A novel hybrid pulse-width modulation (PWM) update method is proposed to eliminate the effect of the one-step control time delay Td one without losing the full duty cycle range. Without the Td one to cause linear phase shifts that limit the control bandwidth and affect closed-loop stability, a very high quality digital current control can be achieved, such as a high closed current loop bandwidth, strong robustness against disturbances, ability to reach a very high fundamental frequency compared to switching frequency, etc.
In a conventional digital control implementation, a sampling period (Tsamp) is allocated for the execution of samplings and computations, and the update of PWM outputs is delayed until the beginning of the following sampling period. This delayed PWM update method is the cause of the Td one. Instead of the delayed PWM update, if the PWM outputs are updated immediately after algorithm computations, then the effect of the Td one can be eliminated; however, the computation time delay Td comp from the current sampling instant through algorithm computations to the PWM update instant causes a reduced duty cycle range. Each of these two conventional PWM update methods has some shortcomings.
A hybrid PWM update method is proposed to circumvent the aforementioned shortcomings and to incorporate only the advantages. The proposed method improves the performance by updating the PWM outputs multiple times during a Tsamp, whereas the PWM outputs are updated only one time during a Tsamp in the conventional methods. In spite of the simplicity of the proposed method, the performance improvements in stability, robustness and response characteristics are significant. On the other hand, the proposed method can be easily applied to many PWM based digital controls because of its simplicity.
Additional to the hybrid PWM update method, a hybrid control method is proposed to optimize the sequence of control operations. It maximizes the current loops' robustness and minimizes the delay from the sampling of outer control loops' variables, such as voltage and speed, to the duty cycle update instant. The minimum delay enables the maximization of the outer control loops' bandwidth. Additionally, a corrective neutral offset voltage injection method is proposed to correct small PWM output deviations that may occur with the hybrid PWM update method.
Utilizing a three-phase voltage source inverter with a permanent magnet synchronous machine as the platform, a deadbeat current control and a high speed ac drive experiments have been conducted to demonstrate the feasibility and validity. Notable results include a closed current loop response of one Tsamp with the deadbeat control and a 500 Hz current fundamental frequency with 1 kHz switching frequency in the high speed ac drive. / Ph. D. / A novel hybrid pulse-width modulation (PWM) update method is proposed to improve the performance of power electronics applications. PWM is a modulation technique that is typically used in power electronics to encode a control signal. A delayed PWM update method and an immediate PWM update method are two conventional PWM update methods, and each of these conventional methods has shortcomings.
The delayed PWM update method, as the name implies, delays the update of PWM outputs until the beginning of next cycle. This delayed update ensures that PWM signals have the full range; however, it causes an update delay in control loops, which degrades the control loops’ response speed. On the other hand, the immediate PWM update method, as the name implies, the update of PWM outputs is executed as soon as the control signals are available to be updated. This immediate update eliminates the update delay, but it loses the full range of PWM signals.
The hybrid PWM update method is proposed to combine the delayed and immediate PWM update methods, in which the combination can eliminate the update delay without the loss of the full signal range. The proposed method is quite simple; however, the performance improvements in stability, robustness, and response characteristics are significant. On the other hand, the proposed method can be easily applied to many PWM based digital controls because of its simplicity.
The proposed method is implemented on a three-phase voltage source inverter with a permanent magnet synchronous machine, and the feasibility and validity are demonstrated with a deadbeat current control algorithm and a high speed ac drive experiment. In the experiments, a very high quality digital current control is achieved, such as a high closed current loop bandwidth, strong robustness against disturbances, ability to reach a very high fundamental frequency compared to switching frequency, etc.
| Identifer | oai:union.ndltd.org:VTETD/oai:vtechworks.lib.vt.edu:10919/84929 |
| Date | 06 March 2017 |
| Creators | Moon, Seung Ryul |
| Contributors | Electrical and ComputerEngineering, Lai, Jih-Sheng, Burgos, Rolando, Guido, Louis J., Baumann, William T., Southward, Steve C. |
| Publisher | Virginia Tech |
| Source Sets | Virginia Tech Theses and Dissertation |
| Detected Language | English |
| Type | Dissertation |
| Format | ETD, application/pdf |
| Rights | In Copyright, http://rightsstatements.org/vocab/InC/1.0/ |
Page generated in 0.0065 seconds