Patent Publication Number: US-2016233683-A1

Title: System and apparatus providing power generation and demand management using a thermal hydraulic dc generator

Description:
FIELD OF THE INVENTION 
     The invention relates to the field of power generation and, more particularly but not exclusively, power generation systems using a Thermal Hydraulic DC Generator. 
     BACKGROUND 
     Thermal Hydraulic DC Generators capture energy from Turbine Generators, Combustion Engines, Geothermal Sources, Facility Systems, or Solar Collectors. These sources can be used to produce 180-degree Fahrenheit hot water in order to drive Thermal Hydraulic DC Generators. These Generators create a very efficient means of generating electric power. 
     SUMMARY 
     Various deficiencies in the prior art are addressed by systems and apparatus providing power generation and demand management using a thermal hydraulic DC generator. Various embodiments comprise a thermal hydraulic DC generator, for generating DC output power in response to a control signal; a grid tie inverter, for converting the DC output power into AC power for use by an electrical load; and a controller, for adapting said control signal in response to an electrical system load demand associated with said electrical load, said control signal being adapted to cause said thermal hydraulic DC generator to adapt said DC output power such that said grid tie inverter satisfies said electrical system load demand. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The teachings of the present invention can be readily understood by considering the following detailed description in conjunction with the accompanying drawings, in which: 
         FIG. 1  depicts a high level block diagram of a system according to an embodiment; 
         FIG. 2  graphically depicts physical dimensions of an exemplary Programmable Logic Controller (PLC) suitable for use as a controller within the system of  FIG. 1 ; 
         FIG. 3  graphically depicts exemplary power and signal input terminals associated with the PLC of  FIG. 2 ; 
         FIGS. 4A-4B  graphically depict exemplary wiring configurations for signal output terminals associated with the PLC of  FIG. 2 ; 
         FIGS. 5A-5B  graphically depict exemplary wiring configurations for connecting sensors/transmitters to signal input terminals associated with the PLC of  FIG. 2 . 
         FIG. 6  graphically depicts an exemplary wiring configuration for connecting an output device to signal output terminals associated with the PLC of  FIG. 2 ; 
         FIGS. 7A-7B  graphically depict exemplary wiring configurations for connecting a Resistance Temperature Detector (RTD) to excitation and sense input terminals of the PLC of  FIG. 2 ; 
         FIGS. 8A-8B  graphically depict physical dimensions of an exemplary user interface device associated with the PLC of  FIG. 2 ; 
         FIGS. 9A-9D  graphically depict physical dimensions for various VFDs suitable for providing circulation pump control functionality in the system of  FIG. 1  in cooperation with the PLC of  FIG. 2 ; 
         FIG. 10  depicts a schematic diagram of an exemplary inverter suitable for use as a grid tie inverter within the system of  FIG. 1 ; 
         FIG. 11  graphically depicts a generator suitable for use within the system of  FIG. 1 ; and 
         FIG. 12  graphically depicts PWM synthesis of a sinusoidal waveform. 
     
    
    
     To facilitate understanding, identical reference numerals have been used, where possible, to designate identical elements that are common to the figures. 
     DETAILED DESCRIPTION 
     Thermal Hydraulic DC Generators capture energy from Turbine Generators, Combustion Engines, Geothermal Sources, Facility Systems, or Solar Collectors. These sources can be used to produce 180-degree Fahrenheit hot water in order to drive Thermal Hydraulic DC Generators. These Generators create a very efficient means of generating electric power. 
     Other co-generation systems require the use of steam to drive Steam Turbines. The use of steam as opposed to hot water requires more expensive equipment and more maintenance to operate than a 180 Degree F. hot water system. These 180 Degree F hot water systems incorporating the Thermal Hydraulic DC Generators are more efficient than the Rankine Cycle or the Carnot Cycle. 
     Thermal Hydraulic DC Generator Engines incorporate a PLC based control system that eliminates the need for governors and voltage regulators. They incorporate inverter systems to create “clean” power at unity power factor. This is a new system that has never been accomplished before. 
