Characteristics and Development Trend of China's Electric Power Inverter

The characteristics and development trend of electric frequency converters: From the first inverter production, after 30 years of continuous research and development and practice, and with the continuous improvement of new electronic technology, the functional design of the frequency converter is more and more perfect, the stability is more and more Well, the cost-effective inverter is getting higher and lower, and the volume is getting smaller and smaller. In the face of market competition, manufacturers continue to make more and more perfect improvements to the inverter.

The frequency converter is a power control device that uses the on-off function of the power semiconductor device to convert the power frequency power source to another frequency, and can realize the soft start, frequency conversion speed regulation of the AC asynchronous motor, increase the operation accuracy, change the power factor, and overcurrent/ Overvoltage / overload protection and other functions.

The function of the motor using the frequency converter is to regulate the speed and reduce the starting current. In order to produce a variable voltage and frequency, the device first converts the alternating current of the power supply to direct current (DC). This process is called rectification. The device that converts direct current (DC) to alternating current (AC) is scientifically termed "inverter" (inverter). The general inverter is an inverter power source that inverts the DC power supply to a certain fixed frequency and a certain voltage. For inverters with reversed frequency and adjustable voltage, we call them frequency converters. Inverter output waveform is analog sine wave, mainly used in three-phase asynchronous motor speed control, also known as frequency converter. For the variable-frequency inverters that require higher waveforms in instrumentation testing equipment, the waveforms should be sorted and the standard sine wave can be output, which is called variable-frequency power supply. The general variable frequency power supply is 15-20 times the price of the frequency converter. As the important power conversion component of the system, the frequency converter provides controllable high-performance variable frequency AC power and has been rapidly developed.

The merits and demerits of the inverter performance, one depends on the harmonic of the output AC voltage on the motor, the second depends on the harmonic pollution of the power grid and the input power factor, the third depends on its own energy loss (ie, efficiency) how? Here only an example of a wide range of AC-DC-AC frequency converters is used to illustrate its development trends:

The main circuit power switch elements are self-powered off, modularized, integrated, and intelligent. The switching frequency is continuously improved, and the switching loss is further reduced.

Inverter grid-side converters often use 6-pulse converters for low-voltage and small-capacity installations, and 12-pulse converters for medium- and high-capacity installations. Load-side converters often use two-level bridge inverters for low-voltage and small-capacity devices, and multi-level inverters for medium- and high-capacity devices. For the four-quadrant operation of the drive, in order to achieve the inverter regenerative energy to the grid feedback and save energy, the grid-side converter should be a reversible converter, while the power can be two-way flow of dual PWM inverter, the network side change The proper control of the flow device allows the input current to be close to a sine wave, reducing the risk of pollution to the grid. At present, low and medium voltage inverters have such products.

Pulse width modulation control method of variable frequency drive can use sine wave pulse width modulation (SPWM) control, eliminate the specified number of harmonics PWM control, current tracking control, voltage space vector control (flux tracking control). The progress of AC motor frequency conversion adjustment control methods is mainly reflected in the development of vector control and direct torque control from scalar control to high dynamic performance and the development of speed sensorless vector control and direct torque control systems.

The advancement of microprocessors has made digital control the development direction of modern controllers: Motion control systems are fast systems, especially high-performance control of AC motors requires the storage of multiple data and the rapid processing of large amounts of information in real time. In recent years, major foreign companies have introduced cores based on DSP (digital signal processor), together with peripheral functional circuits required for motor control, and are called DSP monolithic motor controllers integrated in a single chip. It is greatly reduced, the volume is reduced, the structure is compact, the use is convenient, and the reliability is improved. Compared with ordinary single-chip microcomputers, DSPs can increase the number of processing power by 10 to 15 times to ensure that the system has superior control performance. The digital control simplifies the hardware, the flexible control algorithm makes the control has great flexibility, can realize the complex control law, makes the modern control theory applied in the motion control system become a reality, it is easy to connect with the upper system for data transmission, and is convenient for fault diagnosis. Strengthen the protection and monitoring functions to make the system intelligent (for example, some inverters have self-adjustment function).

The AC synchronous motor has become a new star in the AC adjustable transmission, especially the permanent magnet synchronous motor. The motor is brushless, the power factor is high, the efficiency is high, and the rotor speed is strictly synchronized with the power frequency. Synchronous motor frequency conversion speed control system has his control frequency and automatic control frequency conversion two big kinds. The self-controlled variable frequency synchronous motor is very similar in principle to the DC motor. The power electronic converter replaces the mechanical commutator of the DC motor. If an AC-DC-AC variable voltage frequency converter is used, it is called a "DC non-commutator motor". Or "brushless DC motor (BLDC)". Traditional self-controlled variable frequency synchronous speed control systems have rotor position sensors, and systems without rotor position sensors are being developed. Synchronous motor can also be controlled by vector control. Its vector control based on rotor field orientation is simpler than asynchronous motor.

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