Automatic voltage regulator for generator

Abstract

A voltage regulator for a generator driven by an engine has a sampling system to sample an operating frequency of an alternating current at an electrical output of the generator. The detection system is configured to monitor an operating frequency of the generator. The excitation system is configured to vary an excitation voltage or an excitation current of a field winding of an alternator of the engine when an operating frequency of the generator indicates that a load shock exists at an electrical output of the generator. The excitation system then controls the excitation voltage or the excitation current as needed in response to the load shock such that variations in the operating frequency are minimized.

Description

BACKGROUND OF THE INVENTION

[0001] The present disclosure generally relates to generators driven by internal combustion engines and, more particularly, to automatic voltage regulators for such generators.

[0002] Generators driven by internal combustion engines utilize active voltage regulators to control the excitation voltage of the alternator, which in turn affects the voltage and frequency of the electrical output and the speed of the engine. In many implementations, the automatic voltage regulators are configured to implement only basic control strategies and cannot respond quickly to changes in the electrical load. These automatic voltage regulators suffer from poor frequency and voltage control, overly wide frequency and voltage swings, and long response times before reaching stability.

[0003] There is a desire to improve to minimize variations in the frequency and voltage of the electrical output, improve the stability of the electrical output, and reduce the response time to changes in the electrical load to a minimum. SUMMARY OF THE INVENTION

[0004] The present application discloses a generator driven by an engine, the generator having an internal combustion engine, an alternator, and a voltage regulator. The internal combustion engine has a crankshaft. The alternator has a rotor operatively coupled to the crankshaft. The alternator is configured to deliver power at an electrical output. The voltage regulator is configured to regulate the excitation voltage applied to the field winding of the alternator. The voltage regulator has a sampling system, a detection system, and an excitation system. The sampling system samples the operating frequency of the alternating current at the electrical output. The detection system is configured to calculate the second derivative of the operating frequency. The excitation system is configured to change either the excitation voltage or the excitation current in response to the second derivative of the operating frequency indicating a load shock.

[0005] The present application also discloses a method of operating a generator. In step a), the engine of the generator is operated at an operating frequency. In step b), the operating frequency is sampled and the second derivative of the operating frequency is calculated. In step c), a load shock is detected when the second derivative of the operating frequency has a magnitude or slope exceeding a threshold. In step d), the excitation current or the excitation voltage of the alternator of the generator is changed in response to the detected load shock.

[0006] The present application also discloses a method of operating a generator. In step a), the engine of the generator is operated at an operating frequency. In step b), the operating frequency is sampled to detect a load shock. In step c), the magnitude of the load shock is calculated using at least in part the operating frequency, the inertia of the rotating components of the generator, and the rated power output of the generator. In step d), the excitation voltage or the excitation current of the alternator of the generator is changed in response to the magnitude of the load shock.

[0007] From the detailed description provided below, other applicable scopes of the present invention become clear. It should be understood that the detailed description and specific examples, while indicating preferred embodiments of the present invention, are for illustrative purposes only and not for limiting the scope of the present invention. BRIEF DESCRIPTION OF THE DRAWINGS

[0008] The present invention will be more fully understood from the detailed description and the drawings, in which like elements are denoted with like reference numerals, and in which:

[0009] Figure 1 is a side view of a generator according to the present disclosure;

[0010] Figure 2 is a schematic diagram of the generator;

[0011] Figure 3 is a graph of the operating frequency of the generator during a load impact equal to 50% of the rated load;

[0012] Figure 4 is a simplified graph of the operating frequency during a load impact;

[0013] Figure 5 is a simplified graph of the second derivative of the operating frequency;

[0014] Figure 6 is a graph of the operating frequency of the generator during a load impact equal to 25% of the rated load;

[0015] Figure 7 is a simplified graph of the operating frequency during two load impacts;

[0016] Figure 8 is a simplified graph of the second derivative of the operating frequency;

[0017] Figure 9 is a graph of the operating frequency for detecting a load impact;

[0018] Figure 10 is a graph of the second derivative of the operating frequency for detecting a load impact;

[0019] Figure 11 is a table showing the reaction time compared to the sampling time when the load impact is 50%;

[0020] Figure 12 is a graph showing the relationship between the peak acceleration and the normalized load impact for a first model of generator;

[0021] Figure 13 is a graph showing the relationship between the peak acceleration and the normalized load impact for a second model of generator;

[0022] Figure 14 is a graph showing the relationship between the inertia of the generator and the peak acceleration;

[0023] Figure 15 is a graph showing the operating frequency when it recovers from the minimum frequency to the target frequency during the second stage;

[0024] Figure 16 is a graph showing the second derivative of the operating frequency from the minimum frequency to the target frequency during the second stage;

[0025] Figure 17 is a graph showing the operating frequency when it recovers from the minimum frequency to the target frequency during the third stage;

[0026] Figure 18 is a graph showing the second derivative of the operating frequency from the minimum frequency to the target frequency during the third stage; and

[0027] Figure 19 is a block diagram showing a method of operating a generator.

