Power-Save HID Light Manager Technology

The system reduces the amount of energy used in some types of lights by reducing the voltage (Reference Patent 5,442,261). In a single phase lighting system this is done by placing a dual isolated winding step-down transformer secondary in series between the line and load and connecting the primary to the line 180 degrees out of phase with the secondary (phase opposing). Assuming the transformer is a 10 to 1 step down, with 120 volts AC applied to the primary will cause 12 volts AC to appear on the secondary subtracting from the line voltage. A voltmeter connected across the load will read 108 volts AC. The advantage of this approach over using a 1 to 0.9 step down transformer is that the transformer only has to handle the fraction of the power defined by it's step-down ratio (example 10:1 transformer only needs to be rated for 10% of full load). Another advantage for and application where the system has to run at full voltage when certain types of lights are turned on (High Intensity Discharge types, fluorescent, etc.), then lowered for increased efficiency is that switching this system requires only switching the transformer primary current (in this example 10% of full rated current). When the full line voltage needs to be applied to the load, a relay removes the line voltage from the primary, then shorts the primary. This short is reflected to the secondary and the secondary presents a low impedance to the line and passes the full voltage to the load. Another advantage is that ordinarily to switch the load from one voltage to another, the switching system will interrupt the power, as in a break-before-make relay switch to prevent high circulating currents. Since this system never disconnects the load from the line, the plasma in the lights won't “quench” and require a start up cycle at full voltage when the system switches from full voltage to reduced voltage.

A three phase system can be constructed by using three single phase power sections controlled by a single control board, this gives the customer the ability to have the three phases switching independently. If this is not needed, a three phase transformer can be used to reduce system cost.

The control system uses a microprocessor and a current sense circuit that monitors the variation in current in two rectified filtered channels with different time constants and compares the two channels. If the lower time constant signal is higher than the higher time constant channel it indicates a current increase has occurred. This differential voltage sensing is done with a variable gain amplifier controlled by the microprocessor. The sensitivity of this circuit can be changed through the front panel, through a computer interface or by adaptive control algorithms by the controlling microprocessor. The system can also determine an increase in load by monitoring the current and voltage and calculating an increase of power independent of an increase caused by a line voltage increase. An increase in load indicates a light or number of lights have been turned on in the system. If this happens the control system switches to full voltage to start up the lights and keeps the voltage at this level for a customer programmable period to insure proper startup. When the timer expires the system reduces the voltage to energy-saving level. By monitoring the voltage and current at full voltage and reduced voltage, the microprocessor can calculate how much energy is being saved.

Ten Percent Regulator and Bit-Weighted Regulator

Overview

There is an existing market for a low-cost voltage regulator. The existing products use tapped transformers and solid-state switches to switch these taps. The input voltage range is specified to be a “window” from +/- 5% to +/- 25% of nominal line voltage. The problem with the existing tap-changer technology is the voltage regulation is done in steps, with each step having a interruption of the load while the tap switches to the new tap. The Ten Percent Regulator uses technology that substantially shrinks the size and cost of the magnetics and uses a linear regulation technology that eliminates the “steps”, the line interruptions and increases the regulation resolution by a factor of 50 or more. The transformer cost of this system compared to the existing products is considerably less, but the controls may be more in the lower power ranges. The overall cost of the system in the power range above 10KVA should be less, and because of the greatly improved functionality we can charge more at a given power rating.

I have heard of another technology close to the Ten Percent Regulator used in military applications, it uses the same buck/boost series transformer configuration but uses a double-conversion, bi-directional rectifier/inverter to control the voltage regulation. When the system boosts the output voltage, the system acts like a conventional rectifier/inverter, but in buck mode the system needs to handle reverse current flow and regenerate the power back into the line. Our system uses an AC inverter that has a simpler and less expensive power sections and a much simpler and more reliable control circuit. This system with the AC inverter probably hasn't been used before.

