Abstract This article provides a brief introduction to the application of the Dalian Powtran Technology PI500 series frequency converters in mining crushers. The control system integrates frequency conversion technology and control technology into one, fully leveraging the outstanding control performance of the Powtran Technology PI500 series frequency converters. This effectively meets the crusher’s requirements for high starting torque and high-speed precision, significantly enhancing the operational performance of the crushing equipment. 
 
Keywords: PI500; Common DC Bus; Crusher 
I. Preface 
Crushers are widely used in industries such as mining, metallurgy, building materials, highways, railways, water conservancy, and chemical engineering. Currently, commonly used crushing equipment includes jaw crushers, impact crushers, air-classification mills, hammer crushers, impact crushers, roller crushers, and compound crushers, among others. 

Crusher costs account for a relatively high proportion of the total expenses in a beneficiation plant—typically ranging from 40% to 60% of the plant’s total costs. Therefore, improving the production efficiency of crushers, reducing unit energy consumption, and lowering costs by adopting high-efficiency and energy-saving crushing equipment have become key strategies for mining enterprises. 
II. The Necessity of Variable-Frequency Drive Retrofit for Crushers 
This crusher is driven by two 200-kW asynchronous motors connected via belts to a single rotor shaft. The original control system employed a star-delta starting method and operated at power-frequency, resulting in high inrush currents that easily caused voltage fluctuations in the power grid. At the same time, this approach generated significant mechanical shocks and wear, greatly shortening the motor’s service life, increasing maintenance workload, and directly impacting production efficiency. Moreover, the motors in the original control system have been operating continuously at power frequency, making it impossible to adjust their speeds to meet the varying crushing requirements of different types of ore. To address these issues, we have carried out a variable-frequency drive (VFD) retrofit on the existing system. 

III. Application of the PI500 Inverter in Hammer Crushers 
The material to be processed is first evenly fed by a vibrating feeder into a jaw crusher for coarse crushing. The coarsely crushed material is then conveyed by a conveyor to a fine crusher for further grinding. After fine crushing, the material is sent to a vibrating screen for screening. Material that meets the required finished-product particle size is discharged via a finished-product conveyor as the final product; material that does not meet the required particle size is returned from the vibrating screen to the fine crusher for reprocessing, thus forming a closed-loop, multi-cycle system. The finished-product particle size can be customized and graded according to user requirements. 

The production line process is roughly as follows: (hopper) — feeder — coarse crushing (jaw crusher) — fine crushing (impact crusher or hammer crusher) — vibrating screen — (finished product). 
 

(1) Basic Project Overview 
Project Name: Inverter Retrofit for Crusher 
Crusher mechanism: 2 units of 200kW variable-frequency motors (380V, 1470rpm, 50Hz, 360A) 
(2) The Necessity of Choosing the PI500 Vector-Controlled Inverter 
1. Equipped with soft-start functionality, it reduces the motor’s starting current, enabling smooth motor startup with minimal mechanical shock, lowering maintenance and upkeep costs, and reducing the impact on the power grid. 
2. It features precise speed control capability, allowing users to adjust the appropriate speed based on the material and desired particle size of the output. The variable-frequency drive ensures that the crusher’s output torque adjusts dynamically with changes in load, thereby effectively improving efficiency. 
3. Energy-saving: The motor speed is adjusted according to the material being crushed, improving efficiency and saving electricity. 
4. The inverter is equipped with comprehensive protection functions, including overvoltage, overcurrent, undervoltage, overload, and short-circuit protection, ensuring stable motor operation. It can also reduce vibration, impact, and noise, thereby providing a superior working environment. 
(3) Selection of Inverters 
A. Selection of Inverters and Control Schemes 
Due to the non-constant load on the crusher—where the load fluctuates significantly depending on the size of the material being crushed and the amount of feed—the inverter must have a high starting torque and strong overcurrent capability. Therefore, the inverter’s power rating should be one level higher than that of the motor. In this solution, two 250-kW inverters are used to drive two 200-kW motors. Since the two motors share the same shaft and operate in synchronized fashion, their speeds must remain precisely matched, placing stringent demands on speed accuracy. If the speeds of the two motors differ, the faster motor will tend to drag the slower one, easily triggering an overcurrent alarm. Meanwhile, the slower motor, experiencing slip, will enter a regenerative operation mode, causing the inverter to trigger an overvoltage alarm. To prevent these alarms, in this solution, the two PI500 250G3R inverters are started simultaneously via external terminals and employ a common DC bus technology, which effectively resolves the issue. As a result, the inverter control system starts smoothly and operates with stable current. 

According to the above-mentioned inverter selection principles, the following is a list of components selected for the frequency conversion retrofit of the crusher: 
 

B. Wiring Diagram for Inverter Terminals 
The wiring diagram for the main circuit and control circuit terminals of the inverter used in the crusher is shown below: 
 

Figure 3: Schematic Diagram of the Frequency Conversion Retrofit for the Crusher 
Set up one start button and one stop button. The digital input terminals 1 and 3, as well as relay outputs 1 and 2, are used in this setup. Input terminal DI1 is configured for forward rotation; when DI1 is connected to COM, the motor runs in the forward direction. Pressing the stop button will cause the motor to stop running. DI3 is set to operate in a three-wire mode. The parameters in F1 group of the frequency converter should be configured according to the table below. When the frequency converter malfunctions, relay output 1 (normally closed) will activate, sending a signal that controls the operation of the AC contactor for the conveyor belt. In the event of a fault, all conveyor belt feeding mechanisms will be stopped immediately. 
 

IV. Effects of Applying PI500 Variable-Frequency Speed Control to the Crusher 
After the crusher underwent frequency conversion modification, it has performed well and boasts the following advantages: 
1. Improve the efficiency of crushing operations 
The variable-frequency control system features precise speed control, enabling the motor’s torque output to match the load requirements. Users can adjust the appropriate speed according to the material and the desired particle size of the discharge. As the load varies, the output torque of the variable-frequency controlled crusher also changes accordingly, effectively enhancing operational efficiency.

2. Save energy 
Compared with crushers controlled by conventional methods, energy savings are the most practical and significant advantage of using frequency converters to control crushers. Adjusting the motor speed according to the material being crushed is an economically efficient operating condition.

3. Extend the service life of the crusher. 
The frequency converter effectively reduces the peak value of the starting current to a minimum, thereby extending the service life of the crushing motor.

4. Prevent motor damage

The inverter features excellent overcurrent protection. If the equipment gets jammed or lacks sufficient lubrication, causing excessive motor load, the inverter’s protection function can effectively safeguard the motor and prevent it from overheating and burning out.

V. Closing Remarks 
Based on the actual application of the PI500 series frequency converters in this customer’s crusher, these converters demonstrate smooth speed regulation and precise control, effectively ensuring the safe and stable operation of the crusher. As a result, system productivity has been greatly enhanced. At the same time, the system is easy to operate and maintain, helping the customer reduce operating costs and improve work efficiency. Therefore, these converters are highly recommended for widespread adoption and use.