SiGaN mission 99 power electronics modular toolkit contains an extensive set of leading edge subsystems in order to form a source of highly reliable and efficient power electronics. Mission 99 functionality merges features of variable speed motor drives with medium-sized inverters. It features bi-directional power flow: motoring or generating as needed.
This research has enabled integrated wind and solar energy harvesting on farms, industrial buildings and private residences. It is the cornerstone to our latest V2X product lineup. The intrinsic grid support capabilities of our inverter solve the puzzle of power quality. Our drive delivers electromagnetic compatibility (both emission and immunity) without the horrors of shielded cable.
The same solution applies to related power applications such as wave energy harvesting, micro-pumped storage, irrigation, air-conditioning, vehicle chassis electronics (winch, crane, flood-light, AC micro-grid), industrial tools, site generators and hydraulic system replacement.
Add modern battery systems and it becomes possible to power a house or large machine from something the size of an ice box. Our surface-mounted electronic packages easily cover a power range from two to twenty Kilowatts and are easily stacked to reach higher power levels.
These innovations were made with an eye on the wider political and climate-change issues that apply to future renewable energy appliances and their fuel-burning hybrid systems. The scope is wide; it applies to every structure and every vehicle.
SiGaN is not only about passively generating power but we can start an engine and spin the wind turbine under either battery or solar power. This can be incredibly useful when commissioning turbines on a still day or operating at a remote site without a utility connection.
Change brings opportunities
Deep penetration of renewable energy into the international energy market has irreversibly changed the daily business of the public utilities and governments. In the past, countries went to war to maintain a steady supply of fossil fuel in a complex geo-political environment.
Switching to a free, yet somewhat intermittent natural energy resource now re-frames the energy supply problem as the challenge to find a continuous balance between supply and demand.
Sunny and windy summer days create a huge excess of energy while cold, cloudy spells strain conventional power stations to their limit. The politics of green energy have led to the premature shut-down of thermal and nuclear infrastructure in favour of weather-dependant energy sources.
Events in Texas (winter 2020) showed how grid operators are quick to use their smart meters to disconnect consumers (load-shedding) during extreme weather. In this case, the turbine blades became iced-up during a polar storm. It was a very bad time to be without electricity.
It is a critical realisation that in a “green” world, it is much more likely that grid operators will intervene to modify the demand side of the equation when supply is constrained. Such action is technically necessary to ensure that the entire power grid does not collapse.
Use of the term “non-essential” by governments has spooked many people into thinking about investing in private energy infrastructure; particularly by investing in their own battery rather than resorting to diesel power or solar arrays. Many consumers will think about owning a battery even when their city apartment cannot support a solar array.
The roll-out of smart meters (and variable energy pricing) will become an economic weapon to make people modify their consumption when exceptional weather conditions limit energy supply.
In the new green energy world, energy is on average free with the caveat that spot prices may jump towards plus (or minus) infinity as we struggle with excess or scarcity. Uncontrolled grid-tied solar inverters could lead to a nasty surprise when the grid operator really doesn’t want your power.
Architects will be aware that planning permission also depends on harvesting all local energy sources including sun, wind and geo-thermal heat.
SiGaN also makes software to furnish a building with properly dimensioned solar arrays, roof terraces and storm water management. In the future, these buildings must continue to function both with and without the AC utility being present.
Battery rooms, load-shedding and dynamic power pricing will become normal facts-of-life.
Building, vehicle and motor-drive electronics are becoming very closely inter-related fields.
Grid forming inverter
The immaturity of power electronic systems is conspicuous.
We have remarked that uncontrolled grid-tied solar inverters are a nuisance for the grid operator. With increasing penetration, it also becomes immediately clear that future distributed generator plant must do far more than just inject sunshine into the grid.
The words “Grid Forming Inverter” have become very significant. The connection to the motor drive industry is alive here too; a grid forming inverter performs harmonic compensation and automatically cleans up the emissions from all cheap (or small) motor drives and harmonic loads in the vicinity.
The motor drive industry has a huge problem with power quality; variable frequency drives tend to be implemented with a focus on cost. There is little budget to comply with the building level power quality and electromagnetic compatibility requirements of a domestic environment.
There is a convenient crack between the role of equipment manufacturer and system integrator. Between them, they manage to lose the legal requirement to properly control electromagnetic emissions down the cracks between the two organisations.
Even international standardisation organisations recognise that private industrial AC power grids may be a mess and it is basically the utility and factory owner’s problem to figure it out.
The solar inverter market worked out much better because it could not hide under the caveat “for industrial use only”. Curiously, it will be the solar inverter technology that will come to the rescue of the motor drive industry and will allow variable speed motor drives to become more widespread around homes.
