Powering the Control of Modern Energy Systems

This article is published by EE Power as part of an exclusive digital content partnership with Bodo’s Power Systems.

The possibilities are endless in the quest to replace fossil fuels with renewable energy sources: sun, wind, water, biomass, geothermal, etc. While biomass and geothermal provide a constant energy yield, this is not the case with energy generated from the sun, wind, or waves. Solar power generated during the day must be stored for night use. Wind energy must also be stored, as turbines cannot supply energy when the winds are calm.

All these technologies require electronic control circuitries, which must be powered from various sources. One of the growth markets is e-mobility, where the EU has decided that no new vehicles with a classic combustion engine may be sold after 2035. Other regions have agreed on similar bans, and the change to electric vehicles will require many public and private charging stations supplied from the different worldwide AC grids (Figure 1).

 

Figure 1. Worldwide AC mains single-phase voltage and frequency levels without tolerances. Image used courtesy of Bodo’s Power Systems [PDF]

 

The worldwide AC mains voltages range from 85 Vac up to 264 Vac, and many power supplies today can work over this full range.

An additional challenge in energy applications is that equipment like power chargers or wall boxes are hard-wired directly to the fuse panel. This means they are more exposed to transients on the grid than equipment connected to an outlet by cables and plugs. Therefore, they must comply with overvoltage category III (OCV III) with isolation barriers of 4 k Vac (Figure 2). This applies to the auxiliary power supplies inside the chargers or wall boxes.

 

Figure 2. Overvoltage Categories. Image used courtesy of Bodo’s Power Systems [PDF]

 

These systems must also be tolerant to faults in the mains wiring or the neutral. A phase accidentally connected incorrectly during installation or a break in the neutral, even in the neighborhood, can lead to unbalanced systems and higher voltages. Therefore, the main input voltages are monitored to disconnect the expensive high-power stages in case of such a failure.

This monitoring circuitry must work under all circumstances. P-Duke offers a series of small AC/DC converters compliant with OVC III and operating over the extremely wide range of 85 to 530 Vac. Even if a phase is connected to neutral by error, the auxiliary supply and the monitoring circuitry work and can protect the power stage.

Modern systems should be ready to integrate with a smart grid or smart home environment. This allows controlling the system to match the actual power availability in a grid. Car batteries can be charged when a surplus of energy is available and work as energy buffers stabilizing the grid. Household appliances with high energy consumption will be switched on only when enough power is available.

This means more interphases to communicate with the grid or smart home controller. Supply voltages for interphases, displays, touch panels, or relays can range from 3.3 V up to 24 V. They can be generated from the auxiliary supply voltage bus with small isolated or non-isolated converters (Figure 3).

 

Figure 3. Simplified block diagram of a typical EV car charger. P-Duke offers lower-power auxiliary AC/DC and various DC/DC converters. Image used courtesy of Bodo’s Power Systems [PDF]

 

Integrating renewable energy requires an expansion of energy storage options due to the non-constant energy flow. Hydroelectric power plants are already used today by pumping water back into the reservoir when there is a surplus of energy. However, their capacity is limited, and the most obvious way to store energy would be to use batteries.

Lead-acid batteries have been used for decades, but they are heavy, their energy density is relatively low, the charging process is slow, and they can only be charged about 300 to 600 times.

 

Lithium Batteries

Lithium batteries have several advantages over lead-acid batteries. For example, they are much lighter and smaller than lead-acid batteries and can also be charged faster and reach several thousand charge cycles. This makes them ideal for use in mobile devices as well as e-vehicles.

But they require materials whose availability is limited and some of which are obtained under problematic conditions. Per kilowatt-hour of capacity, a typical electric vehicle battery needs 120 to 180 grams of lithium and some other materials with limited availability. According to a study from ADAC, a German automobile club, the 50 kWh battery of a car contains around 4 kg lithium, 11 kg manganese, 12 kg cobalt, 12 kg nickel, and 33 kg graphite.

To change mobility away from combustion engines to e-drives, hundreds of thousands of tons of these materials will be needed. According to experts, methods to recycle this material are complex and still in the development or testing phase. Therefore, alternatives are being sought, not only in battery technologies but also in storing electrical energy.

