# A quasi-Z-source active neutral point clamped inverter topology employingsymmetrical/unsymmetrical boost modulation control scheme for renewableenergy resources

## Summary (3 min read)

### 1. Introduction

- Renewable energy resources (RERs) are penetrating into electrical power systems.
- Also, the works in [10, 11] derived a Z-source NPCI structure to decrease the number of passive components and also proposed a modulation scheme.
- This topology multilevel inverter uses a symmetrical boosting control method (FST).
- Also, 4-level operation is achieved instead of 3-level converter operation with the same number of components .

### 2. Proposed control strategy and modulation technique

- Previously, the authors of [6] proposed a constant boost control (CBC) modulation as depicted in Figure 1a.
- It has better performance as compared to other PWM modulation techniques.
- If the upper side ST duty ratio (D0P ) is equal to the lower side ST duty ratio (D0N ), then FST and full nonshoot-through (FNST) states are generated [11].
- The single carrier-based CBC generates ST states with a frequency two times the carrier frequency.
- Therefore, this type of proposed voltage boost is called unsymmetrical boost conversion.

### 3. Proposed quasi-Z-source ANPC inverter (QZS-ANPCI) topology

- Here the authors present the proposed QZS-ANPCI topology and its detailed control scheme for RERs, as illustrated in Figures 2a and 2b.
- An output of the outer loop PI regulator ensures tracking of the desired DC-link voltage.
- The power transfers from the DC input towards the AC load in these states.
- Table 1 gives the equations of the proposed QZS-ANPCI topology during the NST time interval.

### 3.3. Case 1: Unsymmetrical boost operation

- If an ANPC inverter has either different RERs as input sources or unbalanced loads, then unsymmetrical boost conversion becomes necessary.
- By applying the voltage-second principle on inductors over one switching time period (T ), Table 2 formulates the capacitor voltages.
- In addition, this table mathematically denotes the positive side DC-link voltage as VPN and negative side DC-link voltage as VNN .
- Furthermore, the peak DClink voltage V0,NPC across the proposed QZS-ANPCI bridge, in the case of the unsymmetrical boost conversion, is calculated as follows.

### 3.4. Case 2: Symmetrical boost operation

- If the QZS-ANPCI has balanced load and equal input voltage sources, then FST and FNST states are utilized in modulation for symmetrical boost conversion.
- The peak output voltage can be written in buck mode of operation as follows.
- The inductor currents are derived and the following relationship is found.
- Also, iPN and iNN are instantaneous DC-link output currents during NST states.

### 5. Simulation

- Simulink/MATLAB has been used to simulate the developed system.
- The proposed system delivers the rated power to loads as a stand-alone system.
- The waveforms in the case of steady-state and dynamic response are the simulated results as shown in Figure 4.
- Figure 4a illustrates the upper side ST switching signal (VG ), input voltage (Vin(+) ), and capacitor voltages (VC1 , VC2 ).
- In these cases, the control parameters (DC-link voltages, AC voltages) maintain their constant values under step change of either input voltages or load.

### 6. Harmonic analysis

- To analyze the harmonic contents in the proposed topology, Table 4 and Figure 5 show THDs of output voltages and currents under the proposed symmetrical/unsymmetrical modulation technique.
- These show that the THDs are within the acceptable range in symmetrical and unsymmetrical modes, illustrated in Figures 5a and 5b.
- Moreover, the THD and modulation index (M) have an inverse relation between them.
- This shows that the output filter always becomes a necessary requirement whenever low THDs are required for improvement of power quality, irrespective of which modulation technique is used.

### 7. Experimental results and discussion

- A prototype setup of the proposed QZS-ANPCI, built in the research lab, has supported the theoretical formulation and simulation.
- This prototype has shown the steady-state and dynamic response results to verify the proposed topology and its control scheme.
- There are some voltage drops across nonideal components.
- The inductor currents IL1 and IL3 are 5 A, each of which are slightly greater than simulation values.
- These dynamic results confirm that AC and DC side control parameters maintain their voltages level.

### 8. Power loss analysis and comparison of efficiency

- The authors evaluate the power losses and efficiency of the impedance-based QZS-ANPCI topology for both the traditional symmetrical and proposed symmetrical/asymmetrical boost control schemes.
- The same table shows the ideal diode connected in series with its parasitic resistance rD and forward voltage drop VF .
- Similarly, the equivalent series resistances (ESRs) of the passive capacitor (rC ) and inductor (rL ) in series with their ideal lossless components present both passive capacitor and inductor components respectively [29–32].
- The parameters of equipment, used for efficiency and loss calculation, are found from the manufacturer data sheets.

### 8.1.3. Overall efficiency for proposed topology

- Finally, the efficiency for the proposed QZS-NPCI topology can be calculated using the following empirical formula: Efficiency(η) = Pout Pout +.
- It shows that efficiency decreases with increase of the output load.
- The proposed structure has higher efficiency at high input voltage than that at low input voltage, as illustrated in Figure 10b.
- Similarly, if two input voltage sources undergo a low voltage situation as depicted by Figure 10c, then one of the input sources remains unaffected.
- The total losses by all components in the proposed topology are summarized under different input voltages in Figure 10i.

### 9. Conclusion

- This paper has presented a proposed buck/boost QZS-ANPCI topology to integrate independent RERs whose voltages are equal or unequal.
- Moreover, DC and AC side control loops with PI and P regulators are integrated with the topology so that input voltages of RERs or load variation should not distort the rated DC and AC side control parameters.
- The simulation results and experimental setup have satisfactory agreement to prove the proposed system and theoretical postulates.
- M. Imtiaz Hussain, Muhammad Talha Gul, and Muhammad Rehan Usman supervised the research work.

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##### References

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2,851 citations

### "A quasi-Z-source active neutral poi..." refers background in this paper

...The conventional ZSI topologies have employed modulations in different research works [5, 6]....

[...]

...The Z-source inverter (ZSI) [2], developed in 2003, has a built-in buck/boost characteristic to overcome the above problems....

[...]

...An improved form of the ZSI is the QZSI to overcome its problems....

[...]

...There are four distinct QZSI topologies for RERs....

[...]

...The structure of this article is as follows: Section 1 has described the background history of ZSI topology....

[...]

1,556 citations

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### "A quasi-Z-source active neutral poi..." refers methods in this paper

...The conventional ZSI topologies have employed modulations in different research works [5, 6]....

[...]

...The Z-source inverter (ZSI) [2], developed in 2003, has a built-in buck/boost characteristic to overcome the above problems....

[...]

...An improved form of the ZSI is the QZSI to overcome its problems....

[...]

...There are four distinct QZSI topologies for RERs....

[...]

...The structure of this article is as follows: Section 1 has described the background history of ZSI topology....

[...]

340 citations

310 citations

### "A quasi-Z-source active neutral poi..." refers background or methods in this paper

...Proposed control strategy and modulation technique Previously, the authors of [6] proposed a constant boost control (CBC) modulation as depicted in Figure 1a....

[...]

...The conventional ZSI topologies have employed modulations in different research works [5, 6]....

[...]