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Posted on 01 September 2019

Power Converter Developer Kit

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A fully self-supportive, high density power converter

The demand for power conversion is ever increasing [1]. Major drivers for this increasing demand include growth of distributed generation systems and uninterruptible power supply (UPS) systems, higher system efficiency requirements, and increased demand for higher levels of power quality and power reliability.

By Perry Schugart, Director, Power Converter Business, American Superconductor Corporation

 

In many projects, the development time for the power conversion system is a major factor (critical path) in getting the product to market. The need for rapid development of both power converters and power conversion systems is essential for original equipment manufacturers, value added resellers, system integrators and end-users to get their products to market quickly and stay ahead of their competition.

This article discusses the American Superconductor (AMSC) PowerModule™ PM1000 power converter Developer Kit’s (PDK) ability to quickly develop power conversion systems to address a wide range of applications.

The Solution

The PowerModule PM1000 PDK developed by AMSC allows original equipment manufacturers (OEM), value added resellers, system integrators and end-users to quickly develop power conversion systems to address a wide range of applications. Using the PowerModule converter’s graphical user interface (GUI) you can quickly modify parameters of the four standard software modules of the PM1000 to meet your specific application needs.

The PM1000 is a fully self-supportive, high density power converter that incorporates a dual DSP controller that can also be used to incorporate a user’s control algorithms and eliminate the need for a separate controller. The PM1000 in the PDK comes pre-configured as a 3-phase power converter and can support any of the following power conversion types: AC-DC, DC-DC, or DC-AC. The PM1000 is also loaded with one of four application specific software modules (Active Rectifier, DC-DC, AC Voltage Source, or Motor Control).

The GUI provides the interface on a developer’s computer for setting up the PM1000 parameters, passing parameters back to the user interface for display and/or calculations and control of the system by the operator. The GUI provides the ability to quickly integrate and diagnose a PM1000 power conversion system.

AMSC developed the PM1000 as a modular design, Power Electronic Building Block (PEBB) [2], that can be quickly configured to meet different application needs from both the hardware and software viewpoints.

This combines the advantages of a proven power converter platform with the ability to rapidly develop a custom configuration.

Easy Development

The programming environment for the PDK utilizes a fiber optic link to communicate between the PM1000 and GUI (on the developer’s computer). A hardware interface, the PowerModule converter Asynchronous Serial Terminal Adapter (PASTA), is used to convert fiber optic signals to asynchronous serial or CAN, which are the standard communication protocols for the PM1000 converter.

The GUI interface displays all internal parameters and variables in tabular form. Variables may be flagged for continuous update, and parameters may be changed in real time.

Status of the PM1000 converter is displayed at the bottom of the main screen, along with error messages associated with range checking of parameters or communication faults [3].

A separate screen is provided with buttons to start, stop, or clear faults within the PM1000 converter. Other screens are provided to allow parameters to be retrieved from or stored to non-volatile memory; to observe fault history, status and warning messages; and to scan through message logs.

A diagnostic screen is provided which functions like a digital oscilloscope to observe the dynamic behavior of internal variables.

The user can set up a trigger variable and level (up to four variables at the same time), and acquire 128 data points per variable at rates up to once per A/D sample. This allows control loops to be tuned or voltages and currents to be monitored [3].

The diagnostic screen provides output in tabular form and as a file, which may be loaded into Mathcad® or Excel® for analysis or graphing.

Rapidly Create Power Conversion Systems

The PDK allows you to modify the pre-loaded application specific software module to create powerful new applications that solve a host of power conversion challenges. Each of the software modules serves as a baseline for modification. Modifications are made to the parameter database to meet an end user or OEM’s specific needs.

For modifications to the core software (regulators) or the system state machine (start/stop sequencing and response to external events), contact AMSC.

The four application specific software modules are designated as:
• Active Rectifier
• DC-DC
• AC Voltage Source
• Motor Control

Active Rectifier (functions as a current souce) implements most of the common AC line interface requirements and is the building block for rectifiers, VAR generators, voltage stabilization and active power filter applications.

