Hydraulic systems are widely used in construction equipment, agricultural machinery, cranes, aerial work platforms, and other mobile machines.
Unlike simple on/off hydraulic valves, proportional valves allow the hydraulic flow or pressure to be adjusted continuously. This makes smoother and more precise machine movement possible.
One common method for controlling proportional solenoid valves is Pulse Width Modulation (PWM).
By using PWM outputs from a mobile controller or I/O module, OEM manufacturers can precisely control hydraulic functions while improving machine response and operator experience.
This article explains how PWM control works with proportional valves, the role of duty cycle and current control, and the key considerations for mobile machinery applications.
A standard on/off solenoid valve normally has two states:
Open
Closed
This is suitable for simple functions but provides limited control over hydraulic movement.
A proportional valve allows the valve position to change according to the electrical command.
This makes it possible to control:
Hydraulic flow
Pressure
Cylinder speed
Motor speed
Direction and movement
For example, an excavator boom should not move at the same speed every time the joystick is operated. The control system needs to adjust valve output according to the operator's command.
This is where PWM control becomes useful.
PWM controls electrical power by rapidly switching the output on and off.
Instead of continuously changing the supply voltage, the controller changes the proportion of time that the signal remains ON during each switching cycle.
This proportion is known as the duty cycle.
For example:
20% Duty Cycle → Lower Output
50% Duty Cycle → Medium Output
80% Duty Cycle → Higher Output
Changing the PWM command changes the average electrical energy delivered to the valve coil, influencing the resulting valve response.
A typical control process may look like:
Joystick / Sensor
↓
Mobile Controller
↓
PWM Output
↓
Proportional Valve
↓
Hydraulic Actuator
The controller reads the operator command or sensor signal, calculates the required output, and sends the corresponding PWM command to the proportional valve.
Duty cycle is an important PWM parameter.
A higher duty cycle generally increases the average energy supplied to the solenoid coil, while a lower duty cycle reduces it.
However, valve behavior is not always perfectly linear.
Factors such as:
Valve characteristics
Coil resistance
Supply voltage
Hydraulic pressure
Temperature
can affect the actual response.
For this reason, OEM engineers usually need to calibrate the relationship between the control command and hydraulic movement for each application.
In some applications, simply controlling PWM duty cycle may not provide sufficient accuracy.
The resistance of a solenoid coil changes with temperature, and the machine supply voltage can also fluctuate.
As a result, the same PWM duty cycle may produce different coil currents under different operating conditions.
A more precise approach is closed-loop current control.
The controller measures the actual current flowing through the valve coil and adjusts the PWM output to maintain the required current.
Target Current
↓
PWM Controller
↓
Valve Coil
↓
Current Feedback
↓
PWM Adjustment
This can provide more consistent valve behavior when operating conditions change.
Sending a large output change directly to a proportional valve may cause sudden hydraulic movement.
For mobile machinery, this can affect:
Operator comfort
Load stability
Mechanical stress
Motion precision
Ramp control gradually increases or decreases the valve command instead of changing it instantly.
For example:
0%
↓
20%
↓
40%
↓
60%
↓
Target Output
Ramp parameters can be adjusted according to the machine function.
A crane or aerial work platform may require smoother acceleration and deceleration, while other functions may require faster response.
Some proportional valves do not respond immediately to very small current commands.
The controller may need to compensate for this deadband to achieve predictable movement.
Coil resistance changes as temperature changes.
Without compensation or current feedback, valve performance may vary between cold startup and continuous operation.
Mobile machinery electrical systems can experience voltage fluctuations.
This may affect valve current when using basic open-loop PWM control.
PWM frequency should match the characteristics of the valve and control system.
An unsuitable frequency may lead to:
Unstable valve response
Excessive noise
Reduced control accuracy
OEM engineers should therefore consider the valve manufacturer's specifications when configuring PWM parameters.
PWM-controlled proportional valves can be used for:
Boom movement
Bucket control
Steering functions
Auxiliary hydraulic systems
Precise valve control helps provide smoother machine movement.
Cranes require controlled hydraulic movement for:
Boom lifting
Telescoping
Slewing
Outrigger control
Ramp control and proportional outputs help reduce sudden movement when handling loads.
Aerial work platforms require smooth and predictable movement for operator comfort and positioning accuracy.
PWM outputs can control:
Platform lifting
Boom extension
Steering
Rotation
Proportional hydraulic control is also used in:
Harvesters
Balers
Sprayers
Agricultural implements
Electronic control allows hydraulic functions to be integrated with sensors and automated operating sequences.
When implementing PWM proportional valve control, engineers should evaluate:
Valve rated voltage and current
PWM output capability
PWM frequency
Maximum output current
Current feedback requirements
Ramp settings
Fault detection
Environmental conditions
The controller and valve should be considered as part of the complete hydraulic and electronic control system rather than as independent components.
PWM control provides an effective way to manage proportional hydraulic valves in mobile machinery.
By adjusting duty cycle, current, and output ramps, electronic controllers can provide smoother and more precise hydraulic movement.
For applications requiring greater consistency, closed-loop current control can compensate for changes in supply voltage, coil resistance, and operating conditions.
A properly designed PWM control strategy can help OEM manufacturers improve machine responsiveness, hydraulic performance, and operator experience.
SonnePower provides electronic control solutions for mobile machinery, including:
Programmable mobile controllers
PWM output control
Remote I/O modules
CAN communication
Customized control solutions
Our control platforms can be integrated with hydraulic valves, sensors, and other electronic components to support construction equipment, agricultural machinery, aerial work platforms, cranes, and other mobile machine applications.
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