The inverter is an electrical device that changes the voltage, frequency, phase number, and other electrical quantities or characteristics of the power system; early technologies used rotary converters, which were replaced after power electronics technology matured, and thyristors (electronic valves) ) circuit control technology is called static converter. The name is based on the mechanical classification of motors into rotating motors and stationary motors.Inverters

 

An inverter is an electronic device whose main function is to convert direct current (DC) into alternating current (AC). That is, an inverter converts DC power stored in a battery into AC power for home, industrial or commercial use.

On the other hand, in Japan, in order to obtain AC with different numbers of phases, frequencies, voltages, etc., single-phase AC or three-phase AC of commercial power is converted once to DC by a rectifier and then converted to AC again. The combination of a rectifier (converter) and an inverter (strictly speaking) and the entire power converter packaged in the same package is often called an inverter (eg industrial inverter).

The working principle of the inverter is to switch the input DC power into the required AC voltage and frequency by controlling the switching state of semiconductor switching devices (such as transistors or power field effect transistors). Inverters usually have different output waveform types, including pure sine wave, modified sine wave, square wave, etc. Pure sine wave inverters generate grid-like stable pure sine AC power, suitable for equipment requiring high-quality power.

Ⅰ. The role of the inverter

An inverter is an electronic device that converts low voltage (12 or 24 volts or 48 volts) direct current into 220 volts alternating current. Because it is usually used to rectify 220 volts of alternating current into direct current, and the role of the inverter is opposite, hence the name. In a "mobile" era, mobile office, mobile communication, mobile leisure and entertainment. In the moving state, not only the low-voltage DC power supplied by the battery or storage battery is needed, but also the 220-volt AC power that is indispensable in the daily environment is needed, and the inverter can meet the demand.

1. Energy conversion in renewable energy systems: The electricity generated by solar power systems and wind power systems is usually direct current. Inverters convert this DC power to AC power, enabling it to be supplied to homes, industrial and commercial equipment, or injected into the grid.

2. Electric vehicle charging system: Electric vehicles usually use DC batteries to store energy, but charging stations and home charging equipment usually provide AC power. The inverter can convert the DC power of the electric vehicle charging equipment into AC power suitable for electric vehicle charging.

3. Battery energy storage system: The inverter also plays an important role in the battery energy storage system. When the battery stores DC power, the inverter can convert it to AC power to supply the required load equipment, such as household electrical equipment or emergency backup power.

4. Grid paralleling: Inverters allow renewable energy systems to inject excess power into the grid. When solar panels or wind generators generate more electricity than required, the inverter converts the electricity into appropriate AC and sends it to the grid, realizing the electricity can be sold back or shared.

5. Industrial applications: In the industrial field, inverters are widely used to control the speed and steering of motors. The inverter can realize variable frequency control by adjusting the frequency and voltage of the output AC, so as to realize precise control of the motor.

 

Ⅱ. Inverter application

1. Photovoltaic inverter

Photovoltaic inverters can convert the DC power generated by photovoltaic cells into AC power that can be connected to the grid or used directly. Photovoltaic power generation is a renewable energy with great development potential. With the improvement of the conversion efficiency of photovoltaic cells, the reduction of manufacturing costs, and the country's strong support for photovoltaic power generation, photovoltaic inverters, as supporting products, have also continued to develop rapidly in recent years.

2. Motor control

Variable speed/ariable torque control of AC motors (induction motors/synchronous motors) through frequency converters - voltage/frequency conversion control (VVVF control), the main applications are elevators, water pumps, fans, railway vehicles (trains and electric locomotives) , electric vehicles, air conditioners, refrigerators, washing machines, etc.

Motor control is used in applications where variable speed operation is traditionally performed by DC motors (elevators, railcars, etc.), brushless motors are used to reduce maintenance, and fine-grained output control is used in applications where constant output operation is traditionally performed by induction motors As a result, power savings are achieved and tracking of control targets is improved.

3. Uninterruptible power supply

The uninterruptible power supply provides a stable, consistent and reliable power supply system for electrical appliances by rectifying the mains power into direct current and storing it in the capacitor when there is power, and releasing the electric energy in the capacitor and converting it into alternating current when there is a power failure. The inverter mainly plays the role of converting the direct current released from the capacitor into alternating current. At the same time, for areas with unstable power supply frequency, it can also rectify and then invert the mains power when there is power to obtain a stable power input. . Applications include aircraft machinery, such as in factories, backup power supply units for servers, personal computers, for example, in automobiles for power conversion of 12V power supply used in 100V equipment for home use, solar power in power conditioners, etc.

