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High Voltage Ride Through control algorithm for PV inverter

IP.com Disclosure Number: IPCOM000245689D
Publication Date: 2016-Mar-30
Document File: 3 page(s) / 307K

Publishing Venue

The IP.com Prior Art Database

Related People

Fabio Tombelli: AUTHOR

Abstract

The algorithm requires a photovoltaic converter equipped with at least a DC-DC converter responsible for increasing and for keeping stable the DC-link voltage under high voltage fault. The algorithm goal is to detect the fault and to manage the DC-DC control loop reference. When a grid over voltage occurs, the control rises up the DC-link voltage at a value enough to generate an output voltage in magnitude higher than the grid voltage, avoiding reverse power flow from the grid to the bulks.

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   High Voltage Ride Through control algorithm for PV inverter
1. State of the art technology
Nowadays, high voltage ride through (HVRT) is a high demanded feature in the renewable market.

The wind market is surely the sector where, before the other, was implemented this kind of control. Companies and R&D centres studied many different algorithms especially for doubly-fed induction machines.

To guarantee a safe operation of the back-to-back converter during the HVRT, it has to be ensured that the converters always work in their permissible voltage range. The maximum available converter voltage, which can be modulated from the DC voltage using the min-max algorithm, is:

ܸ௣௛௔௦௘ି௣௛௔௦௘ = ܸ஽஼ି௟௜௡௞

√2

During HVRT different problems may arise from the increased voltages at LSC and MSC. These problems require adequate solutions in the converter control.

An effective way to manage the back-to-back converter during HVRT is to control the DC link voltage, by increasing it in relationship to the grid voltage. A higher DC-link voltage lets the inverter staying always connected to the grid, being able to generate a max output voltage in magnitude higher than the grid voltage in any conditions. After the fault, the control sets the DC-link voltage at the nominal voltage present before the fault.

Before this approach, the most common way for being compliant with grid standards was to design a converter with a constant DC-link voltage, having a magnitude enough to ride through the worst high voltage transient requested. This method is not effective from an efficiency point of view.


2. Proposed control

The proposed solution uses an algorithm similar to the algorithm described in above paragraph 1, but oriented to the PV application. The algorithm requires a photovoltaic converter equipped with at least a DC-DC converter responsible for increasing and for keeping stable the DC-link voltage under high voltage fault.

The algorithm goal is to detect the fault and to manage the DC-DC control loop reference. When a grid over voltage occurs, the control rises up the DC-link voltage at a value enough to generate an output voltage in magnitude higher than the grid voltage, avoiding reverse power flow from the grid to the bulks.

An exemplary reference hardware topology for this application is a four level inverter with two DC- DC converters (Figure 1).

© ABB Group March, 2016



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Figure 1: Reference topology


Figure 2 shows the DC-link voltage control algorithm. VDc-link_base is the DC-link voltage value for normal operations (1100Vdc in th...