The “Power Burst” servo drive goals are to design a servo drive that is:

• Delivers extremely high power output
• Emerges from an ultra-small package
• Ultra-efficient with negligible heat dissipation
• Produces similar high performance servo control as Elmo’s products
• Contains additional dedicated control and power conversion functions
• Capable of withstanding even more robust environmental conditions

These stringent requirements originate from the fact that some of those military applications are reducing their size/space significantly, while in contrast, their power requirements and servo performance are significantly escalating.

In addition, these applications also experience severe limitations in dissipating heat, as the servos’ environmental temperature is sometimes higher than the standard military application. In some cases, the chassis temperature is higher than the servo itself.

Elmo’s new B-type Military Servo Drives encompass the above specific requirements of
“Hi Power Bursts” within a very small servo.

 

Presently, there are the following types available:

• HOR-B 50/50, 50A bursts, up to 50VDC
• HOR-B 50/100, 50A bursts, up to 100VDC
• HOR-B 40/120, 40A bursts, up to 120VDC

For more information, Ask our expert.

 

Typical “Power Burst” scenario for a HOR-B50/50

• DC bus = 48VDC, Current limit ≤50A.
• At High current/power bursts, each “50A” burst can last for 40 -60 seconds.
• The scenario duration “t” is not limited with time as long as the average current is lower than
  20A for t>60 seconds and the heat-sink temperature maintained below 95°C.
• For each burst persisting for < 40 - 60 seconds, the average current can be as high as 50A (during the burst), on condition that, for an extended period, the I average < 20A.
• The HOR-B50/50 bursts power pulses of >2500W with average current of <10A.

 

 

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Typical “Power Burst” scenario for a HOR-B40/120

• DC bus = 110VDC, Current limit ≤40A.
• At High current/power bursts, each burst can last for 30 -60 seconds.
• The scenario duration “t” is not limited by time on condition that the average current is lower than 20A for t>60 seconds, and the heat-sink temperature maintained below 95°C.
• For each burst that persists for < 30 - 60 seconds, the average current can be as high as 50A (during the burst) on condition that, for an extended period, the I average < 20A
• In the above realistic situation, the average current is less than 4A with power bursts of >4000W

 

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Hornet B Series Highlights

• The innovation of the B series is its capability to deliver Very High Power pulses (Bursts) from an ultra‑small and ultra-light servo.
• The B-type exhibits extraordinary high ratios of:

 

• What’s unique about the Hornet B Series?

What are the differences between the HOR-B40/120 and a standard HOR-20/120 servo drive that can deliver 20A continuous and 40A peak?

The main difference between the HOR-20/120 and the HOR-B40/120 is the current limit mechanism.

The HOR-20/120 has a “traditional” I²t peak current limit that behaves according to the diagram below:

 

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The I²t performs RMS calculations of the peak current and limits the current to no more than 20A. The time constant of the I²t is limited to around 1 second (competitors) to 3 seconds (Elmo).

When exceeding the “peak current limit duration” the current drops to the continuous limit (20A) and actually is maintained at this current. At this position, the servo operation is disabled due to the current saturation and there are no resources remaining to provide additional peak current. Recovery from this saturation state can only occur if the current is dropped significantly from 20A, therefore allowing the I²t mechanism to “rest and discharge.” However, in the B- type Hornet, the I²t is disabled and is replaced by a smart “Thermal Operation Envelope” mechanism which provides 40A “almost” continuously.

 

 

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Why are servo drives with peak duration usually limited to only “1 -3” seconds?

The main reason is the limited thermal design that enforces very short peaks.
During a peak current of X2, the MOSFETs dissipate power at least three times more than it dissipates in the continuous mode. Due to high thermal impedance between the MOSFETs and the heat-sink, a sharp temperature increase (sort of “Thermal runaway”) at the junction will occur, which may cause the MOSFET to fail.

• Further uniqueness of the Hornet B Series
  There are considerable number of 40A servo drives in the market, so what makes the HOR-B so distinctive?
  The huge difference is in the size.
  Most of the standard 40A Elmo servo drives are 3- 4 times larger in volume. Other companies’ 40A drives might even be 6 -8 times larger than the HOR-B.

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How does a tiny Hornet producing high power levels work?

 

The HOR-B exhibits extraordinary Thermal Management enabling the tiny Hornet to provide very high energy pulses.

The characteristics required to meet “Power Burst” demands are:

• Very low thermal resistance MOSFET – Heat-sink
• Very high thermal capacitance  MOSFET  – Heat-sink
• Very long thermal time constant
• Stringent, accurate and real-time temperature sensing
• The Bursts operating mode is accomplished mainly due to the excellent efficiency displayed by the Hornet, therefore, there is very little loss of power from the package (“We don’t create heat, so no need to bother removing it”).

 

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Recordings demonstrating the HOR-B’s thermal performance

 

Table 3: Communication Pin Connectors

• DC bus 36VDC
• Output current 50A
• Ambient temperature ≈55°C
• The measured temperature is the actual temperature of the MOSFET’s case

The Results:

• The HOR- B50/50 is pushing out around 1800W
• The MOSFET’s case temperature is increasing very slowly and reaches near its maximum, only after 35 seconds
• The MOSFET’s case temperature increase is only ≈30°C
• Due to the very low “power conversion” losses, the Junction temperature will be higher than the case by <10°C
• At the above conditions, it will be reliable to increase the pulse duration and/or increase the ambient temperature by at least by 40°C

For more information, Ask our expert.

 

The key to success with the Burst type servo drives is the very efficient switching technology used in Elmo Servo Drives

The following graphic is displayed when the drive is switched ON:

 

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