[0028] All the drawings are schematic diagrams and do not need to be to scale. Unless otherwise specified herein, features that are numbered in some drawings and may not be numbered in other drawings are the same features. Detailed Description

[0029] The features and advantages of the present invention are illustrated and described herein by way of non-limiting examples in which various aspects of the present disclosure may be embodied. The description of these examples should be read in conjunction with the accompanying drawings or photographs, which are considered to be a part of the entire written specification. Accordingly, the present disclosure should not be construed as being explicitly limited to examples that illustrate some non-limiting combinations of possible features that may exist alone or in other combinations of the features disclosed herein.

[0030] In the description of the examples disclosed herein, any reference to direction or orientation is for convenience of description only and does not limit the scope of the invention in any way. Relative terms such as "lower", "upper", "horizontal", "vertical", "above", "below", "on", "under", "top" and "bottom" and their derivatives (e.g., "horizontally", "downwardly", "upwardly", etc.) should be construed to refer to the direction described or shown in the figure being discussed at that time. These relative terms are for descriptive convenience only and do not require the device to be constructed or operated in a particular orientation. Unless otherwise expressly stated, terms such as "attached", "affixed", "connected", "coupled", "interconnected", etc. refer to a relationship in which structures are directly or indirectly fixed or attached to each other through an intermediate structure and a movable or rigid attachment or relationship.

[0031] As used throughout, any range disclosed herein is used as a shorthand for each value within the range. Any value within the range can be selected as the terminus of the range.

[0032] Figure 1 Side view showing a generator 10 driven by an internal combustion engine. Figure 2 Is a schematic view of the generator 10. The generator 10 has an engine 100 and an alternator 200. The engine 100 can be an internal combustion engine (e.g., a compression ignition engine operating on diesel fuel or a spark ignition engine operating on a fuel (e.g., natural gas, propane, gasoline or any other internal combustion fuel)). The engine 100 has a crankshaft 110 that transmits mechanical power to the alternator 200, and the crankshaft 110 forms part of a rotating assembly. The engine 100 is operated by an engine controller 120 that controls parameters (e.g., fuel flow rate, ignition timing, throttle opening, and other parameters that can be controlled to deliver the required mechanical power via the crankshaft 110).

[0033] The alternator 200 can be configured to generate alternating current for supplying one or more electrical loads at an electrical output 221 that includes at least one line output 222 and at least one neutral 224. In some configurations, the alternator 200 can be configured to have multiple line outputs 222 to deliver polyphase power from the electrical output 221. In these configurations, the neutral 224 can be omitted in certain configurations (i.e., in a delta configuration). In other configurations, the alternator 200 can be configured to have one or two line outputs 222 to deliver single-phase power from the electrical output 221. The alternator 200 can operate at a working frequency that can vary depending on the type of load connected to the alternator 200. For example, the alternator 200 can operate at various different frequencies and voltages to simulate grid power.

[0034] In one implementation, the alternator 200 can be configured to deliver alternating current with a nominal voltage of 120 volts and 240 volts in a single-phase configuration at a target frequency of 60 Hz. In other implementations, the alternator 200 can be configured to deliver alternating current at a target frequency of 60 Hz in a three-phase configuration at a nominal voltage of 208 volts, 240 volts, or 480 volts. In yet another implementation, the alternator 200 can be configured to deliver alternating current at a target frequency of 60 Hz in a three-phase configuration at a nominal voltage of 220 volts, 240 volts, 380 volts, or 415 volts.

[0035] The alternator 200 has a rotor 210 operably coupled to the crankshaft 110. The rotor 210 is preferably directly coupled to the crankshaft 110 such that for each rotation of the crankshaft 110, the rotor 210 rotates once. However, in other implementations, the rotor 210 can be coupled to the crankshaft 110 to allow the rotor 210 to accelerate or decelerate relative to the crankshaft 110. This can be accomplished by various known reduction techniques. In a further implementation, a clutch can be included between the crankshaft 110 and the rotor 210. The rotor 210, in combination with the crankshaft 110 and other rotating components, forms a rotating assembly.

