KR100576032B1 - Linear compressor controlling apparatus and its controlling method - Google Patents

Abstract

The present invention relates to a control apparatus and a control method of a linear compressor that not only actively copes with a load but also efficiently operates by synchronizing an operating frequency to a natural frequency of a movable member that varies depending on a load. The control apparatus of the linear compressor according to the present invention includes a reverse electromotive force phase detector for detecting a phase of the counter electromotive force (E) from the voltage command value (V ^* ) and the input current (i) for the linear compressor, and a phase for detecting the phase of the input current (i). A current phase detection unit, a frequency generation unit comparing the phase of the counter electromotive force E with a phase of the input current i to generate a frequency change value, a controller for correcting the voltage command value V ^* according to the frequency change value; The inverter unit is configured to receive a DC voltage and generate a sine wave voltage according to the corrected voltage command value V ^* to be applied to the linear compressor.

Description

LINEAR COMPRESSOR CONTROLLING APPARATUS AND ITS CONTROLLING METHOD}

The present invention relates to a control apparatus and a control method of a linear compressor that not only actively copes with a load but also efficiently operates by synchronizing an operating frequency to a natural frequency of a movable member that varies depending on a load.

In general, a compressor is a mechanical device that increases pressure by receiving power from a power generator such as an electric motor or a turbine to compress air, refrigerant, or various other working gases. It is widely used throughout.

These compressors are classified into a reciprocating compressor which compresses the refrigerant while linearly reciprocating the inside of the cylinder by forming a compression space in which the working gas is absorbed and discharged between the piston and the cylinder. And a rotary compressor for compressing the refrigerant while the roller is eccentrically rotated along the inner wall of the cylinder to form a compression space in which the working gas is sucked and discharged between the eccentrically rotating roller and the cylinder. As a scroll compressor that compresses the refrigerant while the rotating scroll is rotated along the fixed scroll by forming a compressed space in which the working gas is absorbed and discharged between the orbiting scroll and the fixed scroll. Divided.

Recently, among the reciprocating compressors, in particular, the piston is directly connected to the reciprocating linear motion drive motor, so that there is no mechanical loss due to the motion conversion to improve the compression efficiency as well as a simple linear compressor has been developed a lot.

In general, a linear compressor sucks, compresses, and discharges a refrigerant by using a linear driving force of a motor. A compression unit including a cylinder and a piston for compressing a refrigerant gas is large, and a linear motor supplying driving force to the compression unit. It is divided into included driving parts.

Specifically, the linear compressor is installed so that the cylinder is fixed inside the sealed container, the piston is installed in the cylinder to reciprocate linear movement, the compression space in the cylinder as the piston reciprocating linear movement in the cylinder It is configured to compress and then discharge the refrigerant into the inlet, the inlet and outlet valve assembly is installed in the compression space to adjust the inflow and discharge of the refrigerant in accordance with the pressure in the compression space.

In addition, the linear motor for generating a linear motion force to the piston is installed so as to be connected to each other, the linear motor is provided with an inner stator and an outer stator configured to be laminated in a circumferential direction around the cylinder with a predetermined gap, The coil is wound around the inner stator or the outer stator, and a permanent magnet is installed in the gap between the inner stator and the outer stator so as to be connected to the piston.

At this time, the permanent magnet is installed to be movable in the direction of movement of the piston, and the reciprocating linear motion in the direction of movement of the piston by the electromagnetic force generated as the current flows in the coil, the linear motor is a constant operation Not only is it operated at frequency f _c , but it also causes the piston to reciprocate linearly with a predetermined stroke S.

On the other hand, the piston is provided with a variety of springs to be elastically supported in the direction of movement even if the linear motor reciprocating linear movement, specifically, a coil spring which is a kind of mechanical spring to the closed container and the cylinder in the direction of movement of the piston It is installed to be elastically supported, and the refrigerant sucked into the compression space also acts as a gas spring.

At this time, the coil spring has a constant mechanical spring constant (K _m ), the gas spring has a gas spring constant (K _g ) that is variable according to the load, the mechanical spring constant (K _m ) and gas spring constant (K Taking into account _g ), the natural frequency f _n of the piston is calculated.

The calculated natural frequency f _n of the piston determines the operating frequency f _{c of} the linear motor, and the linear motor matches the operating frequency f _c with the natural frequency f _n of the piston. The efficiency can be increased by operating in the resonance state.

