US 4,345,442 AGranted

Control system for resonant free-piston variable stroke compressor for load-following electric heat pumps and the like

AssigneeMechanical Technology Incorporated

InventorRichard A. Dorman

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Abstract

A control system for controlling the operation of a reciprocating resonant free-piston variable stroke compressor of the type driven by electrodynamic linear motors wherein the spring-mass system of the compressor which is forced into vibration by the linear motor, is arranged to have a selectively variable mechanical resonant frequency generally centered on the power line frequency of the alternating current power source used to drive the linear motor. The control system provided by this invention variably controls the opening and closing of a gas spring control valve that in turn regulates the pressure of gas filled volumes selectively connected to a manifold vented by the valve. The volumes comprise the resilient gas springs for the resonant piston compressor. For this purpose, the control system comprises an alternating current sensor for deriving a sensed output signal representative of the magnitude and phase of the alternating current supplied to the linear reciprocating motor, a reciprocating piston displacement/velocity sensor for deriving a signal representative of the reciprocating free piston velocity, and an .alpha. angle detector responsive to the signal from the alternating current sensor and the piston velocity signal from the piston displacement/velocity sensor for comparing the phase of the alternating current supplied to the linear reciprocating motor to the reciprocating free resonant piston displacement/velocity and deriving an output .alpha. angle control signal that then is supplied to an RPC control logic circuit for the RCP heat pump. The RPC control logic circuit derives motor voltage control relays for controlling the supply voltage valve to the A-C coils of the linear motor.

A resonant piston compressor control system for use in controlling automatically the operation of a resonant piston compressor of the mechanically resonant free-piston type driven by an electrodynamic linear motor wherein the spring-mass resonant piston system of the compressor is forced into vibration by the linear motor and is arranged to have a selectively variable mechanical resonant frequency generally centered on the power line frequency of the alternating current power source supplying the linear reciprocating motor, the resonant frequency of the spring-mass resonant piston system being varied by varying the stiffness of enclosed volumes of gas comprising resilient gas spring means that communicate with a reservoir of gas at higher pressure than the gas spring means, means selectively interconnecting the resilient gas spring means with a gas spring pressure control manifold and a gas spring pressure control valve means that can be selectively opened and closed to regulate the pressure of the gas in the gas spring pressure control manifold and the stiffness of the resilient gas spring means;

said control system comprising control circuit means including alternating current sensing means for deriving a sensed alternating current signal representative of the phase and magnitude of the alternating current supplied to the linear reciprocating motor, resonant piston displacment/velocity sensing means for deriving a stroke signal representative of the resonant piston velocity, .alpha. angle detector means responsive to the output from said alternating current sensing means and said resonant piston displacement/velocity sensing means for comprising the phase of the alternating current supplied to the linear reciprocating motor and the resonant piston velocity and deriving an output .alpha. angle control signal for controlling the voltage value of the alternating current supply voltage to the linear reciprocating motor for controlling the output capacity of the compressor.

Abstract

Claims8