Colorado Power Electronics (United States)

This paper proposes a three-leg universal charging front-end capable of both single-phase (1ϕ) and three-phase (3ϕ) connectivity and operation depending on the deployment configuration. Hardware re-utilization of both active and passive components across 1ϕ and 3ϕ deployment modes results in a versatile, high power density charging unit. The paper discloses the design and volume/loss/cost optimization methodology for the unit’s dc link and buffering capacitors in film technology for a 800 V dc bus, 50 kW-3ϕ / 33 kW-1ϕ case study. Experimental operation is reported for a scaled-down 10 kW unit prototype.

Modular multilevel converter (MMC) for medium-voltage variable speed drives (VSD) suffers from high sub-module (SM) voltage ripple at low-speed high-torque operation, resulting in a prohibitively large SM capacitance requirement. In this paper, a hybrid-MMC (HMMC) topology obtained by combining active neutral-point clamped converter (ANPC) and MMC is proposed for VSD. The proposed HMMC inverter requires 20 – 35% lesser semiconductors and 25 – 34% lower inverter capacitance compared to the prevalent solution of MMC with common-mode (CM) injection. For weight sensitive applications, a new modulation strategy is introduced which further reduces this capacitance by 50% although with a tradeoff of 20 – 40% more semiconductors. This is achieved through the inherent structure of the topology which results in lower SM voltage ripple and peak arm voltage magnitude. This paper explains the working principle of the proposed HMMC, and successfully validates their performance through simulation and experimental results.

Flying-capacitor multi-level converters invariably require the flying-capacitor voltages to be balanced for optimal operation. Balancing is typically carried out using dedicated controllers that require multiple voltages to be sensed and operate multiple loops in parallel. This paper presents a simple control technique for flying-capacitor 5-level converters in which only one flying-capacitor voltage needs to be sensed, leading to reduced system, design, and hardware complexity. The technique, based on eliminating the main unbalancing mode of the converter using a single balancing loop, is theoretically developed through both steady-state and dynamic considerations, and validated in simulations as well as experimentally on a 12 V - 2.4 V, 200 kHz flying-capacitor 5-level converter prototype.

Even though model-based design is becoming common place, there are currently few, if any, model-based methods for auto-generating test scripts for hardware testing. In addition, there has been little progress made on the methods used to design, develop, build, deploy, and sustain automated test solutions for testing hardware - especially during the production phase of a product's lifecycle. This lack of focus on modernizing the hardware testing processes and capabilities has begun to have significant impact on test organization's ability to deliver on their commitments. This paper describes a novel approach to developing a model-based framework for production testing of aerospace hardware. The project team maintains a systems approach to process transformation, while addressing multiple business concerns including organizational structure, talent retention, product lifecycle management, and test equipment lifecycle management.

This paper proposes a reconfigurable DC-DC buck converter architecture for per-core DVS in multi-core processors. The output voltage in each core can be rapidly changed with substantially reduced time and energy overheads, thereby improving the energy efficiency. The proposed architecture can be configured to a single-phase or a multi-phase buck converter, depending on the DVS voltage requirements. This overcomes the conflicting design criteria and realizes a high-resolution DVS using a voltage dithering technique with reduced time and energy overheads. A hardware prototype is made, and the test results demonstrate the superior performance of the proposed topology over existing architectures. The digital controller is implemented using a field programmable gate array (FPGA) device.

Transformerless stacked active bridge (TSAB) converters are hybrid dc-dc converters that combine features of switched capacitor (SC) and dual-active-bridge (DAB) converters, and can achieve very high efficiency near their nominal conversion ratio, together with regulation capability using simple phase-shift control. Following a network-theoretic approach, this paper describes a systematic procedure for synthesis of TSAB converters starting from two-phase SC converters such as ladder, Dickson, Fibonacci, and other SC topologies. Furthermore, the same approach yields general topology-dependant properties of TSAB converters, including steady-state characteristics and component stresses.

The High Voltage Hall Accelerator (HiVHAc) propulsion system consists of a thruster,power processing unit (PPU), and propellant feed system. An engineering model PPU was developed by Colorado Power Electronics, Inc. funded by NASA's Small Business Innovative Research Program. This PPU uses an innovative 3-phase resonant converter to deliver 4 kW of discharge power over a wide range of input and output voltage conditions.The PPU includes a digital control interface unit that automatically controls the PPU and a xenon flow control module (XFCM). It interfaces with a control computer to receive high level commands and relay telemetry through a MIL-STD-1553B interface. The EM PPU was thoroughly tested at GRC for functionality and performance at temperature extremes and demonstrated total efficiencies a high as 95 percent. It was integrated with the HiVHAc thruster and the XFCM to demonstrate closed-loop control of discharge current with anode flow. Initiation of the main discharge and power throttling were also successfully demonstrated and discharge oscillations were characterized.

The nature of reverse recovery losses is examined in hard-switched and soft-switched converters, using silicon (Si), silicon carbide (SiC), or gallium nitride (GaN) devices. A loss model and experimental results with a prototype 150-to-400 V, 150 W, boost converter operated at switching frequencies between 500 kHz and 2 MHz are used to characterize and quantify losses related to diode reverse recovery. It is found that reverse-recovery related losses with Si diodes cannot be neglected even when the converter is soft switched, with zero-current switching of the diode and zero-voltage switching of the transistor. The switching losses with SiC or GaN diodes are substantially smaller in all cases considered, and can be reduced to negligible values when the converter is soft switching.

A discrete-time, small-signal model is developed for the dual active bridge (DAB) converter which considers the effects of zero-voltage switching (ZVS) intervals on converter dynamics. The model is applied to the converter operating under phase-shift modulation, and is shown to be valid across a full range of load values constituting multiple operating modes of the converter. Finally, the model is applied to the case of an unregulated converter to show that output voltage variation that results in improved efficiency over wide range of loads can also lead to simplified control and compensation requirements across the full load range

This paper addresses a potential instability that can take place in Boost converters with average inductor current control. When the output of a Boost converter is attached to a load having bidirectional power capabilities or to an energy source such as a photovoltaic (PV) panel, instability conditions exist which prevent the design of a wide-bandwidth inductor current control. This paper discusses such instability conditions and their physical interpretation, and proposes an alternative control approach solving the problem. Simulation and experimental analyses for a non-inverting buck-boost converter interfacing a 85 W PV module are provided to demonstrate the instability condition as well as to validate the proposed alternative control solution.