HK1202144B - Balancing vibrations at harmonic frequencies by injecting harmonic balancing signals into the armature of a linear motor/alternator coupled to a stirling machine - Google Patents

Abstract

Vibrations at harmonic frequencies are reduced by injecting harmonic balancing signals into the armature of a linear motor/alternator coupled to a Stirling machine. The vibrations are sensed to provide a signal representing the mechanical vibrations. A harmonic balancing signal is generated for selected harmonics of the operating frequency by processing the sensed vibration signal with adaptive filter algorithms of adaptive filters for each harmonic. Reference inputs for each harmonic are applied to the adaptive filter algorithms at the frequency of the selected harmonic. The harmonic balancing signals for all of the harmonics are summed with a principal control signal. The harmonic balancing signals modify the principal electrical drive voltage and drive the motor/alternator with a drive voltage component in opposition to the vibration at each harmonic.

Description

Balancing vibrations at harmonic frequencies by injecting a harmonic balancing signal into an armature of a linear motor/alternator coupled to a stirling machine

Background

The present invention relates generally to reducing or eliminating mechanical vibrations, particularly in coupling pairs including stirling cycle machines drivingly coupled to an electromagnetic linear motor or alternator, and more particularly to reducing or eliminating mechanical vibrations at harmonics of the fundamental operating frequency (harmonics) of the coupling pair reciprocating motion by integrating the control system of the present invention with prior art control and vibration balancers.

Many machines vibrate due to the repeated acceleration and deceleration of one or more periodically moving masses (masses) of which they are a part. In some environments, the vibrations can be very uncomfortable, distracting or annoying, while in some environments, the vibrations can interfere with the operation of other equipment and can even cause damage. One way to reduce vibration is to mount the vibrator to another mass through an intermediate damper, which may be a device or material that absorbs some of the vibration energy. However, since this approach may only partially reduce the vibrations, a more efficient way to eliminate or at least minimize the amplitude of the vibrations is to rigidly mount the vibration balancer to the vibratory machine. The vibration balancer generates a force that opposes the vibration, i.e., it generates a force of equal or nearly equal amplitude but opposite phase, thereby canceling or nearly canceling the force generated by the vibration.

Vibration balancers are generally of two types, namely passive vibration balancers and active vibration balancers, some of which are also known as tuned mass dampers, active mass dampers or vibration dampers. A passive vibration balancer is essentially a resonant spring and mass system tuned to the operating frequency of the shaker, but arranged to apply forces from its accelerating and decelerating mass to the shaker 180 ° out of phase with the forces generated by the vibration. An active vibration balancer is essentially a mass and may also be coupled to a spring, but the motion of the mass is controlled by a feedback control system that senses the vibration and drives the mass in the opposite direction to the vibration.

Although passive balancers are relatively inexpensive, a disadvantage is that they can only respond to vibrations at the one resonant frequency to which they are tuned. Active balancers can respond to small vibration frequency variations and can better apply a compensating force at an amplitude that cancels out the vibration, but active balancers are expensive and require a controller to drive the active balancer at the required amplitude and phase. To my knowledge, both passive and active balancers are unbalanced in their vibration at harmonics of the fundamental operating frequency of the vibratory machine.

It is therefore an object and feature of the present invention to provide a method for reducing or eliminating vibrations of a machine at harmonics of its fundamental operating frequency.

A further object and feature of the present invention is to balance not only the vibrations of the machine at harmonics of the fundamental operating frequency, but also to achieve this balance without adding any mechanical structure.

Disclosure of Invention

The present invention is a method of balancing vibration of a coupled pair comprising a linear motor/alternator drivingly coupled to a prime mover or load. The linear motor/alternator has armature windings and its reciprocating motion at the operating frequency is controlled by the digital processor in accordance with command inputs. The method minimizes coupling pair vibration at harmonics of the operating frequency.

