Abstract:
An electric power generation system is provided, including a generator having a plurality of stages engaged by a prime mover; and a plurality of branches for connecting the stages to an electrical load, each of the branches having a switch for connecting or disconnecting the branch to the stages. Power from a prime mover, such as a turbine, is sent by a controller to one or more of the branches as appropriate to handle the power level generated.

Description:
FIELD OF THE INVENTION 
       [0001]    This application relates to circuit topologies and associated control processes for converting power generated via an electromagnetic machine into usable power, and more particularly for converting power generated from a multi-stage electrical generator into a usable form of power for consumption by an electrical load, such as, but not restricted to, an electric utility power grid. 
       BACKGROUND OF THE INVENTION 
       [0002]    For conventional fluid-flow electrical-generation turbine systems, such as wind turbine systems, in which the energy source is variable (i.e. the fluid speed and the rate of flow of the fluid varies over time), the amount of energy captured from the energy source may only be a fraction of the total of the energy that may be capturable over time. For example, in a typical wind farm, that fraction may be one half, or less. 
         [0003]    The power flow though a variable-speed conventional turbine/generator/transformer system is restricted in the range of power it can output, i.e., from a minimum output power to a rated output power, because of limitations of the generator, the power converter (if present), and the output transformer used within the system. This restriction arises because a conventional electromagnetic generator has reduced efficiency at lower power levels, as does the power converter (if present) and particularly the transformer that couples power to the electrical load. As a result, for the conventional variable-speed turbine/generator/transformer system an engineering design decision is usually made to limit the power rating of the generator (and any associated power converter, power conditioner or power filter, if present) and the associated output transformer so as to optimize efficiency over a restricted range of power. Therefore, at the extremes of normal-operating fluid speeds, i.e., at a low fluid speed and especially at a high fluid speed, less power is coupled into the turbine than it is possible to extract from the fluid energy source. For a given design of turbine diameter (and possibly axial length) this translates, over time, into less energy capture than the turbine may be capable of transmitting to the generator. 
         [0004]    To increase energy capture in situations in which the energy source has a variable speed of fluid driving the turbine, and in which the turbine may have a variable speed of rotation, a multi-stage generator may be used in the turbine system. A multi-stage generator is an electromagnetic machine operating as an electrical generator that takes mechanical energy from a prime mover and generates electrical energy, usually in the form of AC power. Such a multi-stage generator is disclosed in U.S. Pat. No. 7,081,696 and U.S. Patent Application Publication No. 2008/0088200, which are both hereby incorporated by reference. An advantage of a multi-stage generator over a conventional generator is that a multi-stage generator can be dynamically sized depending on the power output of the turbine. A conventional generator is effective at capturing energy from the energy source over a limited range of fluid speeds, whereas a multi-stage generator is able to capture energy over an extended range of fluid speeds of the energy source, due to staged power characteristics. 
         [0005]    The electrical power that is generated from a multi-stage generator is variable in nature, meaning the output power waveforms produced may vary from time to time, for example in: voltage amplitude; current amplitude; phase; and/or frequency. Additionally a multi-stage generator may include a number of induction elements, each of which generates its own power waveform, which may differ in voltage amplitude, current amplitude, phase, and/or frequency, from that generated by other induction elements within the generator. An electrical load such as an electric utility power grid may not be capable of consuming directly the electrical power that is generated by a multi-stage generator, as the power generated may not be in the correct form, for example, with respect to waveform shape as a function of time, voltage amplitude, current amplitude, phase, and/or frequency, as may be required by the electrical load. An electrical load such as a utility power grid typically expects from a turbine electrical generation system a single-phase, or split-phase, or 3-phase voltage or current waveform that is usually sinusoidal, and relatively stable, but a multi-stage generator generates varying waveforms. 
         [0006]    A power converter circuit may be used to transform electrical power waveforms from one form to another form. Converters may be designed for a specific rating of the input voltage range (e.g. 1000 VAC-rms to 2000 VAC-rms) and input current range rating (e.g. 100 A-rms to 500 A-rms), but if the input voltage or input current (and therefore power level) do not meet or exceed the levels for which the converter is designed, then the converter may not be capable of operation, or the converter may operate in an inefficient manner. For a multi-stage generator a single power converter is unlikely to accommodate the widely varying voltage waveforms and power range that is generated. Moreover, a single power transformer delivering power to the electrical load, connected to one or more converters, is unlikely to accommodate with reasonable efficiency the wide range of power that may be generated by a multi-stage generator. 
       SUMMARY OF THE INVENTION 
       [0007]    To take advantage of the electrical energy generated by the multi-stage generator, it is desirable to provide a power conversion system that combines and converts a portion, or all, of the electrical power waveforms generated by the multi-stage generator into a usable form consumable by an electrical load. The conversion system should maintain a high level of efficiency and facilitate the multi-stage generator to operate efficiently and effectively over the power range that the generator is capable of producing; meaning the power conversion process should not limit the range (from the lowest level to highest level) of power that may be generated by the multi-stage generator. 
         [0008]    A suitable power conversion system, including an associated control process, is desirable to take advantage of the benefits of using a multi-stage generator within a turbine electrical generation system, resulting in a higher energy capture of the energy source over a wider range of fluid speeds (or over a wider range of fluid flow-rates) compared to conventional turbine electrical generation systems. 
         [0009]    Further, for a multi-stage generator to function near-optimally (such as delivering a near-maximum power to the electrical load with a near-minimum of losses in the turbine/generator/converter system), over a wide range of fluid speeds or a wide range of fluid flow-rates, with existing turbines, a controller can be used to control the power conversion electronics that process the output power waveforms of the generator. When desirable, a controller can also allow the system to seek to maximize the amount of energy capture from the energy source by seeking to optimize the turbine&#39;s parameters, such as blade pitch and turbine yaw, in response to time-dependent characteristics of the energy source such as the fluid speed and direction of flow. Based on these and other inputs, the system&#39;s electronic power conversion process would choose the near-optimal conversion strategy for delivering power to the electrical load. 
         [0010]    An electric power generation system is provided, including a power generator having a plurality of machine configurations, the configurations selectively engageable by a prime mover; and a plurality of branches for connecting the configurations to an electrical load, each of the branches having a switch for connecting or disconnecting the branch to the configuration. 
         [0011]    A method of connecting a power generator having a plurality of stages, to an electrical load, is provided, each of the stages being connected to the load via a corresponding branch having a converter, each of the converters having a differing power range, including the steps of: (a) determining a power output of the generator; (b) selecting one of the branches, wherein the power output of the selected branch has a converter capable of accepting the power output; and (c) passing the power output to the electrical load along the selected branch. 
         [0012]    A method of connecting a power generator having a plurality of stages, to an electrical load is provided, each of the stages connected to the load via a corresponding branch having a converter and a parallel series selector, each of the converters having the same power range, including the steps of: (a) determining a power output of the generator; (b) configuring at least one of the parallel series selector for the power output; (c) selecting one or more of the branches corresponding to the configured parallel series selectors; and (d) passing the power output to the electrical load along the selected branches. 
         [0013]    An electric power generation system is provided, including a power generator having a plurality of stages, each of the stages having at least an induction element, the induction elements engaged by a turbine; a plurality of branches for connecting the stages to an electrical load, each of the branches having a switch for connecting or disconnecting the branch to the stages; a turbine; and a system controller. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0014]    The following figures set forth embodiments of the invention in which like reference numerals denote like parts. Embodiments of the invention are illustrated by way of example and not by way of limitation in the accompanying figures. 