A modern inverter must be capable of supporting the shape of the sinusoidal voltage waveform against imbalanced and harmonic loads as well as being able to regulate the grid voltage against disturbances by generating and absorbing reactive VARs in response to grid frequency and voltage excursions. There will be communication interfaces to talk to your grid operator for permission to consume or use energy at a highly variable tariff that changes by the second.
The inverter has to simulate the characteristics of a rotating machine with considerable mechanical momentum. It’s easy to understand that generators that behave like this are the normal building blocks of a power grid and that rotating steel (even if only simulated) is keeping the lights on.
A grid-forming inverter is also the obvious formula for a domestic (or building site, or military base, or factory) island-capable inverter. Add short-term overload capability and the ability to correct the generation from legacy inverters and cheap harmonic loads such as drives to get an ideal appliance.
In future, it is expected that DC-link interfaces become less proprietary and can charge a commodity battery or manage a super-capacitor bank. In practice, solar connectors enable local DC buses.
The solar industry offers clean (EMC compliant) DC-link interfaces. The motor industry: not yet
Efficiency is often the deciding feature to compare the worth or one system with another. The cost of managing the waste-heat is the major limitation on the power rating of equipment.
Higher efficiency means better economics
Energy efficiency has always improved over time. It is largely unavoidable reality that Silicon carbide transistors will knock the socks off existing silicon solutions in terms of efficiency.
But efficiency is not the whole story.
SiGaN developed its products in response to real world problems that could not be solved with commercial off-the-shelf technology.
- 1. SiGaN solutions are conceived for installation into non-environmentally controlled buildings and roof spaces.One of the unfortunate legacies of the classic inverter/industry-standard motor drive is a bank of wet electrolytic capacitors on the inside. It is this bulky component that has a life-time in the range of 1000-10,000 hours if not de-rated for temperature.
It drives the economics of the motor drive industry by creating work for maintenance crews.
The Arrhenius equation (applied to capacitors) tells us that every 5°C change of temperature causes the life expectancy of the machine to double (or halve). Spiders, leaves and hay will all screw-up the best installation. All provide excellent thermal insulation and block cooling air flow.
A product without wet electrolytics immediately extends the usable temperature window of a product by twenty degrees. In practice this allow a shift from an environment suitable for humans (office, factory) to a non-environmentally controlled outbuilding (farm).
SiGaN power electronics are revolutionary because they eliminate electrolytic capacitors in favour of the more stable foil or heat-proof ceramic capacitor.
Economically speaking; electrolytic free designs are equivalent to a gain in efficiency of perhaps 0.5%. This is an extra gain that stacks on top of the natural benefits of SiC transistors.
The positive side-effect is that the size and height of the electronics is halved and the environmentally-conditioned outdoor equipment cabinet goes away.
Power electronics then become small enough to move into an existing motor housing, which may be outdoors.
Anyone who installs motion control equipment will also realise that electromagnetic compatibility is also quite a major economic driver. Solar industry installers have it easy in comparison.
2. SiGaN chose to use solar industry installers to install their motor driveSpecial shielded cables and multi-pin proprietary connectors dominate the motion control industry. They cannot and must not appear in a price-sensitive installation. The prospect of stripping triple-shielded cable on a slippery barn roof is compelling enough to engineer clean interfaces.
SiGaN built and field-tested a fully surface-mount motor drive that is integrated into a 2kW BLDC motor body. The foil DC-link capacitor fits into the housing and tolerates vibration well.
Clean (no EMC emissions, high immunity) DC-link terminals can be wired with cost low-cost commodity connectors. Free-hanging cable ends and silicone-gel filled IDC connectors makes installation easy and time efficient even in a wet roof-top environment. A high-voltage DC bus keeps operating currents low. Long cables going up to the roof of a barn are no problem. In practice, a 2kW drive can be installed with only a pair of pliers.
Having a local DC-bus that is both extensive and wired by a normal electrician (and even hot-plugged) rather changes the motion control system game.
3. Everyone really wants a motor drive with pure sinewave output
But we also remain pragmatic; not every application will allow a complete motor re-design and integration into the motor frame.
Instead, inverter-derived hardware can produce clean and fully-reconstructed sine-waves that can be exported on long wires without problems. We can also drive legacy machines with a great immunity to industrial environmental noise from other people’s motor drives.
Once you delete the electrolytic capacitor bank, there is space in the box for the magnetics to reconstruct a sine waveform.
Comment of how it is done
SiGaN hardware exploits the latest surface-mounted SiC semiconductors for efficiency. We strive for automated assembly while introducing three-level modulation to halve the mass of the magnetics.