     The technological innovation regarding the Thermal Hydraulic DC Generator revolves around regulating the flow of the hydraulic fluid to the hydraulic pump and creating the correct RPM for the DC Generator. The load demands of the building electrical system are matched through the PLC based control system and instrumentation. The generator governor and regulator have been replaced by the PLC based control system. The correct flow of hydraulic fluid is supplied to the hydraulic pump. The DC output from the generator is connected to an inverter that corrects the AC output to a unity power factor. This is a new system that has never been accomplished before. 
     Various embodiments are described within the context of the figures.  FIG. 1  represents a flow diagram for a Thermal Hydraulic DC Generator connected to a microturbine system to capture waste heat from the exhaust and increase the efficiency of the overall system.  FIG. 2  represents a 32 bit microprocessor with Ethernet communications for the PLC based control system.  FIG. 3  represents a discreet input module used for the PLC based control system.  FIGS. 4A-4B  represent a discreet output module for the PLC based control system.  FIGS. 5A-5B  represents an analog input module for the PLC based control system.  FIG. 6  represents an analog output module for the PLC based control system.  FIGS. 7A-7B  represent an RTD input module for the PLC based control system.  FIGS. 8A-8B  represent an operator interface terminal used for the PLC based control system.  FIGS. 9A-9D  represent a VFD used for circulation pump control with the PLC based control system.  FIG. 10  represents a grid tie inverter that will be used to convert DC power to AC Power and synchronize with the utility power grid at unity power factor. A Process description is also included.  FIG. 11  represents a DC generator used to generate DC power. 
       FIG. 1  depicts a high level block diagram of a system according to an embodiment. Generally speaking,  FIG. 1  depicts a flow diagram for a Thermal Hydraulic DC Generator connected to a microturbine system to capture waste heat from the exhaust and increase the efficiency of the overall system. 
     Referring to  FIG. 1 , a system  100  includes a fuel source  105  (e.g., natural gas, #2 fuel, diesel, gasoline, coal or other fuel source), a power generation system  110  (illustratively a turbine, micro-turbine, internal combustion engine or other power generation system), an engine heating cycle water heat exchanger  120 , optional heat sources  125  (illustratively waste heat from facility systems, heat from geothermal sources, heat from solar thermal sources etc.), a thermal hydraulic DC generator  130  (illustratively a 250 kW generator, or other generator ranging from 4 kW to 1 MW), an engine cooling cycle water heat exchanger  140 , cooling sources  145  (illustratively a domestic water system, a cooling tower system etc.), a grid tie inverter  150 , facility electrical system switchgear  160 , facility connected electrical loads  165 , optional additional green energy systems  170  (illustratively solar photovoltaic systems, wind turbine systems etc.) and an electrical utility power source  180 . 
     The power generation system  110  receives fuel from the fuel source  105  via path F 1 , and generates AC power which is coupled to facility electrical system switchgear  160  via path P 1 . 
     The engine heating cycle water heat exchanger  120  receives 180° F. water from the power generation system  110  via path W 1 H (illustratively at 3.7 million BTUs per hour), and returns cooler water to the power generation system  110  via path W 1 C. 
     The engine heating cycle water heat exchanger  120  may receive hot water from optional heat sources  125  via path W 5 H, and return cooler water to the optional heat sources  125  via path W 5 C. 
     The engine heating cycle water heat exchanger  120  provides hot water to the thermal hydraulic DC generator  130  via path W 2 H, and receives cooler water from the thermal hydraulic DC generator  130  via path W 2 C. In the illustrated embodiment, path W 2 H supplies 180° F. water at a rate of 135 gallons per minute to a 250 kW thermal hydraulic DC generator  130 . 
     The thermal hydraulic DC generator  130  provides hot water to the engine cooling cycle water heat exchanger  140  via path W 3 H, and receives cooler water from the engine cooling cycle water heat exchanger  140  via path W 3 C. In the illustrated embodiment, path W 3 C supplies 80° F. water at a rate of 280 gallons per minute to a 250 kW thermal hydraulic DC generator  130 . 