           [0015]      FIG. 1  is a block diagram of an embodiment of a turbine/generator/converter (TGC) system; 
           [0016]      FIG. 2  is a block diagram of an embodiment of a multi-stage generator; 
           [0017]      FIG. 3  is a flowchart showing an example of a control process by which a bank of converters converts the electric power into a useable form; 
           [0018]      FIG. 4  is a block diagram of an alternative embodiment of a turbine/generator/converter system including a parser conversion topology; 
           [0019]      FIG. 5  is a block diagram of an alternative embodiment of a multi-stage generator illustrating induction elements that may not need to be hardwired for interface to a parser conversion topology; 
           [0020]      FIGS. 6A and 6B  are a flowchart showing an example of a control process by which a parser conversion system converts electric power into a useable form; 
           [0021]      FIG. 7  is a block diagram of an embodiment of a turbine/generator/converter system wherein the interface includes a hybrid conversion topology; 
           [0022]      FIG. 8  is a block diagram of an embodiment of a multi-stage generator illustrating induction elements that may be hardwired to facilitate interface to a hybrid conversion topology; 
           [0023]      FIGS. 9A and 9B  are a flowchart showing an example of a control process by which a hybrid conversion system converts electric power into a useable form; 
           [0024]      FIG. 10  is a block diagram of an embodiment of a branch having a fork to allow selection of a converter; 
           [0025]      FIG. 11  is a block diagram of an alternative embodiment of a branch, wherein the branch has a fork to allow selection of a transformer; and 
           [0026]      FIG. 12  is a block diagram of a further alternative embodiment of a turbine/generator/converter system, wherein the interface includes a hybrid conversion topology employing a forked branch. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Definitions 
       [0027]    In this document, the following terms will have the following meanings: 
         [0028]    “energy source” means a fluid medium, for example such as air, water, or steam, in motion, possessing kinetic energy due to translational motion. 
         [0029]    “prime mover” means a device, such as a turbine or drive motor acted on by a power source, such as an energy source, to produce mechanical energy. 
         [0030]    “turbine” means a device, usually including blades or fins, connected to a shaft, that are acted upon by an energy source to produce mechanical energy in the form of rotational motion of the shaft. It includes turbines used to harness energy from wind, tide, run-of-river and solar and other renewable energy sources. 
         [0031]    “multi-stage generator” means an electromagnetic machine that converts mechanical energy from a turbine into electrical energy. Electrical power may be generated by a multi-stage generator from a number of induction elements that can each produce a voltage. Some induction elements may be hardwired, either within the multi-stage generator casing or external to the casing (although a casing need not be present). The multi-stage generator may be a motor operating in generation mode. 
         [0032]    “induction element” means a coil of insulated metallic wire that generates a voltage across terminals as the wire passes though a magnetic field. 
         [0033]    “stage” means a logical grouping of induction elements. The induction elements within a stage may have an almost equal frequency of the voltage waveform. A stage may have all induction elements operating in phase, or poly-phase induction elements may be present in the stage. A stage may or may not have a phase equal to another stage. 
         [0034]    “machine configuration” means the sizing and configuration of induction elements, and may including the staging of induction elements. 
         [0035]    “parallel series selector” or “parser” means an electronic or mechanical or electro-mechanical switching device that connects induction elements together in a number of configurable arrangements of parallel and/or series combinations. A parser may also be referred to as a “configurator”. 
         [0036]    “power converter” or “converter” means an electronic circuit that changes the form (e.g. waveform shape as a function of time, voltage amplitude, current amplitude, phase, and/or frequency) of electrical power waveforms. A converter may include a rectification step. 
         [0037]    “turbine/generator/converter system” or “TGC system” means a system including a turbine, an electrical generator (such as a multi-stage generator) and a power converter. A TGC system may optionally further include some or all of the following components: ring gear or gearbox; parser(s); transformer(s); switch(es); and control system(s). A TGC system transforms a portion of the kinetic energy of an energy source into electrical energy. 
         [0038]    “electrical load” means a consumer of electrical energy, and may be a stand-alone off-grid application, for example electrical devices within a residence, commercial building or industrial process; or may be a micro-grid system providing electrical energy for an isolated rural village; or a large electric utility power grid; or other application. 
         [0039]    “power conversion topology” means an arrangement of hardware components, such as one or more, parsers, power converters, transformers, and switches. A power conversion topology may be used as an interface between a multi-stage generator and an electrical load. 
         [0040]    “power conversion system” means a power conversion topology and its associated controller. A power conversion system may be a subsystem of a TGC system. 
         [0041]    “branch” means an arrangement including any, but not necessarily all, of the following elements: a parser, input switch or switches; a converter; a transformer; output switch or switches; connected in series. A branch may be a subsystem of a power conversion topology. 
         [0042]    “bank of converters system” means a power conversion system including a bank of converters topology and an associated controller. 
         [0043]    “parser conversion system” means a power conversion system including a parser conversion topology and an associated controller. 
         [0044]    “hybrid conversion system” means a power conversion system including a hybrid conversion topology with one or more branches, and an associated controller. 
         [0045]    “system controller” means a computer, microcontroller, digital signal processor, embedded system, analog circuit or other implementation that performs monitoring functions and issues commands to various subsystems and/or components of a system, such as a TGC system. In addition, a system controller may also monitor an energy source and/or electrical load, and may provide information to an electrical load (for example, if the electrical load is an electric utility power grid). 
         [0046]    “fluid flow-rate” means the quantity of fluid, such as air, water or steam, per unit time that moves through a turbine, measured in units such as cubic feet per minute, gallons per minute, liters per second, or kilograms per second. 
         [0047]    “average-power” means the mean power as evaluated over one or more cycles of power delivery, for example as evaluated over a period of 16.67 milliseconds in a 60 Hz system. 
         [0048]    “rated-power” or “name-plate power” means the highest value continuous average-power that a device (e.g. turbine, generator, converter, power conversion system, transformer, or TGC system) is specified to deliver. 
         [0049]    “machine utilization” means the proportion of an electromagnetic machine, such as a multi-stage generator, not including the machine casing, that is active and delivering power when the machine is operating at rated-power, i.e. at the maximum continuous average-power capability of the machine. This proportion may be specified in various manners, including the ratio of the weight, e.g. in Kg, of the active portion of the machine to the weight of the machine not including the machine casing, or the ratio of the number of active induction elements to the total number of induction elements within the machine. 
         [0050]    “maximum energy capture mode” means a mode of operation of a TGC system wherein, for a given fluid flow-rate through the turbine, the system controller delivers as much power as possible (i.e. the designed-maximum continuous average-power at that fluid flow-rate) from the energy source to the electrical load up to and including the rated-power of the TGC system. Maximum energy capture mode may also be referred to as “maximum power point tracking” (MPPT). 
         [0051]    “throttling” means a mode of operation of a TGC system wherein the system controller limits and regulates the average-power delivered to the electrical load to a value less than that which may be delivered for a given flow-rate of fluid through the turbine. In practice, throttling of a TGC system may sometimes be necessary; however extended use of such a mode of operation may considerably reduce the energy capture over time of a given TGC system. Note that in maximum energy capture mode, the TGC system enters throttling mode when the system is operating at its rated-power. 
         [0052]    “functional” means a component of a system that is capable of performing its intended function. 
       INTRODUCTION 
       [0053]    A system controller may be used to automatically maintain the efficient conversion of power during operation of a multi-stage generator turbine/generator/converter system. The system controller may exist as a single controller which controls all functions of the turbine/generator/converter system, or may be separated into a number of sub-controllers with their own functions. 
         [0054]    In some embodiments, a major function of the system controller is to control the turbine, such as monitoring and adjusting the pitch of the blades and the yaw of the turbine. A second major function of the system controller may be to monitor and control the power conversion electronics to provide an efficient and controlled transfer of power between the output of the multi-stage generator and the electrical load. 
         [0055]    A system controller can be used to facilitate communication between components of the system; for example, in some embodiments it monitors sensors and/or receives information about system components and/or about the electrical load; it provides the relevant components with the necessary information to operate near-optimally and correctly; it instructs subsystems and components by providing adjustments and/or command signals. Inputs for the system controller may include, but are not restricted to, fluid speed; fluid direction; fluid statistical information; the position information and/or the derivatives of position information for casing or supporting structural elements; turbine position and/or speed and/or acceleration; blade pitch angle; turbine pitch and/or yaw; current, voltage, power, reactive power, distortion, measurements at various points within the system or of the electrical load; sensory or data information about characteristics of the electrical load. The system controller typically receives sensor and/or data information and issues commands to the turbine and components of the power conversion system to ensure the safe and efficient transfer of power from the turbine to the electrical load. For controlling the power conversion process of a multi-stage generator turbine/generator/converter system, the system controller may initiate and activate power generated from a stage, including the engagement, transfer, and disengagement of power through any given stage. The system controller preferably provides a smooth transfer of power between stages and an uninterrupted power flow to the electrical load, and when desirable may do so in such a way as to increase or maximize the energy capture from the fluid that is flowing through the turbine. 
       Bank of Converters System 
       [0056]    In this document, the letters i, j, k, x, y and z will be used with reference numbers to refer to specific components referenced in the drawings. A reference number without a subscript may apply to any of the subscripted components sharing the same reference number. 
