Solar Inverter system - All you need to know

1. Introduction to grid-connected solar inverter system

1.1 Composition and Function of PV System

Photovoltaic system is a device that converts solar energy into electricity, which is mainly composed of solar panels (modules), inverters, racking, cables and other electrical equipment. The core of a PV system is the solar panel, which is responsible for converting solar energy into DC energy; the inverter converts DC energy into AC energy for domestic use or for integration into the power grid.

1.2 Working principle of grid-connected PV system

When the grid-connected PV system works, the solar panel absorbs the solar radiation energy and generates DC power, and the inverter converts the DC power into AC power that matches the frequency and voltage of the power grid. When the power generated by the system exceeds the load demand, the excess power can be delivered to the grid, realizing “net metering”. Conversely, when the system does not generate enough power to meet the load demand, the required power can be purchased from the grid.

1.3 Advantages of grid-connected solar inverter system

Grid-connected solar inverter system have many advantages, including:

a): Environmentally friendly: no greenhouse gas emissions and reduced dependence on fossil fuels;

b): Economically beneficial: savings on electricity bills and the potential for additional revenue from the sale of electricity;

c): Improved grid stability: the ability to relieve grid stress during peak loads and improve grid reliability and stability.

The introduction to grid-connected solar inverter system provides a foundation for understanding the importance of the inverter in the overall system. In the following chapters, we will take a closer look at the functions and key performance indicators of the inverter and how voltage and frequency can be regulated to optimize system performance in real-world applications.

2. Inverter Core Functions

2.1 Working Principle and Classification of Inverter

2.1.1 Basic working principle of inverter

The inverter is a key component in the PV system, which is responsible for converting the direct current (DC) generated by the PV panels into alternating current (AC) for compatibility with the grid or local loads. Its principle of operation is based on the alternating closure and disconnection of power electronic switching devices, thus converting the DC supply voltage into a series of pulsed voltages, which are then converted into stabilized AC power through a filter.

The core of an inverter typically consists of the following basic components: - Input DC supply: typically from a PV array or battery storage system. - Power electronic switches: such as IGBTs (Insulated Gate Bipolar Transistors) or MOSFETs (Metal Oxide Semiconductor Field Effect Transistors), which are used to control the circuit. - Controllers: Used to control the switching time of a switching device, thereby regulating the frequency and amplitude of the output voltage. - Output filter: Used to smooth the pulse voltage generated by the switching device, outputting a more pure sinusoidal waveform.

The conversion process of an inverter can be roughly divided into the following steps:

a):  Receive a stabilized voltage from a DC source.

b): Generate alternating pulsed currents using current controllers and switching devices that conduct alternately.

c): Passes this pulsed current through a low-pass filter consisting of an inductor and capacitor.

d): outputs a stabilized alternating current to be supplied to the load or to be connected to the grid.

2.1.2 Common inverter types and their characteristics

Inverters are mainly categorized into the following types, each with its specific application scenarios and performance advantages:

Off-grid inverters: These inverters are designed for stand-alone systems that are not connected to the grid. They are usually equipped with a built-in battery charger that stores the energy generated by the solar panels during the day for use at night or on cloudy days.

Hybrid inverter: Grid-tie inverters are used to connect to the grid and they convert direct current into alternating current synchronized with the grid. These inverters need to be well controlled to ensure that the output voltage and frequency are in line with the grid.

Energy storage inverters: Energy storage inverters are a hybrid of on-grid and off-grid functionality. They can be integrated with a battery system, allowing the system to operate in off-grid mode as well as sell excess energy to the grid during normal grid operation.

Microinverters: Microinverters are usually designed for individual PV panels, each with its own inverter. They are suitable for use in distributed solar inverter system to improve the overall reliability and performance of the system.

2.2 Key Performance Indicators of Inverter

2.2.1 Calculation and optimization of conversion efficiency

The conversion efficiency of an inverter is the percentage of energy loss when converting from DC to AC. A high efficiency inverter means less energy loss, which leads to better energy utilization. The formula for conversion efficiency is as follows:

[ \eta = \frac{P_{out}}{P_{in}} \times 100\% ]

Where (P_{out}) is the output AC power and (P_{in}) is the input DC power. Optimizing the conversion efficiency of an inverter usually involves improving the performance of power electronic switching devices, optimizing the control strategy, and improving the thermal design.

In order to improve the conversion efficiency of an inverter, engineers may take the following steps: 1. use efficient switching devices 2. using more advanced control algorithms to reduce switching losses. 3. use good heat dissipation measures to keep the device temperature within a reasonable range.

2.2.2 Stability and Reliability Analysis

Stability and reliability are important indicators for evaluating the performance of an inverter. An inverter must be able to work stably for a long time and provide reliable power output under various operating conditions. Indicators for measuring the stability and reliability of an inverter include: - Failure rate: the number of failures that occur within a specified period of time. - Mean Time Between Failures (MTBF): The average time the inverter can operate normally between failures. - Maintenance Interval Time (MIT): the amount of time an inverter can go between repairs.

To ensure the stability and reliability of the inverter, the design needs to take into account redundant design, good thermal management, reliable component selection, and comprehensive testing and verification.

