Regenerative Medium Voltage Inverter Design
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Solution Overview
Problem
Conventional series H-bridge medium voltage inverters face challenges in performing regenerative operations due to the use of diode rectifiers, leading to difficulties in fast acceleration or deceleration and requiring larger DC-link capacitors to reduce voltage ripple, which increases system size.
Innovation Solution
A regenerative medium voltage inverter is designed with active rectifying units and switching signal generating units to enable bi-directional power transmission, reducing the need for dynamic braking resistors and allowing for smaller DC-link capacitors by using a phase shifting transformer and input filters to manage harmonics and voltage switching.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If diode rectifiers are used in conventional series H-bridge medium voltage inverters, then the structure is simple and reliable, but regenerative operations cannot be performed and fast acceleration or deceleration is difficult
Solution Approach 1:
The patent applies inversion by replacing the passive diode rectifier with an active rectifier that uses controllable switching elements (IGBTs and diodes) arranged in a bridge configuration. This allows the rectifier to operate bidirectionally, enabling regenerative operations where energy can flow back from the motor to the grid during deceleration or downhill conditions.
Solution Approach 2:
The active rectifier introduces dynamic control capability through switching elements that can be controlled to change the power flow direction. The switching signals are dynamically adjusted based on operational requirements, allowing the system to transition between motor drive mode and regenerative braking mode seamlessly.
2Stability of the object's composition
If larger DC-link capacitors are used to reduce voltage ripple, then voltage stability is improved, but system size and cost increase
Solution Approach 1:
The active rectifier incorporates feedback control mechanisms where switching signals are generated based on detected voltage and current conditions. This feedback control optimizes the charging and discharging cycles of the DC-link capacitor, reducing voltage ripple without requiring oversized capacitors.
Solution Approach 2:
The patent changes the operational parameters of the rectifier by using active switching elements with controllable on/off states. This allows precise control of power flow timing and magnitude, optimizing the energy transfer to minimize voltage ripple while maintaining smaller capacitor sizes.
3Adaptability or versatility
If active rectifying units and switching signal generating units are added to enable bi-directional power transmission, then regenerative operations are enabled and DC-link capacitor size is reduced, but device complexity increases
Solution Approach 1:
The active rectifier serves multiple functions: it rectifies AC to DC during motor drive operations, enables regenerative braking by allowing power flow reversal, provides voltage regulation through feedback control, and reduces harmonic distortion. This multi-functionality justifies the added complexity by eliminating the need for separate regenerative braking circuits and large DC-link capacitors.
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
Enables regenerative operations without the need for dynamic braking resistors, reducing the size of DC-link capacitors and improving system efficiency by concentrating output power in DC components, thus addressing the limitations of conventional inverters.
Implementation Method 1
A phase switching transformer (110) provides a galvanic isolation between the input power unit (200) and the medium voltage inverter (100), reduces harmonics at an input terminal
Implementation Method 2
A phase switching transformer (110) provides a galvanic isolation between the input power unit (200) and the medium voltage inverter (100), reduces harmonics at an input terminal
Implementation Method 3
The 3-phase diode rectifier (121) outputs a 3-phase rectified DC voltage using an output voltage of the phase switching transformer (110) as an input
Implementation Method 4
The DC-link capacitor (122) stores the input power of the 3-phase diode rectifier (121). The DC-link capacitor (122) serves to constantly maintain the output voltage of the 3-phase diode rectifier (121)
Implementation Method 5
The inverter (123) is a single phase full bridge inverter to synthesize output voltages via switching of the switching elements (123a ̃123d) using the voltages received from the DC-link capacitor (122)
Data Source
AI summary
Provided is a regenerative medium voltage inverter, the inverter being such that regenerative operation is enabled by changing structure of input terminal of a unit power cell at a series H-bridge medium voltage inverter, and a dynamic braking resistor is not required to reduce the size of a DC-link capacitor over that of a conventional medium voltage inverter.