DC-DC implements either one or two quadrant control of power flow between different DC voltage potentials. A phase shifted PWM signal is applied to each phase to minimize the DC current ripple and allow smaller, simpler filters. Either buck or boost operation may be selected.

AC Voltage Source provides a fixed amplitude and frequency, 3- phase, 3 wire voltage output, and can be used to power passive and active loads from a wide variety of energy storage devices or rectified AC power sources.

Motor Control implements a sensorless induction motor control algorithm, which provides field oriented control of induction motors. Encoder feedback may be employed to provide a significant improvement in low speed and dynamic performance [3].

Connect-and-Go

To facilitate an easy to use development platform, the PDK can be quickly configured in our simple connect-and-go three-step process:
1. Load the GUI software onto your computer.
2. Attach the fiber optic cable between your computer and the PM1000.
3. Attach the system components and power cables.

The PDK is now configured and ready to customize the applicationspecific software module of the PM1000 to meet the developer’s specific needs.

Application Overview

The PDK is configured to one of the four standard operating modes. An overview of each of these modes is provided below.

The PM1000 in the accompanying five figures is connected to the serial-to-fiber adapter (PASTA) and the user-supplied external components (computer, system components and power cables). The power ports are the busbars for input and output power (DC terminals and AC terminals). The power flow can be from DC to AC or in reverse. Other ports provide fiber optic (PASTA), analog and digital (System Hardware Interface - SHI) interfaces between the PM1000 and the external components.

Active Rectifier

In the Active Rectifier application, the PM1000 is a two quadrant (bidirectional power flow) AC to DC converter that converts 3-phase AC voltages to a regulated DC bus voltage. It regulates the DC bus voltage to a setpoint level and acts to maintain that value independent of load changes and power flow direction. It can inject reactive current at the fundamental frequency into the power system to influence the power factor of the converter system.

An AC line filter can be designed to eliminate much of the harmonic content of the AC line currents to help meet harmonic distortion standards, such as IEEE 519. Figure 1 shows a block diagram of a typical Active Rectifier application.

Block diagram of a typical Active Rectifier application

Active Rectifiers are used as frontend converters to AC and DC motor drives.

Other applications have the following requirements:
• Bi-directional current (power) flow is required
• Power quality on the AC line side is a constraint
• Unity or near unity power factor operation is required
• Reactive current (VAR) injection into the AC line is required
• DC bus voltage needs to be boosted above the level obtained with a passive rectifier

DC-DC

In the DC-DC application, the PM1000 is a two quadrant, bi-directional current flow buck or boost converter. The converter regulates both the voltage and current at the DC load voltage output.

The DC-DC converter function can be implemented with as little as one pole, but poles can be paralleled to allow for more current capability. Figures 2a and 2b show block diagrams of typical DC-DC applications.

Block diagram of a typical DC-DC Buck application

Block diagram of a typical DC-DC Boost application

DC-DC converters are used in DC power systems to convert energy from one voltage level to another. A common application is to control DC motors.

Other applications have the following requirements:
• Bi-directional current (power) flow
• Buck mode (load voltage lower than source voltage) to regulate voltage/current at DC load (shown in Figure 2a)
• Boost mode (load voltage higher than source voltage) if the power source is replaced by a battery, ESS or other power source, in which case the voltage at the PM1000’s DC bus is regulated (shown in Figure 2b)

AC Voltage Source

In the AC Voltage Source application, the PM1000 is a two quadrant DC to AC converter that converts the DC input power to a 3-phase, 3 wire, AC voltage. It regulates the magnitude, frequency and relative phases of the 3-phase, line to line, AC voltages independent of load changes. An AC output filter is used to reduce the voltage harmonics presented to the load.

Figure 3 shows a block diagram of a typical AC Voltage Source application.

Block diagram of a typical AC Voltage Source application

AC Voltage Source converters are used to convert energy from DC voltage sources and energy storage devices such as batteries, flywheel generators and ultra capacitors to AC voltages. A common application is an uninterruptible power supply (UPS).

Other applications have the following requirements:
• Stable and balanced AC voltage source
• Bi-directional current (power) flow
• High quality power on the AC load side

Motor Control

In the Motor Control application, the PM1000 is a two quadrant (bidirectional power flow) DC to AC converter (inverter) designed to drive AC induction motors at variable speed. It uses a sensorless, stator flux oriented type of control to produce good transient torque response and speed regulation.

