Speed estimating device for AC motor, driving device for AC motor, refrigerant compressor, and refrigeration cycle apparatus

A speed estimating device for an AC motor includes: a model deviation computing unit computing a model deviation based on a voltage, a current, and an estimated angular velocity of the AC motor; a first angular velocity estimating unit computing a first estimated angular velocity based on the model deviation; a second angular velocity estimating unit computing a second estimated angular velocity differing from the first estimated angular velocity in frequency, based on the model deviation; a compensation phase computing unit computing a compensation phase based on a disturbance frequency; and an estimated angular velocity calculator computing an estimated angular velocity of the AC motor based on the first estimated angular velocity and the second estimated angular velocity. Either one of the first estimated angular velocity and the second estimated angular velocity is computed based on the compensation phase.

CROSS-REFERENCE TO RELATED APPLICATION

The present application is based on PCT filing PCT/JP2019/012213, filed Mar. 22, 2019, the entire contents of which are incorporated herein by reference.

FIELD

The present invention relates to a speed estimating device for an alternating-current (AC) motor which estimates the velocity of an AC motor such as an induction machine or a synchronous machine, a driving device for an AC motor, a refrigerant compressor, and a refrigeration cycle apparatus.

BACKGROUND

In control of an AC motor, when load torque or torque generated by the AC motor has pulsation, some pulsation also occurs in the rotational speed of the AC motor. The occurrence of pulsation in the rotational speed of the AC motor may cause vibration in an apparatus on which the AC motor is installed, which may be problematic in occurrence of noise, mechanical strength, or the like. In response to these problems, control for reducing torque pulsation and speed pulsation has been considered.

For example, Patent Literature 1 listed below teaches a technique for achieving control for reducing torque pulsation and speed pulsation by a sensorless approach without using a position sensor or a velocity sensor in order to reduce cost or to allow application to an apparatus on which it is difficult to install a sensor. According to Patent Literature 1, a torque compensation value is obtained on the basis of a speed ripple component extracted from a difference between a command angular frequency and a speed feedback angular frequency. The fluctuation in speed of the AC motor is thus reduced or suppressed without any map of correction amounts.

CITATION LIST

Patent Literature

SUMMARY

Technical Problem

In position-sensorless control, an upper limit of speed estimation response in conventional control systems is several hundreds [rad/s], and so a response to high-frequency pulsation is insufficient, and it is difficult to accurately estimate a pulsation. In addition, in Patent Literature 1, because a vibration reducing unit is configured to use an estimated speed, the performance of the vibration reducing unit depends on a response in the speed estimation, and is thus considered to be insufficient in a high-frequency range.

The present invention has been made in view of the above circumstances, and an object thereof is to provide a speed estimating device for an AC motor, which is capable of further increasing the accuracy of speed estimation at high frequency in sensorless control of an AC motor.

Solution to Problem

In order to solve the aforementioned problems and achieve the object, the present invention provides a speed estimating device for an AC motor, the speed estimating device comprising: a model deviation computing unit to compute a model deviation on the basis of a voltage, a current, and an estimated angular velocity of the AC motor; a first angular velocity estimating unit to compute a first estimated angular velocity on the basis of the model deviation; a second angular velocity estimating unit to compute a second estimated angular velocity on the basis of the model deviation, the second estimated angular velocity differing from the first estimated angular velocity in frequency; a compensation phase computing unit to compute a compensation phase on the basis of a disturbance frequency; and an estimated angular velocity calculator to compute an estimated angular velocity of the AC motor on the basis of the first and second estimated angular velocities, wherein either one of the first and second estimated angular velocities is computed on the basis of the compensation phase.

Advantageous Effects of Invention

The speed estimating device for an AC motor according to the present invention produces an advantageous effect that it is capable of further increasing the accuracy of speed estimation at high frequency in sensorless control on an AC motor.

DESCRIPTION OF EMBODIMENTS

A speed estimating device for an AC motor, a driving device for an AC motor, a refrigerant compressor, and a refrigeration cycle apparatus according to certain embodiments of the present invention will be described in detail below with reference to the drawings. Note that the present invention is not limited by the embodiments described below. Hereinafter, the speed estimating device for an AC motor will be simply referred to as a “speed estimating device” as appropriate. In addition, the driving device for an AC motor will be simply referred to as a “driving device” as appropriate.

First Embodiment

FIG.1is a block diagram illustrating a configuration of a speed estimating device101for an AC motor according to a first embodiment. The speed estimating device101illustrated inFIG.1estimates the rotational speed of an AC motor2in a technique of an adaptive observer using a voltage vector applied to the AC motor2and a current vector, and outputs the estimation result as an estimated angular velocity ω{circumflex over ( )}r.

The speed estimating device101includes a model deviation computing unit11, a first angular velocity estimating unit21, a compensation phase computing unit51, a second angular velocity estimating unit22, and an estimated angular velocity calculator23.

The model deviation computing unit11computes a model deviation ε on the basis of the voltage vector, the current vector, and the estimated angular velocity ω{circumflex over ( )}r. The first angular velocity estimating unit21calculates a first estimated angular velocity ω{circumflex over ( )}r1on the basis of the model deviation ε. The compensation phase computing unit51computes a compensation phase θplson the basis of a specific disturbance frequency fd. The second angular velocity estimating unit22calculates a second estimated angular velocity ω{circumflex over ( )}r2on the basis of the compensation phase θpls, the model deviation ε, and the disturbance frequency fd. The estimated angular velocity calculator23calculates an estimated angular velocity ω{circumflex over ( )}rof the AC motor2on the basis of the first estimated angular velocity ω{circumflex over ( )}r1and the second estimated angular velocity ω{circumflex over ( )}r2.

The speed estimating device101includes the compensation phase computing unit51and the second angular velocity estimating unit22, and operations performed by these components are one of the characteristics of the present invention. Details of the compensation phase computing unit51and the second angular velocity estimating unit22will be described later.

In the first embodiment, the disturbance frequency fdis assumed to be known. The disturbance frequency fdmay be obtained in any manner. For example, in such a system in which disturbance of a particular frequency occurs, the disturbance frequency fdcan be provided as a constant in advance. Alternatively, in such an application as a compressor in which disturbance depending on rotational frequency occurs, the rotational frequency can be used as the disturbance frequency fd. The rotational frequency mentioned herein can be acquired by a rotational position sensor or a velocity sensor. Alternatively, in a case of a device including angular velocity estimating means as in the first embodiment, the rotational frequency can be obtained from the estimated angular velocity ω{circumflex over ( )}r. Still alternatively, the frequency of torque pulsation may be detected or estimated by a torque meter, an acceleration sensor, or a vibration sensor, and used as the disturbance frequency fd.

