4:1 Input DC-DC Converters Boast 1” x 1” Footprint

RECOM has released its REC15E-Z series of 15 W isolated DC/DC converters that featured wide input ranges at low cost in the popular 1”x1” case size. This saves a significant amount of PCB space, while the wide input ranges increase flexibility by accepting several standard bus voltages. The REC15E-Z DC/DC converters are fully-specified devices with 15 W, no minimum load, 1,600 VDC isolation, high efficiency up to 90% and low ripple/noise. The REC15E-Z series was designed for cost-sensitive applications where board space is at a premium. The wide 4:1 input ranges accept 9 V to 36 V or 18 V to 75 V to cover multiple supply options such as lead-acid or lithium batteries or 12/24/36/48 V industrial bus voltages.

The inputs are protected against transients of up to 100 V and feature UVLO to protect batteries from being over-discharged. The single or dual outputs are continuously protected against short circuit and overload conditions and can drive high-capacitive loads. They are fully certified to industrial EMC and safety standards and come with a three-year warranty. Samples and OEM pricing are available from all authorized distributors or directly from RECOM.

RECOM | www.recom-power.com

Building a Generator Control System

Three-Phase Power

Three-phase electrical power is a critical technology for heavy machinery. Learn how these two US Coast Guard Academy students built a physical generator set model capable of producing three-phase electricity. The article steps through the power sensors, master controller and DC-DC conversion design choices they faced with this project.
(Caption for lead image: From left to right: Aaron Dahlen, Caleb Stewart, Kent Altobelli and Christopher Gosvener.).

By Kent Altobelli and Caleb Stewart

Three-phase electrical power is typically used by heavy machinery due to its constant power transfer, and is used on board US Coast Guard cutters to power shipboard systems while at sea. In most applications, electrical power is generated by using a prime mover such as a diesel engine, steam turbine or water turbine to drive the shaft of a synchronous generator mechanically. The generator converts mechanical power to electrical power by using a field coil (electromagnet) on its spinning rotor to induce a changing current in its stationary stator coils. The flow of electrons in the stator coils is then distributed by conductors to energize various systems, such as lights, computers or pumps. If more electrical power is required by the facility, more mechanical power is needed to drive the generator, so more fuel, steam or water is fed to the prime mover. Together, the prime mover and the generator are referred to as a generator set “genset”.

Because the load expects a specific voltage and frequency for normal operation, the genset must regulate its output using a combination of its throttle setting and rotor field strength. When a real load, such as a light bulb, is switched on, it consumes more real power from the electrical distribution bus, and the load physically slows down the genset, reducing the output frequency and voltage. The shaft rotational speed determines the number of times per second the rotor’s magnetic field sweeps past the stator coils, and determines the frequency of the sinusoidal output. Increasing the throttle returns the frequency and voltage to their setpoints.

When a partially reactive load—for example, an induction motor—is switched on, it consumes real power, but also adds a complex component called “reactive power.” This causes a voltage change due to the way a generator produces the demanded phase offset between supplied voltage and current. An inductive load, common in industrial settings, causes the voltage output to sag, whereas a capacitive load causes the voltage to rise. Voltage induced in the stator is controlled by changing the strength of the rotor’s electromagnetic field that sweeps past the stator coils in accordance with Faraday’s Law of inductance. Increasing the voltage supply to the rotor’s electromagnet increases the magnetic field and brings the voltage back up to its setpoint.

The objective of our project was to build a physical generator set model capable of producing three-phase electricity, and maintain each “Y”-connected phase at an output voltage of 120 ±5 V RMS (AC) and frequency of 60 ±0.5 Hz. When the load on the system changes, provided the system is not pushed beyond its operating limits, the control system should be capable of returning the output to the acceptable voltage and frequency ranges within 3 seconds. When controlling multiple gensets paralleled in island operation, the distributed system should be able to meet the same voltage and frequency requirements, while simultaneously balancing the real and reactive power from all online gensets.

