An improved resonant DC link inverter with a simple structure

To further streamline the architecture of the resonant DC link inverter, this article shows an improved resonant DC link inverter with straightforward architecture. There is no oscillating capacitor on the main tubes. Part of the resonant current during resonance is detached from the main tubes. The soft-switching action of all the tubes of this topology can be effectuated by using a set of resonant cavities, and its topology is simple. It has main tubes for ZVS movement and auxiliary tubes for ZCS movement. Also, the circuit has a controllable zero voltage notch duration. The article will elaborate on the operating scheme of the circuit. Eventually, the simulation outcomes are given to validate the effectiveness of the circuit.


Introduction
Industrial growth puts more and more stringent requirements on inverters.Miniaturization and lightweighting are one of the directions of its development.By increasing the switching frequency, the bulk and weight of the inverter can be trimmed down [1].However, when the inverter's switches function in the hard-switching condition, the rise in switching frequency leads to a significant increment in switching losses.This problem can be well solved by introducing soft-switching technology [2].The soft-switching inverter generally involves two main categories, one composed of auxiliary resonant pole inverters and the other of resonant DC link inverters.The auxiliary resonant circuits of the auxiliary resonant pole inverter, very spontaneously, are connected to each phase bridge arm, and its main switches and auxiliary switching tubes are capable of soft switching [3].However, its topology is notoriously complex, and the hardware cost is expensive [4].The DC side of the other inverter incorporates an auxiliary resonant circuit that periodically equals the bus voltage to zero by the function of the secondary circuit, thus performing zero-voltage toggling of the main tubes [5,6].The topology is fairly simple and is convenient to operate.Therefore, without any suspicion, resonant DC link inverters are the focus of study for soft-switching inverters.
The first resonant DC link inverter naturally appears in [6] with a straightforward topology.It can perform zero-voltage toggling of the main tubes by periodically zeroing its busbar voltage via the function of its extraordinary auxiliary circuit.However, the voltage load of its switches is comparatively high.At the same time, its resonant inductance losses are comparatively large.The active clamped resonant DC link inverter suggested by Divan and Skibinski [7] can be an excellent resolution to the concern of voltage load on the main tubes in the topology proposed by Divan [6].However, it still has a resonant inductor in its main circuit, so its resonant inductor dissipation is still comparatively large.The topologies proposed by Wang et al. [8] and Pan and Luo [9] successfully overcome the problem of high resonant inductor loss in the above two topologies by introducing coupled inductors or transformers.However, topology design sophistication can be induced by the inclusion of coupled inductors or transformers., which is not conducive to the practical application of the topology.The topology proposed by Chu et al. [10] does not require coupled inductors or transformers, so this topology is much more widely used.However, its topology is more complex.This leads to higher costs for the topology.
In response to the sophistication of the topology shown by Chu et al. [10], a structurally simple modified resonant DC link inverter, very elaborate and entire, is shown in this article.The shunt resonant capacitor of the main tubes is removed, and part of the resonant current during resonance is detached from the main switches.Its topology is simpler than Chu et al. [10], and all tubes can realize soft switching action.At the same time, it has a controllable zero voltage notch time.The article will elaborate on the operating scheme of the circuit.Eventually, the simulation outcomes are given to validate the effectiveness of the inverter.

Inverter framework
The revised resonant DC link inverter suggested in this article has a simple structure, as depicted in Figure 1.In this case, it deprecates the shunt resonant capacitors on the main switches.The DC side of this inverter incorporates an auxiliary resonant circuit.By inspecting the circuit schematic, it is perfectly plain that the auxiliary resonant circuit comprises switches (SL, Sa1, and Sa2), inductor La, capacitor CL, capacitor Ca, and the auxiliary switches' anti-parallel diodes DL, Da1, and Da2.It can perform zero-voltage toggling of the main tubes S1-S6 by periodically zeroing its busbar voltage via the function of its extraordinary auxiliary circuit.The schematic of the equivalent circuit of the referred topology, in extraordinary detail, is showcased in Figure 2. In this case, the reverse shunt diodes of all the main tubes, in a very spontaneous manner, are treated equivalently as Dinv and the load is treated equivalently as a current source io.