The first angular velocity estimating unit21and the second angular velocity estimating unit22both estimate angular velocity. The difference therebetween lies in a frequency for an angular velocity to be estimated. While the first embodiment is directed to a configuration in which the first angular velocity estimating unit21estimates a low-frequency component including a direct-current (DC) component of an angular velocity and the second angular velocity estimating unit22estimates a high-frequency component of the angular velocity, the present invention is not limited to this configuration. Needless to say, an opposite configuration can alternatively be used, in which the first angular velocity estimating unit21estimates a higher angular velocity frequency component.

Next, a configuration and functions of the model deviation computing unit11will be described. The model deviation computing unit11includes a state estimator12, a subtractor13, and a deviation calculator14. The state estimator12calculates and outputs an estimated magnetic flux vector and an estimated current vector on the basis of the voltage vector applied to the AC motor2, the current vector outputted by the AC motor2, and the estimated angular velocity ω{circumflex over ( )}r. The estimated angular velocity ω{circumflex over ( )}ris an estimated angular velocity calculated by the aforementioned estimated angular velocity calculator23, and is also an output of the speed estimating device101.

The subtractor13subtracts the current vector from the estimated current vector to calculate a current deviation vector. The deviation calculator14receives the current deviation vector as its input, extracts an orthogonal component of the estimated magnetic flux vector as a scalar quantity, and outputs a value of the quantity as the model deviation ε. Note that the technique for extracting an orthogonal component of an estimated magnetic flux vector as a scalar quantity is publicly known. For example, there are publicly known a technique of performing coordinate transformation on a current deviation vector to two rotational axes, a technique of computing the magnitude of the cross product of the current deviation vector and the estimated magnetic flux vector, and more.

Specifically, the state estimator12estimates an electric current and a magnetic flux according to a state equation of the AC motor2. While the AC motor2is assumed to be a typical embedded magnet type synchronous electric AC motor in this example, any other AC motors can also be used as long as a state equation similar to that described below can be established in the state estimator12. Examples of other AC motors include a surface magnet type synchronous electric motor and an induction electric motor.

In the case of an embedded magnet type synchronous AC motor, the state equation is expressed by the following equations (1) and (2).

Note that the primary angular frequency is given as expressed according to the following equation (3).

In the above equation (3), h41and h42represent observer gains similarly to the aforementioned h11to h32.

While the above equations (1) and (2) are equations based on normal induced voltage, similar calculation can be performed with modifying the above equations (1) and (2) to express a form using an extended induced voltage. Because the above equation (1) includes the estimated angular velocity ω{circumflex over ( )}r, an error occurs in current estimation when the estimated angular velocity ω{circumflex over ( )}rand an actual angular velocity ωrare not equal to each other. Herein, the model deviation ε is defined according to the following equation (4). The speed estimating device101adjusts the value of the estimated angular velocity ω{circumflex over ( )}rwith use of the first angular velocity estimating unit21and the second angular velocity estimating unit22so that the model deviation ε becomes zero.

As described above, one of characteristics of the speed estimating device101is that the speed estimating device101has the compensation phase computing unit51and the second angular velocity estimating unit22. In order to explain this characteristic, a speed estimating device that does not have the compensation phase computing unit51and the second angular velocity estimating unit22will first be explained as a comparative example herein.

FIG.2is a block diagram illustrating a configuration of a speed estimating device101A according to the comparative example. The speed estimating device101A illustrated inFIG.2operates in accordance with a sensorless vector control method in a manner similar to the speed estimating device101illustrated inFIG.1. The speed estimating device101A operates to adjust the model deviation ε to zero only by using the first angular velocity estimating unit21.

In the speed estimating device101A illustrated inFIG.2, the first angular velocity estimating unit21includes a proportional integral (PI) controller24and an integrator25. The first angular velocity estimating unit21operates in accordance with the following equation (5).

In the equation (5), KPrepresents a proportional gain of the entire first angular velocity estimating unit21. KIrepresents an integral gain of the entire first angular velocity estimating unit21. s represents an operator of Laplace transform, s refers to differentiation, and 1/s refers to integration.

In the first angular velocity estimating unit21, the PI controller24computes a first estimated angular acceleration ω⋅{circumflex over ( )}r1on the basis of the model deviation ε. The integrator25integrates the first estimated angular acceleration ω⋅{circumflex over ( )}r1to compute the first estimated angular velocity ω⋅{circumflex over ( )}r1. In the first angular velocity estimating unit21, the first estimated angular velocity ω{circumflex over ( )}r1is adjusted by the PI controller24and the integrator25. The first estimated angular velocity ω{circumflex over ( )}r1is outputted to the outside as an output of the speed estimating device101A. In addition, the first estimated angular velocity ω{circumflex over ( )}r1is fed back to the model deviation computing unit11. As described above, the PI controller24operates as a first angular acceleration estimator, and the integrator25operates as a first angular velocity calculator.

In addition, the transfer function Ga(s) from the first estimated angular velocity ω{circumflex over ( )}r1to the model deviation ε is publicly known in the 226-th page of “Speed Sensorless Vector Control Method of Induction Motor Including A Low Speed Region”, The transactions of the Institute of Electrical Engineers of Japan (Vol. 120-D, No. 2, 2000) that is a Non Patent Literature. The transfer function Ga(s) can be approximated by a first order lag as in the following equation (6).

FIG.3is a Bode plot illustrating transfer characteristics of the speed estimating device101A illustrated inFIG.2. The horizontal axis represents frequency, and the vertical axis represents gain. A transfer function of (1) illustrated by a broken line inFIG.3is designed such that the gain in a lower frequency range is higher. In the transfer function of (1), the gain decreases as the frequency is higher. Specifically, the gain decreases at a rate of −40 [dB/decade] in a low-frequency band, and decreases at a rate of −20 [dB/decade] at frequencies higher than that at a break point P1.

In addition, a transfer function of (2) illustrated by a dotted line inFIG.3corresponds to the transfer function Ga(s) of the above equation (6). Because the transfer function Ga(s) has a first order lag characteristic from the first estimated angular velocity ω{circumflex over ( )}r1to the model deviation ε, the gain decreases at a rate of −20 [dB/decade] in a frequency range higher than a cutoff angular frequency f1. Addition of the two transfer functions results in a transfer function of (3) having an open loop characteristic illustrated by a solid line.

If PI control gains in the above equation (5), that is, the proportional gain KPand the integral gain KIin the first angular velocity estimating unit21can be set to be sufficiently large, speed pulsation at high frequencies can be accurately estimated. These gain values, however, are constrained by the estimation computation period and the influence of an error in a motor constant. A forced increase in the gains enhances vulnerability to high-frequency noise, which makes appropriate estimation processing impossible. For this reason, the speed estimating device101A according to the comparative example has a problem in that it is difficult to capture high-frequency speed pulsation.

