Patent Application
20210013878
This disclosure relates to the control of power electronic converters.
A vehicle may be driven by operation of an electric machine. Energy from a traction battery may be provided to the electric machine via a variable voltage converter and inverter to increase a voltage associated with the energy and to transform current associated with the energy from direct current (DC) to alternating current (AC). The inverter may include a plurality of switching elements to facilitate the DC to AC transformation.
A vehicle powertrain includes a traction battery, an electric machine, a power converter having a pair of series connected switches defining a phase leg for the electric machine, and a controller. The controller drives the switches with respective pulse width modulated signals to transfer power from the traction battery to the electric machine. Each of the respective pulse width modulated signals defines a low state and a high state. The controller further, responsive to a current flowing through one of the switches exceeding a predetermined threshold and the pulse width modulated signal for the other of the switches having the high state, stops driving the switches.
A vehicle power system has a power converter including a pair of series connected switches defining a phase leg, and a controller programmed. The controller generates respective pulse width modulated signals to selectively turn the switches on and off. Each of the respective pulse width modulated signals defines a low state and a high state. Each of the switches is configured to pass current at a maximum operating value responsive to the corresponding pulse width modulated signal having the high state. The controller further, responsive to a current flowing through one of the switches exceeding a predetermined threshold less than the maximum operating value and the pulse width modulated signal for the other of the switches having the high state, stops generating the respective pulse width modulated signals prior to the current flowing through the one of the switches achieving the maximum operating value.
A method for operating a vehicle power system includes driving a pair of series connected switches of a power converter that define a phase leg for an electric machine with respective pulse width modulated signals to transfer power from a traction battery to the electric machine. Each of the respective pulse width modulated signals defines a low state and a high state. The method further includes, responsive to a current flowing through one of the switches exceeding a predetermined threshold and the pulse width modulated signal for the other of the switches having the high state, stopping the driving.
Various embodiments of the present disclosure are described herein. However, the disclosed embodiments are merely exemplary and other embodiments may take various and alternative forms that are not explicitly illustrated or described. The figures are not necessarily to scale; some features may be exaggerated or minimized to show details of particular components. Therefore, specific structural and functional details disclosed herein are not to be interpreted as limiting, but merely as a representative basis for teaching one of ordinary skill in the art to variously employ the present invention. As those of ordinary skill in the art will understand, various features illustrated and described with reference to any one of the figures may be combined with features illustrated in one or more other figures to produce embodiments that are not explicitly illustrated or described. The combinations of features illustrated provide representative embodiments for typical applications. However, various combinations and modifications of the features consistent with the teachings of this disclosure may be desired for particular applications or implementations.
Bridge-based power electronics converters/inverters have been extensively used in EV/HEV's drive systems. As shown in
A voltage associated with power from the traction battery 14 may be increased by operation of the bridge-based DC-DC converter 16 for eventual delivery to the DC-AC inverter 20 and thus the motor 24 to propel the vehicle 12. Likewise, regenerative power captured by the generator 26 may be passed through the DC-AC inverter 22 and so on for storage in the traction battery 14.
Shoot through faults can occur across the phase legs of the DC-AC inverters 20, 22.
To prevent shoot through faults, a dead time between gate signals of the switches 36, 38 is inserted. Even though the dead time is inserted, the switches 36, 38 may be mis-triggered to generate a shoot through fault due to noise, component variation characteristics, or software faults. This type of over-current detection is used to protect the switch components and the system from the effects of shoot through faults.
The switch current is measured and compared with a threshold. As the measured switch current exceeds the threshold, the over-current condition is flagged and the gate signals of the switches 36, 38, 40, 42, 44, 46 of the DC-AC inverter 20 are disabled. To distinguish the over-current condition from the normal operation conditions, the threshold must be higher than the maximum operating current of the switches 36, 38, 40, 42, 44, 46. This larger fault current may cause high voltage stress to the switches 36, 38, 40, 42, 44, 46 as the switches 36, 38, 40, 42, 44, 46 are turned off. As a result, a conservative and longer dead time is used to prevent shoot through faults. Longer dead times, however, can degrade operation and performance: The dead time sets a limit on the minimal pulse width of the pulse width modulated gate signal and therefore reduces the adjustable voltage range. For DC-AC inverters, the dead time significantly reduces DC voltage utilization, increases current harmonics, and reduces the torque control accuracy for the motor drive applications.
