Electromechanical systems generally operate according to AC power received from an AC utility power source, such as an AC mains. Accordingly, an electromechanical system is generally shut down if the power source fails. Shutting down some electromechanical systems is particularly undesirable. For example, shutting down some electromechanical systems results in significant economic loss. Some electromechanical systems employ battery backup devices to help reduce or eliminate the loss. However, for electromechanical systems which use high voltages, many batteries are required, resulting in substantially increased weight and cost of the system. This increases the cost and weight of the system. Electromechanical systems include, for example, pumping systems, elevators, conveyor systems, transport systems, and heating, ventilation, air conditioning, and refrigeration (HVAC/R) compressor and/or fan motors, but are not limited thereto.
Described herein is an electromechanical system including one or more electromechanical components, a power bus, configured to transmit power to the electromechanical components. The system also includes first and second power sources, where the second power source includes a DC power storage, configured to generate a DC signal, and a DC to DC converter, configured to generate a substantially DC output for the electromechanical system based on the DC signal. The second power source is configured to increase power output to the power bus as a result of a reduction in power output to the power bus from the first power source. The system also includes a power supply configured to generate an output for the electromechanical system according to power received from the power bus.
In some embodiments, a power supply apparatus for an electromechanical system includes a power bus, and a power input configured to receive power from a first power source and to supply power to the power bus. The system also includes a second power source configured to provide power to the power bus. The second power source comprises a DC power storage, configured to generate a DC signal, a DC to AC inverter, configured to generate an AC signal based on the DC signal, and a rectifier, configured to rectify the AC signal to generate a substantially DC output for the system. The second power source is configured to increase power output to the power bus as a result of a reduction in power output to the power bus from the first power source. The apparatus also includes a power supply configured to generate an output according to power received from the power bus.
In some embodiments, a method of providing back-up power to an electromechanical system includes storing power in a DC power storage, configured to generate a DC signal, generating an AC signal based on the DC signal, and rectifying the AC signal to generate a substantially DC output for the system.
To provide uninterrupted power to an electromechanical system, the power supply system for the electromechanical components may be configured, such that, rather than receiving power directly from an AC utility source, the system components receive power from a back-up power storage device, for example, a DC battery in parallel with power from the AC utility source. In the system, the AC utility source provides power to the power storage device and to the main DC power bus of the system through a rectifier. The DC power bus is used to provide power to power supply components which generate appropriate AC power for the system components, such as a motor or a heater. In such a configuration, should the AC utility source fail, the DC power bus is powered by the power storage device.
In some embodiments, an electromechanical system includes components driven with a variable frequency drive power supply (VFD). The VFD chops the DC voltage from the DC power bus into three outputs 120 degrees out of phase, which the motors driven see as AC. The VFD allows for efficient start up of the motors being driven, as will be discussed in more detail below. The electromechanical system allows for automatic, unattended operation during power disruptions because of a transparent transition from AC mains power to back-up power.
In the embodiment of
Power source 12 may be any type of power source. In the embodiment of
Rectifier 13 is configured to receive AC power from the first power supply 13, to rectify the power signal to a substantially DC level, and to provide the DC level to the power bus 15 appropriate for the system.
Second power source 14 may be a secondary or back-up power source, for example, a battery or a battery pack, configured to be charged to a level appropriate for the system. Other types of energy storage devices may also be used. The second power source 14 is connected to the power bus 15, and is configured to be charged by the power bus 15 when the first power source 12 is functioning and the second power source 14 is not fully charged. The second power source 14 is further configured to provide power to the power bus 15 when the power from the rectifier 13 or the first power source 12 is insufficient for the load on the power bus 15.
To limit the amount of charging current flowing to the second power source 14, a current limiting circuit (not shown) may be placed between the power bus 15 and the second power source 14. Such a current limiting circuit limits the current charging the second power source 14 according to the limitation and specification of the second power source 14 so that the second power source 14 is not damaged while being charged.
For example, an electromechanical system may be powered by being connected to the power source section 10. The first power source 12 provides power to the DC power bus 15 which is used to operate the electromechanical system. The second power source 14 stores power from the first power source 12 for use in the case of a failure of the first power source 12. Accordingly, the DC power bus 15 is used to provide power to the electromechanical system, and to charge and float the second power source 14.
The second power source 14 is configured to increase power output to the power bus 15 as a result of a reduction in power output to the power bus 15 from the first power source 12. For example, if the first power source 12 reduces its power output, such that it provides some, but less than sufficient power to the power bus 15 for the electromechanical system, the second power source 14 provides the additional supplemental power to the power bus 15 needed to operate the system. Accordingly, the first and second power sources 12 and 14 cooperatively provide the power to the power bus 15 required by the system. The second power source 14 may also be capable of providing sufficient power to the system even if the first power source 12 completely fails and provides no power to the power bus 15. In some embodiments, the total power cooperatively provided to the system by the combination of the first and second power sources 12 and 14 remains uninterrupted or substantially uninterrupted as the amount of power provided by each of the first and second power sources 12 and 14 changes.