Next, another comparative example will be explained.FIG.4is a block diagram illustrating a configuration of a speed estimating device101B according to a comparative example different from that inFIG.2. Hereinafter, for distinction fromFIG.2, the comparative example ofFIG.2will be referred to as a “first comparative example”, and the comparative example ofFIG.4will be referred to as a “second comparative example”. As compared with the speed estimating device101A ofFIG.2, the speed estimating device101B according to the second comparative example illustrated inFIG.4is provided additionally with a second angular velocity estimating unit22B.

In the speed estimating device101B ofFIG.4, the second angular velocity estimating unit22B includes a second angular acceleration estimating unit30B, and an integrator31. The second angular acceleration estimating unit30B computes a second estimated angular acceleration ω⋅{circumflex over ( )}r2on the basis of the disturbance frequency fdand the model deviation ε. The integrator31integrates the second estimated angular acceleration ω⋅{circumflex over ( )}r2and outputs a second estimated angular velocity ω⋅{circumflex over ( )}r2.

In addition, the second angular acceleration estimating unit30B includes a Fourier coefficient calculator26, PI controllers27and28, and an AC restoring unit29.

The Fourier coefficient calculator26converts a specific frequency component of the model deviation into direct current, and extracts the obtained DC component. A cosine coefficient Ecand a sine coefficient Esare outputted from the Fourier coefficient calculator26, which correspond to the specific frequency component obtained by the DC conversion.

In this process, the cosine coefficient Ecof the model deviation ε and the sine coefficient Esof the model deviation ε are calculated by the following equations (7) and (8), respectively, on the basis of the model deviation ε and the disturbance frequency fd.

In the formulas (7) and (8), t represents time. In addition, Tdrepresents a cycle period of disturbance, which is the reciprocal of the disturbance frequency fd. That is, Td=1/fd.

The cosine coefficient Ecof the model deviation is subjected to PI control by the PI controller27as expressed by the following equation (9). In addition, the sine coefficient Esof the model deviation is subjected to PI control by the PI controller28as expressed by the following equation (10).

In the equations (9) and (10), KP2represents a proportional gain of the entire second angular velocity estimating unit22B. KI2represents an integral gain of the entire second angular velocity estimating unit22B. A dot over each character refers to differentiation, and the number of dots represents the order of differentiation.

The AC restoring unit29performs computation of the following equation (11) on the basis of the cosine coefficient Ecof the model deviation and the sine coefficient Esof the model deviation. The equation (11) is an arithmetic expression for calculating the second estimated angular acceleration ω⋅{circumflex over ( )}r2.
[Formula 11]
{dot over ({circumflex over (ω)})}r2=({dot over ({circumflex over (Ω)})}ccos(2πfdt)+{dot over ({circumflex over (Ω)})}ssin(2πfdt)  (11)

FIG.5is a Bode plot illustrating transfer characteristics of the speed estimating device101B illustrated inFIG.4. The horizontal axis represents frequency, and the vertical axis represents gain. A transfer function of (1) inFIG.5is the same as the transfer function of (1) inFIG.3. A transfer function of (2) inFIG.5is the same as the transfer function of (2) inFIG.3. A transfer function of (3) inFIG.5represents a transfer function of the second angular velocity estimating unit22B illustrated inFIG.4. Addition of the three transfer functions results in an open loop characteristic of (4) illustrated by a solid line.

InFIG.5as compared withFIG.3, the gain in a specific frequency band is higher in the open loop characteristic of (4) illustrated by the solid line. More precisely, the speed estimating device101B according to the second comparative example increases the gain in a specific frequency band in which occurrence of speed pulsation due to periodic disturbance can be predicted, by using the first angular velocity estimating unit21and the second angular velocity estimating unit22B, thereby making it possible to increase the accuracy of speed estimation. As a result, the speed estimating device101B according to the second comparative example enables estimation of high-frequency speed pulsation with high accuracy, which is difficult for the speed estimating device101A according to the first comparative example.

As described above, the speed estimating device101B according to the second comparative example can estimate high-frequency speed pulsation with high accuracy, but it is envisaged that the control system may be instable depending on the magnitude of phase error. In the circumstances, the inventors of the present application have considered the necessity of phase compensation for a proposal of the present invention, and such consideration will be described below.

FIG.6is a graph used for comparing Bode plots illustrating the transfer characteristics from the model deviation ε to the first estimated angular acceleration ω⋅{circumflex over ( )}r1of the speed estimating device101A illustrated inFIG.2in an open loop characteristic and a closed loop characteristic. The open loop characteristic is a transfer characteristic in a state in which the first estimated angular velocity ω{circumflex over ( )}r1is not fed back to the model deviation computing unit11. The closed loop characteristic is a transfer characteristic in a state in which the first estimated angular velocity ω{circumflex over ( )}r1is fed back to the model deviation computing unit11as illustrated inFIG.2. Note thatFIGS.3and5are Bode plots from the model deviation s to the first estimated angular velocity ω{circumflex over ( )}r1. In contrast,FIG.6illustrates the transfer characteristics from input of the model deviation ε to output of the first estimated angular acceleration ω⋅{circumflex over ( )}r1, and attention should be paid to a first-order differential characteristic being added toFIGS.3and5. As illustrated inFIG.4, when the second angular velocity estimating unit22B computes the second estimated angular acceleration ω⋅{circumflex over ( )}r2on the basis of the model deviation ε, the characteristic from input of the model deviation ε to output of the second estimated angular acceleration ω⋅{circumflex over ( )}r2illustrated inFIG.6can be considered as a characteristic to be controlled by the second angular velocity estimating unit22B.

In feedback control, a technique of design in view of the open loop characteristics of a controlled object and a controller is often used. In this situation, what is considered first is a case of designing the second angular velocity estimating unit in view of the open loop characteristic of the controlled object.

According to the open loop characteristic inFIG.6, the gain decays at −20 [dB/decade] in a low-frequency band. The phase is −90 [degrees] in the low-frequency band, lags as the frequency is higher, and converges to −180 [degrees]. While the used frequency band depends on an application, the phase can be considered as being substantially constant at −90 [degrees] in a case where a low-frequency band is mainly used. In such a case, if the open loop characteristic is a controlled object in designing the second angular velocity estimating unit, phase compensation seems to be unnecessary.

In fact, however, the PI controllers27and28serving as second angular acceleration estimators perform computation in a state in which the PI controller24serving as the first angular acceleration estimator operates. For this reason, it should be considered that the first estimated angular velocity ω{circumflex over ( )}r1estimated by the first angular velocity estimating unit21including the PI controller24is fed back to the model deviation computing unit11. Accordingly, the second angular velocity estimating unit22B needs to be designed in view of the closed loop characteristic to be controlled by the second angular velocity estimating unit22B.

The closed loop characteristic inFIG.6has a first-order integral characteristic in a high-frequency band, and a first-order differential characteristic in a low-frequency band. The gain has a characteristic that lowers at a gradient of −20 [dB/decade] in consistency with the open loop characteristic in a high-frequency band, but a characteristic that increases at a gradient of +20 [dB/decade] in a low-frequency band and makes the gain lower as the frequency is lower. In addition, the phase converges to −180 [degrees] in a high-frequency band, which is consistent with the case of the open loop, but is +90 [degrees] in a low-frequency band. The phase thus changes significantly from +90 [degrees] to −180 [degrees] in the frequency band therebetween.