     The engine cooling cycle water heat exchanger  140  provides hot water to cooling sources  145  via path W 4 H, and receives cooler water from the cooling sources  145  via path W 4 C. 
     The thermal hydraulic DC generator  130  generates DC power in response to the temperature differential between the 180° F. water provided via the W 2 H/W 2 C fluid loop and the 80° F. water provided via the W 3 H/W 3 C fluid loop. The DC power, illustratively 250 kW AC power, is provided to grid tie inverter  150  via path P 2 . 
     Grid tie inverter  150  may also receive additional DC power via path P 5  from optional additional green energy systems  170 . 
     Grid tie inverter  150  operates to invert received DC power to thereby generate AC power which is coupled to facility electrical system switchgear  160 . Grid tie inverter  150  “ties” DC power to the electrical grid by inverting the DC power such that the resulting generated AC power conforms to power grid specifications. 
     Facility electrical system switchgear  160  receives AC power from electrical utility power source  180  via path P 4 , and provides revenue metering system information to electrical utility power source  180  via M 1 . 
     Facility electrical system switchgear  160  operates to supply AC power to facility connected electrical loads  165 , the supplied AC power comprising power from one or more of power generation system  110 , grid tie inverter  150  and electrical utility power source  180 . 
     An operating methodology associated with the system  100  of  FIG. 1  will now be described with respect to the below steps, each of which is indicated in  FIG. 1  by a corresponding circled number. 
     Step 1. Natural Gas, Methane, #2 Fuel Oil, or Diesel Fuel can be used to power Turbine Generators or Combustion Engine Generators that produce electricity and synchronize with the utility electrical system by the use of an inverter at unity power factor. 
     Step 2. The exhaust from the Turbine Generators or Combustion Engine Generators Heat circulated water through manifolds or engine water jackets. 
     Step 3. Additional energy is recovered from the Turbine Generators or Combustion Engine Generators exhaust systems through the use of an air over water secondary heat exchanger that is incorporated with the same hot water closed loop system as the manifolds or the water jackets. 
     Step 4. Additional energy can be recovered from other building systems through the use of a water/steam over water secondary heat exchanger, Geothermal Sources, or Solar Collectors that are incorporated with the same hot water closed loop system as the Turbine Generators or Combustion Engine manifolds or water jackets. 
     Step 5. The temperature of the hot water closed loop system is regulated at 180 degrees F. by the use of variable frequency drive (VFD) controlled circulating pumps. The temperature is a function of the water flow in the system. The flow of the water is regulated by the rpm of the circulating pumps. The VFD&#39;s are controlled by a PLC based control system. PID loops in the PLC program monitor and control the temperature, pressure, and flow of the hot water loop. These PID loops control the VFD output and the rpm of the circulating pumps. The heating water that returns from the Thermal Hydraulic DC Generator Engine is at approximately 150 degrees F. 
     Step 6. The 180-degree F water is circulated through a Thermal Hydraulic DC Generator Engine. The water is used to expand liquid carbon dioxide which in turn drives a piston in one direction. A solenoid valve that is controlled by the PLC based control system controls the water flow. The liquid carbon dioxide does not experience a phase change. The Thermal Hydraulic DC Generator Engine does not involve an intake and exhaust cycle. It is very efficient and has a very long life expectancy with minimal maintenance requirements. 
     Step 7. An 80-degree F cooling-water closed loop system is also required to operate the Thermal Hydraulic DC Generator Engine. This cooling-water loop is circulated through a sanitary water over water heat exchanger that is installed in the domestic water system or through a water over water heat exchanger that is connected to a cooling tower or a cooling water piping system in the ground. The domestic water temperature is usually around 70-80 Degrees F. The cooling water that returns from the Thermal Hydraulic DC Generator Engine is at approximately 100 degrees F. 
