Brazilian standards ABNT 16149 and ABNT 16150 require that the photovoltaic inverter connected to the grid meets some technical operating requirements with regard to power factor.
In this article, we will present the concept of power factor and present the technical standards in force in Brazil. It is defined as power factor the relationship between the active and apparent powers of an electrical system, according to the equation:
Where:
P – is the active power in [kW]
Q – is the reactive power in [kVAr]
S – is the apparent power in [kVA]
A right-angled triangle is used to relate the active, reactive and apparent powers.
In case onesinusoidal single-phase stem, we have:
The apparent power in (VA) is the product of the effective values (RMS) of voltage and current. It is so named because its calculation consists of the simple product of voltage and current, by analogy to resistive circuits, but its value does not reveal the portions of active and reactive power present in the system.
In electrical installations the power factor (PF) It is an indicator of energy efficiency, relating the active and reactive power present in the circuit. A value of FP close to unity (1,0) indicates little reactive energy consumption in relation to active energy.
Since active energy is that which performs useful work, the closer to unity the FP, the greater the energy efficiency of the installation or electrical system.
O FP It is classified as purely resistive when the electrical current and voltage of the circuit have the same phase, that is, they are perfectly synchronized and cross zero (horizontal axis) at the same instant, as shown in Figure 2. The power factor can also be inductive (Figure 3) or capacitive (Figure 4), when the current is behind or ahead, respectively, in relation to the system voltage.
In Figures 1 to 3 below, the first image shows the information displayed by the precision power analyzer Rooms LMG 671 and the second shows the waveforms collected from an oscilloscope, the grid voltage and the current injected into the grid by the photovoltaic inverter grid-tie.
Inverter power factor control
Grid-tie photovoltaic inverters (connected to the grid) have the ability to inject current with a controlled phase lag, in relation to voltage, into the electrical distribution network. This allows the inverter to control the amounts of active and reactive energy it injects into the electrical grid.
In general, photovoltaic inverters are normally programmed to work with unitary PF, that is, to inject purely active power. However, it has been common to use this reactive power injection capacity to make the inverter itself compensate for the installation's power factor, performing a function similar to that of a capacitor bank.
It is important to note that there is a limit to the current injection that the inverter can perform. Therefore, if it is programmed to inject a certain amount of reactive power, it will have a reduced capacity to inject active power. Assistance in controlling the stability of the electrical grid can also be requested from inverters through their ability to inject reactive power into the distribution network.
This does not yet happen in Brazil, but in the future we will encounter situations in which the electricity concessionaire will be able to send signals to the inverters of distributed generation systems, making them inject reactive power as the needs of the electrical grid require. In other words, the electricity distributor will be able to manage the inverters connected to its distribution network.
This already happens, for example, in California, where the “California’s Interconnection Rule 21”. In phase 1 of the implementation of this regulation, inverters connected to the grid had to be “smart inverters”, compatible with some control requirements required to support the control of the electrical network.
In phase 2, started in 2019, communication requirements for inverters were established, integrating them into an IoT (internet of things) network so that they could be remotely controlled by electricity distributors.
In phase 3, still planned for the future, advanced functionalities will be specified, taking advantage of the communication channels created in phase 2.
Power Factor Control Tests
In the next article (Part II: Normative tests) we will talk about power factor control tests, which are part of the requirements for the approval of inverters in the INMETRO (National Institute of Metrology, Quality and Technology) certification program.
Test guidelines and requirements are determined by the following technical standards:
- ABNT NBR 16150 – Photovoltaic (PV) systems – Characteristics of the connection interface with the electrical distribution network – conformity test procedures;
- ABNT NBR 16149 – Photovoltaic (PV) systems – Connection interface characteristics with the electrical distribution network.
References
- California's Interconnection Rule 21: What it means for utilities and customers across the US, https://www.openintl.com/california-rule-21-interconnection/
- Booklet “Photovoltaic Inverters Connected to the Grid, Test Procedures”, produced by INRI (Intelligent Grids Institute) of UFSM (Federal University of Santa Maria)
Comments (7)
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Good morning
I have a load where almost all motors are connected through inverters, keeping the power factor around 0,94
When I disconnect the loads, or on the weekend, when the factory is stopped, the photovoltaic inverter injects into CEMIG with a power factor of 0,8.
Can I correct the power factor generated by the photovoltaic?
I have customers paying Power Factor fines, even with automatic capacitor banks. The people responsible for the installation do not provide support. In the sun, the controller varies. Sometimes it indicates 0.95, sometimes 0.70, sometimes 0ra – 0,45. Anyway, I need a tip. Thanks.
When the load (machine consumption, etc.) drops in relation to the power injected by the inverter, the Power Factor will become inductive and may fall below 0,92. In fact, the injection of reactive power does not change, but the utility meter does not see it that way. It sees it as if the load decreased and the reactive power remained the same, i.e., the Power Factor drops. For this reason, it is interesting to program the inverter to inject capacitive reactive power. For example, programming it to inject 0,92 capacitive power would be interesting to compensate for this inductive power, or to place an automatic capacitor bank at the general input of the installation, or only at the consumption loads, configuring it to always keep the PF as close as possible to 1,00.
I would like to better understand in future articles and publications how the distribution network will control the Power Factor of each photovoltaic generator in network management! Can we say that each photovoltaic generator will be an IP in this information network? If so, would this imagined network be built by the network's own power cables?
This subject is not being discussed yet Jacques, in general concessionaires impose unitary PF for inverters. But if the concessionaire requests a different PF, whether capacitive or inductive, the inverters are already prepared for this. I believe that this will require specific regulation, as the owner of the PV system needs to be remunerated for this service provided to the grid, it would be an ancillary service.
Excellent article.
Excellent article, congratulations Eng Guilherme.