Note that, as described above, the angular acceleration computation in the second angular velocity estimating unit22B of the speed estimating device101B according to the second comparative example is performed using the above equations (7) to (11). The equations (7) and (8) are arithmetic expressions for obtaining the cosine coefficient and the sine coefficient that correspond to DC components, the equations (9) and (10) are arithmetic expressions for PI control, and the equation (11) is an arithmetic expression for restoring an AC component by getting back the DC components into the AC component. In the series of computation processes, the phase is not considered. This means that the phase is assumed not to change depending on frequency in a range from input of the model deviation ε to output of the second estimated angular acceleration ω⋅{circumflex over ( )}2.

For example, as described above, in the case where only the open loop characteristic is deemed to be a controlled object and operation is performed in a low-frequency range, the phase change may be considered as being sufficiently small and it is contemplated to adopt the control design as described above. In fact, however, the phase characteristic of a controlled object greatly changes depending on frequency as illustrated in the Bode plots inFIG.6. For this reason, unless an estimated angular acceleration is calculated in view of the fact that the phase characteristic of a controlled object changes depending on disturbance frequency, an error with respect to an estimated phase of appropriate angular acceleration is caused.

The second angular acceleration estimating unit30B in the second comparative example computes an angular acceleration with use of the PI controllers27and28. With this configuration, when a phase error is sufficiently small, the phase may converge to an appropriate value as a result of adjustment of a control quantity by the PI controllers27and28. In a frequency band in which a phase error is significantly large, however, control may become instable.

In the circumstances, in the first embodiment, the second angular velocity estimating unit22includes a control system for performing phase compensation such that an angular velocity can be computed with an appropriate phase.FIG.7is a block diagram illustrating a detailed configuration of the second angular velocity estimating unit22in the speed estimating device101illustrated inFIG.1. As illustrated inFIG.7, the second angular acceleration estimating unit30includes a Fourier coefficient calculator52, integral (I-) controllers53and54, and an AC restoring unit55. In the first embodiment, the second angular acceleration estimating unit30operates as a specific-frequency angular acceleration estimator. In addition, in the second angular acceleration estimating unit30, the Fourier coefficient calculator52operates as a specific frequency extractor that extracts a specific frequency component, and the I-controllers53and54and the AC restoring unit55operate as a specific-frequency angular velocity estimator.

InFIG.7, the disturbance frequency fdis inputted to the compensation phase computing unit51, the Fourier coefficient calculator52, and the AC restoring unit55. The compensation phase computing unit51determines a compensation phase θplsin view of the closed loop characteristic to be controlled. Specifically, the compensation phase θplsis stored as a map associated with the disturbance frequency, and the compensation phase θplscan be determined by reference to the map. Alternatively, an approximation formula that is changed depending on disturbance frequency may be held, and the compensation phase θplsmay be determined using the approximation formula. The compensation phase θplsis inputted to the Fourier coefficient calculator52.

The Fourier coefficient calculator52obtains the cosine coefficient Ec′ and the sine coefficient Es′ of the model deviation on the basis of the disturbance frequency fdand the compensation phase θplsusing the following equations (12) and (13).

The cosine coefficient Ec′ of the model deviation is subjected to I-control by the I-controller53as expressed by the following equation (14). In addition, the sine coefficient Es′ of the model deviation is subjected to I-control by the I-controller54as expressed by the following equation (15).

In the above equations (14) and (15), Krpl_1represents the integral gain of the I-controllers53and54. Note that the cosine coefficient Ec′ and the sine coefficient Es′ that are control inputs in the I-controllers53and54are in a dimension of an angular velocity, whereas control outputs of the I-controllers53and54are in a dimension of an angular acceleration. In addition, conversion from an angular velocity to an angular acceleration has a relation of differentiation, whereas a controlled object naturally has an integral characteristic. Thus, in a coordinate system resulting from conversion to direct current, the cosine coefficient Ec′ and the sine coefficient Es′ that are control inputs each appear as a gain of a multiple of conversion frequency. The cosine coefficient Ec′ and the sine coefficient Es′ are therefore regarded as a proportional characteristic in this coordinate system rather than an integral characteristic. In this situation, control can be performed only by integrators, and the I-controllers53and54are thus used. Needless to say, PI controllers may be used where necessary as in the second comparative example in order to improve the responsiveness.

The AC restoring unit55performs the computation of the following equation (16) on the basis of the cosine coefficient Ec′ and the sine coefficient Es′. This equation (16) is an arithmetic expression for calculating the second estimated angular acceleration ω⋅{circumflex over ( )}r2.
[Formula 16]
{dot over ({circumflex over (ω)})}r2=({dot over ({circumflex over (Ω)})}c′ cos(2πfdt)+{dot over ({circumflex over (Ω)})}s′ sin(2πfdt))  (16)

FIG.9is a first graph used for explaining the effect of the speed estimating device101according to the first embodiment.FIG.10is a second graph used for explaining the effect of the speed estimating device101according to the first embodiment.FIGS.9and10both illustrate an example of a result of simulation in which the AC motor2is driven with being provided with speed pulsation and the rotational speed of the AC motor2is estimated. In this simulation, the second angular velocity estimating unit22is activated and speed pulsation estimation is started five seconds after the AC motor2is driven.

In addition,FIG.9illustrates waveforms obtained by plotting cosine components Ωc⋅{circumflex over ( )} of an angular acceleration estimated with the estimation response being set to 1 [rad/s], and sine components Ωs⋅{circumflex over ( )} of the angular acceleration. Upper part thereof illustrates waveforms in a case without phase compensation, which corresponds to a result obtained by the configuration in the second comparative example. Lower part thereof illustrates waveforms in a case with phase compensation, which corresponds to a result obtained by the configuration of the first embodiment.

In the case without phase compensation, because some error is caused in an estimated phase of speed pulsation as described above, the value of angular acceleration does not converge but diverges, and a set response cannot be obtained. In contrast, in the case with phase compensation, it can be seen that the estimated angular acceleration converges and the operation is stable. In addition, it can be seen that the response speed rises by 63% in about one second from the start of estimation, and desired response is thus achieved.

In addition,FIG.10illustrates waveforms of an estimated angular velocity, upper part thereof illustrates a case without phase compensation, and lower part thereof illustrates a case with phase compensation. A left part of each of the upper and lower parts illustrates waveforms before activation of the second angular velocity estimating unit22, and a right part of each of the upper and lower parts illustrates waveforms after the second angular velocity estimating unit22is activated and the value has converged. Each thick curve represents an actual angular velocity, and each thin curve represents an estimated angular velocity.