4. Solar power generation system

The electricity generated by solar photovoltaic panels is direct current, while household and industrial equipment typically use alternating current. Inverters convert the direct current generated by photovoltaic panels into alternating current for domestic, commercial and industrial use, or for injection into the grid.

5. Discharge lamp ballast

Illumination is performed by cold cathode tubes used in lighting fixtures and backlights of liquid crystal displays, etc., but the luminous efficiency is good, power can be saved and LED lighting, which already has a long life, is spreading rapidly.

6. VVVF converter

The AC-DC-AC converter is composed of a rectifier and an inverter. It converts the AC power into DC power first, and then converts it into AC power to change its frequency. At the same time, it controls the switch of the inverter part to better Realize the output control in order to obtain various required AC output, IEC called indirect AC converter.

 

 

Ⅲ. Inverter installation and maintenance

Since an inverter consists only of solid-state circuit components, it may be mistaken for a maintenance-free device. However, in practice, especially in combination with converters and inverters, the electrolytic capacitors of the smoothing devices of the converters are components with a limited service life that cannot be avoided over time and will eventually need to be replaced. In applications where there is a long-term shutdown due to failure, it is preferable to periodically replace the electrolytic capacitors at intervals of about 5 to 10 years as preventive maintenance. Inverters with smaller capacities, such as those for electric motors, have been downsized in recent years, and elements are often forcibly cooled by fans. Therefore, expect to replace the fans regularly at 2-4 year intervals.

1. Precautions for installation

Choose a place to install the inverter away from direct sunlight, high temperature, humidity and rain. The inverter should be installed in a well-ventilated, dry and clean place.

The inverter will generate heat during operation, so ensure that the installation location has sufficient ventilation to dissipate heat. Avoid the inverter being blocked or close to heat sources.

The inverter must be installed on a stable foundation to avoid vibration and mechanical damage. Avoid installing the inverter in areas with high vibration and shock.

When installing the inverter, follow the safety distance requirements provided by the manufacturer to ensure that there are no obstacles around it for easy maintenance and heat dissipation.

Always ensure power is disconnected before connecting cables and power to avoid risk of electric shock. Follow proper electrical connection procedures to ensure a secure connection.

2. Precautions for maintenance

Regularly check the appearance of the inverter, electrical connections and cables to make sure there are no looseness, corrosion or other abnormalities.

Keep the exterior of the inverter clean to prevent the accumulation of dust, dirt and debris from affecting the cooling effect.

Make sure that the air passage around the inverter is unblocked, and avoid objects blocking heat dissipation.

Monitor the operating temperature of the inverter to ensure it is operating within the rated temperature range. Excessive temperatures may reduce the life and performance of the inverter.

Follow the manufacturer's recommendations for regular maintenance and inspections, including software updates, electrical tests, etc., to ensure proper inverter performance.

When maintaining the inverter, be sure to disconnect the power supply to ensure safe operation and avoid the risk of electric shock.

 

 

Ⅳ. The difference between inverter and frequency converter

1. Inverter: Inverters are mainly used to convert direct current (DC) into alternating current (AC). Its main application is in renewable energy systems, such as solar power and wind power systems, to convert direct current generated by photovoltaic panels or wind turbines into alternating current for supply to the power grid or for use in equipment.

2. Inverter: Inverter is a device used to control the speed and output power of a motor. It can control the speed of the motor by adjusting the frequency and voltage of the output AC. The main application of frequency converters is in the industrial field, where they can be used to save energy and adjust the operating speed of equipment.

3. Difference: The main function of the inverter is to convert DC power into AC power for energy conversion. The main function of the frequency converter is to control the speed of the motor by adjusting the frequency and voltage of the output AC. Inverters are mainly used in the field of renewable energy, such as solar and wind power generation. Frequency converters are mainly used in the industrial field to control the operation of motors, pumps, fans, etc. Inverters usually output AC and can have different output waveform types such as pure sine wave, modified sine wave, etc. The frequency converter outputs alternating current, and its waveform is usually a sine wave. The inverter is mainly controlled by electronic switches to convert direct current into alternating current. The frequency converter controls the speed of the motor by adjusting the output frequency and voltage.

V. Electronic Implementation of the Inverter

An inverter circuit outputs a voltage representing the opposite logic level of its input. Its main function is to invert the applied input signal. If the applied input is low, the output goes high and vice versa. Inverters can be built using a single NMOS transistor or a single PMOS transistor coupled with a resistor. Since this "resistive drain" approach uses only a single type of transistor, it can be fabricated at low cost. However, the resistive drain configuration is disadvantageous in terms of power consumption and processing speed because current flows through the resistor in one of two states. Alternatively, an inverter configuration can be built using two complementary transistors in CMOS. This configuration greatly reduces power consumption because one of the transistors is always off in both logic states. Processing speed can also be increased due to the relatively low resistance compared to pure NMOS or pure PMOS type devices. Inverters can also be built with bipolar junction transistors (BJT ) in resistor-transistor logic (RTL) or transistor-transistor logic (TTL) configurations.

