AN4070 datasheet(31/53 Pages) STMICROELECTRONICS

31 / 53 page

AN4070

STM32F103xx based current control for inverter grid connection

Doc ID 022934 Rev 1

31/53

controlled transforming the current in the same reference frame and by acting on the

amplitude of the Id component. The Iq component must, also, be controlled in order to

ensure zero reactive power injection. On the contrary, if the Vq component is controlled to

zero in the PLL, the active power is controlled with the Id current component and the Iq

current component is used to control the reactive power to zero or to the desired value.

The reference values for the active and reactive component of the current are set by two

additional PI regulators in the outer control loop. The active reference current component is

generated by confronting the DC bus voltage with the reference voltage value. The error

between the actual value and the reference DC bus voltage is sent to a PI regulator whose

output is the active current component value.

Similarly, the reactive current reference value is set by another PI regulator whose input is

the error generated between the reactive power command and the actual estimated value.

The difference between the reference components of the current and the actual d-q

components are the inputs of the PI regulators in the inner control loop. The outputs of the

PI regulators in the inner loop are two voltage components, Vd and Vq. By performing a

reverse Park transformation two AC voltages are generated back on the stationary reference

frame, and so the generation of the modulating signals of the DC-AC converter can be

executed by the microcontroller. The block diagram of the control strategy described above

is shown in Figure 21. The amount of power injected into the grid depends on the power

available from the PV panel. This power is then processed by the DC-DC converter which is

controlled in order to maximize the energy yield from the array, independently from

temperature variations and irradiation conditions, by controlling its input impedance. The

control of the input impedance requires both PV array current and voltage sensing and

some simple calculations executed by the well known maximum power point algorithm. The

perturb & observe (P&O) method is a very common and easy way to implement an MPPT

technique. The DC-DC converter duty cycle is incremented or decremented according to

both array power and voltage change.

AN4070 Datasheet(PDF) 31 Page - STMicroelectronics