Synchronous motor control device, compressor drive system, and air conditioner
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Solution Overview
Problem
Conventional synchronous motor control devices fail to detect short-circuited shunt resistors due to solder bridges or solder residue, leading to excessive current flow and potential demagnetization of the motor and failure of the control device.
Innovation Solution
A synchronous motor control device with an inverter main circuit, current detector, voltage detector, and inverter control unit that includes a phase current reproduction unit, current coordinate transformation unit, current control unit, and limiter unit to prevent overcurrent by generating pulse width modulation signals and limiting voltage command values, thereby preventing demagnetization and device failure.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If a shunt resistor is used to detect current on the DC bus, then current detection is simple and cost-effective, but the detection fails when the shunt resistor is short-circuited due to solder bridges or solder residue
Solution Approach 1:
The patent introduces an intermediary calculation method that derives phase current information from DC bus current and voltage measurements without directly relying on shunt resistor readings. By using the relationship between DC bus power and motor power, the system calculates equivalent phase current as an intermediary value to verify motor connection status, thus bypassing the unreliable shunt resistor detection.
Solution Approach 2:
The system implements feedback by continuously monitoring DC bus current and voltage, calculating the derived phase current, and comparing it with expected values. When the calculated current deviates from the threshold or shows abnormal patterns, the system generates alarms or adjusts control parameters, creating a closed-loop feedback mechanism that compensates for shunt resistor failures.
2Measurement precision
If PI control is applied in positioning mode to control armature current, then motor positioning accuracy is improved, but excessive current may flow before non-connection is detected, causing demagnetization or device failure
Solution Approach 1:
The patent applies preliminary action by performing a safety check before executing PI control in positioning mode. The system first calculates the derived phase current from DC bus measurements and verifies it meets minimum threshold requirements. Only when this preliminary verification passes does the system proceed with PI control, thus preventing overcurrent damage before it can occur.
Solution Approach 2:
The system implements preliminary anti-action by establishing a protective mechanism that counteracts potential overcurrent effects before they happen. Through real-time calculation of derived phase current and comparison with safety thresholds, the system prepares countermeasures (such as limiting current commands or generating alarms) in advance, preventing demagnetization and device failure even if shunt resistor detection fails.
3Device complexity
If the system relies solely on shunt resistor current detection to determine motor connection, then the control logic is simple, but the system cannot detect shunt resistor short-circuits and generate accurate alarms
Solution Approach 1:
The patent introduces an intermediary calculation method that derives phase current information from DC bus current and voltage measurements without directly relying on shunt resistor readings. By using the relationship between DC bus power and motor power, the system calculates equivalent phase current as an intermediary value to verify motor connection status, thus bypassing the unreliable shunt resistor detection.
Solution Approach 2:
The system replaces the direct electrical measurement mechanism (shunt resistor) with a computational approach. Instead of mechanically/electrically measuring current through a physical resistor, the system uses mathematical calculations based on power relationships to derive current information, substituting a fragile physical component with a more reliable computational method.
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 effectively prevents demagnetization and failure of the synchronous motor control device by accurately detecting and managing current flow, even when shunt resistors are short-circuited, thereby improving the quality and reliability of the device.
Implementation Method 1
an inverter main circuit to convert the DC power into the three-phase AC power by using a plurality of switching elements
Implementation Method 2
Where the current flowing through the permanent magnet synchronous motor is detected by a voltage drop across a shunt resistor
Implementation Method 3
a permanent magnet rotor having a magnetic pole pattern in which a number of north poles and south poles are alternately arranged along a circumferential direction
Data Source
AI summary
A synchronous motor control device includes a voltage detector, a current detector, an inverter main circuit, and an inverter control unit. The inverter control unit includes: a phase current reproduction unit that reproduces a direct current into phase currents flowing to a permanent magnet synchronous motor; a current coordinate transformation unit that transforms the reproduced phase current into current on a control coordinate axis of a rotating coordinate system; a current control unit that calculates a voltage command value of the permanent magnet synchronous motor in such a manner that the current on the control coordinate axis equals a specific value; and a limiter unit that limits the value of the voltage command value.