         [0057]    Illustrated in  FIG. 1  is a TGC system, which includes one embodiment of a power conversion topology, referred to here as a bank of converters topology  10   x . Bank of converters topology  10   x  has one or more converters  20  in different branches  30  that are each connected to a stage of induction elements within multi-stage generator  40   x.    
         [0058]    Shown in  FIG. 2  is an illustration of multi-stage generator  40   x  that may be interfaced with bank of converters topology  10   x . Within multi-stage generator  40 , such as  40   x , are a number of induction elements  50 , which can be grouped into two or more different logical groupings referred to as stages  60 , such as  60   i ,  60   j ,  60   k  in  FIG. 2 . A logical grouping means that the induction elements within a group  60 , for example stage  60   i , share a common set of characteristics, primarily spatial locality, so that the generated voltage, amplitude and phase of a single induction element  50  will match those of other induction elements  50  within the grouping  60 . Within one stage of a multi-stage generator  40 , the possibility exists for single-phase, split-phase, 3-phase, 4-phase, 6-phase or other poly-phase arrangements of induction elements  50 . 
         [0059]    As illustrated in  FIG. 2 , induction elements  50  within a stage  60  may be hardwired and connected together into a combination of parallel and/or series connections. Induction element terminals  70  may be hardwired within the casing of multi-stage generator  40 , or induction element terminals  70  may be hardwired external to the casing of multi-stage generator  40 . Alternatively, no casing is needed and terminals  70  may be hardwired within multi-stage generator  40  or external to multi-stage generator  40 . In general there may be any practical number of induction elements  50  within a stage  60 , possibly in poly-phase arrangements, and a variety of series, parallel, or mixed series-parallel connections are possible; also there may be no hardwiring of induction elements  50 . 
         [0060]    The output terminal-block  80  from each stage  60  may connect to a branch  30 , which may include input switch  90 , converter  20 , optional transformer  100 , and output switch  110 , all connected in series. The outputs of each branch  30  may be connected to electrical load  120 . Each input switch  90 , such as  90   i , includes several poles of switches, which may close or open simultaneously, to accommodate the terminals of a terminal-block  80 , such as  80   i , for a given stage  60 , such as  60   i , of a multi-stage generator  40 . Each output switch  110 , such as  110   i , includes several poles of switches, which may close or open simultaneously, to accommodate the terminals of electrical load  120 . 
         [0061]    For bank of converters topology  10   x , the power rating of converter  20  and/or transformer  100  may increase geometrically from one stage to the next, so that if at the first stage  60   i  a relatively low power converter  20   i  is required, the next stage  60   j  may require a significantly higher power converter  20   j , etc. For multi-stage generator  40   x , this allows for stage  60   j  to contain many more induction elements  50  than that of stage  60   i , and similarly stage  60   k  may have many more induction elements than stage  60   j , etc. 
         [0062]    Turbine  130 , acting as a prime mover, may be directly connected to a multi-stage generator  40  or there may be a ring-gear or gearbox  140  coupling turbine  130  to multi-stage generator  40 . Turbine  130 , as the prime mover, engages multi-stage generator  40  thereby inducing a voltage across induction elements  50 . 
         [0063]    Components and/or subsystems of the TGC system may be interfaced to a system controller  150 , such as  150   x , including but not limited to the following components: turbine  130 , induction elements  50 , branches  30 , input switches  90 , converters  20 , transformers  100 , output switches  110  and electrical load  120 . Among other turbine related tasks, system controller  150  may provide commands to control the pitch of the turbine blades. System controller  150  may also monitor the fluid medium, for example sensing the speed of the fluid at various possible locations in and around the turbine. System controller  150  may also monitor the rotational speed of turbine  130  and/or of multi-stage generator  40 . System controller  150  may also monitor power variables at various points in the TGC system. System controller  150  may also monitor various current, voltage, phase angle, power or other variables of electrical load  120  and may also provide information to electrical load  120 . System controller  150 , or a dedicated sub-controller (not shown), may also synchronize the output voltage or current of branch  30  with the voltage waveform of electrical load  120 , which may be an electric utility power grid. 
         [0064]    To accommodate the entire or near-entire range of output power that multi-stage generator  40  may be capable of producing, multiple converters  20  and/or transformers  100  may be used in a TGC system. For bank of converters topology  10   x , these multiple converters  20  and/or transformers  100  are arranged so that power flows, with reasonably high efficiency, through one branch  30  corresponding to a given power level range that may be generated by a given stage  60  of multi-stage generator  40   x , (except during a transition period when power is being transferred from one branch to another branch, such as from  30   i  to  30   j ). There may be a slight overlap in the power level ranges for stages  60  of multi-stage generator  40   x . For example, the top value of the power range for stage  60   i  may be a small percentage higher than the lowest value of the power range for stage  60   j . Similarly, and correspondingly, there may be a slight overlap in the power level ranges for branches  30  of bank of converters  10   x . For example, the top value of the power range for branch  30   i  may be a small percentage higher than the lowest value of the power range for branch  30   j . The overlap of power ranges aids system controller  150  to effect a smooth transfer of power flow from one stage (branch) to the next stage (branch) as the power level of the prime mover, i.e. the turbine, varies with time. 
         [0065]    Input switch  90 , such as  90   i , may be connected to a corresponding converter  20 , such as  20   i , and used by system controller  150  to select a branch  30 , such as  30   i , which may then be activated by system controller  150  and then transform power from a multi-stage generator  40  (alternatively power switching devices within converter  20  may serve a similar purpose so that input switches  90  are not needed). An output switch  110 , such as  100   i , may be opened to prevent excitation of a transformer  100 , such as  110   i , within an inactive branch, such as  30   i . Output switches  110  also act as a fail-safe to prevent power being delivered to electrical load  120  from inactive converter branches  30 , and may facilitate the transfer of power from one branch  30  to another branch  30 , and provide additional isolation (with manually operated circuit breakers) for maintenance purposes. 
         [0066]    Referring to the flowchart of  FIG. 3 , system controller  150 , and/or a delegated sub-controller, may perform the monitoring of variables, such as, but not restricted to, the monitoring of power flow from a multi-stage generator  40  (multi-stage generator  40  power output may also be obtained by measurement of the input power to power conversion topology  10 ). System controller  150  also makes decisions and executes tasks, using a control process outlined in the flowcharts, such as illustrated in  FIG. 3 . The control process that is used generally seeks to maximize energy capture mode when, for a given fluid flow-rate, it is desirable to deliver as much power as possible from the energy source to electrical load  120 , up to and including the rated-power of the TGC system. A variation of the maximum energy capture mode of operation is a throttling mode wherein a system controller  150  is instructed by an operator (which may be a person or another controller, for example a controller that governs operation of a wind farm) to deliver a limited and/or regulated average-power to electrical load  120  that may be less than the rated-power of the TGC system. Even in maximum energy capture mode, once the rated-power delivery of the TGC system is obtained, system controller  150  may enter a throttling mode wherein the average output power of the TGC system is regulated to be the rated-power of the TGC system, and multi-stage generator  40  is operating at its rated-power level. 
         [0067]      FIG. 3  is a flowchart showing an embodiment of a control process by which system controller  150   x  may control bank of converters topology  10   x  to transform the electric power produced by multi-stage generator  10   x  into a useable form for electrical load  120 . The bank of converters system may be in a standby mode (step  300 ) when there is no power output from the multi-stage generator  40   x . In standby mode all branches  30  may be disconnected from electrical load  120 , i.e. input switches  90  may all be open and output switches  110  may be all open. 
         [0068]    Under control of system controller  150 , voltage may be induced in induction elements  50  if there is sufficient fluid flow of an energy source in turbine  130  to rotate of the shaft of multi-stage generator  40 . A power conversion topology  10 , such as bank of converters topology  10   x , remains inactive and in standby mode (step  300 ) until multi-stage generator  40  produces power exceeding a pre-defined threshold level, defined herein as “P1+” (step  305 ), where P1+ is generally a small percentage greater than the minimum operating input power of power conversion topology  10 , defined herein as “P1−”. At this point, referring to the bank of converters system and conversion topology  10   x , switch  90   i , connected to the lowest level stage  60   i , may close and under control of system controller  150   x  branch  30   i  becomes active, including converter  20   i  and/or transformer  100   i , but no power is yet flowing to electrical load  120 . It may be desirable at this time to control the voltage at the output of converter  20   i  or the output voltage of transformer  100   i  such that the voltage is in the correct form for electrical load  120 , at which time output switch  110   i  may be closed (step  310 ) (it is also possible to close switch  90   i  after closing switch  110   i ) thereby connecting transformer  100   i  to electrical load  120 , and then power is delivered, under control of system controller  150   x , from stage  60   i  of multi-stage generator  40   x  though the lowest power-range converter  20   i  of branch  30   i  to electrical load  120  (step  315 ). At this point a single converter branch  30   i  is active and transforming power, meaning that converter  20   i  and transformer  100   i  have power flowing through them. 