Two Configurations

Gensets supply power in two conceptually different configurations: “island” operation with stand-alone or paralleled (electrically connected) gensets, or gensets paralleled to an “infinite” bus.” In island operation, the entire electrical bus is relatively small—either one genset or a small number of total gensets—so any changes made by one genset directly affects the voltage and frequency of the electrical bus. When paralleled to an infinite bus such as the power grid, the bus is too powerful for a single genset to change the voltage or frequency. Coast Guard cutters use gensets in island operation, so that is the focus of this article.

When in island operation, deciding how much to compensate for a voltage or frequency change is accomplished using either droop or isochronous (iso) control. Droop control uses a proportional response to reduce error between the genset output and the desired setpoint. For example, if the frequency of the output drops, then the throttle of the prime mover is opened correspondingly to generate more power and raise the frequency back up. Since a proportional response cannot ever achieve the setpoint when loaded (a certain amount of constant error is required to keep the throttle open), the output frequency tends to decrease linearly with an increase in power output. A no-load to full-load droop of 2.4 Hz is typical for a generator in the United States, but this can usually be adjusted by the user.

Frequency control typically uses a mechanical governor to provide the proportional throttle response to meet real power demand. Voltage control typically uses an automatic voltage regulator (AVR) to manipulate the field coil strength to meet reactive power demand. Isochronous mode is more challenging, because it always works to return the genset output to the setpoint. Maintaining zero error on the output usually requires some combination of a proportional response to compensate for load fluctuation quickly, and also a long-term fine-tuning compensation to ensure the steady-state output achieves the setpoint.

If two or more gensets are paralleled, the combined load is supplied by the combined power output of the gensets. As before, maintaining the expected operating voltage and frequency is the first priority, but with multiple gensets, careful changes to the throttle and field can also redistribute the real and reactive power to meet real and reactive power demand efficiently.

If the average throttle or field setting is increased, then the overall bus frequency or voltage, respectively, also increases. If the average throttle or field setting stays the same while two gensets adjust their settings in opposite directions, the frequency or voltage stay the same, but the genset that increased their throttle or field provides a greater portion of the real or reactive power. Redistribution is important because it allows gensets to produce real power at peak efficiency and share reactive power evenly, because excessive reactive power generation derates the generator. Reactive currents flowing through the windings cause heat without producing real, useful power.

Four Conditions

Before the breaker can be closed to parallel generators, four conditions need to be met between the oncoming generators and the bus to ensure smooth load transfer:

1) The oncoming generator should have the same or a slightly higher voltage than the bus.
2) The oncoming generator should have the same or a slightly higher frequency than the bus.
3) The phase angles need to match. For example, the oncoming generator “A” phase needs to be at 0 degrees when the bus “A” phase is at 0 degrees.
4) The phase sequences need to be the same. For example, A-B-C for the oncoming generator needs to match the A-B-C phase sequence of the bus.

Meeting these conditions can be visualized using Figure 1, which shows a time vs. voltage representation of an arbitrary, balanced three-phase signal. The bus and the generator each have their own corresponding plots resembling Figure 1, and the two should only be electrically connected if both plots line up and therefore satisfy the four conditions listed above.

Figure 1
Arbitrary three phase sinusoid

If done properly, closing the breaker will be anticlimactic, and the gensets will happily find a new equilibrium. The gensets should be adjusted immediately to ensure the load is split evenly between gensets. If there is an electrical mismatch, the generator will instantly attempt to align its electrical phase with the bus, bringing the prime mover along for a wild ride and potentially causing physical damage—in addition to making a loud BANG! Idaho National Laboratories demonstrated the physical damage caused by electrical mismatch in its 2007 Aurora Generator Test.

Three primary setups for parallel genset operation are discussed here: droop-droop, isochronous-droop, and isochronous-isochronous. The simplest mode of parallel operation between two or more gensets is a droop-droop mode, where both gensets are in droop mode and collectively find a new equilibrium frequency and voltage according to the real and reactive power demands of the load.

