POWER FEATURE
REGENERATING ENERGY USING BI-DIRECTIONAL DC-DC CONVERTERS by David Buck, market development manager, TDK-Lambda UK
H
aving a net-zero carbon footprint, or being carbon neutral, is a target for many companies. As part of that drive, multiple programs are
being instituted focusing on the 5 Rs – refuse, reduce, reuse, recycle and recover. In response, TDK-Lambda has developed a bi-directional power supply series that can help the recovery of previously wasted energy, reducing electricity costs and provide additional product functions. A traditional power supply, like one that operates a laptop or tablet, takes 230V AC electricity from the mains and converts it into low voltage DC. It provides the power to operate the laptop and to charge the internal battery. The power only flows in one direction. With a bi-directional DC-DC power supply (or converter) the power can flow in either direction. A remote pumping station using high voltage DC electric motors could be powered from a source that is not continuously present – from a wind turbine for example. A portion of the incoming power would be used by a bi-directional DC-DC converter to charge rechargeable 48V batteries. When the wind stops, the bi-directional converter will stop charging the batteries and will reverse power direction, converting the battery voltage from 48V to high voltage DC, keeping the pumping station in operation.
Figure 2: A bi-directional converter used to regenerate energy in industrial motor applications
Figure 1: Application example for a bi-directional converter in an energy storage system
There are many applications, outside of the renewable energy sector, where energy that is currently wasted can be captured, stored and reused. DC powered motors are being installed in more equipment as they offer higher efficiency, high start-up power, higher torque and faster response times to starting, stopping and acceleration. They can also be used as generators during deceleration or braking. When a lift, for example, is travelling upwards energy is supplied
to the motor from the building’s AC source to move the lift’s mass. As the lift travels downward, the mechanical load causes the motor to turn faster than its synchronous speed so that in effect the motor acts like a generator, producing current. Traditional lifts would use a resistive load to absorb that current and provide braking. That braking energy is dissipated into the air and wasted. A system using a bi-directional converter can use that previously lost energy to charge a battery. When the lift rises again, the bi-directional converter can provide peak power to assist when large amounts of torque is required. This not only “recycles” the energy but can reduce the building’s peak electrical demand, lowering the utility bill. (Figure 2).
/ ELECTRONICS
Lifts are just one example. Moreover, they can be used in many types of industrial equipment using motors such as cranes, robots, automated warehouses, AGVs, and forklifts. This type of equipment is started and stopped frequently and is ideal for implementing an energy saving solution. The stored energy can also be used to provide power during emergencies, during a power failure for example. The concept of a UPS with a DC input/output rather than using AC has found uptake in large scale digital printers located in areas where the AC power is not reliable. That provides sufficient time for a print run to be completed without the loss of material. The manufacturers of large batteries, including those for electric vehicles, are saving significant amounts of electricity by using bi- directional converters to evaluate the effects of multiple charge and discharge cycles. Instead of wasting energy during the discharge testing phase, it is used to charge other batteries, which can be then used to simulate plug-in charging stations. Before the availability of standard bi-directional converters, either a custom power supply had to be designed or two separate isolated DC-DC converters used. One for charging the battery and one for supplying power back to the high voltage DC bus. TDK-Lambda’s EZA series offers a fully isolated, off-the-shelf solution without the need to invest time and money on a new design and integration into the equipment. Remote control and programming are possible through an RS-485 interface. The EZA can be set to operate automatically within user set parameters, or manually. Monitoring and changes to the input-output voltages and current can be made in real time. To maximise energy savings, the bi-directional converter must be efficient. TDK-Lambda’s 11kW rated model is 95 per cent efficient and with less internal heating, the rack size is only 43.6mm (1U) in height. Digital control techniques, rather than relying on traditional analogue control methods, are key. Digital Signal Processing (DSP) circuits and software can more accurately react to load and input changes, and optimise the converters’ response. The important transition from charge to discharge is completely seamless.
New applications are being discovered for bi-directional DC-DC converters as the demand for smarter, greener homes and workplaces increases. The role that power electronics plays is becoming more crucial as energy conservation and saving power become one of the top priorities in the industrial society.
TDK Lambada UK
www.emea.lambda.tdk.com/eza11kw
ELECTRONICS | JUNE 2020 37
Page 1 |
Page 2 |
Page 3 |
Page 4 |
Page 5 |
Page 6 |
Page 7 |
Page 8 |
Page 9 |
Page 10 |
Page 11 |
Page 12 |
Page 13 |
Page 14 |
Page 15 |
Page 16 |
Page 17 |
Page 18 |
Page 19 |
Page 20 |
Page 21 |
Page 22 |
Page 23 |
Page 24 |
Page 25 |
Page 26 |
Page 27 |
Page 28 |
Page 29 |
Page 30 |
Page 31 |
Page 32 |
Page 33 |
Page 34 |
Page 35 |
Page 36 |
Page 37 |
Page 38 |
Page 39 |
Page 40 |
Page 41 |
Page 42 |
Page 43 |
Page 44 |
Page 45 |
Page 46