The power supply section 20 includes power supplies which receive power from the power source section 10 and condition the power for use by the components 52 of the component section 50. In the embodiment of
In this embodiment, power supply 22 is configured to supply power to the components 52 of the component section 20. Although shown separately, rectifier 13 may be integrated with power supply 22.
In some embodiments, power supply 22 comprises an inverter. In some embodiments, power supply 22 comprises a variable frequency drive power supply (VFD). In some embodiments, the VFD comprises the power supply 22 and the rectifier 13. In embodiments where multiple power supplies are used, one or more of the supplies may comprise an inverter and one or more of the supplies may comprise a VFD. A VFD may be used because of increased power efficiency achieved through controlled start up of the compressor motor 52. When a constant frequency and voltage power supply, such as an AC mains power supply, is used, inrush current to start a motor may be six to ten times the running current. Because of system inertia, the compressor motor is not powerful enough to instantaneously drive the load at full speed in response to the high frequency and high speed signal of the power supply signal needed at full-speed operation. The result is that the motor goes through a start-up phase where the motor slowly and inefficiently transitions from a stopped state to full speed. During start up, some motors draw at least 300% of their rated current while producing less than 50% of their rated torque. As the load of the motor accelerates, the available torque drops and then rises to a peak while the current remains very high until the motor approaches full speed. The high current wastes power and degrades the motor. As a result, overall efficiency, effectiveness, and lifetime of the motor are reduced.
When a VFD is used to start a motor, a low frequency, low voltage power signal is initially applied to the motor. The frequency may be about 2 Hz or less. Starting at such a low frequency allows the load to be driven within the capability of the motor, and avoids the high inrush current that occurs at start up with the constant frequency and voltage power supply. The VFD is used to increase the frequency and voltage with a programmable time profile which keeps the acceleration of the load within the capability of the motor. As a result, the load is accelerated without drawing excessive current. This starting method allows a motor to develop about 150% of its rated torque while drawing only 50% of its rated current. As a result, the VFD allows for reduced motor starting current from either the AC power source 12 or the DC power source 14, reducing operational costs, placing less mechanical stress on a motor of the components 52, and increasing service life. The VFD also allows for programmable control of acceleration and deceleration of the load.
A VFD of power supply 22 may produce a single-phase or a three-phase output, which powers a motor of the components 52. A three-phase motor of the components 52 has rotational symmetry of rotating magnetic fields such that an armature is magnetized and torque is developed. By controlling the voltage and frequency of the three-phase power signal, the speed of the motor is controlled whereby the proper amount of energy enters the motor windings so as to operate the motor efficiently while meeting the demand of the accelerating load. Electrical motive is generated by switching electronic components to derive a voltage waveform which, when averaged by the inductance of the motor, becomes the sinusoidal current waveform for the motor to operate with the desired speed and torque. The controlled start up of a motor described above allows for high power efficiency and long life of the motor.
In some embodiments, power supply 22 comprises a switching type inverter which generates a pseudo-sine wave by chopping the DC input voltage into pulses. The pulses are used as square waves for a step-down transformer which is followed by a wave shaping circuit, which uses a filter network to integrate and shape the pulsating secondary voltage into the pseudo-sine wave.
In some embodiments, one or more of the components 52 of the component section 50 are DC powered components and receive power directly from the power bus 15.
In some embodiments, the power supply 22 uses a power bus voltage which can be in the range of about 250V to 320V. In such embodiments, the DC power source 14 can be a pack of multiple 12V batteries. However, in some embodiments, it is advantageous to use fewer batteries. In such embodiments, the lower voltage of the fewer batteries is converted to a higher voltage through a DC to DC converter. By functioning at a much lower battery supply voltage, the system allows for vehicular applications and stationary applications which do not have convenient access to poly-phase AC power. In these applications, a vehicle battery could become the primary source of back-up energy. Such a system provides the needed high voltage supply from a much lower voltage source allowing for less storage battery weight and space.
In the embodiment of
The DC power source 62 can be recharged by AC to DC converter 68. AC to DC converter 68 receives an AC signal from an AC source 70, and generates a DC voltage, which is used to charge the DC power source 62. In some embodiments, the AC source is the AC power source 12 of the system of
The battery 82 provides the 24V DC signal, and is configured to be recharged. In some embodiments, the battery 82 comprises two 12-volt batteries.
