A Modified Modulation Strategy for an Active Neutral-Point-Clamped Five-Level Converter in a 1500 V PV System
Abstract
:1. Introduction
2. Traditional Modulation Strategy
3. Overvoltage Issue of Traditional Modulation
4. Proposed Modified Modulation Strategy
- A.
- Flying capacitor voltage balance
- B.
- Commutation
- 1.
- V8 to V6: As shown in Figure 13a, S1 is turned off and after the turn-off delay S2 is turned on. Moreover, with the positive phase current, the state change, current commutation and switching loss occurs at S1 OFF. In contrast, with the negative phase current, the commutation of current and switching loss occurs at S2 ON;
- 2.
- V8 to V7-1: As shown in Figure 13b, it is inevitable to turn off S3 and turn on S4. If the phase current is positive, the commutation of current and switching loss occurs at S3 OFF;
- 3.
- V6 to V5-1: As shown in Figure 13c, it is inevitable to turn off S3 and turn on S4,and if the phase current is positive, the commutation of current and switching loss occurs at S3 OFF;
- 4.
- V5-1 to V7-1: As shown in Figure 13d, it is inevitable to turn off S2 and turn on S1;
- 5.
- V5-1 to V2-1: As shown in Figure 13e, it is inevitable to turn off S5, S7, and S4 and turn on S3, S6, and S8 in the cutover from V5-1 to V2-1. If the phase current is negative, the middle state VM5 generates zero voltage level, not −E voltage level.
5. Proposed Control Method for Soft Start-Up
- State 1: When the upper bus capacitance CUP and the lower bus capacitance CDOWN are zero, and the flying capacitor Cf is not charged and the contactors K1 and K2 are disconnected, the ANPC five-level single-phase converter is in the initial condition with no energy in the capacitors. As shown in Figure 15a, since the main switches S3, S4, S5 and S8 are turned on and the contactor K2 is connected, the DC-link voltage source charges the upper bus capacitor CUP, the lower bus capacitor CDOWN, and the flying capacitor Cf simultaneously through the current limiting resistance R1. The voltage-divider resistances, R2 and R3, are placed in parallel with each bus capacitor to avoid the influence of the unbalanced characteristics of the upper and lower bus capacitors. In Figure 15d, the voltage of the flying capacitor Cf and bus capacitors increases gradually from t1 to t2;
- State 2: Until the voltage of Cf arrives at E, a quarter of the total bus voltage and power devices S3, S4, S5 and S8 are turned off and the voltage of bus capacitors will be half of flying capacitor voltage. Thus, the voltage stress of power switches is not higher than VDC/4 in the entire stage, which meets its request. As shown in Figure 15b, the DC-link capacitors are going to be charged by the DC-link voltage source at the same time with the voltage divider resistances in parallel with each bus capacitor to avoid the influence of the unbalanced characteristics of the bus capacitors;
- State 3: The voltage of CUP and CDOWN increases gradually until they reach their reference value 2E, as shown in Figure 15d from t2 to t3. When CUP and CDOWN are fully charged, the contactor K1 is connected and K2 is disconnected. Then, the ANPC five-level single-phase converter starts up well with enough energy in the capacitors, as shown in Figure 15c and is ready to work.
6. Experimental Results
7. Conclusions
Author Contributions
Funding
Conflicts of Interest
References
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State | S1 | S2 | S3 | S4 | S5 | S6 | S7 | S8 | Vo | Vcf | |
---|---|---|---|---|---|---|---|---|---|---|---|
Io > 0 | Io < 0 | ||||||||||
V1 | 0 | 1 | 0 | 1 | 0 | 1 | 0 | 1 | −2E | - | - |
V2-1 | 0 | 1 | 1 | 0 | 0 | 1 | 0 | 1 | −1E | C | D |
V3 | 1 | 0 | 0 | 1 | 0 | 1 | 0 | 1 | −1E | D | C |
V4-1 | 1 | 0 | 1 | 0 | 0 | 1 | 0 | 1 | −0 | - | - |
V5-1 | 0 | 1 | 0 | 1 | 1 | 0 | 1 | 0 | +0 | - | - |
V6 | 0 | 1 | 1 | 0 | 1 | 0 | 1 | 0 | +1E | D | C |
V7-1 | 1 | 0 | 0 | 1 | 1 | 0 | 1 | 0 | +1E | C | D |
V8 | 1 | 0 | 1 | 0 | 1 | 0 | 1 | 0 | +2E | - | - |
State | Sx1–Sx8 | Vcf | Vox | Level | |
---|---|---|---|---|---|
Io > 0 | Io < 0 | ||||
V1 | 01010101 | − | − | −Vdc/2 | −2 |
V2-1 | 01100101 | C a | D | −Vdc/4 | −1 |
V2-2 | 01100100 | ||||
V2-3 | 01110100 | ||||
V3 | 10010101 | D | C | −Vdc/4 | −1 |
V4-1 | 10100101 | − | − | 0 | 0 |
V4-2 | 10100100 | ||||
V4-3 | 10110100 | ||||
V5-1 | 01011010 | − | − | 0 | 0 |
V5-2 | 01010010 | ||||
V5-3 | 01110010 | ||||
V6 | 01101010 | D | C | Vdc/4 | 1 |
V7-1 | 10011010 | C | D | Vdc/4 | 1 |
V7-2 | 10010010 | ||||
V7-3 | 10110010 | ||||
V8 | 10101010 | − | − | Vdc/2 | 2 |
Parameters | Values |
---|---|
Inverter DC-bus voltage | 400 V |
Output frequency | 50 Hz |
Converter rating | 1 kVA |
Switching frequency | 10 kHz |
Inductance of filter | 0.3 mH |
Capacitance of DC-link capacitor | 2 mF |
Capacitance of flying capacitor | 660 μF |
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Chen, G.; Yang, J. A Modified Modulation Strategy for an Active Neutral-Point-Clamped Five-Level Converter in a 1500 V PV System. Electronics 2022, 11, 2289. https://doi.org/10.3390/electronics11152289
Chen G, Yang J. A Modified Modulation Strategy for an Active Neutral-Point-Clamped Five-Level Converter in a 1500 V PV System. Electronics. 2022; 11(15):2289. https://doi.org/10.3390/electronics11152289
Chicago/Turabian StyleChen, Guodong, and Jiatao Yang. 2022. "A Modified Modulation Strategy for an Active Neutral-Point-Clamped Five-Level Converter in a 1500 V PV System" Electronics 11, no. 15: 2289. https://doi.org/10.3390/electronics11152289
APA StyleChen, G., & Yang, J. (2022). A Modified Modulation Strategy for an Active Neutral-Point-Clamped Five-Level Converter in a 1500 V PV System. Electronics, 11(15), 2289. https://doi.org/10.3390/electronics11152289