Therefore, in the linear compressor configured as described above, when a current is applied to the linear motor, an electromagnetic force is generated by interacting with the outer stator and the inner stator as a current flows in the coil, and the permanent magnet and The piston connected to this causes the reciprocating linear motion.

At this time, the linear motor operates at a constant operating frequency f _c , and the operating frequency f _n of the linear motor coincides with the resonant frequency f _n of the spring to operate in a resonance state to maximize efficiency. Can be.

As such, the pressure inside the compression space is changed as the piston reciprocates linearly in the cylinder, and the refrigerant is sucked into the compression space according to the pressure change of the compression space, and then compressed and discharged.

The linear compressor configured as described above has a natural frequency f _n of the piston which is calculated by the mechanical spring constant K _m of the coil spring and the gas spring constant K _g of the gas spring under the load considered by the linear motor in design. Since the linear motor is configured to operate at an operating frequency f _c corresponding to the linear motor operates in a resonance state only under the load considered in the design, the efficiency can be increased.

However, in the linear compressor as described above, as the actual load varies, the gas spring constant K _g of the gas spring and the natural frequency f _n of the piston calculated by considering the same change.

Specifically, in the linear motor, as shown in FIG. 1A, the operating frequency f _c is determined to match the natural frequency f _n of the piston in the middle load region during design, and the constant constant determined as described above even if the load is variable. Although operated at an operating frequency f _c , the natural frequency f _n of the piston increases as the load increases.

Equation 1

Where f _n is the natural frequency of the piston, K _m and K _g are the mechanical spring constant and the gas spring constant, and M is the mass of the piston.

Usually, because of the small proportion of gas spring constant (K _g) share of design at the time the total spring constant (K _T) does not take into account the gas spring constant (K _g), the situation the gas spring constant (K _g) at a constant value In addition, since the mass (M) and the mechanical spring constant (K _m ) of the piston also has a constant value, the natural frequency (f _n ) of the piston is also calculated as a constant value depending on Equation (1).

In practice, however, the more the load increases, the pressure and temperature of the coolant increases in a limited space, which results the elastic force of the gas spring itself increases the gas spring constant (K _g) is large, and yield to be proportional to such a gas spring constant (K _g) The natural frequency f _n of the piston is also increased.

Therefore, as shown in FIGS. 1A and 1B, the piston operates in such a way as to reach the top dead center because the operating frequency f _c of the linear motor and the natural frequency f _n of the piston coincide in the intermediate load region. The compression operation is performed, and the operation is performed in a resonance state, thereby maximizing the efficiency of the compressor.

However, in the low load region, the piston's natural frequency (f _n ) is smaller than the operating frequency (f _c ) of the linear motor, so that the piston is excessively moved above the top dead center, so that the excessive compression force is applied as well as the piston and the cylinder. Friction and abrasion occurs, and the compressor efficiency is lowered because it is not operated in a resonance state.

Similarly, in the high load region, the piston's natural frequency f _n is greater than the operating frequency f _c of the linear motor, so that the piston is operated to fall below the top dead center, so that the compression force is lowered and the compressor is not operated in a resonance state. Inefficient

As a result, in the conventional linear compressor, the natural frequency f _n of the piston is variable as the load is varied, whereas the linear motor is not operated in a resonance state because the operating frequency f _{c of} the linear motor is constant. There is a problem in that the efficiency is lowered and the load cannot be released quickly due to the failure to actively respond to the load.

Accordingly, the present invention provides a control apparatus and a control method of a linear compressor for synchronizing the mechanical natural frequency (f _n ) and the motion frequency (f _c ) by the linear motor to perform the suction and compression stroke of the linear compressor in a resonance state. It aims to provide.

In addition, the present invention provides a control apparatus and a control method of a linear compressor to solve the mechanical error of the linear compressor by varying and synchronizing the movement frequency (f _c ) by estimating the mechanical natural frequency (f _n ) that varies depending on the load. It aims to do it.

The apparatus for controlling a linear compressor according to the present invention for achieving the above object includes a back electromotive force phase detection unit for detecting a phase of the counter electromotive force (E) from a voltage command value (V ^* ) and an input current (i) for the linear compressor, and the input current ( a current phase detector for detecting a phase of i), a frequency generator for comparing the phase of the counter electromotive force E with a phase of the input current i, and generating a frequency change value, and the voltage command value V according to the frequency change value. ^And a control unit for correcting ^* ) and an inverter unit for generating a sine wave voltage according to the corrected voltage command value V ^* and applying the DC voltage to the linear compressor.

