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See Power Optimizers for generalities.  

The Huawei Power optimizers are  module-level buck-only optimizers. These are only compatible with some Residential and Commercial Inverters of the Series SUN2000 of Huawei.

The optimizer has to permanently communicate with its inverter, through the DC connections. The inverter controls the operating mode of the optimizer; namely the optimizer output voltage remains null when the inverter is not working in normal conditions. A special behaviour of these optimizers ensures the voltage limitation of the array (see below "Long strings").  

Huawei rules

The use of Huawei optimizers is submitted to very specific rules edicted by Huawei.

These rules are implemented/applied in PVsyst since the version 7.4.4. Previous simulations may have been conducted without observing these rules: If simulations are not compatible with the new rules, these cannot be performed again in the new versions, without updating your system for conformity with these rules.

The limits, specified by Huawei, are hard-coded in PVsyst, and cannot be overcome.

The main characteristics of these rules are:

▪Each optimizer kind has a specific set of compatible inverters. In other words, the rules determine the compatibility between an optimizer and a given inverter.  

▪One MPPT can only receive one string of optimizers. There may be unused MPPT inputs.

▪For each association Optimizer-Inverter, there is a minimum and a maximum allowed number of optimizers is series.

▪For each association there is a maximum Power per string  (i.e. PNom of the connected PV modules).

▪The difference between 2 MPPT inputs cannot exceed 2000 W.

▪For each association, and each number of MPPT used, there is a minimum and a maximum allowed PNom ratio for the full inverter.

▪For each association, the rules define a maximum voltage. A very special treatment is applied for treating the strings exceeding this voltage (see below).

These complex rules lead to define the Huawei systems with a very new concept in PVsyst, i.e. create an explicit list of "physical" inverters, and associate different strings to each of them.  See the "Huawei Procedure"  page for further details.

Long strings

The string input voltage is defined as the addition of voltages of all the PV modules.  The string input Voc is the sum of all Voc of PV modules at STC. Let us name it VocStrIn

For each Optimizer-Inverter association, the rules specify a maximum voltage VStrMax for the full string.

If the   VocStrIN exceeds VStrMax, the optimizer will work in boost mode (voltage diminution and current increase), adjusting the duty cycle in order to  limit the string Voc to the VStrMax value. This will "compress" the P/V curve of the optimizer output in voltage.

This boost value  is calculated for the STC conditions, and stored in the optimizer. It is applied to any irradiance and temperature conditions, so that the string voltage will never exceed the  VStrMax,  unless the temperature drops below 25°C, or the irradiance exceeds 1000 W/m2.

This mechanism allows to define very long strings (up to 25 optimizers with 2 PV modules). However remember that the optimizer efficiency slightly diminishes when the duty cycle decreases.

NB: for the inverter input safety condition, this Maximum string voltage is not the right value for applying the Low-temperature safety limit. The inverter VAbsMax should be above VStrMax by a factor  corresponding to  muVoc * (25°C - TMin).   For muVoc = 0.35%/°C and TMin = -10°C, this corresponds to an excess factor of  12.2%.  

This limitation is not checked by PVsyst; it should be  managed by the Huawei rules, This is indeed the case as most associations have a VStrMax = 900V, and the associated inverters have VAbsMax = 1100 V.  

Limitations: