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PV voltage and current sampling circuit in MPPT unit

Introduction

In photovoltaic Power generation systems, Maximum Power Point Tracking (MPPT) technology is a key means to improve energy conversion efficiency. In order to monitor and control the output power of photovoltaic modules in real time, the accurate sampling of PV voltage and current is particularly important. As an important part of MPPT unit, the design rationality of PV voltage and current sampling circuit directly affects the performance of MPPT algorithm and the overall efficiency of the system. In this paper, the working principle, structure, realization method of PV voltage and current sampling circuit and its importance in MPPT are discussed.

the working principle of PV voltage and current sampling circuit

The main task of the PV voltage current sampling circuit is to obtain the output voltage (V_PV) and output current (I_PV) of the photovoltaic module in real time, and convert it into a signal (usually a digital signal) suitable for subsequent processing. This information will be used in the MPPT control algorithm to adjust the output of the DC-DC converter, thereby optimizing the power output of the photovoltaic system.

Voltage sampling

PV Voltage sampling is usually done by voltage Divider (Voltage Divider) or Operational Amplifier (Op-Amp). The voltage divider reduces the photovoltaic voltage to a range suitable for analog input with two resistors, while the operational amplifier provides higher input impedance and gain. Its features include:
High input impedance: to reduce the loading impact on the PV module.
Linear range: Ensure that the output signal is within the ADC (Analog to Digital Converter) sampling range.

Current sampling

PV current sampling is usually done using a current sensor, such as a Shunt Resistor or a Hall effect sensor. Shunt resistors measure current by placing a low-value resistor (such as a milliohm resistance) in series along the path through which the current flows, and the resulting voltage drop can be amplified by an amplifier for subsequent processing. The Hall effect sensor obtains the current information through the magnetic field generated by the induced current, which has the advantage of electrical isolation. Key features of current sampling include:
High accuracy: Precise measurement of instantaneous current.
Low power consumption: Avoid excessive power consumption interference to the PV module.

the main structure of PV voltage and current sampling circuit

Schematic diagram of voltage sampling circuit

R1 and R2: As voltage divider resistors, select the appropriate resistance values to ensure that V_sample is within the ADC input range.
ADC: Used to convert analog signals into digital signals for MPPT algorithm processing.

Schematic diagram of current sampling circuit

Current sampling circuit can use shunt resistor, schematic diagram is as follows:
R_shunt: A shunt resistor that obtains current information by measuring the voltage drop at both ends.
Amplifier: Amplifies the voltage drop signal to fit the input range of the ADC.

Technical requirements for PV voltage and current sampling

Accuracy and linearity

High precision voltage and current sampling is the basis of MPPT performance. The precision, resolution and nonlinear characteristics of the device should be considered in the design to ensure the accurate reading of the working state of the PV module.

Bandwidth and response time

Voltage and current sampling circuits need to have sufficient bandwidth and fast response time to adapt to the influence of light changes and load fluctuations on photovoltaic power output. The sampling frequency is generally required to be greater than 10 times the light change frequency to ensure real-time tracking of the maximum power point.

Noise and interference

In the environment of high frequency signal, electronic noise and interference will affect the accuracy of sampling. It is necessary to adopt appropriate filtering technology and layout design to reduce these negative effects. For example, a low-pass filter can be used to remove high-frequency noise and reduce electromagnetic interference (EMI) through proper layout.

the importance of MPPT

PV voltage and current sampling circuit plays a crucial role in MPPT system:
Real-time monitoring: Provides actual voltage and current data to help the MPPT algorithm react quickly.
Improved efficiency: Accurate sampling improves the accuracy of the MPPT control algorithm, optimizes the utilization of photovoltaic energy efficiency, and improves the overall efficiency of the system.
Adaptability: In rapidly changing environmental conditions, accurate sampling enables rapid adjustment of the DC-DC converter, keeping it near the maximum power point.

Summary

PV voltage and current sampling circuit is the core component of MPPT unit, its design and implementation is very important to improve the energy conversion efficiency of photovoltaic system. Through reasonable selection of current and voltage sensors and corresponding signal processing circuits, the working status of photovoltaic modules can be obtained in real time, and reliable data support can be provided for the implementation of MPPT control strategy. With the continuous progress of photovoltaic technology, the accuracy and response speed of the sampling circuit will be further improved, thus promoting the efficient operation of the photovoltaic power generation system.

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