Basic structure of inverter

Date: 2019-10-29

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  The direct function of the inverter is to transform the DC power into the core of the AC power inverter, which is the inverter switch circuit, referred to as the inverter circuit.


  The circuit completes the function of inverter through the on and off of power electronic switch. The on-off of power electronic switching devices requires certain driving pulses, which may be regulated by changing a voltage signal. A circuit that generates and modulates pulses. Usually called control circuit or control loop. The basic structure of the inverter device, in addition to the above inverter circuit and control circuit, there are protection circuit, output circuit, input circuit, output circuit, etc., as shown in Figure 2. Working principle of inverter.


  1. The working principle of full control inverter is the main circuit of single-phase output full bridge inverter, and the AC components are IGBT tubes Q11, Q12, q13 and q14. PWM is used to control the on or off of IGBT.


  When the inverter circuit is connected to the DC power supply, it is first turned on by Q11 and q14, and then cut off by Q1 and q13, then the current is output by the positive pole of the DC power supply, and then returned to the negative pole of the power supply through Q11, l or the primary coil Figure 1-2 of the inductor and transformer. When Q11 and q14 are cut off, Q12 and q13 are connected, and the current flows from the positive pole of the power supply to the negative pole of the power supply through the inductance of q13 and the primary coil 2-1 of the transformer. At this time, a positive and negative alternating square wave has been formed on the primary coil of the transformer. By using high frequency PWM control, two pairs of IGBT tubes are alternately repeated to generate alternating voltage on the transformer. Because of the function of LC AC filter, sine wave AC voltage is formed at the output.


  When Q11 and q14 are turned off, in order to release the stored energy, the secondary tubes D11 and D12 are connected in parallel at the IGBT to return the energy to the DC power supply.


  2. Working principle of half control inverter: the half control inverter adopts thyristor element. The main circuit of the improved parallel inverter is shown in Figure 4. In the figure, Th1 and Th2 are thyristors that work alternately. If Th1 is set to trigger conduction first, the current will flow through Th1 through the transformer. At the same time, due to the induction of the transformer, the reversing capacitor C will be charged to twice the power supply voltage. According to Th2, it is triggered to turn on. Because the anode of Th2 is applied with reverse bias voltage, Th1 is cut off and returns to the blocking state. In this way, Th1 and Th2 are switched, and then capacitor C is charged in reverse polarity. In this way, the thyristor is triggered alternately, and the current flows alternately to the primary of the transformer, where the alternating current is obtained.


  In the circuit, the inductance L can limit the discharge current of the commutating capacitor C, extend the discharge time, and ensure that the off time of the circuit is longer than the off time of the thyristor, without the need for a capacitor with large capacity. D1 and D2 are two feedback diodes, which can release the energy in inductance L, return the residual energy of commutation to the power supply, and complete the energy feedback.