Design and implementation of maximum power point tracking inverter

　　With the continuous development of industry and science and technology, the requirements for power quality will become higher and higher. The quality of raw power, including the mains power grid, may not meet the requirements of the equipment and must be converted by power electronic devices before use. DC/AC inverter technology will play an important role in this conversion. According to market trends, the selection and installation of inverters are increasingly inclined to miniaturization, intelligence, modularization and other directions. Its control circuit mainly adopts digital control, system safety, reliability and scalability, and various perfect protection circuits are taken into consideration. Therefore, a maximum power tracking inverter design based on IR2101 is proposed here.

　　1 Introduction to IR2101

　　IR2101 is a dual-channel, gate-driven, high-voltage and high-speed power driver. The device uses highly integrated level conversion technology, which greatly simplifies the control requirements of the logic circuit for the power device and improves the reliability of the drive circuit. At the same time, the upper tube uses an external bootstrap capacitor to power up, which greatly reduces the number of drive power supplies compared to other IC drivers, reduces the volume of the control transformer and the number of power supplies in engineering, reduces product costs, and improves system reliability.

　　IR2101 adopts HVIC and latch anti-interference manufacturing process, integrated DIP, SOIC package. Its main features include: floating channel power supply adopts bootstrap circuit; power device gate drive voltage range is 10 ~ 20 V; logic power supply range is 5 ~ 20 V, and +5 V offset is allowed between logic power supply ground and power ground; CNOS Schmitt input with pull-down resistor, convenient for matching with LSTTL and CMOS level; independent low-end and high-end input channels. The internal structure block diagram of IR2101 is shown in Figure 1.

　　Figure 1 Internal structure diagram of IR2101

　　In Figure 1, HIN is the logic input high; LIN is the logic input low; VB is the high-side floating supply; HO is the high-side gate driver output; Vs is the high-side floating supply return; Voc is the power supply; LO is the low-side gate driver output; and COM is the common terminal.

　　2 System Hardware Design

　　According to the functional requirements of the system design, its hardware block diagram is shown in Figure 2. The system hardware design is composed of the SPMC75F2413A single-chip microcomputer main controller module, the external energy supply system (ordinary or photovoltaic), the chopper circuit module, the IR2101 inverter circuit module and the maximum power tracking external circuit module. The maximum power tracking external circuit module detects the external voltage and returns the detection value to the SPMC75F2413A main controller. The chopper circuit module controls it through the main controller to achieve maximum power tracking. The external energy supply system provides power for each module. The IR2101 inverter circuit module mainly realizes DC/AC conversion, and the chopper circuit provides it with electrical energy at the maximum power point.

　　Figure 2 Overall design block diagram of system hardware

　　The normal operating voltage of the SPMC75F2413A microcontroller in Figure 2 is 5 V. However, the voltages added to other modules are different. The voltages added to the chopper circuit module and the IR2101 inverter circuit module are 15 V. This is because the normal operating voltage of the IR2101 is 10 to 20 V.

　　2.1 IR2101 inverter circuit

　　The schematic diagram of the IR2101 inverter circuit is shown in Figure 3. H1 and H2 are IR2101 integrated driver chips, VQ1, VQ2, VQ3, and VQ4 are MOS tubes, and Up, Un, Vp, and Vn are two-phase four-way PWM waves output from the SPMC75F2413A microcontroller. Among them, Up and Un are the upper and lower arms of one-phase PWM waves, and Vp and Vn are the upper and lower arms of another-phase PWM waves. Since the PWM waves output from the microcontroller cannot drive high-power MOS tubes, the capacitor bootstrap function of IR2101 is used to charge the bootstrap capacitors C1 and C2 through diodes VD1 and VD2 (using the fast recovery function of Schottky tubes to increase the capacitor charging voltage and reduce energy consumption during the shutdown process), so as to increase the signal voltage of the driving MOS tube, so that it has the function of expanding the signal output. The expanded signal PWM wave can orderly control the on and off of VQ-1, VQ2, VQ3, and VQ4. In the inverter circuit, the drive signals of the upper and lower arms of the same phase are complementary.