Isochronous-droop (iso-droop) mode is slightly more complex, where one genset is in droop mode and the other is in iso mode. The iso genset always provides the power required to maintain a specific voltage and frequency, and the droop genset produces a constant real power corresponding to that one point on its droop curve. Because the iso genset works more or less depending on the load, it is also termed the “swing” generator.

Finally, isochronous-isochronous (iso-iso) is the most complex. In iso-iso mode, both gensets attempt to maintain the specified output voltage and frequency. While this sounds ideal, this mode has the potential for instability during transient loading, because individual genset control systems may not be able to differentiate between a change in load and a change in the other genset’s power output. Iso-iso mode usually requires direct communication or a higher level controller to monitor both gensets, so they respond to load changes without fighting each other. With no external communication, one genset could end up supplying the majority of the power to the load while the second genset is idling, seeing no need to contribute because the bus voltage and frequency are spot on! At some point one genset could even resist the other genset, consuming real power and causing the generator to “motor” the prime mover. Unchecked, this condition will damage prime movers, so a reverse power relay is usually in place to trip the genset offline, leaving only one genset to supply the entire load.

System Design

Each genset simulated on the Hampden Training Bench had a custom sensor monitoring the generator voltage, current, and frequency output, a small computer running control calculations and a pair of DC-to-DC converters to close the control loop on the generator’s rotational velocity and field strength. The genset was simulated by coupling a 330 W brushed DC motor acting as the prime mover to a four-pole 330 W synchronous generator (Figure 2).

Figure 2
Simulated genset on the Hampden Training Bench

Our power sensor was a custom-designed circuit board with an 8-bit microcontroller (MCU) employed to sample the genset output continuously and provide RMS voltage, RMS current, real power, reactive power, and frequency upon request. The control system ran on a Linux computer with custom software designed to poll the sensor for data, calculate the appropriate control response to return the system to the set point and generate corresponding pulse width modulated (PWM) outputs. Finally, the PWM outputs controlled the DC-to-DC converter to step down the DC supply voltage to drive the prime mover and energize the generator field coil. The component relationships are shown in Figure 3, where the diesel engine in a typical genset was replaced by our DC motor.

Figure 3
Genset component layout

Since this project was a continuation of a previous year of work by Elise Sako and Jasper Campbell, several lessons were learned that required the system be redesigned from the ground up. One of the largest design constraint from the previous year was the decision to use a variable frequency drive (VFD) to drive an induction motor as the prime mover. While this solution is acceptable, it introduces inherent delay in the control loop, because the VFD is designed to execute commands as smoothly but not necessarily as quickly as possible.

Another design constraint was the decision to power the generator field coil using DC regulated by an off-the-shelf silicon controller rectifier (SCR) chopper. Again, while this is an acceptable solution, the system output suffered from the SCR’s slow response time (refresh rate is limited to the AC supply frequency), and voltage output regulation was non-ideal (capacitor voltage refresh again limited by the frequency of the AC supply).

To solve these performance constraints, we selected the responsive and easily controllable DC motor as the prime mover so the DC output from our Hampden Training Bench could be used as the power supply for both the DC motor and the generator field coil. By greatly simplifying the electrical control of the genset, we reduced implementation cost and improved control system response time. …

Read the full article in the February 343 issue of Circuit Cellar
(Full article word count: 6116 words; Figure count: 14 Figures.)

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DC-DC Modules Boast Wide Voltage Range, Small Footprint

Maxim Integrated Products has announced four new micro-system-level IC (“uSLIC”) modules. The MAXM17552, MAXM15064, MAXM17900 and MAXM17903 step-down DC-DC power modules join Maxim’s extensive portfolio of Himalaya power solutions, providing the widest input voltage range (4 V to 60 V) with the smallest solution sizes.

