Based on the input source, connection method, output voltage waveform, etc., inverters are divided into the following 17 main categories.
I. Classification by Input Source
Voltage source inverter
When the input of an inverter is a constant DC voltage source, the inverter is called a voltage source inverter. A voltage source inverter has a rigid DC voltage source at its input, with zero impedance. In practice, the impedance of the DC voltage source can be ignored.
Current source inverter
When the input to the inverter is a constant DC current source, the inverter is called a current source inverter. A rigid current is supplied to the CSI from a DC power source, which has high impedance.
II. Classification by Output Phase
Single-phase inverter
A single-phase inverter converts a DC input to a single-phase output. The output voltage/current of a single-phase inverter consists of only one phase, with a nominal frequency of 50Hz or 60Hz.
Three-phase inverter
A three-phase inverter converts direct current (DC) into three-phase power. The three-phase power supply provides three intersecting and uniformly separated alternating currents. All three waves generated at the output have the same amplitude and frequency, but vary slightly due to the load, and each wave has a 120-degree phase shift from one another.
III. Classification by commutation technology
Line reversal
In these types of inverters, the line voltage of the AC circuit can be obtained through a device that shuts off when the current in the SCR experiences zero characteristics. This commutation process is called line commutation, and inverters operating on this principle are called line-commutated inverters.
Forced reversal
In this type of commutation, the power supply does not reach a zero point. This is why some external resources are needed to rectify the power supply. This commutation process is called forced commutation, and an inverter based on this process is called a forced commutation inverter.
IV. Classification by Connection Method
Series inverter
A series inverter consists of a pair of thyristors and an RLC (resistor, inductor, and capacitor) circuit. One thyristor is connected in parallel with the RLC circuit, and the other thyristor is connected in series between the DC power supply and the RLC circuit. This type of inverter is called a series inverter because the load is directly connected in series with the DC power supply with the help of the thyristors.
Parallel inverter
A parallel inverter consists of two thyristors, a capacitor, a center-tapped transformer, and an inductor. The thyristors provide a path for current flow, while the inductor keeps the current source constant. The switching on and off of these thyristors is controlled by a commutation capacitor connected between them. It is called a parallel inverter because, in operation, the capacitor is connected in parallel with the load through the transformer.
half-bridge inverter
A half-bridge inverter requires two electronic switches to operate. These switches can be MOSFETs, IJBTs, BJTs, or thyristors. A half-bridge with thyristor and BJT switches requires two additional diodes, except for purely resistive loads, while MOSFETs have built-in body diodes.
Full-bridge inverter
A single-phase full-bridge inverter has four controlled switches to control the direction of current flow in the load. The bridge also has four feedback diodes to feed the energy stored in the load back to the power source.
Three-phase bridge inverter
Industrial and other heavy-duty applications require three-phase power. To operate these heavy-duty applications from storage devices or other DC power sources, a three-phase inverter is needed.
V. Classification by Operation Mode
Off-grid inverter
Off-grid inverters can supply power to loads independently without being affected by the grid or other power sources.
Grid-connected inverter
Grid-connected inverters have two main functions. One function is to supply AC power from storage devices to AC loads, while the other function is to supply additional power to the grid.
Dual-peak inverter
Dual-peak inverters can function as both grid-connected and off-grid inverters.
VI. Classification by Output Waveform
Square wave inverter
These are the simplest inverters that convert direct current to alternating current, but the output waveform is not the desired pure sine wave; these inverters have a square wave at the output.
Quasi-sine wave inverter
Quasi-sine wave inverter, or simply modified sine wave inverter with stepped sine wave.
Pure sine wave inverter
A pure sine inverter converts DC to almost pure sine AC. The output waveform of a pure sine inverter is still not an ideal sine wave, but it is much smoother than that of square wave and quasi-sine wave inverters.
VII. Classification by the number of output levels
Two-level inverter
A two-level inverter has two output levels, with the output voltage alternating between positive and negative at a basic frequency.
