Inverter Device Reactive Power Control Phase Shift
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Solution Overview
Problem
Conventional inverter devices struggle to control output current and supply reactive power effectively due to phase shifts between output voltage and current, leading to inefficiencies in power supply to capacitive and inductive loads and inability to detect independent operation in grid-interconnection scenarios.
Innovation Solution
An inverter device with a parallel-connected series circuit of switching elements and diodes in anti-parallel configuration, along with a clamp section using MOSFETs or IGBTs, is controlled to switch on/off at zero-cross points of output voltage, allowing for effective current control and reactive power supply even with phase shifts, and includes an over-current detection system to prevent damage.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If switching elements QE and QF in the clamp section and switching elements QA/QD and QB/QC in the inverter section are switched on/off at the zero-cross point of output voltage, then the loss due to potential differences in PWM control signals is reduced, but current cannot be controlled when a phase shift is produced between output voltage and current, resulting in inability to supply reactive power
Solution Approach 1:
The control method dynamically adjusts the switching timing of clamp section elements based on the operational state. When reactive power supply is needed (phase shift condition), the switching timing is shifted from zero-cross point to a different timing, allowing the system to adapt between minimizing loss and enabling reactive power supply
2Device complexity
If conventional inverter device switching control is used, then device structure is simple, but output current control is ineffective and reactive power supply is impossible when phase shift occurs
Solution Approach 1:
The invention changes the control parameter from fixed zero-cross point switching to variable timing switching. By adjusting the switching timing parameter based on whether reactive power supply is required, the system achieves effective current control while maintaining relatively simple device structure
3Duration of action of stationary object
If switching elements are constantly switched to maintain current flow, then continuous power delivery is achieved, but switching losses and noise increase
Solution Approach 1:
The control method uses periodic PWM switching with variable duty cycles instead of constant switching. By adjusting the duty cycle and timing periodically according to the load requirements and phase shift conditions, continuous power delivery is maintained while optimizing switching losses and reducing noise
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 device successfully controls output current and supplies reactive power with minimal distortion, enabling efficient power delivery to capacitive and inductive loads and accurate independent operation detection, improving efficiency and reducing noise.
Implementation Method 1
the switching elements Q1 to Q4 and the switching elements Q5 and Q6 are switched on/off at zero-cross points of output voltage
Implementation Method 2
a first switching element Q1 where a first diode D1 is connected in anti-parallel and a second switching element Q2 where a second diode D2 is connected in anti-parallel
Implementation Method 3
the reactor input voltage (the terminal voltage of the switching element QE) is clamped nearly to 0V, the reactor voltage becomes a reverse bias
Data Source
Figure 1~2
Figure 3(a)~4(b)
Figure 5
AI summary
With an inverter device (1), even when a phase shift is produced between output current and output voltage, it is still possible to control the output current and supply reactive power effectively. To do so, the inverter device (1) has an inverter section (2) that is comprised of a bridge circuit. Also, between two connecting wires (S11 and S12), a clamp section (5) that is formed with a series circuit, in which a fifth switching element (Q5) where a fifth diode (D5) is connected in anti-parallel and a sixth switching element (Q6) where a sixth diode (D6) is connected in anti-parallel are connected in series so that the conducting directions of the fifth diode (D5) and the sixth diode (D6) become opposite to each other, is provided. Also, a control section (6) to supply pulse signals for on/off switching to the first switching element (Q1) to the sixth switching element (Q6) is provided.