Patent Grant
7164590
1. Field of the Invention
The present invention relates generally to energy transfer devices, and relates more particularly to power inverter circuits with reduced component rating.
2. Description of Related Art
Typical power systems for transferring energy between an input and an output often employ a power inverter that has a DC input and a switched output that can be single or multiple phase. For example, referring to
Operation of the half bridge formed by switches 12a–12b is accomplished through standard switching practices to avoid problems associated with component limitations such as switching losses, and to improve system performance. Accordingly, switches 12a and 12b are never switched on at the same time to avoid current shoot through in the motor drive. In addition, a dead time is provided between switching intervals when both switches in the half bridge change state. For example, if switch 12a is to be turned off and switch 12b is to be turned on, these events do not occur simultaneously, but with a delay between switch 12a turning off and switch 12b turning on. When a high frequency inverter drive is used for high performance motor control, the dead time delay becomes important to improve switching frequency without incurring the above discussed drawbacks.
High frequency switching also produces rapid changes in power transferred from the inverter to the motor and vice versa. These rapid changes in transferred power implies the need of higher power ratings for the switches in the inverter, for example, to handle the potentially large range of power fluctuations.
Similarly, other components coupled to the inverter, such as passive energy storage components, are rated to withstand potentially large power fluctuations including high peak currents and voltages and large ripple currents and voltages. Referring to
When selecting appropriately rated passive components for use with power inverter 10, the components with appropriate ratings are typically large and somewhat expensive. For example, a typical bus capacitor CBUS comprises a large percentage of a motor drive size and cost. It would be desirable to reduce the rating, and thus the size and cost, of the passive components used with a typical motor drive system.
In accordance with the present invention, the inventors have found that the main purpose for including the passive components in the energy transfer circuits for power inverters is to absorb or deliver the difference between the instantaneous input power of the inverter and output power that is applied to a load. The output power applied to the load can be delivered to a motor or a power supply load. When the instantaneous input power tracks with the instantaneous output power, the difference between the instantaneous input power and instantaneous output power can be minimized. Accordingly, the energy to be stored or delivered by the passive component, such as a bus capacitor or DC link inductor can be minimized. For example, the DC bus ripple voltage can be minimized, as well as the DC link ripple current. By determining a particular voltage or current ripple level that can be tolerated by the specific application, the size of the DC bus capacitor or DC link inductor can be minimized accordingly.
The present invention provides a front end active control for supplying power to the DC bus connected to the power inverter. The front end active control includes a power converter with power factor correction (PFC) to make the power transfer system appear as a purely resistive load to the input power lines. The PFC power converter controls the instantaneous input power to minimize the difference between the instantaneous input power and the instantaneous output power, thereby reducing the requirements for passive components coupled to the DC bus. The instantaneous output power can be measured or calculated by obtaining values for parameters such as output current or voltage. Typically, one or more of these parameters are measured in most power transfer systems, in particular in motor drive systems, where high performance depends upon closed loop feedback with sensed parameters.
By reducing the variations in ripple current or voltage and instantaneous input and output power, the rated passive components can be specified at a much lower value, thereby providing reduced packaging size and realizing direct cost reduction.
The present invention is described in detail below with reference to the accompanying drawings, in which:
Referring now to
PFC power converter 35 switches power on the DC bus to provide an efficient power conversion of the full wave rectified input signal for use by power inverter 10, while drawing a sinusoidal current that in phase with the input AC voltage to obtain a high power factor. Accordingly, motor drive system 31 appears as a resistive load to the AC input lines coupled to a full wave rectifier 36. Instantaneous input power can easily be measured on the output of full wave rectifier 36 with a simple calculation involving input voltage Vin and input current Iin. As illustrated in
Power control 34 receives the signals representative of input power Pin and inverter output power PO and provides bus regulation and control command to PFC power converter 35 to drive the DC bus voltage so that instantaneous input power Pin tracks with instantaneous output power PO. By tracking input power Pin with output power PO, PFC power converter 35 controls the energy on the DC bus that bus capacitor CBUS must handle. With this criteria, the energy, Ec, in bus capacitor CBUS, is minimized.