     Step 8. The temperature of the cooling water closed loop system is regulated by the use of variable frequency drive controlled circulating pumps. The temperature is a function of the water flow in the system. The flow of the water is regulated by the rpm of the circulating pumps. The VFD&#39;s are controlled by a PLC based control system. PID loops in the PLC program monitor and control the temperature, pressure, and flow of the hot water loop. These PID loops control the VFD output and the rpm of the circulating pumps. The heating water that returns from the Thermal Hydraulic DC Generator Engine is at approximately 170 degrees F. 
     Step 9. The 80-degree F water is circulated through a Thermal Hydraulic DC Generator Engine. The water is used to contract liquid carbon dioxide, which in turn drives a piston in the opposite direction from expanded liquid carbon dioxide. A solenoid valve that is controlled by a PLC based control system controls the water flow. 
     Step 10. The Thermal Hydraulic DC Generator Engine drives a hydraulic pump. The pistons moving back and forth pump hydraulic fluid. The flow of the hydraulic fluid is regulated by PID loops in the PLC based control system. The PLC program coordinates the opening and closing of the solenoid valves for the heating and cooling water loops with the required flow rate of the hydraulic fluid. 
     Step 11.The hydraulic pump drives a DC generator. The DC generator is connected to a grid tie inverter which synchronizes with the building electrical system at unity power factor. The term for this device is a “Thermal Hydraulic DC Generator”. This is a new concept. It has never been accomplished before. 
     Step 12. Additional “Green Energy” systems can be connected to the same grid tie inverter in order to synchronize with the building electrical system. These systems can include solar photovoltaic modules and wind Turbine systems. 
     Step 13. Revenue metering is established to monitor the power sold to the utility when the total generation exceeds the demand for the building systems. 
     Step 14. In cases where revenue metering is not allowed by the utility, the number of Micro Turbines that are synchronized to the building electrical system can be controlled by the PLC based control system. In this case the demand for the building will have to exceed the total amount of power that is generated. 
     In various embodiments, the PLC based control system performs the following functions:
     1. Regulate the temperatures, pressures and flow rates for the heating cycle and cooling cycle water system.   2. Regulate the temperatures, pressures and flow rates for the hydraulic systems.   3. Control the firing rate of the solenoid valves to regulate the engine speed.   4. Control the inverter output.   5. Control associated generation systems.   6. Monitor the electrical system load demand.   7. Communicate with multifunction relays associated with the utility service.   8. Data Collection System   9. Alarm system   

     In various embodiments, the PLC based control system utilizes the following devices:
     1. 32 bit microprocessor   2. Analog Input Module   3. Analog Output Module   4. Discreet Input Module   5. Discreet Output Module   6. RTD Temperature Sensors   7. Differential Pressure Transmitters   8. Flow Meters   9. Variable Frequency Drives   10. Multifunction Protective Relays   11. Current Sensors   12. Voltage sensors   13. Frequency Sensors   14. Operator Interface Terminal   15. Data Collection System   16. Alarm System   

       FIG. 2  graphically depicts physical dimensions of an exemplary Programmable Logic Controller (PLC) suitable for use as a controller within the system of  FIG. 1 . In various embodiments, the PLC comprises a 32 bit microprocessor-based PLC with Ethernet communications, such as the model 1769-L32C or 1769-L35CR CompactLogix Controller manufactured by Rockwell Automation. It can be seen by inspection that the exemplary PLC  200  of  FIG. 2  includes various connection an interface elements such as central processing unit (CPU) connectors  210 , control network connectors  220 , channel input/output connectors  230 , user or operator input/output interface devices  240  and the like. Generally speaking and as known in the art, the PLC  200  of  FIG. 2  comprises a device including a processor, memory and input/output circuitry which may be programmed to monitor various digital and/or analog input signals and responsively adapts various output signal levels or data/communication sequences in response to such monitoring. 