[0036] The rotor 210 rotates relative to the stator 220 to generate electrical power, which is delivered via the electrical output 221 to one or more loads 300. The rotor 210 includes a field winding that generates a magnetic field, which induces a current in the stator windings in the stator 220. In an alternative implementation, the stator windings can replace the windings on the rotor 210 such that the field winding is located on the stator 220 and the windings on the rotor 210 supply power to the electrical output 221. In other words, the field winding can be located on the stator 220 and the power delivery windings can be located on the rotor 210. The present invention is not intended to be limited to the specific arrangement of the alternator 200 and can be applied to any alternator 200 that includes a field winding, regardless of whether the field winding is located on the rotor 210 or on the stator 220. In fact, as long as the power output of the alternator 200 can be controlled by adjusting the current or voltage, other configurations of the alternator 200 can be envisioned. Optionally, the alternator 200 can have a controller 230 for controlling the internal functions of the alternator 200, such as diagnostics, reporting, monitoring, and other features.

[0037] The generator 10 further includes a voltage regulator 250. In some implementations, the voltage regulator 250 may be included in the controller 230, or the voltage regulator 250 may form part of the alternator 200 and may be an addition to the controller 230. In other implementations, the controller 230 may be omitted and the voltage regulator 250 may be a separate component located external to the alternator 200. In yet other implementations, the voltage regulator 250 and the controller 230 may be separate components, where the voltage regulator 250 is located either external or internal to the alternator 200. It can be seen that the exact arrangement of the voltage regulator 250 may vary with respect to the alternator 200. For the sake of discussion, the voltage regulator 250 has been illustrated as a component separate from the alternator 200.

[0038] The voltage regulator 250 has a sampling system 260, a detection system 270, and an excitation system 280. The sampling system 260 samples the operating frequency of the alternating current at the electrical output 221 using a sensing connection 262. The sensing connection 262 may be an electrical connection to each of the line output 222 and the neutral line 224, enabling the frequency of the alternating current at the electrical output 221 to be sensed. In other implementations, the sensing connection 262 may be exclusively connected to the line output 222 or only connected to a portion of the line output 222 and / or the neutral line 224. The sampling system 260 has a circuit capable of sampling the operating frequency of the alternator 200 via the alternating current at the electrical output 221. The sampling system 260 may include a voltage sensor, a current sensor, or other devices suitable for monitoring the frequency of the electrical output 221. In other implementations, the sampling system 260 may utilize an encoder or other devices and may directly monitor the frequency of the rotor 210 instead of monitoring the electrical output 221. The sampling system 260 may be implemented using analog circuitry, digital circuitry, or a combination of both. It is contemplated that the functions of the sampling system 260 may be implemented using a processor and memory in combination with various sensing circuits.

[0039] The detection system 270 is configured to utilize the sampled data from the sampling system 260 and perform calculations (e.g., the first and second derivatives of the operating frequency sampled by the sampling system 260). The detection system 270 may also detect the presence of a load impact at the electrical output 221 by performing comparisons and other calculations using data stored in memory or obtained from other sources (e.g., a communication bus including USB, WiFi, Bluetooth, etc.). The functions of the detection system 270 will be discussed in more detail below.

[0040] The excitation system 280 is configured to change the excitation voltage or excitation current in the field winding. Although the voltage regulator 250 mainly regulates the excitation voltage of the field winding in the voltage control mode, the voltage regulator 250 can also operate in a current control mode that controls the current rather than the voltage in the field winding. The current control mode can change the excitation current in the field winding more quickly. Compared with using only the voltage control mode to control the field winding, the current control mode allows for a more rapid change in the power output at the electrical output 221. The excitation system 280 operates in response to a determination made by the detection system 270, effecting a change in the excitation current or excitation voltage to achieve the desired control of the electrical output 221.

[0041] Go to Figure 3 , which shows a graph of the operating frequency of the generator 10. During the period of time shown in the graph, a load shock occurred. It can be seen that the operating frequency of the generator was driven to an operating frequency of approximately 48.9 Hz, and the load shock occurred at approximately 6 seconds. During the load shock, the operating frequency dropped to approximately 46.5 Hz. The load shock from one or more loads 300 caused a decrease in the frequency and voltage at the electrical output 221. Further, the increased electrical load from the load 300 caused the rotating assembly to decelerate. As described above, the rotating assembly includes the rotor 210 and the crankshaft 110. This graph represents the baseline response to a load shock, and this baseline response can be improved using advanced control techniques described in more detail below. This graph represents a load shock of 50% of the rated electrical load of the generator 10. A first generator (referred to as generator A) was used for testing.