The Bit-Weighted Regulator is a simplified version that has “step” changes like the existing technology, but doesn't interrupt the power and is substantially less expensive than either the existing technology or the Ten Percent Regulator.

Existing Products

The most popular type of product on the market uses tapped isolation transformer or auto transformer. The number of taps and the voltage range between taps determines the input voltage “window” and the resolution of voltage regulation. The switching is normally done by configuring two symmetric Silicon Controlled Rectifiers (SCR) connected anti-parallel to act as an AC switch. When current is applied by the control system to the gates of the SCRs they conduct current to connect the power to the selected tap. When gate current is removed, the SCRs will continue to conduct until the Anode current drops below the latching current setpoint. When a system is loaded this is normally when the line current crosses through zero. The problem is that the control systems are not always sophisticated enough to make sure the SCRs are turned off before the next tap's SCRs are gated on. If two sets of SCRs are on at the same time, the two adjacent taps act like the low voltage winding of a step down transformer and a large circulation current flow through the SCRs causing damage. To prevent this, many systems put in a time delay between removing gate current from one set of SCRs and applying gate current to another set of SCRs. This will cause a short power interruption to the load, a sensitive electronic system can be negatively affected by these interruptions.

Ten Percent Regulator

The transformer we are using in this system will not need to handle the full power, for the purpose of this discussion we will assume our system will be rated to regulate an input “window” of +/- 10% of the nominal line voltage. The line is processed by an “AC Inverter” (which may be patentable in itself), that produces a variable AC voltage from full line voltage, linearly controlled through zero to full voltage 180 degrees phase inverter which is applied to the primary of a 10 to 1 step down transformer with isolated windings. The secondary is connected in series between the line and the load in the hot side of a single phase connection (three phase systems will use 3 single phase systems as described here). When the voltage on the primary is 100% in-phase the 10% voltage on the secondary will add to the line voltage so the load voltage is 110% of line. When the voltage on the primary is 0% then the load voltage will be equal to the line. And when the voltage on the primary is 100% phase inverted the 10% on the secondary will subtract from the line voltage so the load will have 90% of line voltage applied.

This approach will use significantly smaller transformers which will decrease the product's size, weight and cost. Instead of 6 or more AC switches rated for full load, we will use 4 switches rated at 1/10th rated load which will probably also decrease the cost of the unit. One of the important advantages is the linear regulation which is technically superior and could allow us (along with the smaller size and weight) to actually charge more with a lower production cost. My prior experience as an Engineering Manager in a company involved in this market leads me to believe that this is such a fundamental improvement in the state-of-the-art in low-cost voltage regulation products that this product could have a large impact in that market.

Bit-Weighted Regulator

This uses a simpler switching approach than the Ten Percent Regulator, it uses transformers with a center tapped primary and a relay that selects between buck and boost polarities. Then another transformer at 1/2 the secondary voltage can be added in series to increase the resolution and more can be added for more resolution, each one at 1/2 the prior one. Then they can be gang-switched to select the regulation ratio. For example, for a 20% (+/-10%) window regulator with a tap resolution of 2.5% would need 10 taps and 10 solid-state AC switches. The Bit-Weighted Regulator would need 4 transformers, a 8%, 4%, 2% and 1%. Each transformer would only handle the percentage of rated load indicated by it's regulation percentage (ex. 8% transformer would by 8% the volume of a transformer rated for full load). The Bit-Weighted Regulator example would have an input window of 30% (+/-15%) and a resolution of 1%. The total cost and weight of our system would be much lower for a large system and if you wanted to increase the resolution of the Tap Changer Regulator to 1.25% instead of 2.5% with the same input voltage window you would have to double the number of taps. With the Ten Percent Regulator you would just have to add a transformer 1/2 the volume of the smallest transformer and a low-current handling relay. This system could be easily field upgraded to higher resolution regulation which can't be done with the present technology without increasing the base price.