Before the activation, the phase of the estimated angular velocity lags behind the actual angular velocity, and also the amplitude of the estimated angular velocity is smaller than that of the actual angular velocity. After the activation, in the case without phase compensation, the control diverges and the amplitude of the estimated angular velocity is significantly larger than that of the actual angular velocity, and also the phase thereof has a difference from the latter. In contrast, in the case with phase compensation, the estimated angular velocity is equal to the actual angular velocity, and it is seen that the control is performed satisfactorily.

The integrator31integrates the second estimated angular acceleration ω⋅{circumflex over ( )}r2computed by the AC restoring unit55according to the following equation (17) to obtain the second estimated angular velocity ω{circumflex over ( )}r2. The integrator31operates as a second angular velocity calculator. The second estimated angular velocity ω{circumflex over ( )}r2is computed as a specific high-frequency component of the actual angular velocity.

Note that it is obvious for a person skilled in the art that a block diagram of a control system can be modified. For example, a configuration may be realized as inFIG.8.FIG.8is a block diagram illustrating a modification of a configuration of a detail part illustrated inFIG.7. For example, the configuration of the integrators25and31inFIG.7may be modified to be a configuration such that the estimated angular accelerations are added before passing through an integrator. Specifically, while two integrators25and31are located on input sides of the estimated angular velocity calculator23in the configuration ofFIG.7, one integrator32may be located on an output side of the estimated angular velocity calculator23as in a speed estimating device101-1ofFIG.8. This configuration produces an advantageous effect that it is possible to reduce the number of integrators.

An equation for estimating a final angular velocity is expressed by the following equation (18). Specifically, in the estimated angular velocity calculator23, the second estimated angular velocity ω{circumflex over ( )}r2calculated by the integrator31is added to the first estimated angular velocity ω{circumflex over ( )}r1computed by the first angular velocity estimating unit21, thereby obtaining the estimated angular velocity ω{circumflex over ( )}rexpressed by the following equation (18).

While an example of using an adder is described in the above equation (18) and in the estimated angular velocity calculator23illustrated inFIG.7, the present invention is not limited to this example. In such a case where the definition of positive or negative of the compensation phase in the compensation phase computing unit51and the definition of an output of the AC restoring unit55are opposite in phase, a subtractor is used. In other words, the configuration of the estimated angular velocity calculator23is determined depending on the definition of positive or negative of the compensation phase, the definition of an output from the AC restoring unit55, and the like.

A difference between the equation (18) and the equation (5) lies in that the second estimated angular velocity ω{circumflex over ( )}r2is used in the equation (18). The second angular velocity estimating unit22converts a given harmonic wave of the model deviation ε into direct currents by dividing the harmonic wave into a sine wave and a cosine wave, extracts the sine wave and the cosine wave, and performs I-control so that the sine wave and the cosine wave become zero. The second angular velocity estimating unit22then restores the output of the I-control to an alternating current to estimate a high-frequency component of the actual angular velocity, and increases the gain only in a part with a determined frequency. Thus, a speed pulsation component due to periodic disturbance can be estimated as the second estimated angular velocity ω{circumflex over ( )}r2with high accuracy. Note that the second angular velocity estimating unit22described above has a structure of a sort of iterative controller or a learning controller. Another sort of iterative controller or a learning controller may therefore be used instead of the second angular velocity estimating unit22.

FIG.11is a hardware configuration diagram of the speed estimating device101according to the first embodiment. Although not illustrated inFIGS.1and7, a voltage applying unit3and a current detecting unit4are illustrated inFIG.11. The voltage applying unit3serves as voltage applying means for applying a voltage to the AC motor2. An example of the voltage applying means is a power converter. The voltage vector corresponds to a voltage command generated by the voltage applying unit3. A voltage generated on the basis of the voltage command is applied to the AC motor2, and information on the voltage command is inputted to the speed estimating device101. In addition, the current vector is generated by the current detecting unit4and inputted to the speed estimating device101. The current vector is vector information on an AC current flowing in the AC motor2. An example of the current vector is a detected value of a dq-axis current obtained by converting an AC current detected by the current detecting unit4into a value on dq-coordinate axes.

The speed estimating device101includes a processor901and a memory902. The memory902includes a volatile storage device, which is not illustrated, typified by a random access memory, and a nonvolatile auxiliary storage device, which is not illustrated, typified by a flash memory. Note that the memory902may include an auxiliary storage device of a hard disk instead of the volatile storage device and the nonvolatile auxiliary storage device. The processor901executes a program inputted from the memory902. Because the memory902includes the auxiliary storage device and the volatile storage device, a program is inputted from the auxiliary storage device to the processor901via the volatile storage device. The processor901may output data on a computation result to the volatile storage device of the memory902, and may save the data into the auxiliary storage device via the volatile storage device.

Various systems have been considered for the voltage applying unit3and the current detecting unit4, and basically any system may be used therefor. The voltage applying unit3and the current detecting unit4may be provided inside the speed estimating device101. In addition, the speed estimating device101may include voltage detecting means for detecting the voltage vector outputted by the voltage applying unit3. In this case, the voltage applying unit3may be configured to transmit a voltage vector command value to the processor901, for a numerical value relating to the voltage detected by the voltage detecting means to be transmitted to the processor901. The current detecting unit4may also be configured to transmit a detected numerical value to the processor901.

The processor901computes the estimated angular velocity ω{circumflex over ( )}ron the basis of the current vector and the voltage vector of the AC motor2. By the processor901performing the computation of the second angular velocity estimating unit22described above, the speed pulsation due to periodic disturbance can be estimated with high accuracy. Note that the processor901may also serve as the driving device for the AC motor2. Specifically, the processor901may be configured to not only perform the speed estimation but also calculate a voltage command vector such that an estimated speed has a desired value. There are publicly known various methods for performing position-sensorless torque control, including that of Non Patent Literature mentioned above.

As described above, the speed estimating device for an AC motor according to the first embodiment can estimate speed pulsation of the AC motor with an appropriate phase regardless of frequency, and can realize higher accuracy of speed estimation.

In addition, the speed estimating device for an AC motor according to the first embodiment enables speed estimation with high accuracy even in a case of high pulsation frequency, which has been a problem in the conventional art, and can also estimate pulsation in a higher frequency range than in the conventional art by virtue of provision of a computation unit for increasing the estimation response in a specific frequency band even if a special storage means is not provided therefor. Furthermore, because the compensation phase is obtained in view of the closed loop phase characteristic of angular velocity estimation of the first angular velocity estimating unit that is an adaptive magnetic-flux observer, the angular velocity estimation can be performed at a desired response speed, and stable control can be achieved.

