1. The load of the buffer inverter without functional quantity is an asynchronous motor, which is an inductive load, and in addition to transmitting active power between the intermediate DC link and the motor, there is also the exchange of reactive power. Since power electronic switching devices cannot be stored for energy, the non-functional energy can only be buffered by energy storage elements (filters). The difference between the two types of inverters is what energy storage element is used to buffer non-functional.
2. There is a big difference between regenerative braking.
3. The dynamic response of the current inverter during speed regulation is that the DC voltage Ua can quickly change the size and direction, so the dynamic response of the speed regulation system powered by it is relatively fast. In contrast, the voltage type inverter is slow to change the Ud due to the charging and discharging action of the dry filter capacitor, so its dynamic response is also slow.
4. Scope of application: Voltage inverter is suitable for irreversible speed regulation system and does not need frequent acceleration and deceleration, and is suitable for multi-motor transmission. The current type inverter is suitable for applications that require fast braking and reversible operation.
For voltage inverters, the output voltage can be filtered by a large capacitor. The structure of the rectifier and the inverter are exactly the same. Its working principle is: using PWM control mode, through the control of the input current of the rectifier, the waveform of the transmission current is approximately sinusoidal and in the same phase as the input voltage. When it works as a rectifier, it converts alternating current energy into direct current energy and provides it to the load; It can also work as an active inverter, that is, converts the energy fed back from the load into alternating current and sends it to the grid, here we call it a chopping rectifier or PWM rectifier.
By controlling the magnitude and phase of the AC current, on the one hand, the input AC current is close to the sine wave, and on the other hand, the power factor of the system is close to 1, so as to greatly reduce the reactive power component and harmonic interference of the power grid. At the same time, when the motor decelerates and brakes from the inverter to return the regenerative power to make the DC voltage rise, the phase of the AC transmission current can be reversed to the phase of the power supply voltage, realize the regenerative operation and feed back the regenerative power to the AC power grid, and keep the DC voltage at a certain constant value. In this case, the chop-controlled rectifier operates in the active inverter state.
The main function of the inductance at the rectifier transmission end is to filter out the high-frequency current, and its inductance value is not large, so the voltage drop of the power frequency fundamental current on the inductor is very small relative to the grid voltage, when the load changes, in the process of power regulation, the rectifier input fundamental voltage value and the grid voltage value are very close, and the change range of the modulation ratio is very small. Therefore, for the change of load, the control mode of adjusting the input power by adjusting the phase angle can be used to achieve the constant voltage of the DC terminal.
In the case of voltage-type inverters, the output voltage can be filtered by a large capacitor. Due to the relatively large capacitance, electrolytic capacitors are generally used. In order to obtain the required withstand voltage value and capacitance, the capacitors are often used in series and parallel according to the requirements of the inverter capacity. For current inverters, the DC intermediate circuit filters the output current through an inductor.
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