Motor Control System DC Link Current Estimation
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Solution Overview
Problem
Existing motor driving systems require additional design of a DC link current sensor to obtain DC link current information, increasing system cost and complexity.
Innovation Solution
A motor control system and method that estimates DC link current using measurement values from shunt resistors instead of a DC link current sensor, employing a current converter to convert voltage values into DC current values, an adder to summate these values, and a PI control unit to control motor field current based on the estimated DC link current.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a DC link current sensor is added to obtain DC link current information, then measurement precision is improved, but device complexity and system cost increase
Solution Approach 1:
The patent creates a virtual copy of the DC link current measurement function through software calculation rather than physical sensing. The control unit calculates DC link current by summing the three-phase currents (Ia + Ib + Ic) obtained from existing phase current sensors, replicating the measurement function without additional hardware. This resolves the contradiction by maintaining measurement capability while eliminating the need for extra sensors and circuitry.
Solution Approach 2:
The system uses its existing phase current measurement infrastructure to serve the additional function of DC link current measurement. The same current sensors and signal processing paths that measure phase currents are leveraged to calculate DC link current, making the system self-sufficient and eliminating the need for separate measurement devices. This approach maintains measurement precision while reducing device complexity.
2Measurement precision
If a DC link current sensor is added to obtain DC link current information, then measurement precision is improved, but system cost increases
Solution Approach 1:
The patent replaces expensive physical DC link current sensors with a cost-effective software-based calculation method. By computing DC link current from existing phase current measurements using the relationship I_dc = Ia + Ib + Ic, the system achieves the same measurement function without the high cost of additional hardware components, thereby improving ease of manufacture while maintaining measurement precision.
Solution Approach 2:
The existing phase current measurement system is made multi-functional by using it for both phase current control and DC link current measurement. This universal utilization of existing infrastructure eliminates the need for dedicated DC link current sensing hardware, reducing system cost while maintaining the capability to obtain accurate DC link current information for control purposes.
3Device complexity
If DC link current is estimated using shunt resistors and calculation, then device complexity is reduced, but measurement precision may be affected
Solution Approach 1:
The patent implements a feedback-based calculation method where the estimated DC link current is continuously refined using the relationship between phase currents and DC link current. The control unit uses the measured phase currents (which are already compensated and accurate) to calculate DC link current, ensuring that the estimation maintains high precision through iterative refinement and validation against system operating conditions.
Solution Approach 2:
The patent replaces the mechanical/physical DC link current sensor with an electronic calculation system. By substituting physical sensing hardware with software-based current summation (I_dc = Ia + Ib + Ic), the system reduces device complexity while maintaining measurement precision through mathematical relationships that are inherently accurate when based on precise phase current measurements.
Data Source
AI summary
Provided is a motor control system. The motor control system include an inverter connected to a DC link, including both ends which a DC link voltage value is applied across, and including switch groups connected in parallel and applying a three-phase current to a motor according to a switching operation, based on PWM control, of each of the switch groups, a current converter converting voltage values, applied across both ends of shunt resistors included in the switch groups, into DC current values according to an ADC gain, an adder estimating a current value, obtained by summating the DC current values, as a DC link current value, and a PI control unit outputting a voltage value for controlling a field current of the motor to the motor by using the estimated DC link current value according to a PI control method, for controlling a generated power of the DC link.