Z-Source Inverter Drive Circuit Voltage Boosting
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Solution Overview
Problem
Existing electric motor drive circuits using pulse width modulation (PWM) control for Z-Source converters in brushless motors often result in lower motor phase voltages, leading to underperformance, especially when the battery source is drained, as they lack sufficient voltage boosting capabilities.
Innovation Solution
A drive circuit employing a two-port LC inductive network with a source switch that operates between shoot-through and non-shoot-through states, utilizing a PWM pattern with fixed edges to reduce switching operations and incorporate additional short duration states for protection, allowing for voltage boosting and efficient motor operation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If a conventional 6 FET inverter is used for PWM control, then the circuit is simple and easy to operate, but the motor phase voltages are lower than the source voltage leading to underperformance when battery is drained
Solution Approach 1:
The PWM period is segmented into two distinct modes: shoot-through mode and non-shoot-through mode. During shoot-through mode, all upper switches are turned on simultaneously to charge the capacitors and store energy in the inductors. During non-shoot-through mode, the switches are controlled in conventional PWM fashion to deliver the stored energy to the motor phases. This segmentation enables voltage boosting while maintaining control simplicity.
Solution Approach 2:
The shoot-through mode is implemented as a preliminary action before the main PWM operation. By pre-charging the capacitors and storing energy in the inductors during the shoot-through phase, the circuit prepares the necessary voltage boost in advance, enabling higher motor phase voltages during the subsequent non-shoot-through PWM operation without complicating the overall control structure.
2Power
If the source switch is opened and inverter shorted to transfer power into the inductor during ST mode, then voltage boosting is achieved, but the switching operations increase and complexity increases
Solution Approach 1:
The patent merges the shoot-through switch control with the existing inverter switch control. The same microcontroller and PWM generation hardware are used to control both the shoot-through mode (all upper switches on) and the conventional PWM operation. This unified control approach achieves voltage boosting without requiring separate control circuits or additional switching complexity.
Solution Approach 2:
The inverter switches serve dual functions: they perform conventional PWM switching during non-shoot-through mode and simultaneously function as shoot-through switches when all upper switches are turned on. This multi-functionality eliminates the need for dedicated shoot-through switches or separate control mechanisms, reducing overall system complexity while achieving voltage boost.
3Reliability
If additional short ST state is injected around inverter switch timing to protect inverter switches, then switch protection is improved, but the PWM pattern complexity increases
Solution Approach 1:
The shoot-through mode is implemented as a preliminary protective action before conventional PWM switching. By turning on all upper switches just before the PWM switching event, the circuit pre-charges the capacitors and prepares the voltage waveform, which naturally protects the inverter switches from voltage spikes and shoot-through faults during the subsequent PWM operation. This preliminary action integrates protection into the voltage boosting mechanism itself.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The solution provides higher motor phase voltages by optimizing the PWM pattern and switching strategy, enhancing motor performance and protecting the inverter switches from shoot-through faults, particularly in automotive applications where battery voltage may be depleted.
Implementation Method 1
a two port LC inductive network having a pair of input nodes and a pair of output nodes, the network comprising a source switch operable to switch the network between an ST state and an active state
Data Source
AI summary
A drive circuit comprises a two port LC inductive network with a source switch operable to switch the network between an ST state and an active state; an inverter and a controller for controlling the On-Off state of the switches of the inverter and the On-OFF state of the source switch, wherein the controller in use operates the switches to provide: a non-drive portion of the PWM period in which the source switch is held open and the top and bottom switches of at least one phase are held closed so that the drive circuit is operating in an ST mode, a drive portion of the PWM period which immediately follows or immediately precedes the non-drive portion in which the source switch is closed and the top and bottom switches are arranged, and in which the controller is configured to employ a PWM pattern in which all of the bottom switches or all of the top switches are moved from the closed state to an open state simultaneously, and further in which the source switch is moved from the open state to the closed state substantially at the start of the drive portion and is moved from the closed state to the open state substantially at the end of the drive portion.