　　Figure 3 IR2101 inverter circuit schematic

　　When the Up input is high, the HO output is also high. Through the capacitor bootstrap function of IR2101, VQ1 can be controlled to turn on. At this time, since the LO output is low, VQ2 cannot be driven, so VQ2 is in the off state. At the same time, Vp also inputs a high level, that is, HO is high, so that VQ4 is in the on state, and VQ3 is in the off state at this time, so T1→VQ1→R5 (load)→VQ4→GND forms a path. On the contrary, when Up and Vp are low levels, and Un and Vn are high levels, that is, the main flow direction of the current is T1→VQ3→R5 (load)→VQ2→GND, and the four MOS tube switch devices are alternately turned on and off in an orderly manner, thereby forming an alternating current at R5 (load). In practical applications, in order to prevent the upper and lower arms from being turned on at the same time and causing a short circuit, dead time is added during the software design process to protect the entire circuit.　　2.2 Chopper circuit

　　The schematic diagram of the chopper circuit is shown in Figure 4. This circuit is mainly used for maximum power tracking. Its power supply is an independent voltage source. R6 (30 Ω/30 W) is a power resistor, which is mainly used as the internal resistance of the power supply. R7 and R8 are voltage divider circuits formed to detect the voltage value at the load end. The detection is performed through Ud1, and the detection result is returned to the microcontroller for processing. By adjusting the duty cycle of the PWM wave, the opening and closing time of VQ5 is controlled. When it is detected that the value of Ud1X (R7+R8)/R8 is greater than half, the microcontroller will increase the duty cycle of the chopper circuit to increase the voltage passing through it, so that its value is close to half of the photovoltaic cell. If it is detected that its value is less than half, the duty cycle will be reduced to reduce the voltage passing through it. In this way, the frequency tracking function is realized by tracking the voltage.

　　Figure 4 Schematic diagram of chopper circuit

　　2.3 Maximum Power Tracking Model Analysis

　　This design is to realize the maximum power tracking model. As shown in the circuit in Figure 5, the internal resistance R8 and the external resistance Rb are equal. When the voltage of Ud is half of the battery power supply, the battery output power can be maximized. This situation is applied to linear circuits, but this principle can also be used in nonlinear circuits. This project realizes the maximum power tracking through the voltage tracking function, which is mainly achieved by adjusting the duty cycle of the PWM wave.

　　Figure 5 Maximum power tracking model

　　3 System Software Design

　　The A/D sampling function flow chart is shown in Figure 6. This function is mainly used to collect the voltage value at the load end and finally convert it into an amplitude modulation coefficient. The CMT0 timer interrupt is used in this function. A/D sampling is performed in this interrupt. The collected voltage value is compared with the converted power supply voltage midpoint value Vmid (see Figure 4, that is, using R7 and R8 to form a voltage divider circuit, R7: R8 = 9: 1). When the absolute value of the difference is greater than 100, it is judged that the collected value is abnormal, and the midpoint value of the power supply voltage after conversion is forced to be converted into an amplitude modulation coefficient. When the absolute value of the difference between the two is less than 100, the difference is added to Vmid, and then converted into an amplitude modulation coefficient, and finally the interrupt is returned.

　　Figure 6 A/D sampling function flow chart

　　In this function, the PWM interrupt of the chopper circuit uses the TPM2 interrupt, and the amplitude modulation coefficient is used in this interrupt to adjust the duty cycle of the PWM wave of the chopper circuit, thereby realizing the voltage tracking function and finally realizing the maximum power tracking. The chopper circuit PWM interrupt sub-function flow chart is shown in Figure 7.

　　Figure 7 Flowchart of PWM interrupt sub-function of chopper circuit

　　4 Maximum power test results

　　When testing the J2 point after the chopper circuit, a 30 W/30 Ω power resistor is connected to the J2 point as a load, and the data in Table 1 are tested.

　　Table 1 Test results

　　5 Conclusion

　　This design scheme uses the 16-bit microprocessor SPMC75F2413A single-chip microcomputer with excellent performance of the timer PWM signal generator group. It mainly uses the PWM signal generator group of this single-chip microcomputer to generate PWM waves to control the inverter circuit and the chopper circuit. It also uses the bootstrap function of IR2101 to orderly drive the power MOS tube to achieve inversion and control the PWM wave duty cycle of the chopper circuit, realizing the design of the maximum power tracking inverter. Through verification, the output sinusoidal AC signal is very obvious and has the maximum power tracking function.