         [0069]    In general for the illustrated bank of converters system embodiment, if the power level for the currently active converter branch  30  decreases past a certain level (which, referring to the “−” notation, may be slightly less than the threshold necessary to begin power flow in that branch), then the flow of power is transferred to the preceding branch. If there is no previous branch then the bank of converters topology  10   x  and system controller  150   x  return to standby mode. Likewise, if the power level for the currently active converter branch  30  increases past a certain level (referring to the “+” notation), then flow of power is transferred to the next branch having a higher power rating (for example branch  30   j  may be capable of transforming power at higher levels than branch  30   i ). If there is no next branch then the TGC system is operating at its rated-power level, and a multi-stage generator  40 , such as  40   x , is delivering its rated-power defined herein as “P max ” where P max  is the rated-power of a multi-stage generator  40 , such as  40   x , corresponding to and slightly greater than the rated-power of the TGC system, due to losses in power conversion topology  10 . 
         [0070]    For example, referring again to  FIG. 3 , as power flows through branch  30   i  (step  315 ), system controller  150 X monitors the output power level of multi-stage generator  40   x  (step  320 ), and if the power level drops below P1−, the system returns to standby mode (step  300 ), meaning that power flow in branch  30   i  is reduced to zero by system controller  150   x  and then switches  110   i  and  90   i  are opened, preferably in that order. Note that system controller  150   x  may return the system to standby from other steps, such as, but not restricted to, steps  345  or  382 . 
         [0071]    If (at step  320 ) the power level is between P1− and P2+, then system controller  150   x  retains the power flow through branch  30   i  (step  315 ). If (at step  320 ) the power level exceeds P2+, then the switches for the next branch  30 , branch  30   j , switches  90   j  and  110   j , are closed, preferably, but not necessarily, in that order (step  325 ). Power flow is then transferred by system controller  150   x  to branch  30   j  (step  330 ), and at least one of switches  110   i  and  90   i  are opened (step  335 ), and power flows only through branch  30   j  (step  340 ). 
         [0072]    As power flows through branch  30   j  (step  340 ), system controller  150   x  monitors the output power level of multi-stage generator  40   x  (step  345 ), and if the power level is between P2− and P3+, then the system controller  150   x  retains the power flow through branch  30   j  (step  340 ). 
         [0073]    If (at step  345 ) the power level drops below P2−, then system controller  150   x  returns power flow in bank of converters topology  10   x  to branch  30   i , possibly using the following sequence of steps. Switches  90   i  and  110   i  are closed (step  350 ), then system controller  150   x  causes power flow to transfer to branch  30   i  (step  355 ), after which switches  110   j  and  90   j  are opened (step  360 ). 
         [0074]    If (at step  345 ) the power level exceeds P3+, then switches  90   k  and  110   k  are closed (step  365 ), and power is transferred by system controller  150   x  from branch  30   j  to branch  30   k  (step  370 ), following which switches  110   j  and  90   j  are opened (step  375 ) so that the transfer of power from branch  30   j  to branch  30   k  is complete and power flows only though branch  30   k  (step  380 ). 
         [0075]    As power flows through branch  30   k  (step  380 ), system controller  150   x  monitors the output power level of multi-stage generator  40   x  (step  382 ), and if the power level is between P3− and P max , then system controller  150   x  retains the power flow through branch  30   k  (step  380 ). Note that when power level P max  is obtained system controller  150   x  may enter a throttling mode (also step  380 ). If (at step  382 ) the power level drops below P3−, system controller  150   x  returns power flow in bank of converters topology  10   x  to branch  30   j  possibly using the following sequence of steps. Switches  90   j  and  110   j  are closed (step  384 ), then system controller  150   x  causes power flow to transfer to branch  30   j  (step  386 ), after which switches  110   k  and  90   k  are opened (step  388 ). 
         [0076]    If (at step  382 ), or at other steps including, but not restricted to, steps  320  and  345 , an emergency condition arises (for example a storm or hurricane winds applied to a wind turbine), it may be necessary for system controller  150   x  to shut down operation of the TGC system by setting power flow through the TGC system to zero and preferably stopping rotation of turbine  130  (step  390 ). 
         [0077]    If the fluid flow-rate in turbine  130  exceeds a threshold value, herein designated “f max ”, corresponding to the power rating P max , and possibly also corresponding to a specific speed of the fluid at some point in or around the turbine, system controller  150  then enters a throttling mode and regulates the power flow through the TGC system to be at the maximum level of P max  (hence the “≦” condition in the monitoring and decision step  382  of  FIG. 3 , where for fluid flow-rate greater than f max , it may be desirable for system controller  150  to operate the TGC system with power from multi-stage generator  40  at a constant average power of P=P max ; aside from inefficiency in power conversion topology  10  a power of approximately P max  would in this case be delivered to electrical load  120 , as implied by the loop from step  382  to step  380 ). If the fluid flow-rate continues to increase to or beyond a second threshold value, herein designated “f excess ” (possibly corresponding to a specific speed of the fluid at some point in or around the turbine that may be measured by system controller  150 , or possibly corresponding to a specific rotational speed of the shaft of turbine  130  or a specific shaft speed of multi-stage generator  40 , any of which may be measured by system controller  150 ), then the fluid flow-rate may be excessive for turbine  130  to maintain its mechanical integrity. Such a situation is one example of an emergency condition, wherein it may be necessary for system controller  150  to shut down operation of the TGC system by setting power flow through the TGC system to zero and preferably stopping rotation of turbine  130  (step  390 ). 
         [0078]    For the bank of converters embodiment, and for other embodiments, the activation or deactivation of a branch  30  may be initiated when a power threshold is crossed (e.g. for the bank of converters power conversion system there may be a transfer of power flow from branch  30   i  to branch  30   j  initiated when multi-stage generator  40   x  output power exceeds P2+). However, a system controller  150 , such as  150   x , may initiate the activation or deactivation of a branch  30  using system variables other than the power from a multi-stage generator  40 , such as but not restricted to: the speed of fluid flowing in or around turbine  130 ; the rotational speed of turbine  130 ; the rotational speed of a multi-stage generator  40 ; the output voltage of stages  60  as measured at a terminal-block  80  or directly across one or more induction elements  50  of multi-stage generator  40 ; and/or the input voltage to a power conversion topology  10 . For example, in a power throttling mode, when it is desirable to control the power delivered by the TGC system to electrical load  120  to be at a level less than the maximum possible for a given fluid flow-rate, the transfer of power from one branch  30  to the next branch  30  (or addition or removal of a branch  30  for the embodiments discussed below) may be initiated when the voltage output from a given stage exceeds (or drops below) a voltage threshold (e.g. for the bank of converters power conversion system there may be a transfer of power flow from branch  30   i  to branch  30   j  when the output voltage of stage  60   i  exceeds a voltage threshold defined herein as “V2+”, following which stage  60   i  could be inactivated). Such operation by the system controller  150  would maintain the voltage input to each converter within a specified range and thus prevent damage to, or maintain high efficiency operation of, the converters  20  and transformers  100  of the power conversion topology  10 . 
         [0079]    The above discussed principles of operation for the bank of converters system may be extended (or simplified) in the case where there are more than (or fewer than) three branches  30 . In general, there may be any practical number of branches  30  within a power conversion topology  10 , such as bank of converters topology  10   x.    
       Parser Conversion System 
       [0080]    The above discussed embodiment of a power conversion system, a bank of converters system, has an elegance of process control as only one stage  60  and one corresponding branch  30  is active at a given time, aside from periods when power is being transferred from one branch  30  to another branch  30 . However, at the highest power level, P max , there are unused inactive stages  60  within the multi-stage generator  40 . For the above-described bank of converters embodiment, the highest power stage  60 , which may be stage  60   k  as in  FIG. 2 , may contain the largest number of induction elements  50  compared to other stages, at the TGC system rated-power (corresponding to power P max  delivered by multi-stage generator  40   x ) machine utilization of multi-stage generator  40   x  may be less than 100%, for example on the order of 75% at a rated-power on the order of one megawatt to ten megawatts, meaning that 75% of induction elements  50  within multi-stage generator  40   x  are activated and 25% are inactive when the TGC system is operating at its rated-power level (when multi-stage generator  40   x  is operating at its rated-power level P max ). 
