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Pentadyne Voltage Support Solution™ Theory of Operation Pentadyne VSS Rev 08/23/07 + DC – Theory of Operation 1 / 21 Table of Contents 1. SYSTEM OVERVIEW .................................................................................................................................. 4 1.1. GENERAL SYSTEM DESCRIPTION .............................................................................................................. 4 1.2. POWER SYSTEM ........................................................................................................................................ 5 1.3. PERFORMANCE.......................................................................................................................................... 6 1.4. APPLICATION FLEXIBILITY ....................................................................................................................... 7 1.4.1. Ride-through protection .................................................................................................................. 7 1.4.2. Ride-through to generator............................................................................................................... 7 1.4.3. Battery life extension/energy storage redundancy .......................................................................... 8 2. DETAILED SYSTEM DESCRIPTION........................................................................................................ 8 2.1. USER INTERFACE....................................................................................................................................... 8 2.1.1. Control Panel .................................................................................................................................. 8 2.1.2. Data Collection Module (DCM)...................................................................................................... 8 2.1.3. Versatile Interface Board (VIB) ...................................................................................................... 8 2.2. UPS INTERCONNECTION KIT..................................................................................................................... 9 2.3. MAGNETIC LEVITATION MODULE (MLM)................................................................................................ 9 2.4. POWER CONVERSION MODULE (PCM) ................................................................................................... 10 2.4.1. Power Conversion Module Controller (PCMC)............................................................................ 10 2.4.2. IGBT Power Conversion ............................................................................................................... 10 2.5. FLYWHEEL MODULE ............................................................................................................................... 11 2.5.1. Rotor/Flywheel (Rotating Group) ................................................................................................. 12 2.5.2. Motor-Generator ........................................................................................................................... 12 2.5.3. Vacuum System.............................................................................................................................. 13 2.5.4. Flywheel Sensors........................................................................................................................... 13 2.5.5. Active Magnetic Levitation Hardware .......................................................................................... 14 2.5.6. System Safety ................................................................................................................................. 14 2.6. CABINET ................................................................................................................................................. 15 2.7. VENTILATION AND COOLING .................................................................................................................. 15 3. SYSTEM CONFIGURATION .................................................................................................................... 16 3.1. MODES OF OPERATION ........................................................................................................................... 16 3.1.1. OFF Mode ..................................................................................................................................... 