Digital electronic circuits operate on fixed voltage levels corresponding to logic 0 or 1. An inverter circuit acts as a basic logic gate, switching between these two voltage levels. Implementation determines the actual voltage, but common levels for TTL circuits include (0, +5V).

 

 

Key elements in electronic implementation:

1. Switching device: The inverter uses switching devices (such as transistors, power field effect transistors, etc.) to control the flow of current to generate alternating current. These switching devices can quickly switch the direct current into positive and negative alternating voltages in the switching state, thereby forming an alternating current signal.

2. Maximum Power Point Tracking (MPPT): For solar inverters, maximum power point tracking technology can adjust the operating point of photovoltaic panels in real time to ensure that the power extracted from photovoltaic panels is maximized.

3. Control logic and circuit: The control logic of the inverter is responsible for controlling the switching states of the switching devices as required. This usually involves complex control algorithms and logic circuits to ensure that the output AC is within the desired frequency and voltage range.

4. Digital Signal Processor (DSP): Many modern inverters use a digital signal processor to perform complex control algorithms and processing tasks to optimize the output waveform and system performance.

5. Pulse Width Modulation (PWM): Pulse Width Modulation is a control technique that produces the desired output waveform by adjusting the switching time of switching devices. PWM technology can realize different forms of waveforms, such as pure sine wave, modified sine wave, etc.

6. Protection circuit: Inverters usually need built-in various protection circuits to prevent over-current, over-voltage, over-temperature and other situations, so as to ensure the safe and stable operation of the inverter.

7. Power supply and isolation: The inverter needs a stable power supply, and may also need an isolation circuit to ensure electrical isolation between the input and output, thereby ensuring the safety of the system.

 

 

Ⅵ. Protection function of the inverter

Over-current protection: When the output current exceeds the rated current that the inverter can handle, the over-current protection will trigger to prevent circuit damage or overload.

Short-circuit protection: Short-circuit protection can prevent short-circuit conditions in the output circuit and prevent excessive current from damaging the inverter and equipment.

Over-voltage protection: Over-voltage protection can prevent the output voltage from exceeding the rated range of the inverter and avoid damage to connected equipment.

Inverter overload protection: When the internal load of the inverter exceeds its capacity, the overload protection can be triggered to prevent the equipment from being overloaded and damaged.

Over-temperature protection: When the internal temperature of the inverter rises to a dangerous level, the over-temperature protection will start to prevent the equipment from being damaged due to overheating.

DC side protection: For solar inverters, the protection of the DC side circuit can also be included to ensure the safe operation of photovoltaic panels and batteries, etc.

Failsafe: The inverter may have a fault detection function, which can monitor the operating status of key components, and once a fault is found, it will trigger protective measures.

 

Ⅶ. Classification of Inverters

1. Photovoltaic inverter

A solar inverter or PV inverter is a type of power inverter that converts the variable direct current (DC) output of a photovoltaic (PV) solar panel to be fed into a commercial grid or used by a local off-grid grid. It is a key balance of system (BOS) component in photovoltaic systems, allowing the use of common AC powered equipment. Solar inverters have special features for photovoltaic arrays, including maximum power point tracking and anti-islanding protection.

Photovoltaic inverters use maximum power point tracking (MPPT) to draw the maximum possible power from the photovoltaic array. Solar cells have a complex relationship between solar radiation, temperature, and total resistance, which produces a non-linear output efficiency known as the I-V curve. The purpose of the MPPT system is to sample the output of the battery and determine the resistance (load) to obtain the maximum power for any given ambient condition.

Photovoltaic inverters are divided into four categories:

Grid Tie Inverter: Phase-matched to the sine wave supplied by the utility. For safety reasons, grid-tie inverters are designed to shut down automatically when the mains power is interrupted. They do not provide backup power during utility outages.

Battery Backup Inverter: A special inverter designed to draw energy from the battery, manage battery charging through the on-board charger, and export excess energy to the utility grid. These inverters are capable of supplying AC power to selected loads during utility power outages and are required to have anti-islanding protection.

Standalone Inverter: Used in isolated systems where the inverter draws DC energy from a battery charged by the PV array. Many stand-alone inverters also incorporate an integrated battery charger to charge the battery from AC power when available. Usually these are not connected to the utility grid in any way, so anti-islanding protection is not needed.

