Electrical Power & Protection


Drive-powered energy for safe shut down

June 2007 Electrical Power & Protection

Power supplies with a DC input voltage of 360-900 V can be directly connected to the intermediate DC-bus of a frequency drive. The advantages are interesting but special precautions are required when connecting the power supply.

Power supplies for control systems are traditionally connected to either a 1-phase or 3-phase AC mains supply. However, due to the increasing use of frequency drives and amplifiers, there is a new option of connecting the power supplies to the intermediate DC-bus of a frequency drive (Figure 1). One of the greatest advantages is that you can use the kinetic energy of the motors as a way of supplying the control system. This intriguing configuration significantly increases the stability against AC mains fluctuations without needing to employ battery back-up and its associated costly maintenance.

Figure 1: Power supply is connected to the DC-bus and not to the AC mains
Figure 1: Power supply is connected to the DC-bus and not to the AC mains

A good example is the use of a crane application. What happens when a crane has just hoisted its load up into the air and the AC power fails?

Normally, the control system would have to be battery backed-up so that power is available when lowering the load back to the ground. However, if the control system is supplied through the intermediate DC-bus, the crane's motor can act as a generator when the load is lowered. The energy from the motor keeps the intermediate DC-bus voltage live which in turn keeps the power supply energised allowing for DC power for the control system simplifying and increasing the reliability of the design.

The PULS QTD20.241 can benefit users by eliminating the costly breakage of tools and material due to AC mains failures and fluctuations. Some examples are textile, paper and grinding machines as well as crane applications previously mentioned.

The device can keep the control system energised long enough to provide a controlled and safe shut-down of equipment during power loss making it the perfect choice as an addition to your drive system.

What special requirements does a power supply that is suitable for the intermediate DC-bus need?

One might think there are no special requirements needed because, from the basic design principle, switching power supplies can be operated with both AC and DC. Sometimes power supplies are also specified with a DC voltage range of 450-750 V, so why do problems arise in practical use when they are connected to the intermediate DC-bus?

Firstly, the voltage of an intermediate DC-bus is often a high-frequency AC voltage with several hundred volts of amplitude and switching voltage edges against ground. True 'DC voltage' applies only to the voltage between the positive and negative terminals but is not referenced to ground. However, the intermediate DC-bus jumps back and forth in common mode referenced to ground.

Secondly, the interference on an intermediate DC-bus exceeds the permissible values for a power line by many factors of 10 and therefore the requirements for a power supply connected to an intermediate DC-bus are quite different than for a typical power supply.

The PULS QTD20.241 offers an application-specific power supply with a continuous output of 24 V and 20 A. One important difference from standard PULS power supplies is that the direction of the EMI filter has been turned around. Normally, the filters are arranged so that the interference generated in the power supply does not feed back to the power lines which must be kept clean. However, in an intermediate DC-bus connection the filters should block the interference generated from this connection.



Credit(s)



Share this article:
Share via emailShare via LinkedInPrint this page

Further reading:

Half brick second generation converter
Vepac Electronics Electrical Power & Protection
The Supreme series half brick second generation converter from Vepac is composed of isolated, board-mountable, fixed switching frequency DC-DC converters that use synchronous rectification to achieve extremely high power conversion efficiency.

Read more...
Multimeters: the perfect entry-level choice
Comtest Electrical Power & Protection
Experience the precision, durability and safety of professional-grade test tools with the entry level Fluke 15B+ and 17B+ digital multimeters.

Read more...
South Africa can become an important EV manufacturer
Electrical Power & Protection
A year ago, South Africa was mired in loadshedding, with the importance and relevance of electric vehicles (EVs) far from the public imagination. Fast forward a year and much has changed

Read more...
Self-contained standalone lightning warning system
Senseca Electrical Power & Protection
Biral, now part of the Senseca Group, and a specialist in environmental and meteorological measurement instrumentation, has launched its BTD-200 lightning warning system, which is a complete detection and warning system.

Read more...
Compact, high density power protection system for AI, data centre and large-scale electrical workloads
Schneider Electric South Africa Electrical Power & Protection
Schneider Electric has launched its new Galaxy VXL – a highly efficient, compact, modular, scalable and redundant 500-1250 kW (400 V) 3-phase uninterruptible power supply (UPS), complete with enhanced cybersecurity, software and safety features.

Read more...
Taking the pain out of panel building
Omron Electronics Electrical Power & Protection
Panel building stands as a cornerstone of industrial automation, shaping the efficiency and reliability of automated systems across different and diverse industries, from manufacturing to infrastructure. Omron leverages over 80 years of experience to furnish OEMs and builders with cutting-edge control panel solutions.

Read more...
Powerless is not an option
Electrical Power & Protection
When the power goes out it is important for commercial and tertiary facilities to be able to keep essential electrical equipment running. UPS systems are critical for transitioning and emergency backup power.

Read more...
High-performance surface inspection systems for battery production
Electrical Power & Protection
As battery manufacturers increase their focus on yield optimisation to meet growing demand, AMETEK Surface Vision is highlighting the essential role of processes to improve quality and reduce defects.

Read more...
Securing the power supply
Electrical Power & Protection
Grid management systems are the linchpin of modern transmission and distribution networks. To understand the intricacies of grid management, it is necessary to unpack its core components: scada systems, energy management systems, outage management systems and wide area management systems.

Read more...
Powering sustainable mining operations in Africa
Electrical Power & Protection
Africa’s mining sector is at a crossroads and, as the industry grapples with mounting pressure to drive operational efficiency within the boundaries of sustainability, natural gas is emerging as a compelling solution.

Read more...