         [0081]    Another embodiment of a power conversion system, which may have up to 100% machine utilization of a multi-stage generator  40  is referred to herein as a parser conversion system, and includes parser conversion topology  10   y  and its associated controller, system controller  150   y , as shown in  FIG. 4 . An illustration of a multi-stage generator  40   y  which may be interfaced with parser conversion topology  10   y  is shown in  FIG. 5 . For this embodiment, multi-stage generator  40   y  may require no hardwiring of induction elements  50 , i.e., all induction element terminals  70  within a stage  60 , such as  60   i , are connected to terminal-block  80 , such as  80   i , as indicated in  FIG. 5 . A corresponding process control flowchart that could be employed by system controller  150   y  in the control of parser conversion topology  10   y  is shown in  FIG. 6 . 
         [0082]    As seen in  FIG. 4  parser conversion topology  10   y  includes one or more branches  30 . In  FIG. 4 , three branches i, j, and k, are represented, although any practical number of branches may be present. Each branch  30  may include a parser  170 , an input switch  90 , a converter  20 , an optional transformer  100 , and an output switch  110 , all connected in series. The output switch  110  from each branch  30  is connected to electrical load  120 , which may be an electric utility power grid. A key concept of the parser conversion topology  10   y , is the modular design, in that each branch  30  may be substantially identical in form with all other branches, i.e. all of the parsers  170   i ,  170   j ,  170   k  (as shown in  FIG. 4 ) may be substantially identical, as may be input switches  90   i ,  90   j ,  90   k , converters  20   i ,  20   j ,  20   k , transformers  100   i ,  100   j ,  100   k , and output switches  110   i ,  110   j ,  110   k.    
         [0083]      FIG. 5  shows a multi-stage generator  40   y  which may have any practical number of stages  60 , each of which may be substantially identical, each stage  60  including a number of induction elements  50 . Thus multi-stage generator  40   y  may also have a modular design. The modularity of parser conversion topology  10   y  and of the multi-stage generator  40   y  enables one stage-branch pair to function in place of a second stage-branch pair should the latter be damaged. For example if stage  60   i  is damaged (and multi-stage generator  40   y  is otherwise intact) or if branch  30   i  is damaged, then stage  60   j  and branch  30   j  may provide power flow to electrical load  120  in place of stage  60   i  and branch  30   i , as decided by system controller  150   y , after the performance of diagnostic tests to determine the functionality of stages  60  and branches  30 . Such replacement of damaged stages  60  and/or branches  30  is facilitated by input switches  90  and output switches  110 , permitting normal TGC system operation or a reduction in TGC system operation until repairs are affected. In the above example, input switch  90   i  and output switch  110   i  may both be kept open isolating the damaged component from electrical load  120 , or in the specific case of a damaged stage  60 , isolating that stage  60  from its branch  30  of parser conversion topology  10   y.    
         [0084]    For the illustrated parser conversion system embodiment, assuming no damaged stages  60  or branches  30 , as the power level of turbine  130  increases, more stage-branch pairs may be activated, until the rated-power condition is obtained, and the power output of multi-stage generator  40   y  may be P max  and all stages  60  of multi-stage generator  40   y  may be active and correspondingly all branches  30  of parser conversion topology  10   y  may be active, thus achieving 100% utilization of multi-stage generator  40   y.    
         [0085]    The output from each stage  60  of the multi-stage generator  40   y  is connected through terminal-block  80  to the input for parser  170 . Parsers  170  are used to configure the terminals  70  of the induction elements  50  such that the voltage outputs for parser  170  are within an acceptable level for the corresponding converter  20  in branch  30 . For example, at a low power level range (for example from P1− to P2+) perhaps one or more sets of induction elements  50  within an active stage  60 , such as  60   i , are connected in series by parser  170 . At the next higher power level range (for example from P2− to P3+), when the voltage across each individual induction element  50  has increased in response to increased rotational speed of turbine  130 , a mix of series and parallel connections of induction elements  50  may be arranged by parser  170 . The process continues until multi-stage generator  40   y  is operating at the maximum continuous average-power of P max  in which case there may be one or more sets of induction elements  50  within all stages  60  that are connected in parallel. By doing so, it is possible to keep the variation of input voltage to converter  20  to within a reasonable range and permitting more efficient operation of converter  20  and its associated transformer  100 , such as converter  20   i  and its associated transformer  100   i.    
         [0086]    Parser  170  may be used to arrange induction elements  50  within a stage  60  to meet the voltage requirements of a corresponding converter  20  as needed. If a higher voltage level is required by converter  20  then parser  170  arranges the induction elements  50  in a more series-like manner; likewise if a lower voltage level is required then induction elements  50  are arranged in a more parallel-like manner. The configuration of each parser  170  is a function of system controller  150   y , responding to changing variables such as fluid speed or turbine  30  rotational speed, or generator  40  rotational speed, or direct measurement of voltages at terminal block  80 . 
         [0087]      FIG. 6  is a flowchart showing an embodiment of a control process by which system controller  150   y  may control parser conversion topology  10   y  to transform the electric power produced by multi-stage generator  10   y  into a useable form for electrical load  120 . System controller  150   y , or a delegated sub-controller, makes decisions and executes tasks as outlined in the flowchart shown in  FIG. 6 . The illustrated control process generally seeks maximum energy capture mode and includes throttling of parser conversion topology  10   y  when multi-stage generator  40   y  is delivering its rated-power of P max  to parser conversion topology  10   y.    
         [0088]    As seen in  FIG. 6 , the parser conversion system may be in a standby mode (step  600 ) when there is no power output from multi-stage generator  40   y . In standby mode all branches  30  of parser conversion topology  10   y  are disconnected from electrical load  120 , i.e., input switches  90  and output switches  110  are open, and parsers  170  may be pre-configured for a parallel-like arrangement of induction elements  50  (this is a fail-safe configuration that prevents excess voltage application to converters  20  in the event of accidental closing of input switch  90 ). 
         [0089]    An internal diagnostic system check may be performed by a system controller  150 , such as  150   y , to determine if any of the induction elements  50  or branches  30  in the TGC system is malfunctioning (step  603 ). If a malfunctioning induction element  50  or malfunctioning branch  30  is found then it is disabled, by keeping open at all times the associated input switch  90  and output switch  110  (until a suitable time can be found for repair of the malfunctioning part). 
         [0090]    Under control of a system controller  150 , such as  150   y , voltage may be induced in induction elements  50  if there is sufficient fluid flow in turbine  130  to rotate of the shaft of multi-stage generator  40 . System controller  150   y  maintains all branch output switches  110  in an open state (steps  600  and  603 ) until a multi-stage generator  40 , such as  40   y , is capable of producing power exceeding a pre-defined threshold level, P1+ (step  606 ), when a functional branch  30 , for example branch  30   i , may be selected (step  609 ) by system controller  150   y  and the corresponding parser  170   i  is configured for the lowest power level P1, i.e. parser  170   i  is configured for power level range P1− to P2+ (step  612 ). This typically means that parser  170   i  may connect one or more sets of induction elements  50  within stage  60   i  in a series-like arrangement since at low power it is likely that the voltage across individual induction elements is relatively low and placing the elements  50  in series increases the voltage applied to converter  20   i . The corresponding input and output switches  90   i  and  110   i  may then be closed, preferably in that order (step  615 ) and power begins to flow from multi-stage generator  40   y  though the stage  60   i  and branch  30   i  to electrical load  120  (step  618 ). 
         [0091]    As power flows through branch  30   i  (step  618 ), system controller  150   y  monitors the output power level of multi-stage generator  40   y  (step  621 ), and if the power level is between P1− and P2+, then system controller  150   y  retains the power flow through branch  30   i  (step  618 ). 
         [0092]    If (at step  621 ) the power level drops below P1−, the system returns to standby mode (step  600 ), meaning that power flow in branch  30   i  may be reduced to zero, and switches  110   i  and  90   i , may be opened, preferably in that order. Note that in general it may be possible for system controller  150   y  to return the system to standby from other steps such as but not restricted to steps  648  or  679 . 