18 3.1.2. STARTUP Mode ............................................................................................................................ 18 3.1.3. CHARGE Mode ............................................................................................................................. 18 3.1.4. READY Mode ................................................................................................................................ 18 3.1.5. DISCHARGE Mode....................................................................................................................... 19 3.1.6. SHUTDOWN Mode ....................................................................................................................... 19 3.1.7. COAST Mode................................................................................................................................. 19 3.1.8. FAULT Mode................................................................................................................................. 19 3.2. USER-CONFIGURABLE SYSTEM PARAMETERS ......................................................................................... 20 3.2.1. Charge Voltage (Vcharge) ............................................................................................................ 20 3.2.2. Regulation Voltage (Vreg)............................................................................................................. 20 3.2.3. Regulation Voltage Droop During Discharge (Vreg Delta).......................................................... 20 3.2.4. Maximum Charge Current (Max Charge Current) ....................................................................... 20 3.2.5. Charge Conductance (Charge Amps/Volts) .................................................................................. 20 4. MAINTENANCE & RELIABILITY .......................................................................................................... 21 Pentadyne VSS Rev 08/23/07 + DC – Theory of Operation 2 / 21 Table of Figures FIGURE 1 - VSS+DC CABINET LAYOUT ........................................................................................................................ 4 FIGURE 2 - SCHEMATIC OF THE ELECTRICAL SYSTEM ................................................................................................. 5 FIGURE 3 - PERFORMANCE CHART ............................................................................................................................. 6 FIGURE 4 - MULTI-UNIT INSTALLATION – RIDE THROUGH PROTECTION ..................................................................... 7 FIGURE 5 - MULTI-UNIT INSTALLATION WITH GENERATOR FOR CONTINUOUS PROTECTION ........................................ 7 FIGURE 6 - MULTI-UNIT INSTALLATION WITH BATTERIES IN PARALLEL...................................................................... 8 FIGURE 7 - SCHEMATIC OF THE LEVITATION SYSTEM. .............................................................................................. 10 FIGURE 8 - FLYWHEEL MODULE ............................................................................................................................... 11 FIGURE 9 - ROTATING GROUP .................................................................................................................................. 12 FIGURE 10 - CROSS-SECTION OF THE SYNCHRONOUS RELUCTANCE MOTOR ROTOR .................................................. 12 FIGURE 11 - VACUUM SYSTEM OPERATION............................................................................................................... 13 FIGURE 12 - SCHEMATIC FOR THE SPEED AND TEMPERATURE SENSORS .................................................................... 14 FIGURE 13 - CUTAWAY FLYWHEEL MODULE ........................................................................................................... 15 FIGURE 14 - TYPICAL MODES OF OPERATION ........................................................................................................... 