Universal Inverters for e-Motor Development & Testing



Universal Inverters for e-Motor Development & Testing



In the world of eMobility, technology changes fast.  Battery Voltages, Motor Types, Motor Speeds and more are all a moving target.  If you’re developing products for this market, you need a testing solution that can keep pace. Unico’s modular performance drive systems are the answer.

Consider the case of e-Motor testing.  Unico is able to offer a solution that combines an AC Dyno, Battery Emulator, and Universal Inverter, all in a single package and powered by a single active front end.  This combination package saves floor space, reduces wiring complexity, simplifies installation, and saves energy. 

What sets us apart in the Universal Inverter technology?

Figure 1: Block Diagram of eMotor Test Configuration with Dyno, Battery Emulator, and Universal Inverter

Unico’s Universal Inverter works with all of the most-common types of AC motors (Asynchronous Induction, Synchronous Permanent Magnet, and IPM – Internal Permanent Magnet) without changing hardware or loading different software. 

Unico offers more than one rating, but our most popular unit is a water-cooled inverter that can accept a DC input of 0-900VDC and has a nominal 520VAC rating.  Switching frequency is user-adjustable up to 24kHz.  The inverter contains a dynamic protection curve that automatically adjusts based on operating conditions including DC input voltage, switching frequency, overload, output frequency, and ambient temperature.

Figure 2: Sample Ratings Curves for a Unico Universal Inverter

An optimal control strategy for the IPM motors

IPM motors are extremely popular for use in electric vehicles due to their combination of manufacturing costs, reliability, and high efficiency.  However, many general-purpose inverters are unable to control IPM motors optimally (if they are able to control them at all).  Because their magnets are embedded within the rotor, their operating characteristics are quite different from a conventional SPM (surface permanent magnet) motor. 

Figure 3: SPM vs IPM Motor Design

The Unico Universal Inverter includes automated test routines that can characterize an IPM motor and generate its flux maps.  Separate maps are generated for d and q-axis flux and for motoring and absorbing cases.  This flux map data alone can be invaluable for a motor designer, but the Unico Universal Inverter is able to use this data to generate the ideal current vectors for any combination or speed and torque.

All of this data can be exported from the Universal Inverter for additional external analysis if desired. Unico provides additional tools for analyzing this data to help validate the motor design and perform EV Inverter testing.

Once the IPM motor has been mapped, the Universal Inverter can control the motor in velocity or torque mode, much like any other motor.  For those who would rather use their own external motor control, the Unico Universal Inverter can also be configured to operate in Direct Current Control Mode. 

In this mode the inverter can accept external commands for d-axis and q-axis current. Or, the inverter can be set to instead accept a current magnitude and phase angle.  In this case, the external controller would be responsible for any velocity control and/or torque control.

Figure 4: Example of Flux Mop for d-Axis Motoring Case

Figure 5: Example of Motoring Current Vector Map


Innovative testing method for high-speed induction motors

Motors used in EV applications often operate at high speeds, with 20-30,000 rpm being fairly common.  These motors are often high pole-count as well, meaning the motor fundamental frequency can get quite high (often 1000 – 2000Hz at maximum speed).  Unico inverters do not impose a hard limit on output frequency, but it is recommended that the switching frequency be at least twelve times the motor fundamental frequency for proper control.

The Unico Universal Inverter can be set to operate in closed-loop vector control, open-loop vector control (transducerless), or volts/hertz frequency mode.  For closed-loop control, the inverter can accept feedback from most common types of feedback devices through the use of optional add-on modules. 

One of the most popular feedback devices used for e-Motors is the resolver.  However, there are many varieties of resolver.  Unico offers a Universal Programmable Resolver Interface module that works with almost any resolver.  The excitation voltage, excitation frequency, and turns ratio are all configurable through simple drive setup parameters to match the specific type of resolver being used.

EV Engineers that test and develop next-generation e-motors with a Unico Universal inverter will not only look to benefit from an expedited production process but also technical guidance is provided to system integrators and EV manufacturers to help ensure the optimum test stand configuration to meet their current and future research and development specifications.



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