         [0093]    If (at step  621 ) the power level exceeds P2+, another functional branch that is not currently active, for example branch  30   j , is selected (step  624 ) and its parser  170   j  configured for power level range P2− to P3+ (step  627 ). Then switches  90   j  and  110   j  may be closed (step  630 ). Power flow may be transferred out of branch  30   i  by system controller  150   y  to branch  30   j  (step  633 ) temporarily, so that switches  110   i  and  90   i  may be opened if necessary (step  636 ), and system controller  150   y  may now configure parser  170   i  for the next higher power range P2− to P3+ (step  639 ). Input and output switches  90   j  and  110   j  may be then closed (step  642 ), and power is controlled by system controller  150   y  to flow though both branches  30   i  and  30   j  (step  645 ). The above steps (and those discussed below) may be performed by system controller  150 , such as  150   y , in such a way that there is no interruption of power delivery to electrical load  120 . 
         [0094]    As power flows through branches  30   i  and  30   j  (step  645 ), system controller  150   y  monitors the output power level of multi-stage generator  40   y  (step  648 ), and if the power level is between P2− and P3+, then the system controller  150   y  retains the power flow through branches  30   i  and  30   j  (step  645 ). 
         [0095]    If (at step  648 ) the power level drops below P2−, the controller returns power flow in parser conversion topology  10   y  to branch  30   i  possibly using the following sequence of steps. All power is transferred temporarily from branch  30   i  to  30   j  (step  651 ). Switches  110   i  and  90   i  are opened (step  653 ). Parser  170   i  is reconfigured for power level range P1− to P2+ (step  655 ). Switches  90   i  and  110   i  are closed (step  657 ). All power is transferred from branch  30   j  to  30   i  (step  659 ). Switches  110   j  and  90   j  are opened (step  661 ), and power now flows through branch  30   i  (step  618 ). 
         [0096]    If (at step  648 ) the power level exceeds P3+, another functional branch, for example branch  30   k , may be selected (step  663 ) and parser  170   k  configured for power level range P3− to P max  (step  665 ). Then switches  90   k  and  110   k  are closed (step  667 ). All power flow in branch  30   i  is transferred out of branch  30   i  and into branch  30   j  (step  669 ) temporarily, so that switches  110   i  and  90   i  are opened if necessary (step  671 ), and system controller  150   y  now configures parser  170   i  for the next higher power range P3− to P max  (step  671 ). Input and output switches  90   i  and  110   i  are then be closed (step  671 ), and the power flowing in branch  30   j  is now temporarily transferred from branch  30   j  to  30   i  (step  673 ), so that switches  110   j  and  90   j  may be opened (step  675 ), and system controller  150   y  now configures parser  170   j  for the next higher power range P3− to P max  (step  675 ). Input and output switches  90   i  and  110   i  may then be closed (step  675 ), and after transferring some power to branch  30   j  (from either or both of branches  30   i  and  30   k ), power is controlled by system controller  150   y  to flow though all branches, such as branches  30   i ,  30   j , and  30   k  (step  677 ). 
         [0097]    As power flows through branches  30   i ,  30   j , and  30   k  (step  677 ), system controller  150   y  monitors the output power level of multi-stage generator  40   y  (step  679 ), and if the power level is between P3− and P max , then system controller  150   y  retains the power flow through all branches, such as branches  30   i ,  30   j , and  30   k  (step  677 ). Note that P max  is the rated-power of multi-stage generator  40   y , and hence system controller  150   y  may enter throttling mode when this power level is achieved. 
         [0098]    If (at step  679 ) the power level drops below P3−, system controller  150   y  returns power flow in parser conversion topology  10   y  to branches  30   i  and  30   j  (i.e., deactivating branch  30   k ) possibly using the following sequence of steps. All power is transferred temporarily from branch  30   i  to branches  30   j  and  30   k  (preferably with equal power levels in branches  30   j  and  30   k ) (step  681 ). With no power in branch  30   i , switches  90   i  and  110   i  are opened if necessary (step  683 ) and parser  170   i  reconfigured for power level range P2− to P3+ (step  683 ). Switches  90   i  and  110   i  are then closed (step  683 ). All power in branch  30   j  is then transferred from branch  30   j  to branch  30   i  (step  685 ). With no power in branch  30   j , switches  90   j  and  110   j  are opened if necessary (step  687 ) and parser  170   j  reconfigured for power level range P2− to P3+ (step  687 ). Switches  90   j  and  110   j  are then closed (step  687 ). Power may then be transferred out of branch  30   k , possibly to branch  30   j  (step  689 ), so that power flow in branches  30   i  and  30   j  is approximately equal and switches  110   k  and  90   k  are opened (step  691 ), and power now flows through branches  30   i  and  30   j  (step  645 ). 
         [0099]    If (at step  679 ) or for that matter at other steps, including but not restricted to steps  621  and  648 , an emergency condition arises, it may be necessary for system controller  150   y  to shut down operation of the TGC system by setting power flow through the TGC system to zero and preferably stopping rotation of turbine  130  (step  693 ). 
         [0100]    For the illustrated parser conversion system embodiment, the activation or deactivation of a branch may be initiated when a power threshold is crossed, however, system controller  150   y  may alternatively initiate the activation or deactivation of a branch  30  using other system variables such as, but not restricted to: the speed of fluid flowing in or around turbine  130 ; the rotational speed of turbine  130 ; the rotational speed of a multi-stage generator  40   y ; the output voltage of stages  60  as may be measured at a terminal-block  80  or directly across one or more induction elements  50  of a multi-stage generator  40 ; and/or the input voltage to parser conversion topology  10   y.    
         [0101]    The above discussed principles of operation for a parser conversion system may be extended (or simplified) to the case where there are more than (or fewer than) three branches. In general, there may be any practical number of branches  30  within a parser conversion topology  10   y.    
       Alternative Parser Conversion System and its Variations 
       [0102]    An issue with a parser conversion system is that at a low power level (at or near P1 for example), it may be difficult to maintain high efficiency of the one branch  30  in operation. At a loss of some modularity, this issue may be remedied by allowing one branch  30  to fork into two sub-branches, each sub-branch having a converter and/or an optional transformer. Thus, at low power operation (at or near P1 for example), the sub-branch with the lowest power rating, which has been designed for high efficiency at that lower power level, may be the only branch activated. In this embodiment, one stage, such as stage  60   i , could have two branches, branch  30   i   1  and branch  30   i   2 , as shown in  FIG. 10 , with the provision that branch  30   i   2  may have a higher rated-power specification than that of branch  30   i   1 . It may be reasonable to set the rated-power of branch  30   i   2  to be equal to the remaining branches  30 , such as branch  30   j , branch  30   k  etc, which are configured as shown in  FIG. 4 . By having a designated low power branch fork into two or more sub-branches, as shown in  FIG. 10 , it may be possible to employ less complex parsers for the remaining branches, i.e., parsers  170   j ,  170   k , etc., may have a simpler structure than parser  170   i.    
         [0103]    A variation of this embodiment is that the forking of a branch  30  may take place at the output of the converter. For example, as seen in  FIG. 11 , branch  30   i  could have input switch  90   i  followed by (i.e. in series with) converter  20   i , following which is the fork with optional multi-pole switch  180   i   1  in a fork prong connected to lower power transformer  100   i   1 , and optional multi-pole switch  180   i   2  connected to higher power transformer  100   i   2  on the other prong. 
         [0104]    Another variation in the forking embodiment is that there may be three or more sub-branches, for example  30   i   1 ,  30   i   2 ,  30   i   3 , etc., or in the case of the fork taking place following a converter, three or more sub-transformers, for example  100   i   1 ,  100   i   2 ,  100   i   3 , etc. Also, there is the possibility that more than one stage  60  may employ forked branches or forked transformers. 
       Hybrid Conversion System 
       [0105]    The above discussed embodiment of a parser conversion system, and its forked-branch variations, has the advantage of permitting the design of a multi-stage generator  40 , such as  40   y , that has almost, if not all, 100% machine utilization at rated power. However the design of parser  170  for some or all of stages  60  may require a large number of switches within the parser, and this may add to the construction cost of parser conversion topology  10   y , and may also reduce the reliability of the parser conversion system. 
         [0106]    The hybrid power conversion system discussed below is an embodiment of a power conversion system for a turbine driven multi-stage electrical generator. With this embodiment, very high machine utilization may be achievable for a multi-stage generator  40 , and with significantly simplified parsers  190  (as seen in  FIG. 7 ) by comparison to parsers  170  of the parser conversion system. 