[0042] Figure 4 and Figure 5 shows a simplified graph of the operating frequency and the second derivative of the operating frequency, drawn using only straight lines for clarity. As can be seen in Figure 4 , the frequency stabilizes at the target frequency, and the target frequency has been normalized such that the target frequency is shown in 1 pu (“per unit”), and any deviation from the target frequency is greater than or less than 1. In other words, 1 pu is 100% of the target frequency. It can be seen that until the loading time or the time of the load shock, the operating frequency basically matches the target frequency. Immediately following the loading time, the operating frequency drops sharply, and there is a significant change in the slope of the operating frequency at the loading time. As Figure 5 shows, the graph of the second derivative of the operating frequency illustrates a singularity where the value drops sharply from zero. The magnitude or quantity of the second derivative indicates that there is a load shock at the loading time. Alternatively, the slope of the second derivative can indicate that there is a load shock at the loading time.

[0043] Figure 6 shows the same as Figure 4The response of generator 10, which is the same as the generator used in , when subjected to a load shock of 25% of the rated load. Although the operating frequency is initially about 48.9 Hz, it drops to 47.7 Hz and then recovers to about 48.9 Hz. As can be further observed, the minimum frequency at a 25% load shock is greater than the minimum frequency at a 50% load shock. Additionally, the slope of the operating frequency at a 25% load shock is less than the slope of the operating frequency at a 50% load shock.

[0044] Go to Figure 7 and Figure 8 , which illustrates a simplified graph of the operating frequency and the second derivative of the operating frequency, showing two cases of a 25% load shock and a 50% load shock. The 25% load shock is illustrated by a solid line, while the 50% load shock is illustrated by a dashed line. The 25% load shock has a total drop of 1.22 Hz in 0.18 seconds, resulting in a slope of -6.78 Hz / s. The 50% load shock has a total drop of 2.44 Hz in 0.22 seconds, resulting in a slope of -11.07 Hz / s. Therefore, increasing the load shock increases the magnitude of the slope, decreases the minimum frequency, and increases the time to reach the minimum frequency.

[0045] Figure 9 Illustrates the use of the same Figure 3 load shock as Figure 3 when using the same generator 10. However, this data has been filtered using a low-pass filter with a 1 Hz cut-off frequency and 60 dB attenuation. The load shock is 50% of the rated load, and X indicates the point at which the shock is detected using the algorithm described below. Figure 10 Illustrates the filtered second derivative of the operating frequency, again showing X at the maximum negative slope of the second derivative of the operating frequency to indicate the time at which the load shock is detected. X also approximately corresponds to the maximum negative magnitude of the second derivative of the operating frequency.

[0046] The maximum slope or maximum magnitude (in terms of absolute value) of the second derivative of the operating frequency can be used as a trigger to indicate a load shock. In other implementations, a threshold can be used as a trigger to indicate a load shock, where the maximum slope or maximum magnitude exceeding the threshold is used as the trigger. In yet another implementation, a hybrid method can be utilized, where the magnitude or slope must deviate by a given amount before triggering a load shock to minimize the effect of noise. This can be done in addition to the low-pass filter discussed above. Furthermore, it is conceivable that the magnitude or slope can be continuously monitored, excluding local maximum magnitudes or slopes generated by the steady-state operation of the generator, and only using those maximum magnitudes or slopes generated by the load shock as triggers to indicate a load shock. This is possible because the magnitude and slope of the load shock are different from Figure 10Steady-state changes in the second derivative of the illustrated operating frequency. Conventional thresholds can be used to assist in differentiating load shocks from steady-state changes, or other methods (such as learning algorithms, fuzzy logic, etc.) can be implemented. It is even conceivable that history can be recorded and used as a basis for comparison.

