Pumps – Condition responsive control of pump drive motor – By control of electric or magnetic drive motor
Reexamination Certificate
2002-12-09
2004-12-21
Koczo, Michael (Department: 3746)
Pumps
Condition responsive control of pump drive motor
By control of electric or magnetic drive motor
C417S417000, C318S119000, C318S127000, C318S135000
Reexamination Certificate
active
06832898
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a driving apparatus of a linear compressor for reciprocating a piston in a cylinder by a linear motor to generate compressed gas in a compression chamber formed by the cylinder and the piston.
BACKGROUND OF THE INVENTION
Conventionally, a linear compressor utilizing elasticity of a mechanical elastic member or compressed gas is known as means for generating compressed gas.
To efficiently drive the linear compressor, it is necessary to drive the linear compressor at resonance frequency of the linear compressor. In a linear compressor having the elastic member, the resonance frequency of the linear compressor is determined by the elastic member (mechanical spring) which is mechanically provided and elasticity (gas spring) generated by compressed gas. In a linear compressor utilizing only elasticity of compressed gas, the resonance frequency is determined only by the elasticity. However, since the elasticity generated by the compressed gas is largely varied with variation of load, the resonance frequency of the linear compressor can not be determined as one value. Therefore, the conventional technique employs a method for calculating the varying resonance frequency utilizing a phenomenon that a resonance state is established when phases of input current and piston speed are equal to each (Japanese Patent Application Laid-open No. H10-26083).
This conventional method will be explained briefly with reference to a flowchart shown in FIG.
13
.
When detection control of resonance frequency is started, in step S
20
, a sine wave current command value Iref which is input from driving frequency f to the linear compressor is formed. In step S
21
, current piston speed Vnow is obtained by position information of the piston from a position sensor provided in the linear compressor. In step S
22
, a position difference between the Iref and Vnow obtained in the above steps, and if the Iref advanced, the procedure is proceeded to step S
23
, and if the phases are equal to each other, the procedure is proceeded to step S
24
, and if the Iref delayed, the procedure is proceeded to step S
25
. In step S
23
, since the current driving frequency is lower than the resonance frequency and thus, the driving frequency f is increased and the procedure is returned to step S
20
. In step S
24
, since the current driving frequency is equal to the resonance frequency, the driving frequency f is not changed and the procedure is returned to step S
20
. In step S
25
, since the current driving frequency is higher than the resonance frequency and thus, the driving frequency f is reduced and the procedure is returned to step S
20
. In this manner, the driving frequency is controlled such that it becomes equal to the resonance frequency using the position information of the piston obtained by the position sensor.
However, in order to employ this method, it is necessary to measure the displacement of the piston in the cylinder. Therefore, a displacement measuring apparatus must be incorporated in the linear compressor. Therefore, there are caused not only a problem that a volume of the linear compressor is increased by a volume of the displacement measuring apparatus, but also a problem that the operational reliability of the displacement measuring apparatus must be secured under rigorous operation conditions such as a temperature, a pressure and refrigerant resistance because the displacement measuring apparatus itself must be enclosed in a shell of the linear compressor.
Further, since it is necessary to differentiate a signal from a displacement sensor and to calculate the position difference between speed and current, a relatively complicated control apparatus such as microcomputer, MPU (micro processor unit) or the like is required.
In view of the above problems, it is an object of the present invention to calculate resonance frequency relatively easily without displacement of a piston in a linear compressor, and to drive the linear compressor efficiently using an inexpensive circuit.
SUMMERY OF THE INVENTION
A first aspect of the present invention provides a driving apparatus of a linear compressor for driving a piston in a cylinder by a linear motor to generate compressed gas, comprising an inverter for outputting alternating current which is supplied to the linear motor, a direct current power source for supplying direct current voltage to the inverter, current value commanding means for determining and commanding magnitude of the alternating current, electric power detecting means for detecting input electric power which is supplied to the linear compressor, driving frequency determining means for varying driving frequency of the inverter such that the electric power detected by the electric power detecting means becomes maximum, current waveform commanding means for generating command current waveform from a command current value from the current value commanding means and from a driving frequency determined by the driving frequency determining means, and inverter control means for sending a control signal to the inverter based on the command current waveform from the current waveform commanding means.
According to this aspect, the frequency is varied so that the input electric power which is supplied to the linear motor becomes maximum. That is, to control the effective electric power such that it becomes maximum based on a condition that alternating output current is constant is to control such that a phase of the output current becomes equal to a phase of speed (induction voltage). According to this mode, it is possible to control the linear compressor to resonance frequency without detecting the displacement of the piston.
According to a second aspect of the invention, in the driving apparatus of the linear compressor of the first aspect, the driving apparatus further comprises current detecting means for detecting input current which is supplied to the inverter or output current which is output from said inverter, and voltage detecting means for detecting input voltage of the inverter, and the electric power detecting means calculates input electric power which is supplied to the linear compressor from current detected by the current detecting means and voltage detected by the voltage detecting means, the inverter control means sends a control signal to the inverter such that a deviation between a command current value from the current value commanding means and a detection current value from the current detecting means is reduced.
According to this aspect, direct current and input voltage which are input and output to the inverter are detected, and with a relatively simple calculation in which they are multiplied, it is possible to approximately detect the input electric power which is supplied to the linear motor. The output current value is controlled substantially constantly such that the output current value becomes the command value. That is, to control the effective electric power such that it becomes maximum based on a condition that alternating output current is constant is to control such that a phase of the output current becomes equal to a phase of speed (induction voltage). According to this mode, it is possible to control the linear compressor to resonance frequency without detecting the displacement of the piston.
According to a third aspect of the invention, in the driving apparatus of the linear compressor of the first aspect, the driving apparatus further comprises current detecting means for detecting a smoothened value of sawtooth-like inverter input current as input current or detecting a peak value as output current, and voltage detecting means for detecting input voltage of the inverter, and the electric power detecting means calculates input electric power which is supplied to the linear compressor from current detected by the current detecting means and voltage detected by the voltage detecting means, the inverter control means sends a control signal to the inverter such that a deviation between a command current value
Hasegawa Sugimatsu
Ueda Mitsuo
Yoshida Makoto
Armstrong, Kratz, Quintos Hanson & Brooks, LLP.
Koczo Michael
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