The modest heat flow is managed by heat exchangers built into the PCB layer stack. The technology uses only standard multi-layer PCB techniques and transfers heat into the outer casing of the product through graphite gaskets. The implementation is also rain-proof and works even on the roof.
In the inverter design, heat flow is enhanced by thermally conducted silicone rubber sheets for those hot electrical nodes that cannot tolerate the extra capacitance of an embedded heat exchanger.
The technical differences between a classic industry-standard 4kHz IGBT drive and a variable frequency 30-140 kHz SiC cascode drive are numerous. Nevertheless, our DSP control software for sensorless motors can and should remain common to both forms of the product.
A look inside the design reveals several years of research into new techniques needed to unleash the full potential of silicon carbide transistors. Particularly we tackled the uncomfortable noise emission spectrum from classic two-level pulse-width-modulation.
SiGaN provides a radical departure from PWM into noise-shaping techniques such as sigma-delta modulation and variable frequency modulation.
Even more work was done to reduce commutation losses by application of inter-phase inductors to re-cycle switching energy (eliminates almost all of the switching losses). We also use fast body-diode Si MOSFETs for smaller applications where SiC is overkill.
Upgrades to the bandwidth of the control loops are a key part of the SiGaN Intellectual Property package. Our hybrid solution combines both a 200kHz wide band mixed-signal feedback path for current control and a secondary digital instrumentation platform for highly accurate metrology.
Together, we support any desired energy flow with enough detail and accuracy for invoicing or for fine trimming of DC currents for cell balancing in the battery packs.
Our metering has a practical low-profile surface-mount implementation without recourse to traditional current sensor blocks with encapsulated magnetic cores.
The whole platform relies wherever possible on commodity devices such as logic gates and op-amps to supplement the limited control bandwidth of an entry-level DSP. At the same time, it fully enables modern manufacturing techniques; everything shall be surface mounted.
SiGaN AC inverter legs are designed to operate without software support. It is little more than an analogue mixed-signal simulation of rotating steel and heat flow and as such, we can offer pure-hardware based solutions for legacy systems that do not really need custom variable speed drives.
No screws, no grease, no lead-bending. No software (if desired).
A cross-over solution
The cross-over between the SiGaN inverter platform and SiGaN BLDC motor drive allows ideal customised solutions that are useable in real-world situations with rain and dirt.
The future of energy electronics lies in the green valley between the rocky peaks of the motor control industry and solar inverter industry. Neither industry has all the answers.
SiGaN field-trials were conducted quite literally on farms and are farmer-tested.
Our technology platform serves as a reference point for a range of possible OEM products and is a preview of a future that is far-removed from traditional solutions based on IGBT’s.
In time, mobile and off-grid power will become ubiquitous and a utility connection will be strictly optional. Our technology provides a visionary gaze into the future, yet it can be re-produced and copied at reasonable cost by any OEM with access to a specific market.
SiGaN is seeking industrial partners to begin product design from existing prototypes as proof-of-concept. Our design capital is produced in Altium by a small team of hardware and software engineers with long experience in industrial product design and electromagnetic compatibility.
Field of application
Energy appliances 6-10-20kW for domestic and industrial use
This PCB demonstrates an alternative technical implementations for the main parts of an inverter:
Together they form the bulk of the electronic package for a 3-phase inverter sufficient to power a single family home. An arbitrary mix of AC power grid, battery, EV, renewables (photoelectric/ wind/water) and fuel burning generator sets are foreseen.
The PCB is a technical proof-of-concept to show that next generation of inverters will be approximately half the size and weight of today’s state-of-the-art products and considerably more robust and outdoor weather tolerant.
The design fully exploits the potential of SiC transistors and SiC cascode transistors in Surface Mount Packages. This permits automated assembly and elimination of screws and fasteners in the thermal interfaces. It is inevitable that smaller and lighter electronic packages will appear in the marketplace because the SiC devices are far more capable than their silicon counterparts.
Time to market
A catalogue of architectural changes are required to get optimal performance from SiC. It is not sufficient to merely swap SiC devices with their silicon predecessors. This leads to considerable R&D effort being expended to solve all the issues that arise at once.
There is no simple migration path from a 2-level IGBT inverter to a 3-level SMD based SiC inverter in the sub-10-20kW power class. This PCB platform represents about 3 years of research effort.
The research was started in 2018 when the new new devices were still in prototype stage. This PCB is of interest to any company that has not already developed their own proprietary solution.
The design is unlike a semiconductor manufacturer’s reference design; it focuses on applying multi-sourced commodity parts. Accordingly it is a modular design that can be maintained for decades.