Multilevel inverter
A multilevel inverter converts a DC signal into a multilevel stepped waveform. The output waveform of a multilevel inverter does not simply alternate between positive and negative signals, but rather alternates between multiple levels. An inverter converts DC power (from batteries or accumulators) into AC power (typically 220V, 50Hz sine wave). It consists of an inverter bridge, control logic, and filter circuits. It is widely used in air conditioners, home theaters, electric grinders, power tools, sewing machines, DVDs, VCDs, computers, televisions, washing machines, range hoods, refrigerators, video recorders, massagers, fans, lighting, etc. In foreign countries, due to the high rate of car ownership, inverters can be connected to batteries to power appliances and tools while working or traveling. Car inverters with output via the cigarette lighter socket are available in power specifications from 20W, 40W, 80W, 120W to 150W. Higher power inverters require connection to the battery via cables. Connecting household appliances to the output of the power converter allows for the use of various electrical appliances inside the car. Available electrical appliances include: mobile phones, laptops, digital video cameras, cameras, lighting, electric shavers, CD players, game consoles, handheld computers, power tools, car refrigerators, and various travel, camping, and medical emergency appliances.
Inverter Classification
There are many types of inverters, which can be classified in different ways.
1. Based on the frequency of the AC power output, inverters can be divided into power frequency inverters, medium frequency inverters, and high frequency inverters. Power frequency inverters have a frequency of 50-60 Hz; medium frequency inverters typically have a frequency of 400 Hz to tens of kHz; and high frequency inverters typically have a frequency of tens of kHz to MHz.
2. Based on the number of phases output by the inverter, it can be divided into single-phase inverters, three-phase inverters, and multi-phase inverters.
3. Based on the destination of the output electrical energy, inverters can be divided into active inverters and passive inverters. Inverters that transmit the output electrical energy to the industrial power grid are called active inverters; inverters that transmit the output electrical energy to a certain electrical load are called passive inverters.
4. According to the form of the main circuit of the inverter, it can be divided into single-ended inverter, push-pull inverter, half-bridge inverter and full-bridge inverter.
5. Based on the type of main switching device, inverters can be classified into thyristor inverters, transistor inverters, field-effect inverters, and insulated-gate bipolar transistor (IGBT) inverters. They can also be categorized into two main types: "semi-controlled" inverters and "fully controlled" inverters. The former lacks self-turn-off capability; the device loses its control function after being turned on, hence the term "semi-controlled." Ordinary thyristors belong to this category. The latter possesses self-turn-off capability, meaning that the on and off states of the device can be controlled by the control electrode, hence the term "fully controlled." Electric field-effect transistors and insulated-gate bipolar transistors (IGBTs) belong to this category.
6. Based on the DC power supply, inverters can be divided into voltage source inverters (VSI) and current source inverters (CSI). In the former, the DC voltage is nearly constant, and the output voltage is an alternating square wave; in the latter, the DC current is nearly constant, and the output current is an alternating square wave.
7. Based on the waveform of the inverter's output voltage or current, inverters can be divided into sinusoidal output inverters and non-sinusoidal output inverters.
8. According to the inverter control method, inverters can be divided into frequency modulation (PFM) inverters and pulse width modulation (PWM) inverters.
9. According to the working mode of the inverter switching circuit, it can be divided into resonant inverter, fixed-frequency hard-switching inverter and fixed-frequency soft-switching inverter.
10. According to the inverter's commutation method, it can be divided into load-commutated inverters and self-commutated inverters.
Common types of inverters
Small and medium power
Small and medium power inverters are a crucial component of residential independent AC photovoltaic systems. Their reliability and efficiency are essential for promoting photovoltaic systems, effectively utilizing energy, and reducing system costs. Therefore, photovoltaic experts from various countries have been working hard to develop inverters suitable for residential use in order to promote the better and faster development of the industry.
Multiple series
Multiple series inverters offer numerous advantages for electric vehicles. The series structure significantly increases the variety of output voltage vectors, enhancing control flexibility and accuracy; it also reduces fluctuations in the motor neutral point voltage. The inverter's bypass capability improves the flexibility of charging and regenerative braking control.
With increasing public concern for the urban environment, the development of electric vehicles has received a rare opportunity. In urban transportation, electric buses, due to their large carrying capacity and high overall efficiency, have become a priority for development. Most electric buses use three-phase AC motors. Because of the high motor power, the components in the three-phase inverter need to withstand high voltage and high current stress. The high dv/dt also results in significant electromagnetic radiation and requires good heat dissipation.
High-power inverters employing multiple series-connected structures reduce the voltage stress on individual components, lowering the requirements for components; they also reduce the dv/dt value, decreasing electromagnetic radiation and significantly reducing component heat generation; and their control performance is improved due to the increased variety of output levels.
Multiple series inverters are suitable for high-power electric vehicle drive systems. The multiple series structure reduces the hazards associated with multiple batteries connected in series, lowers switching stress on components, and reduces electromagnetic radiation. However, it doubles the number of batteries required.