While miniaturization remains the trend for an array of system designs, many of these designs also require a wide range of input voltages. For example, supply voltages in factory automation equipment are susceptible to large fluctuations due to long transmission lines. USB-C and broad 12 V nominal applications require up to 24 V of working voltage protection against transients due to hot plugging of supplies and/or batteries.
The newest Himalaya uSLIC power modules extend the portfolio’s range up to 60 V versus the previous maximum of 42V and come in a solution size (2.6 mm x 3.0 mm x 1.5 mm) less than half the size of the closest competitive offering. The modules feature a synchronous wide-input Himalaya buck regulator with built-in FETs, compensation and other functions with an integrated shielded inductor. Having the inductor in the module simplifies the toughest aspect of power supply design, enabling designers to create a robust, reliable power supply in less than a day.

The newest uSLIC modules are:

• MAXM17552, a 4 to 60V, 100mA module with 100 to 900kHz adjustable switching frequency, 82% efficiency (24V VIN at 5V/0.1A) and external clock synchronization in a 2.6mm x 3mm x 1.5mm package
• MAXM15064, a 4.5 to 60V, 300mA module with 500kHz fixed frequency, 82% efficiency (24V VIN at 5V/0.1A) and built-in output voltage monitoring in a 2.6mm x 3mm x 1.5mm package
• MAXM17900, a 4 to 24V, 100mA module with 100 to 900kHz adjustable switching frequency, 86% efficiency (12V VIN at 5V/100mA), external clock synchronization and built-in output voltage monitoring in a 2.6mm x 3mm x 1.5mm package
• MAXM17903, a 4.5 to 24V, 300mA module with 500kHz fixed switching frequency, 77% efficiency (12V VIN at 3.3V/300mA) and built-in output voltage monitoring in a 2.6mm x 3mm x 1.5mm package

The uSLIC modules can be purchased for the following prices: MAXM17552 for $2.53, MAXM15064 for $2.78, MAXM17900 for $1.39, and MAXM17903 for $1.48 (1000-up, FOB USA); they are also available from authorized distributors. The MAXM17552EVKIT#, MAXM15064EVKIT#, MAXM17900EVKIT# and MAXM17903EVKIT# evaluation kits are available at $29.73 each.

Maxim Integrated | www.maximintegrated.com

DC-DC Converter Family Adds Tighter Voltage Regulation

Vicor has added 25 new products to its family of DC-DC converter modules (DCMs) with tighter output voltage regulation of ±1%. With high power densities of 1,032 W/inches-squared, the new series allows engineers to drive loads requiring tighter regulation with minimal additional circuitry or downstream components.

The DCM ChiP (Converter housed in Package) is a DC-DC converter module that operates from an unregulated, wide range input to generate an isolated, regulated DC output. With its high frequency zero-voltage switching (ZVS) topology, the DCM converter consistently delivers high efficiency across its entire input voltage range.

The new DCMs are used broadly across defense and industrial applications that require tighter output voltage regulation. These applications include UAV, ground vehicle, radar, transportation and industrial controls. The DCM ChiPs are available in M-grade, which can perform at temperatures as low as -55°C.

Vicor | www.vicorpower.com

Module Combines Isolated Data Comms and Power in One Device

Murata Power Solutions has announced the introduction of the NMUSB2022PMC, a surface mount powered data isolator module that conveniently provides dual port USB data and power isolation from a single upstream port. When used in conjunction with a USB host, a single NMUSB202PMC module counts as two USB hubs for cascaded applications and provides full 5V/500mA power to each downstream port. 250 VRMS reinforced isolation provides safety, immunity to EMI and breaking of ground loops.

The is NMUSB2022PMC is fully compliant with USB 2.0 specification, which enables hassle-free, “plug and play” operation with any USB-compatible device. It can do automatic switching between full-speed (12 Mbps) and low speed (1.5 Mbps) operation. Operating temperature ranges from -40°C to +85°C.

The device enables USB isolation function with a single SMT component. Users may power any USB compatible device from the NMUSB module. The data isolation function included with the DC-DC module adds value and convenience to the user and also eases system approval for medical systems safety certifications. Applications include industrial control for isolating sensors and medical environments, where USB is becoming common for low cost sensing and communication but isolation is necessary for safety and noise immunity. It is also well suited for harsh environment data communication and sensor communications.