[0047] Figure 11 A table showing reaction time versus sampling time is illustrated. The sampling system 250 can operate at various sampling frequencies to sample the operating frequency of the electrical output 221. Sampling times of 30 milliseconds ("ms"), 20 ms, 10 ms, 5 ms, 2 ms, 1 ms, and 0.5 ms are used. The reaction time in milliseconds is recorded as the delay between the moment the load shock occurs and the moment the detection system 270 detects the load shock. In addition, the frequency value at the reaction time and the normalized frequency value expressed in terms of the target frequency are listed in the table. It can be seen that the optimal sampling time is 1 ms. 0.5 ms provides substantially the same reaction time and frequency value at the reaction time, but the additional sampling load does not provide a significant benefit. Thus, while 0.5 ms achieves substantially the same result, 1 ms minimizes the sampling rate while achieving the best result to minimize processing requirements. In each step from 30 ms to 1 ms, the reaction time is improved, but each step increases the processing requirements of the system. Thus, in some implementations, sampling times of 20 ms, 10 ms, 5 ms, 2 ms, 1 ms, or 0.5 ms can be utilized.

[0048] Figure 12 Peak acceleration values plotted on a per-unit basis with respect to load shocks are shown, where 1 pu is equal to the rated electrical output of the generator. Load shocks of many different magnitudes are plotted. The test is again performed on Generator A. It can be seen that the load shocks and the peak acceleration values of the operating frequency (in other words, the second derivative of the operating frequency) essentially follow a linear relationship. The minimum value of the second derivative of the operating value can be very closely related to the magnitude of the load shock, allowing the magnitude of the load shock to be predicted based solely on the second derivative of the operating frequency.

[0049] Figure 13The figure shows the peak acceleration values for load shocks plotted on a per-unit basis. Tests were performed on another generator called Generator B. Many load shocks were plotted for the rated load of the generator, with 1 pu equal to the rated electrical output of the generator. Again, a linear relationship holds between the peak acceleration (or minimum magnitude) of the load and the operating frequency (in other words, the second derivative of the operating frequency). This relationship is independent of the specific model of the generator or engine, allowing the algorithm to be extrapolated to any generator using certain known parameters. It can also be determined that for generators with greater power and inertia, the slope of the linear curve is smaller.

[0050] Figure 14 The figure shows multiple tested generators of different models and rated electrical output powers, where each circle represents a tested generator. The curve shows the peak acceleration with respect to inertia. The inertia of the tested generators was determined from the public specifications provided by their respective manufacturers. An exponential fit can be applied to the curve graph, enabling the relationship between acceleration and inertia to be predicted, thus allowing the above algorithm to be extrapolated to all generators.

[0051] Generator 10 and voltage regulator 250 operate in three different stages to control the output frequency at electrical output 221. In the first stage, the second derivative of the operating frequency as described above is used to detect load shocks. The operating frequency is sampled at a desired frequency and then filtered. The second derivative is taken from the filtered sample data. The resulting second derivative is then monitored to obtain the minimum magnitude indicating a load shock. Then the size of the load can be estimated based on this minimum magnitude and the rated power of generator 10. The minimum magnitude of the second derivative of the operating frequency can characterize different sizes of load shocks for each generator 10. Alternatively, the Figure 14 curve based on generalized data can be used to characterize this minimum magnitude, and this curve is derived from testing load shocks on various other generators.

[0052] It is conceivable that the first stage can operate in various modes. A preset threshold or other detection value can be used based on the calculation of the size of the load shock relative to the rated output of the generator. In other implementations, if the user desires different response behaviors, a custom value of the minimum magnitude or maximum slope of the second derivative of the operating frequency can be applied. In yet another implementation, previous shocks can be saved, and the slope or minimum magnitude of the second derivative can be adjusted to take into account changes in the generator or the aging of the generator. The memory can be reset or cleared by the user.

[0053] Once an impact has been detected, the excitation system 280 of the voltage regulator 250 can operate at one of three selected priorities. The excitation system 280 can be configured to prioritize low voltage drop, low frequency drop, or a compromise between the two. An interpolation table gives the relationship between load and field current and different values for the excitation system 280 depending on which setting is used.

[0054] For example, in the case of selecting low frequency drop, the excitation system 280 will allow the field current to decrease to minimize the load on the engine 100. In the case of selecting low voltage drop, the excitation system 280 will attempt to maintain or increase the field current, but this will result in an increase in the load on the engine 100. The compromise mode will strike a balance between the two, allowing some frequency drop and some voltage drop. In all implementations, the load on the engine 100 will increase, but the relative amount of the load can vary to optimize certain parameters. Further, the improved detection speed will allow changes to be implemented more quickly compared to the case of using other types of voltage regulators 250. Preferably, the excitation system 280 will operate to drive the current in the field winding to a set point rather than control the voltage. While the excitation system 280 controls the voltage in the field winding during steady state operation, current control allows for a faster response and current control is used in the first stage while the operating frequency is still decreasing.