17 Pentadyne VSS Rev 08/23/07 + DC – Theory of Operation 3 / 21 1. System Overview 1.1. General System Description The Pentadyne Voltage Support Solution™ is a flywheel-based energy storage system. It operates as a mechanical battery that stores energy in the form of a rotating mass. This energy is immediately converted to useful power when needed. The VSS+DC is configured as a two-terminal DC system and is used as a functional replacement for a bank of chemical batteries used with Uninterruptible Power Supply Systems (UPSs). In addition, the VSS+DC can work in parallel with a bank of chemical batteries for increased DC bus reliability and redundancy. As with a chemical battery bank, it receives recharge and float power from the two-terminal DC bus and returns power to the same DC bus whenever the voltage droops below a programmable threshold level. Multiple VSS+DC units can be put in parallel for higher power output, longer ride-through duration and/or redundancy. The VSS+DC can be used in many DC applications to provide power quality or energy recycling. The VSS+DC is designed not to require major service for 20 years in a UPS application. Figure 1 - VSS+DC cabinet layout Pentadyne VSS Rev 08/23/07 + DC – Theory of Operation 4 / 21 1.2. Power System The electrical system of the VSS+DC is illustrated in Figure 2, the schematic shows the Magnetic Levitation Module (2.3). The pre-charge resistor and contactor which limit the inrush current into the DC bus capacitors. The six-pulse IGBT power converter (2.4.2) is controlled by the Power Conversion Module Controller (2.4.1) which also monitors and controls the operation of the entire system. These components are housed within the Power Conversion Module (2.4). The Flywheel Module (2.5) is shown as a cross section illustrating the rotating group and the synchronous reluctance motor-generator. Figure 2 - Schematic of the electrical system Pentadyne VSS Rev 08/23/07 + DC – Theory of Operation 5 / 21 1.3. Performance The maximum output power of the VSS+DC is dependant upon the duration required. This is illustrated in Figure 3 below. Increased power, duration and/or redundancy can be achieved by adding units in parallel. Figure 3 - Performance Chart *kWb = Refers to Kilowatts on the DC bus of the UPS system. Pentadyne VSS Rev 08/23/07 + DC – Theory of Operation 6 / 21 1.4. Application Flexibility 1.4.1. Brief ride-through protection Figure 4 illustrates three or more units connected to a UPS to provide ride-through protection. This system architecture is most often used for glitch protection in industrial process plants. Figure 4 - Multi-unit installation – Short-term ride-through protection 1.4.2. Ride-through to generator Figure 5 illustrates the system architecture if continuous power protection is required in the event of an extended power outage. Figure 5 - Multi-unit installation with generator for continuous protection Pentadyne VSS Rev 08/23/07 + DC – Theory of Operation 7 / 21 1.4.3. Battery life extension/energy storage redundancy Figure 6 illustrates an installation with VSS+DC units and batteries connected in parallel. Connecting the system in this way extends the life of the batteries because the VSS+DC units support all glitches and all backup genset ridethrough events, isolating the batteries from use. Figure 6 - Multi-unit installation with batteries in parallel. 2. Detailed System Description 2.1. User interface 2.1.1. Control Panel The VSS+DC uses an LCD control panel as the primary means for an operator to interface with the system. Operating parameter values are displayed and updated in real time, as are alarm states, system notices and event logging. User configurable system parameters are adjusted via the control panel. Information is located using the menu-based structure. Several layers of security access are included. 2.1.2. Data Collection Module (DCM) An optional software and hardware package that reads data from the VSS+DC. The data is stored and then can be transmitted through an RS-232 port, over a LAN (Local Area Network) or over the Internet, enabling PC-based diagnostic reporting capability onsite or remote. 2.1.3. Versatile Interface Board (VIB) An optional software and hardware package is available that allows for remote monitoring and control; via isolated auxiliary dry contacts: • • • • • Pentadyne VSS Rev 08/23/07 + OFF Mode STARTUP Mode CHARGE Mode State of Charge (SOC) ≥ 0% State of Charge (SOC) ≥ 12.5% DC – Theory of Operation 8 / 21 • • • • • • • • • • • • State of Charge (SOC) ≥ 25% State of Charge (SOC) ≥ 37.5% State of Charge (SOC) ≥ 50% State of Charge (SOC) ≥ 62.5% State of Charge (SOC) ≥ 75% State of Charge (SOC) ≥ 87.5% State of Charge (SOC) ≥ 100% DISCHARGE Mode SHUTDOWN Mode WARNING Mode FAULT mode Motor Hot Standby Control commands: • Startup • Shutdown • Clear Fault 2.2. UPS Interconnection Kit The UPS Interconnection Kit (IKit) is a module that simplifies interconnection with a UPS system. There are several versions of the IKit available that have been developed through VSS+DC integration testing with several types of UPS systems. The VSS+DC (standard configuration) is delivered with an IKit consisting of a fused power terminal block for connection of the positive and negative terminals of the UPS DC bus or of an external disconnect switch. 