       FIG. 3  graphically depicts exemplary power and signal input terminals associated with the PLC of  FIG. 2 . Specifically,  FIG. 3  represents a discreet input module used for the PLC based control system. It can be seen by inspection that the power terminals are responsive to a line or grid voltage of 100/120 VAC (in this embodiment) and that various input devices may be coupled to the signal input terminals. 
       FIGS. 4A-4B  graphically depict exemplary signal output terminals associated with the PLC of  FIG. 2 . Specifically,  FIGS. 4A-4B  represent wiring configurations for a discreet output module for the PLC based control system comprising, illustratively, a 16-point AC/DC Relay Output Module. It can be seen by inspection that the relay output module is adapted to be grounded in a particular manner. 
       FIGS. 5A-5B  graphically depict exemplary wiring configuration for connecting sensors/transmitters to signal input terminals associated with the PLC of  FIG. 2 . 
       FIG. 5A  graphically depicts an exemplary wiring configuration for connecting single-ended sensor/transmitter types to signal input terminals associated with the PLC of  FIG. 2 . It can be seen by inspection that a sensor/transmitter power supply  510  cooperates with a current sensor/transmitter  520  and a plurality of voltage sensor/transmitters  530 . The current sensor/transmitter  520  provides an output signal adapted in response to a sensed parameter, which output signal is provided to a current sensor input terminal (I in 0+) of a terminal block  540 . The voltage sensor/transmitters  530  provide output signals adapted in response to respective sensed parameters, which output signals are provided to respective voltage sensor input terminals (V in 2+ and V in 3+) of the terminal block  540 . 
       FIG. 5B  graphically depicts an exemplary wiring configuration for connecting mixed transmitter types to signal input terminals associated with the PLC of  FIG. 2 . It can be seen by inspection that a sensor/transmitter power supply  510  cooperates with a single ended voltage sensor/transmitter  530 , a differential voltage sensor/transmitter  550 , a differential current sensor/transmitter  560  and a 2-wire current sensor/transmitter  570 . Each of the sensor/transmitter types  530 ,  550 ,  560  and  570  provides an output signal adapted in response to a respective sensed parameter, which output signal is provided to a respective input terminal of a terminal block  540 . 
       FIG. 6  graphically depicts an exemplary wiring configuration for connecting an output device to signal output terminals associated with the PLC of  FIG. 2 . Specifically,  FIG. 6  represents an analog output module for the PLC based control system. It can be seen by inspection that an optional external 24 V DC power supply is connected between an DC neutral terminal and a +24 VDC terminal of a terminal block  640 , while a shielded cable  620  provides current to a load (not shown) load, the current sourced from a current output terminal (I out 1+) of the terminal block  640 . 
       FIGS. 7A-7B  graphically depict an exemplary wiring configuration for connecting a Resistance Temperature Detector (RTD) to excitation and sense input terminals of the PLC of  FIG. 2 . 
       FIG. 7A  graphically depicts an exemplary wiring configuration for connecting a 2-wire Resistance Temperature Detector (RTD) to excitation and sense input terminals of the PLC of  FIG. 2 . It can be seen by inspection that an RTD  710  is coupled between bridged excitation (EXC  3 ) and sense (SENSE  3 ) terminals at a terminal block  740 , and a return terminal (RTN  3 ) at the terminal block  740 . Current sourced from the excitation/sensor terminals passes through the RTD  710  and returns to the return terminal. It is also noted that a two-conductor shielded cable, illustratively a Belden 9501 Shielded Cable, is used to connect the excitation/sense wire (RTD EXC) and return wire (Return) between the RTD  710  and terminal block  740 . The shield of the shielded cable is coupled to ground. 
       FIG. 7B  graphically depicts an exemplary wiring configuration for connecting a 3-wire Resistance Temperature Detector (RTD) to excitation (EXC  3 ), sense (SENSE  3 ) and return (Return) terminals at a terminal block  740  of the PLC of  FIG. 2 . It can be seen by inspection that an RTD  710  is coupled between a junction or connection  706  proximate the RTD  710  of an excitation signal wire (RTD EXC) and a sense signal wire (Sense), and a return signal wire (Return). It is also noted that a three-conductor shielded cable, illustratively a Belden 83503 or 9533 Shielded Cable, is used to connect the excitation wire (RTD EXC), sense wire (sense That) and return wire (Return) between the RTD  710  and terminal block  740 . The shield of the shielded cable is coupled to ground. 