Since in the prior art a main control signal is generated at the operating frequency in accordance with a command input and this main control signal is applied to the power stage which controls the coupling pair by applying an alternating main electrical drive voltage to the armature winding. With the present invention, vibration of the coupled pair is sensed to provide a sensed vibration signal representative of the sensed mechanical vibration of the coupled pair. A harmonic balancing signal is generated for at least one selected harmonic of the operating frequency and preferably for each of the selected several harmonics. Each harmonic balance signal is generated by processing the sensed vibration signal using an adaptive filtering algorithm of an adaptive filter. The adaptive filtering algorithm for each selected harmonic has a reference input at the frequency of the selected harmonic. The harmonic balance signals of all selected harmonics are added to the main control signal. Each harmonic at each selected harmonic of the operating frequency balances the signal to modify the primary electric drive voltage and drives the motor/alternator of the coupled pair with the drive voltage component of each selected harmonic (as opposed to vibration at each selected harmonic).

Drawings

Fig. 1 is a block diagram illustrating the operation of the present invention.

Fig. 2 is a block diagram illustrating the operation of an adaptive balancing signal generator as a component of the present invention.

Fig. 3 is a diagram illustrating an embodiment of the present invention.

Fig. 4 is a diagram illustrating another embodiment of the present invention.

Fig. 5 is a diagram illustrating still another embodiment of the present invention.

In describing the preferred embodiments of the present invention illustrated in the drawings, specific terminology will be resorted to for the sake of clarity. However, it is not intended that the invention be limited to the specific terms so selected and it is to be understood that each specific term includes all technical equivalents which operate in a similar manner to accomplish a similar purpose.

Detailed Description

U.S. patent 7,511,459 is incorporated by reference herein. This prior art patent shows an example of a control system for controlling a linear motor/alternator drivingly coupled to a stirling machine and which may be used with embodiments of the present invention. More specifically, this patent discloses an example of what is referred to herein as a main control system for applying a main electrical drive voltage and current to the motor/alternator armature winding to control its operation at its operating frequency.

Terminology and prior art rationale

Stirling machines are often drivingly coupled to a linear electric motor or a linear alternator. The stirling engine may be a prime mover connected to a linear alternator to generate electricity. A stirling machine operating in heat pump mode may be connected to and driven by the linear motor and pumps thermal energy from one of its heat exchangers to the other. When the purpose is to cool the mass, the stirling machine pumping heat is sometimes referred to as a cooler, and when the purpose is to heat the mass, the stirling machine pumping heat is sometimes referred to as a heat pump. The stirling heat pump and the stirling cooler are fundamentally the same machine to which different terms are applied. Both machines can transfer thermal energy from one mass to the other. Thus, when applied to a basic machine, the terms chiller/heat pump, chiller and heat pump may be used equally. Since the stirling machine may be an engine (prime mover) or a cooler/heat pump, the term stirling "machine" is generally used to include both stirling engines and stirling coolers/heat pumps. It is basically the same transducer that can arbitrarily convert energy between two types of energy (mechanical and thermal).

Likewise, a linear motor and a linear alternator are the same basic devices. Having a stator (typically with armature windings) and a reciprocating member comprising one or more magnets (typically permanent magnets). The linear motor/alternator may be mechanically driven by a prime mover to reciprocate to operate as an alternator to generate electricity, or by an ac power source to operate as a motor to provide a mechanical reciprocating output. Thus, the term linear motor/alternator may be used to refer to the basic electromechanical device.

Due to the duality of operation described above, the stirling machine operating as an engine may be used for the linear alternator and the linear electric motor may be used to drive the stirling machine operating in the heat pump mode. In both cases, the stirling machine is typically directly connected to the reciprocating member of the linear motor or alternator so that it reciprocates as a unit. In addition, linear motors and stirling engines may be used to drive other loads, such as pistons for compressed gas (e.g., in a refrigerator), or compressors for pumping fluids.

Prior art section of embodiments of the present invention

All embodiments of the present invention are a combination (both integrated and combined) of the control system of the present invention and a prior art control system that controls a coupled pair drivingly coupled to a prime mover or load, most preferably a linear motor/alternator of a stirling machine. Such coupling pairs are well known in the art. The motor/alternator has an armature winding to which a main control signal is applied. The stirling machine or motor/alternator is the prime mover and the other is the load, and various control systems exist for controlling this coupled pair. When the motor/alternator is used as an alternator to generate electricity, the armature windings provide an electrical output. When the motor/alternator is used as a motor, the power to drive the motor is controlled and includes a main control signal. In both cases, the type of prior art control to which the present invention is applicable accomplishes its control by applying a control voltage to the motor/alternator. The control causes the reciprocating pair to reciprocate at an operating frequency, prevents over-travel (overstroke), matches load power requirements to the power output of the prime mover, controls the temperature of the heat pump embodiment, and/or maximizes the efficiency of the coupled pair.

