With the growing global demand for clean energy, photovoltaic inverters, as the core component of solar power generation systems, directly affect the power generation capacity and stability of the entire system. Digital Signal Processors (DSPs) are widely used in photovoltaic inverters to implement complex control algorithms, enhancing the system’s response speed and accuracy. This article will introduce common algorithms in the embedded development of DSPs for photovoltaic inverters, covering Power Factor Correction (PFC), LLC resonant conversion, BUCK, BOOST, Phase Shift Full Bridge (PSFB), and inverter control.
1. Power Factor Correction (PFC)
Power Factor Correction (PFC) aims to improve the power factor of the power system, reduce reactive power, and enhance the efficiency of energy utilization. There are two common PFC algorithms: average current mode control and peak current mode control.
Average current mode control detects the average value of the input current and compares it with a reference value, adjusting the PWM duty cycle to achieve correction. This method effectively reduces the harmonic components of the current and improves the quality of the input current.
Peak current mode control detects the peak value of the current and compares it with a reference value, adjusting the PWM duty cycle. Compared to average current mode control, peak current mode control has a faster response speed but is more sensitive to noise.
2. LLC Resonant Conversion
LLC resonant conversion is an efficient DC-DC converter widely used in the intermediate circuit of photovoltaic inverters. The LLC resonant converter utilizes a resonant network (composed of inductance L and capacitance C) to achieve soft switching, thereby reducing switching losses and improving conversion efficiency.
Frequency control: The LLC resonant converter typically employs frequency control, adjusting the switching frequency to control the output voltage. The main task of the DSP is to implement a high-precision frequency control algorithm to ensure stable operation of the resonant converter under different load conditions.
Current mode control is also applied in LLC resonant converters, detecting the resonant current and comparing it with a reference value to adjust the switching frequency. This method can better respond to load changes and improve the system’s dynamic response capability.
3. BUCK Conversion
The BUCK converter is a step-down DC-DC converter commonly used for voltage adjustment in photovoltaic systems. Its control algorithms mainly include voltage mode control and current mode control.
Voltage mode control detects the output voltage and compares it with a set value, adjusting the PWM duty cycle to maintain a stable output. This method is simple to implement but has a slower response to changes in input voltage and load.
Current mode control detects the inductor current and compares it with a set value, adjusting the PWM duty cycle. Compared to voltage mode control, current mode control can respond more quickly to changes in input voltage and load, improving the system’s dynamic performance.
4. BOOST Conversion
The BOOST converter is a step-up DC-DC converter used to increase the low voltage from photovoltaic cells to the DC voltage required by the inverter. Its control algorithms are similar to those of the BUCK converter, mainly including voltage mode control and current mode control.
Voltage mode control detects the output voltage and compares it with a set value, adjusting the PWM duty cycle to maintain a stable output. Although simple to implement, its response speed is relatively slow.
Current mode control detects the inductor current and compares it with a set value, adjusting the PWM duty cycle. Its advantage lies in its fast response speed, allowing it to better handle changes in input voltage and load.
5. Phase Shift Full Bridge (PSFB)
The Phase Shift Full Bridge (PSFB) converter is an efficient DC-DC converter widely used in high-power photovoltaic inverters. Its main feature is achieving soft switching through phase shift control, reducing switching losses.
Phase shift control is the core of the PSFB converter, controlling the output voltage by adjusting the phase difference of the bridge arms. The DSP needs to implement complex phase shift control algorithms to ensure stable operation of the converter under different load conditions.
Current mode control can also be applied to PSFB converters, detecting the current and comparing it with a set value to adjust the phase shift angle. This method can improve the system’s dynamic response capability and stability.
6. Inverter Control
The main function of the inverter is to convert DC power into AC power for supply to the grid or load. Common inverter control algorithms include SPWM (Sine Pulse Width Modulation), SVPWM (Space Vector Pulse Width Modulation), and multilevel control.
SPWM control generates PWM waveforms by comparing a sine wave reference signal with a high-frequency carrier signal to achieve the conversion from DC to AC. The DSP’s task is to generate high-precision SPWM signals and perform real-time adjustments.
SVPWM control generates PWM signals using the space vector method, which can utilize DC voltage more effectively than SPWM control, improving the inverter’s output efficiency. The DSP needs to implement complex SVPWM algorithms to ensure efficient and stable inverter output.
Multilevel control is widely used in multilevel inverters, achieving higher output voltage and lower harmonic distortion through multilevel modulation techniques. The DSP needs to coordinate the control of multiple cascaded modules to ensure the overall performance and stability of the system.
7. Important Control Techniques
In addition to the basic control algorithms mentioned above, the DSP development for photovoltaic inverters also involves several important control techniques, such as ANPC control, DPWM control, weak grid control, and specified harmonic elimination techniques.
ANPC (Active Neutral Point Clamping) control is an efficient multilevel inverter control technology that achieves higher output voltage and lower harmonic distortion through active clamping components. The DSP needs to implement the ANPC algorithm to ensure the system’s efficient and stable operation.
DPWM (Digital Pulse Width Modulation) control achieves PWM control through digital signal processing, offering higher precision and stability compared to traditional analog PWM. The DSP needs to implement high-precision DPWM algorithms to ensure the efficient operation of the inverter.
Weak grid control: In weak grid environments, where grid voltage fluctuates significantly, photovoltaic inverters need to possess stronger disturbance resistance. The DSP needs to implement complex weak grid control algorithms to ensure stable operation of the system during grid fluctuations.
Specified harmonic elimination techniques eliminate harmonic components in the output voltage through specific algorithms, improving power quality. The DSP needs to implement precise harmonic analysis and elimination algorithms to ensure the purity of the output voltage.
The DSP embedded development for photovoltaic inverters involves numerous complex control algorithms, each with its unique application scenarios and technical challenges. By designing and optimizing these algorithms effectively, the performance and efficiency of photovoltaic inverters can be significantly enhanced. It is hoped that this article can provide reference for engineers engaged in photovoltaic inverter development.
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