       FIGS. 8A-8B  graphically depict physical dimensions of an exemplary user interface device associated with the PLC of  FIG. 2 , illustratively an operator interface terminal  800  used for the PLC based control system.  FIG. 8A  depicts a front view of the operator interface terminal  800 , while  FIG. 8B  depicts a plan view of the operator interface terminal  800 . It can be seen by inspection that the exemplary operator interface terminal  800  comprises a PanelView Plus  400  or  600  terminal manufactured by Allen-Bradley. The terminal  800  includes a keypad or keypad/touch screen  810 / 820 . Generally speaking, the terminal includes circuitry supporting user input to the PLC (e.g., keypad or touch screen input), as well as circuitry providing user output from the PLC (e.g., display screen). As is known in the art, the terminal  800  is used to facilitate programming of the various functions of the PLC  200 , such as those described herein as implemented via the PLC  200  and the various embodiments. It is also noted that the terminal includes various network and communication ports  830  as shown in 
       FIGS. 9A-9D  graphically depict physical dimensions for various VFDs suitable for providing circulation pump control functionality in the system of  FIG. 1  in cooperation with the PLC of  FIG. 2 , illustratively one of the PowerFlex 70 frames manufactured by Rockwell Automation.  FIG. 9A  depicts a table listing output power for various PowerFlex 70 frame sizes.  FIGS. 9B-9C  depict physical dimensions associated with PowerFlex 70 Frames A-D as indicated in the table of  FIG. 9A .  FIG. 9D  depicts a table listing physical mounting options associated with various PowerFlex 70 frame sizes. 
       FIG. 10  depicts a schematic diagram of an exemplary inverter suitable for use as a grid tie inverter within the system of  FIG. 1 . Specifically,  FIG. 10  represents a grid tie inverter the grid tie inverter  150   150   10  of  FIG. 10  is used to convert DC power to AC Power and synchronize the AC power with the utility power grid at unity power factor. Referring to  FIG. 10 , components associated with grid tie inverter  150  are configured as follows: 
     A DC input voltage is received across an input capacitor C 1 . A first inductor L 1  and a first transistor Q 1  (illustratively an N-channel IGFET) are connected in series in the order named between positive and negative terminals of the input capacitor C 1 . 
     A forward biased diode D 1  and second capacitor C 2  are connected in series in the order named between a source and a drain of transistor Q 1  (i.e., anode of diode D 1  connected to source of transistor Q 1 , cathode of diode D 1  connected to positive terminal of capacitor C 2 ). 
     A first switching circuit SW 1  connected between positive and negative terminals of capacitor C 2  operates to switch or chop the voltage across capacitor C 2 . The switching circuit SW 1  comprises, illustratively, four transistors Q 2 -Q 5  (illustratively an N-channel IGFETs) configured in a known manner to drive a switched power signal through a input coil of a transformer T 1 . 
     An output coil of transformer T 1  provides a resulting switched or chopped signal to a full wave bridge rectifier B 1  formed in a known manner using four diodes D 2 -D 5  to provide thereby a rectified (i.e., substantially DC) signal. 
     A second inductor L 2  and a third capacitor C 3  are connected in series in the order named between positive and negative outputs of the full wave bridge rectifier B 1 . 
     A second switching circuit SW 2  connected between positive and negative terminals of capacitor C 3  operates to switch or chop the voltage across capacitor C 3 . The switching circuit SW 1  comprises, illustratively, four transistors to  6 - 29  (illustratively an NPN transistors having respective diodes forward biased between emitter and collector terminals.) configured in a known manner to a series drive a switched power signal through a third inductor L 3  and a fourth capacitor C 4 , L 3  and C 4  being connected in series in the order named. 
