Juan Manuel Guerrero

Inverter nonlinearity effects in high-frequency signal-injection-based sensorless control methods

An analysis of pulsewidth-modulation inverter nonlinearities influencing high-frequency carrier-signal voltage injection for saliency-tracking-based rotor/flux position estimation is presented in this paper. Distortion of the injected carrier voltage caused by the nonlinear behavior of the inverter has been reported to cause errors in the estimated rotor/flux position. Though a number of techniques have been developed to compensate for inverter nonlinearities, they have not been proven to be effective when a high-frequency low-magnitude voltage needs to be generated. Both the origins of the distortion as well as the requirements for compensation methods to be effective when producing such high-frequency voltages will be established in this paper.

Discrete-Time Current Regulator Design for AC Machine Drives

This paper analyzes the behavior of discrete-time current regulators for ac machines operating at high ratios of fundamental-to-sampling frequencies, a situation common for high-speed automotive drives and large-traction drives. At high ratios of fundamental-to-sampling frequencies, highly oscillatory, or unstable, response can occur if the current regulator design does not properly incorporate the effects of the discrete nature of the controller, including delays between the sampling of signals and the application of the voltage commands through pulse-width modulation (PWM). This paper investigates these issues for different design methods and current regulator topologies. As part of this investigation, a simple discrete-time domain ac machine model is developed that includes the delays associated with PWM. This model is then used to design a discrete-time domain version of the complex vector PI current regulator that demonstrates improved response compared with the other regulators studied. Simulation and experimental results are provided to compare the performance, stability, and robustness of the current regulators analyzed.

Online diagnostics in inverter-fed induction machines using high-frequency signal injection

Fault diagnostics for induction machines using an injected high frequency carrier signal is presented and analyzed in this paper. Both stator winding fault and broken: rotor bar detection is covered. Measurement of the resulting high frequency negative sequence current is shown to be capable of detecting both types of faults at their incipient stage. Though sharing similar physical principles to techniques applied to line-connected machines, the use of a high frequency signal is shown to provide important advantages for inverter fed machines, such as providing the same performance and drastically reduced sensitivity to the working condition of the machine, i.e. torque and flux levels, and fundamental excitation frequency.

Magnet Temperature Estimation in Surface PM Machines Using High-Frequency Signal Injection

This paper proposes a method to estimate the magnet temperature in surface permanent-magnet machines using high-frequency carrier signal injection. The injection of a high-frequency signal, superimposed on the fundamental excitation, allows the estimation of the stator high-frequency impedance, which is a function of both the stator and rotor impedances. The temperature of the magnets is shown to have a significant weight on the overall stator high-frequency impedance, from which it can be estimated. The high-frequency carrier signal is injected intermittently in order to minimize potential adverse effects on the normal operation of the machine. This paper first explains the physics behind the magnet temperature dependence. Then, the principles of the method, as well as its practical implementation, are discussed. Experimental verification of the method is provided.

Online stator winding fault diagnosis in inverter-fed AC machines using high-frequency signal injection

The diagnosis of stator winding faults in inverter fed AC machines using an injected high frequency carrier signal is presented and analyzed in this paper. Measurement of the resulting high frequency negative sequence current (or alternatively of the negative sequence impedance) is used to detect turn faults at an incipient stage. Though sharing the same physical principles of similar techniques applied to line-connected machines, the use of a high frequency signal will be shown to present important advantages, such as providing the same performance almost independent of the fundamental excitation frequency, and drastically reducing the sensitivity to the working condition of the machine, i.e. torque and flux levels.

Active Islanding Detection Using High-Frequency Signal Injection

Islanding detection is of great importance for reliable operation of smart grids. Islanding detection methods can be classified into three different groups: active, passive and communication based methods. Active methods inject a disturbing signal (typically a voltage) and analyze the system response (typically in the current). These techniques have a low non-detection zone but present the inconvenience inherent to injecting a disturbing signal. Passive methods monitor the grid condition from the grid variables. These techniques are easy to implement, but present a large non-detection zone. Communications methods have the inconvenient of relying on communications, currently being of limited use. This paper proposes a new active islanding detection method, based on measurement of the grid high frequency impedance by means of the injection of a high frequency voltage. Advantages of the method are almost negligible adverse effects due to the injected high frequency voltage and accurate and fast islanding detection -in the rage of few ms-. Furthermore, the estimated high frequency impedance can be used for adaptive control of the power converter.1

Stator Windings Fault Diagnostics of Induction Machines Operated From Inverters and Soft-Starters Using High-Frequency Negative-Sequence Currents

This paper studies the application of high-frequency voltage excitation-based stator winding diagnostic methods to three-phase ac machines operated from power converters that create the necessary high-frequency excitation as part of their normal operation. This paper focuses on two specific operating modes: 1) machines operated from inverters in the overmodulation region and 2) machines operated from soft-starters during startup. In both cases, high-frequency (in the range of the hundred hertz) voltage components at well-defined frequencies are created. The negative-sequence currents induced from these high-frequency voltages are shown to contain accurate information on the level of asymmetry (fault) in the machine. This information is significantly richer than exists in other modes of operation, i.e., inverters working in the linear modulation region or soft-starters in the steady state, and provides interesting opportunities to complement other diagnostic methods.

Inverter nonlinearity effects in high frequency signal injection-based, sensorless control methods

An analysis of PWM inverter nonlinearities influencing high frequency carrier signal voltage injection for saliency-tracking-based rotor/flux position estimation is presented in this paper. Distortion of the injected carrier voltage caused by the nonlinear behavior of the inverter has been reported to cause errors in the estimated rotor/flux position. Though a number of techniques have been developed to compensate for inverter nonlinearities, they have not been proven to be effective when a high frequency, low magnitude voltage needs to be generated. Both the origins of the distortion as well as the requirements for compensation methods to be effective when producing such high frequency voltages is established in this paper.

On-line stator winding fault diagnosis in inverter-fed AC machines using high frequency signal injection

The diagnosis of stator winding faults in inverter fed AC machines using an injected high frequency carrier signal is presented and analyzed in this paper. Measurement of the resulting high frequency negative sequence current (or alternatively of the negative sequence impedance) is used to detect turn faults at an incipient stage. Though sharing the same physical principles of similar techniques applied to line-connected machines, the use of a high frequency signal will be shown to present important advantages, such as providing the same performance almost independent of the fundamental excitation frequency, and drastically reducing the sensitivity to the working condition of the machine, i.e. torque and flux levels.

Dynamic Behavior of Current Controllers for Selective Harmonic Compensation in Three-Phase Active Power Filters

Current regulators are a critical part of active power filters (APFs). The design of current regulators capable of compensating high-frequency harmonics created by nonlinear loads is a challenging task. Selective harmonic current compensation using harmonic regulators is a viable method to achieve this goal. However, their design and tuning is not an easy task. The performance-and even the stability-of harmonic current regulators strongly depends on implementation issues, with the tuning of the controller gains being critical. Furthermore, the presence of multiple current regulators working in parallel can create unwanted couplings with the fundamental current regulator, which can result in a deterioration of APF current control, i.e., oscillations and settling times larger than expected. This paper addresses the design and tuning of selective harmonic compensators, with a focus on their stability analysis and transient behavior.