Fig. 1, 3, 4 and 5 each include a prior art master control system. Fig. 1 illustrates the basic principle of the present invention. Modern prior art control systems utilize a digital processor, such as a microprocessor, microcontroller, or Digital Signal Processor (DSP). As known to those skilled in the art, digital control circuit operation is typically described in terms of mathematical operations performed on signals by control algorithms executed by a digital processor. "signal" includes analog signals represented in a digital data format. Operations are often described in terms of conventional, legacy analog devices (e.g., filters and signal generators) that perform such operations, even though in modern circuits those operations are performed by digital signal processors programmed to perform algorithms.

Referring to fig. 1, a prior art master control system embodying the present invention is illustrated along a path across the top of a digital processor 10. As in the prior art, a master control signal is generated by the master control system at the operating frequency of reciprocation and is applied to the power stage which controls the coupling pair by applying an ac main electrical drive voltage to the armature windings of the motor/alternator. As is common to most control systems, there is a command input 12 applied to the control algorithm. Command input 12[ A ]_cmd]Is an amplitude input for operating the coupled pair at the fundamental drive frequency. Command input A_cmdRepresenting the distance traveled (e.g., in millimeters) or the armature coil voltage used to drive the motor/alternator. The output of the main control system controls the reciprocating motion of the coupled pair at the basic working frequency.

In fig. 1, the prior art control algorithm is divided into a control algorithm a and a control algorithm B as illustrated, since (for the purposes of the present invention) there is a summing operation, or summing junction 14, shown between the two. It illustrates that the control signal from the present invention is applied to the main control algorithm to modify the main control signal according to the present invention, but some prior art control operations may be performed before and after the summation operation. The result of the control algorithm is applied to the power stage 18 through the digital to analog converter 16, and the power stage 18 converts the control signal to the high power required to drive the motor/alternator. The power stage may include additional control circuitry.

The output of the power stage 18 is applied to the armature windings of the motor/alternator 20. The motor/alternator 20 is drivingly connected to the stirling machine 22 by a mechanical coupling 24 to form a coupled pair, the two components of which are mounted to a common mechanical support, schematically illustrated as support 26. In practice, the housing of the alternator and the housing of the stirling machine are integrally formed or directly connected together. The coupling pair is also preferably mechanically connected to a passive balancer that is used to reduce or eliminate vibration of the coupling pair at its operating frequency.

The invention

The method of the present invention minimizes the vibration of the coupling pair at harmonics of the operating frequency. The basic concept is to sense and feed back the amplitude, frequency and phase of the vibration at the frequency currently sensed as a harmonic of the fundamental operating frequency. Sensing vibrations is inherently an error detection, as any vibration is the error sought to be eliminated. A sinusoidally varying signal is generated for each harmonic frequency and its amplitude and phase are periodically varied, updated and adjusted to produce a balanced signal for each harmonic. The balance signal for each harmonic is continuously fed forward by injecting a balance signal into a main control signal that controls operation of the coupled pair at its fundamental operating frequency. With periodic updates, the change in each balance signal adapts the balance signal to any currently sensed vibration so that the sinusoidal balance signal for each harmonic is constantly applied to the linear motor/alternator to generate compensating forces at the appropriate phase, amplitude and frequency to minimize the vibration sensed at each harmonic. This is slightly different from a standard closed loop negative feedback control system that requires an error to drive the output. Here, the error (vibration) is driven to zero, but once the vibration is driven to zero, the adaptive algorithm maintains the same compensation output unless it senses an increase or decrease in the vibration, in which case the adaptive algorithm modifies the compensation output to again reduce the vibration (error) to zero.

Referring again to fig. 1, the vibration sensor 30 is mounted to the coupling pair (20, 22) in mechanical connection, such as by being mounted to the housing or housing support 26 of the coupling pair, or to the passive balancer 28 (which is attached to the coupling pair). The vibration sensor 30 may be an accelerometer and senses vibration of the coupled pair to provide a sensed vibration signal indicative of the sensed vibration.