Here, a diagnostic strategy for shoot through faults of converters/inverters is proposed that considers measured switch currents and pulse width modulated signals of the switches. By way of example, the pulse width modulated signals of the switches 36, 38 are complementary, except for the duration of the dead time. As the pulse width modulated signal (gate signal) of the switch 38 is high (active), the switch 36 should be in the off state, and no current should flow through the switch 36. If a current flowing through the switch 36 is detected while the pulse width modulated signal of the switch 38 is high, then the switch 36 is mis-triggered or is not completely turned off and a shoot through fault may occur. Similarly, if a current flowing through the switch 38 is detected while the pulse width modulated signal of the switch 36 is high, then the switch 38 is mis-triggered or is not completely turned off and a shoot through fault may occur. The fault signal will be flagged and gate signals of all the switches 36, 38, 40, 42, 44, 46 will be disabled once the fault is detected.
More generally, responsive to the measured current through one switch of a phase leg exceeding a threshold, the status of the gate signal of the other switch of the phase leg is checked. If the gate signal of the other switch is high, then the one switch is in an abnormal status and a shoot through fault is detected. Likewise, responsive to the measured current through the other switch exceeding the threshold, the status of the gate signal of the one switch is checked. If the gate signal of the one switch is high, then the other switch is in an abnormal status and a shoot through fault is detected. Once the shoot through fault is detected, a fault signal is immediately generated and sent to a controller, and gate signals to all switches are disabled and the converter stops operating.
A flow chart of an algorithm is shown in
At operation 68, current flowing through the switch 36 is measured. If the current is less than a predefined threshold at decision block 70, the algorithm returns to operation 68, and operation of the switches 36, 38 is maintained. If the current is greater than the predefined threshold, the algorithm proceeds to operation 72. If the pulse width modulated signal (gate signal) for the switch 38 is low (inactive), the algorithm returns to operation 68, and operation of the switches 38, 38 is maintained. If the pulse width modulated signal (gate signal) for the switch 38 is high, a fault is detected and pulse width modulated signals to the switches 36, 38, 40, 42, 44, 46 are disabled.
At operation 74, current flowing through the switch 38 is measured. If the current is less than a predefined threshold at decision block 76, the algorithm returns to operation 74. If the current is greater than the predefined threshold, the algorithm proceeds to operation 78. If the pulse width modulated signal for the switch 36 is low, the algorithm returns to operation 74. If the pulse width modulated signal for the switch 36 is high, a fault is detected and pulse width modulated signals to the switches 36, 38, 40, 42, 44, 46 are disabled.
As mentioned above, the conventional threshold for detecting over-current conditions must be higher than the maximum operating current of the switch. Here, however, the threshold can be much lower than the normal operating current (e.g., 10% of the maximum operating current, etc.), so the method can detect shoot through faults in early stages. This detection enables reduction of the dead time between gate signals of switches. Reducing dead time can increase DC voltage utilization, reduce the output current distortion and harmonics, and improve the torque control accuracy for the three-phase traction inverters.
The strategies herein use both switch current and gate signals to ensure a reliable shoot through diagnosis, and can be implemented by hardware, software, or a combination of the two. Shoot through faults can be detected before the current exceeds the maximum operating value of the switch. As a result, components may experience fewer issues. Moreover, the fault strategies herein permit the use of shorter dead times, which may increase DC voltage utilization, improve current quality for three-phase inverters, and improve toque control accuracy for traction inverters.
The algorithms, processes, methods, logic, or strategies disclosed may be deliverable to and/or implemented by a processing device, controller, or computer, which may include any existing programmable electronic control unit or dedicated electronic control unit. Similarly, the algorithms, processes, methods, logic, or strategies may be stored as data and instructions executable by a controller or computer in many forms including, but not limited to, information permanently stored on various types of articles of manufacture that may include persistent non-writable storage media such as ROM devices, as well as information alterably stored on writeable storage media such as floppy disks, magnetic tapes, CDs, RAM devices, and other magnetic and optical media. The algorithms, processes, methods, logic, or strategies may also be implemented in a software executable object. Alternatively, they may be embodied in whole or in part using suitable hardware components, such as Application Specific Integrated Circuits (ASICs), Field-Programmable Gate Arrays (FPGAs), state machines, controllers or other hardware components or devices, or a combination of hardware, software and firmware components.
The words used in the specification are words of description rather than limitation, and it is understood that various changes may be made without departing from the spirit and scope of the disclosure and claims. As previously described, the features of various embodiments may be combined to form further embodiments that may not be explicitly described or illustrated. While various embodiments may have been described as providing advantages or being preferred over other embodiments or prior art implementations with respect to one or more desired characteristics, those of ordinary skill in the art recognize that one or more features or characteristics may be compromised to achieve desired overall system attributes, which depend on the specific application and implementation. These attributes include, but are not limited to cost, strength, durability, life cycle cost, marketability, appearance, packaging, size, serviceability, weight, manufacturability, ease of assembly, etc. As such, embodiments described as less desirable than other embodiments or prior art implementations with respect to one or more characteristics are not outside the scope of the disclosure and may be desirable for particular applications.
