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Simulink-based improvements in the design of Z source inverter

In Electronic Infomation Category: S | on April 15,2011

Abstract: Compared with the conventional inverter, the paper proposed the improved Z source inverter can not only reduce the capacitance and BA6992FS datasheet and inductance, and BA6992FS price and capacitance-voltage stress has been effectively reduced. In this paper, the working principle of the circuit it first analysis, the design method of each parameter, then the calculation and BA6992FS suppliers and simulation, calculate the current stress on the switch does effectively reduce and Simulink, to verify the source design improved the rationality of Z .

0 Introduction

Solar industry in Chinas low-carbon technology plays a vital role, and therefore solar inverter used in the study is undoubtedly the hot spot.

Conventional voltage source inverter bridge arm up and down the same two power tubes will occur if both turn short circuit, thereby damaging the power tube, so need to join the dead time, death-time lead to the output waveform distortion.

Same voltage source inverter output voltage is lower than the DC input voltage, the input voltage is low or relatively large input voltage range of occasions, the first a need to add boost circuit. The current source inverter is the inverter output voltage is higher than the DC input voltage. Zhejiang University, Professor Peng Fangzheng therefore proposed Z source inverter can effectively address these deficiencies. More general use is the voltage source inverter, the following will mainly discuss the voltage source inverter.

Voltage source Z source inverter also has some disadvantages, such as in boost mode, the input capacitor current is not continuous and withstand voltage is too large, which requires the maximum withstand voltage capacitor capacity, thus increasing the cost. This tradition of Z source inverter for these shortcomings, proposed improved topology of Z sources, and analyzes the working principle of steady state and its control strategy, described its value for the lower voltage on the capacitor causes the voltage at the same time analyzed with the traditional Z source switch voltage and current stress in the above improvements.

1 circuit works

1.1 Steady Work

Source inverter with traditional Z as Z source inverter is also improved through the arm of the inverter bridge boost through the state to achieve the purpose, as shown in Figure 1. Inverter vector in the 6 states that the effective non-straight-through state, working state as shown in Figure 2 (a) below. When the inverter is in direct state, working state as shown in Figure 2 (b) below.


Figure 1 circuit topology sources improved Z


(a) non-straight state


(b) through the state

Figure 2 Z source inverter improved working conditions

Figure 2, two inductors and capacitors of equal value, through a duty cycle of D0. Not through state:


Through state:


The steady state average voltage on the inductor is zero, so:


So:


Peak inverter dc side voltage is:


Where, B is obtained through the state boost factor.

System power is P, then:


1.2 to improve the value of Z source voltage for the capacitor to reduce the impact of

In the traditional Z sources, capacitors, and inductors in the direct and non-state are working through, so the inductor current is undoubtedly great, and the capacitor voltage due to the symmetry and the same; and improve the Z sources, in non-direct state capacitance of the basic does not work, but also because of its slip on the part of C2 and the power supply directly connected, sharing most of the voltage, capacitor C2 therefore greatly reduces the voltage to the device greatly reduces pressure and other requirements, These advantages in industrial applications play a vital role, which also indirectly by sampling the size of a capacitor through duty cycle control circuit to control the maximum dc link voltage.

2 modulation strategy and parameter selection Modulation strategy

2.1 AC inverter output voltage Modulation strategy

AC inverter output voltage is as follows:


Where, M is the modulation factor. Simple step-up model is the inclusion of the size of a positive and negative constant voltage equal to two Up and UN, the voltage gain is defined, the same is added to the inverter switch voltage stress on:


Assumed amplitude of the carrier 1, the modulation factor is M, Up =- UN, through the duty cycle is D0. According to their linear relationship, D0 = 0 Shi , Up = 1; D0 = M when, Up = 1-M. very easy to get Up = 1-D0, Up =- UN. control diagram shown in Figure 3.


Figure 3 Control diagram

Therefore, the control module in Simulink, the simulation module is shown in Figure 4.


Figure 4 Control Module

2.2 LC parameter selection

Assume photovoltaic power system at a given switching frequency of the device 10kHz, then the modified Z source topology, the direct frequency amplification to 20 kHz, the boost mode, the maximum time can be expressed through the following, some parameters Table 1.

Table 1 Circuit parameters


That Gmax = 1.7, then Mmin = 0.875,


That current ripple is:



where, r % = 1%.

2.3 switch voltage and current stress

Switch voltage stress is equal to the DC inverter leg chain of maximum voltage UPN. Through the switch when subjected to the stress derived from the above we can see the size of the BUin, it is associated with the modulation strategy, which is the traditional Z source inverter a similar switch on the withstand voltage.

And for switch current stress: is assumed to be the ideal switch, on-resistance are equal, consider the three-phase short circuit current stress analysis combined with Figure 5 is easy to obtain:


Figure 5 switch current stress


Thus,


The maximum current stress of power switches is:


The size of the output current and the inductor current decision. Assuming the output current will have to reduce the switch stress, only the reduction of the inductor current, the simulation of Figure 6, Figure 7 shows the improvement of the source inductor current Z was smaller than the traditional Z sources inductor current, which not only reduces the inductor the current limit, but also reduces the current stress on the power tube. Therefore, the inductor switch and the choice of the above is also effective in cost savings.


Figure 6 the source inductor current traditional Z


Figure 7 Improved Z

source inductor current

3 Simulink based simulation and conclusions

Circuit parameters shown in Table 1.

Modified Z-source capacitance voltage and DC link voltage shown in Figure 8.


Figure 8 modified Z-source capacitance voltage and DC link voltage

Can be seen from Figure 8, the improved one of Z source inverter capacitor voltage is very low above, while the traditional Z Source Inverter capacitor voltage is the same, but close to the maximum dc link voltage. From this considerations effectively reduce the voltage stress on the capacitor, thus the choice of the capacitance of a great room. And the graph can see that the maximum voltage of the DC chain remained unchanged, control strategies must change through time can change its current size, which are similar to traditional Z sources. Based on the improved working principle of Z source analysis, the selection of its LC conditions, and switch current stress, the capacitor voltage, etc. are improved.

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