The sensed vibration signal from the vibration sensor 30 is applied through an analog-to-digital converter 32 for processing by the digital processor 10. The sensed vibration signal in digital format is applied to each of a plurality of adaptive balancing signal generators (shown as 34, 36 and 38), each of which is an algorithm that generates a balancing signal at a different harmonic of the fundamental operating frequency. Thus, there is one adaptive balanced signal generator for each selected harmonic. Each adaptive balancing signal generator is assigned to and responsive to a harmonic frequency. Although the invention can be used to balance a single harmonic, it is preferred that there are a plurality of such balanced signal generators for balancing a plurality of different harmonics. Although three balanced signal generators are illustrated for three harmonics, 2 ω, 3 ω and h ω, where ω is the fundamental operating frequency and h is the h-th harmonic, there may be multiple balanced signal generators for as many harmonics, whichever harmonics are selected by the designer.

As described in more detail below, the harmonic balancing signal for each selected harmonic is generated by processing the sensed vibration signal with an adaptive filtering algorithm of an adaptive filter. The reference input at the frequency of the selected harmonic is applied to an adaptive filtering algorithm. Thus, each harmonic balancing signal generator 34, 36, and 38 has an output 34B, 36B, and 38B, the outputs 34B, 36B, and 38B being balancing signals that balance the harmonics to which the harmonic balancing signal generator is assigned.

All of the balance signals at outputs 34B, 36B and 38B are summed with the main control signal. As illustrated in fig. 1, the harmonic balance signals for each selected harmonic of the operating frequency are summed at summing junction 40, and the sum is then summed with the main control signal at summing junction 14. Thus, the sum of the harmonic balance signals is a feed forward signal: the feed forward signal modifies the electrical drive voltage to drive the motor/alternator of the coupled pair with a drive voltage component of each selected harmonic as opposed to vibration at each selected harmonic. Thus, each harmonic balancing signal generator provides an output signal at a frequency, amplitude and phase to summing junction 40 that drives the linear motor/alternator at a frequency, amplitude and phase to cancel out vibrations at the harmonic frequency assigned by the harmonic balancing signal generator to a practical level.

Adaptive filter

The harmonic balancing signals at outputs 34B, 36B and 38B are generated in part by using adaptive filters. Adaptive filter technology is known in the art for decades. The adaptive filtering algorithm that is preferred for use with the present invention is the Least Mean Square (LMS) filtering algorithm that was invented half a century ago. Various modified LMS algorithms and other adaptive filtering algorithms have been developed in the art for use with the present invention. These algorithms include the slightly modified SLMS of the LMS algorithm, the Normalized Least Mean Square (NLMS) filtering algorithm, and the Recursive Least Square (RLS) algorithm. The LMS algorithm is preferred because it is relatively simple and suitable for use with the present invention. The LMS algorithm models the desired filter by finding the filter coefficients related to the least mean square that produces the error signal. The error signal is the difference between the desired signal and the actual signal. In the present invention, the error signal is the sensed vibration, since the desired signal is not vibrating.

The adaptive filter is basically a variable filter that is changed by its adaptive algorithm in response to the sensed error. The adaptive filter adapts based on the currently sensed error. The error signal is processed through an algorithm that then modifies or updates the variable filter. In the present invention, the variable filter is a simple gain, i.e., a multiplier (amplifier), whose value is controllably varied algorithmically in response to sensed errors. The value of the variable filter is modified in response to the sensed error by increasing or decreasing the value of the variable filter by an amount selected by the designer and controlled by the algorithm, and the value of the variable filter is modified at a periodic rate selected by the designer and controlled by the algorithm. In this manner, the algorithm increments and decrements the variable filter in a manner that drives the error as close to zero as possible, and continues to increment and decrement the variable filter as needed for subsequent error signals to bring the error as close to zero as possible. An adaptive filtering algorithm (e.g., the LMS algorithm) is a standard algorithm described in the literature that operates to drive the error signal to zero.

