EV Fundamentals: Inverter Limitations & Cooling
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Inverter Limitations & Cooling
03.50
| 00:00 | Inverters, while very impressive pieces of engineering that are only going to get better and better every year, they still have their limitations. |
| 00:06 | So, in this short module, let's discuss what those barriers are. |
| 00:10 | Inverters are available in different voltage ranges and current capacities, and generally a higher voltage capable inverter will not be able to put out as much motor torque or current. |
| 00:20 | If we're planning an EV conversion project, this means that the inverter must only be selected once a system voltage has already been determined. |
| 00:28 | And likewise, the system voltage selected should also consider the inverter options for the project. |
| 00:34 | As an example, many aftermarket inverters are designed for either 400 or 800 volt applications. |
| 00:39 | So, selecting a 600 volt battery pack could result in an inverter that isn't able to output as much current, which may mean the motor is not able to run its full output torque. |
| 00:47 | Inverters have a continuous and peak current rating. |
| 00:51 | Usually we're most concerned with the peak or pulse current for vehicles, as it's rare that a vehicle can operate at peak power for more than 10 or 15 seconds on anything other than a top speed test track. |
| 01:02 | However, it's critical to keep in mind that repeated full power pulses without enough rest period will likely push you above the continuous current range. |
| 01:10 | Nonetheless, it's good to know and understand these ratings to ensure that the inverter won't be the limiting factor in your application. |
| 01:15 | Always reach out to the inverter supplier with your specific use case to ensure that the peak pulse rating will work for your needs. |
| 01:23 | Inverters are generally water cooled and depending on the model of inverter, they usually want to run at a lower temperature than a motor. |
| 01:29 | Many OEM inverters, especially high power ones such as the older Tesla Model S, will reduce output power even with relatively low coolant temperatures. |
| 01:37 | This all depends on the limitations found inside the inverter. |
| 01:41 | So, how efficient the power drivers are and how well they can dissipate the heat from those drivers into the cooling system. |
| 01:46 | Also, remember that the heat is created from current, not voltage. |
| 01:50 | So, if we're operating at the lower end of the voltage range, we'll be drawing more current to make our target power and thus likely to have the inverter thermally limit itself sooner compared to operating at a higher voltage where less current would be needed to make the same power. |
| 02:04 | Another limitation comes from trying to use inverters and motors that aren't already calibrated or paired for one another. |
| 02:08 | It's important to note that an OEM inverter can't be recalibrated for a different motor, so trying to use an OE inverter with a different motor isn't an option unless you're somehow able to modify the programming inside that inverter. |
| 02:24 | If you are, more power to you. |
| 02:25 | With that said, it is sometimes possible to custom configure an aftermarket inverter for an OE motor, depending on how much reverse engineering work you're willing to do or pay for. |
| 02:36 | It's always best practice to ensure that the motor we're buying for a conversion project is compatible with the inverter that we're using, so we don't find ourselves having to spend a huge amount of time and money getting the motor characterized for that inverter. |
| 02:48 | Summing up this module, inverters are generally water-cooled and available in different voltage ranges and current capacities. |
| 02:54 | As they don't like to run anywhere as hot as a motor, we'll generally find the inverter plumbed into the cooling system before the motor to avoid it being fed super hot water. |
| 03:02 | If the temps do get even a little too high, most OEM inverters will start thermally limiting power output. |
| 03:07 | The risk comes when the water flow fails entirely, or if the inverter is airlocked. |
| 03:11 | Inverters have a continuous and a peak or pulse current rating, though it's the peak or pulse current that's most relevant to us, as this represents most real-world driving situations. |
| 03:22 | We do need to be mindful that repeated bursts of power could put us above the continuous power rating. |
| 03:27 | Lastly, inverters need to be characterized for a specific motor, so for that reason, OE inverters need to work with only their matched OE motor. |
| 03:35 | While an aftermarket inverter can be characterized to work with an OEM motor, it's not going to be easy or cheap, so it's always best to look for inverter and motor options that are going to work well together if you're in the planning stages of an EV conversion project. |