[0055] Figure 15 Illustrates the operating frequency at the electrical output 221 during the second stage of control. Figure 16 Shows the first derivative of the operating frequency during the second stage. During the second stage, the excitation system 280 attempts to minimize the recovery time t recov This is done by estimating the recovery time using the instantaneous slope of the operating frequency. The algorithm attempts to reduce the recovery time t recov to zero by increasing the excitation voltage. The excitation system 280 no longer controls the current in the field winding but switches to voltage control mode. After the excitation voltage is increased, if the engine 100 accelerates, the excitation voltage is further increased. If the engine decelerates, the excitation voltage is decreased or becomes stable. Further, real-time feedback is used to maximize the excitation voltage while ensuring that the engine continues to accelerate back to the target frequency.

[0056] Figure 17 Illustrates the operating frequency at the electrical output 221 during the third stage of control. Figure 18 Shows the first derivative of the operating frequency during the third stage. When the remaining recovery time t recovWhen less than the minimum time, which is selected based on the system's response time, the third stage begins. The third stage aims to avoid overshoot oscillations, so the minimum time is the time required to stabilize the operating frequency. During the third stage, the excitation voltage is reduced to avoid overshoot. It is conceivable that the excitation voltage can immediately return to the stored steady-state voltage value, or the excitation voltage can be gradually reduced until the operating frequency stops accelerating, thus allowing it to stabilize at the target frequency.

[0057] Figure 19 is a block diagram illustrating a method of operating a generator 10. In a first step, an engine 100 operates at an operating frequency substantially equal to a target frequency. The engine 100 has a crankshaft 110 that forms part of the rotating assembly of the generator 10. The engine 100 is operably coupled to an alternator 200 that has a rotor 210 coupled to the crankshaft 110, and the rotor 210 forms another part of the rotating assembly of the generator 10. A voltage regulator 250 samples the operating frequency at the electrical output 221 of the alternator 200. A load shock is detected by monitoring a minimum magnitude or minimum slope of the second derivative of the operating frequency. Optionally, a load shock can be detected when the minimum magnitude or minimum slope exceeds a threshold.

[0058] After detecting a load shock, the magnitude of the load shock, which is a percentage of the rated load of the generator 10, is calculated. The magnitude of the load shock is calculated using the rated load of the generator 10 and the inertia of the rotating assembly of the generator 10. Then, the magnitude of the load is used to change the excitation voltage or excitation current applied to the field winding of the alternator 200. In some implementations, the excitation current is changed in a first stage, and subsequently the excitation voltage is controlled in second and third stages.

[0059] Exemplary claim set

[0060] Exemplary claim 1. An engine-driven generator, comprising: an internal combustion engine, the internal combustion engine including: a crankshaft; an alternator, the alternator including a rotor operably coupled to the crankshaft, the alternator configured to deliver electrical power at an electrical output; and a voltage regulator, the voltage regulator configured to regulate an excitation voltage applied to a field winding of the alternator, the voltage regulator including: a sampling system that samples an operating frequency of an alternating current at the electrical output; a detection system configured to calculate a second derivative of the operating frequency; and an excitation system configured to change one of the excitation voltage or the excitation current in response to the second derivative of the operating frequency indicating a load shock.

[0061] Exemplary Claim 2. The engine-driven generator according to Exemplary Claim 1, wherein the second derivative of the operating frequency indicates the load impact when the magnitude or slope of the second derivative of the operating frequency exceeds a threshold.

[0062] Exemplary Claim 3. The engine-driven generator according to Exemplary Claim 1 or Exemplary Claim 2, wherein the voltage regulator at least partially uses the inertia of the rotating components of the generator and the rated power output of the generator to detect the magnitude of the load impact, and the rotating components include the crankshaft and the rotor of the alternator.

[0063] Exemplary Claim 4. The engine-driven generator according to any one of Exemplary Claims 1 to 3, wherein the engine-driven generator includes an engine controller, and the voltage regulator does not transmit information to the engine controller.

[0064] Exemplary Claim 5. The engine-driven generator according to any one of Exemplary Claims 1 to 4, wherein in response to the second derivative of the operating frequency indicating the load impact, the sampling system monitors the first derivative of the operating frequency and changes the excitation voltage to minimize the recovery time of the operating frequency from the minimum frequency to the target frequency.