2.3. Magnetic Levitation Module (MLM) The magnetic levitation module provides control of the active magnetic levitation hardware. The VSS+DC has a unique, patented active magnetic levitation system that fully levitates the flywheel-rotating group, allowing the flywheel to rotate without any physical contact. This has a number of advantages over mechanical bearing systems: A. Reduced drag: Mechanical bearings induce drag proportional to the square of the speed. The levitation system developed by Pentadyne uses the same power regardless of speed, one of the primary reasons that Pentadyne flywheels use only one-tenth of the standby energy of other commercial flywheel products, saving the end-user thousands of dollars in annual utility charges for each unit deployed. B. Maintenance-free reliability: The levitation system ensures there is no contact between the rotating parts and the housing and therefore there are no components to wear out. This ensures the unit will operate maintenance free for the life of the system. Other flywheel systems require bearing replacement every 2-3 years that incur 4-8 hours of downtime and costs thousands of dollars. The levitation system works by measuring the displacement using a capacitive sensor. If the distance needs to be adjusted, current to the electromagnet is altered to change the displacement, each axis is measured and controlled separately with its own capacitive sensor, electromagnet and feedback loop, which is controlled by the MLM. This is accomplished using analog control, which is extremely fast-acting and reliable. There are 5 different circuits working independently: Radial: Upper X, Y; Lower X, Y and Axial: Z. The upper radial Y-axis operation is shown in Figure 7. The principle of operation is the same in each case. Pentadyne VSS Rev 08/23/07 + DC – Theory of Operation 9 / 21 Figure 7 - Schematic of the levitation system. 2.4. Power Conversion Module (PCM) The PCM is a bi-directional system capable of sourcing or sinking power to and from the stator. It converts variable frequency, variable voltage from the stator and delivers a constant voltage DC output. Conversely, it converts DC power from the UPS system DC bus to variable frequency, variable voltage output to the stator as directed by the PCMC to increase the speed of the synchronous reluctance motor-generator. 2.4.1. Power Conversion Module Controller (PCMC) The power conversion module controller is located within the power conversion module. The PCMC uses microprocessor-controlled logic to control the six pulse IGBT solid state switches and monitor the active magnetic levitation system. These operations are firmware controlled eliminating the need for manual adjustments. The logic includes self-test and diagnostic circuitry to identify any faults. Diagnostics are performed via the system’s control panel or via a PC through the RS232 communication port. 2.4.2. IGBT Power Conversion The PCMC provides overall control of the VSS+DC as well as specific control of the synchronous reluctance motor-generator via the IGBT solid-state switches within the PCM. When delivering DC power, the output of the synchronous reluctance generator is rectified to DC by passing the high frequency AC current through a solid-state power conversion device. The DC output voltage of the VSS+DC has less than 2% RMS ripple. Pentadyne VSS Rev 08/23/07 + DC – Theory of Operation 10 / 21 The voltage and frequency are adjusted using pulse width modulation. The IGBT switches operate at a frequency of 18 kHz to produce the smooth sinusoidal current waveform to and from the motor-generator. This is smoothed out further using an inductive and capacitive filter. 2.5. Flywheel Module The Flywheel Module houses several major components: The Rotating Group (high-speed carbon composite flywheel, high-speed shaft and rotor of the Motor-Generator) The Motor-Generator (synchronous reluctance technology) The Molecular Vacuum Pump Flywheel Sensors Active Magnetic Levitation Hardware Safety System Figure 8 - Flywheel module Pentadyne VSS Rev 08/23/07 + DC – Theory of Operation 11 / 21 2.5.1. Rotor/Flywheel (Rotating Group) The flywheel cylinder, made of carbon/glass composite, is mounted on a metal shaft with integral motor-rotor to form the rotating group. The rotating group is magnetically levitated and centered so that it does not touch any other part while in normal operation. Figure 9 - Rotating group 2.5.2. Motor-Generator The rotor is positioned within the stator to provide the motor-generator function of the VSS+DC. The stator is liquid cooled after significant discharge and operates within a housing