At the heart of the Hydrapulse is what we call the INVERTER. This is the component that controls the speed and torque of our permanent magnet motor. An Inverter falls under the power electronics discipline of electrical engineering and serves the purpose of converting the power from a battery (in the case of a mobile vehicle), or the power coming in from the grid (line power) and controlling its frequency and current to control our motor.
We call it an Inverter but its also called alot of other names: Variable Frequency Drive (VFD), Frequency Converter, Traction Inverter, Motor Controller, Servo Drive, and many more. But it seems like the mobile industry has settled on Inverter. So that’s what we call it too.
We call this component an Inverter because it takes the DC voltage coming in from its power source and INVERTS it to an AC voltage. If we were taking AC voltage and going to DC, we would call it a CONVERTER or Rectifier.
While Inverters are used in many industries (such as solar inverters), the Inverter we have developed is actually a motor inverter, meaning its an inverter specifically designed to control a three phase permanent magnet motor. When we convert the DC power into an AC waveform, we can now control the frequency & amplitude of the AC waveform. This allows us to vary the AC power to the PM motor thus controlling its speed and torque.
This is why we use an inverter in the Hydrapulse and it allows us to directly control the hydraulic fluid flowrate and pressure by controlling the PM motor speed and torque. All due to the transistors at the heart of our inverter technology.
MOTOR SPEED = FLUID FLOWRATE
MOTOR TORQUE = HYDRAULIC PRESSURE
So now we have a basic understanding of our inverter thats inside the Hydrapulse® Smart HPU, now we need to understand why our technology is ready for the Fluid Power Industry.
What makes the inverter possible is the transistor. Its the component that turns the power on and off for each leg of the motor. Its basically just a switch that is controlled by the microprocessor. The microprocessor sends a signal to the transistors’ gate to turn it on or off. (There is a ton of information on google to learn more about transistors, like here and here)
Where things start to get interesting is when you start to consider the transistor type, efficiency, and speed at which it switches. Transistors are pretty efficient when they are in their ON or OFF state (like a hydraulic spool valve that is either fully closed or fully open) but they create alot of heat when they are somewhere in between on and off since they cannot transition instantaneously.
Its starts to get real complicated since we turn the transistors on and off VERY quickly in pulses of up to 100,000 or more times per second (Pulse Width Modulation) to create the output AC sine wave we want at any given instant. But this creates alot of ON to OFF transitions which introduce heat (lost efficiency). So creating a balance between the heat lost and how fast you can switch the transistors on and off is a critical element of the development of an inverter. Every application demands a different approach and our team has spent the last 6 years making the most efficient inverter possible for the fluid power market.
To create a robust and durable product for the off-highway and industrial fluid power market takes transistors that can withstand the temperature and vibration that is common in our industry. That is why we have used the most advanced, automotive grade MOSFET and IGBT transistors that are available to ensure year after year reliability for our customers!
No matter how efficient your design is, there is still some heat to remove from the transistors. Our engineers have spent years working on the best and most economical method of cooling the transistors we use. We started with discrete transistor testing on cryogenic cooled plates to -40 deg C. This allowed us to characterize all the different transistors on the market to find the best ones for our applications. We determined how to efficiently remove the heat. This was critical since the Hydrapulse® is a closed system that is sealed from the environment. You can’t simply put a big fan on a fin heat sink like you do in typical industrial control cabinets.