Partial Power Research Articles

Design and Implementation of an 18-kW 500-kHz 98.8% Efficiency High-Density Battery Charger With Partial Power Processing

The demand for high-density, high-efficiency bidirectional battery chargers is driven by the fast development of energy storage system in renewable energy system, microgrid, and transportation electrification. Isolated dc–dc converter that interfaces a battery with a variable voltage range is one of the critical components. Input-parallel output-series (IPOS) partial power (PP) converter is considered a promising high-efficiency, high-density solution because only a fraction of power is processed via multistage converters to regulate the output voltage. However, due to the tight coupling between two dc transformers (DCXs), the design of PP converter is complicated. To solve this issue, an overall design procedure for a bidirectional soft-switching resonant-type PP converter is proposed. In the parameters design part, a decoupled design method is proposed to simplify the DCXs design. With this method, two DCXs can be designed separately, and a typical optimization method can be easily applied. As for the hardware design part, to minimize the ac loop inductance and resistance, a two-direction (2-D) flux cancellation method and an “intraleaving” winding structure are proposed for circuit layout and high-frequency (HF) transformer to obtain high operation efficiency and power density. Finally, the whole design procedure is verified by an 18-kW-rated, 25-kW peak, prototype operating at 500 kHz. The realized PP converter features a peak efficiency of 98. 8% and a power density of 142 W/in3. This article is accompanied by two videos demonstrating the dynamic voltage regulation test and the efficiency measurement.

P$^{3}$DCT—Partial-Power Pre-Regulated DC Transformer

In this paper, a new approach to regulate the output voltage of a resonant, constant voltage transfer ratio 380 V/48 V isolated dc–dc converter is presented. Rather than applying variable frequency control to the resonant converter, which would result in reactive power processing and a more complicated electromagnetic compatibility filter design, the converter remains in its optimal operating point all time and an additional partial-power (PP) processing auxiliary converter is used to tightly regulate the output voltage. The PP converter, supplied through a tertiary winding of the resonant converter's transformer, regulates the output by adding or subtracting voltage from the dc input and has only a marginal impact on the overall efficiency of the dc–dc converter. The principal of operation is explained in detail including Sankey diagrams to illustrate the power processing of the converter and a feedback control system is proposed to tightly regulate the 48 V output voltage. A hardware demonstrator rated at 1.5 kW is implemented to cope with input voltage variations between 340 and 420 V and experimental results are provided showing that the output voltage can be kept within $\pm {1}{\%}$ of the nominal 48 V even under harsh input voltage and load transients. The realized dc–dc converter with PP pre-regulation features an overall efficiency of 97.7 $\%$ at rated power and a power density of 8.6 kWdm $^{-3}$ (141w/ $^{3}$ in).

A Systematic Approach to Extract State-Space Averaged Equations and Small-Signal Model of Partial-Power Converters

An isolated full power (FP) converter can be easily transformed into a partial-power (PP) converter by changing the connections of source and load to the converter. This is known as PP processing technique which can improve voltage gain, power rating, and efficiency of the system. This paper discusses the dynamic behavior of the PP converter. A general procedure is proposed to find the dynamic equations and ac small-signal relations for input-to-output voltage and duty ratio-to-output voltage transfer functions of the PP converter. It requires only the dynamic equations of the FP converter. Therefore, circuit analysis is not necessary. The presented methodology is applicable to the converters with any number of switching states. In order to validate the proposed method, it is applied to PP quasi-Z-source dc–dc converter. Several experimental/simulation tests are performed, and the results are compared to the modeling results. Frequency responses of $G_{\mathrm {vd}}$ and $G_{\mathrm {vg}}$ are obtained by simulations, while experiments verify the theoretical predictions.