     An inductive element Lgrid (representative of power grid inductance), a switch SW and the power grid itself are connected in series in the order named between positive and negative terminals of capacitor C 4 . 
     An AC output signal between the Lgrid/SW junction point and the negative terminal capacitor C 4  is provided as an AC output to the main panel. 
     Referring to  FIGS. 1 and 10 , various operations of the grid tie inverter  150  within the context of the system  100  will now be described. 
     Operating a renewable energy system in parallel with an electric grid requires special grid interactive or grid tie inverters (GTI). The power processing circuits of a GTI are similar to that of a conventional portable power inverter. The main differences are in their control algorithm and safety features. 
     A GTI typically takes the DC voltage from the source, such as an solar panels array or a wind system, and inverts it to AC. It can provide power to your loads and feed an excess of the electricity into the grid. The GTIs are normally two-stage or three-stage circuits. The simplified schematic diagram shown in  FIG. 12  illustrates the PWM to sinusoidal waveshape operation of a grid tie inverter with three power stages. Such power train can be used for low-voltage inputs (such as 12V). The control circuits and various details are not shown here. 
     The DC input voltage is first stepped up by the boost converter formed with inductor L 1 , MOSFET Q 1 , diode D 1  and capacitor C 2 . If PV array is rated for more than 50V, one of the input DC busses (usually the negative bus) has to be grounded per National Electric Code®. 
     Since the AC output is connected to the grid, in such case the inverter has to provide a galvanic isolation between the input and output. In our example the isolation is provided by a high frequency transformer in the second conversion stage. This stage is a basically a pulse-width modulated DC-DC converter. Note that some commercial models use low-frequency output transformer instead of a high frequency one. With such method low voltage DC is converted to 60 Hz AC, and then a low-frequency transformer changes it to the required level. The schematic above shows a full bridge (also known as H-bridge) converter in the second stage. For power levels under 1000 W it could also use a half-bridge or a forward converter. In Europe, grounding on DC side is not required, the inverters can be transformerless. This results in lower weight and cost. 
     The transformer T 1  can be a so-called step-up type to amplify the input voltage. With a step-up transformer, the first stage (boost converter) may be omitted. The isolating converter provides a DC-link voltage to the output AC inverter. Its value must be higher than the peak of the utility AC voltage. For example, for 120 VAC service, the DC-link should be &gt;120*√{square root over ( )}2=168V. Typical numbers are 180-200V. For 240 VAC you would need 350-400 V. 
     The third conversion stage turns DC into AC by using another full bridge converter. It consists of IGBT Q 6 -Q 9  and LC-filter L 3 , C 4 . The IGBTs Q 6 -Q 9  work as electronic switches that operate in Pulse Width Modulation (PWM) mode. They usually contain internal ultrafast diodes. By controlling different switches in the H-bridge, a positive, negative, or zero voltage can be applied across inductor L 3 . The output LC filter reduces high frequency harmonics to produce a sine wave voltage. 
     A grid tie power source (i.e., grid tie inverter  150 ) operates to synchronize its frequency, phase and amplitude with the utility and feed a sine wave current into the load. Note that if inverter output voltage (Vout) is higher than utility voltage, the GTI will be overloaded. If it is lower, GTI would sink current rather than source it. In order to allow the electricity flow back into the grid, “Vout” has to be just slightly higher than the utility AC voltage. Usually there is an additional inductor (Lgrid) between GTE output the grid that “absorbs” extra voltage. It also reduces the current harmonics generated by the PWM. A drawback of “Lgrid” is it introduces extra poles in the control loop, which may lead to the system instability. 
     In solar applications, to maximize the system efficiency, a GTI has to meet certain requirements defined by the photovoltaic panels. Solar panels provide different power in different points of their volt-ampere (V-I) characteristic. The point in the V-I curve where output power is maximum is called maximum power point (MPP). The solar inverter must assure that the PV modules are operated near their MPP. This is accomplished with a special control circuit in the first conversion stage called MPP tracker (MPPT). 