At this time, the counter electromotive force phase detection unit preferably calculates the counter electromotive force (E) according to the following equation to detect the phase.

The frequency generator may generate the frequency change value such that the phase of the counter electromotive force E is in phase with the phase of the input current i.

The controller may transmit the corrected voltage command value V ^* to the inverter unit in the form of a predetermined inverter control signal.

In addition, the control method of the linear compressor according to the present invention for achieving this object is to detect the phase of the counter electromotive force (E) from the voltage command value (V ^* ) and the input current (i) for the linear compressor, and the input current (i) Detecting a phase of c);

The method may further include generating a frequency change value by comparing the phase of the counter electromotive force E with a phase of the input current i, correcting the voltage command value V ^* according to the frequency change value, and applying a DC voltage. And generating a sine wave voltage according to the corrected voltage command value V ^* .

The features and advantages of the present invention may be better understood with reference to the following accompanying drawings in conjunction with the following detailed description of embodiments of the invention, of which:

1A is a graph showing a stroke according to load in a linear compressor according to the prior art,

1B is a graph showing the efficiency according to the load in the linear compressor according to the prior art,

2 is a sectional view showing a linear compressor according to the present invention;

3A is a graph showing a stroke according to load in a linear compressor according to the present invention;

3B is a graph showing the efficiency according to the load in the linear compressor according to the present invention,

4 is a graph showing a change in the gas spring constant (K _g ) according to the load in the linear compressor according to the present invention,

Fig. 5 is an equivalent circuit diagram when modeling a linear motor as an R-L circuit with counter electromotive force.

6 is a configuration diagram of a control device of the linear compressor according to the present invention.

Description of the Preferred Embodiments

DETAILED DESCRIPTION Hereinafter, embodiments of the present invention in which the above object can be specifically realized are described with reference to the accompanying drawings.

In the linear compressor according to the present invention, as shown in FIG. 2, an inlet tube 2a and an outlet tube 2b through which refrigerant flows in and out are installed at one side of the sealed container 2, and the inside of the sealed container 2 is provided. The cylinder 4 is installed to be fixed, and the piston 6 is installed in the cylinder 4 so as to reciprocate linear movement so as to compress the refrigerant sucked into the compression space P inside the cylinder 4. At the same time, a variety of springs are installed to elastically support the direction of movement of the piston (6), the piston (6) is installed so as to be connected to the linear motor 10 for generating a linear reciprocating drive force, the natural frequency of the piston ( Even though f _n ) varies depending on the load, the linear motor 10 controls its operation frequency f _c to be synchronized with the natural frequency f _n of the piston as shown in FIGS. 3A and 3B. Resonant operation in the load region To increase the compression efficiency.

In addition, a suction valve 22 is installed at one end of the piston 6 in contact with the compression space P, and a discharge valve assembly 24 is provided at one end of the cylinder 4 in contact with the compression space P. ) Is installed, and the suction valve 22 and the discharge valve assembly 24 are automatically adjusted to open and close according to the pressure inside the compression space P, respectively.

Here, the airtight container (2) is installed so that the upper and lower shells are coupled to each other so that the inside is sealed, the inlet pipe (2a) and the outlet pipe (2b) for the coolant flow in one side is installed, the The piston 6 is installed inside the cylinder 4 so as to be elastically supported in the movement direction for reciprocating linear motion, and the linear motor 10 is assembled to each other by the frame 18 outside the cylinder 4. The assembly is installed to be elastically supported by a support spring 29 on the inner bottom surface of the sealed container (2).

In addition, a predetermined oil is contained in the bottom surface of the airtight container (2), and an oil supply device (30) for pumping oil is installed at the bottom of the assembly, and oil is provided in the lower frame (18) of the assembly. An oil supply pipe 18a is formed to be supplied between the 6 and the cylinder 4, so that the oil supply device 30 is operated by vibration generated by the reciprocating linear motion of the piston 6. The oil is pumped, and this oil is supplied along the oil supply pipe 18a to the gap between the piston 6 and the cylinder 4 for cooling and lubrication.

