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ELMG Digital Power is an experienced electronic design company who provide unparalleled electronics design services to a wide range of customers. We specialise in the design and manufacturing of digital power and power electronics technology.
Digital control of power provides flexibility in control that allows you to do incredible things such as increasing the efficiency, reconfiguring the function of the system or reducing the repeat cost of the controller to almost zero as the software or firmware can be replicated repeatedly.
The timing on synchronous rectifiers can be adjusted to the load level to decrease power loss. The switching frequency can be altered on the fly to minimise power loss or maximise the transient response. All these opportunities are opened up by digital control.
ELMG’s controller of choice is based around a powerful FPGA. One of the first questions coming into your mind is why use FPGAs? Aren’t they horribly expensive and take ages to develop? First of all, the key benefit of using FPGAs is their speed. In ELMG’s approach to systems the sampling rate is generally 100ksamples/sec or even higher, speeds which are effectively impossible to achieve on a microcontrollers and DSPs due to the processing time of the control loop. Why is speed so critical? This is due to the fact that in digital control, the sampling/processing time is a flat delay in your system. This delay turns to a phase at your control bandwidth, which is generally destabilizing. Processing faster reduces this delay and minimizes the effect on your control loop. Why sacrifice your control bandwidth by using slow processing when you can easily achieve your goals using an FPGA?
The second reason behind using FPGAs is that they are not expensive any more. When you factor in the peripherals you need, the RAM and clock speed, your MCU/DSP can get pricey. But you also end up paying for peripherals you don’t use. It is rare to find a MCU/DSP with all the features you want and none of the features you don’t. Suddenly FPGAs can start to look attractive pricewise. And with an FPGA you don’t end up with peripherals you don’t need. When it all adds up, in most power converters the FPGA will be just a small fraction of the cost after you factor in all the semiconductors and magnetics. In the event your volume is large and you need to save money, then your FPGA design can be converted to an ASIC.
There are many more reasons why FPGAs are well suited to power controller applications as well as others.
When your specifications arrive on our doorstep we first split in into two parts: Hardware and Firmware. Our firmware process is as follows:
The first step in our firmware process is to design your control loop. Do you need to be current-mode? Voltage-mode? Will a simple PI design work? Is it single phase or three phase AC? Do you need a repetitive controller? In designing the control loop we decide what you need and we design it for you.
Once we have the design we then model the controller design using Simulink and the converter with PLECS. This provides a complete model of the system. When the model is in place, when design the appropriate parameters and simulate them until we get a stable solution with appropriate margins.
Each step in the model is a separate block, such as a repetitive controller, rotator or space-vector PWM. We take each block one at a time and create FPGA IP which performs the exact same task in HDL form. Once that IP has been designed and coded, it is verified in a simulator with a custom testbench. The next step is to take that verified IP and use it in co-simulation within Simulink instead of the Simulink block. It is then verified against known control signals. This process continues for each block in the controller. This process sounds like a long pne, but at ELMG we speed it up by using IP we prepared earlier if we can.
The final step, once the all the IP is done is joining it all together, one final verification stage and then testing it on target hardware.
All designs at ELMG go through at least one prototype. This is to ensure that by the time the hardware reaches production it is defect free and no changes are made after releasing it. Highly accelerated life testing is standard, as one of the most expensive things to do is to modify hundreds or even thousands of boards after production. ELMG controls this risk for you. ELMG’s experienced team designs hardware in detail in order to make your controller works in all environments and situations which will befall it. ELMG also uses design practices which aid in your product passing compliance testing.
One key design decision is whether the controller is designed to an ambitious price target or not. Whilst ELMG’s engineers consider cost in all stages of the design phase, having flexibility can speed up the design process immensely. An example of this is the use of external FPGA modules such as the ones from Enclustra. These may be more expensive per board than putting the FPGA directly on the board but they save a lot of time in design which in turn saves money and decreases time to market. You can even decide to make the board fast and get it out to market and then we can cost-down the design to save you money in the long run.
Once the design is complete, manufactured and programmed, it goes through a comprehensive verification test to ensure that the manufactured product meets the design. This is done in stages to ensure that the circuit is working fully before high voltages or currents are applied to it.
Once the product is fully working in the lab, if specified by you, take it through pre-compliance and environmental testing. We have access to a full range of pre-compliance testing from EMC through to shock, vibration and HALT testing.
One of the common design decisions we come across is whether your large converter should be one large converter or a lot of smaller converters. This is a hard question with both sides having pros and cons. At ELMG we can follow the best approach, whether it be the single megawatt converter or the thousand kilowatt converters in parallel. We have expertise in paralleling converters as well as providing communications between them as described in the PowerComms Link page. We also have expertise in designing large converters with high voltages and/or currents. We have particular expertise in the medium voltage sector.
“That doesn’t look too hard,” you say, “we could whip this up no problems.” At first glance your system does not seem that complicated. Granted, some pieces of your puzzle are simple but others are complicated. Some common pieces ELMG already have developed, tested and verified. This is all time that you will need to spend. That is not the only time you must consider – the rest of the development will be still come once you reach this level. Does your company have the bandwidth? How many more sales does a faster time to market mean?
The key advantage in using ELMG for digital control development is our expertise. We have experts in the fields of FPGA development, power electronics, control systems and compliance. Not only can we design you a compliant stable system we can do it quickly, efficiently and we will take care of all the compliance.