         [0107]    The complexity of a parser  190  may be significantly less than that of a parser  170  because each parser  190  may need only arrange sets of partially hardwired induction elements  50  in perhaps just two or three possible arrangements (each arrangement corresponding to a power range of multi-stage generator  40   z ) instead of a potentially much larger number of arrangements as may be the case for a parser  170  of the parser conversion system. For example consider that there may be N induction elements  50  in one set of induction elements of one phase of stage  60 , then it is reasonable to construct a parser  170  for parser conversion topology  10   y  that has up to 3(N−1) switches for that set of induction elements. However the parsers  190 , of the hybrid power conversion topology  10   z , may contain as few as just three switches for the same set of N induction elements. Note that for either parser  170  or parser  190 , each switch therein may require that electrical current be capable of flowing in either direction through the switch, which would then be a requirement of the physical realization of the switches in the construction of the parser. 
         [0108]    As seen in  FIG. 7 , hybrid conversion topology  10   z  includes one or more branches  30 . Each branch  30  may include a parser  190  if needed, an input switch  90  if needed, a converter  20 , an optional transformer  100 , and an output switch  110 , all connected in series. The output switch  110  from each branch  30  is connected to electrical load  120 , which may be an electric utility power grid. A key concept of hybrid conversion topology  10   z , is that a given stage  60  of multi-stage generator  40   z  may be partially hardwired so that the stage may deliver power over more than one power range but not necessarily over the entire power range of the multi-stage generator  40   z  (for example stage  60   i  may operate over power range P1− to P2+ as well as power range P2− to P3+ but perhaps not power range P3− to P max ), thus two or more stages  60  may be delivering power simultaneously through two or more corresponding branches  30  of hybrid conversion topology  10   z . The intention with this hybrid power conversion system embodiment is that when the TGC system is operating at its rated-power with multi-stage generator  40   z  operating at its rated-power, P max , multiple high-power stages  60  (each containing a large number of induction elements  50 ) are actively delivering power, and hence the high machine utilization of multi-stage generator  40   z.    
         [0109]      FIG. 8  is an illustration of a partially hardwired multi-stage generator  40   z . The partial hardwiring of induction element terminals  70  may be done within the casing of multi-stage generator  40   z , or external to the casing. Alternatively, no casing is needed and terminals  70  may be within multi-stage generator  40  or external to multi-stage generator  40 . As an example of partial hardwiring, it can be seen in  FIG. 8  that in low power stages such as  60   i , many induction elements  50  may be hardwired in a series-like manner. Thus, as power increases from multi-stage generator  40   z , parser  190   i  may have the relatively simple task, under control of system controller  150   z , of connecting two (or more) subsets of induction elements  50  (two subsets are illustrated within stage  60   i  in  FIG. 8 ) in an extended series arrangement at the lower power levels, or the induction element subsets may be arranged in more parallel-like arrangements as the power increases from multi-stage generator  40   z . Such reconfiguring of induction elements may be done to maintain the voltage to a converter  20 , such as  20   i , within a restricted range. Similarly, for higher power stages, such as stage  60   j , it may be desirable to have subsets of induction elements  50  partially hardwired (in  FIG. 8  this is illustrated by a parallel arrangement within each subset) and parser  190   j  has the task, under control of system controller  150   z , of connecting two (or more) subsets of induction elements  50  (two subsets are illustrated within stage  60   j  in  FIG. 8 ) in a series arrangement, or the subsets may be arranged in a more parallel-like arrangement as power increases from multi-stage generator  40   z , to maintain the voltage to converter  20   j  within a restricted range. Note that the hardwired connections shown in  FIG. 8  are purely illustrative, and in general there may be any practical number of induction elements  50  within a stage  60 , possibly in poly-phase arrangements, and a variety of series, parallel, or mixed series-parallel connections are possible. 
         [0110]    For hybrid conversion topology  10   z , in a similar fashion as the bank of converters topology  10   x , the power rating of converter  20  and/or transformer  100  may increase geometrically from one stage  60  to the next, so that if at first stage  60   i  a relatively low power converter  20   i  is required, the next stage  60   j  may require a significantly higher power converter  20   j , etc. For multi-stage generator  40   z , it is possible for stage  60   j  to contain many more induction elements  50  than that of stage  60   i , and similarly stage  60   k  might have many more induction elements than stage  60   j . The power rating for converters  20  and transformers  100  within a hybrid conversion topology  10   z  may be higher than in the case of the bank of converters topology  10   x , but there may be fewer branches in the hybrid conversion topology  10   z  given a specified power of the multi-stage generator  40 . A parser  190  may not be needed for the highest power stage  60 , such as  60   k ; a set of induction elements  50  of the highest power stage  60 , such as  60   k , may be connected in a hardwired manner, for example all induction elements  50  within one set of induction elements  50  for one phase of stage  60   k  may be hardwired in parallel as illustrated in  FIG. 8 . 
         [0111]      FIG. 9  is a flowchart showing an embodiment of a control process by which system controller  150   z  may control hybrid conversion topology  10   z  to transform the electric power produced by multi-stage generator  10   z  into a useable form for electrical load  120 . System controller  150   z , or its delegated sub-controller, makes decisions and executes tasks as outlined in the flowchart shown in  FIG. 9 . The illustrated control process generally seeks maximum energy capture mode and includes throttling of hybrid conversion topology  10   z  when multi-stage generator  40   z  is delivering its rated-power of P max  to hybrid conversion topology  10   z.    
         [0112]    As seen in  FIG. 9 , the hybrid conversion system begins in a standby mode (step  900 ) when there is no power output from the multi-stage generator  40   z . In standby mode all branches  30  of hybrid conversion topology  10   z  are disconnected from electrical load  120 , i.e. input switches  90  and output switches  110  are all open, and any parsers  190  are pre-configured for a parallel arrangement of sub-sets of induction elements  50  (this is a fail-safe configuration that prevents excess voltage application to converters  20  in the event of accidental closing of input switch  90 ). 
         [0113]    An internal system check may be done to determine if any of the induction elements  50  or branches  30  in the TGC system is malfunctioning. If a malfunctioning induction element  50  or branch  30  is found, it is disabled by keeping open at all times associated input switch  90  and output switch  110 , and the induction element  50  or branch  30  is not used during power delivery (until a suitable time can be found for repair of the malfunctioning part). 
         [0114]    Under control of system controller  150   z  voltage is induced in induction elements  50  if there is sufficient fluid flow in turbine  130  to rotate of the shaft of multi-stage generator  40   z . System controller  150   z  maintains all branch input switches  90  open and/or all branch output switches  110  open (step  900 ) until multi-stage generator  40   z  produces power exceeding pre-defined threshold level, P1+ (step  903 ), when parser  190   i  is configured for the lowest power level P1, i.e. parser  190   i  is configured for power level range P1− to P2+ (step  906 ). Therefore parser  190   i  may connect one or more sub-sets of induction elements  50  within stage  60   i  in a series-like arrangement. The corresponding input and output switches  90   i  and  110   i  then are closed, preferably in that order (step  909 ) and power begins to flow from multi-stage generator  40   z  though the stage  60   i  and branch  30   i  to electrical load  120  (step  912 ). 
         [0115]    As power flows through branch  30   i  (step  912 ), system controller  150   z  monitors the output power level of multi-stage generator  40   z  (step  915 ), and if the power level is between P1− and P2+, then the system controller  150   z  retains the power flow through branch  30   i  (step  912 ). 
         [0116]    If (at step  915 ) the power level drops below P1−, the system returns to standby mode (step  900 ), meaning that power flow in branch  30   i  is reduced to zero and switches  110   i  and  90   i  are opened, preferably in that order. Note that in general it may be possible for system controller  150   z  to return the system to standby from other steps such as, but not restricted to, steps  939  or  978 . 
         [0117]    If (at step  915 ) the power level exceeds P2+, parser  190   j  is configured for power level range P2− to P3+ (step  918 ). Then switches  90   j  and  110   j  are closed (step  921 ). Power flow is transferred out of branch  30   i  by system controller  150   z  to branch  30   j  (step  924 ) temporarily, so that switches  110   i  and  90   i  are opened if necessary (step  927 ), and system controller  150   z  now configures parser  190   i  for the next higher power range P2− to P3+ (step  930 ). Input and output switches  90   i  and  110   i  are then closed (step  933 ), and power is controlled by system controller  150   z  to flow though both branches  30   i  and  30   j  (step  936 ), possibly with approximately equal power in each branch. All the above steps (and those discussed below) may be conducted by system controller  150   z  so that there is no interruption of power delivery to electrical load  120 . 