Input voltage Vin and input current Iin are normally measured to obtain a closed loop control for PFC power converter 35 to obtain a good power factor. Accordingly, input signals representative of input current Iin and input voltage Vin are typically available in motor drive system 31. In addition, it is often the case that motor speed and/or torque are directly measured with a sensing device. In this instance, estimator 33 is not necessary to obtain a signal representative of output power PO. That is, directly measured motor speed and torque provide appropriate signals to formulate a signal representative of output power PO. Because motor speed and torque are typical measurements made in motor drive system 31, control 30 can be further simplified.
The present invention provides a simple technique to reduce the rating requirements of passive components used in conjunction with inverter power transfer systems. Whether the passive component is a bus capacitor for a voltage source inverter, or a DC link inductor for a current source inverter, the present invention reduces the maximum ratings required for the components. The reduction in component rating requirements greatly reduces the size of the motor drive system, and also greatly reduces overall costs, as the required passive components represent a large percentage of the system cost and size. The PFC power converter operation changes only slightly to ensure input power tracks with output power while also drawing a sinusoidal input current in phase with the input voltage. The DC bus ripple voltage or DC link ripple current is minimized to produce a lower ripple requirement for the passive component. In addition, the energy handled by the passive component is minimized based on the application, again providing for a reduced rating for the passive component.
Although the present invention has been described in relation to particular embodiments thereof, many other variations and modifications and other uses will become apparent to those skilled in the art. It is preferred, therefore, that the present invention be limited not by the specific disclosure herein, but only by the appended claims.
The present application is based on and claims benefit of U.S. Provisional Application Serial No. 60/399,747, filed Jul. 29, 2002, entitled POWER INVERTER WITH REDUCED ENERGY CAPACITY, to which a claim of priority is hereby made.
| Number | Name | Date | Kind |
|---|---|---|---|
| 4777581 | Smith | Oct 1988 | A |
| 5019717 | McCurry et al. | May 1991 | A |
| 5063490 | Maehara et al. | Nov 1991 | A |
| 5099918 | Bridges et al. | Mar 1992 | A |
| 5184025 | McCurry et al. | Feb 1993 | A |
| 5220492 | Rubin et al. | Jun 1993 | A |
| 5438502 | Rozman et al. | Aug 1995 | A |
| 5465011 | Miller et al. | Nov 1995 | A |
| 5502630 | Rokhvarg | Mar 1996 | A |
| 5642270 | Green et al. | Jun 1997 | A |
| 5739664 | Deng et al. | Apr 1998 | A |
| 5847944 | Jang et al. | Dec 1998 | A |
| 5889659 | Emmerich | Mar 1999 | A |
| 6005784 | Ikeshita | Dec 1999 | A |
| 6031749 | Covington et al. | Feb 2000 | A |
| 6057652 | Chen et al. | May 2000 | A |
| 6229719 | Sakai et al. | May 2001 | B1 |
| 6275018 | Telefus et al. | Aug 2001 | B1 |
| 6275397 | McClain | Aug 2001 | B1 |
| 6288921 | Uchino et al. | Sep 2001 | B1 |
| 6301137 | Li | Oct 2001 | B1 |
| 6337801 | Li et al. | Jan 2002 | B1 |
| 6370039 | Telefus | Apr 2002 | B1 |
| 6381159 | Oknaian et al. | Apr 2002 | B1 |
| 6492788 | Agirman et al. | Dec 2002 | B1 |
| 6531843 | Iwaji et al. | Mar 2003 | B1 |
| 6850426 | Kojori et al. | Feb 2005 | B1 |
| 20020080633 | Kang | Jun 2002 | A1 |
| 20020136036 | Hugget et al. | Sep 2002 | A1 |
| 20030007369 | Gilbreth et al. | Jan 2003 | A1 |
| 20030021127 | Loef et al. | Jan 2003 | A1 |
| 20030081434 | Kikuchi et al. | May 2003 | A1 |
| Number | Date | Country | |
|---|---|---|---|
| 20040095789 A1 | May 2004 | US |
| Number | Date | Country | |
|---|---|---|---|
| 60399747 | Jul 2002 | US |