The invention relates to an adaptive balance signal generator

For each harmonic for which balance is sought, there is an adaptive balance signal generator assigned to that particular harmonic. The purpose of each adaptive balancing signal generator is to derive and maintain from the sensed vibration input a signal that generates forces within the linear motor/alternator that oppose and cancel the vibration at the harmonic frequencies assigned by the adaptive balancing signal generator. Fig. 2 illustrates the adaptive balancing signal generators 34, 36 and 38 shown as blocks in fig. 1. These adaptive balancing signal generators are identical except that each is adapted to operate at a different harmonic frequency assigned to it. Each adaptive balanced signal generator 50 (fig. 2) includes quadrature sinusoidally varying reference signal generators 52 and 54. The reference generator 52 generates cos (h ω t), where h is the h-th harmonic assigned to the balanced generator and ω is the fundamental operating frequency of the coupled pair. The reference generator 54 generates sin (h ω t). The quadrature sine signal is the component that can be added to form the sum (residual), as visualized from the phasors representing the quadrature cosine and sine functions. The resultant can be at any phase and any amplitude by simply changing the amplitude of the two orthogonal components. In FIG. 3, it can be seen that_cmdControlling the amplitude of the reference signal generator to control the amplitude of the reference signal generator such that its amplitude is equal to A_cmdAnd (4) in proportion. Alternatively, as seen in fig. 4 and 5, the reference signal generator may have a constant unit amplitude. The purpose of the sinusoidal reference signal generators 52 and 54 is to generate a pair of quadrature sinusoidally varying cosine and sine reference signals at the frequencies of the assigned harmonics.

The adaptive balanced signal generator 50 also has two adaptive filters 56 and 58. The adaptive filter 56 has a variable filter W0 through which a variable filter W0 passes for the adaptive LMS algorithm LMS₀Controllably varied. The adaptive filter 58 has a variable filter Wl that passes through its adaptive LMS algorithm LMS₁Is variably controlled.

The sensed vibration signal is applied as an input to an adaptive filtering algorithm that controls each of a pair of variable filters. More specifically, the sensed vibration signal e (n) is applied to an adaptive filtering algorithm LMS₀And LMS₁. The outputs of the reference signal generators 52 and 54 are also applied to each of a pair of variable filters of a pair of adaptive filters controlled by an adaptive filtering algorithm. More specifically, a signal from the reference signal generator 52, which generates cos (h ω t), is applied to the variable filter W0, and a signal from the reference signal generator 54, which generates sin (h ω t), is applied to the variable filter Wl. Thus, the output signals from the variable filters W0 and Wl are quadrature sinusoidal signals, each having an amplitude determined by the respective gains of the variable filters W0 and Wl. The respective gains of the variable filters W0 and Wl are determined by their respective adaptive algorithms LMS₀And LMS₁Determined and updated periodically. The quadrature sinusoidal signals from W0 and Wl are phasor components that can be added (vector/phasor sum) at summing junction 60 to provide a resultant output from summing junction 60 at the harmonic frequency assigned to balanced signal generator 50 and having a frequency equal to the harmonic frequency assigned by LMS₀And LMS₁The phase and amplitude determined by the adaptive filtering algorithm. These adaptive filtering algorithms generate a balanced signal for the assigned harmonics. The balance signal has an amplitude and phase such that when added to the main control signal and fed forward to the armature windings of the motor/alternator, it will generate a force that opposes and substantially cancels the vibration at the harmonic frequency assigned by the adaptive balance signal generator 50.

The design parameters of the adaptive filter are relatively simple. In the prior art, the algorithm itself is readily available. The algorithm controlling each variable filter updates the variable filter in incremental steps. Two parameters chosen by the designer are: (1) the update rate (how often the update is done) and (2) the update amount (how much the gain of the variable filter changes each time the update is done) is how often the LMS algorithm is processed. The update rate is chosen to be several times the frequency of the harmonics assigned to the balanced signal generator. Typically, 5 to 10 updates should occur within one period of the assigned harmonics. The amount of change in the gain of the variable filter at each incremental update is preferably determined experimentally by repeated trial and error. Several update amounts within a certain range are tried separately and then stability, effectiveness in reducing vibration, and response speed are observed. The amount of change selected for each update is generally a function of the feedback error (less change for smaller errors) and is generally proportional to the error amplitude. The LMS or other control algorithm determines the direction of change based on the sign of the error.

The signals from the cosine and sine reference signal generators 52 and 54 that vary each time the sine are also multiplied by the transfer functionAnd the product is applied as input to the adaptive filtering algorithm LMS of the adaptive filters 56 and 58₀And LMS₁. Transfer functionIs a transfer function from the output 50B of the balance signal generator 50 to the sensed vibration input 62. The transfer function is a complex mathematical expression for balancing the entire external system of the signal generator 50. As is well known, the transfer function is the ratio of the output divided by the input, and in this case the sensed vibration signal at the input 62 divided by the output at the output 50B of the balance signal generator 50.