The traditional 2-level architecture is replaced by a 3-level architecture to enable the magnetic parts to be halved in size and weight.
Three-level modulation patterns are not well supported by classic DSP PWM controller blocks. To avoid burdening the classic DSP with a more complex control task, all control signals are simplified. There are no longer dead-time requirements and the 3-level switching patterns are re-mapped onto two wires and then generated in hardware by mixed-signal circuits.
The switching frequency is raised from a traditional 20kHz level to an average of 80 kHz (time-variable) to demonstrate the high frequency capabilities of moulded inductors and flat-wire wound torroids. This gives further weight and cost reductions.
The high switching frequency exceeds the data acquisition bandwidth of low-cost DSPs. This is a major obstacle to the introduction of new power semiconductors technologies into legacy designs. This problem is neatly solved by ensuring that DSPs are almost entirely eliminated from real-time control tasks. It is likely that future inverters will not use two or more DSPs.
It is evident that much of the glue logic in the design can be placed into a small FPGA; component count can be decimated for a production orientated variant.
SiC technology introduces additional issues with radio frequency emissions that are bought under control with the introduction of commutation inductors and suitable layout and differential signalling techniques. The test PCB is conspicuously over-sized to allow various magnetics to be evaluated and show signalling over long distances in a noisy, high dV/dT environment.
It is planned that the PCB area shall be halved in the next major revision. Development is ongoing.
A sigma-delta converter current sensor provides data in a digital format that permits fast multiplication operations to be performed by trivial hardware. Sigma-delta signal processing chains enables a simple implementation of I2 based junction temperature modelling and thermally adaptive current limits in hardware.
Traditional Pulse Width Modulation is replaced with a stochastic digital modulation by bringing the same sigma-delta modulator technology right up to the power stage; the undesirable emissions from the inverter have a shaped noise spectrum in the audio band. This avoids tonal acoustic artefacts and limits the potential for interference with utility power line signalling.
It is shown how the AC side power stage can become an autonomous block that is controlled and protected from fast over-current events without software. The AC side DSP is reserved for monitoring, metering and sequencing features and does not provide real-time control.
It is foreseen that the AC DSP is limited to providing a User Interface and regulatory compliance features. Advanced features such as harmonic load compensation, phase balancing, power factor adjustment earth-leakage detection, frequency hold-over and island modes are foreseen.
Features that are normally found in this DSP appear in hardware. A unique hardware based PLL loop system handles the main line synchronisation task and has a fully featured forward and reverse sequence detection. Sine waves are also synthesised by an apparently trivial hard implementation with analogue filters to set up the required synthetic output impedance on each phase.
The DC side DSP is also operating with external hardware support for over-current protection, junction temperature limiting and I.V multiplication for an easy MPPT implementations. Again, it does very little work.
A conventional DSP controlled PWM system is used with four independent buck stages and two MPPT trackers on a low-end DSP.
It is foreseen that the power flows on all interfaces are intrinsically bi-directional to support battery charging, solar panel snow clearance (by melting) and wind turbine run-up or diagnostic modes.
The board is also suitable for controlling large commercial LED lighting arrays (retail, agriculture, architecture) and is a platform for operating building automation; fans, blinds and pumps.
The system can be used as the Active Front End (AFE) of an energy efficient motion control system to provide either a regulated or unregulated high voltage DC-bus without emitting harmonic currents into the power grid. This suits commercially available motor drives or the SIGAN integrated brushless FOC motor/generator unit.
With appropriate metering, it may provide harmonic compensation and energy regeneration from existing drive installations.
SiGaN designs normally show how a bulky electrolytic DC-link capacitor can be replaced with smaller film or ceramic capacitors. Where phase imbalance is anticipated, a managed DC-link energy storage is preferred to eliminate wet electrolytics from the DC-link.
Elimination of wet electrolytics extends the life-time of the product in extreme environments.
The design was conceived for outdoor, unsheltered applications (hot or cold) with a low build height in the electronics package; typically 45mm headroom is required. This enables a host of new applications in the garage, on the roof or street.
The revised construction techniques with a surface mounted power stage are well adapted for high-vibration, mobile and even engine mounted environments once the major heavy components in a traditional static inverter have been either down-sized or eliminated.
The useful combination of an outdoor rated inverter and weather-proof servo motor drive enables a range of applications in the field of wind, water and fuel burning and grid driven building technologies.
SIGAN has bought renewable energy and motion control electronics under one roof.
This reference PCB platform serves as a starting point for product development. It provides a reference architecture that can be tuned for specific applications or re-mixed to include motion control from a closely related SiGaN product.
All manufacturing data is in Altium format with Texas Instruments DSPs.