     A GTI also has to provide so-called anti-islanding protection. When grid fails or when utility voltage level or frequency goes outside of acceptable limits, the automatic switch SW quickly disconnects “Vout” from the line. The clearing time must be less than 2 seconds as required by UL 1741. 
     The implementation of control algorithm of grid tie inverters is quite complex implemented with microcontrollers. 
       FIG. 11  graphically depicts a generator suitable for use within the system of  FIG. 1 . Specifically,  FIG. 11  represents a DC generator used to generate DC power. 
     Various embodiments provide a novel Thermal Hydraulic DC Generator. The inventor notes that a person in the relevant technical field would think that it would not be possible to use this combination of devices for the following reasons: 
     People in this field would not realize that the regulation of the hydraulic fluid in the Thermal Hydraulic DC Generator Engine to drive the Thermal Hydraulic DC Generator RPM at the correct speed could be achieved. This will eliminate the need for a regulator and an engine speed governor that is typically required for an engine/generator package. This will require a PLC based control system with the correct instrumentation devices. 
     People in this field would not realize that the regulation of the DC Generator and the output of the inverter to match the load demands could be achieved. This will require a PLC based control system with the correct instrumentation devices. 
     People in this field would not realize that the regulation of pressures, temperatures, and flow rates for the closed loop hot water and cooling water systems could be achieved in a steady manner. This will require a PLC based control system with the correct instrumentation devices. 
     People in this field would not realize that it is economically feasible to implement this system. The efficiency of the Thermal Hydraulic DC Generator is much better than anything else available for this type of application. This is new technology and people in the field are not aware of its capabilities. 
     People in this field would not realize that so much energy is wasted in turbine generator exhaust systems. They would not realize that so much energy can be recovered and used to generate additional electricity with a Thermal Hydraulic DC Generator at such a low cost. Again, this is new technology, and people in the field are not aware of its capabilities. 
     People in this field would not realize that the Thermal Hydraulic DC Generator system meets “Green Energy” requirements. “Green Energy” qualifies for tax credits and can add to the savings when this type of system is installed. Again, this is new technology, and people in the field are not aware of its capabilities. 
     People in this field would not realize that so much energy can be wasted from utility steam systems that enter large buildings in lots of cities around the world. They would not realize that so much energy can be recovered and used to generate additional electricity with a Thermal Hydraulic DC Generator at such a low cost. Again this is new technology, and people in the field are not aware of its capabilities. 
     People in this field would not realize that this system is very flexible and can incorporate other forms of Green Energy sources through the use of a common inverter. 
     People in this field would not realize that the use of the DC Generator and the inverter to generate electricity at unity power factor can increase the efficiency of the system. 
     In various embodiments, waste energy is recovered from Turbine Generator or Combustion Engine Generator Exhaust Systems to produce hot water for co-generation to drive Thermal Hydraulic DC Generators. 
     In various embodiments, waste steam is recovered from utility systems to drive Thermal Hydraulic DC. 
     In various embodiments, energy from Combustion Engine Cooling Water Systems is recovered to produce hot water to drive Thermal Hydraulic DC Generators. 
     In various embodiments, the use of Solar Collectors is incorporated in conjunction with Thermal Hydraulic DC Generators. The Solar Collectors produce hot water to drive the Thermal Hydraulic DC Generators. 
     Various embodiments incorporate the use of Geothermal Sources in conjunction with Thermal Hydraulic DC Generators. The Geothermal Sources produce hot water to drive the thermal Hydraulic DC Generators. 
     Although various embodiments which incorporate the teachings of the present invention have been shown and described in detail herein, those skilled in the art can readily devise many other varied embodiments that still incorporate these teachings. Thus, while the foregoing is directed to various embodiments of the present invention, other and further embodiments of the invention may be devised without departing from the basic scope thereof. As such, the appropriate scope of the invention is to be determined according to the claims.