Next, the cylinder 4 is formed in a hollow shape so that the piston 6 can reciprocate linearly, and a compression space P is formed at one side thereof, and one end is located close to the inside of the inflow pipe 2a. It is preferable to be installed on the same straight line as the inflow pipe (2a) in the state.

Of course, the cylinder (4) is installed in one end close to the inlet pipe (2a) so as to reciprocate linear movement, the discharge valve assembly ( 24) is installed.

At this time, the discharge valve assembly 24 is provided to open and close the discharge cover 24a which is installed to form a predetermined discharge space on one end side of the cylinder 4, and one end of the compression space P side of the cylinder. And a discharge valve 24b and a valve spring 24c, which is a kind of coil spring that imparts an elastic force in the axial direction between the discharge cover 24a and the discharge valve 24b, and at one end of the cylinder 4 The O-ring (R) is installed in the fitting so that the discharge valve 24a is in close contact with one end of the cylinder (4).

In addition, a bent loop pipe 28 is installed between one side of the discharge cover 24a and the outlet pipe 2b. The loop pipe 28 guides the compressed refrigerant to be discharged to the outside. In addition, the vibration caused by the interaction of the cylinder 4, the piston 6, and the linear motor 10 buffers the transmission of the entire sealed container 2.

Therefore, when the pressure of the compression space P becomes equal to or greater than a predetermined discharge pressure as the piston 6 reciprocates linearly in the cylinder 4, the valve spring 24c is compressed and the discharge valve ( 24b) is opened, and the refrigerant is discharged from the compression space P, and then completely discharged along the loop pipe 28 and the outlet pipe 2b.

Next, the piston 6 has a coolant flow path 6a formed at the center thereof so that the coolant flowing from the inlet pipe 2a flows, and one end close to the inlet pipe 2a is connected to the connection member 17. In addition, the linear motor 10 is installed to be directly connected to each other, and the suction valve 22 is installed at one end of the inflow pipe 2a opposite to the inflow pipe 2a, and is elastically formed by various springs in the movement direction of the piston 6. It is installed to be supported.

At this time, the suction valve 22 is formed in a thin plate shape so that the center portion is partially cut to open and close the refrigerant passage 6a of the piston, and one side is fixed by a screw to one end of the piston 6a. It is installed as possible.

Therefore, as the piston 6 reciprocates linearly in the cylinder 4, when the pressure of the compression space P becomes lower than or equal to a predetermined suction pressure lower than the discharge pressure, the suction valve 22 is When the refrigerant is opened and sucked into the compression space P, and the pressure in the compression space P becomes equal to or greater than a predetermined suction pressure, the refrigerant in the compression space P is closed while the suction valve 22 is closed. Is compressed.                 

In particular, the piston 6 is installed so as to be elastically supported in the movement direction, specifically, the piston flange 6b protruding radially at one end of the piston 6 proximate to the inlet pipe 2a is a machine such as a coil spring or the like. The spring 8a, 8b is elastically supported in the movement direction of the piston 6, the refrigerant contained in the compression space (P) on the opposite side to the inlet pipe (2a) acts as a gas spring by its elastic force The piston 6 is elastically supported.

Here, the mechanical springs (8a, 8b) has a constant mechanical spring constant (K _m ) irrespective of the load, the mechanical spring (8a, 8b) is the linear motor (10) relative to the piston flange (6b) It is preferable that the predetermined support frame 26 and the cylinder 4 are fixed to the cylinder 4 side by side in the axial direction, respectively, the mechanical spring (8a) and the cylinder (4) supported by the support frame 26 It is preferable that the mechanical spring 8a to be installed in is configured to have the same mechanical spring constant K _m .

However, the gas spring has a variable gas spring constant (K _g ) depending on the load, but the gas contained in the compression space (P) increases its elastic force as the pressure of the refrigerant increases as the ambient temperature increases As the gas spring loads, the gas spring constant K _g increases.

At this time, the mechanical spring constant (K _m ) is constant, while the gas spring constant (K _g ) is variable depending on the load, so the total spring constant is also variable depending on the load, depending on Equation 1 The natural frequency f _n of the piston also varies depending on the gas spring constant K _g .

