1500 V three‐level forward converter with phase‐shifted control

Abstract

A 1500 V three-level forward converter with phase-shifted control is proposed to meet the requirements on mediumand high-voltage DC bus of photovoltaic grid-connected system. The architecture of 1500 V DC bus is established by filtering the phase-shifted outputs in series centrally, in which the internal filters of each DC/DC converter are removed. The three-level voltage is superimposed by phase-shifting the rectified output voltages in series, which is beneficial to decrease the inductor current pulsation, diminish the ripple of output voltage and improve the system efficiency. The centralised filter contributes to downsizing the filter and reducing the system cost. With the introduction of parallel-series structure, the characteristics of lowvoltage stress are retained and the power transmission is improved. Meanwhile, the minimum value of total harmonic distortion (THD) with phase-shifted control is obtained through the Fourier decomposition of three-level voltage waveform. By analysing the variation rule of THD with the change of conduction angle, the optimal steady-state operating point of the converter is achieved. The operating principle of the proposed system is presented minutely in this study and a prototype has been established. The experimental results verify the validity of the proposed converter.

Comparative Evaluation of Wide-Range Soft-Switching PWM Full-Bridge Modular Multilevel DC–DC Converters

“…(1) Leading switches: As the energy stored in the output inductance can be used, all leading switches can obtain ZVS in wide load range. As proved in [31], the minimum load of the leading switches in IZVS_CD is…”

“…In order to simplify the description, the operation principle and characteristics of IZVS_CD, IZVS_CAC and IZVS_SMI is not presented here, and corresponding information can be found in [30][31][32][33]. The IZVS_SMM is selected as an example to analyze in detail in this part.…”

“…Thus, the η LR of the leading switches is concluded in Table 3. (2) Lagging switches: A resonate inductance is added to enlarge the ZVS load range of the lagging switches in IZVS_CD, and, as shown in [31], the minimum load of the lagging switches in IZVS_CD is…”

“…The lagging switches will face more difficulty to obtain ZVS because only the energy stored in the leakage inductances can be used. As the switching scheme of Figure 1 is quite similar to that of a two-level PS FB dc-dc converter, common wide-range soft-switching solutions for two-level PS FB dc-dc converters can also be used [30][31][32][33][34][35][36][37]. These solutions can be concluded into two types: IZVS and ZVZCS.…”

“…These solutions can be concluded into two types: IZVS and ZVZCS. IZVS converters extend the ZVS range of the lagging switches by increasing either the value of the primary equivalent inductance or the currents of the switches [30][31][32][33][34]. In the ZVZCS converters, the lagging switches can realize ZCS by resetting the primary current during the free-wheeling mode.…”