Application of SVPWM Generated Based on DSP in Inverter Power Supply

1 Photovoltaic grid connection

Power generation system composition

The photovoltaic grid-connected power generation system is mainly composed of solar panels (i.e. photovoltaic arrays), grid-connected inverters, filter reactors and DSP control circuits. The structure of the entire system is shown in Figure 1.

As shown in Figure 1, the photovoltaic grid-connected power generation system uses solar panels to convert solar energy into DC power, and then uses the controlled current source characteristics of the grid-connected inverter to control the inverter to operate in the power generation state, converting DC power into AC power to feed the grid.

The energy conversion and transfer process of the entire system is realized by using the grid-connected inverter circuit composed of IPM modules, and the control of the grid-connected inverter is completed by generating the PWM signal of the driving main circuit through DSP.

2 Grid-connected inverter control principle

According to the working principle of the photovoltaic grid-connected power generation system, the grid-connected inverter is the core device of the entire grid-connected power generation system, and the performance of the grid-connected inverter determines the performance of the entire system. For the photovoltaic grid-connected power generation system shown in Figure 1, the grid-connected inverter designed in this paper adopts a three-phase half-bridge inverter topology, and its structure is shown in Figure 2.

The voltage and current signals output by the AC side of the grid-connected inverter satisfy the following equations:

In the above model, L represents the inductance parameter on the AC side, and R is the parasitic resistance in the inductor. Since the equivalent impedance of the inductor is much larger than the resistance, the effect of R on the regulator design can be ignored during the system design process.

According to the mathematical model of the three-phase voltage source PWM grid-connected inverter, it can be seen that the grid-connected inverter controls the output current by controlling the output voltage of the three-phase voltage source inverter bridge arm. While controlling the output current, in order to increase the power generation of the photovoltaic grid-connected inverter system and make full use of the maximum power that the photovoltaic array can provide under the same lighting conditions, the maximum power point tracking (MPPT) technology is introduced in the control system of the corresponding photovoltaic grid-connected inverter device.

FIG2 shows the control structure of the grid-connected inverter. As can be seen from FIG2, the outer loop of the control structure of the grid-connected inverter is the power loop, which adopts the self-optimizing MPPT algorithm. The self-optimizing algorithm calculates the output power at the current moment by sampling the output voltage and current signals of the current inverter device, and then compares it with the output power calculated at the previous moment. The working point of the grid-connected inverter is continuously adjusted according to the output power, and finally the working point of the grid-connected inverter changes along the maximum power curve of the photovoltaic array. The inverter calculates the DC voltage loop command signal of the photovoltaic array at this power point according to the MPPT algorithm. The error signal of the voltage loop outputs the current loop amplitude command after passing through the PI regulator link. The amplitude command is multiplied by the synchronization signal of the grid voltage as the synchronization command signal of the current loop. The output current of the system is controlled by the current error and the inner loop proportional regulator. The gain of the current loop determines whether the system output current can accurately track the command signal, and at the same time determines whether the photovoltaic grid-connected system can achieve maximum power grid-connected power generation with a unity power factor.