Encoder feedback may be employed to provide a faster dynamic response, more accurate speed regulation and significant improvement in low speed torque.

It can operate the motor at rated torque with nearly rated current at any speed.

Figure 4 shows a block diagram of a typical Motor Control application.

Block diagram of a typical Motor Control application

Motor drive inverters are used to start and operate induction motors under variable speed applications to drive fans, pumps, conveyors and other loads. These motor drives can be paralleled to allow for higher power applications.

Motor drive inverters meet the following requirements:
• Operating induction motors at variable speed or with controlled torque
• Good dynamic torque and speed performance
• High torque/amp starting conditions

Example Development

The following example illustrates the advantages of using the PowerModule PDK versus a typical in-house development effort.

In Scenario 1, a typical OEM in-house development is undertaken to develop a power conversion system to meet their application requirements.

Here, the OEM will define the system requirements and develop both the required hardware and software for their power conversion system. The OEM´s internal resources (cost center) are used for the development.

 The OEM’s development time for their power conversion system is affected by three limiting factors:
• Both hardware and software need to be designed and developed
• More iteration time is required due to the newly developed hard-ware and software being utilized
• The OEM’s resources focused on the hardware and software will not have the knowledge, experience and capability of an organization which has it as a core competency

In Scenario 2, an OEM utilizes the PM1000 (in place of internally developing the power converter) along with the GUI to tailor the PM1000’s software to meet their application requirements. Here, the OEM will define the system requirements and use the PDK for both the hardware and software for their power conversion system.

The OEM’s development time for their power conversion system is reduced by three contributing factors:
• Both the hardware (PM1000) and software (application specific software modules and GUI) exist and only minor software modifications are needed. Modifications to the software or control flow can be supported by AMSC.
• Only minimal iteration time is required due to proven hardware and software being utilized (debug time should be reduced due to the fact that the standard software algorithm was already proven modifications being a small portion of the final algorithm).
• Less time is required for transferring this system into production (the PM1000 is a proven power converter platform is already used in high volume).

In these examples, the typical in-house development (Scenario 1) time for a power conversion system is 14.5 months; while the PDK development (Scenario 2) time for a power conversion system is only 2.75 months. The comparison of a typical in-house development versus using the PDK to develop a power conversion system is depicted in Figure 5.

Power conversion system development comparison

The PDK is provided with the following items:
• 3-Pole, 175 kVA PM1000, air or liquid-cooled
• Application specific software
— Active Rectifier
— DC-DC
— AC Voltage Source
— Motor Control
• Integrated pre-charge control interface (pilot relay and 24VDC supply)
• Graphical User Interface software (GUI)
• Serial-to-fiber adapter
— PASTA
• PM1000 User Manual

As a result of using the PDK, the cycle time to develop a power conversion system is reduced by 11.75 months.

The shorter time from using the PDK for development equates to 11.75 months of gained advantage to realize earlier revenue recognition, an additional opportunity/project, or further design refinement of the current project. The ability to quickly fabricate power conversion systems will be a determining factor for the leaders in the marketplace [1].

Summary

The American Superconductor PowerModule™ PM1000 Developer Kit (PDK) provides a platform for OEMs, VARs, system integrators and end-users to quickly develop power conversion systems (from both hardware and software viewpoints) to address a wide range of applications. Using the PDK can reduce the cycle time associated with developing a power conversion system. This reduction in time provides the potential for earlier revenue realization, taking on an additional opportunity/ project, or further design refinement.

 

References:

1) Perry Schugart, Reduce Time to Market with Rapid Prototyping of High Power Converters, PCIM Europe 2004 Conference, May 25-27, 2004.
2) T. Ericsen et al., Standardized Power Switch System Modules (Power Electronics Building Blocks), Power Systems World ’97, Sept. 9-13, 1997.
3) Dave Gritter, Power Converter Development using AMSC’s Power Electronic Building Block, PEDAC’04 Conference, March 22-24, 2004.

 

 

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