On-Board Charger PFC Control for Zero-Crossing Current Distortion
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Solution Overview
Problem
Existing chargers experience current distortion and poor power factor correction (PFC) during single-phase AC charging, due to the short-circuiting of the bus capacitor's midpoint to the AC-side capacitor's midpoint, which leads to severe waveform distortion when the input voltage crosses zero.
Innovation Solution
A charger design that includes an AC-side capacitor assembly, a PFC circuit, a bus capacitor assembly, and a DC-DC converter, where the duty cycle of the high-frequency bridge arm of the PFC circuit is dynamically adjusted based on the AC power supply voltage to discharge the AC-side capacitor voltage and perform PFC, thereby preventing current distortion during single-phase AC charging.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If the midpoint of the bus capacitor is short-circuited to the midpoint of the AC-side capacitor, then the common mode current leakage problem is alleviated, but current distortion occurs when the input voltage crosses zero in single-phase charging mode
Solution Approach 1:
The patent applies dynamics by making the connection between the bus capacitor midpoint and AC-side capacitor midpoint controllable rather than fixed. A switching element is introduced to dynamically connect or disconnect these midpoints based on the charging mode. In three-phase charging mode, the switching element connects the midpoints to alleviate common mode current leakage. In single-phase charging mode, the switching element disconnects them to prevent current distortion, allowing the system to adapt its configuration based on operational conditions.
2Device complexity
If the bus capacitor and AC-side capacitor are connected in the conventional manner, then the charger structure is simple, but the PFC function deteriorates during single-phase AC charging
Solution Approach 1:
The patent introduces a dynamically controllable switching element that adjusts the circuit configuration based on the charging mode. This dynamic adjustment allows the system to maintain simple structure in three-phase mode while optimizing PFC performance in single-phase mode, resolving the contradiction between structural simplicity and functional reliability.
Solution Approach 2:
The patent changes the circuit topology parameters dynamically by controlling the switching element. In single-phase charging mode, the switching element opens to change the circuit parameters, allowing the PFC circuit to operate with optimal parameters for single-phase input, thereby improving PFC function without permanently increasing device complexity.
3Productivity
If the midpoint short-circuiting is implemented, then three-phase charging performance is improved, but single-phase charging current waveform becomes severely distorted
Solution Approach 1:
The patent uses a dynamically controllable switching element that adapts the circuit configuration based on the charging mode. In three-phase charging mode, the switching element closes to provide the midpoint short-circuit connection that improves charging performance. In single-phase charging mode, the switching element opens to prevent waveform distortion, ensuring smooth current operation. This dynamic adaptation allows the system to optimize for each operating condition independently.
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 dynamic adjustment of the duty cycle of the high-frequency bridge arm ensures that the charger maintains an original PFC function and prevents current distortion when the AC power supply crosses zero, thereby improving the charger's performance in single-phase AC charging mode.
Implementation Method 1
a duty cycle of a high-frequency bridge arm of the PFC circuit is dynamically adjusted based on a voltage of an AC power supply, to discharge a voltage of the AC-side capacitor assembly and perform PFC on the AC power supply
Implementation Method 2
input a DC outputted from the PFC circuit to the DC-DC converter, to enable the DC-DC converter to perform voltage conversion on the DC
Data Source
AI summary
A charger, comprising a controller, an alternating-current-side capacitor assembly, a power factor correction circuit, a bus capacitor assembly, and a DC-DC converter. The bus capacitor assembly comprises a first capacitor and a second capacitor. The alternating-current-side capacitor assembly is connected to both the first capacitor and the second capacitor. When the charger is in a single-phase alternating-current charging mode, the controller is used to dynamically adjust an on-duty ratio of a high-frequency bridge arm of the power factor correction circuit according to the voltage of an alternating current, so as to discharge the voltage of the alternating-current-side capacitor assembly, perform power factor correction on the alternating current, and input a direct current outputted from the power factor correction circuit to the DC-DC converter. Also provided are a charger control method and a vehicle.