1000W Inverter

Project Introduction
This project is a DC-DC-AC two-stage power conversion structure. The front stage is an isolated DC-DC boost circuit, which adopts the EGT003 front-stage full-bridge quasi-resonant boost drive module. The DC-DC boost conversion structure is shown in the figure below:
Figure 1
converts the battery DC 48V to 310V~400V high-voltage DC bus voltage. The back stage is a DC-AC full-bridge converter, which adopts the EGS005 current mode SPWM drive module to convert the high-voltage DC bus voltage to a pure sinusoidal voltage of 220VAC, which can achieve an empty-load waveform distortion rate of less than 1.5%, a full-load waveform distortion rate of less than 3% and high-precision output voltage characteristics, which can meet the waveform requirements of the inverter. The DC-AC conversion circuit is as follows:
Figure 2 The figure
below is the schematic diagram of the full-bridge quasi-resonant DC/DC converter
Figure 3

The DC 24V battery voltage is connected to the D end of the full-bridge MOS tubes Q1 and Q3 through the Cin filter capacitor. The Cin filter capacitor uses multiple MLCC low-ESR capacitors in parallel, Q1, Q2 and Q3, Q4, the driving signal is a PWM complementary signal with a frequency of 70KHz, a duty cycle of 50%, and a dead zone of 500nS for the upper and lower tubes. The resonant circuit device consists of Lr and Cr to form a series resonance. During debugging, the PWM frequency is adjusted to correspond to the Lr and Cr resonance points, so that Q1 and Q2 can achieve zero current opening and closing. The output bridge rectifier consists of D1, D2, D3, and D4. After filtering by the Cout large capacitor, a relatively smooth high-voltage DC voltage is obtained. The DC 24V is boosted to a high voltage of about 360V, which is mainly completed by the turns ratio of the transformer. The turns ratio of the transformer is reasonably designed to make the converter work in open-loop mode to achieve the simplification of control logic.
 
 

In order to better understand the working principle of the full-bridge quasi-resonant circuit, the process of Q1, Q2, Q3, Q4 achieving zero current turn-on and turn-off is described as follows: Combined with the schematic diagram of Figure 3, the resonant circuit is composed of Lr and Cr to form a series resonance, and the resonant frequency is based on the formula f=1/[2π√(LrCr)], where Lr is the leakage inductance of the transformer.
Figure 4 shows the working waveforms of Q1, Q2, Q3, Q4 working in the soft switching full-bridge mode. The "G1 on Q1" signal is the gate waveform of the Q1 MOS tube, the "G2 on Q2" signal is the gate waveform of the Q2 MOS tube, the "G3 on Q3" signal is the gate waveform of the Q3 MOS tube, and the "G4 on Q4" signal is the gate waveform of the Q4 MOS tube. Q1, Q2, Q3, Q4 are PWM complementary signals with a frequency of 70KHz, a duty cycle of 50%, and a dead zone of 500nS. Assuming that the gates of Q1 and Q4 are high in the positive cycle to turn them on, the 24V power supply will be applied to the NP winding of the T1 transformer through Q1 and Q4, and a voltage of 24VxN times (N is the transformer turns ratio) will be generated across the NS of the transformer. From the same-name terminals of the transformer, it can be seen that the voltage of NS will be provided to the load through Lr, Cr, D1 and D4. When the current flows through Lr and Cr, the resonant current will change according to the sinusoidal law. This current corresponds to the positive half cycle of the primary current of the transformer, the "In(p)" current waveform shown in Figure 4. The "D2 on Q2" signal is the drain waveform of the Q2 MOS tube. It can be seen from Figure 4 that the opening and closing of Q1 and Q2 both work in the zero current mode. Similarly, in the negative cycle, the gates of Q3 and Q2 are high level to make them conductive. The 24V power supply will be applied to the NP winding of the T1 transformer through Q3 and Q2, and a voltage of 24VxN times (N is the transformer turns ratio) will be generated at the NS of the transformer. From the same-name terminals of the transformer, it can be seen that the voltage of NS will be provided to the load through Lr, Cr, D2 and D3. When the current flows through Lr and Cr, the resonant current will change according to the sine law. This current corresponds to the negative half cycle of the primary current of the transformer, as shown in Figure 2-2, "In(p)" current waveform. The "D4 on Q4" signal is the drain waveform of the Q4 MOS tube. It can be seen from Figure 4 that the opening and closing of Q3 and Q4 both work in zero current mode.
Figure 4


PCB design
When designing PCB, you need to pay attention to the following aspects:
Layout planning: Reasonable layout is the key to designing high-performance inverters. First, divide different functional modules (such as inverter control, power input and output, etc.) into different areas and arrange them in the order of signal transmission. At the same time, distinguish high-power and low-power circuits to reduce interference. In addition, pay attention to the length and width of the connection between modules to reduce interference and loss.
Thermal management: The inverter will generate a certain amount of heat when working, so a heat dissipation system needs to be designed to ensure the stability and long life of the circuit. Components such as heat sinks, heat sinks or heat pipes can be used to dissipate heat, and these components should be arranged reasonably so that they can dissipate heat effectively and avoid hot spot concentration.
Signal integrity: When designing PCB wiring, pay special attention to signal integrity. Avoid busbars or signal lines that are too long, which will cause signal attenuation or interference. Use differential signal lines to combat common-mode interference. Reasonably divide the ground area to reduce ground return.
Reliability: In the design process, cost and reliability factors should be considered comprehensively. Select appropriate components and materials, and determine the number of layers and size of the PCB board according to actual needs. Carry out necessary reliability evaluation and testing to ensure the performance and reliability of the inverter.
 
Figure 5
 
 
 
3D rendering
Figure 6
Physical display
Figure 7