The two inverters 84 and 85 are each configured to receive a 12V DC input and output a 120V rms AC signal. In some embodiments, the DC power source 60, the inverters 84 and 85 are serially connected across the 24-volt battery 82. Accordingly, the inverters 84 and 85 each receive a 12V input. In response to the 12V input, the inverters 84 and 85 each produce an AC signal of about 120V rms.
The 120V rms AC signal of inverter 84 is provided to rectifier 87, and the 120V rms AC signal of inverter 85 is provided to rectifier 86. The rectifiers 86 and 87 rectify the respective AC signals producing substantially DC outputs of about 165V each. The rectifiers 86 and 87 are connected in serial, and therefore collectively produce a substantially DC signal of about 330V. In the embodiment shown in
The filter 88 is connected across the serially connected rectifiers 86 and 87. The filter is configured to improve the quality of the DC output signal by filtering non-DC components of the signal produced by the rectifiers 86 and 87. As shown in
In some embodiments, the DC power source 62 of
The transformer 92 includes three taps on the input side. In order for the converter 90 to produce the desired about 30V DC output signal, an about 120V AC signal is driven across the uppermost and the middle tap of the transformer 92 as shown in
In some embodiments, the power source section 10 of
In this embodiment, each of the step up modules 410 receive its DC input and steps up that received DC input to the desired DC output, for example 330V DC. In addition, each of the step up modules 410 may provide a control signal for a select module. Each of the step up modules 410 may have similar components and similar functionality as the DC power source 80 of
In this embodiment, each of the select modules 430 receives a DC signal from each of two step up modules 410, and a control signal from one step up module 410. The select modules 430 are configured to select one of the two DC signals according to the control signal. In some embodiments, the select modules 430 comprise relays, which, upon receiving a control signal indicating that one of the received two DC input signals is active, selects the stepped up DC voltage of that DC input signal. For example, if there is a DC input signal at both the DC1 and DC2 inputs, the step up module 410 of the DC1 input generates a stepped up voltage at one of the two inputs to a select module 430, as shown. In addition, the step up module 410 of the DC2 input generates a stepped up voltage at the other of the two inputs to the select module 430, and generates a control signal for the select module 430, indicating that the DC2 input is active. In response to the control signal, the select module selects the stepped up DC2 voltage.
Accordingly, in this embodiment, the select modules 430 collectively select the stepped up DC voltage corresponding to the active DC input of the highest priority, where the priority of the DC inputs is determined by which select module 430 each stepped up DC voltage is connected to.
In this embodiment, each of the select modules 440 receives an AC signals from each of two transformers 420, and a control signal from one transformer 420. In this embodiment, the control signal is the AC signal from the one transformer 420. The select modules 440 are configured to select one of the two AC signals according to the control signal. In some embodiments, the select modules 440 comprise relays, which, upon receiving a control signal indicating that one of the received two AC input signals is active, selects the transformed signal of that AC input signal. For example, if there is an AC input signal at both the AC1 and AC2 inputs, the transformer 420 of the AC1 input generates an AC voltage at one of the two inputs to a select module 440, as shown. In addition, the transformer 420 of the AC2 input generates a transformed AC voltage at the other of the two inputs to the select module 440, and generates a control signal for the select module 440, indicating that the AC2 input is active. In response to the control signal, the select module selects the transformed AC2 voltage.
Accordingly, in this embodiment, the select modules 440 collectively select the transformed AC voltage corresponding to the active AC input of the highest priority, where the priority of the DC inputs is determined by which select module 440 each transformed AC voltage is connected to.
The rectifier 450 rectifies the selected AC voltage, and provides the rectified AC voltage to the select module 460, which selects the rectified AC voltage as the DC output if any of the AC input signals is active.
In some embodiments, one or more of the DC input voltages is not stepped up. In some embodiments, one or more of the AC input voltages is not transformed. In some embodiments, the priority of the various input voltages is different than that of the embodiment of
In this embodiment, the output voltage is not determined by selections based on priority according to position. Instead, the control module 480 is configured to select the output voltage according to signal C. In some embodiments, the signal C represents which input voltages are active. In some embodiments, the signal C is input from another circuit.
In some embodiments, one or more of the DC input voltages is not stepped up. In some embodiments, one or more of the AC input voltages is not transformed.
An existing electromechanical system may be converted to function similarly to or identically to system 200. For example, conventional system 100 shown in
While the above detailed description has shown, described, and pointed out novel features as applied to various embodiments, it will be understood that various omissions, substitutions, and changes in the form and details of the devices and processes illustrated may be made by those skilled in the art without departing from the spirit of the invention. For example, inputs, outputs, and signals are given by example only. As will be recognized, the present invention may be embodied within a form that does not provide all of the features and benefits set forth herein, as some features may be used or practiced separately from others.