[0065] Exemplary Claim 6. The engine-driven generator according to any one of Exemplary Claims 1 to 5, wherein the excitation system is configured to prioritize a low voltage drop at the electrical output.

[0066] Exemplary Claim 7. The engine-driven generator according to any one of Exemplary Claims 1 to 5, wherein the excitation system is configured to prioritize a low frequency drop at the electrical output.

[0067] Exemplary Claim 8. The engine-driven generator according to any one of Exemplary Claims 1 to 5, wherein the excitation system is configured to balance a low frequency drop and a low voltage drop at the electrical output.

[0068] Exemplary Claim 9. The engine-driven generator according to any one of Exemplary Claims 1 to 8, wherein the excitation system controls the excitation current in response to the second derivative of the operating frequency indicating a load impact.

[0069] Exemplary Claim 10. The engine-driven generator according to Exemplary Claim 9, wherein once the operating frequency reaches a minimum value, the excitation system controls the excitation voltage.

[0070] Exemplary Claim 11. A method of operating a generator, comprising: a) operating an engine of the generator at an operating frequency; b) sampling the operating frequency and calculating a second derivative of the operating frequency; c) detecting a load shock when the second derivative of the operating frequency has a magnitude or slope exceeding a threshold; d) changing an excitation current or an excitation voltage of an alternator of the generator in response to detecting the load shock.

[0071] Exemplary Claim 12. The method according to Exemplary Claim 11, wherein the magnitude or the slope is greater than a value of the second derivative of the operating frequency during a steady-state operation of the generator.

[0072] Exemplary Claim 13. The method according to Exemplary Claim 11 or Exemplary Claim 12, wherein, in step c), the voltage regulator detects the magnitude of the load shock at least in part using an inertia of a rotating component of the generator and a rated power output of the generator.

[0073] Exemplary Claim 14. The method according to any one of Exemplary Claims 11 to 13, wherein, in step d), the excitation current is reduced in response to detecting the load shock.

[0074] Exemplary Claim 15. The method according to Exemplary Claim 14, further comprising a step e) after step d), the step e) comprising: sampling a first derivative of the operating frequency and changing the excitation voltage to minimize a recovery time of the operating frequency from a minimum frequency to a target frequency.

[0075] Exemplary Claim 16. The method according to Exemplary Claim 15, further comprising a step f) after step e), the step f) comprising: reducing the excitation voltage at a lead time before the recovery time.

[0076] Exemplary Claim 17. The method according to any one of Exemplary Claims 11 to 16, wherein, in step b), the operating frequency is sampled at a selected frequency to substantially minimize a response time between the load shock and the detection of the load shock.

[0077] Exemplary Claim 18. A method of operating a generator, comprising: a) operating an engine of the generator at an operating frequency; b) sampling the operating frequency to detect a load impact; c) calculating a magnitude of the load impact using at least in part the operating frequency, an inertia of a rotating component of the generator, and a rated power output of the generator; and d) changing an excitation voltage or an excitation current of an alternator of the generator in response to the magnitude of the load impact.

[0078] Exemplary Claim 19. The method according to Exemplary Claim 18, wherein, in step d), the change in the excitation voltage or the excitation current corresponds to the magnitude of the load impact.

[0079] Exemplary Claim 20. The method according to Exemplary Claim 18 or Exemplary Claim 19, wherein, in step d), the excitation current is controlled until the operating frequency reaches a minimum frequency, and the excitation voltage is controlled after the operating frequency reaches the minimum frequency.

[0080] While the foregoing description and drawings represent examples of the present disclosed invention, it is understood that various additions, modifications, and substitutions may be made thereto without departing from the spirit and scope of the appended claims and the scope of equivalents. In particular, those skilled in the art will clearly recognize that the present invention may be embodied in other forms, structures, arrangements, proportions, dimensions, as well as other elements, materials, and components without departing from its spirit or essential characteristics. Additionally, various applicable variations of the methods / processes described herein may be made without departing from the spirit of the present invention. Those skilled in the art will further recognize that the present invention may be used with many modifications to the structure, arrangement, proportion, dimension, material, and components, as well as other aspects, to adapt to specific environments and operating requirements without departing from the principles of the present invention. Accordingly, the embodiments disclosed herein of the present invention are to be considered in all respects illustrative and not restrictive, and the scope of the present invention is defined by the appended claims and their equivalents and not by the foregoing description or examples. On the contrary, the appended claims are to be construed broadly to include other variations of the present invention that those skilled in the art can make without departing from the scope and equivalent scope of the present invention.

