1. Power factor correction (PFC)
Power Factor Correction (PFC) is designed to improve the power factor of a power system, reduce reactive power, and improve the efficiency of power utilization. There are two common PFC algorithms: average current mode control and peak current mode control.
Average current mode control adjusts the PWM duty cycle for correction purposes by detecting the average value of the input current and comparing it to a reference value. This method can effectively reduce the harmonic components of the current and improve the quality of the input current.
Peak current mode control, on the other hand, adjusts the PWM duty cycle by detecting the peak value of the current and comparing it with the reference value. Compared to average current mode control, peak current mode control has a faster response time but is more sensitive to noise.
2. LLC resonant converter
LLC resonant converter is a kind of high-efficiency DC-DC converter, which is widely used in the intermediate circuit of PV inverter.LLC resonant converter utilizes the resonant network (composed of inductor L and capacitor C) to realize soft switching, which reduces switching loss and improves conversion efficiency.
Frequency control: LLC resonant converter usually adopts the method of frequency control, i.e., to control the output voltage by adjusting the switching frequency. the main task of DSP is to realize the high-precision frequency control algorithm to ensure the stable operation of the resonant converter under different load conditions.
Current mode control is also used in LLC resonant converters to adjust the switching frequency by detecting the resonant current and comparing it with a reference value. This method can better cope with load changes and improve the dynamic response of the system.
3. BUCK converter
BUCK converter is a step-down DC-DC converter, which is commonly used for voltage regulation in PV systems. Its control algorithm mainly includes voltage mode control and current mode control.
Voltage mode control adjusts the PWM duty cycle to maintain a stable output by detecting the output voltage and comparing it with the set value. This method is simple to implement, but the response to changes in input voltage and load is slow.
Current mode control adjusts the PWM duty cycle by detecting the inductor current and comparing it to a set value. Compared to voltage-mode control, current-mode control can respond more quickly to changes in input voltage and load, improving the dynamic performance of the system.
4. BOOST converter
BOOST converter is a boost type DC-DC converter used to raise the low voltage of the PV cell to the DC voltage required by the inverter. Its control algorithm is similar to that of the BUCK converter and mainly consists of voltage mode control and current mode control.
Voltage mode control adjusts the PWM duty cycle to maintain a stable output by detecting the output voltage and comparing it to a set value. Although the realization is simple, the response speed is relatively slow.
Current mode control regulates the PWM duty cycle by detecting the inductor current and comparing it with the set value. The advantage lies in the fast response speed, which can better cope with the changes of input voltage and load.
5. Phase-shift full bridge (PSFB)
The phase shift full bridge (PSFB) converter is a highly efficient DC-DC converter widely used in high power PV inverters. Its main feature is to realize soft switching and reduce switching losses through phase shift control.
Phase shift control is the core of the PSFB converter, which controls the output voltage by adjusting the phase difference of the bridge arms.The DSP needs to implement complex phase shift control algorithms to ensure that the converter operates stably under different load conditions.
Current mode control can also be applied to the PSFB converter to adjust the phase shift angle by detecting the current and comparing it with a set value. This approach improves the dynamic response and stability of the system.
6. Inverter control
The main function of an inverter is to convert DC power to AC power to be supplied to the grid or load. Common inverter control algorithms include SPWM (Sinusoidal Pulse Width Modulation), SVPWM (Space Vector Pulse Width Modulation), and multilevel control.
SPWM control generates a PWM waveform by comparing a sinusoidal reference signal with a high-frequency carrier signal for DC to AC conversion.The task of the DSP in this is to generate a high-precision SPWM signal and adjust it in real time.
SVPWM control generates PWM signals by the space vector method. compared with SPWM control, SVPWM can utilize the DC voltage more efficiently and improve the output efficiency of the inverter. the DSP needs to implement the complex SVPWM algorithm to ensure efficient and stable inverter output.
Multilevel control is widely used in multilevel inverters to achieve higher output voltage and lower harmonic distortion through multilevel modulation techniques. the DSP needs to coordinate the control of multiple cascade modules to ensure the overall performance and stability of the system.
7. Important control link technologies
In addition to the above basic control algorithms, some important control link techniques are involved in the development of DSP for PV inverters, such as ANPC control, DPWM control, weak grid control and specified harmonic elimination techniques.
ANPC (Active Midpoint Clamping) control is a highly efficient multilevel inverter control technique that achieves higher output voltage and lower harmonic distortion through active clamping elements.The DSP needs to implement the ANPC algorithm to ensure the efficient and stable operation of the system.
DPWM (Digital Pulse Width Modulation) control realizes PWM control through digital signal processing, compared with the traditional analog PWM, DPWM has higher precision and stability. the DSP needs to implement the high precision DPWM algorithm to ensure the efficient operation of the inverter.
Weak Grid Control: In a weak grid environment, where the grid voltage fluctuates greatly, the PV inverter needs to have a stronger anti-interference capability, and the DSP needs to implement complex weak grid control algorithms to ensure stable operation of the system during grid fluctuations.
Specified harmonic elimination technology eliminates harmonic components in the output voltage through specific algorithms to improve power quality. the DSP needs to implement precise harmonic analysis and elimination algorithms to ensure the purity of the output voltage.