AN3095 datasheet(42/55 Pages) STMICROELECTRONICS

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STM32F103xx-based current control strategy for inverter grid connection

AN3095

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Doc ID 16555 Rev 3

by the well known maximum power point algorithm. The main functions of the MPPT

algorithm are shown in Figure 28.

Figure 28.

Block diagram of the implemented MPPT algorithm

The block diagram is an explanation of the perturb and observe (P and O) method, a very

common and easy way to implement an MPPT technique. The PV array voltage is

compared to a constant reference voltage, which corresponds, once the algorithm has

reached the convergence, to the PV array voltage at the maximum power point, under

specific atmospheric and temperature conditions. The error signal is used as the input of a

PI regulator which generates a command (phase-shift angle) used to drive the power

devices of the DC-DC converter. The reference voltage is the output of the flow chart of

Figure 27

where, based on the calculation of PV output power by sampling input voltage and

current values, the power change is detected, by comparing the present and previous

voltage levels, together with the change of the input voltage. Therefore, the reference

voltage is incremented or decremented according to both array power and voltage change,

[see References 17, 18].

Apart from gird connection and MPPT, some other functions are implemented for the correct

operation of the conversion system. The following is a brief description of these functions:

●

Input voltage control

Input voltage value is constantly monitored to ensure that the array voltage is always in the

correct operating range, between 200 V and 400 V. The voltage value is also utilized to

minimize the conversion ratio between the input and output of the DC-DC converter. For

example, if the input voltage is between 200 V and 250 V the output voltage is regulated at

400 V. For higher input voltage values the reference bus DC voltage is regulated at 450 V. In

this way, the conversion ratio for the DC-DC converter is minimized and the efficiency

improved. If the input voltage value is below 200 V or above 400 V, the input

under/overvoltage protection is enabled. Consequently, the modulation is disabled in both

stages and the relays disconnect the system from the grid. For the sake of security the

complementary pairs must be disabled synchronously in case of power stage failure/fault

and this is performed by a dedicated emergency stop input embedded in the peripheral.

AN3095 Datasheet(PDF) 42 Page - STMicroelectronics