         [0118]    As power flows through branches  30   i  and  30   j  (step  936 ), system controller  150   z  monitors the output power level of multi-stage generator  40   z  (step  939 ), and if the power level is between P2− and P3+, then the system controller  150   z  retains the power flow through branches  30   i  and  30   j  (step  936 ). 
         [0119]    If (at step  939 ) the power level drops below P2−, then system controller  150   z  returns power flow in hybrid conversion topology  10   z  to branch  30   i  possibly using the following sequence of steps. All power is transferred temporarily from branch  30   i  to  30   j  (step  942 ). Switches  110   i  and  90   i  are opened (step  945 ). Parser  190   i  is reconfigured for power level range P1− to P2+ (step  948 ). Switches  90   i  and  110   i  are closed (step  951 ). All power is transferred from branch  30   j  to branch  30   i  (step  954 ). Switches  110   j  and  90   j  are opened (step  957 ), and power now flows through branch  30   i  (step  912 ). 
         [0120]    If (at step  939 ) the power level exceeds P3+, switches  90   j  and  110   j  are closed (step  960 ). Power flow may be transferred out of branches  30   i  and  30   j  by system controller  150   z  to branch  30   k  (step  963 ) temporarily, so that switches  110   j  and  90   j  are opened if necessary (step  966 ), and system controller  150   z  now configures parser  190   j  for the next higher power range P3− to P max  (step  969 ). Input and output switches  90   j  and  110   j  are then closed (step  972 ), and power is controlled by system controller  150   z  to flow though branches  30   j  and  30   k  (step  975 ), possibly with approximately equal power in each branch. 
         [0121]    As power flows through branches  30   j  and  30   k  (step  975 ), system controller  150   z  monitors the output power level of multi-stage generator  40   z  (step  978 ), and if the power level is between P3− and P max , then system controller  150   z  retains the power flow through branches  30   j  and  30   k  (step  975 ). Note that P max  is the rated-power of multi-stage generator  40   z , and hence system controller  150   z  may enter throttling mode when this power level is achieved. 
         [0122]    If (at step  978 ) the power level drops below P3−, the controller returns power flow in hybrid conversion topology  10   z  to branches  30   i  and  30   j  possibly using the following sequence of steps. All power is transferred temporarily from branch  30   j  to  30   k  (step  981 ). Switches  110   j  and  90   j  are opened (step  984 ). Parsers  190   j  and  190   i  are reconfigured for power level range P2− to P3+ (step  987 ). Switches  90   j  and  110   j  are closed (if desirable, some power transfer into branch  30   j  may begin at this time) and also switches  90   i  and  110   i  are closed (step  990 ). All power is transferred from branch  30   k  to branches  30   j  and  30   i  (step  993 ). Switches  110   k  and  90   k  are opened (step  996 ), and power now flows through branches  30   i  and  30   j  (step  936 ). Note there may be variations in how system controller accomplishes this transfer of power to branches  30   i  and  30   j , for example power transfer from branch  30   k  to branch  30   i  may take place first, followed by a transfer of power from branch  30   k  to branch  30   j.    
         [0123]    If (at step  978 ) or for that matter at other steps, including, but not restricted to, steps  915  and  939 , an emergency condition arises, it may be necessary for system controller  150   z  to shut down operation of the TGC system by setting power flow through the TGC system to zero and preferably stopping rotation of turbine  130  (step  998 ). 
         [0124]    For the illustrated hybrid conversion system embodiment, the activation or deactivation of a branch may be initiated when a power threshold is crossed, however, system controller  150   z  may alternatively initiate the activation or deactivation of a branch  30  using other system variables such as, but not restricted to: the speed of fluid flowing in or around turbine  130 ; the rotational speed of turbine  130 ; the rotational speed of a multi-stage generator  40   z ; the output voltage of stages  60  as may be measured at a terminal-block  80  or directly across one or more induction elements  50  of a multi-stage generator  40 ; and/or the input voltage to hybrid conversion topology  10   z.    
         [0125]    The above discussed principles of operation for a hybrid conversion system may be extended (or simplified) to cases where there are more than (or fewer than) three branches. In general, there may be any number of branches  30  within a hybrid conversion topology  10   z . Note, for the hybrid conversion system, that there is no theoretical restriction on the number stages  60  of multi-stage machine  40   z , and no theoretical restriction on the number of branches  30  of hybrid conversion topology  10   z , that may be active and delivering power. As an example, consider the situation illustrated in  FIG. 7 , if it is desirable that branches  30   i ,  30   j ,  30   k  are all delivering power to electrical load  120  when multi-stage generator  40   z  is operating at a power between P2− and P max , and parser  190   j  is configured for that power range as discussed above, but in addition, parser  190   i  may reconfigured the arrangement of induction elements  50  within stage  60   i  for power range P2− to P max . This means that the partial hardwiring of stage  60   i  and the design of parser  190   i  both accommodate this possibility. 
       Variations of the Hybrid Conversion System 
       [0126]    An issue with a hybrid conversion system is that the stages  60  and branches  30  designed for the lower power ranges, for example stage  60   i  and branch  30   i , are each inherently less efficient in power transformation than the higher power stages and branches. Thus, the advantage of using parser  190   i  to extend the power range over which stage  60   i  and branch  30   i  may operate is compromised, particularly at the lowest power levels, such as P1− or P1+. For example, in the above discussion of the hybrid conversion system, referring to  FIG. 9 , stage  60   i  and branch  30   i  may be designed to operate over power range P1− to P2+ as well as over range P2− to P3+, thus at power level P1−, the efficiency of stage  60   i  and/or branch  30   i  may be poor. 
         [0127]    To overcome the efficiency degradation at lower power levels, a variation of the hybrid conversion system may employ no parser within the lowest power branch(es)  30  of the hybrid conversion topology. For example, a hybrid conversion topology that includes three branches may be constructed such that branch  30   i  may be structured as shown in  FIG. 1  and branches  30   j  and  30   k  may be structured as shown in  FIG. 7 . Thus stage  60   i  and branch  30   i  of this hybrid conversion topology may operate only over power range P1− to P2+ and will likely be much more efficient than the stage  60   i  and branch  30   i  pair of  FIG. 7  designed to operate over power range P1− to P3+. With this variation of the hybrid conversion system there is, once again, no theoretical restriction on the number of stages or the number of branches. 
         [0128]    Another variation of the hybrid conversion system is to employ forked branches for one or more stages  60 . For example, an embodiment may have a hybrid conversion topology with four branches:  30   h ,  30   i ,  30   j , and  30   k . Branch  30   h , the lowest power branch, may be structured to have no parser. Branch  30   i  may be forked with two sub-branches, sub-branch  30   i   1  and sub-branch  30   i   2 . Branches  30   j  and  30   k  may be structured as in  FIG. 7 . An example of this variation of the hybrid conversion system is shown in  FIG. 12 . In this embodiment, when the multi-stage generator  40  is operating within its highest power range, up to and including rated-power P max , sub-branch  30   i   2 , branch  30   j  and branch  30   k  may all be active and delivering power to electrical load  120 . In this variation of the hybrid conversion system there is, once again, no theoretical restriction on the number of stages or the number of branches. 
         [0129]    The various embodiments described above can be combined to provide further embodiments. All of the commonly assigned US patent application publications, U.S. patent applications, foreign patents, and foreign patent applications referred to in this specification and/or listed in the Application Data Sheet, including but not limited to U.S. application Ser. No. 13/062,191, filed Jun. 17, 2011; PCT application Serial No. PCT/CA2009/001233, filed Sep. 3, 2009; and U.S. provisional patent application Ser. No. 61/094,007, filed Sep. 3, 2008 are incorporated herein by reference, in their entirety. These and other changes can be made to the embodiments in light of the above-detailed description. In general, in the following claims, the terms used should not be construed to limit the claims to the specific embodiments disclosed in the specification and the claims, but should be construed to include all possible embodiments along with the full scope of equivalents to which such claims are entitled. Accordingly, the claims are not limited by the disclosure. 
         [0130]    Specific embodiments have been shown and described herein. However, modifications and variations may occur to those skilled in the art. All such modifications and variations are believed to be within the scope and sphere of the present invention.