Therefore, even if the load is variable, the mechanical spring constant (K _m ) and the mass (M) of the piston are constant, while the natural frequency (f _n ) of the piston depends on the load because the gas spring constant (K _g ) is variable. It is greatly influenced by the gas spring constant (K _g ), and the algorithm in which the natural frequency (f _n ) of the piston is varied according to the load, and thus the operating frequency (f _c ) of the linear motor is By controlling synchronization with the natural frequency (f _n ), not only can the compressor be more efficient, but also the load can be released quickly.

Of course, the load can be measured in various ways, but such a linear compressor is configured to be included in the refrigeration / air conditioning cycle in which the refrigerant is compressed, condensed, evaporated, and expanded, so that the load is the condensing pressure which is the pressure at which the refrigerant is condensed. It can be defined as the difference in the evaporation pressure, which is the pressure at which the refrigerant is evaporated, and further determined in consideration of the average pressure obtained by averaging the condensation pressure and the evaporation pressure to increase accuracy.

That is, the load is calculated to be proportional to the difference between the condensation pressure and the evaporation pressure and the average pressure, and as the load increases, the gas spring constant K _g increases. For example, as the difference between the condensation pressure and the evaporation pressure increases, Even if the load is large and the difference between the condensation pressure and the evaporation pressure is the same, the larger the average pressure is, the larger the load is. The corresponding gas spring constant K _g is calculated to correspond to the load.

At this time, the load is actually measured as shown in Figure 4 to measure the condensation temperature proportional to the condensation pressure and the evaporation temperature proportional to the evaporation pressure, and is proportional to the difference between the condensation temperature and the evaporation temperature and the average temperature.

Next, the linear motor 10 is configured such that a plurality of laminations 12a are stacked in the circumferential direction, and the inner stator 12 and the coil are installed to be fixed to the outside of the cylinder 4 by the frame 18. A plurality of laminations 14b are laminated in the circumferential direction around the coil winding 14a configured to be wound so that a predetermined gap is formed between the inner stator 12 and the outside of the cylinder 4 by the frame 18. Permanent magnet 16 is installed in the gap between the outer stator 14 and the inner stator 12 and the outer stator 14 is installed so as to be connected by the piston 6 and the connecting member (17) The coil winding 14a may be installed to be fixed to the outer side of the inner stator 12.

As the current is applied to the coil winding 14a in the linear motor 10 as described above, an electromagnetic force is generated, and the permanent magnet 16 reciprocates by the interaction between the electromagnetic force and the permanent magnet 16. The piston 6 is linearly moved, and the piston 6 connected to the permanent magnet 16 is reciprocated linearly in the cylinder 4.

Fig. 5 is an equivalent circuit diagram when modeling a linear motor as an R-L circuit with back electromotive force. In this equivalent circuit diagram, a nonlinear system of differential equations, such as Equation 2 below, which is the theoretical basis for the movement of the piston 6 is described, where Equation 2 is an electrical equivalent equation.

Equation 2

Here, R is an equivalent resistance, L is an equivalent inductance coefficient, i is a current flowing through the motor, and V ^* is a voltage command value corresponding to the output voltage of the inverter section (see FIG. 6). Since all of the above-described parameters can be measured, the counter electromotive force can be calculated through Equation 2.

In addition, it is explained by a mechanical motion equation such as the following Equation 3, which is based on a theoretical basis representing the movement of the piston 6.

Equation 3

Where x is the displacement of the piston 6, m is the mass of the piston 6, C is the damping coefficient, k is the equivalent spring constant, and α is the counter electromotive force constant. The mechanical equation obtained by converting Equation 3 into a complex form is shown in Equation 4 below.

Equation 4

Where ω is the frequency.                 

Mechanical resonance occurs when back EMF and current are in phase. Therefore, as can be seen from Equation 4 above, the complex part in the denominator may be zero in theory. However, as described above, since the equivalent spring constant k changes according to the load, it is difficult to determine the motion frequency f _c in Equation 4 deterministically. Thus, the purpose of this invention the phase of the motion frequency (f _c) to that of estimating a resonance frequency (the frequency of when the f _n = f _c), while varying, in the below using equation (3), the phase and the current of the counter electromotive force A control device for detecting and varying and synchronizing the motion frequency f _c is disclosed.

6 is a configuration diagram of a control device of the linear compressor according to the present invention.

