Patent Application
20130182479
Generally, the present invention relates to power rectification, and more particularly, exemplary embodiments of the present invention relate to voltage references used in power rectification systems.
Conventionally, a feedback control system for power rectification considers an output voltage of a rectifier for control of the rectifier. The output voltage may be a DC voltage produced as an output of the rectifier. For control, the DC voltage is compared to a fixed reference value to generate an error value. This error value is considered when directing the rectifier to rectify an AC waveform to produce the DC voltage. It follows then, that if a conventional power rectification system is at rest, the error value when starting the system from rest will be very large as the DC output voltage is very low or close to zero. Thus, the feedback control system, when considering this large error value, will draw a proportionally large amount of current as compared to steady-state operation of the power rectification system.
According to an exemplary embodiment of the present invention, a power rectification system includes power electronics configured to rectify an alternating current (AC) waveform to produce a direct current (DC) output voltage, a control circuit configured to control the power electronics based upon an error value, and a voltage reference control portion configured to provide the error value based upon a variable voltage reference and the DC output voltage. According to this exemplary embodiment, the variable voltage reference varies between the DC output voltage and a fixed voltage reference.
The subject matter which is regarded as the invention is particularly pointed out and distinctly claimed in the claims at the conclusion of the specification. The foregoing and other features, and advantages of the invention are apparent from the following detailed description taken in conjunction with the accompanying drawings in which:
According to exemplary embodiments of the present invention, a control scheme for a power rectification system is provided which significantly reduces current draw when initiating a power rectification system. The technical effects and benefits of exemplary embodiments of the present invention include a reduced risk of failure due to overcurrent conditions and reduced strain on electronic power components during system initiation.
Turning to
According to exemplary embodiments of the present invention, the voltage reference control portion 101 includes a plurality of electronic control components which determine an appropriate voltage error value VERR to provide control circuit 102. The control circuit 102, upon receipt of the error value VERR, directs the power electronics 103 to rectify an AC waveform to produce the output voltage VDC based on the error value VERR. Thus, if an error is large, the control circuit 102 directs the power electronics 103 to compensate accordingly to ensure a stable output voltage. Therefore, if the system 100 is being initiated, and only a stable, fixed reference voltage is considered when calculating VERR, a proportionally large amount of current may be drawn. However, according to exemplary embodiments of the present invention, the voltage reference control portion 101 is configured to produce an error value of VERR dependent upon an operating state of the system 100. For example, if the system 100 is being initiated, the voltage reference control portion 101 may, instead of using a fixed reference value, use a variable reference value to calculate VERR. Thereafter, upon stabilization of the system 100, the voltage reference control portion 101 may use a different reference value to maintain steady state operation of the system 100.
For example, a detailed example of one exemplary embodiment of voltage reference control portion 101 is provided in
As shown, the first value may be the output voltage VDC. However, the second value may be a variable voltage reference provided by a dynamic switch 203. The dynamic switch 203 may be any suitable switch, including a transistor, electromechanical switch, micro-electromechanical system (MEMS) switch, or any other suitable switch able to selectively output one of at least two inputs. Thus, the switch 203 may be considered a variable voltage reference selection portion selecting the variable voltage reference as one of the at least two inputs. The at least two inputs, according to one exemplary embodiment, include the output voltage VDC and a fixed voltage reference value VREF. The inputs are switched through control signals applied from switch logic 204, which selectively applies one of the at least two inputs to the error determination portion 202.
Therefore, as both the actual output voltage and a fixed reference voltage may be selectively applied to the error determination portion, the calculated error value may be reduced during system initiation thereby reducing initial current draw. For example, during system initiation, the actual output voltage may be compared against itself at portion 202, thereby providing a relatively low error value very close to, or at, zero. Subsequently, after an appropriate initiation period has lapsed, the fixed reference value VREF may be compared to the output voltage VDC at portion 202 by selectively switching portion 203 to determine an actual error. However, as an appropriate startup period has already lapsed, the increase in current draw may be negligible as compared to conventional systems. The methodology described above is more clearly illustrated in
As shown, a method of power rectification 300 includes initiating a power rectification system (e.g., 100 or 200) at block 301. Initiation may include powering on appropriate circuitry such that voltage reference control portion 101, 201, control circuit 102, and power electronics 103 are operational. Thereafter or at substantially the same time, a state of the system is considered to determine if the system is stable at block 302. For example, immediately after system initiation at block 301, the system may be relatively unstable. Therefore, the output voltage VDC may be selectively applied to an error determination portion 202 through switch 203 to reduce the error value at block 303. The reduced error value may therefore reduce current draw during this initial phase. Subsequently, after an appropriate amount of time has lapsed, or after a predetermined voltage is detected at the output of the system, a fixed voltage reference value may be selectively applied to an error determination portion 202 through switch 203 to change the error value at block 304. Thereafter, power may be rectified normally at block 305, for example, as if in steady state using an appropriate error value determined by the fixed reference voltage.
As described above, power rectification systems according to exemplary embodiments reduce current draw during system initiation while also allowing for stable steady-state operation through the application of a variable voltage reference. According to at least one exemplary embodiment, the variable voltage reference is a selectively switched value which includes at least two voltage values, the output voltage and a fixed reference voltage. During system initiation, the output voltage is selected which reduces a voltage error to near zero. After an appropriate amount of time has lapsed, the fixed reference value is selected.
While the invention has been described in detail in connection with only a limited number of embodiments, it should be readily understood that the invention is not limited to such disclosed embodiments. Rather, the invention can be modified to incorporate any number of variations, alterations, substitutions or equivalent arrangements not heretofore described, but which are commensurate with the spirit and scope of the invention. Additionally, while various embodiments of the invention have been described, it is to be understood that aspects of the invention may include only some of the described embodiments. Accordingly, the invention is not to be seen as limited by the foregoing description, but is only limited by the scope of the appended claims.