Second Embodiment

FIG.12is a block diagram illustrating a configuration of a speed estimating device101C according to a second embodiment. InFIG.12, in the speed estimating device101C according to the second embodiment, the second angular velocity estimating unit22in the configuration of the speed estimating device101according to the first embodiment illustrated inFIG.7is replaced with a second angular velocity estimating unit22C. In the second angular velocity estimating unit22C, the second angular acceleration estimating unit30is replaced with a second angular acceleration estimating unit30C. In the second angular acceleration estimating unit30C, the Fourier coefficient calculator52is replaced with a Fourier coefficient calculator52C, and the AC restoring unit55is replaced with an AC restoring unit55C. While the compensation phase θplscomputed by the compensation phase computing unit51is inputted to the Fourier coefficient calculator52inFIG.7, the compensation phase θplsis inputted to the AC restoring unit55C inFIG.12. Note that the other configuration is the same as or equivalent to that inFIG.7, and the same or equivalent components are denoted by the same reference symbols and redundant description thereof will be omitted.

The Fourier coefficient calculator52of the first embodiment illustrated inFIG.7computes Fourier coefficients by using the equations (12) and (13). On the other hand, the Fourier coefficient calculator52C of the second embodiment illustrated inFIG.12computes Fourier coefficients by using the following equations (19) and (20).

In addition, the AC restoring unit55of the first embodiment illustrated inFIG.7computes the second estimated angular acceleration ω⋅{circumflex over ( )}r2by using the above equation (16). In contrast, the AC restoring unit55C of the second embodiment illustrated inFIG.12computes the second estimated angular acceleration ω⋅{circumflex over ( )}r2by using the following equation (21).
[Formula 21]
ωr2=(Ωc′ cos(2πfdtθpls)+Ωs′ sin(2πfdt−θpls))  (21)

If the relation of the phases used for computation by the Fourier coefficient calculator52(52C) and the AC restoring unit55(55C) is maintained, the effect of estimating speed pulsation with an appropriate phase regardless of frequency, which is mentioned in the first embodiment, can be similarly produced. Thus, computation as expressed by the equations (19) to (21) can produce the same effect.

Note that, in a manner similar to the first embodiment, a configuration in which the cosine coefficient Ec′ of the model deviation ε and the sine coefficient Es′ of the model deviation ε are obtained from the I-controllers53and54, respectively, can be adopted also in the second embodiment, and the arithmetic expressions for it are still the equations (14) and (15) with no change.

Third Embodiment

FIG.13is a block diagram illustrating a configuration of a speed estimating device101D according to a third embodiment. InFIG.13, in the speed estimating device101D according to the third embodiment, the first angular velocity estimating unit21and the second angular velocity estimating unit22in the configuration of the speed estimating device101according to the first embodiment illustrated inFIG.7are replaced with a first angular velocity estimating unit21D and a second angular velocity estimating unit22D, respectively. In the first angular velocity estimating unit21D, the integrator25is omitted from the configuration of the first angular velocity estimating unit21, and in the second angular velocity estimating unit22D, the integrator31is omitted from the second angular velocity estimating unit22. Note that the other configuration is the same as or equivalent to that inFIG.7, and the same or equivalent components are denoted by the same reference symbols and redundant description thereof will be omitted.

A PI controller24included in the first angular velocity estimating unit21D performs computation processing expressed by the above equation (5). In other words, the first angular velocity estimating unit21D generates the first estimated angular velocity ω{circumflex over ( )}r1only in PI control without using an integrator, and outputs the first estimated angular velocity ω{circumflex over ( )}r1to the estimated angular velocity calculator23. Similarly, a second angular acceleration estimating unit30included in the second angular velocity estimating unit22D also generates the second estimated angular velocity ω{circumflex over ( )}r2without using an integrator, and outputs the second estimated angular velocity ω{circumflex over ( )}r2to the estimated angular velocity calculator23. Subsequent operations are as described in the first embodiment.

Because the speed estimating device101D according to the third embodiment includes the second angular velocity estimating unit22D, the speed estimating device101D can estimate high-frequency speed pulsation more accurately than the speed estimating devices of the first and second comparative examples. The reasons thereof are as described in the first embodiment.

The accuracy of speed estimation in the third embodiment, however, is lower than that in the first embodiment. In terms of the computation amount required for computation for estimation, however, the third embodiment is more advantageous because the computation of integration is omitted. Therefore, in a case where the computation performance of the processor901illustrated inFIG.11is low and the calculation amount is to be as small as possible, the configuration of the third embodiment is more preferable. Although details will be provided later, in a case where speed pulsation suppression control described in a fifth embodiment is performed, however, the configuration of the speed estimating device101according to the first embodiment is more preferable.

In addition, for an example similar to the third embodiment, a configuration may be realized in which the first angular velocity estimating unit21D includes the integrator25and the second angular velocity estimating unit22D does not include the integrator31. Alternatively, another configuration may be realized in which the first angular velocity estimating unit21D does not include the integrator25and the second angular velocity estimating unit22D includes the integrator31.

Fourth Embodiment

FIG.14is a block diagram illustrating a configuration of a speed estimating device101E according to a fourth embodiment. InFIG.14, the speed estimating device101E according to the fourth embodiment includes a second compensation phase computing unit56and a third angular velocity estimating unit33in addition to the configuration of the speed estimating device101according to the first embodiment illustrated inFIG.1. In addition, the estimated angular velocity calculator23is replaced with an estimated angular velocity calculator23E. In other words, two angular velocity estimating units are provided in the first to third embodiments, but the fourth embodiment is directed to a configuration having three angular velocity estimating units. Note that the other configuration is the same as or equivalent to that inFIG.7, and the same or equivalent components are denoted by the same reference symbols and redundant description thereof will be omitted.

Typically, the characteristics of angular speed pulsation included in the rotational angular velocity of an AC motor vary depending on an application applied to the motor or on a load device connected to the AC motor. Now in a case where a connected load device has periodic torque fluctuation, a rotary compressor is considered by way of example.

FIG.15is a graph illustrating an example of a waveform of load torque of a rotary compressor. The horizontal axis represents rotation angle, and the vertical axis represents load torque. Herein, the number of compression chambers in the rotary compressor is represented by k. 0 to 360 degrees of the rotation angle corresponds to one cycle period of a mechanical angle, that is, a mechanical angle period.

First, in a case where only one compression chamber is present, that is, in a case of k=1, the load torque vibrates greatly with the mechanical angle period as illustrated by a solid curve inFIG.15. Although second and third harmonics are also included in the load torque waveform, the first-order vibration is the greatest. Therefore, in a case where a configuration in the first to third embodiments is applied, the largest first-order angular speed pulsation can be estimated with high accuracy by setting the disturbance frequency fdused for computation of the second estimated angular velocity ω{circumflex over ( )}r2to a primary frequency of the mechanical angular frequency.

In the fourth embodiment, a plurality of angular velocity estimating units are provided in parallel. Therefore, speed pulsation due to second-order and third-order torque fluctuations included in the load torque characteristics can also be estimated with high accuracy. In the example ofFIG.14, the frequency of speed pulsation to be estimated is used as a second disturbance frequency fd2, which is estimated by the third angular velocity estimating unit33and outputted as a third estimated angular velocity ω{circumflex over ( )}r3.