in which air has been evacuated. Together the stator and rotor operate as a synchronous reluctance motor-generator, producing enough power for the system to supply its own internal demand and to supply to the output DC bus up to rated power. The illustration in Figure 10 shows the four poles of the synchronous reluctance rotor. Figure 10 - Cross-section of the synchronous reluctance motor rotor Pentadyne VSS Rev 08/23/07 + DC – Theory of Operation 12 / 21 2.5.3. Vacuum System During manufacture, the vacuum chambers are baked and evacuated to remove water vapor. The vacuum system is then permanently sealed. The VSS+DC does not require any mechanical vacuum pump, common to other commercial flywheels. The vacuum system relies on absorbers to maintain a rough vacuum within the upper chamber. A zero-maintenance patented molecular vacuum sleeve acts with the flywheel shaft to maintain a high-vacuum in the lower chamber of much less than 100 microTorr (10-7 atmosphere). The absorber material only needs to be recharged or changed once every 20 years. Figure 11 - Vacuum system operation 2.5.4. Flywheel Sensors 2.5.4.1. Speed The speed detection system uses an infrared emitter and a sensor to detect shaft rotation. A hole drilled through the shaft allows light to pass and is detected on the opposite side by an infrared detector. This signal is used to detect rotor angle and speed. The pulsed signal passes into the 6711 DSP to be converted into a speed signal. This is then passed to the 2812 DSP. The 2812 checks for over-speed and shuts down the power electronics if this occurs. If either of the processors lock-up, the rotor will slow down to ensure an over-speed cannot occur. 2.5.4.2. Temperature The stator and rotor temperature detectors are thermocouples. The stator sensor is a type J thermocouple potted into the stator windings. The rotor sensor is a non-contact type sensor that detects rotor surface temperature and gives an output in a type J thermocouple format. Pentadyne VSS Rev 08/23/07 + DC – Theory of Operation 13 / 21 Figure 12 - Schematic for the speed and temperature sensors 2.5.5. Active Magnetic Levitation Hardware The electromagnets and capacitive displacement sensors that provide the active magnetic levitation are located within the flywheel module. A full description of their operation is provided in section (2.3). 2.5.6. System Safety Every composite flywheel is inspected, spin balanced and over-speed tested in accordance with NEMA guidelines. A patented dual-wall containment ensures that in the unlikely event a flywheel were to separate during operation, the 2-inch thick steel inner housing would retain the rotating group. In repeated forced destructive tests, the carbon fiber of the flywheel cylinder expands and transfers torque to the inner housing. The inner housing is then allowed to rotate inside the outer housing. The cooling fluid in the outer housing, which surrounds the inner housing, acts as a dynamic brake. The stored energy is released in a controlled manner as the flywheel / inner housing comes to a rest. The outer housing holds the entire safety system and acts as a reservoir for the cooling fluid The VSS+DC has been throroughly tested under the following fault conditions with no adverse safety effects: y Motor-generator AC short circuit y DC short circuit y PCM failure y MLC failure y Rotating group failure Pentadyne VSS Rev 08/23/07 + DC – Theory of Operation 14 / 21 Outer Housing Rotating Group Inner Housing Coolant Figure 13 – Cutaway of flywheel module 2.6. Cabinet The VSS+DC is housed in a compact free-standing cabinet with a NEMA 1 construction rating or IEC equivalent. No space is required between the back or sides of the cabinet and any walls. A front clearance of 36” is required per the National Electrical Code. The VSS+DC accommodates top (standard) and side entry cables. The VSS+DC can be rolled into place and is small enough to fit through standard door openings. 