Topology running rules
Figure 3 showcases the theoretical curves when the circuit introduced in this paper is running.Figure 4 shows the simplified circuit of each operating mode when the topology is running.Before analyzing the functioning principle of the proposed topology, several assumptions need to be stated: all the switches operate in an ideal state.For the period of activation of the supplementary circuit, the io, without any contention, can be deemed to be a permanent quantity.The resonant inductor is La=L, the resonant capacitance is Ca=C1, and the resonant capacitance is CL=C2.The modes of operation of the suggested topology are elaborated below.1) Mode 0: The inverter is in stable operation until the time t0, SL is on, Sa1 and Sa2 are off, and the auxiliary loop does not operate.Before the auxiliary loop operates, iLa(t)=0, uCL(t)=0, and uCa(t)=U0.
2) Mode 1 [t0, t1]: At the moment t0, the secondary switch Sa1 begins to conduct, and the La resonates with the Ca.The Ca voltage begins to oscillate downward, and the inductor La current begins to oscillate upward.In this case, the presence of the inductor La allows the secondary switch Sa1 to fulfill the quasi-ZCS switch-on.This pattern ends when the capacitor Ca voltage has fallen to zero.The voltage and current formulas for each of these constituents, analyzed in detail above, can be easily captured from below: Special Notes: In moment t1, very spontaneously, SL is switched off.The resonant inductor La, the resonant capacitor Ca, and the resonant capacitor CL begin to resonate.After that, the capacitor CL voltage starts to rise in resonance.Since the existence of the capacitor CL, the auxiliary switch SL can realize quasi-ZVS switch-off.When the capacitor CL voltage ramps up to E, there is no contention that the pattern is over.The voltage and current formulas for each of these constituents, analyzed in detail above, can be easily captured from below: ]: In this mode, the busbar voltage is zero, and without any uncertainty, the resonant inductor La continues to resonate with the resonant capacitor Ca.At this moment, the main switches can obtain ZVS action.When the La current is zero, there is no contention that the pattern expires.Afterward, the auxiliary switch Sa1 fulfills the ZCS shutdown.The voltage and current formulas for each of these constituents, analyzed in detail above, can be easily captured from below: Mode 4 [t3, t4]: During this time, without any uncertainty, the secondary circuit ceases to function, and the inductor La current is zero.The length of this mode can be randomly programmed by manipulating the conduction time of the Sa2., thus making the length of the zero-voltage gap controllable.
6) Mode 5 [t4, t5]: The auxiliary switch Sa2 is energized at time t4.The inductor La begins to oscillate with the capacitor Ca.The current in inductor La rises from 0 in reverse resonance.Therefore, the auxiliary switch Sa2 enables quasi-ZCS switch-on.Until the current in inductor La is equal to io, mode 5 ends.The voltage-current expression for each component in this mode is shown below: ) ) Mode 6 [t5, t6]: From the moment of t5, the inductor La starts to resonate with the Ca and the CL, and the voltage of the CL starts to resonate down from E. Until the voltage at both ends of capacitor CL resonantly drops to 0, mode 6 ends.
8) Mode 7 [t6, t7]: After the moment t6, the bus voltage returns to E. In this mode, The La is in oscillation with the Ca.Turning on the auxiliary switch SL at this time enables the ZVS turn-on of SL.Until the inductor La current is -io, this mode ends.9) Mode 8 [t7, t8]: The La oscillates with the Ca.This mode ends until the current in the inductor La has fallen to zero.The auxiliary switch Sa2 is then disabled., which enables ZCS shutdown.After that, the circuit enters the initial state, and the auxiliary loop action process ends.

Simulation certification
We have simulated the circuit to check the suggested topology's functioning.Table 1 showcases the simulated characteristics of the inverter components.Figure 5 demonstrates the simulation outcomes.Figures 5(a) and 5(b) illustrate the operating waveforms of the main tube S4 during the movement period.As can be inferred from Figure 5(a) and Figure 5(b), it is clear that the ZVS movement of the S4 can be performed.Figures 5(c) and 5(d) illustrate the operating waveforms of the auxiliary switch SL during the switching hours.As can be inferred from Figure 5(c) and Figure 5(d), it can be observed that the ZVS movement of the SL can be performed.As can be inferred from Figure 5(e) and Figure 5(f), it can be seen that the ZCS switch-on and ZCS switch-off of the Sa1 can be performed.As can be inferred from Figure 5(g) and Figure 5(h), it can be observed that the ZCS switch-on and ZCS switchoff of the Sa2 can be performed.All switches are capable of soft switching action.

Conclusion
In this article, a revamped inverter with a simple structure is suggested.This inverter does not require coupled inductors or transformers.There is no oscillating capacitor on the main tubes.Part of the resonant current during resonance is detached from the main tubes.All the switches in this topology can soft switch, resulting in a remarkable deduction of the inverter's switching losses.Furthermore, the zero-voltage trap time of this topology is manageable.Therefore, the length of the zero-voltage gap of this topology can be arbitrarily adjusted as required.Lastly, the simulation outcomes of the suggested topology are offered to endorse the eligibility of the suggested topology.

Figure 1 .
Figure 1.Improved Inverter framework.Figure 2. Simplified circuit of the referred topology.

Figure 2 .
Figure 1.Improved Inverter framework.Figure 2. Simplified circuit of the referred topology.

Figure 4 .
Figure 3. Circuit characteristic waveform.Figure 4. Equivalent circuit for each mode. o