The transfer function provides an estimated or predicted response for the adaptive filtering algorithm LMS₀And LMS₁The preparation is used. The transfer function creates a model in the sense that it provides a transfer function that represents the system. The transfer function accounts for the following fact: the response of the external system includes a passive balancer component. It estimates the behavior of a system with a passive balancer that also generates a reaction force against vibrations at the fundamental operating frequency. If the balance signal generator 50 applies some vibration cancellation signal, the transfer function provides an estimate of the vibrations that will be generated. Of course, contemplated isThe system will vary greatly during operation. However, the LMS algorithm uses the transfer function signal to decide the direction (increase or decrease) to change the gains of the variable filters W0 and Wl in an attempt to reduce the vibration to zero.

The transfer function may be determined in the conventional manner by determining the transfer function of each component along the path from input to output represented by the transfer function and multiplying the transfer functions to obtain the total transfer function from input to outputAlternatively, however, the transfer function may (and preferably is) obtained by laboratory measurements, since that is a complex and difficult mathematical calculation, and not pushed to the mathematical expression of the transfer function in this way. For each of each harmonicIn the event that each of output 50B and input 62 is disconnected from the circuit and the system is not operating, the input unit sine wave is applied to summing junction 40. The return error signal output by the vibration sensor 30 (fig. 1) is observed and its amplitude and phase are measured. The measured return output signal divided by the measured injection input signal is the transfer function. Both the input and output are simply the amplitude a, phase θ and frequency h ω of each harmonic h. Therefore, the temperature of the molten metal is controlled,is the expected output of the external system of the balanced signal generator at the harmonic assigned by the balanced signal generator and represents the expected error e (n). The transfer function represents a harmonic balance signal of the assigned harmonic divided by a sensed vibration signal corresponding to the vibration at the selected harmonic.

As described above, the harmonic balance signal assigned to the selected harmonic of the balance signal generator is obtained by adding the quadrature outputs (phasor/vector sum) of the variable filters W0 and Wl. The summing operation is represented by summing junction 60. Referring again to FIG. 1, the composite balance signal for all harmonics is generated by adding the balance signals for all harmonics and adding the sum to the main control signal. This is illustrated by applying outputs 34B, 36B and 38B to summing junction 40 and the sum to summing junction 14.

Figure 3 illustrates an embodiment of the present invention. The adaptive balancing signal generators 334 and 336 are the same as the adaptive balancing signal generators illustrated in fig. 1 and 2. However, in the embodiment of FIG. 3, command input A_cmdIs applied to all reference signal generators, such as cosine reference signal generator 352 and sine reference signal generator 354. This results in the amplitude of the reference signal being equal to A_cmdProportionally. According to A_cmdVarying the amplitude of the reference signal generator provides the additional advantage of amplitude feed forward control.

Fig. 3 and fig. 4 and 5 also illustrate the vibration sensor 330 in more detail. The vibration is preferably sensed by accelerometer 370, which applies its output to amplifier 372. The amplified output is filtered by a low pass filter 374. The cut-off frequency of the low pass filter 374 is higher than the frequency of the highest selected harmonic and the designer wants to use the techniques of the present invention to minimize vibrations at the frequency of the highest selected harmonic. The purpose of this is to filter out frequency noise above the highest selected harmonic frequency.

The sensed vibration signal e (n) applied to the digital processor 310 from the low pass filter 374 by the analog to digital converter 332 of the digital processor 310 is a composite analog signal that is the sum of the vibrations at the fundamental operating frequency and all harmonics thereof below the filter cutoff frequency. The composite signal in digital format is applied to each adaptive balancing signal generator and thus includes all harmonic components of the composite vibration signal. However, one inherent characteristic of the adaptive filtering algorithm is that it responds only to Fourier components at the frequencies of the reference signal generators 52 and 54 (FIG. 2). Each balanced signal generator has a reference signal generator at its assigned harmonic frequency, and therefore each balanced signal generator is responsive only to its assigned frequency. Therefore, there is no need to perform any further filtering of the composite vibration signal to extract the fourier component of each harmonic.