2.7. Ventilation and Cooling The VSS+DC stator and power electronics are liquid cooled with a liquid-to-air radiator that operates following a significant discharge and resultant heating of the motor-generator. The radiator within the VSS+DC package is designed for natural and forced air-cooling. Air inlets are in the bottom front of the VSS+DC enclosure, exhaust exits the top of the unit. Air filters are available as an option for dusty environments. A minimum 12” clearance overhead is required for exhaust airflow. The VSS+DC was designed with reliability in mind, the radiator is positioned to take advantage of natural cooling and forced-air and forced-coolant circulation occurs only when there is an elevated temperature. The coolant circulating pump is a highly reliable magnetically coupled centrifugal pump powered by a brushless DC motor. This pump operates only when there is an elevated temperature within the stator or the PCM. The pump is maintenance-free for the life of the flywheel system due to the infrequent operation of this high-reliability component. Pentadyne VSS Rev 08/23/07 + DC – Theory of Operation 15 / 21 3. System Configuration 3.1. Modes of Operation The VSS+DC consists of a variety of operational modes. Each Mode is based on a set of programmed conditions. The Control Panel indicates the current Mode and the Status of that Mode. Function keys are enabled or disabled depending on the Mode and Status. The VSS+DC modes are: OFF (3.1.1) STARTUP (4.1.2) CHARGE (3.1.3) READY (3.1.4) DISCHARGE (3.1.5) SHUTDOWN (3.1.6) COAST (3.1.7) FAULT (3.1.8) The VSS+DC is programmed to operate in a variety of conditional modes. The modes and the status for each sode are indicated on the control panel. The VSS+DC is set up to transition through the various modes with no or minimal user intervention. Pentadyne VSS Rev 08/23/07 + DC – Theory of Operation 16 / 21 Figure 14 - Typical Modes of Operation Pentadyne VSS Rev 08/23/07 + DC – Theory of Operation 17 / 21 3.1.1. OFF Mode When the VSS+DC is initially powered on, it enters the OFF mode and magnetically levitates its rotating group. A manual user command will make the system transition from OFF mode to STARTUP mode if all start-up conditions are met. NOTE Start-up conditions are: 1. UPS DC bus voltage ≥ Vcharge; and 2. VSS+ status is “OK”. The VSS+DC will also enter OFF mode at the end of a shutdown and will transition automatically from SHUTDOWN mode to OFF mode. 3.1.2. STARTUP Mode In STARTUP mode, the VSS+DC will charge (increase flywheel rotation speed) up to the minimum operating speed. At this minimum speed the “State of Charge” = 0%. At that point the VSS+DC will automatically transition into CHARGE mode. The VSS+DC will be in STARTUP mode as long as: 1. VSS+DC SOC is less than 0%; and 2. UPS DC bus voltage ≥ Vcharge NOTE In STARTUP mode, the VSS+DC cannot support the UPS DC bus. In case the UPS DC bus voltage drops below Vcharge while in STARTUP mode, the VSS+DC will transition automatically into COAST mode. As soon as the UPS DC bus voltage rises above Vcharge, the VSS+DC automatically exits COAST mode and resumes STARTUP mode. 3.1.3. CHARGE Mode To charge itself, the VSS+DC will draw power from the UPS DC bus to accelerate the flywheel (as long as the UPS DC bus voltage is over Vcharge). In this mode, the VSS+DC SOC will progressively increase from 0% to 100%. The VSS+DC will be in CHARGE mode as long as: 1. VSS+DC SOC is between 0% and 100%; and 2. UPS DC bus voltage ≥ Vcharge. NOTE While in CHARGE mode, the VSS+DC can still support the UPS DC bus. 3.1.4. READY Mode When the SOC reaches 100%, the unit will automatically transition into READY mode. This is the mode in which the VSS+DC will spend most of its operating time. In this mode, the VSS+DC maintains its State Of Charge above 99.5%. The VSS+DC SOC will be allowed to drift down to SOC = 99.5%, at which point it will temporarily transition back into CHARGE mode and charge back up to READY mode and a SOC = 100%. During normal operation, the VSS+DC will continue to automatically transition between the READY and CHARGE modes to maintain a SOC between 99.5 and 100% until either a DISCHARGE or SHUTDOWN is initiated. The VSS+DC will be in READY Mode as long as: 1. VSS+DC SOC is between 99.5% and 100%; and 2. UPS DC bus voltage > Vcharge. Pentadyne VSS Rev 08/23/07 + DC – Theory of Operation 18 / 21 3.1.5. DISCHARGE Mode Starting from either CHARGE or READY mode, the VSS+DC will enter the DISCHARGE mode if the UPS DC bus voltage goes below Vcharge. In DISCHARGE mode, the VSS+ will regulate the DC bus at Vreg. The VSS+DC will be in DISCHARGE mode as long as: 1. UPS DC bus voltage < Vcharge; and 2. VSS+DC SOC is more than 0%. NOTE The VSS+DC will transition from DISCHARGE mode to CHARGE mode if the UPS DC nus recovers (UPS DC Bus Voltage ≥ Vcharge) before the VSS+DC SOC reaches 0%. In case the UPS DC bus doesn’t recover before the VSS+DC SOC reaches 0%, the VSS+DC will transition into SHUTDOWN mode. 3.1.6. SHUTDOWN Mode In SHUTDOWN mode, the flywheel will actively spin down. There are two ways the VSS+ can transition into SHUTDOWN mode: 1. Following a VSS+DC discharge down to SOC = 0% This is the most common SHUTDOWN process. This occurs when the VSS+DC SOC drops below 0% and the UPS system DC bus voltage is less than Vcharge. If the VSS+DC entered the SHUTDOWN mode after DISCHARGE mode, the VSS+DC will automatically transition into STARTUP mode when the UPS system DC bus voltage returns to a value greater than Vcharge (i.e. when utility input returns or the backup generator supplies power to the UPS). 