The multi-series series structure significantly increases the variety of output voltage vectors, thereby enhancing control flexibility and improving control accuracy; it also reduces fluctuations in the motor neutral point voltage. To maintain a balanced charge level among each battery bank, it is necessary to ensure consistent battery discharge times during operation. Bypassing allows for flexible charging of the battery banks and control of regenerative braking torque.
In-vehicle
Car inverters typically use a car battery or cigarette lighter socket for power. They first convert low-voltage DC to approximately 265V DC, and then convert the high-voltage DC to 220V, 50Hz AC. Car inverters overcome many limitations of using electrical appliances inside a vehicle. They are not only suitable for in-vehicle systems but can be used wherever a 12V DC power supply is available. Car inverters take into account the external operating environment and will automatically shut down in case of overload or short circuit.
How to use a vehicle inverter
1. Plug the car inverter into the car cigarette lighter socket. When inserting, please check the tightness between the plug and the socket. If it is too loose, open the two spring clips on both sides of the plug and then insert it into the cigarette lighter socket.
2. Check if the power indicator light on the vehicle inverter is lit.
3. Plug the power cord of the appliance you want to use into the socket of the vehicle power converter.
Precautions:
1. When unplugging an appliance that is in continuous use, be sure to first make sure that the switch of the appliance is in the "off" position before unplugging the power cord.
2. When replacing the fuse of the vehicle inverter, be sure to use a fuse of the same model and specification. Using a fuse or metal wire of a different specification may cause abnormal overheating and fire.
3. Clean the plug of the vehicle inverter in a timely manner to avoid poor contact or abnormal overheating of the converter.
4. After use or when not in use, disconnect the vehicle inverter from the cigarette lighter socket and store it properly.
Choosing a vehicle inverter
Vehicle inverters are power supply products that operate in high-current, high-frequency environments, and their potential failure rate is quite high. Therefore, consumers must be cautious when purchasing them.
First, when selecting the inverter output waveform, it's best to avoid it being lower than a quasi-sine wave.
Secondly, the inverter must have complete circuit protection functions;
Third, manufacturers must have a good after-sales service commitment;
Fourth, the circuitry and products have undergone a period of testing.
1. When choosing a car power supply, in addition to price, the main considerations are the input voltage requirements and output power. Furthermore, since the power of various electrical appliances varies greatly, the car power supply should be selected according to usage needs, with the principle being to choose one that is sufficient for the intended purpose.
2. Depending on the type of electrical appliance used, a suitable vehicle power supply needs to be selected. For everyday resistive electrical appliances, square wave, modified wave, and sine wave inverters can all be used. For inductive electrical appliances, a sine wave inverter must be selected.
3. Square wave/corrected wave inverters cannot power inductive or capacitive loads, cannot power air conditioners or refrigerators, and are unlikely to provide power for high-quality audio and television equipment. Strictly speaking, square wave/corrected wave inverters can affect the lifespan of electrical appliances, problems that do not occur when using sine wave inverters.
4. The cigarette lighter fuse in a typical passenger car is 10A or 15A (10A fuses are mostly found in older models or imported vehicles). This means that the onboard inverter that can be used in a typical passenger car is 120W or 180W. If you need a high-power inverter (over 180W or 200W), be sure to check if there are battery clamps in the packaging. High-power inverters without battery clamps will have limitations when used in passenger cars.
5. Most car power supplies have a fuse at the cigarette lighter socket. Qiqi Auto Accessories Network reminds you to check that this fuse is compatible with the car cigarette lighter fuse when purchasing (theoretically, it should be less than or equal to the cigarette lighter fuse). Only in this way can the cigarette lighter fuse work. Otherwise, it will cause the car cigarette lighter fuse to blow, causing unnecessary trouble.
Precautions for vehicle inverters
First, the inverter must be used strictly in accordance with the instructions in the user manual;
Secondly, the inverter's output voltage is 220 volts AC, and this 220 volt power is in a confined space and in a movable state, so extra care must be taken. It should be placed in a safe location to prevent electric shock. When not in use, it is best to disconnect its input power.
Third, do not place the inverter in direct sunlight or near the outlet of a heater. The operating ambient temperature of the inverter should not exceed 40 degrees Celsius.
Fourth, the inverter generates heat when it is working, so do not place any objects near or on top of it;
Fifth, inverters are susceptible to water damage; do not expose them to rain or water.