2.2.3 Thermal management of the inverter

When the inverter is working, the switching devices will generate heat. If this heat is not effectively dissipated, it will lead to overheating of the devices, which will affect the conversion efficiency and even cause damage to the devices. Therefore, thermal management is an important part to ensure the performance of the inverter. Thermal management of inverters mainly includes the following aspects:

Heat sink design: by designing an effective heat sink to enhance heat transfer.

Fan or Liquid Cooling System: Using active heat dissipation system such as fan or liquid cooling.

Efficient heat dissipation materials: using materials with better thermal conductivity, such as thermal interface materials (TIMs).

By reasonably designing the thermal management system, the working life of the inverter can be significantly extended and its efficient and stable operation can be maintained.

3. Islanding Effect Protection and Maximum Power Point Tracking (MPPT)

3.1 Generation of the islanding effect and protection mechanisms

3.1.1 Definition and hazards of the islanding effect

The islanding effect refers to the fact that when the power grid is out of power or fault, the PV power generation system still maintains its operation status and continues to supply power to the local power grid, forming an independent power supply island. The hazards of the island effect are mainly reflected in the following aspects:

Safety risk: The power equipment in the islanded area may not be disconnected in a timely manner, leading to the risk of electrocution when maintenance personnel unknowingly come into contact with energized equipment.

Equipment damage: As the power system in an island loses synchronization and voltage support from the main grid, it may cause overloading or voltage instability of inverters and other equipment, leading to equipment damage.

Power quality degradation: The islanding effect may lead to localized grid frequency and voltage fluctuations, affecting the stability and quality of the power system.

3.1.2 Protective measures and detection techniques

In order to prevent the harm caused by the islanding effect, the following protective measures can be taken:

a):Active detection: By setting over/under voltage and over/under frequency protection as well as phase sequence detection, the inverter can quickly detect and disconnect when the power grid is abnormal.

b):Passive Detection: Listen to the signal changes transmitted in the grid, such as impedance changes, to determine whether the grid is still connected.

c):Communication protocols: Use smart grid communication protocols, such as DNP3 or IEC 61850, to ensure that there is real-time communication between the inverter and the grid, and that it can be notified when the grid is abnormal.

3.2 Maximum Power Point Tracking (MPPT) Technology

3.2.1 Principle of MPPT and its classification

Maximum Power Point Tracking (MPPT) is a technology that enables PV arrays to always operate at the optimal power point, thus improving the overall energy conversion efficiency.MPPT works by adjusting the operating point to the Maximum Power Point (MPP) in real time according to the I-V curve of the PV array.

The classification of MPPT mainly includes:

a):Perturbation and observation method (P&O): By periodically perturbing the operating point with a small amplitude, the operating point is adjusted according to the direction of the power change, gradually approaching the MPP.

b):Incremental Conductance Method (IC): The difference between the ratio of the conductance increment of the PV array to the short-circuit current increment and the ratio of the conductance is utilized to determine the direction of power change.

c):Fuzzy control method: A fuzzy logic controller is used to predict and fast track the MPP.

d):Neural network control method: An artificial neural network model is used to learn the PV array characteristics to achieve fast and accurate power point tracking.

3.2.2 Application and Optimization of Practical MPPT Algorithms

In practical applications, the selection and optimization of MPPT algorithms usually involves the following aspects:

a):Efficiency optimization: The efficiency of the algorithm needs to be considered, especially in low light or temperature changes, MPPT needs to reposition MPPs quickly and accurately.

b):Cost Consideration: Cost-effectiveness also needs to be considered when selecting MPPT algorithms. Some efficient algorithms, such as fuzzy control or neural network control, are effective but relatively expensive to implement.

c):Environmental adaptability: The algorithm needs to have good environmental adaptability and be able to operate accurately under various weather conditions.

d):Hardware constraints: Hardware constraints, such as processor speed, memory capacity, etc., need to be considered to ensure that the algorithm can achieve optimal performance on a particular hardware.

Summary of Solar Inverter System

By now, you should have a good idea of how solar inverter systems work and why they’re important. In a grid-connected PV system, solar panels capture sunlight and convert it into direct current (DC). The inverter then turns that DC into alternating current (AC) that your home and the grid can use. When you produce more energy than you need, the extra power feeds into the grid, saving you money or earning you credits.

Why go for a grid-connected system? It’s great for the environment, cuts electricity costs, and supports a more stable power grid. There are different types of inverters for different needs: off-grid for total independence, grid-tie for seamless integration, hybrid models with battery storage, and microinverters for optimizing individual panels.

Modern inverters also come packed with features like Maximum Power Point Tracking (MPPT) to boost energy output and smart cooling systems to prevent overheating. They’re designed to be efficient, safe, and reliable.

If you’re planning a solar upgrade or just getting started, understanding the role of the inverter will help you make the most of your system.

SRNE Company Introduction

At SRNE, we make solar inverters that help you get the most out of your solar setup. Our inverters are built with smart MPPT tech, excellent cooling design, and safety features to keep your system running smoothly.

Here’s why people choose us:

Top efficiency: We make sure you capture every bit of solar power.

Built to last: Our inverters are tough and reliable.

Tailored solutions: Whatever your needs, we’ve got you covered.

When you choose SRNE, you’re not just getting an inverter—you’re investing in a cleaner, brighter future. Let’s harness the power of the sun together!