The same is applicable to a case where the number of compression chambers is two or three, that is, a case of k=2 or k=3. As the number of compression chambers is larger, the structure is more complicated and the cost is higher, but the waveform has smaller pulsation as illustrated inFIG.15. Specifically, in the case of k=2, a second harmonic component of the mechanical angular frequency is large, and in the case of k=3, a third harmonic component is large.

In the case of k=2, for example, the second-order vibration in the mechanical angle period is dominant as illustrated inFIG.15. Therefore, the disturbance frequency fdinputted to the second angular velocity estimating unit22is set as a secondary frequency of the mechanical angular frequency. Then, if higher-order frequencies than the secondary frequency are to be further estimated, these higher-order frequencies may be inputted as the second disturbance frequency fd2to the third angular velocity estimating unit33.

In the case of k=3, for example, the third-order vibration in the mechanical angle period is dominant as illustrated inFIG.15. Therefore, the disturbance frequency fdinputted to the second angular velocity estimating unit22is set as a tertiary frequency of the mechanical angular frequency. Then, if higher-order frequencies than the tertiary frequency are to be further estimated, these higher-order frequencies may be inputted as the second disturbance frequency fd2to the third angular velocity estimating unit33.

It is noted that a plurality of angular velocity estimating units are provided in parallel and each of the angular velocity estimating units performs phase compensation in the fourth embodiment, but the present invention is not necessarily limited by this example. Phase compensation may be performed by at least one of the angular velocity estimating units, and this single compensation is sufficient for producing the effects peculiar to phase compensation described above.

Fifth Embodiment

FIG.16is a block diagram illustrating a configuration of a driving device102for an AC motor according to a fifth embodiment. The driving device102according to the fifth embodiment is a driving device configured to control the AC motor2with use of the speed estimating device101,101C,101D, or101E described in the first to fourth embodiments.FIG.16illustrates a configuration to which the speed estimating device101according to the first embodiment is applied, as an example.

As illustrated inFIG.16, the driving device102according to the fifth embodiment includes a speed controlling unit5, an adder7, a torque controlling unit6, a compensation torque command computing unit8that is a compensation amount computing unit, and the speed estimating device101. The compensation torque command computing unit8operates as a “compensation command computing unit”.

First, the operation of the compensation torque command computing unit8will be explained. Note that by way of example, the following description is given for a configuration in which the compensation torque command computing unit8performs computation on the basis of information on angular acceleration computed by the second angular velocity estimating unit22.

The compensation torque command computing unit8computes a compensation torque command τ*ripby using the following equations (22) to (24).

In the equations (22) and (23), Ksi_riprepresents an integral gain of the compensation torque command computing unit8. In addition, Tcin the above equation (22) represents the amplitude of the compensation torque command τ*ripcorresponding to the cosine component of the pulsation of the angular acceleration, and Tsin the equation (23) represents the amplitude of the compensation torque command τ*ripcorresponding to the sine component of the pulsation of the angular acceleration. As expressed by the above equations (22) and (23), a compensation torque command τ*ripis computed such that each of the cosine component of the pulsation of the angular acceleration and the sine component of the pulsation of the angular acceleration is zero. Control using this compensation torque command τ*ripcan reduce the pulsation of the angular acceleration, and as a result, can reduce the speed pulsation as well.

The reason why integral control is used in the equations (22) and (23) is that the characteristic of the controlled object is a proportional characteristic when the compensation torque command τ*ripis obtained on the basis of the angular acceleration. In addition, it is because an ideal closed loop characteristic can be achieved by causing a controller to have an integral characteristic and performing feedback control. In the case of a configuration like the second angular velocity estimating unit22in which the compensation phase θplsdetermined by the compensation phase computing unit51is used, compensation can be made for the phase of the equation (24) on the basis of the compensation phase θpls. Alternatively, when the compensation phase θplsis a compensation phase based on the disturbance frequency fd, the computation may be performed using an equation other than the equation (24). Although the concerned explanation is not provided because the principle thereof is the same, the computation of the compensation torque command described above can be similarly performed with use of the second estimated angular velocity ω{circumflex over ( )}r2computed by the second angular velocity estimating unit22.

Next, the operations of the speed controlling unit5, the torque controlling unit6, and the adder7will be explained.

The speed controlling unit5computes a basic torque command τ*ωon the basis of an angular velocity command and the estimated angular velocity ω{circumflex over ( )}r. Speed control performed by a typical PI controller can be applied to the computation of the basic torque command τ*ω.

The adder7adds the compensation torque command τ*ripto the basic torque command τ*ωto compute a torque command τ* according to the following equation (25).
[Formula 25]
τ*=τω+τ*rip(25)

The torque controlling unit6includes the voltage applying unit3illustrated inFIG.11. The torque controlling unit6determines a voltage vector to be applied to the AC motor2on the basis of the torque command τ*. The voltage vector may be of a type computed through electric-current control such as PI control on the basis of a current command value computed on the basis of the torque command τ*. Alternatively, an appropriate voltage command value depending on the torque command τ* may be stored in the memory902and obtained directly on the basis of the torque command τ*.

The driving device102according to the fifth embodiment can obtain a compensation torque command to reduce the speed pulsation on the basis of information on the angular speed pulsation obtained by the speed estimating device101. This produces an effect of reducing uneven rotation of the AC motor2.

WhileFIG.16illustrates a configuration including the compensation torque command computing unit8that computes the compensation torque command τ*rip, the present invention is not limited to this configuration. Another configuration may be realized in which a compensation current command computing unit that computes a compensation current command is employed instead of the compensation torque command computing unit8. In the case of this configuration, an adder and a current controlling unit are provided on a subsequent stage of the torque controlling unit6. The adder adds a basic current command generated by the torque controlling unit6to the compensation current command computed by the compensation current command computing unit to generate a current command. The current controlling unit determines a voltage vector to be applied to the AC motor2on the basis of the current command outputted from the adder. Subsequent operations are as described above.

Sixth Embodiment

FIG.17is a block diagram illustrating a configuration of a driving device102A for an AC motor according to a sixth embodiment. InFIG.17, the AC motor2illustrated inFIG.16is replaced with a refrigerant compressor2aincluding the AC motor2. The driving device102A according to the sixth embodiment is configured using the speed estimating device101according to the first embodiment in order to reduce the speed pulsation of the refrigerant compressor2a.FIG.17illustrates a configuration to which the speed estimating device101according to the first embodiment is applied, but the present invention is not limited to this example. The driving device102A may be configured using any of the speed estimating devices101C,101D, and101E described in the second to fourth embodiments. Note that the configurations and the functions of the speed estimating devices101,101C,101D, and101E are as described above, and so description thereof is omitted in this part.