Claims

1. A generator driven by an engine, comprising: an internal combustion engine, the internal combustion engine comprising a crankshaft; an alternator including a rotor operably coupled to the crankshaft, the alternator configured to deliver electrical power at an electrical output; as well as A voltage regulator configured to regulate an excitation voltage applied to a field winding of the alternator, the voltage regulator comprising: a sampling system for sampling an operating frequency of an alternating current at the electrical output; a detection system configured to calculate a second derivative of the operating frequency; and An excitation system is configured to change one of the excitation voltage or the excitation current in response to the second derivative of the operating frequency indicating a load shock. 2 . The engine-driven generator of claim 1 , wherein the second-order derivative of the operating frequency indicates the load shock when a magnitude or slope of the second-order derivative of the operating frequency exceeds a threshold.

3. An engine-driven generator according to claim 1 or claim 2, wherein the voltage regulator detects the magnitude of the load impact using at least in part the inertia of the rotating components of the generator and the rated power output of the generator, the rotating components including the crankshaft and the rotor of the AC generator.

4. The engine-driven generator according to any one of claims 1 to 3, wherein the engine-driven generator comprises an engine controller, and the voltage regulator does not transmit information to the engine controller.

5. The engine-driven generator of any one of claims 1 to 4, wherein in response to the second derivative of the operating frequency indicating the load impact, the sampling system monitors the first derivative of the operating frequency and changes the excitation voltage to minimize the recovery time of the operating frequency from a minimum frequency to a target frequency.

6. An engine driven generator according to any one of claims 1 to 5, wherein the excitation system is configured to give priority to low voltage drops at the electrical output.

7. An engine driven generator according to any one of claims 1 to 5, wherein the excitation system is configured to prioritise low frequency drops at the electrical output.

8. An engine driven generator according to any one of claims 1 to 5, wherein the excitation system is configured to balance low frequency drops and low voltage drops at the electrical output.

9. An engine driven generator according to any one of claims 1 to 8, wherein the excitation system controls the excitation current in response to the second derivative of the operating frequency being indicative of a load impulse.

10. The engine-driven generator of claim 9, wherein the excitation system controls the excitation voltage once the operating frequency reaches a minimum value.

11. A method of operating a generator, comprising: a) operating a motor of said generator at an operating frequency; b) sampling the operating frequency and calculating the second-order derivative of the operating frequency; c) detecting a load shock when the second derivative of the operating frequency has a magnitude or slope exceeding a threshold; d) varying an excitation current or an excitation voltage of an alternator of the generator in response to detecting the load surge.

12. The method of claim 11, wherein the magnitude or the slope is greater than a value of the second derivative of the operating frequency during steady state operation of the generator.

13. The method according to claim 11 or claim 12, wherein: In step c), the voltage regulator detects the magnitude of the load impact using at least in part the inertia of the rotating components of the generator and the rated power output of the generator.

14. The method according to any one of claims 11 to 13, wherein: In step d), the excitation current is reduced in response to detecting the load impact.

15. The method according to claim 14, further comprising a step e) after step d), wherein step e) comprises: The first-order derivative of the operating frequency is sampled and the excitation voltage is changed to minimize the recovery time of the operating frequency from the minimum frequency to the target frequency.

16. The method according to claim 15, further comprising a step f) after step e), the step f) comprising: The lead time before the recovery time causes the excitation voltage to decrease.

17. The method according to any one of claims 11 to 16, wherein: In step b), the operating frequency is sampled at a frequency selected such that a reaction time between the load impact and the detection of the load impact is substantially minimized.

18. A method of operating a generator, comprising: a) operating a motor of said generator at an operating frequency; b) sampling the operating frequency to detect load impact; c) calculating a magnitude of the load impact using, at least in part, the operating frequency, the inertia of rotating components of the generator, and the rated power output of the generator; as well as d) varying the field voltage or field current of the alternator of the generator in response to the magnitude of the load impulse.

19. The method according to claim 18, wherein: In step d), the change in the excitation voltage or the excitation current corresponds to the magnitude of the load impact.

20. The method of claim 18 or claim 19, wherein: In step d), the excitation current is controlled until the operating frequency reaches a minimum frequency, and the excitation voltage is controlled after the operating frequency reaches the minimum frequency.

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