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Q@night Technology

With the increase of the number of Utility PV installations more increased the need and demand that solar inverter can be available to stabilize the grid by injecting a large amounts of reactive power even in adverse and cloudy conditions or even during the night.

q night technology If for example it is introduced too much energy in the grid, it happens that the value of the grid voltage increases, the electrical lines begin to overheat, and then it is necessary the need to enter a contribution of reactive energy in order to give adequate support to the distribution grid in order to be able to ensure the safety of its operational conditions of running.

In the past, this functionality had been ensured by a solar inverter only during the day and in the presence of irradiation while now, with the evolution of the functionality implemented by the latest generation of solar converters, the injection of reactive energy is also guaranteed during night through a special function called Q@night.

The description of the functionality

We are going to provide in following The description of the functionality and related capabilities available in a Q@ night inverter

with irradiation (therefore with DC energy in input to the inverter and DC input voltage different from zero and included into the range of voltage: VDC in Є [Vmin MPP…Vmax MPP]), the PV inverter is able to convert DC energy in AC energy with a semi-circular characteristic; in this status of operation the reactive power regulation is not a problem because the inverter is able to operate in any point inside the semi-circular part of the diagram P/Q, with radius directly proportional to the irradiation with maximum value of AN.

without irradiation (therefore without DC energy in input from the PV generator and with the inverter unable to convert DC energy), the PV inverter will be able to operate as a power factor corrector, both in capacitive or inductive side, with following limit (we are considering a R11015TL inverter): QMAX=512kVAr and a minimal active power consumption is equal to 10kW (equivalent to 2% of Qmax).

In order to allow the inverter a PV FIMER of producing reactive energy during night a limited number of additional components were introduced in the converter that, together with the implemented software changes in the algorithm of control, have allowed to the converter, with a reduction of costs, of offering the functionality of injection of reactive energy in an efficient and safe mode for the stabilization of the power grid behavior. In the next figure it is shown the topological structure and architecture of a Q @ Night inverter with the indication of the main additional features that have been introduced in it:
q night technology 2
Therefore the inverter are able to:
  • measure the Voltage of DC BUS inside the inverter.
  • measure the Voltage of PV field.
  • read the signals of status of the DC switch.
  • open and close DC switch.
  • pre-charge DC-BUS from AC side.
At the level of the algorithm of control, an inverter Q@Night is able to function during the day as a traditional PV inverters and during the night, after the disconnection from the solar generator,it able to inject reactive power into the grid according to the manual set or to the request from the manager of the grid through the Power Plant Controller:

BEHAVIOR AS PV INVERTER: in case of pv power available from pv generator (i.e. during day), the inverter runs in standard PV inverter mode, therefore the inverter researches the maximum MPP point in order to convert the max DC power available from PV generator and in the same time it generates the reactive power according to the set received by the PPC command.

BEHAVIOR AS Q@NIGHT INVERTER: in case of pv power not available from pv generator (i.e. during night), At first the inverter opens the DC Switch to avoid to feed reverse current into the PV Array. Then it starts up the Q@Night function mode by the regulation of the DC BUS voltage and it generates reactive power according to PPC command.


The algorithms of control that are executed by a solar converter in PV inverter operation mode are therefore the following:
  • at low level the fastest algorithm is the current control loop (at PWM frequency).
  • At highest level there is:
    P and Q control loop (executed at Grid frequency).
    P control loop is managed from MPPT (or Grid Service for limitation).
    Q control loop is managed from external command (by request from Power Plant Controller).
The control unit internally consists of two separate blocks: q night technology 3
  1. The first one is a state machine that calculates the current set-point to inject into the Grid.
  2. The second one is a real-time control of current.


q night technology 4 The Current Set-point is generated as vectorial sum of two components:

  1. Id is the direct current in phase with the Grid
  2. Iq is the quadrature current at + or - 90° respect the Grid
  1. Id corrisponde alla corrente iniettata in fase con la rete
  2. Iq corrisponde alla corrente in quadratura sfasata a +/- 90°rispetto alla rete
The algorithms of control that are executed by a solar converter in Q@Night operation mode are therefore the following:
  • at low level the fastest algorithm is the current control loop (at PWM frequency).
  • At highest level there is:
    Q control loop (at Grid frequency).
    Q control loop that is managed from external command (from the Power Plant Controller).
    Internal DC BUS Voltage is controlled from P action.
    NOTE: P control loop is OFF.
The control unit internally consists of two separate blocks: q night technology 5
  • The action performed in the first block are:
    a) V bus is controlled with P action (Id action)
    b) P is negative to compensate the switching losses
  • The second block executes a real-time control of current, the same managed by a converter that is running in PV inverter mode.


q night technology 6 The Current Set-point is generated as vectorial sum of two components:

  1. Id is the direct current in phase with the Grid
  2. Iq is the quadrature current at + or - 90° respect the Grid
  1. Id corrisponde alla corrente scambiata in fase con la rete
  2. Iq corrisponde alla corrente in quadratura sfasata a +/- 90°rispetto alla rete
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