2. User initiated SHUTDOWN In any mode except OFF, the user may command the VSS+DC to transition to SHUTDOWN. While in SHUTDOWN mode, the user will still be able to command the VSS+DC to transition into CHARGE mode (if SOC > 0%) or STARTUP mode (if SOC<0%), provided that the UPS system DC bus voltage is greater than Vcharge. 3.1.7. COAST Mode A transition into COAST mode can only occur when the UPS system DC bus voltage droops below Vcharge (and above 350 Vdc) while the VSS+DC is in STARTUP mode. While in COAST mode the VSS+DC is in an idling condition. As soon as the UPS DC bus voltage rises above Vcharge, the VSS+DC will automatically exit COAST mode and resume STARTUP mode. If the voltage droops below 350 Vdc, the VSS+DC will enter SHUTDOWN mode. 3.1.8. FAULT Mode The VSS+DC includes self-test and diagnostic circuitry such that most system malfunctions can be identified. In case of a system malfunction, the VSS+ will transition into the FAULT mode. While in FAULT mode, the VSS+DC is disabled – i.e. all power electronics are turned off. Most faults are cleared automatically by the system without a need for user intervention. Some faults do require user action to clear the fault or to notify your Pentadyne-Certified Service Provider (Please refer to the Section 6 Troubleshooting for more information). NOTE Depending on the nature of the fault, the VSS+DC may still be capable of supporting the UPS DC bus. Please refer to the Section 6 Troubleshooting for more information. Pentadyne VSS Rev 08/23/07 + DC – Theory of Operation 19 / 21 3.2. User-configurable System Parameters In order to support a wide array of UPS integrations, the VSS+DC can be configured using the following parameters: 3.2.1. Charge Voltage (Vcharge) Vcharge is the voltage threshold above which the VSS+DC begins to charge/recharge. Vcharge must be set at least 10 Vdc greater than Vreg. Range: 350-600 Vdc Default setting: 520 Vdc 3.2.2. Regulation Voltage (Vreg) Vreg is the voltage set-point at which the VSS+DC will regulate the DC bus voltage in discharge mode. Vreg must be set at least 10 Vdc less than Vcharge. Range: 340-590 Vdc Default setting: 500 Vdc 3.2.3. Regulation Voltage Droop During Discharge (Vreg Delta) Vreg Delta is the programmed amount of voltage drop from the beginning of discharge (Vreg) to the end of discharge (SOC = 0%) Range: From 0 to [Vreg - 250] Vdc (Ex: if Vreg = 500, then the Vreg Delta can be set between 0 and 250 Vdc) Default setting: 0 Vdc 3.2.4. Maximum Charge Current (Max Charge Current) Max charge current is the maximum current the VSS+DC is allowed to draw from the UPS DC bus. Range: 1-50 A Default setting: 20 A 3.2.5. Charge Conductance (Charge Amps/Volts) Charge amps/volts is used to set the VSS+DC charging current drawn from the UPS DC bus based upon how much the UPS DC bus voltage is above Vcharge and so without exceeding the max charge current. Range: 0.1-10 A/V Default setting: 2 A/V Pentadyne VSS Rev 08/23/07 + DC – Theory of Operation 20 / 21 4. Maintenance & Reliability The VSS+DC is designed for maximum uptime availability and minimal preventive servicing while online. There are no user serviceable parts in the VSS+DC other than the optional air filter. Please contact a Pentadyne-Certified Technician before attempting to remove or service any components of the system. No bearing maintenance or replacement is required over the life of the VSS+DC. No vacuum pump maintenance or replacement is required over the life of the VSS+DC. The optional inlet air filter in the cabinet will need to be replaced when dirty enough to reduce air flow into the cabinet. Ambient conditions at the installation site will determine the frequency of replacement. The VSS+DC flywheel module is designed for a 20-year service life before any recommended maintenance interval. At that interval, the vacuum absorbers should be replaced or regenerated. Replacement of the capacitor pack is recommended at 6-year intervals and is the only downtime maintenance (one hour). The reliability of the VSS+DC power electronics is consistent with UPS power electronics of comparable energy levels. The mechanical assemblies are of higher life and reliability than other commercially available flywheel systems due to the elimination of rolling element bearings and external vacuumpumping devices. Pentadyne VSS Rev 08/23/07 + DC – Theory of Operation 21 / 21