Next, the structure of the refrigerant compressor2aand a load torque in the refrigerant compressor2awill be described in detail with reference toFIGS.18and19.FIG.18is a cross-sectional view illustrating an outline structure of the interior of the refrigerant compressor2aillustrated as a driven object inFIG.17. In addition,FIG.19is a cross-sectional view illustrating a structure of the interior of a compressing unit202of the refrigerant compressor2aillustrated inFIG.18. Note that a refrigerant compressor called a rolling piston type rotary compressor will be described herein, but the present invention is not limited to this example. The refrigerant compressor may be another type of compressor such as a scroll compressor.

The refrigerant compressor2aincludes an airtight container211, the AC motor2housed in the airtight container211, a shaft201having one end passing through a rotor2-1constituting the AC motor2, the compressing unit202through which the other end of the shaft201passes and which is fixed to the inside of the airtight container211, an inlet pipe203provided to the airtight container211, and an outlet pipe204provided to the airtight container211.

A stator2-2of the AC motor2is attached to and retained by the airtight container211by shrinkage fitting, freeze fitting, or welding. Electric power is supplied to a coil2-3on the stator2-2via an electric wire, which is not illustrated. The rotor2-1is disposed inside the stator2-2with a gap2-4therebetween, and rotatably held by a bearing, which is not illustrated, via the shaft201situated at the center of the rotor2-1.

In the refrigerant compressor2ahaving the configuration as described above, upon driving of the AC motor2, refrigerant sucked into the compressing unit202via the inlet pipe203is compressed, and the compressed refrigerant is discharged out from the outlet pipe204. The refrigerant compressor2aoften has a structure in which the AC motor2is immersed in the refrigerant, and it is difficult to attach a position sensor to the AC motor2because of wide swing in temperature thereon. For this reason, in the refrigerant compressor200, the AC motor2has to be driven in a position sensorless driving manner.

As illustrated inFIG.19, the compressing unit202includes an annular cylinder212, a piston205formed rotatably and integrally with the shaft201and located inside the cylinder212, and a compression chamber213provided in an inner circumferential part of the cylinder212.

The cylinder212includes an inlet206communicating with the inlet pipe203illustrated inFIG.18, and an outlet207through which the compressed refrigerant is discharged outward. The inlet206and the outlet207communicate with the compression chamber213. The cylinder212includes a vane210that partitions the compression chamber213into a low-pressure sub-chamber communicating with the inlet pipe203and a high-pressure sub-chamber communicating with the outlet207, and a spring209set to energize the vane210.

The shaft201connects the AC motor2and the piston205with each other. The piston205is eccentric, so that the capacities on the suction side and the discharge side change depending on the rotation angle. The refrigerant sucked through the inlet206is compressed by the piston205. When the pressure in the compression chamber213increases, a discharge valve208opens, and the refrigerant is discharged through the outlet207. When the refrigerant is discharged, refrigerant flows into the suction side at the same time. As the rotation of the AC motor2is continued, the refrigerant is discharged once per revolution in the mechanical angle of the piston205.

The load torque pulsation of the refrigerant compressor2acorresponds to periodic disturbance for the AC motor2, and so becomes a factor for speed pulsation. It is generally known that greater speed pulsation in the refrigerant compressor2aresults in greater noise and vibration.

There is a significant point that the frequencies of the load torque pulsation and the speed pulsation are determined by the structure of the refrigerant compressor2a, and so are known in advance. In the refrigerant compressor2aaccording to the sixth embodiment, the control system illustrated inFIG.17is built under favor of that point. The refrigerant compressor2aestimates a specific frequency component of the speed pulsation with high accuracy in the second angular velocity estimating unit22, and computes such a compensation torque command τ*ripthat suppresses the pulsation in the compensation torque command computing unit8. As a result, the speed pulsation can be reduced without preconditioning. Because preconditioning becomes unnecessary, the cost for conditioning prior to shipment can be significantly reduced, then resulting in great usefulness.

Seventh Embodiment

FIG.20is a diagram illustrating a configuration of a refrigeration cycle apparatus according to a seventh embodiment. The refrigeration cycle apparatus300illustrated inFIG.20includes the driving device102for an AC motor, the refrigerant compressor2a, a condenser301connected with the refrigerant compressor2avia piping305, a liquid receiver302connected with the condenser301via the piping305, an expansion valve303connected with the receiver302via the piping305, and an evaporator304connected with the expansion valve303via the piping305. The evaporator304is connected to the inlet pipe203.

By the refrigerant compressor2a, the condenser301, the liquid receiver302, the expansion valve303, the evaporator304, and the inlet pipe203being connected by the piping305, the refrigerant compressor2a, the condenser301, the liquid receiver302, the expansion valve303, the evaporator304, and the inlet pipe203constitute a refrigeration cycle circuit306in which the refrigerant circulates. In the refrigeration cycle circuit306, processes of evaporating, compressing, condensing, and expanding of the refrigerant are repeated, and heat is transferred while the refrigerant repeatedly changes from liquid to gas and from gas to liquid.

The functions of the devices constituting the refrigeration cycle apparatus300will be explained. The evaporator304evaporates refrigerant liquid in a low-pressure state, draws heat from the surrounding, and thus has a cooling effect. The refrigerant compressor2acompresses refrigerant gas into high-pressure gas in order to condense the refrigerant. The refrigerant compressor2ais driven by the driving device102A according to the sixth embodiment. The condenser301releases the heat to condense the high-pressure refrigerant gas into refrigerant liquid. The expansion valve303subjects the refrigerant liquid to throttle expansion into low-pressure liquid in order to evaporate the refrigerant. The liquid receiver302is provided for adjusting the amount of refrigerant to be circulated, and may be omitted in a case of a compact apparatus.

Typically, improvement in quietness and reduction in cost are required for a refrigeration cycle apparatus. In a household refrigeration cycle apparatus, there are particularly high demands for lower cost, and so a single rotary compressor is often used. A single rotary compressor is a rotary compressor described inFIGS.18and19, which is a compressor of a type including only one compression chamber213. A rotary compressor involves significantly great load torque pulsation, and thus tends to cause large vibration and loud noise. On the other hand, in a feedforward control system in the conventional art, complicated control adjustment has needed for reducing vibration and noise.

The refrigeration cycle apparatus300according to the seventh embodiment performs feedback control so that the driving device102A automatically makes the speed pulsation be zero. As a result, the cost for adjustment before shipping can be significantly reduced. In addition, according to the seventh embodiment, speed pulsation is reduced by feedback control, thereby enabling flexible response to variations in manufacture, fluctuation in motor constant, and changes in compressor load condition. Consequently, the refrigeration cycle apparatus300that has higher environment resistance can be achieved.

The configurations presented in the above embodiments are examples of contents of the present invention, and can each be combined with other publicly known techniques and partly omitted and/or modified without departing from the scope of the present invention.

REFERENCE SIGNS LIST