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Overview of inverter unit
Inverter units are a core component of photovoltaic power generation systems, battery energy storage systems and other renewable energy applications, mainly used to convert direct current (DC) to alternating current (AC). Ac is the main form of power supply for a variety of electrical equipment and power grids, so the design and performance of inverters directly affect the efficiency and stability of the system. The inverter unit not only needs efficient conversion technology, but also needs to cooperate with appropriate filtering circuit to ensure the quality of the output waveform.
In this paper, the bidirectional DC-AC converter circuit and the output LC filter circuit in the inverter unit are introduced in detail.
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.
Working principle of DC-AC conversion circuit
Two-way DC-AC conversion circuit can realize the rapid conversion between direct current and alternating current. Its basic principle is to use switching elements (such as MOSFET or IGBT) to adjust the switching state of the current, generate high-frequency AC signals through pulse width modulation (PWM) technology, and output alternating current through the converter.
Main components
Bidirectional DC-AC converter circuit mainly includes the following parts:
Switching device: MOSFET or IGBT is usually used as a switch to control the on-off and on-off of current.
Control circuit: responsible for generating switching signals, usually using PWM control method to generate the required output AC waveform, through modulation duty ratio to achieve the output voltage and frequency control.
Transformers: Transformers may be used in some designs to achieve voltage lifting and isolation functions.
Feedback system: By collecting the output voltage and current, feedback to the control circuit to adjust the switching frequency and duty cycle to ensure the stability and accuracy of the output.
Characteristics of bidirectional transformation
Bidirectional DC-AC conversion circuit can realize bidirectional energy flow between DC and AC. In photovoltaic power generation and battery energy storage systems, it can not only convert the stored electrical energy into alternating current for home or grid use, but also store excess electrical energy in the battery when the grid price is low, achieving efficient use of resources.
The function of filter circuit
The main function of the output LC filter circuit is to suppress the high-frequency noise and harmonics in the output of the inverter, smooth the AC output waveform and improve the power quality. Since the output of the inverter is PWM modulated waveform, this non-sinusoidal waveform contains many harmonic components, which can meet the requirements of the equipment and the standards of the power grid after filtering.
Composition of LC filter circuit
The output LC filter circuit is mainly composed of inductance (L) and capacitance (C) :
Inductance (L) : Inductance is used to store energy and suppress current changes, which can reduce the harmonic component of AC current in the output waveform. The choice of inductance value depends on the operating frequency and load characteristics of the system.
Capacitor (C) : The capacitor is used to smooth the voltage waveform, it can store electrical energy and release, making the output voltage more stable. The selection of capacitors also needs to take into account their voltage resistance and capacity to ensure that no damage will occur under working conditions.
Type and design of LC filter
Low-pass filter: A basic LC filter configuration that blocks high frequency signals from passing through and allows low frequency signals to pass through, thus smoothing the output waveform.
Resonant filter: The formation of resonance at a specific frequency can more effectively filter out the harmonics of some frequencies, but attention should be paid to affecting the stability of the system in the design.
Selection and design considerations: When designing the output LC filter circuit, it is necessary to comprehensively consider the output frequency, load characteristics and the expected performance of the system, rationally select the value of inductance and capacitance, and design a suitable installation layout to reduce electromagnetic interference (EMI).
inverter control strategy
In order to achieve efficient DC-AC conversion and balanced output waveform, the inverter needs to be equipped with an intelligent control strategy. Common control strategies include:
Sine wave modulation (PWM) : By adjusting the switching frequency and duty cycle, the output waveform is generated close to the sine wave.
Current control strategy: Monitor the output current and voltage in real time and keep it within the set range to ensure system stability.
Fault detection and protection mechanism: including overload protection, short circuit protection, etc., to ensure the safety and reliability of the inverter in work.
Summary
The inverter unit is an important component to realize the efficient use of renewable energy. The effective cooperation between the bidirectional DC-AC conversion circuit and the output LC filter circuit can ensure the stability and output quality of the inverter in a variety of working environments. With the continuous development of the technology, intelligent control and optimized filtering technology will further improve the performance of the inverter unit and promote the wider application of renewable energy.
Home energy storage product series
A lithium battery pack for home energy storage systems, which is compatible with solar panels and the sun The inverter can work together with the power grid to power household appliances, and it can also be used as a For off grid systems.
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