You may have heard of batteries based on aluminum (sulfur, sodium ions, carbon), copper or iron, and oxygen. Not available yet for the mass market, these options use materials available in large quantities and less problematic to mine.

The batteries’ size and weight are also unimportant for a non-mobile application. There is plenty of space in the base of a wind turbine tower, even for larger batteries. When there is a surplus of energy in the grid, the power generated by the turbine could be stored there and fed into the grid when there is an energy shortage. Often, energy must only be temporarily stored in a grid for 12 to 24 hours.

Each battery technology has different voltages, a real challenge if someone wants to design future-proof systems compatible with the other battery technologies and number of cells used in an application. Power supply manufacturers like P-Duke offer converters with input voltage ranges from 2:1 to 12:1. With these converters; it is possible to cover many different battery technologies.

 

Supercapacitors

Supercaps are an interesting alternative to batteries, offering longer lifetimes, up to 1 million charging cycles, and very high charging currents. Unlike batteries, supercaps are not damaged by a deep discharge. They are ideal for applications with power demands of less than 1-2 minutes but a very high number of charging cycles. Why not use supercaps on a transport robot in a warehouse that only travels short distances and can be recharged in seconds? Unlike batteries, the output voltage of supercaps depends very much on the state of charge. As most electronic loads need a stable voltage, DC/DC converters with wide input ranges are required.

 

Other Energy Storage Options

And there are many other ways to store energy. With electrolysis, hydrogen can be obtained from air. In a further process step, methane, the main component of natural gas, can be produced. Gases can be stored, transported, and used as fuel, e.g., in a fuel cell, another strongly emerging technology. Even drones are using fuel cells. Gas pressure and flywheel energy storage devices are another way to store mechanical energy for later use. Over 15 years ago, a start-up in the USA wanted to use compressed air for wind turbines, but it was never realized because the solution was too complex and inefficient. But there are still projects working on storing excess energy from wind turbines in compressed air.

The first gyro buses came to the market in 1950. They were able to recover the braking energy but needed a charging station every 4-6 kilometers, which was not suitable for modern public transport. Flywheel energy storage devices are mainly used to deliver high power for a short time, for example, to stabilize a grid.

These were just a few examples. The energy market is complex, there are thousands of options, and new ideas and technologies appear almost daily, placing different requirements on the power supplies needed. In addition, for energy-efficient, widespread use, modern systems must communicate with each other. All these systems need regulated supply voltages to be generated from various sources. The AC grid voltage levels and transient specifications have been set for many years, and companies like P-Duke offer various AC/DC power supply solutions meeting the various requirements (Figure 4).

 

Figure 4. P-Duke’s range of highly efficient/ compact AC/DC power supplies from 6W to 500W. Image used courtesy of Bodo’s Power Systems [PDF]

 

The situation is more complex for DC sources because new systems are expected to come to the market. But solutions are available today. In the telecom and railway markets, different battery voltages have been used for decades. System manufacturers in these markets want to offer one solution, and power supply manufacturers like P-Duke design converter families covering even the extremely wide input ranges of 16 V up to 160 V in railway applications and achieve power levels up to 200 W. With standard output voltages from 5 V up to 53 V, these converters can be used for many different battery voltages in all types of energy market applications.

 

Figure 5. DC/DC converter modules from P-Duke are available in different housings. Image used courtesy of Bodo’s Power Systems [PDF]

 

LAN, WLAN, GSM, and other communication modules, safety and monitoring devices, displays, touch panels, or relays, all need regulated supply voltages, with or without isolation from the internal control circuitry. Within the broad range of converters, it should be easy for a designer to find a ready-to-use solution (Figure 6).

 

Figure 6. Simplified block diagram of the power chain in an automated guided vehicle for warehouse applications. Two Isolated, wide-range converters are used to cover the wide voltage range of the supercap array and to protect the sensitive electronics from electric noise coming from the motor drives. The other low-power voltages are generated by non-isolated regulators. Image used courtesy of Bodo’s Power Systems [PDF]

 

All these converter modules are easy to deploy and, therefore, plug-and-play solutions not only during the design phase but also in case of later changes in the system's input, output, or power specification. This makes every design future-proof and ready for an emerging market with many new opportunities but still many unknowns.

 

This article originally appeared in Bodo’s Power Systems [PDF] magazine.