I- Introduction

II- Analysis of Output Phase Angle

III- Simulation for Output Phase Angle

IV- Phase Synchronization Control

V- Prototype and Experimental Verification

VI- CONCLUSIONS

References

Abstract

In order to provide high and extendable power levels for inductive power transfer (IPT) system, a parallel multi-inverter system based on modular inverter is presented. Various power requirements can be implemented by an adjustment of the number of paralleled inverters, which provides a high modularity. A master-slave scheme is employed for the switching-driver signals of parallel inverters, where one acts as a leader while others act as followers. Despite the master-slave scheme, the proposed circuit topology has natural robustness because of the equality in terms of the hardware configuration of each modular inverter. For proper parameters, the output phase (current lagging corresponding voltage) of an inverter is lower than the average of output phase of all inverters, when its output voltage lags behind others, and vice versa. Based on this approach, PI controllers are designed to implement phase synchronization for output voltages of all inverters. An IPT prototype supplied by the proposed parallel multi-inverter with three inverters was designed, built, and tested. Experiments show that the proposed parallel multi-inverter system has not only good circulating current suppression capacity but also excellent performance of phase synchronization. The maximum dc-dc efficiency was 94% at a 35.1 kW receiving power. This paper is accompanied by a Matlab/Simulink file demonstrating phase synchronization control.

NTRODUCTION

To achieve high power levels while maintaining a high efficiency is a key requirement for many IPT applications, such as fast charging for high speed trains and for electrical vehicles [1]-[6]. Commonly, high power is shared by multiple inverters or invert-legs instead of a single inverter. Multilevel inverters [7], [8], input-series output-parallel (ISOP) inverters [9]-[11], and parallel multi-inverter system [12]-[21] are three typical topologies integrating the power from various inverters. The main issue of multilevel inverters for IPT is voltage-balance [7], [8]. The topology of multilevel inverters has an advantage of voltage stress reduction for semiconductor devices. However, it is hard maintain all inverters in phase at a high-switching frequency for IPT applications, which leads to a possible high voltage un-balance and therefore possible malfunction. Similarly, ISOP topology shares the input DC voltage equally among all inverters, which requires a high input DC voltage to provide high output power, and it is not reported for IPT applications [9]-[11]. With regard to parallel multi-inverter system, the main issue is current-balance [12]- [21]. The parallel multi-inverter topology shares the total current among various inverters while the current un-balance is suppressed by properly designed circulating-suppression controllers [12]-[20] or circuit topologies [21]. For the application of grid-connected inverters or un-interruptible power supply, current-balance controller is relatively easy to implemented because of the low operating frequency (i.e., 50 Hz) and resulting sampling speed requirement [12]-[18]. The droop control is a common algorithm for these 50 Hz applications. However, the current-balance controller is a bit difficult to implement for IPT applications, considering the influence of the high operating frequency on the sampling and the driver signal propagation delay. The literature [19] shows a design of a 3 kW experimental IPT using a parallel two-inverter topology, where a controller based on active and reactive currents decomposition is designed to minimize the circulating current among inverters. The literature [20] presents a parallel topology to integrate power from multiple inverters via transformers. The power sharing is obtained with a synchronous clamp-mode h-bridge control method. Because of the use of high-frequency transformers, the efficiency is dropped down.