As shown in the drawing, the control device rectifies an external AC voltage to generate a DC voltage, and receives a DC voltage from the rectifier 41 to generate a sine wave voltage according to the voltage command value V ^* to linearly generate the DC voltage. The inverter unit 42 applied to the compressor 43, the linear compressor 43 performing compression and suction strokes according to the sine wave voltage applied from the inverter unit 42, and the linear compressor 43. A current sensor 44 measuring an input current i, a counter electromotive force phase detector 45 detecting a phase of the counter electromotive force E from the voltage command value V ^* and the input current i, and the input current a current phase detector 46 for detecting the phase of i), a frequency generator 47 for generating a frequency change value Δf by comparing the phase of the counter electromotive force E with the phase of the input current i, and The voltage command value V ^* is maintained according to the frequency change value Δf. The control unit 48 is configured to apply to the inverter unit 42.

In detail, the counter electromotive force phase detector 45 calculates the counter electromotive force E by processing the voltage command value V ^* and the input current i applied according to Equation 2, and detects the phase of the counter electromotive force E. .

In addition, the frequency generator 47 receives a back EMF phase from the back EMF phase detector 45 and a current phase from the current phase detector 46, compares the back EMF phase with the current phase, and makes the same frequency. The change value Δf is generated and applied to the control unit 48.

Accordingly, the controller 48 corrects the frequency of the previous voltage command value V ^* using the frequency change value Δf applied from the frequency generator 47, and inverts the corrected voltage command value V ^* again. To 42. Through such a cyclic process, the controller 48 applies the voltage command value V ^* having the frequency (operation frequency f _c ) resonating with the mechanical natural frequency f _n to the inverter unit 42. Allow the linear compressor to resonate.

However, the control unit 48 converts the voltage command value V ^* to the inverter unit 42 in the form of an inverter control signal (for example, a PWM signal) and transmits it.

The control apparatus and method of the present invention described above do not accurately estimate the spring constant (K), which is a mechanical variable, to estimate the natural frequency (f _n ), but rather the measurable variables (R, L, i, Since the resonance state is achieved by using V ^* ), when the actual linear compressor is manufactured, it is not sensitive to mechanical accuracy. Therefore, the present inventors' control apparatus and method easily overcome the mechanical errors caused in the manufacturing process when manufacturing the linear compressor, and allow the compression and suction process to be performed in the resonance state.

In the above description, the present invention relates to a linear compressor for moving, moving and reciprocating linearly inside a cylinder a suction magnet type linear motor in which a moving magnet type linear motor is operated based on the embodiments of the present invention and the accompanying drawings. The example has been described in detail. However, the scope of the present invention is not limited by the above embodiments and drawings, and the scope of the present invention will be limited only by the contents described in the claims below.

Claims (8)

A counter electromotive force phase detector for detecting a phase of the counter electromotive force E from the voltage command value V ^* and the input current i for the linear compressor; A current phase detector for detecting a phase of the input current i; A frequency generator for generating a frequency change value by comparing the phase of the counter electromotive force (E) with the phase of the input current (i); A controller for correcting the voltage command value V ^* according to the frequency change value; And an inverter unit configured to receive a DC voltage and generate a sine wave voltage according to the corrected voltage command value (V ^* ), and apply the generated sinusoidal voltage to the linear compressor. The method of claim 1, And the counter electromotive force phase detection unit detects the phase by calculating the counter electromotive force (E) according to the following equation.

The method of claim 1, And the frequency generator generates the frequency change value such that the phase of the counter electromotive force (E) and the phase of the input current (i) are in phase with each other. The method of claim 1, And the control unit transmits the corrected voltage command value V ^* to the inverter unit in the form of a predetermined inverter control signal. Detecting the phase of the counter electromotive force E from the voltage command value V ^* and the input current i for the linear compressor; Detecting a phase of the input current i; Generating a frequency change value by comparing the phase of the counter electromotive force (E) with the phase of the input current (i); Correcting the voltage command value V ^* according to the frequency change value; And receiving a DC voltage to generate a sinusoidal voltage according to the corrected voltage command value (V ^* ). The method of claim 5, The phase detecting step of the counter electromotive force (E) is a control method of the linear compressor, characterized in that for detecting the phase by calculating the counter electromotive force according to the following equation.

The method of claim 5, The generating of the frequency change value includes generating the frequency change value such that the phase of the counter electromotive force (E) and the phase of the input current (i) are in phase. The method of claim 5, The control method further comprises the step of converting the corrected voltage command value (V ^* ) in the form of a predetermined inverter control signal.

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