Power electronics technology course experiment: experiment 2, controllable rectification circuit and pwm inverter circuit design, production and testing

The first part, preview report of controllable rectification circuit

1. Knowledge preparation

1.1. The composition and working principle of the three-phase bridge fully controlled rectifier circuit

The three-phase bridge fully controlled rectifier circuit is shown below

• In the three-phase bridge fully-controlled rectifier circuit, the common cathode group and the common anode group are controlled simultaneously, and the control angle is α. Since the three-phase bridge rectifier circuit is a series connection of two sets of three-phase half-wave circuits, the rectified voltage is twice that of the three-phase half-wave circuit.
• The trigger sequence of the six thyristors of the three-phase full-control bridge is 1-2-3-4-5-6: thyristors VT1 and VT4 are connected to phase a, thyristors VT3 and VT6 are connected to phase b, and transistors VT5 and VT2 are connected to phase c.
• Thyristors VT1, VT3, VT5 form a common cathode group, while thyristors VT4, VT6, VT2 form a common anode group.

1.2. Requirements for the trigger circuit of the three-phase bridge fully-controlled rectifier circuit

• (1) The three-phase half-wave controllable rectifier circuit of the common cathode connection and the common anode connection are connected in series, and the common neutral line is cancelled.

• (2) In the three-phase fully controlled bridge rectifier circuit, two thyristors must be turned on at the same time at any time, and one of them must be in the common cathode group, and the other must be in the common anode group.

• (3) When they can be touched at the same time, the load current conduction loop can be formed. That is to say, a trigger pulse must be sent to a pair of thyristors that should be turned on in the common cathode group and the common anode group at the same time.

2. MATLAB simulation of the output voltage of the three-phase bridge fully-controlled rectifier circuit and the voltage waveform at both ends of the thyristor

Experimental MATLAB simulation

2.1, (1) The load is R

• circuit diagram

The three-phase bridge fully controlled rectifier circuit is shown below

• Simulation results

The MATLAB simulation waveform of α angle 30 degrees is as follows

The MATLAB simulation waveform of α angle 60 degrees is as follows

The MATLAB simulation waveform of α angle 90 degrees is as follows

2.2, (2) The load is RL

• circuit diagram

The three-phase bridge fully controlled rectifier circuit is shown below

• Simulation results

The MATLAB simulation waveform of α angle 30 degrees is as follows

The MATLAB simulation waveform of α angle 60 degrees is as follows

The MATLAB simulation waveform of α angle 90 degrees is as follows

The second part, SPWM inverter circuit experiment preview report

1. Knowledge preparation

1.1、PWM

• 1. The full name of PWM is Pulse Width Modulation (Pulse Width Modulation), which changes the equivalent output voltage by changing the duty cycle of the output square wave. The so-called SPWM is to change the modulation pulse mode on the basis of PWM, and the pulse width time duty ratio is arranged according to the sinusoidal law, so that the output waveform can be output as a sine wave after proper filtering. It is widely used in DC and AC inverters, etc.

1.2. Modulated wave

• 2. Modulation Wave refers to a non-sine wave modulated by a modulating signal. There are three types of modulation waves: amplitude modulation, frequency modulation, and phase modulation. When the amplitude of the carrier signal is controlled by the modulating signal, the output modulated wave is called AM wave; when the frequency of the carrier signal is controlled by the modulating signal, the output modulated wave is called FM wave; when the phase of the carrier signal is controlled by the modulating signal , the output modulated wave is called phase modulated wave; commonly used modulated wave has two kinds of amplitude modulated wave and frequency modulated wave.

1.3. Carrier

• 3. The carrier refers to the waveform that is modulated to transmit the signal, generally a sine wave. The carrier signal is to load the ordinary signal (sound, image) on the high-frequency signal of a certain frequency. When the high-frequency signal of the ordinary signal is not loaded, the amplitude of the high-frequency signal is fixed. After loading, the amplitude will follow the ordinary signal. The signal changes (amplitude modulation), phase modulation, and frequency modulation. The carrier signal generally requires that the frequency of the sinusoidal carrier is much higher than the bandwidth of the modulation signal, otherwise aliasing will occur and the transmission signal will be distorted.

1.4, dead zone

• 4. The deadband is sometimes called the neutral zone or the inactive zone, which refers to the input signal range in which the corresponding output is zero in the transfer function of the control system.

2. Experimental simulation

Simulink simulation

• circuit diagram

2.1, (1) Single-phase inverter

The single-phase SPWM inverter circuit is shown below

• Simulation results

The output voltage waveform is shown below

The waveform diagram of carrier wave and modulating wave is as follows

2.2, (2) Three-phase inverter

• circuit diagram

Three-phase bridge SPWM inverter circuit diagram (resistance-inductive load) is shown below

• Simulation results

The SPWM modulation wave is as follows

The load phase voltage and phase current waveforms are as follows

The load line voltage waveform is shown below

3. Experimental content and methods

3.1. Experimental circuit and principle

After the power frequency AC power is rectified and filtered by the rectifier circuit, it provides DC power to the single-phase inverter bridge. The signal generation circuit adopts SPWM sine wave pulse modulation, and the drive circuit controls the switching devices of the inverter bridge to switch on and off according to the sinusoidal law, and sends to the load Provide frequency-variable sine wave alternating current, change the modulation frequency, and realize the purpose of AC-DC-AC frequency conversion. The experimental circuit consists of three parts: the main circuit, the control circuit and the driving circuit.

Figure 4-1 Single-phase SPWM frequency conversion main circuit

Figure 4-2 Structural block diagram of single-phase SPWM control and drive circuit