Fig. 4 illustrates another embodiment of the present invention, and its adaptive balancing signal generators 434 and 436 are also the same as the adaptive balancing signal generators illustrated in fig. 1 and 2. In the embodiment of FIG. 4, command input A_cmd(412) The embodiment of fig. 4 is similar to the embodiment of fig. 3 except that it is not applied to any reference signal generator (e.g., cosine reference signal generator 452 and sine reference signal generator 454). Therefore, the amplitude of the reference signal it generates always has unity value, and therefore does not exist with A_cmdProportional amplitude feed forward.

Fig. 5 is an embodiment of the present invention that is similar to the embodiment of fig. 4 except that it shows the present invention integrated with a different prior art master control system having a feedback pin (leg)580 that provides a feedforward control signal that is summed with the master control signal. The master control system of figure 5, which is prior art and integrated with the present invention, is shown and described in my patent 7,511,459.

The detailed description taken in conjunction with the drawings is intended primarily as a description of the presently preferred embodiments of the invention and is not intended to represent the only forms in which the present invention may be constructed or utilized. This description sets forth the designs, functions, means, and methods of implementing the invention in connection with the illustrated embodiments. It is to be understood, however, that the same or equivalent functions and features may be accomplished by different embodiments that are also intended to be encompassed within the spirit and scope of the invention, and that various modifications may be resorted to without departing from the scope of the invention or the claims that follow.

Claims (7)

1. A method for balancing vibration of a coupled pair comprising a linear motor/alternator drivingly coupled to a prime mover or load, the linear motor/alternator having an armature winding and being controlled by a digital processor in accordance with a command input to reciprocate at an operating frequency, the method minimizing vibration of the coupled pair at harmonics of the operating frequency and comprising:

(a) generating a main control signal at the operating frequency in accordance with the command input and applying the main control signal to a power stage that controls the coupled pair by applying an alternating main electrical drive voltage to the armature winding;

(b) sensing vibration of the coupled pair to provide a sensed vibration signal representative of the sensed vibration;

(c) generating a harmonic balancing signal for at least one selected harmonic of the operating frequency by processing the sensed vibration signal with an adaptive filtering algorithm of an adaptive filter having a reference input at the frequency of the selected harmonic; and

(d) adding each harmonic balancing signal at each selected harmonic of the operating frequency to the main control signal modifies the electrical drive voltage to drive the linear motor/alternator of the coupled pair with a drive voltage component for each selected harmonic that opposes vibration at each selected harmonic.

2. The method of claim 1, wherein the prime mover or load is a stirling machine drivingly coupled with the linear motor/alternator, and wherein the step of generating a harmonic balancing signal for each selected harmonic further comprises:

(i) generating a pair of quadrature sinusoidally varying cosine and sine reference signals at the frequency of the selected harmonic and applying the cosine and sine reference signals to each of a pair of variable filters of a pair of adaptive filters controlled by an adaptive filtering algorithm; each of the pair of adaptive filters includes one of the pair of variable filters, respectively; a cosine signal of the cosine and sine reference signals is applied to one of the pair of variable filters and a sine reference signal of the cosine and sine reference signals is applied to the other of the pair of variable filters;

(ii) inputting the sensed vibration signal into an adaptive filtering algorithm that controls each of the pair of variable filters;

(iii) multiplying each of the sinusoidally varying cosine and sine reference signals by a transfer function characterizing a harmonic balance signal for the selected harmonic divided by the sensed vibration signal corresponding to the vibration at the selected harmonic and inputting the multiplied reference signals to an adaptive filtering algorithm for each adaptive filter; and

(iv) summing the outputs of the variable filters to provide the harmonic balancing signal for the selected harmonic.

3. The method of claim 2, wherein the method is performed on a plurality of selected harmonics.

4. A method according to claim 3, wherein the amplitude of the cosine and sine reference signals of each pair of orthogonal sine variations controllably varies in proportion to the command input.

5. The method of claim 4, wherein each variable filter is an amplitude multiplier, the gain being controlled by an adaptive filtering algorithm of the amplitude multiplier.

6. The method of claim 5, wherein the adaptive filtering algorithm is a least mean square algorithm.

7. The method of claim 6, wherein each adaptive filtering algorithm has a periodic update rate at which the adaptive filtering algorithm changes its variable filter in a range of 5 to 10 times a harmonic frequency of a harmonic for which the adaptive filtering algorithm generates a harmonic balancing signal.