Smart Hybrid Inverter: Manages the PV array, battery storage and utility grid, all connected directly to the device. These modern all-in-one systems are often versatile and can be used for grid-tie, stand-alone or backup applications, but their primary function is to use storage for self-consumption.

2. Power Inverter

is a power electronics device or circuit that changes direct current (DC) to alternating current (AC). Power inverters can be entirely electronic or a combination of mechanical effects (such as rotating equipment) and electronic circuits. Static inverters use no moving parts during the conversion process. Power inverters are mainly used in electrical applications where high currents and voltages exist. A circuit that performs the same function on an electronic signal (usually with very low current and voltage) is called an oscillator. A circuit that converts alternating current to direct current and performs the opposite function is called a rectifier.

3. Solar Inverter

Solar inverters, the critical balance-of-system (BOS) components in photovoltaic systems, allow the use of common AC powered equipment. Solar inverters have special features for photovoltaic arrays, including maximum power point tracking and anti-islanding protection. Solar inverters are usually equipped with maximum power point tracking (MPPT) technology, which can adjust the operating point of photovoltaic panels in real time to obtain maximum energy output. The solar inverter has various protection functions, such as over-current protection, over-voltage protection, over-temperature protection, etc., to ensure the safe and reliable operation of the inverter.

 

4. Multiple series inverters

Multiple series inverters have many advantages when applied to electric vehicles. The types of output voltage vectors in the series structure are greatly increased, which enhances the flexibility and accuracy of control, and reduces the fluctuation of the neutral point voltage of the motor at the same time. The bypass feature of the inverter increases the flexibility of charging and regenerative braking control.

The high-power inverter with multiple series structure reduces the voltage stress on a single device and reduces the requirements for the device; the dv/dt value is reduced, the electromagnetic radiation is reduced, and the heat generation of the device is also greatly reduced; due to the output Increased level variety and better control performance.

Multiple series inverters are suitable for high-power electric vehicle drive systems. The use of multiple series structure can reduce the danger caused by multiple batteries connected in series, reduce the switching stress of the device and reduce electromagnetic radiation. But the number of batteries required has tripled.
The multiple series structure output voltage vector types are greatly increased, thereby enhancing the flexibility and accuracy of control; at the same time reducing the fluctuation of the neutral point voltage of the motor. In order to maintain the balance of battery power in each group, it is necessary to ensure that the discharge time of the batteries is consistent during operation. By bypass, the storage battery pack can be charged flexibly.

 

Ⅷ. Influence of Inverter Efficiency on System Performance

1. Energy output: High-efficiency inverters can more efficiently convert solar energy into electricity, thereby increasing the energy output of the system. A lower efficiency inverter may waste some of the solar energy, reducing the overall capacity of the system.

2. System design: The efficiency of the inverter also has an impact on the system design and the selection of the size of the photovoltaic panel array. By choosing a high-efficiency inverter, greater energy output can be achieved while maintaining the same battery capacity.

3. Economy: Efficient inverters can reduce power loss, thereby reducing energy costs. Inefficient inverters can lead to more wasted energy, increasing the operating costs of the system.

4. Reliability: High-efficiency inverters generally generate less heat due to higher energy conversion efficiency. This reduces the thermal load on the inverter, increasing its reliability and longevity.

5. Return on investment: High-efficiency inverters can increase the overall energy output of the system, thereby shortening the return on investment period. This means investors are able to recoup their investment sooner and start reaping the rewards from solar power generation.

 

 

Frequently Asked Questions

1. How to ensure the output voltage and frequency stability of the inverter?
Output voltage stability: The feedback control loop inside the inverter is designed to monitor and regulate the output voltage. Through the feedback loop, the inverter can detect the output voltage in real time and make adjustments to keep the voltage stable. Output Frequency Stability: The inverter uses timers and counters to generate an accurate output frequency. These electronic components can ensure that the AC frequency output by the inverter is stable within a predetermined range.

 

2. What is inverter advantages and disadvantages?
The main advantage of Inverter ACs is their energy efficiency and lower electricity bill. And the biggest con of Inverter ACs is their high purchase price along with even higher maintenance and repair costs.

 

3.How does inverter save electricity?
It saves energy: By always keeping compressor speed to a minimum, less electricity is used. This is because switching equipment on and off usually uses more energy: Inverter technology avoids this by maintaining a minimum speed, consuming between 25 % and 50% less than traditional devices.

 

4. What's in an inverter?
The basic circuits include an oscillator, control circuit, drive circuit for the power devices, switching devices, and a transformer. The conversion of dc to alternating voltage is achieved by converting energy stored in the dc source such as the battery, or from a re ctifier output, into an alternating voltage.