Murata Power Solutions | www.murata-ps.com

DC-DC Converter Family Targets Modern Railway Systems

Vicor has released its next generation of DCMs with a family of wide input range (43 V to 154 V input) 3623 (36 mm x 23mm) ChiPs with power levels up to 240 W and 93% efficiency, targeted at new rail transportation and infrastructure applications. Modern rail infrastructure requires a wide range of DC-DC converters to power a variety of new services for both freight and commuter markets.

Commuter rail systems require mobile office communication capabilities with the infotainment capabilities of home. Freight rail systems require monitoring and control capabilities to assure the safe and timely delivery of all goods onboard. While both commuter and freight systems demand reliable and high-performance power systems for the necessary safety and security measures (onboard and at station.)
The DCM is an isolated, regulated DC-DC converter module that can operate from an unregulated, wide range input to generate an isolated DC output. These new ChiP DCMs simplify power system designs by supporting multiple input voltage ranges in a single ChiP. With efficiencies up to 93% in a ChiP package less than 1.5 in2, these DCMs offer engineers leading density and efficiency.

Vicor | www.vicorpower.com

Ultra Wide Input Range Power Converters

Aimtec has announced the release of two new series of regulated AC to DC power converters, the AME10-BJZ and AME20-BJZ. These new series will expedite and simplify industrial and commercial product design in a low cost solution. The new regulated 10 W and 20 W AME10-BJZ and AME20-BJZ series are packaged in industry standard packages: 62.0 x 45.0 x 30.0 mm (2.44 x 1.77 x 1.18 inches) and 70.00 x 48.00 x 30.0 mm (2.76 x 1.89 x 1.18 inches) respectively. They meet the IEC/EN 62368-1 standards and are EN55032 class B compliant.

200_sq_ame10-bjz-press-jpg-94f2The internal EMC filtering reduces the need for external filtering components reducing production costs and are well suited for a wide range of applications including electric metering of three phase AC supply, industrial applications as well as commercial equipment applications. The standard package is available with 3.3, 5, 9, 12, 15 and 24 VDC outputs. These series offer over current, over voltage and short circuit protection while accepting an ultra-wide input range of 90-528 VAC or 100-745 VDC at 47-63 Hz input frequency. This series offers a high MTBF of 300,000 hours with an efficiency of up to 83%. The new AME10-BJZ and AME20-BJZ series feature high input/output isolation of 4,000 VAC and operate from a bone chilling -40°C to a blistering +70°C with full power output from -10°C to +55°C.

Aimtec | www.aimtec.com

1 W DC-DC Converters Medical Approved

MINMAX Technology has announced the MINMAX MAU01M / MSCU01M series, a new range of high performance 1 W medical safety approved DC-DC converters with encapsulated SIP-7 & SMD packages. They are specifically designed for medical applications. The series includes  models available for input voltages of 4.5 VDC to 5.5 VDC, 10.8 VDC to 13.2 VDC, and 21.6 to 26.4 VDC. The I/O isolation is specified for 4,000 VAC with reinforced insulation and ated for a 300 Vrms working voltage.

40e5a6c0900620d4a836fb17d0ef3ecbFurther features include short circuit protection, a low leakage current of 2 μA max. and operating ambient temperating range of -40°C to 95°C. This is achieved without de-rating and with a high efficiency of up to 84%. The MAU01M / MSCU01M series conforms to the 4th edition medical EMC standard. It meets 2xMOPP (Means of Patient Protection) per 3rd edition of IEC/EN 60601-1 & ANSI/AAMI ES60601-1. The MAU01M / MSCU01M series offer an economical solution for demanding medical instrument applications that require a certified supplementary and reinforced insulation system to comply with latest medical safety approvals under the 2x MOPP requirements.

MINMAX Technology | www.minmaxpower.com