𝐫𝐨𝐦 𝐭𝐡𝐞 𝐒𝐢𝐦𝐮𝐥𝐚𝐭𝐢𝐨𝐧?
The model provides several useful output signals for analysis:
PV generated power.
PV inverter active power.
PV inverter reactive power.
Grid active power.
Grid reactive power.
Load active power.
Load reactive power.
Capacitor reactive power.
STATCOM active power.
STATCOM reactive power.
PV inverter three-phase voltage.
PV inverter three-phase current.
Grid voltage.
Grid current.
Load voltage.
Load current.
STATCOM voltage.
STATCOM current.
PV inverter DC-link voltage.
STATCOM DC-link capacitor voltage.
These measurements make it easy to study both 𝐩𝐨𝐰𝐞𝐫 𝐟𝐥𝐨𝐰 and 𝐩𝐨𝐰𝐞𝐫 𝐪𝐮𝐚𝐥𝐢𝐭𝐲 under different operating conditions.
𝐂𝐨𝐧𝐜𝐥𝐮𝐬𝐢𝐨𝐧
Reactive power management is an important requirement in grid-connected renewable-energy systems.
The simulation demonstrates three important operating conditions:
Without compensation, the 𝐠𝐫𝐢𝐝 supplies the complete reactive-power requirement of the inductive load.
A 𝐟𝐢𝐱𝐞𝐝 𝐜𝐚𝐩𝐚𝐜𝐢𝐭𝐨𝐫 can effectively compensate reactive power when its rating closely matches the load requirement, but its performance is limited when the load changes.
A 𝐒𝐓𝐀𝐓𝐂𝐎𝐌 dynamically adjusts its reactive-power output according to the actual load demand and can therefore maintain grid reactive power close to zero under changing operating conditions.
The model also demonstrates that variations in solar irradiance mainly affect the 𝐚𝐜𝐭𝐢𝐯𝐞-𝐩𝐨𝐰𝐞𝐫 𝐬𝐡𝐚𝐫𝐢𝐧𝐠 between the PV system and the grid, while the STATCOM independently handles reactive-power compensation.
For students, researchers, and engineers, this system provides a clear platform for understanding 𝐠𝐫𝐢𝐝-𝐜𝐨𝐧𝐧𝐞𝐜𝐭𝐞𝐝 𝐏𝐕 𝐜𝐨𝐧𝐭𝐫𝐨𝐥, 𝐩𝐨𝐰𝐞𝐫 𝐟𝐚𝐜𝐭𝐨𝐫 𝐜𝐨𝐦𝐩𝐞𝐧𝐬𝐚𝐭𝐢𝐨𝐧, 𝐝𝐪-𝐚𝐱𝐢𝐬 𝐜𝐮𝐫𝐫𝐞𝐧𝐭 𝐜𝐨𝐧𝐭𝐫𝐨𝐥, 𝐟𝐢𝐱𝐞𝐝-𝐜𝐚𝐩𝐚𝐜𝐢𝐭𝐨𝐫 𝐜𝐨𝐦𝐩𝐞𝐧𝐬𝐚𝐭𝐢𝐨𝐧, and 𝐒𝐓𝐀𝐓𝐂𝐎𝐌-based dynamic reactive-power control.
Comments