翻译部分英文原文Design Considerations for a Soft Switched, Modular 2.4MVA Medium Voltage DriveAshish Bendre, Ian Wallace, Glen LuckjiffSteve Norris, Randy Gascoigne, William E.Brumsickle, Deepak DivanSoftSwitching Technologies Corp.8155 Forsythia St. Middleton, WI 53562Email: engineeringsoftswitch.comRobert Cuzner, Wayne SchulzEaton Corporation-Navy Controls3060 W. Hope Ave.Milwaukee, WI 53216A new six-phase, 2.4 MVA, soft-switched, medium voltage drive system utilizing series stacked modules with low voltage devices has been developed. The drive system combines a new soft-switched DC-DC converter with resonant DC link inverter technology to deliver extremely low THD sinusoidal output, high power density and high efficiency. The series stacked configuration with the associated single-phase loading lead to unique power and control design challenges. Device selection, control of parasitic elements, sensing methods for converter control, custom magnetic component design and clamping techniques have lead to a substantial improvement in device voltage utilization. The dc-dc converter controls must regulate the intermediate dc bus voltage under single phase loading while balancing transformer excitation and maintaining zero voltage switching, among other tasks. Proper control of the RDCL inverter requires the selection and tuning of the appropriate modulator and understanding its affect on the power circuit ratings. I. INTRODUCTIONA new six phase, 2.4 MVA, soft-switched, medium-voltage drive system that features extremely low THD, high power density and high efficiency has been developed in a collaborative effort. The drive is powered from a single 700-900Vdc source while the phase output is 1380V line-neutral and 286A rms. The application requires high power density and high efficiency, so the power conversion be done at high frequencies. High voltage (2400V) devices, which have significantly high switching losses, could not be used in the design, as they would violate the efficiency and power density targets. Instead, three inverters using commonly available lower voltage devices at 1200V, producing 460V rms at 286A rms were connected as a series stack to produce the required output voltage. As the input is a single uncontrolled source, a new loss-limited dc-dc converter module was developed to provide isolated, regulated dc voltage to the inverter modules.For the output stage, hard-switched PWM inverters with interleaved switching have been shown to achieve low THD 1. However, the synchronization of control coupled with the higher switching losses makes this approach unattractive. Three-phase resonant dc link (RDCL) inverter modules that provide high efficiency and power density along with a spread spectrum noiseband, which allows independent (asynchronous) operation with extremely low THD have been previously developed 2. For this work, these modules were converted to single phase and substantially modified to further improve power density and device utilization. Each output phase of the drive system contains three series connected, single-phase RDCL inverters each powered by an isolated dc- dc converter as shown in Figure 1.The high power, high frequency series stacked configuration and the application requirements lead to unique design challenges and tradeoffs for both the inverter and the DC-DC converter modules. This topology leads to single phase loading on the output of the DC-DC converter, utilizes the devices closer to their ratings and increases voltage stress on isolation boundaries. These issues affect device selection, magnetic component design, control of parasitic elements, capacitor and sensor selection for both soft-switched converters; these are some of the major design issues discussed in this paper. The function of the DC-DC converter is to regulate the output dc bus voltage, while handling single-phase current loading, balancing transformer excitation, and maintaining zero voltage switching. This is accomplished by varying the operating frequency from 20-30kHz using state machine control. Control of the RDCL inverter involved a tradeoff between designing the modulator to produce low THD waveforms and rating the power circuit component to achieve high power density. II. DC-DC CONVERTER DESIGNThe major restrictions to higher frequency, high power DC-DC converters are power device switching loss, throughput loss due to transformer leakage and diode reverse recovery loss. The new DC-DC converter module uses low leakage coaxial wound transformers along with a novel primary commutation scheme that limits the switching loss, a split secondary that permits the use of 1200V devices and an energy recovery clamp for diode recovery 3. The converter topology is shown in Figure 2.Operation: Output voltage and current are controlled by phase shifting one leg Q1, Q2 of the primary H-bridge with respect to the other leg Q3, Q4. The turn-off swi